JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 96, NO. C8, PAGES 14,833-14,848, AUGUST 15, 1991
HorizontalTransportandthe Distributionof Nutrientsin the CoastalTransitionZone
off NorthernCalifornia'Effectson PrimaryProduction,PhytoplanktonBiomassand
SpeciesComposition
FRANCISCO
P. CHAVEZ
1,RICHARD
T. BARBER
2,P. MICHAEL
KOSRO
3, ADRIANA
HUYER
3,STEVEN
R. RAMP4,
TIMOTHY
P. STANTON
4, ANDBLANCA
ROJAS
DEMENDIOLA5
Conductivity-temperature-depth
surveysduring1988encountered
strongbaroclinicjets that wereevidentin
acoustic
Dopplercurrentprofilerandhydrographic
data. DuringJuneandJuly1988a filamentwithhighsurface
nitrate,highchlorophyll,
abundant
populations
of neriticcentricdiatoms,
andhigherratesof primaryproduction
wasevidentperpendicular
to the coastbetweenPointArenaandPointReyes. However,the high-nutrient
and
phytoplankton
regionswere not in the baroclinicjets but were southand inshoreof them. Surfacewater
transported
offshoreby the strongbaroclinicjets wasfoundto haverelativelylow nutrientcontent,suggesting
that thejets themselves
do not carrysignificantlevelsof coastallyupwelled,high-nutrient
waterto the ocean
interior. The low nutrientand salinitycontentof the jet suggests
that the water originatedseveralhundred
kilometersupstream.Althoughthe jets themselves
do not appearto transportsignificantlevelsof nutrients
directlyfrom the coastalregimeto the oceanicregime,dynamicprocesses
associated
with a meandering
jet are
likely responsible
for high surfacenutrientsfound severalhundredkilometersoffshore. Processes
suchas
upwellingalongthe southern
edgeof the seawardjet resultin significantenrichment
of the coastaltransition
zoneandin largebloomsof neriticdiatoms. During 1988the high-nutrient,
high-phytoplankton
filamentwas
presentwhenthe surveysequence
beganbut thendecayedafter a month. The surfaceand subsurface
nitrate
fields werecoherentwith the dynamictopography
field throughout
the surveysequence;
however,the surface
andintegrated
chlorophyll
fieldswerecoherent
onlythroughthefirsttwo surveys.A decrease
in phytoplankton
biomassbeganduringthe thirdsurveycoincident
with physicalchanges
whichoccurredin thattime frame:(1)
an intensification
of the undercurrent
and(2) changes
in the surfacecirculationfrom predominantly
offshoreto
predominantly
longshore.Understanding
the processes
responsible
for the uncouplingbetweenbiologyand
physicsis paramount
for realisticbiologicalmodelsof thisregion.
INTRODUCTION
the interior of the oceanbeyondthe continentalmargin. This
conceptof a highly energetictransitionzoneprovidedfocusfor
Easternboundarycurrentsystems,and the strongcoastal the CTZ programin the form of well-definedquestionson the
circulationpatternsthat are imbeddedin them, are major origin,structureandconsequences
of theseenergeticprocesses.
oceanographic
featuresthatdetermine
thephysical,chemical,and
The energeticjets and eddiesof the coastaltransitionzone
biological
character
of a largeportionof theglobalocean[Ryther, were originally identified on the basis of their temperature
1969;Jahnkeet al., 1990;Walsh,1991]. An earlyview of the signature[Bernsteinet al. 1977]. Later,oceancolor [Abbottand
easternboundarysystemwas that they werebroad,shallow,and Zion, 1985],dynamicheightandvelocity[MooersandRobinson,
slow currents[Woosterand Reid, 1963; Wooster,1970] with a 1984;KosroandHuyer, 1986] wereusedto furtherdescribethese
steady,slow,anduniformadvective
character.The concept
of a features.BeforetheCTZ worktherewasa preliminaryphysical
slowanduniformcurrentsystembeganto changerapidlywhen and a partial biologicaldescriptionin terms of oceancolor, but
satellite surveys clearly showed that the California and the
virtually no chemical descriptionor studieson phytoplankton
Canarycurrentsystems
consisted
of a complexsetof eddiesand speciesdistributions(see Traganza et al., [1983], for the only
cross-stream
jets [Bernstein
et al., 1977]. Recently,a numberof previouschemicaldescription). Primarynutrientconcentrations
papers have provided documentation for the existence of
areusefulfor at leasttwo reasons:(1) theyprovidean indication
energeticeddies and cross-stream
jets as a dominant and of the fertility of the region,and(2) theycanbe usefulas tracers
persistent
component
of the dynamics
of the easternboundary for deducingcirculation and water mass structure[Tsuchiya,
currentregions[Huyer,1983;MooersandRobinson,
1984;Huyer 1975, 1985;Chavezet al., 1985]. Nitrate,therefore,canprovide
et al., 1984;Abbott and Zion, 1985; Davis, 1985; Flament et al.,
an excellentmeansof describingthe structure,source,andfateof
the jets and eddies that complementsthat provided by
combinationof traditional oceanographyand satellite-borne temperature,salt, andoceancolor.
1985;Rieneckeret al., 1985;Kosroand Huyer, 1986]. The
The
surveysled to thecoastaltransition
zone(CTZ) conceptthatjets
andeddiesdeterminethe transition
fromthecoastalprocesses
to
work
described
here used nitrate
concentration
and
phytoplanktonbiomass and speciescompositionin order to
providean improvedresolutionof the dynamicprocesses
of the
coastal
transition
zone
and
insight
on
how
these
processes
1Monterey
BayAquarium
Research
Institute,
Pacific
Grove,
California.
determinethe chemicaland biologicalcharacterof the adjacent
2Duke
University
Marine
Laboratory,
Beaufort,
North
Carolina.
3College
ofOceanography,
Oregon
State
University,
Corvallis.
4Department
ofOceanography,
Naval
Postgraduate
School,
Monterey,
ocean.
MATERIALS AND METHODS
California.
57488
Andorra
Pl.,Boca
Raton,
Florida.
Copyright
1991bytheAmerican
Geophysical
Union
Papernumber91JC01163.
0148-0227/91/911C-01163505.00
A seriesof repeatedconductivity-temperature-depth
survey
cruises were completedoff northern California during 1988
(Table 1; Figure 1) as part of the CoastalTransitionZone (CTZ)
program sponsoredby the Office of Naval Research(ONR).
14,833
14,834
CI•vZz ErrAL.:COASTAL
T•,NSmON
ZON•TgANSmRT
• NUT•NTS
Table 1. Cruisesin theNorthernCaliforniaCoastalTransitionZone During 1988With Individuals
Responsible
for theDifferentMeasuremeres
Chief
Map
Ship
Date
Temperature,
Scientist Salinity
ADCP
Nutrients Chlorophyll
1
Wecoma
June20-27, 1988
Kosro
Huyer
Kosro
Chavez
Chavez
2
3
4
5
PointSur
PointSur
PointSur
Wecorna
July5-12, 1988
July12 to July18, 1.988
July21-27, 1988
July29 to Aug.4, 1988
Ramp
Ramp
Stanton
Kosro
Ramp
Ramp
Stanton
Huyer
Ramp
Ramp
Stanton
Kosro
Chavez
Chavez
Chavez
Chavez
Chavez
Chavez
Chavez
Chavez
Duringeachsurvey,surface
nitratewasmapped
witha horizontal wasimmersedin a darkcasethroughwhichwaterfrom theship's
resolution
of 200 m yieldingon theorderof 10,000observations intakeflowed. The ship'sintakewasof the orderof 5 m below
wasmeasuredon
per cruise.Continuous
surfacemeasurements
of phytoplanktonthe sea surface. Chlorophylla concentration
stimulated fluorescence were also collected. At the CTD stations board ship with a Turner Designs model-10 fluorometer
(on theorderof 75 per cruise)surfacesamples
for chlorophyll
a calibratedwith commercialchlorophylla (Sigma)[Chavezet al.,
andphytoplankton
species
werecollected
fromtheship'sintake 1990]. The samplesfor determinationof plant pigmentsare
and from the surface Niskin bottle.
filtered onto 25-mm Whatman GF/F
Discrete water column
filters and extracted in
samples
to 500 m werecollected
withNiskinbottleson a rosette acetonein a freezer for between 24 and 30 hours [Venrick and
Hayward, 1984]. Other than the modificationof the extraction
for theanalysis
of chlorophyll
a andnutrients
at stations
20 km
apart.During1987[Kosroet al. thisissue]
sizeseparations
of procedure,the methodused is the conventionalfluorometric
chlorophyll
a wereperformed
using1- and5- •m Nuclepore procedureof Holm-Hansenet al. [1965]. Nutrientsamples
collected from the CTD
filters [Chavez,1989].
casts were frozen and returned to the
Continuous
analysisof nitrate+nitrite
was performedusing Monterey Bay AquariumResearchInstitute(MBARI), where
reverseflow injectionanalyses[Johnsonand Petty, 1983; theywere analyzedon an Alpkemrapidflow analysissystemfor
Johnson
et al., 1985]witha FlowInjectionSciences
modelATC- phosphate,silicate,nitrate, and nitrite using conventionalwet
30005 on watercollectedfrom the ship'sintake. Phytoplankton chemistry [Sakamotoet al., 1990]. Duplicate samplesfor
stimulatedfluorescence
was measuredevery30 secondsusinga phytoplankton species composition were preserved with
paraformaldehyde
(pH of 7.4) and with
Seatechfluorometerand a Seabirdsealogger.The fluorometer cacodylate-buffered
[
I
I
I
I
I
N
3g ø
'PI.
Areno
A
38 ø
F
127 øW
126ø
E
125ø
D
C
124ø
B
123ø
122ø
Fig.1. Standard
gridfortheCTDsurveys
during
1988.Fullcompletion
ofthegridrequired
1week.
CHxvmm'.sa..'Consr.sa.
TaANSmON
Zot,mTaXNS•RrnN• Ntrr•Nxs
glutaraldehyde
both to a final concentration
of 2%. The
paraformaldehydesampleswere concentratedby gravity in
settling chambersand countedusing an invertedmicroscope
14,835
RESULTS
Thesurveys
during
•988focused
on•thetheregion
offPoint
[Uterrn6hl, 1958]. Settledvolumesrangedfrom 25 to 50 mL
dependingon the chlorophyllconcentration.Large organisms
(i.e., netplankton)were countedoverhalf the baseof the settling
chamberat 100x and small organisms(i.e., nanoplankton)were
countedon transects,representing2 mL of settledvolume, at
400x. Organismswere identifiedto specieswheneverpossible,
however,when identificationto specieswas not possible;as was
the casewith the smallflagellates,individualswere assignedto a
ArenaandPointReyes,wherestrongbaroclinicjets wereknown
to occur [Kosroand Huyer, 1986; Kosroet aL, this issue]. The
genus or group.
(Huyer et al., [thisissue];Figure3).
The spatialdistributionof biologicaland chemicalproperties
showed that a filament with higher surface nitrate, higher
chlorophyll,and abundantpopulationsof neriticcentticdiatoms
wasevidentoff PointArenaandPointReyesduringlate Juneand
early July 1988 (Figures3 and 4). The filamentextendedfrom
the inner portionof the surveyto the outerportionof the survey
grid about250 km from shore. The width of the feature,along
the D line (Figure1), wasof the orderof 75 km. The distinct
mesoscalestructureof the energeticeddiesand cross-stream
jets
that are part of the CaliforniaCurrentsystemwas evidentin the
horizontaldistributionof nitrate,chlorophyll,phytoplankton
taxa,
anddynamictopography
(Figures3 and4).
In view of thepaucityof primaryproductionmeasurements
in
the study area estimateswere made using multiple regression
models. Photosynthetically
activeradiation(PAR) wasmeasured
continuously on the two 1988 Wecoma cruises with a
Biospliefical2401 sensor. The PAR data were providedby
C. Paulsonof Oregon State University. PAR and surface
chlorophyllwere used to estimateprimary production. The
model relating chlorophyll,PAR and primary productionwas
developedfrom observationsin Monterey Bay (F.P. Chavez,
unpublisheddata, 1990). In MontereyBay, surfacechlorophyll
(plus phaeopigments)
and PAR explain70% of the variancein
primaryproduction(Figure2).
zone of interest,definedas the coastaltransitionzone,represents
a transition
between
thenarrow
andproductiv
e coastal
upwelling
zone (about 25 km wide in the area of study) and the extensive
oligotrophiccentral gyre- The .surveysduring 1988 also
encountered
strongbaroclinicjets that were clearlyvisiblein the
acoustic
Dopplercurrent
profiler(ADCP)andhydrographic
data
The horizontal variability in surface nutrients and
phytoplanktonwhile coherentwith the advectiveregimewasnot
as expected. Visual inspectionshowed that the regions of
strongest
offshoreflow were regionsof relativelylow levelsof
nutrientsand phytoplankton. The higher surfacenutrient and
phytoplanktonregionswere primarily to the south(or inshore)
andonly partiallyimbeddedin the regionsof strongflow. Huyer
et al. [this issue]showedthat the strongbaroclinicjets couldbe
definedin termsof dynamictopography.Usingthe analysisof
Huyer et al., it can be shownthat off Point Arena, the strong
offshorejets typicallytransportlow nutrientand phytoplankton
watersat the surface(Figure5).
Continuous measurementsof Surface currents, nitrate,
r2=0.72
m
_
fluorescence,temperatureand density show a clear offset
betweenthelocationof thestrongbaroclinic
jetsandthemaxima
or minimain theseproperties
(Figure6). An exceptionto this
patternis salinitywhoseminimais coincident
with thestrongest
flows. Huyer et aL [thisissue]andKosroet aL [thisissue]have
inferredfrom the low salinity,characteristic
of northernwaters,
andotherevidencethatthe strongbaroclinicjets are part of a
_
meanderingCaliforniaCurrent. The low nutrientlevelsfoundin
5
I
I
I
6
7
8
the jets also suggests
that thesewatersmusthave originated
9
severalhundredsof kilometersupstreamratherthan at the coast.
Thetimescale
ofnutrient
depletion
in coastal
upwelling
systems
is of theorderof 5-10 days[MacIsaacet al., 1985]andthespeed
in thecoreof thejets wasaround70 cm/s. If thewaterin thejet
upwelling
originit hadto havetravelled
from300Figure2. Scatterplot of measured
euphoticzonedepthintegrated wasof coastal
primaryproduction
againstthatpredictedfrom surfacepigments 600 km prim' to arrival at the D line (Figure 6). The D line,
(chlorophyll+phaeopigments)
and PAR (measured at the however, was only 150 km from shore,so it is likely that the
MontereyBay Aquarium). The data were collectedin Monterey watercarriedby thejets originatedupstreamof PointArena.
Bay from April 1989 throughApril 1990. The modelpredicts
The stronggradientsin biologicaland chemicalpropertiesat
bleosured
primory
production
(InmgC/m2/doy)
slightlyhigherratesthanthoseobservedat lowerlevelsand
slightlylowerlevelsthanthoseobservedat thehigherlevels. The
regressionequationis In(primaryprouc
d tion (mgC/m2/day)) =
the surface were also evident subsurface. Nitrate concentration at
100 m showeda stronggradientbelowthejet axis(Figures3, 7,
and 8) with the nitriclinerising sharplyon the southor inshore
,
5.72+ 0.00029
PAR(IxE/cm2/day,
measured
witha cosinesideof thejet (Figures7 and8). A strongandrobustrelationship
sensor) * 0.33 In(surface chlorophyll a + phaeopigments was foundbetweendynamictopography(or pycnoclinedepth)
(mg/m3))
and nitrate concentration
integratedto 100 m and confirmsthat
14,836
Q-•v•z • m..:Co,•rm.Ta•a•moN
Zo• Ta•a•SmRT
• Nuramms
Dynamic height (0/500)
Nitrate at 100 m (pM)
Surface nitrate (pM)
ß
-'r--I'--'T--i ! I ! ! i r-f-- I
30*N
3g
N
3g'N
•
...................
Fig. 3.
ß../;
'"':..
•%.
%.
ß..
Maps of geopotential
anomaly(relativeto 500 dbar), surfacenitrate+nitrite
(from continuous
measurements),
andnilxateat 100 m for the five surveysin Table 1.
therise in thenutriclinebeginson the southern
or inshoresideof
to be a strongcandidatefor supplyingnewnulxientsto thecoastal
thejet (Figure
9). ']'hedoming
of thenitricline,
presumably
asa
transition zone.
resultof dynamicprocesses
associated
with thejets, mustbe in
During 1988 the filament off Point Arena and Point Reyes
partresponsible
fortheincreased
nutrient
levelsatthesurface
but was evident for close to a month and then decayedas flow
the exact mechanismfor surfacenutrientenrichmentis yet to be
fully resolved. Candidatesincludeupwellingalongthejet edges
[Paduanand Niiler, 1990; Deweyand Mourn,1990] andvertical
wind mixing on a shallownutricline[Deweyand Mourn,1990].
becamepredominantlylongshore. The surfaceand subsurface
nitrate fields were coherentwith the dynamictopographyfield
throughoutthe surveysequence(Figures3 and 9). The surface
and integratedchlorophyll fields were well correlatedwith
The nutriclinedomingoccursover a largerscalethanthe surface
enrichment,implying that vertical mixing is not the primary
processat work. The dislxibution
of propertiessuggests
local
upwellingat the southernedgeof the jet (Figure7; see also
Figure10 of Huyeret al., [thisissue])andthismechanism
seems
dynamic
height
(Figure
10)andcoherent
through
thefirsttwo
surveys(Figures4 and 9). A decreasein phytoplankton
biomass
beganduring the third surveyand may be relatedto physical
changeswhich occurredin that time frame: (1) the undercurrent
intensified[Huyer et al., this issue]and (2) the circulation
CHAVEZ
L:rr
AL.:COA3TAL
T]tnN•ON ZON•T]tnNSmRT
•D Ntrr•NTS
Integratedchlorophylla
(O-100m)(mg/m")
Surfacecl','Alorophyll
a
(mg/m
14,837
Diatoms (cells/ml)
38øN
311
38øN
38e1•
38
38'N
38
ß
127'W
.
126
ß
'
125
50
124
":
123
W
128
125
124
123
Fig.4. Mapsof integrated
chlorophyll
a (0-100m), surfacechlorophyll
a, andsurficialabundance
of diatomsfor
the five surveysin Table 1.
changed from predomin•antlyoffshore to predominantly and actuallyincreasedin many of the areaswherephytoplankton
longshore(Figure3). A time seriesof phytoplankton
abundance levelsdiminished(Figures3, 4, and9).
alongthe D line (150 km offshore)showsthe dramaticdecrease
The correlationbetweenchlorophyllconcentration
and •e
in chlorophyll and nerific diatom populations(principally abundanceof diatomswas higherthan with any othertaxonomic
Chaetoceros
debilis,
C. conCavicornis)
frommap1 to m•ap
5 group (Table 2) and diatoms dominatedall sampleswhere
(Figure 11), suggestingthat the decreasein chlorophyllwas chlorophylla (chl a) concen•ationexceeded0.5 I.tg/L, Below
relatedto a decreasein diatomabundance.The diatombloom this concentrationthe relative contributionof coccolithophorids
found during the first two surveys apparentlyresulted in a and small flagellates to phytoplanktonbiomass increased.
were never importantcontributors
to
depletionof silicatewith respectto nitrateoverthecourseof the D'moflage!lates
survey sequence (Figure 12).
It i•s not clear why the phytoplanl•.•ton
biomassduring the study period. Picoplankton
phytoplankton
populationsdecayedas flow becamelongshoreor populationscould not be properly enumeratedusing settled.
the undercurrent
intensified,sincenutrientlevelsremainedhigh samplesbut sizeseparations
during1987 showedthaton avexage
14,838
Ct-•Av• •-?nt..:Consrnt.Tv,nt4smoN
Zo• T•smRr
•
Ntrntmms
24
o 20-27
June
1988
ß 06-12 July
/' 13,-18 July
ß 21-27 July
o 29 July - 04 Aug
20
16
ß Jef
Inshore
12-
ß
Offshore
ß
.o%
6
ß axis.
7
8
•9
10
11
12
12,
o 20-27
June 1988
ß 06-12 July
A 13;-18 July
ß 21-27 July
o 29 July- 04 Aug
E
E
o
ß
Inshore
ß Jet
ß
ß
o
ß
4,
6
7
Offshore
ß axis.
o
ß
8
9
10
11
12
34.0
ß
o 20-27
June 1988
ß 06-12 July
,• 13,-18 July
ß21-27July
33.6-
[3
29July
-04Aug
Inshore •
33.2
ß
ß
ß
ß
ß Jet ß
ß
Offshore
ß
ß axis.
32.8
32.4
6
7
8
9
10
11
12
DynamicHeight O-500m (m:/f )
Fig. 5. Scatterdiagrams
of surfacenitrate,surfacechlorophyll
andsurfacesalinityagainstgeepotential
anomally
(relativeto 500 dbar)for thefive surveysin Table 1. The definitionof theinshore,
jet axis,,andoffshoreportions
of the coastaltransitionzone regionis from Huyer et al. [this issue]. Clearly the areasof high nutrients,
chlorophyll,andsalinityareon theinshore(andsouthern)
sideof thejet.
C•vaz
Er •.:
Consr• T•ssmoN ZoomT•ssvorr
38.0øN
37.5øN
•
Ntrmmms
14,839
37.5øN
38.5øN
0.5
0.5
0.0
0.0
_ '
I
38.00N
....
I
38.50N
....
!
u (m/s)
-0.5
-0.5
'
2.5
2.0
1.5
1.0
0.5
0.0
I
....
I
....
i
I
2.5
2.0
1.5
1.0
0.5
'- fluor (volts)
'
[
'
0.0
,
- NO3 (p,M)
!
!
!
I
fluor (volts)
:
'
•
....
!
!
I
!
i
'
'-' '
I
64
2
.
ß
..
!
....
!
,
I--"
,
s (psu)
32.5
16
15
14
13
12
11
-
32.5
16
.
,
•
ß
s (psu)
33.0
33.0
,
ß
-
T (øC)
15
14
T (øC)
13
12
11
'
I
....
!
26 -
•r (kg/m
.
.
-
26
I
.
....
I
-
•r (kg/ma)_
25
25
25
25
•
!
37.5øN
I
•
I
I
I
,
,
'7'-"--,,--I
38.0øN
'i
38.5øN
D line, 6/26-6/27/88
,
I
37.5øN
,
,
•
[
38.0øN
'-
I
I
38.5øN
E line, 6/25-6/26/88
Fig. 6. Valuesof near-surface
variablesalongtheD andE linesduringthefirstsurveycruise(normalcomponent
of
thecurrent,negativeoffshore(m/s),fluorescence
(volts),nitrate+nitrite
(mM), salinity(psu),temperature
(øC),and
density
anomaly
(kg/m3).Fluorescence
waswellcorrelated
withchlorophyll
a (r=-0.91),
andtheregression
,
equationwaschlorophyll=-0.958 + 4.68 fluorescence.
filters(Figure13); at levelsover
35%of thechlorophyll
in thewarm"eddy"foundto thenorthof retainedby 5-I.tmNuclepore
all of thebiomass,
dominated
by diatoms,
thePointArenafilamentpassed
througha 1-grnNuclepore
filter. 2 [xgchlall almost
by the 5-I.tm filters. The verticaldistribution
of
Recentwork off MontereyBay with epifluorescence
microscopy wasretained
and nitrateshowthat in the oceanic(northor
[K.R. BuckandF.P.Chavez,unpublished
data,1990)showsthat chlorophyll
regions
thereisa deepchlorophyll
maxima
[Cullen
and
the warm eddy regionsof the coastaltransitionzone are offshore)
1981] coincident
withthetopof thenitracline
andthe
dominated
by Synechococcus,
prochlorophytes,
and othervery Eppley,
(Figures
8 and14).
small (less than 5 I.tm) solitaryphytoplankton.The size depthof the1%isolume
The
filament
primary
production
rates predictedby the
separations
also showedthat thereis a relationship
between
andlightmodel(Figure15)aresimilartothoseforrod
chlorophyll
concentration
andthepercentage
of phytoplanktonchlorophyll
14,840
Cm,vez Er ,•.: Co.r,,& T•,,•smo• Zorn T•,,•smar •
Nitrate (pM)
•o•,•'""•\\'•g-;'•.
••.2o.o•%•
•o•••
Ntnamm-s
Chlorophyll
a (mg/m
3)
_. -•
•o•••
150
150....
loo
100
c.o.•
,
. .
.
o.•
.
.•
o.2,•
,
.
,
.
•.•
150
0
150
50
lOO
100
150
0
150
,
"
50•
0 '
e.o
.
•o..
lOO
1O0
•
.
15o
150
,
i
o
50
150
37.4
i
37'.8
i
I
38.2
i
38'.6
i
PJ9.O
•'o
•o
•o
•o
Kilometers
i
,
' '
i
150
•
' 0.2'
'
,
37.4
Latitude along D-line
•
.
,
•
37.8
,
38.2
38.6
LatitudealongD-line
io
,•o
,•o
39.0
i
200
Kilometers
Fig. 7. Sectionsof nitrateandchlorophylla alongtheD line (seeFigure1) for thefive surveysin Table 1.
in other coastalupwellingenvironments[Chavezand Barber,
1987]. Primaryproduction
ramsarecloseto4 timeshigherin the
filamentsthan in the warm oceaniceddies(Figure 15). The
strongoffshorebaroclinicjets resultin ramsthat are commonly
found within the coastalupwellingdomain(i.e., the Rossby
radiusof deformation)fartheroffshore. The meanproduction
upwelled, high-nutrientwater to the ocean interior. The surface
waterstransported
by thejets werefoundto haverelativelylow
levelsof nutrients(Figure3). Watersof highernutrientcontent
were foundseveralhundreds
of kilometersfrom shorebut they
weretypicallyto the southandinshoreof thebaroclinicjets. To
thenorthandoffshoreof thejets thesurfacewaterswerewarmer
rates
forthesurvey
boxwere1240mgC/m2/day
during
thefirst andhad lower nutrientlevels. Althoughthejets themselves
do
survey, when abundantphytoplanktonpopulationswere found, not appearto transportsignificantlevelsof nutrientsdirectlyfrom
andclose
to50%lower
(740mgC/m2/day)
during
thelastsurvey,the coastalregimeto the oceanicregime,dynamicprocesses
whentheoffshorephytoplankton
biomasswaslow.
associated
with the jets are likely responsible
for high surface
nutrients
found
several
hundred
kilometers
offshore.
The high
DISCUSSION
levelsof surfacenutrientsoffshoremay be dueto processes
like
Resultsfrom 1988suggest
thatthe strongbaroclinic
jets upwellingalong the southernedgeof the seawardjet so that
commonly
foundin thecoastal
transition
zone[KosroandHuyer, circulationpatternsassociated
with thejets andeddiesresultin a
1986]arenotresponsible
for significant
transport
of coastally contribution
of new nutrients to the coastal transition zone.
CHAVI•Z
!iTAL.:COASTAL
T•,NSmON
ZON•T•,NSmRT
•'D NUTm•NTS
Nitrate
14,841
Nitrate
Nitrate
lO
20
3O
0
10
20
[]
B-Une
30 o
10
20
F-Line
D-Line
3O
o•o offshore
north
•• June
20,
1988e26,
1988
ß•ßjet
axis
June 22, 1988
[]•[]
south
inshore
5O
0
ß
[]
O• ß
100
0
north
0
,Offshore
ß •ß
[]
jet axis
0•0
offshore
ß •ß
jet axis
[]•[]
[] .south
south
inshore
'inshore
150
Chlorophyll
"a"(mg/m3)
o.o
2
o
4
6
8
10 0.0
Chlorophyll
"a"(mg/m3)
2
/
4
6
8
10 0.0
Chlorophyll
"a"(mg/m3)
2
4
6
8
10
June
20,
1988
D-Une
5O
B-Line
F-Line
June22. 1988
June26, 1988
lOO
north
north
north
0
0 offshore
0----0offshore
0•0 offshore
ß
ß jet axis
ß
•'--•
south
El Elinshore
ß jet axis
[].__[]south
inshore
jet axis
[]"•El south
inshore
15o
Fig.8. Vertical
profiles
ofnitrate
andchlorophyll
a madealong
theB, D, andF linesduring
thefirstsurvey
inJune
1988.Theraised
nutricline
andenhanced
phytoplankton
populations
areevident
in alltheinshore
stations.
Thejet
axisis intermediate
between
theinshore
andoffshore
stations.Thedeepchlorophyll
maximain thenorthor
offshore
watersareatthesamelevelasthe1%isolume
andthetopof thenutricline.
The strongcorrelation
foundin thisstudybetweendynamic
heightandupperoceannutrientcontent(Figure9) is similarin
nature to the strongcorrelationfound by Chavez [1987] and
ChavezandBrusca[1991]for sealevelandupperoceannutrient
contentin the southeastern
Pacific. Barber and Chavez[1986]
arguethatthebasin-wide
patternsin productivity
of the tropical
Pacificarerelatedto dynamic
processes
thatregulatethermocline
topography.The connection
betweenthermocline
topography
and productivityis upper ocean nutrient content:when the
thermocline
andnutricline
aredeep(anddynamic
heightandsea
level are high), the sourceof new nutrientsis fartherfrom the
euphoticzone. Measurements
of sea surfaceheightfrom
14,842
CteAVF.
Z ETAL.:COASTAL
T•,mmor• Zorn T•e,•sPORT
A•mNUT•UEmS
2500
2OO0
13
ß
.
o 20-27
ß
ß
ß
ß
ß
ß
ß
©06-12 July
ß 13-18 July
ß 21-27 July_
o 29 July - 04 Aug
June 1988
ß
o
ß
ß
E
1500
ß
ß Jet
Inshore
'•e'
lOOO
ß
Offshore
axis :
,r'•
,
0
ø
500
o
6
8
9
lO
11
12
lOOOß
-
ß
ß
o
ß axls.
0
100
ß Jef
o 20-27
June
1988
ß 06-12 July
,
Inshore
Offshore
10,
I
6
12
1000ß Jef
ß
ß
ß axis.
ß 21-27 July
a 29 July - 04 Aug
Inshore
100-
Offshore
ß
ß
lO
6
7
8
9
10
11
12
DynamlcheightO-500m (m2/s2)
Fig.9. Scatter
diagrams
of integrated
nitrateandintegrated
chlorophyll
a against
geopotential
anomaly
(relativeto
500dbar)forthefivesurveys
in Table1. Thedefinition
of theinshore,
jet axisandoffshore
portions
of thecoastal
transition
zoneregionis fromHuyeret al. [thisissue].Therelationship
betweendynamicheightandnitrateis the
samefor all surveys,
buttherelationship
changes_
forchlorophyll.Dynamicheightexplained
62%of thevariance
in
integrated
chlorophyll
thefirstcruise,
andther2 value
decreased
witheach
cruise
untilonly16%ofthevariance
couldbe explainedduringthelastcruise.
CHAVEZ
RTAL.:COASTAL
T•,NSmONZoomTRANSmaT
A•D NUTamNTS
r=0.90
•,
lOO
ß /-'
ß •e•e
lO
O.Ol
J
ø
.'-..
ß
I
I
I
0.10
1.00
10.00
Chlorophyll
o__
O- 100m(mg/m2)
Fig. 10. Scatter
plotof surface
andintegrated
chlorophyll
duringthefirstcruise.Therelationship
wasstrong
throughout
thesurvey
sequence
witha correlation
coefficient
of0.81whenallcruises
wereconsidered.
10
Julian Day
o
37.4
.37.8
.38.2
Mop
172
e•e
1
190
"•"
2
196
m--m
5
206
o--o
4
210
*•*
5
.38.6
.39.0
3•).4
150
Julian Day
o
o
o
x
ß
172
Map
e•e
1
,__,
100
E
o
/
•
\
210
*•*
5
5O
0
.37.4
37.8
38.2
38.6
.39.4
•9.0
100
o
o
o
Julian Day
ß
80
190
x
E
ß'•"
2
o•o
4
196
6o
2o6
o
210
40
E
Map
172
20
o
0
37.4
1
37.8
38.2
L•titude
38.6
39.0
39.4
on D-line
Fig.11. Surface
concentrations
of chlorophyll
a, phytoplankton
cells,anddiatoms
alongtheD line(Figure1) for
thefivesurveys
in Table1. Thedecayin phytoplankton
populations,
primarily
diatoms,
frommapI tomap5 is
evident.
14,843
14,844
Cm•,v•z•r nu.: Cossr• Ta•.srno• Zo• TaA•S•I•T •
Ntrram•s
20
ß 20-27
June, 1988
ß 29 July-04 August
"'-'"
15
q)
lO
o
!
I
i
5
10
!5
20
Nitrate (AM)
Fig. 12. Plotof nitrateagainstsilicateshowinga depletionof silicatewithrespectto nitratebetweenthe firstand
thelastsurvey.Thedatawerebinnedandaveraged
onnitrateconcentration
(0-2,2-4,4-6,6-8,8-10,10-15,15-20).
Alsoplotted
arethestandard
error's
of themeans.Nitratereaches
verylowlevelsbefore
silicate
(andphosphate)
in
thisregion.
satellitescan likely be used to estimateupper oceannutrient
contentin this region. More studyis required,at least on the
mesoscale,to better define the relationshipbetweendynamic
topography
andphytoplankton
biomass(Figure9).
Two distinctphytoplanktoncommunitieswere found in the
characteristic of oceanic waters, were found to the north and
offshore.The strongjetswerepartiallyimbeddedin bothsystems
and appearto act as a boundarybetween them [Hood et al.,
1990].Notsurpris'mgly,
thespecies
composition
of zooplankton
showedsimilarspatialstructure[Mackaset al., thisissue].It can
coastal transition zone: (1) a coastal diatom-dominated be inferredfrom productionrates and food web structure that
communityand (2) an oceanicsmall, solitary phytoplankton vertical particulateflux resultingfrom the diatom-dominated
community. The spatial distribution of phytoplankton communities
shouldbe severaltimesthe flux resultingfromthe
populations
wassimilarto thatobserved
for nutrientsin thathigh- small,solitaryphytoplankton
oceaniccommunities[Michaelsand
chlorophyll areas, dominatedby neritic diatom communities, Silver, 1988],
were found to the south and •shore of the jets and low
The dramaticchangesin phytoplankton
populations
observed
chlorophyllareas,dominatedby small solitaryphytoplankton duringthe surveysequencesuggeststhat much of the week-to-
Table2. Statistics
andCorrelation
Coefficients
ofPhytoplankton
groups
vs.Chlorophyll
Concentration
forSamples
Collected
Along
theD Line (Figure1) DuringtheFive Surveys(Table1)
Standard
Variable
N
Mean
Chlorophyll,Ixg/L
Phytoplankton,
32
32
0.81
16297
Deviation
1.68
24108
Correlation
Maximum
8.98
123190
Minimum
0.05
1160
Coefficient
0.95*
cells/50 mL
Coccolithophorids,
32
1876
1921
8425
200
0.43+
32
32
32
32
8587
7548
1019
343
18487
16496
2189
482
86415
76640
9775
2114
9
9
0
0
0.79*
0.75*
0.86*
0.00
32
12
49
275
0
0.56'
32
5498
6674
30350
300
0.64*
cells/50 mL
Diatoms,cells/50mL
Centtics,cells/50mL
Pennates,
cells/50mL
Dinoflagellates,
cells/50 mL
Silicoflagellates,
cells/50 mL
Monads,cells/50mL
* Significantat the99% confidencelevel.
+ Significantat the95% confidence
level.
CHnW.
Z m'st,.: Conxrnt,T•o,•srnoNZorn T•O,•SmRT
nto Ntrr•ms
14,845
lOO
ß
ß
ß
ß
8o
ß
ß
ß
6o
ß
ß
ß
ß
(-
¸
ß
40
o
¸
2o
0
2
4.
6
8
10
Chlorophyll
Fig.13. Scatter
plotof chlorophyll
concentration
against
thepercentage
of chlorophyll
retained
by a 5-gm
Nuclepore
filterforthesurvey
inMay 1987[seeKosroetal., thisissue].
periodandtheoceanic
periodwhenoceanic
watersare
monthvariability'm phytoplankton
biomasscomposition
and upwelling
production
in thisregioncanbe relatedto thevariabilityin the observedcloserto the coast. Episodic•d dramaticdecaysin
populations
areprobably
important
characteristics
mesoscalecirculationof the jets and eddies. Relationships phytoplankton
significantly
to theremovalof
betweencirculation,plankton,and nutrientsin the California 0f thisregionandmaycontribute
Currentsystemderivedfromdatacollectedquarterly[Cheltonet carbon(and silicate)from the surfaceto the deepseaandto the
character
of theregion[Smetacek,
1985;Walsh,1983].
al., 1982] may need to be reinterpretedin light of these ecological
One interpretationfor the decreasesin phytoplankton
observations. The decreasein phytoplanktonbiomass and
mechanism(either
production,associatedwith the disappearance
of diatom populationsis that the diatom-seeding
upwelling
to
the
south
of
the
strong
currents
or offshore
populations,
abouthalfwaythroughthe sequence
of surveysis
disappeared
aftermap3. Theuncoupling
betweenthe
extremelyinteresting
eventhoughwe haveyet to determinethe advection)
fieldswhichoccursaftermap3 would
reasonsfor the demise of the diatoms. The timing of the nutrientandphytoplankton
disappearance
coincided with an intensificationof the thenbe a resultof the lack of supplyof neriticcentricdiatoms
for high biomassin the
undercurrent[Huyer eta!., this issue] and a changein the (the organismsgenerallyresponsible
circulation from a predominantly offshore pattern. to ocean) to the offshoreregions. A similar scenariohas been
for theequatorial
Pacific[Chavez,1989]. Martinand
predominantly
longshore(Figures3, 4, 6, 7, and 8). The proposed
observedchangesmay be relatedto seasonal
variationsin the Gordon[1988] foundthat the filamentsof the coastaltransition
CaliforniaCurrentSystem. Justsouthof this region,$kosberg zone in northernCalifomia had relatively high levels of iron.
(1936) andBolin andAbbott(1963),havedescribed
physicaland Martin and his co-workers[Martin, 1990] suggestthat iron is a
limitingnutrientin the oceanandconceivably
the
biologicalchanges
thatoccurin July andAugustbetweenthe particularly
lOO
Oo
•
'-
60
40
• 20
o
0.01
ß
I
0.10
eeee
ß
!
1.00
i
10.00
Surfc•ce
chlorophyll
c•(mg/mS)
Fig.14. Relationship
between
surface
chlorophyll
andthedepth
of the1%isolume
as..
estimated
fromanoptical
model[Morel, 1988]for stations
of thefirstsurveycruise.
14,846
C}•nVEZ
lit AL.;COASTAL
Tluu•srrloN
gONETluU•SPORT
ANDNtrram•s
PdmaryProduction(mgC/m2/day)
I
I
I?
ß
I
I-
.
57
127 W
59
.
. ß
126
125
124
125
122
126
125
124
125
122
N
127 W
Fig. 15. Horizontaldistribution
of primaryproduction
duringthe first andthe lastcruisesof 1988. Primary
productionwas estimatedfrom a multiple regressionmodel that uses PAR and surface pigments
(chlorophyll+phaeopigments)(see
Figure2).
decreasein phytoplankton
standingstockmay be associated
with
a decreasein the supply of iron. It may also be that vertical
motionis a requirementfor maintenance
of nonmotileorganisms
such as diatomsin the euphoticzone and that vertical motion
alongthejet edgewasrelaxedwhenthe undercurrent
intensified
or thejet changeddirection.Grazingalsoneedsto be considered;
requiredfor development
of realisticbiologicalmodelsof eastern
boundarysystems.
Acknowledgments.
Thisresearch
wassupported
bygrants
fromtheOffice
of NavalResearch
andtheMontereyBayAquarium
Research
Institute.
We aregratefulto P.Whaling,M. Sanderson,
R. Petty,C. Sakamoto,
M.
however,
preliminary
estimates
suggest
thatmacrozooplankton
grazing was not sufficientto explain the dramaticchanges Graham,
andthecrews
of theWecoma
andPointSurwhosupported
our
(T.J. Cowles,personalcommunication,
1990). Understanding
the efforts
at seaandin thelaboratory.
B. Fennerty
worked
ontheprimary
processes
responsiblefor high levels of phytoplankton
biomass production
multipleregression
modelsduringthe 1990 Stanford
andproduction
in the coastaltransition
zoneandperhapsmore University
Spring
course
at Hopkins
MarineStation.Monterey
Bay
importantly the rapid decreasesin phytoplanktonstocks is AquariumResearchInstitutecontributionnumber45.
CHavez•r •.: Cossr• T•,•smo• Zo• T•,•s•Rr •
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14,848
C•v•z
• •.: Co,.,,vr• Ta,•'smon Zorn T•smRT
A• Nm'am•s
S.R. RampandT. P. Stanton,Department
of Oceanography,
Naval
R.T. Barber,Duke UniversityMarine Laboratory,Beaufort,NC
28516.
Postgraduate
School,Monterey,CA 93943.
B. Rojasde Mendiola,7488 AndorraPlace,BacaRaton,FL 33433.
F.P.Chavez,MontereyBayAquarium
Research
Institute,160Central
Avenue, Pacific Grove, CA 93950.
A. Huyerand P.M Kosro,Collegeof Oceanography,
OregonState
University,Corvallis,OR 97331.
(ReceivedAugust13, 1990;
accepted
March 15, 1991)