JOURNAL
JUNE
JOURNAL OF
OF GEOPHYSICAL
GEOPHYSICAL RESEARCH,
RESEARCH, VOL
VOL.106,
106,NO.
NO.C6,
C6,PAGES
PAGES11,451-11,467,
11,451-11,467,
JUNE15,
15,2001
2001
Seasonal
climatology of
of hydrographic
hydrographic conditions
Seasonalclimatology
conditions
in
the
upwelling
region
off
northern
Chile
in the upwelling region off northern Chile
J.L.
AC. Thomas,3
J.L.Blanco,1'2
Blanco,
la A.C.
Thomas,
3M.-E.
M.-E.Carr,4
Carr,4and
andP.T.
P.T.Strub5
Strub
5
Abstract.
Over
30
ofofhydrographic
data
Chile
upwelling
Abstract.
Over
30years
years
hydrographic
datafrom
fromthe
thenorthern
northern
Chile(18°S-24°S)
(18øS-24øS)
upwelling
region
used to
to calculate
calculate the
the surface
surface and
and subsurface
subsurface seasonal
seasonal climatology
climatology extending
extending 400
400 km
regionare
areused
km
offshore.
The data
data are
are interpolated
interpolated to
to aa grid
grid with
with sufficient
sufficient spatial
spatial resolution
resolution to
to preserve
preserve crosscrossoffshore.The
shelf
as
austral
shelfgradients
gradientsand
andthen
thenpresented
presented
asmeans
meanswithin
withinfour
fourseasons:
seasons:
australwinter
winter(July(JulySeptember),
spring
(October-December),
summer
(January-March),
and
fall (April-June).
(April-June).
September),spring(October-December),
summer(January-March),andfall
Climatological monthly
monthly wind
wind forcing,
forcing, surface
surface temperature,
temperature, and
and sea
sea level
level from
from three
three coastal
coastal
Climatological
stations
indicate equatorward
equatorward (upwelling
(upwelling favorable)
favorable) winds
winds throughout
throughout the
the year,
year, weakest
weakest in
in the
the
stationsindicate
north. Seasonal
Seasonal maximum
maximum alongshore
alongshore wind
wind stress
stress is
is in
in late
late spring
spring and
and summer
summer (December(Decembernorth.
March). Major
of
March).
Majorwater
watermasses
masses
ofthe
theregion
regionare
areidentified
identifiedin
in climatological
climatologicalT-S
T-S plots
plotsand
andtheir
their
sources
and
implied
circulation
discussed.
Surface
fields
and
vertical
transects
of
temperature
sourcesandimpliedcirculationdiscussed.Surfacefieldsandverticaltransectsof temperature
and salinity
confirm that
that upwelling
upwelling occurs
in
and
salinityconfirm
occursyear-round,
year-round,strongest
strongest
in summer
summerand
andweakest
weakestin
in
winter, bringing
bringing relatively
relatively fresh
fresh water
water to
to the
the surface
surface nearshore.
nearshore. Surface
flow
winter,
Surfacegeostrophic
geostrophic
flow
nearshore
is
throughout
During summer,
an anticyclonic
anticyclonic circulation
circulation
nearshore
is equatorward
equatorward
throughoutthe
the year.
year.During
summer,an
feature
in
the
north
which
extends
to
at
least
200
m
depth
is
evident
in
geopotential
anomaly
featurein the northwhichextendsto at least200 rn depthis evidentin geopotentialanomaly
and in
in both
both temperature
temperature and
and geopotential
geopotential variance
variance fields.
fields. Subsurface
Subsurface fields
fields indicate
indicate generally
generally
and
poleward
in an
undercurrent near
near the
the coast.
polewardflow
flow throughout
throughoutthe
theyear,
year,strongest
strongest
in
an undercurrent
coast.This
This
undercurrent is
is strongest
strongest in
in summer
summer and
and most
most persistent
persistent and
and organized
organized in
in the
the south
south (south
(south of
of
undercurrent
21°S).
A
subsurface
oxygen
minimum,
centered
at
-250
m,
is
strongest
at
lower
latitudes.
21øS).A subsurface
oxygenminimum,
centered
at ~250m, is strongest
at lowerlatitudes.
Low-salinity
subsurface water
water intrudes
intrudes into
into the
the study
study area
area near
near 100
m, predominantly
predominantly in
in
Low-salinitysubsurface
100 m,
offshore regions,
regions, strongest
strongest during
during summer
summer and
and fall
fall and
and in
in the
the southernmost
southernmost portion
portion of
of the
the
offshore
region.
fields are
are compared
compared to
to features
features off
off Baja
Baja within
within the
the somewhat
region.The
The climatological
climatologicalfields
somewhat
analogous California
California Current
Current and
and to
to measurements
measurements from
from higher
higher latitudes
latitudes within
within the
the Chile-Peru
Chile-Peru
analogous
Current
Currentsystem.
system.
1.
Introduction
1. Introduction
usually available
available from
from global-scale
such as
usually
global-scaleclimatologies,
climatologies,such
asthat
that
provided by
by Levitus
Levitus and
and Boyer
Boyer [1994].
All
climatologies
attempt
provided
[
1994].
All
climatologies
attempt
In addition
In
addition to
to their
theirintrinsic
intrinsicvalue
value in
indescribing
describingoceanic
oceanic to maximize the data for each grid point. Because data density is
to maximizethe datafor eachgrid point. Becausedatadensityis
conditions,
conditions,long-term
long-termmeans,
means,or
or climatologies,
climatologies,are
are essential
essentialfor
for low in most open-ocean regions, large grid box sizes are
identification and
and quantification
quantification of
longer low in most open-oceanregions, large grid box sizes are
identification
of interannual
interannual or
or longer
necessary for
necessary
for global
global climatologies,
climatologies, making
making accurate
accurate
timescale
variability
in
the
ocean.
As
an
example,
the
California
timescalevariabilityin the ocean.As an example,the California representation of coastal features impossible. Basin-scale [Lozier
representation
of
coastal
features
impossible.
Basin-scale
[Lozier
Cooperative
Fisheries
Investigation
(CaICOFI)
time
series
of
CooperativeFisheries Investigation(CalCOFI) time series of et al., 1995] and subbasin-scale climatologies of the North
et
al.,
1995]
and
subbasin-scale
climatologies
of
the
North
physical
in the
the southern
physicaland
andbiological
biologicalmeasurements
measurements
in
southernpart
part of
of the
the Atlantic [Kearns and Rossby 1998] and the Mediterranean
Atlantic
[Kearns
and
Rossby
1998]
and
the
Mediterranean
California
Current has
has made
California Current
made possible
possiblethe
the quantification
quantificationof
of [Brasseur et al., 1996] take advantage of higher data density in
[Brasseuret al., 1996] take advantageof higherdata densityin
variability
on aa range
These
variabilityon
rangeof
of timescales.
timescales.
Theseinclude
includethe
theseasonal
seasonal their regions of interest and are better able to resolve smallertheir regions of interest and are better able to resolve smallercycles
of
currents
and
water
properties
[Chelton,
1984;
Lynn
and
cyclesof cnrrentsand waterproperties[Chelton,1984; Lynnand scale features. Resolution of the Mediterranean Oceanographic
scalefeatures. Resolutionof the MediterraneanOceanographic
Simpson,
Simpson,1987],
1987], interannual
interannualvariability
variabilityin
in currents,
currents,water
watermasses,
masses, Data Base is 0.25° and that of the North Atlantic Current Region
Data
Baseis0.25ø andthatof theNorthAtlantic
Current
Region
and
volumes [Chelton
[Chelton et
er al.,
al., 1982]
as well
andzooplankton
zooplanktonvolumes
1982] as
well as
aslonglong- is 0.5°.
The
climatology
of
the
North
Atlantic
Current
region
has
is
0.5
ø
.
The
climatology
of
the
North
Atlantic
Current
region
has
term
[Roemmich
term changes
changesin
in the
theecosystem
ecosystem
[Roemmichand
andMcGowan,
McGowan, proven useful in identifying the frontal path of the North Atlantic
regional coastal
applicable to
1995]. Climatologies
1995].Climatologies
applicable
to regional
coastal
proven
inidentifying
the
frontal
path
of
theNorth
Atlantic
Currentuseful
[Kearns
and Rossby,
as aa comparison
to
Current
[Kearns
and
Rossby,1998],
1998],as
comparison
to field
field
oceanographic
processes require
require higher
oceanographic
processes
higherspatial
spatialresolution
resolutionthan
thanis
is data
design,
and
data[Carr
[Carretetal.,
al.,1997],
1997],as
asan
anaid
aidin
infield
fieldprogram
program
design,
andas
as
model
and Rothstein,
modelinput
input[Rowley
[Rowleyand
Rothstein,1998].
1998].
Here
the climatological
hydrography
'Instituto
de
Pesquero, Valparafso,
Valparaiso, Chile.
Chile.
and
•Instituto
deFomento
Fomento
Pesquero,
Here we
we present
presentthe
climatological
hydrography
and
2Now
at
Department
of
Ocean,
Earth
and
Atmospheric
Sciences,
Old
circulation
of
the
northern
Chile
upwelling
region
between
18°S
2Now
atDepartment
ofOcean,
Earth
and
Atmospheric
Sciences,
Oldcirculation
ofthenorthern
Chile
upwelling
region
between
18øS
Dominion University, Norfolk, Virginia.
Dominion
Norfolk,
Virginia.
3SchoolUniversity,
of Marine Sciences,
University of Maine, Orono, Maine.
and
(Figure
1)
area
isisembedded
within
the
and24°S
24øS
(Figure
1).This
This
area
embedded
within
thelarger
larger
Current system,
system,which
whichsupports
supportsone
one of
of the
the most
3School
ofMarine
Sciences,
University
ofMaine,
Orono,
Maine.Peru-Chile
•Current
most
Peru-Chile
4Jet
Propulsion Laboratory,
California
Institute of
4jetPropulsion
Laboratory,
California
Institute
ofTechnology,
Technology,
productive
fisheries in
in the
annual
productivefisheries
theglobal
globalocean.
ocean.Combined
Combined
annual
landings
of
all
pelagic
fish
off
Peru
and
Chile
typically
range
5College
of
Oceanic
and
Atmospheric
Sciences,
Oregon
State
•College
of
Oceanic
and
Atmospheric
Sciences,
Oregon
State
landings
of
all
pelagic
fish
off
Peru
and
Chile
typically
range
University, Corvallis, Oregon.
from 12
metric
tonnes
(Mlvii'),
global
University,
Corvallis,
Oregon.
from
12to
to18
18million
million
metric
tonnes
(MMT),out
outof
ofaatotal
total
global
Pasadena,
California.
Pasadena,
California.
Copyright 2001
2001 by
American
Geophysical
Union.
Copyright
bythe
the
American
Geophysical
Union.
Paper number
number 2000JC000540.
2000JC000540.
Paper
0148-0227/01/2000JC000540$09.00
0148-0227/01/2000JC000540509.00
catch of -80 MrVIT. Approximately 5-6 MIvIT are caught off
catch
MMT.
Approximately
5-6
MMT
arecaught
off
Chile,of
and~80
of
Chile,
and
of this
thisamount
amountabout
aboutone
onethird
third(2
(2 MMT
MMT of
ofmostly
mostly
small pelagic
pelagic fish
fish such
and
are
small
suchas
asanchovy
anchovy
andsardines)
sardines)
arecaught
caughtoff
off
northern
Chile.
However,
this
catch
is
large
subject
northernChile. However,this catchis subjectto
to large
11,451
11,451
11,452
11,452
BLANCO ET
CLIMATOLOGY
BLANCO
ET AL.:
AL.' NORTHERN
NORTI-[ERN CHILE
CHILE HYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
740W
74øW
73øW
72øW
71øW
70,øW
s
.18 =
.20 •
.21 c
.23 •
-24
444
444
333
333
222
111
37
222 111
37
DI8tanCe
from coast
coast (km)
Distancefrom
(krn)
44
Figure
region
off
coast
ofofChile
the
grid
calculations
and
Figure1.1.Map
Mapof
ofthe
thestudy
study
region
offthe
thenorth
north
coast
Chileshowing
showing
thespatial
spatial
gridfor
forclimatology
climatology
calculations
and
major
majorcities.
cities.Points
Pointsindicate
indicatethe
thecenter
centerof
of each
eachgrid
gridcell.
cell.
disruptions by
and
climate
Brandhorst [1971]
data
(Februarydisruptions
by interannual
interannual
andinterdecadal
interdecadal
climatevariability,
variability, Brandhorst
[ 1971]combined
combined
datafrom
fromtwo
twocruises
cruises
(Februaryexacerbated by
by extreme
the
circulation
between
150
exacerbated
extreme fishing
fishing pressure.
pressure.For
For instance,
instance,the
the March)
March)to
to describe
describe
theoceanic
oceanic
circulation
between
15øand
and42°S
42øS
anchovy
catch
off
northern
Chile
has
usually
fluctuated
between
in
the
summer
of
one
year
(1960).
He
observed
equatorward
anchovycatchoff northernChile hasusuallyfluctuatedbetween in the summerof one year (1960). He observedequatorward
0.5
flow in
2000.5 and
and2.0
2.0 MMT
MMT since
since1986
1986but
butfell
fell to
to 0.18
0.18MMT
MMT in
in 1987
1987and
and surface
surfaceflow
in the
the100
100km
kmnext
nextto
tothe
thecoast
coastand
andbeginning
beginning
2000.14
influenced
by
these
equatorward
currents,
0.14 MMT
MMT in
in 1998,
1998,22years
years
influenced
byEl
ElNiflo
Nifioconditions
conditions300
300 km
km offshore.
offshore.In
Inbetween
between
these
equatorward
currents,aa
[IFOP,
et al.
extended
from
Other
[IFOP, 1998,
1998,1999].
1999]. Thomas
Thomaset
al. [20011
[2001] show
showthe
theextreme
extreme poleward
polewardsurface
surfacecountercurrent
countercurrent
extended
from19°-35°S.
19ø-35øS.
Other
changes
in
vertical
temperature
structure
and
surface
chlorophyll
authors
have
referred
to
an
offshore
poleward
surface
current
changesin verticaltemperature
structureandsurfacechlorophyll authorshavereferredto an offshorepolewardsurfacecurrentoff
off
patterns in
in this
with
but there
the Peru-Chile
patterns
thisregion
regionassociated
associated
with the
the1996-1998
1996-1998La
LaNifla
Nifia Peru
Peru as
as the
Peru-ChileCountercurrent,
Countercurrent,but
there is
is less
less
and El
here
about its
its existence
and
El Niflo
Nifio events.
events.The
Theclimatology
climatologypresented
presented
herequantifies
quantifies agreement
agreementabout
existenceand
andlocation
locationoff
off Chile
Chile[Fonseca,
[Fonseca,
the mean
Strub et
et al.,
al., 1995].
showed
the
meanphysical
physicalenvironment
environmentassociated
associatedwith
with this
thisvariability
variability 1989;
1989;$trub
1995].Below
Belowthe
thesurface,
surface,Brandhorst
Brandhorst
showed
and provides
a baseline
against
which
anomalies and
and aa poleward
undercurrent
next
slope
from
and
provides
a
baseline
against
whichto
tocalculate
calculate
anomalies
poleward
undercurrent
nextto
tothe
thecontinental
continental
slope
from15°
15øto
to
oxygen
quantify
future
changes.
water
with
extremely
low
40°S
carrying
salty
quantifyfuturechanges.
40øS carrying salty water with extremely low oxygen
Few
south.
This
to the
Few of
of the
theprevious
previousstudies
studiesof
ofthis
thisoverall
overallregion
regioninclude
include concentrations
concentrationsto
the south.
This feature
feature was
wasobserved
observed
information on
on the
the mesoscale
structure
or previously
off Peru
information
mesoscale
structureof
of either
eitherwind
wind forcing
forcingor
previouslyoff
Peruand
andnorthern
northernChile
Chile by
byGunther
Gunther[1936]
[1936]and
and
oceanic
in
ocean.
Wind
off
Chile
with an
oceanicconditions
conditions
in the
theChilean
Chileancoastal
coastal
ocean.
Windforcing
forcing others.
others.Station
Stationspacing
spacing
off northern
northern
Chilewas
wasabout
about10,
1ø,with
an
for
Peru-Chile
drew
for the
thelarger-scale
larger-scale
Peru-ChileCurrent
Currentsystem
system(and
(andother
othereastern
eastern extra
extrastation
stationincluded
includednear
nearthe
thecoast.
coast.Brandhorst
Brandhorst
drewschematic
schematic
boundary currents)
currents) is
is presented
by Bakun
boundary
presentedby
Bakunand
and Nelson
Nelson[1991].
[1991]. diagrams
diagramsshowing
showingcross-shelf
cross-shelfsections,
sections,which
which indicated
indicatedthat
that
and
Their
from
Their seasonal
seasonalclimatology
climatologyis
is constructed
constructed
from merchant
merchantship
ship upwelling
upwellingbrought
broughtwater
waterfrom
fromboth
boththe
theundercurrent
undercurrent
andfrom
froman
an
observations,
binned into
into 10
squares. This
This spatial
scale is
is too
minimum to
to the
Chile.
observations,
binned
1ø squares.
spatialscale
too offshore
offshoresalinity
salinityminimum
thesurface
surfaceoff
off northern
northern
Chile.
this analysis
information
large to
large
to represent
representthe
the nearshore
nearshorewinds
windsover
overthe
thenarrow
narrowshelf,
shelf, Although
Although this
analysisprovided
providedno
no seasonal
seasonal
informationand
and
poorly
resolved
the
region
within
100
km
of
which
at
these
low
latitudes
are
modified
by
strong
land-sea
which at these low latitudesare modifiedby strongland-sea poorly resolvedthe region within 100 km of the
the coast,
coast,the
the
temperature
differences. The
The Bakun
features described
described by
by Brandhorst
Brandhorst [1971]
temperaturedifferences.
Bakunand
andNelson
Nelsonclimatology
climatology essential
essential
features
[1971] are
arethose
thosemost
most
agrees
agrees with
with other
other observations
observationsin
in suggesting
suggestingthat
that the
the wind
wind often
oftenfound
foundin
in later
laterstudies.
studies.
forcing
weakens as
as one
atlas
forcing weakens
one moves
movesnorth
northtoward
towardthe
the change
changein
in Inostroza
Inostroza[1972]
[1972] attempted
attemptedto
to construct
constructaa seasonal
seasonal
atlasusing
using
the
data
available
at
the
time,
which
consisted
of
only
coastal
orientation
at
the
border
of
Peru
and
Chile.
It
does
not
coastalorientationat the border of Peru and Chile. It does not the data availableat the time, which consistedof only 36
36 cruises
cruises
represent
maximum
representthe
the seasonal
seasonal
maximumvery
verywell,
well, however,
however,finding
findingaa between
between1875
1875 and
and1968.
1968.The
The data
datacovered
coveredparts
partsof
of the
theChilean
Chilean
maximum
off
Chile
to 50°S
the
maximumin
in winter
winter(June-September)
(June-September)
off northern
northern
Chile(20°(20ø- coast
coastfrom
from18°
18øto
50øSin
in 10
1øboxes.
boxes.The
Thefields
fieldsagain
againshowed
showed
the
features of
of the
the upwelling
in
24°S).
A 10
wind
24øS). A
10year
yearclimatology
climatologyof
ofalongshore
alongshore
windstress
stressessential
essential
features
upwelling$'stem
system
inthe
thenorth
north(described
(described
at
calculated
Weather
calculatedfrom
from European
EuropeanCentre
Centrefor
forMedium-Range
Medium-Range
Weather above),
above),but
butthe
thepicture
picturein
in each
eachseason
season
ateach
eachlocation
locationwas
wasoften
often
determined
by
only
one
or
a
few
measurements,
resulting
Forecasts
(ECMWF)
winds
[Thomas,
1999]
indicates
a
springForecasts(ECMWF3 winds [Thomas,1999] indicatesa spring- determinedby only oneor a few measurements,
resultingin
in very
very
fields. Silva
Silva and
and Fonseca
Fonseca [1983],
[1983], Bemal
summer
these
summermaximum
maximumbetween
between200
20ø and
and25°S,
25øS,although
although
thesedata
data noisy
noisyfields.
Bernalet
etal.
al.[1982],
[1982],and
and
cruises to
Fonseca
used selected
selected cruises
the
also
to characterize
alsosuffer
sufferfrom
fromaa coarse
coarsegrid
gridscale.
scale.Coastal
Coastalwind
windmeasurements
measurements
Fonseca[1989]
[1989] used
characterizethe
circulation
off
the
northern
half
of
Chile
as
composed
presented
by
Shaffer
et
al.
[1997,
1999]
indicate
a
clear
springpresented
by Shafferet al. [1997, 1999] indicatea clearspring- circulationoff the northernhalf of Chile as composedof
of
bands of
of equatorward
and
summer
maximum
in alongshore
wind
at
summermaximumin
alongshore
windstress
stress
at30°S
30øSconsistent
consistentalternating
alternating
bands
equatorward
andpoleward
polewardflow.
flow. These
Theseare
are
with
seasonal
maximum
similar
to those
[1971],
with the
thespring
springand
andsummer
summer
seasonal
maximumreported
reportedby
by somewhat
somewhat
similarto
thosefound
foundby
byBrandhorst
Brandhorst
[1971],although
although
Bernal
et al.
five or
others
Pizarro et
etal.,
others[Fuenzalida,
[Fuenzalida, 1989;
1989; Pizarro
al., 1994].
1994].
Bernal et
al. describe
describefive
or more
more bands.
bands.Fonseca
Fonseca[1989]
[ 1989] depicts
depicts
BLANCO ET
ET AL.:
AL: NORTHERN
CLIMATOLOGY
BLANCO
NORTHERN CHILE
CHILE HYDROGRAPHIC
HYDROGRAPHIC
CLIMATOLOGY
11,453
11,453
al., submitted
manuscript,
2000),
presented
here
the poleward
poleward surface
surface flow
flow between
between 100
100 and
and 300
300 km
km offshore
offshore as
as al.,
the
submitted
manuscript,
2000),the
theclimatology
climatology
presented
here
is
used
to
quantify
physical
variability
during
the
strong
1997maximum
in
summer
and
present
year-round,
but
the
small
maximumin summerand presentyear-round,
but the small is usedto quantifyphysical
variability
duringthestrong19971998
number
of
used
this conclusion
conclusion tentative.
number
of cruises
cruises
used(six)
(six)makes
makesthis
tentative.
1998El
E1Niflo.
Nifio.
We have
the paper
paper as
as follows:
In section
section 22 we
A more
morerecent
recentatlas
atlasby
byRojas
Rojasand
andSilva
Silva[1996]
[1996]provides
provides We
haveorganized
organized
the
follows:In
we
details
of
data
protocols,
monthly fields
fields of
of temperature,
salinity
at
monthly
temperature,
salinityand
andoxygen
oxygen
atvarious
variouspresent
present
details
ofthe
thehistorical
historical
dataset,
set,data
datacollection
collection
protocols,
methods used
used for
for presentation
presentationof
of the
the data.
data. The
depths for
for the
between
18.5°S
and
again
using
10
depths
theregion
region
between
18.5øS
and50°S,
50øS,
again
using
1ø and
andthe
thegridding
gridding
methods
The
climatological
seasonal
cycles
are
presented
in
section
3,
bins.
These
data
come
from
nearly
200
cruises,
most
between
bins.Thesedatacomefromnearly200 cruises,
mostbetweenclimatological
seasonal
cyclesarepresented
in section
3, first
firstfor
for
meteorological
and
stations,
1957
only
view
1957and
and1995,
1995,but
butstill
stillprovide
provide
onlyaacoarse
coarse
viewof
ofthe
theregion
region three
threecoastal
coastal
meteorological
andtide
tidegauge
gauge
stations,then
thenfor
for
in the
the study
next to
to the
Despite
the
number
of
the
next
thecoast.
coast.
Despite
thegreater
greater
number
ofobservations
observations
the water
watermass
massproperties
properties
in
studyarea,
area,and
andlastly
lastlyfor
for the
the
hydrographic
fields.
Section
4
discusses
the
results
in
light
use of
averages
produces
fields that
that continue
to
use
ofmonthly
monthly
averages
produces
fields
continue
tobe
be hydrographic
fields.Section
4 discusses
theresults
in lightof
of
in
the
Chile-Peru
Current
noisy. The
The offshore
surface
temperature
and salinity
fields
noisy.
offshore
surface
temperature
and
salinity
fieldsare
are other
otherobservations
observations
inthis
thisregion,
region,
thegreater
greater
Chile-Peru
Current
and
similar
California
Current.
Section
55
very similar
similar to
to the
fields
here,
although
the
very
thesurface
surface
fieldswe
wepresent
present
here,
although
the system
system
andin
inthe
thesomewhat
somewhat
similar
California
Current.
Section
aabrief
fields next
lack
cross-shelf
gradients
fields
nextto
to the
thecoast
coast
lackthe
thestrong
strong
cross-shelf
gradientsprovides
provides
briefsummary.
summary.
found in
in our
of the
found
our fields.
fields. Some
Some of
the results
resultsfrom
from the
the 100
100 m
m depth
depth
fields from
from Rojas
Rojas and
and Silva
Silva are
are summarized
sunmiarized in
in section
section 4.
4.
2. Data
Data and Methods
fields
Methods
Within
the
existing
data
set
used
by
Rojas
and
Silva
Within the existingdataset usedby Rojasand Silva[1996],
[1996],
the greatest
data density
is found
the
greatestdata
densityis
foundin
in the
theregion
regionoff
offnorthern
northern 2.1. Hydrographic Data
2.1. Hydrographic Data
Chile. This
monitored
Chile.
This area
areahas
hasbeen
beensystematically
systematically
monitoredby
by the
the
data used
used to
this
were
(Instituto
de
Fomento
Institute
Fisheries Institute (Instituto de Fomento The
Chilean national
Chilean
national Fisheries
Thehydrographic
hydrographic
data
to calculate
calculate
thisclimatology
climatology
were
collected
by
IFOP
in
the
upwelling
region
off
northern
Chile
Pesquero
(IFOP))
because
of
its
economic
value.
The
available
Pesquero
(IFOP))because
of itseconomic
value.Theavailablecollected
by IFOPin theupwelling
regionoff northern
Chile
1). A
sampled
between
1964
IFOP database
database extends
extends over
(1964-1996)
and
this
IFOP
over30
30years
years
(1964-1996)
andmakes
makes
this (Figure
(Figure1).
Atotal
totalof
of4740
4740stations,
stations,
sampled
between
1964and
and
1996 (Figure
(Figure 2)
2) and
between
18°S
and
and
one of
within
the
Current
system
one
ofthe
thefew
fewregions
regions
within
thePeru-Chile
Peru-Chile
Current
system1996
andtaken
taken
between
18øS
and24°S
24øS
andwithin
within
440 km
of the
were used.
used. Figure
22 shows
that
where
of
reliable
climatology
is
wherethe
theconstruction
construction
of aarelatively
relatively
reliable
climatology
is 440
kmof
thecoast
coast(-74°W),
(-74øW),were
Figure
shows
that
with
the
sampling
was
remarkably
consistent
temporally,
possible.
Here
we
use
this
database
to
present
the
seasonal
possible.
Herewe usethisdatabase
to present
the seasonal
sampling
was remarkably
consistent
temporally,
with the
exception
of
the
period
in
the
mid-to
late
1970s.
Spatially,
climatology
on
spatial
scales
small
enough
to
resolve
the
climatology
on spatialscalessmallenoughto resolvethe exception
of the periodin the mid-tolate 1970s.Spatially,
sampling
is representative
of the
the area
area in
in Figure
relatively
narrow region
region of
of upwelling
near the
the coast.
The
relatively
narrow
upwelling
near
coast.
The station
station
sampling
is
representative
of
Figure1,
1,with
with
greatest
sampling density
density within
within -200
-200 km
and
supplemented by
by climatological
are supplemented
hydrographic
data are
hydrographic
data
climatological
greatest
sampling
kmof
ofthe
thecoast
coast
andin
inthe
the
Quality
control
of
the
northern
portion
of
the
study
area.
meteorological
and
tide
gauge
data
from
coastal
stations,
which
meteorological
andtidegauge
datafromcoastal
stations,
whichnorthern
portion
of thestudyarea.Quality
control
of thedata
data
For
were
serve
offshore
hydrography
and
serveas
asaalink
linkbetween
between
offshore
hydrography
andcoastal
coastalwas
wassubjective.
subjective.
Foreach
eachgrid
gridpoint,
point,all
allprofiles
profiles
wereexamined
examined
Only those
deviations
from
processes.
In
(J.L. Blanco
processes.
In aa companion
companionpaper
paper (J.L.
Blanco et
et al.,
al., visually.
visually.Only
thosewith
withobvious
obvious
deviations
fromexpected
expected
such
inversions,
were
Profiles
from
Hydrographic
conditions off
off northern
northern Chile
Chile during
during the
the 1996
Hydrographic
conditions
1996La
La trends,
trends,
suchas
asdensity
density
inversions,
wereremoved.
removed.
Profiles
from
El
Niño
periods
were
purposely
not
filtered
from
our
data
Nina
and
the
1997-1998
El
Nino,
submitted
to
Journal
of
Nina and the 1997-1998E1 Nino, submitted
to Journalof E1Nifioperiods
werepurposely
notfilteredfromourdataset.
set.
3% of
of the
Geophysical
Research, 2000,
referred
Geophysical
Research,
2000,hereinafter
hereinafter
referredto
to as
asBlanco
Blancoet
et Approximately
Approximately
3%
theoriginal
originalprofiles
profileswere
wereeliminated
eliminatedby
by
a)
a)
-18 -
::!;
i Ii
::
-
-19
-19
-
-20
-
ß
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eee
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...:..a,
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I I "• .I I II
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I
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p
59 60 61 tt2 63 84 85 86 67 68 6,9 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 80 87 88 89 90 91 92 93 94 95 •5
97
Ys
Years
b)
b)
-70-71 -
SI
'r.i;
SI
-72 -
.1.1
-73 -
S
I- S SI
II
%upt
$s
..
iC.I,
S
-75
I
ii
-
I
I
I
I
I
£
I
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I
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1 ir1m..
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at
9 .I,S
$
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Si.. S
-74 -
I
£iuç
I
:..
'41
II"tM.
I
I
I
,
I
I
I
Vs
Years
and (b)
distribution
of hydrographic
stations
making
Figure 2.
Figure
2. (a)
(a) Time-latitude
Time-latitude
and
(b) time-longitude
time-longitude
distribution
of
hydrographic
stations
makingup
upthe
thehistorical
historical
database for
for the north of Chile.
Chile.
11,454
11,454
BLANCO ET
El AL.:
BLANCO
AL.: NORTHERN
NORTHERN CHILE
CHILE HYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
this screening.
Although
errors of
of both
this
screening.
Althougherrors
bothinclusion
inclusionand
andexclusion
exclusion
available
were undoubtedly
made,
were
undoubtedly
made, the
the number
numberof
ofstations
stations
available
minimizes the
the biases
biases in
presented here.
here.
minimizes
in the
the climatological
climatologicalmeans
meanspresented
From
1964
to
1991,
samples
were
obtained
using
Nansen
From 1964 to 1991, sampleswere obtainedusingNansenor
or
Niskin bottles
Salinity
Niskin
bottleswith
with calibrated
calibratedreversing
reversingthermometers.
thermometers.
Salinity
and
from
samples
taken
andoxygen
oxygenwere
weremeasured
measured
fromdiscrete
discrete
samples
takenfrom
from
standard
with
standarddepths.
depths.Salinity
Salinitywas
wasmeasured
measured
withAutolab
Autolabinduction
induction
salinometers.
Oxygen concentrations
concentrations were
were obtained
salinometers.
Oxygen
obtainedby
by Winkler
Winkler
titration and
the modification
of Carpenter
titration
and included
includedthe
modificationof
Carpenter[1965]
[ 1965] after
after
1967. Beginning
Beginning in
and
1967.
in 1992,
1992,temperature
temperature
andsalinity
salinitywere
wereobtained
obtained
using
either aa Neil
MK 33 or
usingeither
Neil Brown
Brown MK
or aaSea
SeaBird
Bird(model
(model19)
19)
conductivity-temperature-depth
probe
(Cm).
The
conductivity-temperature-depth
probe (CTD). The CTDs
CTDs are
are
calibrated
every 22 years,
calibratedevery
years,and
anddata
datafrom
fromindividual
individualcruises
cruisesare
are
validated
and
validatedwith
with reversing
reversingthermometers
thermometers
andsalinity
salinitysamples.
samples.
Oxygen
continued
to
by
Oxygenconcentrations
concentrations
continued
tobe
bedetermined
determined
bylaboratory
laboratory
analysis
of
throughout
the
analysis
of water
watersamples
samples
throughout
theperiod.
period.
The
the
Thespatial
spatialgrid
gridused
usedto
tobin
binand
andaverage
average
thedata
datawas
wasdesigned
designed
to
(1) the
to balance
balancetwo
two conflicting
conflictingrequirements:
requirements:(1)
the inclusion
inclusionof
of
Table 1.
Table
1. Number
Numberof
of Surface
SurfaceTemperature
TemperatureStations
Stations
Contributing
Mean
Contributingto
tothe
theClimatological
Climatological
Meanin
inEach
Each
Grid Cell
Cell of
Grid
of Figure
Figure11for
forEach
EachSeasona.
Season
a.
Grid
Gridpositionb
Position
b
11
12
12
15
15
11
11
0
2
4
2
29
29
29
21
4
5
11
11
distance
from shore.
shore. The
distancefrom
Thegrid
gridcell
cellclosest
closestto
tothe
thecoast
coasthas
hasan
an
offshore
offshoreboundary
boundaryat
at 19
19 km.
km, and
andthese
theseincrease
increaseoffshore
offshoreto
to37,
37,
111,
111, 222,
222, 333,
333, and
and444
444 km.
km.This
Thisdistribution
distributionattempts
attemptsto
to
maximize
the number
maximize the
number of
of stations
stationscontributing
contributingto
to the
theaverage
average
values of
of each
values
eachseason
seasonat
ateach
eachspatial
spatialpoint
point[Blanco,
[Blanco,19961.
1996].Table
Table
11 shows
showsthe
the number
numberof
of Stations
stationscontributing
contributingto
tothe
theclimatological
climatological
values of
season, in
each grid
grid cell,
cell, using
of each
values
each season,
in each
using surface
surface
temperature
as
an
example.
Samples
for
salinity
were
temperatureas an example. Samplesfor salinitywere±10%
_+10%of
of
these values.
values.
these
Hydrographic
data were
Hydrographicdata
were averaged
averagedin
in time,
time,within
withinthe
thegrid,
grid, to
to
construct
a
seasonal
climatology
of
temperature,
salinity,
constructa seasonalclimatologyof temperature,salinity,and
and
of seasons
dissolved
dissolvedoxygen.
oxygen. The
The definition
definition of
seasonsused
used here
here is
is
summer
summer(January-March),
(January-March), fall
fall (April-June),
(April-June), winter
winter (July(JulyVertical data
September), and
September),
and spring
spring(October-December).
(October-December). Vertical
data
within
depths
within each
eachgrid
grid cell
cell were
wereinterpolated
interpolatedto
to13
13standard
standard
depths(0,
(0,
10,
25, 50,
10, 25,
50, 75,
75, 100,
100, 125,
125, 150,
150, 200,
200, 250,
250, 300,
300, 400,
400, and
and 500
500 m)
m)
before
resolution in
in the
the upper
before averaging,
averaging, maximizing
maximizing resolution
upper water
water
column.
column. Density
Density variables
variablesand
andgeopotential
geopotentialanomalies
anomalieswere
were
Summer
Summer
38
25
36
22
24
21
4
5
6
38
37
37
39
25
30
30
24
16
36
18
13
12
16
45
45
35
25
25
28
35
20
20
40
23
25
32
14
17
16
15
17
20
20
48
38
57
39
32
32
33
121
100
90
79
82
103
48
47
52
47
48
49
74
87
52
29
20
20
27
26
23
27
56
50
50
70
68
13
13
Fall
Fall
12
8
6
6
6
4
36
15
8
13
36
20
40
28
25
30
19
7
6
4
6
7
37
25
Winter
Win•r
99
49
14
5
8
3
55
55
34
19
22
sufficient stations
stationstoto calculate
calculate aa realistic
mean and
and (2)
sufficient
realistic mean
(2) the
the
retention
retentionof
of sufficient
sufficientresolution
resolutionto
toresolve
resolvethe
thestrong
strongcross-shelf
cross-shelf
gradients
within
40
km
of
the
coast.
Traditional
1°
gradients
within40 kmof thecoast.Traditional
1øgrid
gridsquares
squares
do not
near the
the coast,
but the
do
notprovide
providesufficient
sufficientresolution
resolutionnear
coast,but
the
latitudinal separation
between
occupied
latitudinal
separation
betweenthe
themost
mostconsistently
consistently
occupied
transects
did not
0.50
transects
did
not allow
allowformation
formationof
of aasquare
square
0.5øgrid.
grid. The
The
spatial
grid
used
here
has
10
resolution
in
latitude
and
spatialgridusedherehas1ø resolution
in latitudeandaavarying
varying
longitudinal (cross-shell)
1), based
based on
longitudinal
(cross-shelf) dimension
dimension (Figure
(Figure 1),
on
3
18
55
5
40
12
46
50
50
20
20
Spring
Spring
52
52
34
46
46
14
37
11
11
12
34
37
15
15
41
67
44
43
39
101
101
76
87
84
51
51
47
47
Within each
each season,
values
are
geographically
aWithin
season,
values
arearranged
arranged
geographically
frm north to south (top to bottom).
fr•m
north
to
south
(top
to
bottom).
Grid positions
positions are
Grid
arefrom
fromwest
westto
toeast
eastas
asin
in Figure
Figure1.
1.
subsequent
interpretation.
temperature
means,
subsequent
interpretation.For
For the
thesurface
surface
temperature
means,
the range
was
never
the
rangeof
of S
Sxover
overall
allseasons
seasons
was0.06°C-0.79°C,
0.06øC-0.79øC,
neveras
as
large
as the
Only 11
of the
large as
the contour
contourinterval.
interval.Only
11 of
the total
totalof
of 144
144grid
grid
cells
cells(4
(4 seasons,
seasons,36
36 cells
cellsin
in each)
each)had
hadvalues
values>0.5°C.
>0.5øC. These
These11
11
values
were
grouped
into
two
locations:
in
the
grid
cells
farthest
valueswere groupedinto two locations:in the grid cellsfarthest
offshore
where nn was
low (Table
1) and
offshore where
was relatively
relatively low
(Table 1)
and in
in the
the
upwelling frontal
frontal zone
zone during
upwelling
during spring
spring and
andsummer,
summer,where
where
variance is
is expected
calculated
and
expectedto
to be
begreatest.
greatest. For
For the
thesurface
surfacesalinity
salinity
calculatedin
in each
eachbin
binfrom
fromthe
theaveraged
averagedtemperature
temperature
andsalinity
salinity variance
means,
S
ranged
from
0.010
to
0.114.
Only
5
of
profiles
for
each
season.
means,Sxrangedfrom 0.010 to 0.114. Only 5 of the
the144
144grid
grid
profilesfor eachseason.
than our
our 0.1
0.1 contour
contour interval.
interval. Each
An
with
cells had
had values
values greater
greaterthan
Each of
of
An analysis
analysisof
of the
theexpected
expectederror
errorassociated
associated
with the
thegridded
gridded cells
means
was carried
thesefive
five were
were in
in the
thegrid
gridcells
cellsfarthest
farthestoffshore,
offshore,where
wheren
n was
was
means was
carried out.
out. Our
Our purpose
purpose was
was to
to evaluate
evaluatethe
the these
confidence
(temperature,
temperatureS•
S in
relativelysmall.
small. Subsurface
Subsurfacetemperature
in the
thegrid
gridcells
cells
confidencewith
with which
whichthe
thepatterns
patternsof
ofhydrography
hydrography
(temperature, relatively
salinity,
and
oxygen
contour
intervals
of
1.0°C,
0.1
practical
making
up
the
three
cross-shelf
vertical
sections
(three
transects
salinity,and oxygencontourintervalsof 1.0øC,0.1 practical makingup the three cross-shelfvertical sections(threetransects
locations
salinity
units (psu),
should
be
four seasons
seasonsxx 71
71 depth/space
depth/space
locations=
= 852
852 cells)
cells)had
hadaa
salinityunits
(psu),and
and1.0
1.0mL
mLU'
L'•respectively)
respectively)
should
be xx four
than
interpreted.
Standard
errors, Sx
S ==ss/ /n"2
ssisisthe
ßwider
widertotal
totalrange
range(0.04°C-2.23°C)
(0.04øC-2.23øC)
thansurface
surfacevalues.
values.Fewer
Fewer
interpreted.
Standard
errors,
nm,,where
where
thestandard
standard
deviation
and nn is
of than
deviation and
is the
the number
number of
of stations,
stations, were
were calculated
calculated of
than5%
5% of
of these
thesegrid
gridcells,
cells,however,
however,actually
actuallyhad
hadvalues
valuesgreater
greater
temperature
and salinity
for
than
than0.5°C,
0.5øC,and
andonly
only0.5%
0.5%had
hadvalues
valuesgreater
greater
thanour
our1.0°C
1.0øC
temperatureand
salinityin
in each
eachgrid
gridcell
celland
andseason
season
forsurface
surface than
spatial
interval. Elevated
contourinterval.
Elevatedvalues
valueswere
werelocated
locatedin
in the
thegrid
gridcells
cells
spatial fields
fields and
and of
of temperature,
temperature,salinity,
salinity,and
and oxygen
oxygenfor
for the
the contour
three
sections used
used to
three cross-shelf
cross-shelf vertical
vertical sections
to characterize
characterize the
the farthest
farthestoffshore,
offshore,where
wherenn was
wasrelatively
relativelysmall
smalland
andat
atthe
thedepth
depth
Subsurface salinity
salinity S•
S in
climatological
of the
thethermocline.
thermocline.Subsurface
in the
thegrid
gridcells
cellsof
of the
the
climatological subsurface
subsurfacestructure.
structure. Standard
Standard errors
errors which
which of
vertical sections
sections had
had aa range
approach
three cross-shelf
cross-shelfvertical
rangeof
of 0.005-0.159
0.005-0.159
approachthe
the contour
contourinterval
intervalsuggest
suggestthat
thatthe
thehydrographic
hydrographic three
>0.1 psu.
psu. Subsurface
parameter
at that
psu,with
with fewer
fewer than
than0.6%
0.6% having
havingvalues
values>0.1
Subsurface
parameterat
that particular
particular grid
grid cell
cell might
might be
be shifted
shiftedby
by one
one psu,
oxygen
concentration
S.,
in
the
grid
cells
of
the
three
and
temporally
interval
because
of
uncertainty.
Spatially
oxygen
concentration
S•
in
the
grid
cells
of
the
threecross-shelf
cross-shelf
interval because of uncertainty. Spatially and temporally
sections ranged
rangedfrom
from 0.02
0.02 to
to 0.73
0.73 mL L
U',
coherent
patterns across
verticalsections
-•,with
withfewer
fewer
coherentpatterns
acrossmany
many grid
grid cells
cellsof
of standard
standarderror
error at
at the
the vertical
2% having
having values
values >0.5
>0.5 mL
mL L
L'.
analyses
suggest
that,
same
as the
than2%
-•.These
These
analyses
suggest
that,
same magnitude
magnitude as
the contour
contourinterval
interval call
call into
intoquestion
questionthe
the than
in
general,
the
presented
climatological
means
here
entire
local
pattern
associated
with
the
contours
and
hence
their
are
entire local pattern associatedwith the contoursand hencetheir in general, the climatological means presented here are
LANCO ET
ET AL.:
AL.: NORTI-[ERN
NORTHERN CHILE HYDROGRAPHIC
BLANCO
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
statistically
robust and
and that
statisticallyrobust
thathydrographic
hydrographicpatterns
patternsin
in each
eachseason,
season,
at
chosen, can
can be
interpreted with
with
at the
the contour
contour intervals
intervals chosen,
be interpreted
reasonable confidence.
Maximum uncertainty,
reasonable
confidence. Maximum
uncertainty,although
althoughstill
still
smaller
than the
the contour
contour interval,
interval, is
smallerthan
is present
presentin
in the
themost
mostoffshore
offshore
Jan
Jan
ß
l-.
Apr
Mar
kin
May
Mar Apr May Jun
.1Feb
t
,
I
, 1,1
I
,
I
• I
•
,
I
I
11,455
11,455
Jul
Aug •ep
usp
Jul Aug
I
•
I
II
,
Oct
Oct Nov
Nov Liac
I
,
I
I
,
I
,
lO
grid cells,
grid
cells, where
where gradients
gradientsand
andseasonal
seasonalvariability
variability are
are weak
weak
anyway,
and in
anyway, and
in locations
locations (the
(the upwelling
upwelling frontal
frontal zone
zone and
and
thermocline) where
where variance
variance due
due to
thermocline)
to intraseasonal
intraseasonaland
and interannual
interannual
variability
is expected
expected to
to be
variabilityis
be greatest.
greatest.
2.2. Time
Time Series
Series atat Coastal
Coastal Stations
Stations
2.2.
Monthly averages
averages of
of coastal
coastal sea
sea level
Monthly
level were
were obtained
obtainedfrom
from the
the
University
of
Hawaii
Sea
Level
Center
for
Arica
(18.5°S)
Universityof Hawaii Sea Level Centerfor Atica (18.5øS)and
and
Antofagasta (23.5øS)
(23.5°S) (see
(see Figure
Figure 1)
These data
data are
Antofagasta
1).. These
areavailable
availablefor
for
the period
the
periodJanuary
January1975
1975 to
to April
April 1998.
1998.Climatological
Climatologicalmonthly
monthly
means were
were calculated
calculated after
means
after correcting
correctingfor
for the
the inverse
inversebarometer
barometer
effect, using
pressure obtained
obtained from
from the
effect,
using atmospheric
atmosphericpressure
the U.S.
U.S.
Climate
Analysis
Center.
ClimateAnalysisCenter.
Monthly averages
averages of
of coastal
(SS1')
Monthly
coastalsea
seasurface
surfacetemperature
temperature
(SST)
were calculated
calculated from
from data
data measured
measured daily
daily at
at the
were
the two
two tide
tide gauge
gauge
..................
].'.
-•'"'-.-
•('"i
"•' '•.'•.'' ' ' 2 ':':'""'
1(t
'"""- - '"'"
[15
'$ .•..-'...,..•..
•••--_
'..-o•
.,.,.
1J 4
b)
'".? '--• ,.,--"•'
-
•.•'
.."""
ß
...
..--
stations mentioned
mentioned above
above and
and aa third
stations
thirdstation
stationat
atIquique
Iquique(20.5°S)
(20.5øS)
6
(see Figure
1). These
These data
data were
by the
(see
Figure 1).
were provided
provided by
the Naval
Naval
Hydrographic
Hidrografico yy Oceanografico
Oceanografico de
de
HydrographicService
Service(Servicio
(ServicioHidrografico
Ia Armada
Armada de
de Chile
Chile (SHOA))
(SHOA)) for
for the
the period
period 1960-1997.
la
1960-1997.
Climatological monthly
monthly averages
averages of
of wind
wind speed
speed and
Climatological
and direction
direction
were
calculated
from
daily
measurements
at
were calculated from daily measurementsat the
the airport
airport
meteorological stations
stations of
of Atica,
Arica, Iquique,
Iquique, and
and Antofagasta
for
meteorological
Antofagastafor
the period
the
period 1970
1970 to
to 1997.
1997. These
Thesedata
datawere
were provided
provided by
by the
the
Chilean meteorological
service, Direccion
de
Chilean
meteorologicalservice,
Direccion Meteorologica
Meteorologica de
d)
...............
r"-,
I
i
,
i
I
Jan Fab
Jan
Feb Mar
M•
,
I
I
,
i
,
i
Apr
Apr May
May Jun
Jun
,
I
,
.i
,
i
,
i
,
i
,
1
Jul
Jul Aug
Aug Sep
Sep Oct
Oct Nov
Nov Dec
Dec
Chile.
takenatat 1500
1500 LT
LT was
was used,
Chile. The
The measurement
measurement taken
used, as
as itit Figure 3. Monthly climatologies from coastal stations at Arica
Figure 3. Monthly climatologiesfrom coastalstationsat Arica
corresponds to the maximum wind intensity of the daily cycle (solid line), Iquique (dotted line) and Antofagasta (dashed line)
corresponds
tomaximum
themaximum
wind
intensity
ofthe
daily
cycle(solid
line),
Iquique
(dotted
line)andAntofagasta
(dashed
line)
and presents
persistence
in speed
and
direction
of
(a)
sea
level
(Arica
and
Antofagasta
only),
(b)
sea
surface
and
presents
maximum
persistence
in
speed
and
direction
of
(a)
sea
level
(Atica
and
Antofagasta
only),
(b)
sea
surface
[Pizarro
et
Chilean
coastline
is
(c) alongshore
wind
and
[Pizarro
etal.,
al.,1994].
1994].The
Thenorthern
northern
Chilean
coastline
isoriented
orientedtemperature,
temperature,
(c)
alongshore
windvelocity,
velocity,
and(d)
(d)cross-shore
cross-shore
approximately north-south,
north-south, and
and here
here we
we refer
refer to
approximately
to the
thenorth-south
north-southwind
windvelocity.
velocity.
wind component
component as
as the
the alongshore
alongshore wind
wind at
at each
each location.
location.
wind
3. Results
Results
3.
3.1.
Time
Series
3.1.Coastal
Coastal
Time
Series
Comparison
of the
the relative
of the
the two
Comparison
of
relativemagnitudes
magnitudes
of
twowind
wind
components shows that the alongshore wind is strongly dominant
components
shows
that
thealongshore
wind
isdominant
strongly
dominant
in each month
at Antofagasta,
but is clearly
only in
in eachmonthat Antofagasta,
but is clearlydominant
onlyin
Monthly climatological
climatological means
means of
of the
the annual
annual cycle
cycle of
of sea
at Iquique.
Iquique. At
At the
the northern
northern extreme
extreme of
of the
the study
study area
area
Monthly
sealevel,
level, summer-fall
summer-fall
at
SST, and
coastal
stations
(Arica,
alongshore wind
wind is
is only
stronger than
than the
SST,
andwind
windvelocity
velocityat
atthe
thethree
three
coastal
stations
(Arica, (Arica),
(Arica),alongshore
onlymarginally
marginallystronger
the
Iquique, and
and Antofagasta)
Antofagasta) are
are presented
presentedin
inFigure
Figure3.
3. At
three cross-shelf
cross-shelf component
component throughout
throughoutthe
theyear.
year. The
of
Iquique,
At all
all three
Themagnitude
magnitude
of
locations alongshore
alonphore wind
(Figure
the seasonal
cycle of
of alongshore
wind
locations
windvelocities
velocities
(Figure3c)
3c)are
aremaximum
maximum the
seasonal
cycle
alongshore
windis
is least
leastat
atArica
Atica(annual
(annual
(4.2-6.2 m
m s)
inin
austral
late
spring
totosummer
(Decemberrange
of ~1.6
-1.6 m
greater
atatAntofagasta
(2.4 m
m s-l),
s'), and
(4.2-6.2
s-1)
austral
late
spring
summer
(Decemberrange
of
ms'),
s-i),
greater
Antofagasta
(2.4
and
March) and
and minimum
minimum(2.6-4.0
(2.6-4.0m
m ss')
winter
(Junegreatest at
at Iquique
Iquique (2.9
(2.9 m
m s-i),
s5, in
of
domain.
March)
-l) in
inaustral
austral
winter
(June-greatest
inthe
thecenter
center
ofthe
thestudy
study
domain.
July).
winds
and
in
wind
July).The
Thecross-shore
cross-shore
windshave
haveaasimilar
similarcycle
cyclebut
butare
areweaker
weaker Also,
Also,at
atIquique
Iquiquethe
theminimum
minimum
andmaximum
maximum
inalongshore
alongshore
wind
and
have
a
much
smaller
seasonal
range
(Figure
to both
both last
than at
to
and have a much smaller seasonalrange (Figure3d).
3d). The
The speeds
speedsappear
appearto
lastlonger
longerthan
at the
theother
otherstations
stationsand
andto
alongshore
component
is
equatorward
and
therefore
upwellingbegin
later
in
the
year.
A
large-scale
study
of
coastal
winds
off
alongshore
component
is equatorward
andthereforeupwelling- beginlaterin the year.A large-scale
studyof coastalwindsoff
favorable
throughout the
the year
maximum
favorablethroughout
yearin
in these
theseclimatological
climatologicalmonthly
monthly South
SouthAmerica
America[Bakun
[Bakunand
andNelson,
Nelson,1991]
1991]indicates
indicates
maximum
means. Daily
Daily data
data (not
winds
when
means.
(notshown)
shown)indicate
indicatethat
thatpoleward
polewardwinds
winds equatorward
equatorward
windsin
in austral
australwinter
winter(June-September),
(June-September),
whenthe
the
(downwelling favorable)
favorable)do
do occur
occur in
in winter
of
Intertropical Convergence
ConvergenceZone
Zone (1TCZ)
(1TCZ) has
has moved
(downwelling
winterwith
with timescales
timescales
of Intertropical
movedfarthest
farthest
several days
days and
and with
occurring
north. The
several
with aa latitudinal
latitudinaldependence,
dependence,
occurringmore
more ,orth.
The winds
windspresented
presentedhere
heremake
makeit clear
clearthat
thatthe
the maximum
maximum
often at
than at
at Iquique
and almost
never at
at Arica.
in upwelling-favorable
windsoccurs
occurs in
in austral
often
at Antofagasta
Antofagastathan
Iquiqueand
almostnever
Arica. in
upwelling-favorablewinds
austral summer
summer off
off
Poleward winds
winds are
are seldom
seldom seen
seen in
averages
from
northern Chile,
Chile, even
even at
at the
the northern
border. These
Poleward
in the
themonthly
monthly
averages
from northern
northern
border.
Theseconflicting
conflicting
individual years
years and
and do
do not
not appear
in
monthly
results are
are most
in
and
individual
appear
in the
theclimatological
climatological
monthlyresults
mostlikely
likelydue
dueto
todifferences
differences
insampling
sampling
and
seasonal
cycles.
The
magnitudes
of
the
winds
(and
other
averaging. The
The Bakun
Bakun and
averaged
seasonal
cycles.Themagnitudes
of thewinds(andothercoastal
coastalaveraging.
andNelson
Nelsondata
dataare
arefrom
fromships,
ships,
averaged
variables) may
may be
be affected
by
local
such
of
conditions.
variables)
affected
byspecific
specific
localsiting
sitingfactors,
factors,
such to
toaa10
1øgrid,
grid,and
andare
aremore
morerepresentative
representative
ofoffshore
offshore
conditions.
as
height
of
measurement,
elevation
of
the
airport,
etc.,
so
offsets
Given
the
very
narrow
upwelling
region
and
strong
asheightof measurement,
elevation
of theairport,etc.,sooffsets Giventhe very narrowupwellingregionand strongland-sea
land-sea
between the
the different
different stations
should
be
with
contrasts at
at these
we
the
between
stations
should
beinterpreted
interpreted
withcaution.
caution.thermal
thermalcontrasts
theselow
lowlatitudes,
latitudes,
weexpect
expect
theairport
airport
Despite
wind strength
Despite this,
this, the
the weaker
weaker alongshore
alongshorewind
strengthat
at the
the most
most
northern
station
(Arica)
is
believed
to
reflect
a
true
decrease
northernstation(Arica) is believedto reflect a true decreasein
in
wind forcing
forcing in
in the
the corner
of the
wind
comer of
the large
largebight
bightformed
formedby
by the
the
change in
in coastal
coastal orientation
orientation at
at the
the northern
northern Chilean
Chilean border.
border.
change
wind measurements
measurements at
at the
the coast
coast to be more
more relevant
relevant to coastal
coastal
ocean
oceanprocesses.
processes.
Sea surface
surface temperature
temperature (Figure
3b) at the
is
Sea
(Figure3b)at
thecoastal
coastalstations
stations
isin
in
phase
(maximum
phasewith
with the
theannual
annualcycle
cycleof
ofsolar
solarheating
heating
(maximumin
in
BLMCO
BLANCOET
ETAL.:
AL.:NORTHERN
NORTI-•RN CHILE
CH]LEHYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
11,456
11,456
34.0
30 ....
360
36.0
35.5
35.0
35.5
i , ,._, , i[ .....
34.5
I ....
ANTOFAGASTA
ANTOFAGASTA [(23°30SJ
23ø30'S]
IQUIQUE
IQUIQUE [[20°30S]
20ø30'S]
ARICA [[ 18ø30'S]
18°30S]
ARICA
34535.035.5360
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35.5
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36.0
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season
Season
:24
25
STW,25
20
Summer
Summer
-15
SAW
,,
(J,F,M)
(J,F,M)
-10
0
30
25
-25
-20
-2o
Fail
Fall
(A,M,J)
15
15
10
,10
30_
----
-
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STW
20
o...20
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a..,-
t5
Winter
Winter
(J,A,S)
(J,a,s)
27
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30
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20
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' --•' •---
---•
:
1°
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340
•.0
345
•.5
.•Iw
35.0
•.0
Salinity
s•inity(psu)
(•u)
35.5
•.0
•.5
35.0
salinity
(•u)
35.5
36.0
345
•.5
350
35.0
Spring
': -•
• -'
35.5
Spring
(O,N,D)
(O,N,D)
d ,0
360
•.0
Salinity
(psu)
salinity
(•u)
Figure 4.
climatological
T-S
for
in
curves
Figure
4.Seasonal
Seasonal
climatological
T-Sdiagrams
diagrams
forthree
threeregions
regions
inthe
thenorth
northof
ofChile.
Chile.The
•e multiple
multiple
cu•esrepresent
represent
the six
(Figure
1),
cross-shelf
variability.
characteristics
of
the
sixgrid
•d distances
dist•cesfrom
fromthe
thecoast
coast
(Figure
1),illustrating
illus•ating
cross-shelf
v•iability.Dots
Dotsindicate
indicate
ch•actcfistics
of
source
water
water,
SAW
water,
ESSW
subsurface
water,
and
A1W
isis
source
water(STW
(S• is
issubtropical
sub.epical
water,
SAwisissubantarctic
subant•ctic
water,
ESSwisisequatorial
equatorial
subsurface
water,
and
•
Antarctic intermediate
••ctic
intc•cdiatc water).
water).
sununer). ItIt is
is similar
to the
Seasonal variability
variabilityin
in SST
SST is
summer).
similar to
the annual
annualcycle
cycleof
of wind
wind but
butlags
lagsthe
the Seasonal
is maximum
maximumat
at Antofagasta
Antofagastaand
and
alongshore
wind component
by -1 month,
at Iquique.
Whether this
this is
minimumat
Iquique.Whether
is due
dueto
to Iquique's
Iquique'sstronger
stronger
alongshorewind
componentby-1
month,with
withminimum
minimumSST
SST minimum
seasonal wind
wind signal
signal and
season or
or to
to
(15.2°-16.0°C) in
in July-September
and
SST
and slightly
slightlylonger
longerupwelling
upwellingseason
(15.2ø-16.0øC)
July-September
andmaximum
maximum
SST(18.00_
(18.0ø- seasonal
the
interaction
of
coastal
orientation
(Antofagasta's
unique
cape
20.5°C)
in
January-February.
This
type
of
lag
may
be
caused
by
the
interaction
of
coastal
orientation
(Antofagasta's
unique
cape
20.5øC)in January-February.
This typeof lagmaybe causedby
and/or bathymetry
bathymetry(there
(thereisis aa widening
widening of
of the
the shelf
the
structure)and/or
shelf
theonset
onsetof
of upwelling,
upwelling,which
whichkeeps
keepsSST
SSTlow
lowas
aswinds
windsincrease
increase structure)
around and
and south
in
heating
the
southof
of Iquique)
Iquique)with
with wind
wind forcing
forcingand
andresultant
resultant
in spring,
spring,before
beforeseasonal
seasonal
heatingoverpowers
overpowers
theupwelling.
upwelling.At
At around
upwelling can
can even
more
circulation is
is not
not known.
known.
more temperate
temperate latitudes,
latitudes, upwelling
even move
move the
the circulation
Annual
cycles
of coastal
1987].
[Strub
et
al.,
minimum
into
late
spring
or
early
summer
coastalsea
sealevel
level are
areonly
onlyavailable
availableat
at the
the
minimuminto late springor early summer[Strubet al., 1987]. Annual cyclesof
BLANCO
CHILE
BLANCO ET AL.:
AL.: NORTHERN
NORTI-IE•
CHILE HYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
11,457
11,457
Table
Table 2.
2. Water
Water Mass
Mass Characteristicsa
Characteristicsa
Water
WaterMass
Mass
Depth
Range,
m
Depth
Range,
m
Temperature,
°C
Temperature,
øC
Salinity,
psu
Salinity,
psu
Oxygen, mL
L '•
Oxygen,
mLL
STW
STW
"surface"
"surface"
0-40
0-40
>18.5
> 18.5
17.0-25.0
17.0-25.0
24.0
24.0
34.9
34.9
34.9-35.7
34.9-35.7
35.7
35.7
>5
>5
>5
>5
SAW
SAW
25-40
25-40
40-80
40-80
11.5-14.5
11.5-14.5
11.014.0
11.0-14.0
34.1-34.8
34.1-34.8
34.3-34.8
34.3-34.8
34.25
34.25
2.5-4.5
2.5-4.5
3.0-6.0
3.0-6.0
34.6-34.8
34.6-34.8
34.7-34.9
34.7-34.9
34.9
34.9
0.25-0.5
0.25-0.5
0.25-1.0
0.25-1.0
34.2-34.6
34.2-34.6
1.5-1.9
1.5-1.9
1.5-2.5
1.5-2.5
12
ESSW
ESSW
AIW
AIW
300-350
300-350
100-300
100-300
9.5-10.5
9.5-10.5
>500
10-750)
>500 (7
(710-750)
see text below
below
5.5
5.5
6-8
6-8
11-13
11-13
12.5
12.5
7
>34.5
>34.5
34.4
34.4
B
is subtropical
water, SAW
SAW is
is subantarctic
water, ESSW
ESSW is
is equatorial
equatorial subsurface
subsurface water,
water, and
and
aSTW
STWis
subtropical
water,
subantarctic
water,
AIW is
water. The
The first
first line
line of
of each
AIW
is Antarctic
Antarctic intermediate
intermediatewater.
eachwater
water mass
massdescription
descriptionprovides
providesthe
the
characteristic depth
depth range,
range, temperature,
temperature, salinity,
salinity, and
and oxygen
oxygen concentration
concentration values
values for
for the
the major
characteristic
majorwater
water
masses observed
observed throughout
throughout the
the Chilean
Chilean coast
coast by
by Bernal
Bernal et
et al.
al. [1982].
The second
second line
line provides
provides the
the
masses
[ 1982]. The
ranges actually
actually observed
observedin
in our
our study
study area.
area. The
The third
third line
the values
ranges
line provides
providesthe
valueswe
we have
have used
usedto
to
characterize each
each water
water mass
mass end-member
end-member and
and plotted
plotted in
in Figure
Figure 44 as
as a
a reference
reference point
point against
characterize
againstwhich
which
seasonal
changes can
can be
be viewed.
viewed. AIW
in this
this study;
study; itit is
is generally
generally found
found below
below 500
500
seasonalchanges
AIW was
was not
not sampled
sampledin
m with
with a core
m
core between
between 710
710 and 750
750 m.
northern
and southern
ends of
Although the
the T-S
northernand
southernends
of the
thestudy
studyregion
region(Figure
(Figure3a).
3a). poleward
polewardundercurrent.
undercurrent.Although
T-S curves
curvesdiffer
differ with
with
Seasonal maxima
maximainin sea
sea levels
of
Seasonal
levels are
are caused
causedby
by heating
heatingand
and season
seasonand
andlocation,
location,the
thevertical
verticalsequence
sequence
of the
thewater
watermasses
massesis
is
expansion
of
in
Minimum
STW
occurs at
at the
(with
salinity
expansion
of the
thewater
watercolumn
column
insummer.
summer.
Minimumsea
sealevels
levels conserved.
conserved.
STW occurs
thesurface
surface
(withan
anabsolute
absolute
salinity
lag those
by 1-2
followed by
minimum),
lag
thoseof
of temperature
temperature
by
1-2 months,
months,with
withlowest
lowestvalues
valuesin
in maximum),
maximum),followed
by SAW
SAW (the
(therelative
relativesalinity
salinity
minimum),
late
austral
winter
and
early
spring
(AugustOctober).
This
lag
then
ESSW
(the
relative
salinity
maximum),
finally
lateaustralwinterandearlyspring(August-October).
Thislag then ESSW (the relativesalinitymaximum),finallymoving
moving
may
equatorward
currents
that
(the absolute
temperature
and
maybe
bethe
theresult
resultof
ofthe
thealongshore
alongshore
equatorward
currents
that toward
towardA1W
AIW (the
absolute
temperature
andsalinity
salinityminimum).
minimum).
intensify
in spring,
geostrophic
slope
Most variability
occursin
in the
the upper
upper 150
150 m
m (above
and in
in the
intensifyin
spring,with
withaacross-shelf
cross-shelf
geostrophic
slopethat
that Most
variabilityoccurs
(aboveand
the
serves
to
keep
coastal
sea
levels
low.
Summer
maximum
values
relative
salinity
minimum),
corresponding
to
changes
in
serves
to keepcoastalsealevelslow. Summermaximum
values relativesalinityminimum),corresponding
to changes
in STW
STW
occur
at
as
maximum.
we
on
occurin
in February
February
atAntofagasta
Antofagasta
asaaclear
clearannual
annual
maximum.and
andSAW.
SAW. In
In the
thediscussion,
discussion,
wespeculate
speculate
onthe
thepossible
possible
Elevated
at Arica
over
influence of
of freshwater
coastal runoff
runoff from
on
Elevatedannual
annualsea
sealevels
levelsat
Aticaare
aresustained
sustained
overan
an influence
freshwater
coastal
fromhigher
higherlatitudes
latitudes
on
extended
period
through
summer
and
with
this salinity
minimum. To
degree,
there
extended
period
through
summer
andfall
fall(December-May),
(December-May),
with this
salinityminimum.
Toaalesser
lesser
degree,
themare
aresignificant
significant
maximum
values later
later in
in the
the annual
annual cycle
cycle(April-May).
(AprilMay).
changes in
in the
of
maximum
values
changes
thesignature
signature
of ESSW
ESSW(near
(nearthe
therelative
relativesalinity
salinity
maximum).
Deeper
water
mixing
toward
AIW
maximum).Deeper water mixing toward AIW properties
properties
3.2. Water
Water Masses
3.2.
Masses
undergoes almost no change in its T-S values between seasons.
undergoes
almost
change
insaline
itsT-S
values
STW appears
asno
the
warm,
water
atbetween
the top seasons.
of the T-S
STW appearsas the warm,salinewaterat the top of the T-S
T-S
diagrams provide
provide an
an introduction
to
patterns
influences
are found
found offshore
offshore (100
T-S diagrams
introduction
to hydrographic
hydrographic
patterns curves.
curves. Strongest
Strongest
influencesof
of STS,V
STW are
(100
and
circulation,
focusing
on
the
seasonal
and
spatial
variation
in
km
and
farther)
at
the
surface
in
spring,
summer,
andcirculation,
focusing
on theseasonal
andspatialvariationin km and farther)at the surfacein spring,summer,and
andfall
fall off
off
the distribution
of
climatological
T-S
but only
and
the
distribution
of water
watermasses.
masses.Seasonal
Seasonal
climatological
T-S Arica
Aticaand
andIquique,
Iquique,but
onlyin
in summer
summer
andfall
fall off
offAntofagasta.
Antofagasta.
diagrams from
profiles offshore
offshore of
of Arica,
middepth, carried
by the
the poleward
poleward
diagrams
from profiles
Atica, Iquique,
Iquique, and
and ESSW
ESSW is
is found
found at
at middepth,
carried by
Antofagasta
are
shown
in
Figure
4.
Table
the
and characterized
by
salinity
maximum
Antofagasta
are shownin Figure4. Table 22 presents
presents
the undercurrent
undercurrent
and
characterized
byaarelative
relative
salinity
maximum
characteristics for
for each
each of
of the
the water
characteristics
watermasses
masseswhich
whichare
arepresent
present(or
(or and
andan
anoxygen
oxygenminimum
minimum(Table
(Table2).
2). The
Therelative
relativemaxima
maximacaused
caused
influence
water
properties)
in
the
study
area:
subtropical
water
by
ESSW
become
warmer
and
saltier
moving
from
to
influencewaterproperties)
in the studyarea:subtropical
water by ESSWbecomewarmerandsaltiermovingfromoffshore
offshore
to
(STW), subantarctic
water (SAW),
subsurface
water
concentration of
of the
(STW),
subantarctic
water
(SAW),equatorial
equatorial
subsurface
water onshore,
onshore, suggesting
suggestingaa concentration
the poleward
poleward
(ESSW), and
intermediate
water
next to
to the
the coast
coast (easiest
(easiest to
to see
see at
at Antofagasta).
Antofagasta). In
(ESSW),
andAntarctic
Antarctic
intermediate
water(A1W).
(AIW). Table
Table22 undercurrent
undercurrent
next
In
shows
characteristic
depth
ranges,
salinities,
temperatures,
and
the T-S
showscharacteristicdepth ranges, salinities,temperatures,
and addition,
addition, the
T-S curves
curves show
show that
that the
the influence
influence of
of ESSW
ESSW
oxygen concentrations
from
published
observations
characteristics increases
increases at
at lower
The SAW
oxygen
concentrations
frompreviously
previously
published
observations
characteristics
lowerlatitudes.
latitudes.The
SAWoverlays
overlays
of these
along
the entire
Chilean coast
coast [Bernal
the ESSW.
ESSW. Though
the
of
thesewater
watermasses
masses
alongthe
entireChilean
[Bernalet
et the
ThoughESSW
ESSWis
isfound
foundat
atall
alllatitudes,
latitudes,
theinfluence
influence
1982], ranges
within
al., 1982],
of SAW
to
salinity
minima
al.,
rangesof
of values
valuesobserved
observed
withinthe
the data
dataset
set of
SAWdecreases
decreases
tothe
thenorth,
north,and
andthe
therelative
relative
salinity
minima
analyzed
here,
and
a
reference
T-S
value
chosen
to
represent
the
caused by
by SAW
SAW is
is very
very weak
weak at
at Atica
Arica (Figure
(Figure4).
4). SAW
is most
most
analyzed
here,anda reference
T-Svaluechosen
to represent
the caused
SAW is
end-member
characteristics
of
each
water
mass
(plotted
in
Figure
evident
in
the
Antofagasta
section,
penetrating
to
200
km
from
end-member
characteristics
of eachwatermass(plotted
in Figure evidentin theAntofagasta
section,
penetrating
to 200 km from
This latter
to
4). This
the coast
above
suggesting
4).
lattervalue
valueis
is not
notintended
intended
todefine
definefar-field
far-fieldsource
sourcethe
coastin
in spring
springand
andsummer
summer
above120
120m,
m, suggesting
water characteristics
characteristics but
but simply
simply to
to provide
reference
strong equatorward
equatorward flow
flow in
in the
the southern
part
water
provideaa constant
constant
referencerelatively
relativelystrong
southern
partof
of the
the
point for
of
influences
between
seasons,
study area.
area. The
inferred
from
point
forcomparison
comparison
of water
watermass
mass
influences
between
seasons,study
TheA1W
AIW can
canonly
onlybe
beindirectly
indirectly
inferred
fromthe
the
transects, and
and cross-shelf
cross-shelf profiles.
decrease
in
in
concentration
below
transects,
profiles.
decrease
in salinity
salinityand
andincrease
increase
inoxygen
oxygen
concentration
below
The observed
patterns in
in T-S
result from
from equatorward
equatorward flow
flow of
of 250
the
do
the
The
observed
patterns
T-Sresult
250m,
m,because
because
the500
500m
mprofiles
profiles
donot
notreach
reach
thecore
coreofofA1W
AIW
relatively cold
cold and
and fresh
fresh water
offshore
water
relatively
waterat
at middepths
middepths
offshore(SAW)
(SAW) and
and (Table
(Table2). Figure
Figure4 shows
showsthat
thatthe
thecoldest
coldestand
andfreshest
freshest
waterisis
below 500
500 m
transport
of
below 400
400 m
m off
and
below
m (AIW)
(AIW) and
andthe
thepoleward
poleward
transport
ofequatorial
equatorialobserved
observed
below
off Antofagasta
Antofagasta
andindicates
indicatesthat
thatthe
the
water
at
the
surface
(STW)
and
at
middepths
(ESSW)
of
decreases moving
waterat the surface(STW) and at middepths
(ESSW)in
in the
the influence
influence
ofthe
theA1W
AIW decreases
movingequatorward.
equatorward.
BLANCO
BLANCO ET AL.: NORTHERN
NORTHERN CHILE
CHILE HYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
11,458
11,458
Summer
Summer
7t
l8-74
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-73
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Writer
Winter
Fall
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-73
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(psu•••
•••' ' '.
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Z15(m
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.7.
.
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.
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.
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.
:
Figure
climatologies
of
surface
temperature
(SST),
salinity
(S),
isotherm
Figure5.5.Seasonal
Seasonal
climatologies
of(a)
(a)sea
sea
surface
temperature
(SST),(b)
(b)surface
surface
salinity
(S),and
and(c)
(c)15°C
15øC
isotherm
depth
depth(Z15).
(Z•5).
3.3.
Spatial Patterns
Patterns
3.3.Spatial
salinity are
are zonally
zonally oriented,
oriented, consistent
with
latitudinal
gradients
salinity
consistent
with
latitudinal
gradients
in
heating.
The
isotherm
isisdeepest
offshore
and
temperature,
of
Climatological
seasonal patterns
Climatological
seasonal
patterns
of surface
surface
temperature,
insolar
solar
heating.
The15°C
15øC
isotherm
deepest
offshore
and
slopes upward
upward toward
toward the
the coast
reflecting
the
surface
salinity,
and
of
isotherm
for
surface
salinity,
andthe
thedepth
depth
ofthe
the15°C
15øC
isotherm
fornorthern
northernslopes
coastin
inall
allseasons,
seasons,
reflecting
the
upwelling. The
is
Chile
in
5.5.Surface
temperature
and
Chileare
areshown
shown
inFigure
Figure
Surface
temperature
andsalinity
salinityyear-round
year-round
upwelling.
Theisotherm
isotherm
is<30
<30m
mdeep
deepat
atthe
thecoast
coast
in
all
seasons
and
deepens
to
>70
m
at
the
western
edge
of
have
strong
annual
cycles
with
maximum
offshore
values
in
the
havestrong
annual
cycles
withmaximum
offshore
values
in the in all seasons
anddeepens
to >70m at thewestern
edge
ofthe
the
area.
from
of
provides
summer
and 35.3
values
during
summer(>24°C
(>24øCand
35.3psu)
psu)and
andminimum
minimum
values
duringstudy
study
area.The
Thedistance
distance
fromshore
shore
ofthe
the40
40m
misoline
isoline
provides
of
variability
in
slope
winter
and 34.8-35.0
34.8-35.0 psu).
psu). Within
Within 100
winter(16°-17°C
(16ø-17øC
and
100 km
km of
of the
the an
anindication
indication
ofthe
theseasonal
seasonal
variability
inthe
thesubsurface
subsurface
slope
of
isotherms
upwards
towards
the
coast,
with
minimum
crosscoast,
are
parallel to
to the
coast,isopleths
isopleths
aregenerally
generally
parallel
theshore
shoreeven
evenduring
during of isotherms
upwards
towards
thecoast,withminimum
crossshelf distances
(maximumslope)
slope)in
in summer
and fall,
winter
of
of
less
water
winterbecause
because
of upwelling
upwelling
of cooler,
cooler,
lesssaline
saline
watervia
viathe
the shelf
distances
(maximum
summerand
fall, and
and
maximum
cross-shelf
distances
(minimum
slope)
in
winter
permanent
upwelling-favorable
wind
forcing.
This
upwelling
permanent
upwelling-favorable
windforcing.This upwellingmaximum
cross-shelf
distances
(minimum
slope)in winterand
and
at
and
moderates
the
cycle
and
near
moderates
theannual
annual
cycleof
ofboth
bothtemperature
temperature
andsalinity
salinity
near spring.
spring. This
Thiscycle
cycleis
ismost
mostpronounced
pronounced
atthe
thenorthern
northern
and
southern extents
extents of
of the
shore.
shore. Within
Within 100
100 km
km of
of the
the coast,
coast,summer
summerminimum
minimum southern
the study
studyarea
areaand
andis
isminimum
minimumin
in the
thecenter
center
21.5°
This
with
temperatures
and salinities
are
and
psu,
temperatures
and
salinities
are19°-20°C
19ø-20øC
and34.8-34.9
34.8-34.9
psu, between
between
21.5ø and
and22.5°S.
22.5øS.
Thisisisconsistent
consistent
withthe
theweaker
weaker
annual
range
in
coastal
SST
at
Iquique
(Figure
3b).
respectively,
and
winter
values
are
16°-17°C
and
34.8-34.9
psu.
respectively,
andwintervaluesare16ø-17øCand34.8-34.9psu. annual
rangein coastal
SSTatIquique(Figure
3b).
Climatological seasonal
seasonal geostrophic
geosirophic flow
flow off
off northern
Chile
The
gradients
of
and
which
Thecross-shelf
cross-shelf
gradients
ofboth
bothtemperature
temperature
andsalinity,
salinity,
which Climatological
northern
Chileis
is
of geopotential
anomaly
shown in
patterns of
are
from
are maximum
maximumin summer,
summer,decrease
decrease
fromnorth
northto
tosouth
southin
in all
all shown
in Figure
Figure 66 as
as patterns
geopotential
anomaly
to dynamic
height)
over the
influence of
seasons,
seasons,reflecting
reflectingthe
the decreasing
decreasinginfluence
of offshore
offshore(equivalent
(equivalent
to
dynamic
height)integrated
integrated
over
theupper
upperwater
water
column
(0
to
500
dbar)
and
for
the
subsurface
region
(200
equatorial
surface
water
properties.
Offshore
of
the
coastal
equatorial
surfacewaterproperties.
Offshoreof the coastalcolumn
(0 to500dbar)andforthesubsurface
region
(200to
to500
500
(Figure
6a)
equatorward
upwelling
region (west
isopleths
of
and
upwelling
region
(westof
of -72°W)
~72øW)
isopleths
oftemperature
temperature
and dbar).
dbar).Flow
Flowat
atthe
thesurface
surface
(Figure
6a)isisgenerally
generally
equatorward
BLANCO
BLANCO ET
ET AL.:
AL.: NORTHERN
NORTHERN CHILE
CHILE HYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
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climatologies
of
anomaly
(dcI)for
for(a)
(a)surface
surfacerelative
relativetoto500
500dbar
dbarand
and (b)
(b) 200
200 dbar
dbar
Figure6.
6.Seasonal
Seasonal
climatologies
of geopotential
geopotential
anomaly(A•)
relative
relative to 500
500 dbar.
dbar.
throughout the
the year
year because
because of
of low
heights along
along the
the is
throughout
the
but
or
throughout
low dynamic
dynamicheights
ispresent
present
throughout
theyear
yearat
atAntofagasta
Antofagasta
butdisappears
disappears
oris
is
coast
resulting
from
the
equatorward
winds
and
offshore
Ekman
coastresultingfrom the equatorward
windsandoffshoreEkman weak
weak in
in winter
winter at
at the
thetwo
twomore
morenorthern
northerntransects.
transects.The
Thecrosscrosstransport.
Within
the
current
isis shelf
and
13°C
isothenns
provides
an
transport.
Within200
200km
kmof
ofthe
thecoast
coast
theequatorward
equatorward
current
shelf slope
slopeof
of the
the12°C
12øC
and
13øC
isotherms
provides
an
strongest in
in fall
fall and
difference
in
cycle
of the
from
coastal
strongest
andaa latitudinal
latitudinal
difference
in the
theseasonal
seasonal
cycle indication
indicationof
thetransition
transition
fromupper
upperwater
watercolumn
column
coastal
is
South
of
coastal
flow
equatorward
upwelling
(and
flow)
poleward
flow
ispresent.
present.
South
of-20°S,
~20øS,
coastal
flowisisstrongly
strongly
equatorward
upwelling
(andequatorward
equatorward
flow)to
tosubsurface
subsurface
poleward
flow
throughout
the year,
in
at
an
of
and
variability.
throughout
the
year,with
withaa maximum
maximum
in fall
fallcentered
centered
at21°S.
21øS. and
andprovides
provides
anindicator
indicator
of latitudinal
latitudinal
andseasonal
seasonal
variability.
North
aastronger
seasonal
cycle
Flow
isotherm is
is deepest
deepest at
at Atica
Arica and
and becomes
becomes progressively
progressively
Northof
of20°S,
20øS,
stronger
seasonal
cycleis
isevident.
evident.
Flowis
is The
The12°C
12øC
isotherm
equatorward
in
summer,
fall,
and
winter
but
becomes
weak
in
shallower
at
the
transects
farther
south
in
all
seasons.
The
equatorward
in summer,
fall, andwinterbutbecomes
weakin shallower
atthetransects
farthersouth
in all seasons.
Thedepth
depth
spring
and
has
a
zonal,
onshore
orientation.
Subsurface
flow
at
of
the
12°
isotherm
at
the
coast
(and
the
overall
slope
spring
andhasa zonal,onshore
orientation.
Subsurface
flowat of the 12ø isotherm
at thecoast(andtheoverallslopeof
of the
the
200
the
undercurrent,
which
isotherm between
between 400
400 km
km offshore
offshore and
and the
in
200m
m(Figure
(Figure6b)
6b)shows
shows
thepoleward
poleward
undercurrent,
whichis
is isotherm
thecoast)
coast)is
islargest
largest
in
strongest
in summer
summer and
and weakest
weakest in
in winter.
winter. The
summer (-275
(-275 m
strongest
in
Theundercurrent
undercurrentsummer
m at
atArica)
Atica)and
andleast
leastin
in winter
winter(190
(190m
m at
atArica),
Atica),
appears more
more organized
organized and
and consistent
consistent in
in the
the southern
southern portion
portion of
of except
where
appears
exceptat
at Antofagasta,
Antofagasta,
whereits
itsminimum
minimumdepth
depthis
isin
inspring.
spring.
the
study
area
(south
of
-21°S).
In
all
seasons,
there
appears
to
This
implies
a
general
maximum
in
the
strength
of
the
thestudyarea(south
of ~21øS).
In all seasons,
thereappears
to Thisimplies
a general
maximum
in thestrength
of thepoleward
poleward
be an
component of
of flow
flow at
at 200
in fall
fall and
in
be
anonshore
onshorecomponent
200 m,
m, strongest
strongest
in
and undercurrent
undercurrent
in summer.
summer.
winter.
winter.
Vertical
salinity structure
structure (Figure
(Figure 8)
8) is
by
Verticalsalinity
isdetermined
determined
bythe
the
distributions of
of the
the four
distributions
four principal
principalwater
watermasses
massesin
in the
theregion.
region.
3.4. Vertical Structure
The freshest
freshest water
mass
in
area
is
by
3.4.Vertical
Structure
The
water
mass
inthe
thestudy
study
area
isinfluenced
influenced
byAJW,
AIW,
evident as
as aa salinity
minimum
at depth.
depth. Between
Between 100
and 300
300 m
The seasonal
cross-shelf
vertical
structure (0-500
(0-500 m) of
The
seasonal
cross-shelf
verticalstructure
of evident
salinity
minimum
at
100and
m
adjacent to
to the
ESSW
aa relative
salinity
maximum.
temperature,
salinity, and
and oxygen
are presented
in
7,
temperature,
salinity,
oxygen
are
presented
inFigures
Figures
7,8,
8, adjacent
thecoast,
coast,
ESSWcreates
creates
relative
salinity
maximum.
A relative
located above
above and
and offshore
of
and
extending
400
of
and99 for
fortransects
transects
extending
400km
kmoffshore
offshore
ofArica,
Atica,Iquique,
Iquique,A
relativesalinity
salinityminimum
minimum
located
offshore
of
ESSW
is
modified
SAW.
Highest
salinities
are
found
offshore
and
Antofagasta.
Temperature
structure
7)
shows
that
(Figure
andAntofagasta.Temperature
structure
(Figure showsthat ESSWis modifiedSAW. Highestsalinities
arefoundoffshore
vertical
is maximum
verticalstratification
stratificationis
maximumin summer
summerat
at each
eachlocation
location in
in STW.
STW. This
Thismost
mostsaline
salinewater
water(>35.1
(>35.1 psu)
psu)is
is present
presentin
in the
the
and
Of the
and weakest
weakest in
in winter.
winter. Of
the three
three locations,
locations, surface
surface surface
surfacewater
wateroffshore
offshorein
in summer
summerand
andfall
fall and
andis
is seen
seenas
asaa wedge
wedge
of
extending
southward
and
stratification
in winter
winter is
is strongest
at
stratification
in
strongest
at Arica,
Atica,the
thenorthernmost
northernmost
of warm,
warm,saline
salinewater
waterat
atthe
thesurface
surface
extending
southward
and
transect.
At
each
location,
near-surface
isotherms
(>14°C)
tilt
toward
the
coast,
with
minimum
penetration
in
winter
(Figures
77
transect.At eachlocation,near-surface
isotherms
(>14øC)tilt towardthecoast,with minimumpenetration
in winter(Figures
and 8).
in the
that
upward
toward the
the coast
coast throughout
throughout the
the year,
year, in
in response
response to
to the
the and
upwardtoward
8). Salinities
Salinitiesin
the upper
upper50
50 m
mindicate
indicate
thatupwelling
upwelling
continuous upwelling-favorable
winds. Below
water to
to the
continuous
upwelling-favorable
winds.
Below150
150m,
m,isotherms
isotherms brings
brings lower
lower salinity
salinity water
the surface
surfacenear
near the
thecoast
coast
the
deepen as
as they
deepen
theyapproach
approachthe
thecoast,
coast,indicative
indicativeof
ofpoleward
poleward throughout
throughout
theyear
yearbut
butis
is weakest
weakestin
in winter
winterat
at all
all three
threetransects.
transects.
or
geostrophic
flow associated
associated with
with the
the undercurrent.
undercurrent. This
geostrophic
flow
Thispattern
pattern Upwelled
Upwelledwater
wateris
iseither
eitherESSW
ESSW(from
(fromthe
theundercurrent)
undercurrent)
orSAW
SAW
BLANCO
CLIMATOLOGY
BLANCO ET
ET AL.:
AL.: NORTHERN
NORTH]•RN CHILE
CHILE HYDROGRAPHIC
HYDROGRAPHIC
CLIMATOLOGY
11,460
11,460
Summer
Summer
Fall
Fall
Spring
Spring
Winter
Winter
16
.:i6-u---14.
.1
Arica
(18 0305]
-11-
-14
_.-_-----.--- 13-',
Iquique
(20 °30'S]
-11
10
.-9
Antofagasta
(23 °30'S] 2
400
300
200
100
0400
(km)
Figure 7. Seasonal climatologies of cross-shelf vertical temperature structure (°C) at Arica, Iquique, and Antofagasta.
in summer.
One possible
explanationofof this
this is
is an
(from just
just offshore
of the
or aa combination
of the
the deepest
(from
offshoreof
theundercurrent)
undercurrent)or
combination
of
deepestin
summer.One
possibleexplanation
an
increased
poleward
flow
of
ESSW
in
summer
and
its
stronger
two.
Between
50
and
150
m,
a
tongue
of
low-salinity
SAW
water
two.Between50 and150m, a tongueof low-salinitySAW water increased
polewardflow of ESSW in summerand its stronger
in the
consistent
with
(<34.7) is
is present
portion
and
(<34.7)
presentin
in the
theseaward
seaward
portionof
of the
thesouthern
southern
and influence
influencein
the north
norththan
thanin
inthe
thesouth,
south,
consistent
withthe
the
maximum in
in strength
for
undercurrent
central
extending
from
and
toward
centraltransects,
transects,
extending
fromoffshore
offshore
andthe
thesouth
south
toward summertime
summertime
maximum
strength
for the
thepoleward
poleward
undercurrent
This trend
sections
(Figure
the coast
8), but
in the
the
coast(Figure
(Figure8),
but is
isweak
weakor
ornonexistent
nonexistent
in
theArica
Atica implied
impliedfrom
fromthe
thetemperature
temperature
sections
(Figure7).
7). This
trendis
is
show
the
also
consistent
with
latitudinal
trends
in
the
proportion
of
ESSW
transects.
The
T-S
diagrams
from
Arica
(Figure
4)
transects.
The T-S diagramsfrom Atica (Figure4) showthe alsoconsistent
withlatitudinal
trendsin theproportion
of ESSW
relative salinity
minimum caused
caused by
by SAW
SAW to
to be
be weak
weak but
but present
present evident
relative
salinityminimum
evidentin
inthe
theT-S
T-Splots
plots(Figure
(Figure4).
4).
vertical
The
Salinities within
within this
this tongue
are lowest
in all
all seasons.
seasons. Salinities
tongue are
lowest at
at
The climatological
climatologicalseasonal
seasonalcycle
cycle of
of cross-shelf
cross-shelf
vertical
concentrations is
in
9.
vertical
Antofagasta.
Seasonally,
salinities
are
at
Antofagasta.
Seasonally,
salinities
arelowest
lowest
atboth
bothAntofagasta
Antofagastaoxygen
oxygen
concentrations
ispresented
presented
inFigure
Figure
9.A
Astrong
strong
vertical
is present
present in
in the
Oxygen
and
in fall.
with
onshore
andIquique
Iquiquein
fall. This
Thisisisconsistent
consistent
withthe
thestronger
stronger
onshoregradient
gradient
is
theupper
upper100
100m
rnininall
allseasons.
seasons.
Oxygen
concentrations
drop
from
>5
mL
U'
at
the
surface
to
values
<1.0
flow
in
the
southern
half
of
the
domain
at
200
m
in
summer-fall
flowin thesouthern
halfof thedomain
at200min summer-fall
concentrations
dropfrom>5mLL'• atthesurface
tovalues
<1.0
mL
U'
below
100
m.
Cross-shelf
patterns
provide
clear
evidence
(Figure
6b).
Below
200
m
the
depth
of
the
34.7
isohaline
(Figure
6b).Below
200rnthedepth
of the34.7isohaline
mLL'•below
100m.Cross-shelf
patterns
provideclear
evidence
upwelling
of
concentration
subsurface
provides a
a key
and
variability
in
provides
keyto
toseasonal
seasonal
andlatitudinal
latitudinal
variability
in the
the of
ofcontinuous
continuous
upwelling
oflow
lowoxygen
oxygen
concentration
subsurface
water
near
the
coast
throughout
the
year
at
each
transect.
At
middepth
layer of
of ESSW.
ESSW. In
season
its
becomes
middepth
layer
Ineach
each
season
itsposition
position
becomeswaternearthecoast
throughout
theyearateachtransect.
Atthe
the
extentof
of each
each transect
transectthe
thedepth
depthof
of the
the 1.0
1.0 mL
mL L
U''•
shallower
with increasing
latitude,
centered
between 350
350 and
shallower
with
increasing
latitude,
centered
between
andwestern
western
extent
isopleth
indicates
a
latitudinal
trend
in
the
thickness
of
the
400
m
off
Arica,
and
shoaling
to
250-350
m
off
Antofagasta,
400 rn off Atica,andshoaling
to 250-350rn off Antofagasta,isoplethindicatesa latitudinaltrendin the thickness
of the
in the
and
and at
at each
eachtransect
transectthis
thisisohaline
isohalineis
isshallowest
shallowestin
in winter
winterand
and offshore
offshoreoxygenated
oxygenatedsurface
surface layer
layer from
from shallowest
shallowestin
the
BLANCO
ET AL.:
AL.: NORTHERN
NORTHERN CHILE
CHILE HYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
BLANCOET
Summer
Summer
Winter
Winter
Fall
11,461
11,461
Spring
Spring
Arica
Arioa
[18 °30'S]
[18
ø30'S]
lOO-
Iqulque
Iquique
[20 °30'S]
[20
ø30'S]
200-
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
ß
400ß
5o0
0
100
Antofagasta
(23 °30'S]
2
[23ø30's]
2oo-.ß
ß
ß
ß
-2001
•,.•.o,
ß .•
-30J
-400
•
400
500
I:
300
I :
200
(krn)
I :
1 O0
:J-I
0400
I
300
200
(krn)
1 O0
0400
0400
300
300
200
200
(km)
(krn)
I'
100
1 O0
oo
0400
0400
300
200
200
100
1
O0
0
(km)
(krn)
Figure
climatologies
ofofcross-shelf
vertical
salinity
structure
at
and
Figure8.8.Seasonal
Seasonal
climatologies
cross-shelf
vertical
salinity
structure
atArica,
Atica,Iquique,
Iquique,
andAntofagasta.
Antofagasta.
northern
portion of
of the
the study
area (90-110
(90-110 m
m at
at Arica)
to deepest
deepest Many
of the
are
northernportion
studyarea
Arica) to
Many of
thefeatures
featurespresent
presentin
in the
theclimatology
climatology
aresimilar
similarto
to
in
in the
the south
south(150-200
(150-200 m
matatAntofagasta).
Antofagasta).A
A distinct
distinctoxygen
oxygen those
thoseidentified
identifiedfrom
fromprevious
previousindividual
individualsurveys
surveysoff
off Chile
Chile
minimum
layer is
is present
present at
at middepths,
centered at
at -250
-250 m,
1971;
1989].
calculated
minimum layer
middepths,centered
m, [Brandhorst,
[Brandhorst,
1971;Fonseca,
Fonseca,
1989].The
Theclimatology
climatology
calculated
throughout
the study
This
here, however,
throughoutthe
studyarea
areain
in all
all seasons.
seasons.
Thisoxygen
oxygenminimum
minimum here,
however,quantifies
quantifiesthe
the mean
meancirculation
circulationand
andwater
watermass
mass
is
strongest
in
the
northern
portion
of
the
study
distributions more
more thoroughly
analysis,
is strongestin the northern portion of the studyarea,
area,with
with distributions
thoroughlythan
thanany
anyprevious
previous
analysis,
concentrations
<0.25mL
mLLU'
and presenting
real means
means of
of the
than
conceptual
concentrations
<0.25
'] at
atArica
Aticaand
andIquique,
Iquique,and
presentingreal
thedata
datarather
rather
than
conceptual
concentrations <0.5
<0.5 mL
mL L
U''• dominating
the
from
schematics.ItIt also
also differs
from
cimatologies
that
concentrations
dominating
thewater
watercolumn
column
from schematics.
differsfrom climatologies
thatmight
mightbe
be
100 to
to 450
450 m.
m. The
with
from global
global data
data sets.
sets. Figure
100
Thelow
lowoxygen
oxygenwater
wateris
isassociated
associated
with ESSW.
ESSW. constructed
constructedfrom
Figure 10
10 contrasts
contraststhe
the
Patterns
the seasonal
seasonal climatologies
climatologies of
of surface
and
Patternsof
of low
low oxygen
oxygenconcentration
concentrationare
are consistent
consistentwith
with the
surfacetemperature
temperature
andsalinity
salinityfrom
from
hypothesis
that ESSW
ESSWisis more
more dominant
in the
5
with
contours
derived
from
the
global
data sets
sets of
hypothesisthat
dominant in
the north
north and
and Figure
Figure5 with contoursderivedfrom the globaldata
of
occupies more
more of
of the
the water
water column
column in
in summer
summer than
than in
in winter.
winter.
Levitus
and Boyer
occupies
Levitusand
Boyer[1994].
[1994]. In
In the
theoffshore
offshoreregion,
region,the
theglobal
global
climatology
captures the
gradients,
although
even
climatologycaptures
themeridional
meridional
gradients,
although
even
these
are
underestimated.
Within
200
km
of
the
coast
the
these
are
underestimated.
Within
200
km
of
the
coast
the
4. Discussion
Discussion
relatively
course grid
grid scales
cannot
relativelycourse
scalesof
of the
theglobal
globalclimatology
climatology
cannot
resolve the
The
features quantified
quantified here
here off
with upwelling,
upwelling,
The large-scale
large-scaleclimatological
climatologicalfeatures
off resolve
the zonal
zonal gradients
gradients associated
associatedwith
northern
in
boundary
their applicability
applicability to
to studies
studies of
of processes,
processes, events,
events, and
and
northernChile
Chilehave
havedirect
directanalogues
analogues
in other
othereastern
eastern
boundaryeliminating
eliminatingtheir
current
which
upwelling,
near shore.
shore. In
In aa first
Blanco et
et al.,
currentsystems
systems
whichexhibit
exhibitnearshore
nearshore
upwelling,equatorward
equatorwardanomalies
anomaliesnear
first application,
application,Blanco
al.,
surface
flow, and
undercurrent
next
(submitted manuscript,
manuscript, 2000)
2000) use
fields
surfaceflow,
andaapoleward
poleward
undercurrent
nextto
to the
theslope.
slope.(submitted
usethe
theclimatological
climatological
fields
BLANCO ET
ET AL.:
BLANCO
AL.: NORTHERN
NORTHERNCHILE
CHILE HYDROGRAPIHC
HYDROGRAPHICCLIMATOLOGY
CLIMATOLOGY
11,462
11,462
Spnng
Spring
Winter
Winter
Fall
Fall
Summer
Summer
100-
Arica
AHca
2002OO[18
[18 °30'S]
ø30'S]
<0.5
<0.5
300-
- 0.25-'
40040O-
500-
0.5-------0.6--
Iqulque
Iquique
(20 3o's]
°30'S]
[20
ß
ß
ß
ß
ß
< 0.5
ß
ß
ß
ß
ß
ß
ß
ß
ß
e
ß
ß
ß
ß
ß
4O0-
500
5O0
Antofagasta
Antofa•sta
]•.
[23 °30'S]
r'--:"11'
'
- __ _.
' '"' '
.
<•., .<o.• . 1<o.5;;• . :;-•!1
30
(kin)
(kin)
(kin)
(kin)
structure (mL U') at Arica, Iquique, and Antofagasta.
Figure
9.
climatologies
ofof
cross-shelf
vertical
oxygen
Fibre
9.Seasonal
Seasonal
climamlogies
cross-shelf
vertical
oxygen
st•cture
(• L-•)at•ca,Iquique,
•d •mfagasa.
(our
analogy
to
Current
latitudes)
the
(ourclosest
closest
analogy
toBaja
BajaCalifornia
California
Current
latitudes)
the
maximum
in
the
surface
equatorward
current
shows
signs
of
maximum
in the surface
equatorward
current
showssignsof
moving
from
next
to
the
coast
in
spring
to
150
km
(or
farther)
The
northern
Chilean
portion
of
the
Peru-Chile
Current
system
Thenorthern
Chilean
portion
ofthePeru-Chile
Current
system
moving
fromnexttothecoast
inspring
to150km(orfarther)
may hve specific similarities to low-latitude portions of its from the coast in summer and fall (Figure 6). This is similar to
calculated here
here to
quantifying
1997-1998
El
calculated
toform
formanomalies
anomalies
quantifying
1997-1998
El
Niflo conditions
conditions off
off northern
northern Chile.
Chile.
Nifio
mayh•vespecific
similarities
to low-latitude
portions
of its from
thecoast
insummer
andfall(Figure
6).Thisissimilar
to
offshore migration of the surface equatorward jet in
Current. the
the
analogue,
Northern
NoahcrnHemisphere
Hemisphere
analogue,
the California
California
Current.
theseasonal
seasonal
offshore
migration
ofthesurface
equatorward
jetin
the
California
Current
documented
in a
a number
of
papers
Although
located
at
latitudes
than
our
study
region,
winds
Although
located
athigher
higher
latitudes
than
our
study
region,
windsthe
California
Current
documented
in
number
of
papers
[Chelton,
1984;
Lynn and
and Simpson,
1987;
Kosro
et
1991;
upwellingalso
(23°N-32°N)
off
offBaja
BajaCalifornia
California
(23øN-32øN)
alsoremain
remain
upwelling[Chelton,
1984;
Lynn
Simpson,
1987;
Kosro
etat.,
al.,in
1991;
Strub
et
at.,
1991;
Strub
and
James,
2000]
and
evident
the
favorable
year-round.
Direct
comparisons
to
identical
latitudes
favorable
year'round.
Direct
comparisons
toidentical
latitudes
$trub
et
al.,
1991;
$trub
and
James,
2000]
and
evident
in
the
climatological
hydrographic
data
off
southern
Baja
[Lynn
et
at.,
in
the
Northern
Hemisphere
are
difficult
because
of
the
lack
of
a
intheNorthern
Hemisphere
aredifficult
because
ofthelackofa climatological
hydrographic
dataoffsouthern
Baja[Lynn
etal.,
1982]. The poleward undercurrent appears to be stronger in
high
climatology
off mainland
Mexico
and,
highresolution
resolution
climatology
off
mainland
Mexico
and,more
moresummer
1982].
The
poleward
undercurrent
appears
to bepart
stronger
in
off northern
northern Chile.
Chile. Off
Off the
the southern
of the
importantly,
strongly
dissimilar
oceanic
current
structure
and
importantly,
strongly
dissimilar
oceanic
current
structure
andsummer
off
southern
partof
the
Current
(southern
California
and
California)
the
wind forcing
caused
by
displacement
of the
wind
forcing
caused
bythe
thenorthern
northern
displacement
of
theCalifornia
California
Current
(southern
California
andBaja
Baja
California)
the
undercurrent often appears to have a semiannual nature, with
with
coastal
interaction
its
system,
current
equatorial
equatorial
currentsystem,
its interaction
with coastal
undercurrent
often
appears
to
have
a
semiannual
nature,
with
maxima in
in both
late
and
[Chelton,
1984;
Lynn
the Intertropical
seasonality of
the seasonality
and the
hydrography, and
hydrography,
of the
Intertropical
maxima
both
latesummer
summer
andwinter
winter
[Chelton,
1984;
Lynn
and
Simpson,
1987].
The
presence
of
relatively
fresh
SAW
Convergence
Zone.
These
have
no
counterpart
in
our
study
Convergence
Zone.These
havenocounterpart
in ourstudyandSimpson,
1987].
Thepresence
ofrelatively
fresh
SAWand
and
region. In the southern part of the study region presented here ESSW at middepth off Chile brings fresher water to the surface
region.
In thesouthern
partofthestudy
region
presented
hereESSW
atmiddepth
offChile
brings
fresher
water
tothesurface
BLANCO
CHILE
CLIMATOLOGY
BLANCOET
ET AL.:
AL.:NORTHERN
NORTHIERN
CHILEHYDROGRAPHIC
HYDROGRAPHIC
CLIMATOLOGY
Summer
Summer
(1.J,F,M]
[J,F,M]
-74
-74
-72
-72
-70
-70
-74
Fall
[A,M,J]
-72
-70
-70
I
Winter
Winter
[J,A,SJ
[J,A,S]
-74
-74
-72
-72
-70
-70
I
-74
-74
11,463
11,463
Spring
Spring
[O,N,D]
[O,N,D]
-72
-72
-70
-70
166
18
-18
11
/1
20
I
/I
22
d
1
--24
-24
26
28
I%bI
I
/
I
/
30
-166
-1
18
8
20
22
•2
24
--24
26
--26
28
-74
-72
-70
-70
-74
-74
-72
-70
-72
-70
Longitude
Longitude
-74
-74
-72
-70
-72
-70
Longitude
Longitude
-74
-74
30
-72
-72
-70
Longitude
Longitude
Longitude
Figure 10.
of
calculated
with
seasonal
Figure
10.Comparison
Comparison
of the
theregional
regionalclimatology
climatology
calculatedhere
here(solid
(solidcontours)
contours)
withaaglobal
globalsurface
surface
seasonal
climatology for
for temperature
temperature (top)
(top) and
and salinity
salinity (bottom).
(bottom). Dashed
contours
are
of
and
climatology
Dashed
contours
arethose
those
ofLevitus
Levitus
andBoyer
Boyer[1994].
[ 1994].
during
bcth regions
are similar
to the
duringupwelling.
upwelling. Over
Over much
much of
of the
theCalifornia
CaliforniaCurrent
Currentthe
the the
the coast.
coast.In
In this
thischaracteristic,
characteristic,
both
regionsare
similar to
the
salinity
minimumisis aa surface
salinity minimum
surfacefeature
featurelocated
locatedoffshore
offshoreand
and Benguela
BenguelaCurrent.
Current.
relatively
saline water
water is
is upwelled
upwelled nearshore.
nearshore. Off
Baja,
One
that is
relativelysaline
Off southern
southern
Baja,
One feature
feature that
is not
not seen
seenin
inthe
theCalifornia
CaliforniaCurrent
Currentand
and
however,
the
salinity
minimum
is
subsurface
throughout
the
more difficult
difficult to
cycle
however,the salinityminimumis subsurface
throughouttheyear
year seems
seemsmore
to explain,
explain,is
is the
theseasonal
seasonal
cycleof
of offshore
offshore
(centered
between 100
100 and
and 150
maximum
(centeredbetween
150 m).
m). The
The seasonal
seasonal
maximumin
in surface
surfacesalinities
salinities(Figure
(Figure 5).
5). Off
Off northern
northernChile
Chile these
theseare
are
wind
(April
in winter,
increasingin
in spring
spring to
to aa maximum
windforcing
forcingduring
duringspring
springand
andsummer
summer
(Apriland
andJuly)
July)[Lynn
[LynnCt
et minimum
minimum in
winter, increasing
maximumin
in
al., 1982]
al.,
1982] thus
thusbrings
bringsrelatively
relativelyfresh
freshwater
water to
to the
thesurface
surfacenear
near summer,
summer,implying
implying enhanced
enhancedpoleward
polewardand
andonshore
onshoremovement
movement
11,464
11,464
BLANCO ET AL.: NORTHERN CHILE HYDROGRAPHIC
BLANCO
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
than is
here,
connections to
to be
be made
from an
source (STW,
(STW, Figure
4)
during summer.
The than
from
anequatorial
equatorial
source
Figure
4)during
summer.
The
isexamined
examined
here,allowing
allowing
connections
madeover
over
ranges.
classical
picture
upwelling
circulation
consists
of
classical
pictureof
of wind-driven
wind-driven
upwelling
circulation
consists
of larger
largerlatitudinal
latitudinal
ranges.
flow evident
in
offshore regions during summer
flow when
surface flow
and offshore
maximum
equatorward
maximum
equatorward
and
offshoresurface
when The
Thepoleward
poleward
flow
evident
inoffshoreregionsduringsummer
(and
to
a
lesser
extent
in
spring)
in
For
example,
equatorward
winds are
(summer).
equatorward
winds
arestrongest
strongest
(summer).For example,(andto a lesserextentin spring)
in Figure
Figure6b
6b may
maybe
bethe
the
signature
of
the
offshore
Peru-Chile
Countercurrent,
the
location
southern
Baja
California
(25°N)
decrease
from
salinities
off
salinifies
off southern
Baja California(25øN)decrease
from signature
of theoffshore
Peru-Chile
Countercurrent,
thelocation
Off
totocontroversy.
>34.0
ininJanuary
toto33.7
ininJuly
[Lynn
et
>34.0psu
psu
January
33.7psu
psu
July
[Lynn
etal.,
al.,1982].
1982]. of
of which
whichoff
offChile
Chileisissubject
subject
controversy.
Off Peru,
Peru,the
the
Countercurrent
is
seen
100-300
km
offshore
in
the
This
conceptual
model
of
the
currents
should
move
STW
farther
Thisconceptual
modelof thecurrents
should
moveSTWfartherCountercurrent
is seen~100-300km offshore
in thedata
dataof
of
et al.
al. [1987].
Indeed,
much
of
flow
atat10°S
to
(equatorward)
and
rather
than
to
tothe
thenorth
north
(equatorward)
andoffshore,
offshore,
rather
than
tothe
thesouth
southHuyer
Huyer
et
[1987].
Indeed,
much
ofthe
the
flowoff
offPeru
Peru
10øS
with only
and
Figure
6a
weak
flow
in and
andonshore.
onshore.
Figure
6aindicates
indicates
weakonshore
onshore
flowoff
offArica
Aticain
and15°S
15øSis
is poleward,
poleward,
with
only aa narrow
narrowupper
upperlayer
layerof
of
flow [Brink
[Brink et
etal.,
1981;
Shaffer,
1982;
Huyer
spring, but
but this
zonal.
In
region
(72°W),
spring,
thisisisstrongly
strongly
zonal.
Inthe
theoffshore
offshore
region
(72øW),equatorward
equatorward
flow
al.,1980,
1980,
1981;
Shaffer,
1982;Huyer
et
aL,
1987].
This
predominance
of
poleward
flow
may
show
the
poleward
flow
is
present
in
summer,
but
only
at
lower
latitudes,
poleward
flowis present
in summer,
butonlyat lowerlatitudes,etal., 1987].Thispredominance
of poleward
flowmayshow
the
influence of
of the
and is
and
is directed
directedoffshore,
offshore,not
notonshore.
onshore. This
This offshore
offshorepoleward
poleward influence
theeastward
eastwardEquatorial
EquatorialUndercurrent,
Undercurrent,which
which has
has
been traced
undercurrent
and
flow
into
in
but
flowwould
wouldbring
bringhigher
highersalinity
salinity
intothe
theregion
region
insummer,
summer,
but been
tracedinto
intoboth
boththe
thepoleward
poleward
undercurrent
andthe
thePeruPeruChile
Countercurrent
off
northern
Peru
[Tsuchiya,
1985;
Lukas,
only
at
lower
latitudes,
presumably
as
a
tongue
from
the
north.
onlyat lowerlatitudes,
presumably
asa tongue
fromthenorth. ChileCountercurrent
off northern
Peru[Tsuchiya,
1985;
Lukas,
1986]. Off
Peru
Chile,
figures
Surface salinity
salinity patterns
patterns in
in Figure
imply
Surface
Figure5,
5, however,
however,
implyaabroad
broad 1986].
Offsouthern
southern
Peruand
andnorthern
northern
Chile,schematic
schematic
figures
drawn
by
Wyrtki
[1966],
Bernal
et
al.
[1982],
and
Fonseca
tongue
intruding
from
the
west
over
much
of
the
northern
half
of
tongue
intruding
fromthewestovermuchof thenorthern
halfof drawnby Wyrtki[1966],Bernalet al. [1982],andFonseca
differ in
their depiction
The
is [19891
the
the offshore
offshore domain.
domain. Subsurface
Subsurfaceflow
flow (Figure
(Figure 6b)
6b) is
[1989] differ
in their
depictionof
of the
theCountercurrent.
Countercurrent.
The
schematic figure
figure drawn
drawn by
by Wyrtki
Wyrtki continues
continues the
the path
path of
of the
predominantly
poleward and
and directed
onshore
throughout
the
predominantly
poleward
directed
onshore
throughout
the schematic
the
countercurrent
straight
south
from
its
location
off
Peru,
thus
year,
most
strongly
in
spring
and
summer,
but
does
not
account
year,moststrongly
in springandsummer,
butdoesnotaccountcountercurrent
straight
southfromitslocation
off Peru,thusfar
far
coast,
splitting
the
"Peru
for
increase
in surface
salinity.
of
forthe
thesummer
summer
increase
in
surface
salinity.One
Oneexplanation
explanation
of offshore
offshoreof
of the
theChilean
Chilean
coast,
splitting
theequatorward
equatorward
"Peru
into
and
branches.
The
of
these discrepancies
is that
components
of
these
discrepancies
is
thatdeep,
deep,large-scale
large-scale
components
of flow
flow Current"
Current"
intooffshore
offshore
andcoastal
coastal
branches.
Thedescriptions
descriptions
of
Bernal
et
al.
and
Fonseca
indicate
a
poleward
flow
100-300
km
exist that
by
component
exist
thatare
arenot
notwell
wellrepresented
represented
bythe
thegeostrophic
geostrophic
componentBernalet al. andFonseca
indicate
a poleward
flow 100-300km
offshore.
fields from
relative to
relative
to 500
500 m.
m.
offshore.The
The geopotential
geopotentialanomaly
anomalyfields
from the
the two
two summer
summer
In the
In
the subsurface
subsurfacewater we
we have
havereferred
referredto
to offshore
offshorelow
low cruises
cruisesanalyzed
analyzedby
by Brandhorst
Brandhorst[1971]
[1971]also
alsoshow
showpoleward
polewardflow
flow
Chile
100-200
km
as
here
salinities
as SAW.
We can
on
salinities
as
SAW. We
canspeculate
speculate
on the
thedegree
degreeto
towhich
which off
offnorthern
northern
Chilebetween
between
100-200
kmoffshore
offshore
asfound
found
here
(they did
did not
these low
off
Chile
by
these
lowsalinities
salinities
offnorthern
northern
Chilemight
mightbe
beinfluenced
influenced
bythe
the (they
notsample
samplethe
theregion
regionwhere
whereWyrtki
Wyrtkidraws
drawsthe
the
Strub et
et al.
al. [1995]
of
data
large
dischargefrom
from the
the fjord
fjord region
region of
of Chile
largefreshwater
freshwater
discharge
Chileat
at Countercurrent).
Countercurrent).
Strub
[1995]use
use33 years
years
ofaltimeter
altimeter
data
in
latitudes
>42°S.
The situation
in
to
latitudes
>42øS.The
situation
in this
thiscase
casewould
wouldbe
beanalogous
analogous
to to
to show
showpoleward
polewardsurface
surfacecurrents
currents
in aaregion
regionthat
thatfollows
followsthe
the
about
100-300
from
the
influence
of higher
on
thefreshwater
freshwater
influenceof
higherlatitudes
latitudes
onthe
theCalifornia
CaliforniaPeru
Peruand
andChile
Chilecoasts
coasts
about
100-300km
kmoffshore,
offshore,
fromabout
about
They show
show that
flow
in
Current.
Brandhorst
[1971]
aasubsurface
tongue
of
Current.
Brandhorst
[1971]shows
shows
subsurface
tongue
of fresh
fresh 6°-35°S.
6ø-35øS.
They
thatpoleward
poleward
flowisismaximum
maximum
inspring,
spring,
when
the
trade
winds
decrease
over
the
eastern
equatorial
water
penetrating
north
next
to
the
northern
Chile
and
Peru
waterpenetrating
northnextto the northern
Chile andPeru whenthe tradewindsdecrease
over the easternequatorial
(or
in fall,
winds
coasts,
above
saline
In
and
coasts,
abovethe
therelatively
relatively
salineundercurrent.
undercurrent.
In spring
spring
and Pacific,
Pacific,and
andminimum
minimum
(orreversed)
reversed)in
fall,when
whenthe
thetrade
trade
winds
The increase
in STW
discussed
in
summer,
Rojas and
and Silva
of
summer,
Rojas
Silva[1996]
[1996]show
showtongues
tongues
of fresh
freshwater
water increase.
increase.
The
increasein
STW in
insummer
summer
discussed
in the
the
paragraph
is
with
and
flow
(34.0-34.5
psu) extending
north from
fjord
(34.0-34.5psu)
extending
north
fromthe
thehigher
higherlatitude
latitude
fjord previous
previous
paragraph
isconsistent
consistent
withpoleward
poleward
andonshore
onshore
flow
countercurrent
off
Chile,
region
at 100
sometimes
reaching
as
regionat
100m
mdepth,
depth,
sometimes
reaching
asfar
farnorth
northas
as caused
causedby
by an
anoffshore
offshore
countercurrent
offnorthern
northern
Chile,
integrating
the
effects
of
a
spring
maximum
in
flow
to
result
in a
a
Antofagasta
with
salinities
of
34.5-34.6
psu,
similar
to
values
in
Antofagasta
withsalinities
of 34.5-34.6psu,similarto valuesin integrating
theeffectsof a springmaximum
in flowto resultin
in STW
A
Shaffer et
et al.
the
here
theoffshore
offshoreminima
minimapresented
presented
here(Figure
(Figure8).
8). Shaffer
al. summer
summermaximum
maximumin
STWconcentrations.
concentrations.
A more
moredetailed
detailed
in
isisneeded
to
the
show low-salinity
water with
with aa high-latitude
origin above
above study
[[1995]
1995]show
low-salinity
water
high-latitude
origin
studyof
of the
thecirculation
circulation
inthis
thisregion
region
needed
todescribe
describe
the
existence
and
behavior
of
the
Peru-Chile
Countercurrent
with
180
m at
period
data.
et
180m
at30°S
30øSin
in their
theirspring-summer-fall
spring-summer-fall
period
data.Shaffer
Shaffer
et existence
andbehaviorof the Peru-Chile
Countercurrent
with
al.
mean
alongshore
velocities
of more
al. [1997,
[1997,1999]
1999]report
report
meanpoleward
poleward
alongshore
velocities
of
morecertainty.
certainty.
anomaly
atat30°S.
12 and 12.8 cm
cm ss'-• at 250
250 m,
m, 10
10km
kmoffshore
offshore
30øS. Maps
Mapsof
of geopotential
geopotential
anomalyvariance
variancefor
forthe
theCalifornia
California
and Simpson,
1987] show
show a
a maximum
in the
Alongshore
velocity
at 250
250 m,
at
Alongshore
velocityat
m,150
150km
kmoffshore
offshore
at30°S
30øS[Shaffer
[ShafferCurrent
Current[Lynn
[Lynnand
Simpson,
1987]
maximum
in
the
region
200
km
offshore
off
Baja
(25°-30°N).
Lynn
was poleward
polewardat
at 3 cm
patterns
are
et
etal.,
al., 1999]
1999]was
cms'.
s-•.These
These
patterns
are region~200km offshore
off Baja(25ø-30øN).Lynnand
and
call this
this the
transition
zone"
that
consistent
with
geostrophic
currents
between
200
consistent
withthe
thepoleward
poleward
geostrophic
currents
between
200 Simpson
Simpson
call
the"coastal
"coastal
transition
zone"and
andsuggest
suggest
that
eddies
in
this
region
are
responsible
for
this
maximum
in
and
500
m
in
the
southern
portions
of
our
study
area
(Figure
and500 m in the southern
portions
of our studyarea(Figure eddiesin this regionare responsible
for this maximum
in
although the
the annual
they
includes
the
6b),
that
structure
of
is
6b),suggesting
suggesting
thatthe
thegeneral
general
structure
of the
theundercurrent
undercurrent
is variance,
variance,
although
annualvariance
variance
theypresent
present
includes
the
cross-shelf
variability.
here. seasonal
the latitudes
similar
similar between
between 30°S
30øS and
and the
latitudes examined
examined here.
seasonalcycle
cycle and
andits
itsassociated
associated
cross-shelf
variability.Strub
Strub
and
James
[2000]
show
a
similar
maximum
in
seasonal
maps
of
Examination
of
T-S
properties
(Figure
4)
suggests
that
within
Examination
of T-S properties
(Figure4) suggests
thatwithin andJames[2000]showa similarmaximumin seasonal
mapsof
geostrophic
velocity
variance
derived
from
altimeter
data.
The
the
northern
Chile
region
the
salinity
minima
lie
along
(or
the northernChile regionthe salinityminimalie along(or geostrophic
velocityvariancederivedfrom altimeterdata.The
variance maximum
maximum moves
moves from
from nearshore
nearshore in
in spring
slightly
above) aa line
ESSW
slightlyabove)
lineof
ofmixing
mixingbetween
between
ESSWand
andSAW.
SAW. variance
springto
tooffshore
offshore
in summer
and
of
jet.
Rojas and
Island
(43°S)
with
Rojas
andSilva
Silvashow
showfjord
fjordwater
waternear
nearChiloe
Chiloe
Island
(43øS)
with in
summer
andfall,
fall,following
followingthe
themigration
migration
of the
theseasonal
seasonal
jet.
They
hypothesize
that
the
variance
maximum
is
caused
by
both
psu.
A
90
10°C
and
salinities
of
33.9-34.0
aa temperature
of
temperature
of 9ø-10øCand salinitiesof 33.9-34.0psu.A Theyhypothesize
thatthevariance
maximum
is caused
by both
meanders in
in the
the jet
jet and
created
on
jet as
hypothetical
mixing line
line between
between this
this and
and ESSW
hypothetical
mixing
ESSWon
onthe
theT-S
T-S meanders
andeddies
eddies
created
oneither
eitherside
sideof
of the
thejet
as
it
moves
offshore.
Is
there
an
analog
off
northern
Chile?
There
plots
of
Figure
4
would
fall
below
the
line
connecting
ESSW
and
plotsof Figure4 wouldfallbelowthelineconnecting
ESSWand it moves
offshore.Is thereananalog
off northern
Chile?Them
is indirect
for eddy
front
SAW, farther
of
minima
fartherfrom
fromthe
thecharacteristics
characteristics
of the
thesalinity
salinity
minima is
indirectevidence
evidencefor
eddyactivity
activitywithin
withinthe
theupwelling
upwellingfront
from
satellite
data.
Fonseca
and
Farias
[1987],
Yánez
er
found
Thus we
we accept
for our
foundoff
off Antofagasta.
Antofagasta.
Thus
acceptthe
theSAW
SAW label
labelfor
our from satellitedata. Fonsecaand Farias [1987], YtihezetaL
al.
and Barbieri
examples
of
offshore
salinity
minima,
but
the
data
of
Brandhorst
and
that
offshoresalinityminima,butthedataof Brandhorst
andthatof
of [1995],
[1995],and
Barbierier
etal.
al.[1995]
[1995]show
show
examples
ofsatellite
satellite
from northern
Chile
in
Rojas
that
rule out
out the
the possibility
possibility of
of SST
Rojasand
andSilva
Silvaindicate
indicate
thatwe
wecannot
cannot
rule
SSTimages
images
from
northern
Chilewhich
whichdepict
depictfilaments
filaments
in the
the
mesoscale SST
SST structure.
structure. These
These appear
appear to
to have
have offshore
length
at
from
coastal
fjord
at least
leastsome
someinfluence
influence
fromhigher-latitude
higher-latitude
coastal
fjordwater
water mesoscale
offshore
length
scales of
of 60-125
color
from
Chile
extending
north into
into our
our study
study area.
area. Further
examination
of the
the scales
extending
north
Further
examination
of
60-125km.
km.Surface
Surface
colorimages
images
fromnorthern
northern
Chile
also
include
filaments
on
the
order
of
100-200
km
offshore
influence
and
variability
of
the
freshwater
tongue
on
the
northern
influence
andvariability
of thefreshwater
tongue
onthenorthernalsoincludefilamentson the orderof 100-200km offshore
1999]. Using
data
Chile
region
requires
analysis
of
data
Chileupwelling
upwelling
region
requires
analysis
ofaalarger-scale
larger-scale
dataset
set [Thomas,
[Thomas,
1999].
Usingthe
thehydrographic
hydrographic
datafor
forthe
thenorthern
northern
BLANCO
ET AL.:
AL.: NORTHERN
NORTHERN CHILE
ChILE HYDROGRAPHIC
BLANCO ET
HYDROGRAPHICCLIMATOLOGY
CLIMATOLOGY
-74
-74
-10
Summer
Summer
-73
-73
-72
-72
-71
-71
-74
-7•4
-73
-73
Fall
Fall
-72
-72
-71
-74
-7-•4
,
Winter
Winter
-73
-73
-72
-72
I
I
-4
-71
-71
-7-{•4
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-73
-
r-
c'
A
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Spring
-71
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-72
11,465
11,465
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1E
•20
0
Temt
•20
j
-23-
:::
Temper2r 200
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23
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01:
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240000t500
-74 -•3
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24
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-73 -72
Figure
patterns
of
for
of
temperature,
(b)
at
Figure11.
11.Spatial
Spatial
patterns
ofvariance
variance
foreach
eachseason
season
of(a)
(a)surface
surface
temperature,
(b)temperature
temperature
at 200
200m,
m,and
and(c)
(c)
geopotential
anomaly
geopotential
anomaly(0
(0 to
to500
500dbar).
dbar).
Chile
the
distributions
of
eddy variability,
but elevated
elevated error
error due
due to
Chileregion,
region,Figure
Figure11
11presents
presents
theseasonal
seasonal
distributions
of the
the may
may indicate
indicategreater
greatereddy
variability,but
to
standard
deviations
of
surface
temperature,
temperature
at
200
m
reduced
sampling
in
the
offshore
grid
locations
and
lack
of aa
standard
deviations
of surfacetemperature,
temperature
at 200 m reducedsamplingin the offshoregrid locationsand lack of
and
anomaly (surface
(surface relative
relative to
to 500
500 dbar).
clear seasonal
seasonal progression
progression prohibits
prohibits further
further interpretation.
interpretation. In
and geopotential
geopotential
anomaly
dbar).The
The clear
In the
the
standard deviation
deviation in
in each
each field
field is
from
north the
is consistent
with
standard
iscalculated
calculated
fromthe
theindividual
individual north
the one
onesignal
signalwhich
which is
consistent
withpreviously
previously
temperature
and salinity
salinity profiles
profiles within
within aa season,
identified fields
fields is
associated
with
temperatureand
season,and
and the
the identified
is the
thevariance
variance
associated
withthe
theanticyclonic
anticyclonic
seasonal
mean
is
subtracted
to
form
the
variances.
These
circulation
in
summer
between
18°S
and
21°S,
seasonalmean is subtractedto form the variances. These circulationin summer between 18øSand 21øS, 100-300
100-300 km
standard
deviations
thus
variability
offshore.
standard
deviations
thusrepresent
represent
variabilitywithin
withineach
eachseason
season offshore.
and
years
caused
by
To what
what extent
extent do
the
calculated here
here to
to
andbetween
between
years(not
(notthe
thevariance
variance
caused
bymean
meanseasonal
seasonal To
dowe
weexpect
expect
theclimatology
climatology
calculated
changes).
Spring and
and summer
deviations in
in SST
patterns
changes).
Spring
summerstandard
standard
deviations
SST are
are represent
represent
patternsat
at higher
higherlatitudes
latitudesoff
off Chile?
Chile?Offshore,
Offshore,
highest
next
temporal
variations
in
meridional gradients
gradients suggest
that
of
highest
nextto
tothe
thecoast,
coast,clearly
clearlyreflecting
reflecting
temporal
variations
in meridional
suggest
thatthe
theinfluence
influence
of AIW
AIW and
andSAW
SAW
coastal
upwelling.
This
is
also
true
in
summer
for
temperature
at
should
increase
as
one
moves
toward
higher
latitudes,
coastalupwelling.Thisis alsotruein summer
for temperature
at shouldincreaseas one movestowardhigherlatitudes,while
while
200
North
ofof20°S,
the
feature
in
become
less
Brandhorst
[1971]
200 m
m south
southof
of -20°S.
~20øS.
North
20øS,
thedominant
dominant
feature
in ESSW
ESSWshould
should
become
lessprevalent.
prevalent.
Brandhorst
[1971]traced
traced
the 200
variance
with
undercurrent
next
as far
far
the
200 m
mtemperature
temperature
variancefield
field is
isassociated
associated
withthe
the the
thepoleward
poleward
undercurrent
nextto
tothe
thecoast
coastduring
duringsummer
summer
as
anticyclonic
gyre identified
identified in
in Figure
of
and
[1979]
anticyclonic
gyre
Figure6b.
6b.The
Thepattern
pattern
ofstandard
standardsouth
southas
ashis
hisdata
dataallowed
allowed(-42°S)
(~42øS)
andSilva
Silvaand
andNeshyba
Neshyba
[1979]
deviation in
in surface
geopotential
is less
coherent
than
it as
south as
poleward
deviation
surface
geopotential
is
lessspatially
spatially
coherent
than find
find it
as far
far south
as 48°S.
48øS. The
The offshore
offshorepoleward
that of
It
offshore
maxima
is said
said to occur
that
of temperature.
temperature.
It exhibits
exhibits
offshore
maximaoff
offAntofagasta
Antofagastacountercurrent
countercurrent
is
occuras
asfar
farsouth
southas
as33°S
33øS[Fonseca,
[Fonseca,
(22°-24°S,
100-250km
kmoffshore)
offshore)in
in winter
winter and
and spring
spring and
and off
off 1989;
etal.,
ItItappears
even
farther
to
in
(22ø-24øS,
100-250
1989;Bernal
Bernal
etal.,1982].
1982].
appears
even
farther
tothe
thesouth
south
in
Arica (north
of 20°S)
and
geopotential
the
of
data
by Strub
Strub et
et al.
Atica
(northof
20øS)in
in spring
spring
andfall.
fall.These
These
geopotential
the33 years
years
ofaltimeter
altimeter
datapresented
presented
by
al.[1995];
[1995];
variance
patterns,
predominantly
aligned
zonally,
are
clearly
however,
a
more
systematic
examination
of
a
longer
variancepatterns,
predominantly
alignedzonally,are clearly however,
a moresystematic
examination
of a longertime
timeseries
series
different from
from the
off SST
the true
nature
different
the meridionally
meridionallyaligned
aligned contours
contoursoff
SST of in
in situ
situand
andsatellite
satellitedata
datais
is needed
neededto
to establish
establishthe
truenature
standard deviation,
deviation, associated
associated with
with upwelling.
off
standard
upwelling.These
Thesemaxima
maxima of
of the
thePeru-Chile
Peru-ChileCountercurrent
Countercurrent
off central
centralChile.
Chile.The
Thedata
datahere
here
11,466
11,466
BLANCO
ET AL:
BLANCO ET
AL.: NORTHERN
NORTHERN CHILE
CH]I,E HYDROGRAPHIC
HYDROGRAPHIC CLIMATOLOGY
CLIMATOLOGY
Acknowledgments. The
extensive
hydrographic
data
presented
here,
only
off
Chile.
With
to
onlyhint
hintat
atits
itsexistence
existence
offnorthern
northern
Chile.
Withregard
regard
tothe
the collected
Acknowledgments.
The
extensive
hydrographic
data
presented
here,
over 32 years, are possible only because of the dedicated
equatorward
surface
flow,
wind
forcing
during
winter
becomes
equatorward
surface
flow,wind
forcing
during
winter
becomes
collected
over
32
years,
are
possible
only
because
of
the
dedicated
efforts of a large number of people at multiple institutions. These data
favorable)
at higher
(downwelling
increasingly
poleward
increasingly
poleward
(downwelling
favorable)
at
higher
efforts
ofafor
large
number
of
people
at
institutions.
These
data
and support
support
for
J.L.B.
were
provided
by
IFOP,
funding
by
Fondo
de
and
J.L.B.
were
provided
bymultiple
IFOP,with
with
funding
by
Fondo
de
latitudes
[Bakun
1991;
1999],
Investigacion Pesquera
Pesquera (projects
(projects 95-05,
95-05, 96-07,
96-07, and
Wind
data
latitudes
[Bakunand
andNelson,
Nelson,
1991;Thomas,
Thomas,
1999],making
makingInvestigacion
and97-07).
97-07).
Wind
data
from
Meteorologica
de Chile,
data
upwelling
equatorward
flow
seasonal.
upwellingand
andsurface
surface
equatorward
flowincreasingly
increasingly
seasonal.caine
came
fromthe
theDireccion
Direccion
Meteorologica
de
Chile,and
andtemperature
temperature
data
at coastal tide gauges came from SHOA. Monthly sea levels at the tide
Bathymetry
also changes
at
latitudes;
the
extremely
Bathymetry
also
changes
athigher
higher
latitudes;
the
extremely
at
coastal
tide
gauges
came
from
SHOA.
Monthly
sea
levels
at
the
tide
gauges were obtained from the University of Hawaii. Funding for A.C.T.
narrow
shelf
off
Chile
to 30-50
of
narrow
shelf
offnorthern
northern
Chilewidens
widens
to
30-50km
kmsouth
south
of gauges
were
obtained
from
the
University
of
Hawaii.
Funding
for
A.C.T.
came
from
NASA
grants
NAG5-6558
and
NAG5-6604
and
NSF
grant
camefromNASAgrants
NAG5-6558andNAG5-6604andNSFgrant
30°-33°S,
the latitude
at
distinct
changes
cross-shelf
OCE-97 11919 (part of the U.S. GLOBEC
GLOBEC program).
program). Funding
Funding for
for M.E.C.
M.E.C.
30ø-33øS,
the
latitude
atwhich
which
distinct
changes
cross-shelf
OCE-9711919(partoftheU.S.
phytoplankton
seasonality
occur
1999].
was provided
by
Biogeochemistry
Program
and
phytoplankton
seasonality
occur[Thomas,
[Thomas,
1999].Thus,
Thus,although
although was
provided
bythe
theNASA
NASAOcean
Ocean
Biogeochemistry
Program
andfor
for
P.T.S. by
by JPL
grant
958128
(TOPEX)
and
NASA
grants
NAG5-4947
the
depicted here
here in
half
thecirculation
circulation
depicted
inthe
thesouthern
southern
halfof
ofthe
thestudy
studyP.T.S.
JPL
grant
958128
(TOPEX)
and
NASA
grants
NAG5-4947
(EOS)
and
NAG5-6604.
Additional
funding
for
travel
for
all
authors
to
region
may
represent
the
to
distance
south
of
region
may
represent
thecirculation
circulation
tosome
some
distance
south
of (EOS)
and
NAG5-6604.
Additional
funding
fortravel
forallauthors
to
collaborate in the analysis of these data came from an NSF supplement
24°S,
the
and basic
nature
of
surface
and
24øS,
theseasonality
seasonality
and
basic
nature
ofthe
the
surface
andtocollaborate
inthe
analysis
ofofthese
from
an
NSF
supplement
grant OC-97
11344
(part
thedata
U.S.came
GLOBEC
program).
This is
nearshore
flow
to change
change south
south of
of ~30øS.
-30°S.
nearshore
floware
arelikely
likelyto
5.
5. Summary
Summary
to grantOC-9711344
(partof theU.S.GLOBEC
program).
Thisis
contribution
number
178
program.
contribution
number
178from
fromthe
theU.S.
U.S.GLOBEC
GLOBEC
program.
References
References
Bakun, A.,
A., and
The seasonal
cycle of
of wind
curl in
Bakun,
andC.S.
C.S.Nelson,
Nelson,
The
seasonal
cycle
windstress
stress
curl
in
J. Phys.
Climatological
the upwelling
region off
sub-tropical eastern
eastern boundary
current
regions,
Climatological hydrography
hydrographyin
in the
upwelling region
off
sub-tropical
boundary
current
regions,J.
Phys.Oceanogr.,
Oceanogr.,
21, 1815-1834,
northern
1815-1834, 1991.
1991.
northernChile
Chile is
is presented
presentedfor
for the
thefirst
firsttime
timeatatsufficient
sufficientcrosscrossBarbieri,
M.A., M.
M. Bravo,
Bravo, M.
M. Farfas,
Farfas, A.
A. Gonzalez,
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0. Pizarro,
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E.
Barbieri,
M.A.,
Pizarro, and
shelf
resolution
to
resolve
features
of
coastal
upwelling.
shelf resolution to resolve features of coastal upwelling.
Yáflez, Fen6menos
FenOmenosasociados
asociadosaala
Ia estructura
estructura t•rmica
térinica superficial
superficial del
del
Yfifiez,
Quantified
fields
are
thus
amenable
to
comparison
both
with
Quantified fields are thus amenableto comparisonboth with
mar
aa través
mar observados
observados
travts de
deimagenes
imfigenessatelitales
satelitalesen
en Ia
la zona
zonanorte
nortede
de
similar calculations
in other
similar
calculationsin
othereastern
easternboundary
boundarycurrent
currentregimes
regimes
Chile.
Mar., 23,
Chile. Invest.
Invest. Mar.,
23, 99-122,
99-122, 1995.
1995.
with mesoscale
within the
study area,
and also
area, Bernal,
Bernal, P.A.,
P.A., F.L.
F.L. Robles,
Robles, and
and O.
0. Rojas,
and
also with
mesoscalesurveys
surveys within
the study
Rojas,Variabilidad
Variabilidadfisica
fisicayybiolOgica
bioltgica
en
dedecorrientes
Chile-Perd.
facilitating
examinations of
interannual variability.
The
en Ia
la region
regitn meridional
meridionaldel
delsistema
sistema
corrientes
Chile-Peril.
facilitating examinations
of interannual
variability.
The
Monogr.
Monogr. Biol.,
Biol., 2,
2, 75-102,
75-102, 1982.
1982.
climatological
seasonal
alongshore
wind
climatological
seasonal
alongshore
windforcing
forcingis
isequatorward
equatorward Blanco,
J. L.,
L., Variabilidad
termica yy salina
sauna en
en la
Ia zona
zona norte
forte de
Blanco,
J.
Variabilidad
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