A 14C!)EL OP SEAWATER STRUCTURE NEAR THE
WEST C.ST CF VANCOUVER IS lAND, BRITISH COUJMBL(
by
ROBERT KENNETH lANE
A THESIS
submitted to
OREG
STATE UNITERS IT!
in partial fulfillment of
the requirements for the
degree of
MASTER OF SCIENCE
July 1962
APPROVED:
Redacted for Privacy
Associate
Professor
of Oceanography
In Charge of Major
Redacted for Privacy
Chairman of Department of Oceanography
Redacted for Privacy
Chairman of
School Graduate ComuLttee
Redacted for Privacy
Dean of Graduate School
Date thesis is presented
Typed by Diane
(}f
Frischknecht
AC1NAQLEDGNENT
Grateful aIcnowledginent is made
to the staff at Pacific
Oceanographic Group, Nanaimo, British
project
Columbia1
where the
originated and all the data were collected.
appreciated were the
guidance and
Particularly
suggestions of Dr. 3. P. Tully,
Oceanographer in Chctrge of that group.
A MODEL OF SEAWATER STRUCTURE NEAR TUE
WEST CCWT OF VANCOUVER ISLAND, BRITISH COLUMBIA
by
Robert Kenneth Lane
TABLE OF CONTENTS
I.
II.
Introduction
Seasonal Factors ....... . . ........................
1.
L.
A.
Runoff and its contribution to structure .......
B.
Beating and cooling and their
k
contributions
to structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . .
6
Wind and its contribution to structure .........
8
The Model . .............................................
10
(December through March)
10
C.
III.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . .
A.
B.
Stage
1
Sa 1 inity
2.
Tempe ra tu re .
2.
. . . . ........ . . . . . . . . . . . . . . . . . .
.
. ...... . . . .
............
. .
10
. .
1 6
2.
Stage
20
....................
Salinity ........
20
Temperature ....... .... ......... .. .....
Stage 3 (May through July)
1.
D.
..... ..........
Stage 2(MarchthroughApril) .............
1.
C.
1
Salinity
....... .
Temperature
I
. .
............ ........
. . . .
.........
.
. . .
. . . . .
.
. .
. .
. .
. . .
. . . .
.
(July through October) ..............,..
2k
26
26
31
37
1.
Salinity .. ....eS.s..eS.......
Temperature ..............................
Stage 5 (October through Decebei ..............
2.
E.
1.
Salinity
2.
Temperature ............................
. . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .
37
k2
45
45
IV. Summary . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5].
Bibliography .... . . .. ...... .... ...... .. ........ ..
53
V.
SEAWATER STRUCTURE NEAR THE
A MCVEL (
VANCOUVER
ISLAND, B1UTISH COLUMBIA
WEST COAST (
I.
Introduction
Temperature and salinity structures1 in the coastal region off
the southwestern coast of Vancouver Island, British Columbia
(Fig. 1) have been reviewed by Lane (LI).
A more detailed study of
the data (6) in this region has permitted the definition of five
seasonal stages in the cycle of seasonal changes of the temperature
and salinity structures.
The form of the model is a vertical section normal to the
coast, from the shore to seaward of the continental slope
For the
convenience of description, the structures in the section have been
simplified into their principle zones, idealized, and their features defined.
Each zone defines a layer or depth interval in
which the properties of the water are constant, or consistently
change with depth, and whose limits are defined by features of
structure rather than numerical values (iLl, p. 6; 16, p. 528).
The five stages of salinity and temperature structure
Following the usage of Tully (16, p. 528) the term structure
refers to the distribution of properties of the water, usually in
the vertical sense. A graph of salinity as a function of depth
(cf. e.g. Fig. 2) or a plot of the isopleths of salinity in a
section defined by length and depth defines the salinity structure.
r$ELD
ISL
D
--
V
- lOOm.
--2cm.
"--
/
I,
PACIFIC
,, 2000m.
OCE4N
__E
Figure 1.
48
Chart of the approaches to southe-rn Vancouver
Island, British Columbia, showing positions of
observations, geographic locations, and contours
of depth.
RICA ST
SALR'TY
UPPER ZONE
TEMPEPATURE
L4'PER ZONE
t.
LOWER ZONE
Figure 2.
L01'EI? ZONE
Definitions of temperature and salinity structure.
I!
'4
constitute a model, which is believed
to be applicable to
coastal region defined above and also,
to
the
some degree, to the
entire west-coast Canadian and Alaskan coastal regions.
The salinity structures in the local estuarine regions
subarctic Pacific Ocean have
and the
been described by Tully (16), and by
Tully and Barber (17). An upper and a lower zone, in which the
salinity
structures are nearly isohaline, and which are
separated
by a halocline, were defined in both regions. By analogy, a simple
temperature
structure is defined
zones separated
here as upper and lower thermal
by a thermocline.
II. Seasonal Factors
The five stages of the model a re related to the seasons 1
variations of runoff, heating and cooling, and wind; the factors
determining the character of the
coastal
of precipitation, runoff, insolation,
waters
The
annual cycles
and wind velocity and strength
in this region have been discussed ('4, p. 5]-6'4). These are
briefly reviewed here and the factors pertinent to the discussion
of each stage of the model
A.
Runoff and
its
are
appropriately included
contribution
therein.
to structure
Fresh water enters this region (Fig. 1) mainly as discharged
from small local rivers, e.g. the Stamp R., (as shown in Figure 3),
and larger continental
rivers, e.g. the Fraser IL, (as shown in
Figure 3). The former, subject to a sunmer discharge from the melt
8
.
7\ (&STAMPR.
M
1'l MI
A
.1
.1
I
A
I
I
S
(
I
I
5
fl
M
.1
I
-2
V
IQ
x.
o
5
/
"-
5r
C)
U)
I
/58
U
ci
/
/9O7
E
//
//
,/
-I
i? 3
0
U)
/
:i:
/
/
0)
0
k 2 k
i
3
I
1F, M1 A, .1
300
"
,"
i
I
U
0
a:
/
I
o2-
D
x
,
J
,
,'
i
i
>1
0
I
5
4
l-1
t
A 1S1 0 1N1 D, J
J
8
7
H
'0
x
ci
C)
U')
(3
C)
U)
.4
-t F).
E
w
0
30Ua:
a:
0
U)
a:
.
- (L/./ 1 IT/-4 QL IT
0
I
J
IT.
F MA MJ JASON D
I
I
I
I
I
I
I
I
I
Figure 3. Mean monthly discharge of coastal
(Stamp) and mainland (Fraser)
rivers, 1957-1958.
i
J
U)
a
6
of highland snow storage, as well as the stronger, precipitationinduced (Fig. Zi a) winter discharge,
shows two maxima.
data show the second peak especially well.
The
The 1957
Fraser River data
reflect the single summer maximum discharge from the melt of
continental snow-fields. Both sources of fresh water enter the sea
as eatuarine discharge, resulting
in a brackish
upper zone.
Thily (16) has shown that there is unidirectional upward
transfer of salt (entrainment) from the more dense oceanic water
to the overriding estuarine discharge when there is a velocity
shearbetween the zones. Further, he showed that the greatest
shear occurred in a halocline. It has also been shown (17) that
the features of the estuarine structures are similar to those found
in the eub-&rctic Pacific Ocean. Velocity shears caused by oceanic
mechanisms, such as convergence and divergence, may result in a
demand for lower zone water and, thence, entrainment.
B.
lating and cooling and their contributions to structure
A heat budget has not been computed locally. This has been
done for Triple Island (Let. 54 N., Long. 31) by Tabeta (11),
for the Strait of Georgia (Let. 148.5 N., Long 122.5 W.) by
Waldichuk (18), for the Ocean Station "F" (Lat. SO N., Long. 115 W)
by Tabata (12), but not for any location on the west coast of
Vancouver Island,
Figure 14
b shows the insolation cycle (monthly
values of hours of bright sunshine) for the region studied here,
represented by data for Bamfield, B.C. (Fig. 1) (5).
7
PRECIPITATION AT
50
BAM/ELD
/957 ----'
230-
'
1-
LU
0
20
I
/9;9---
ii
i/i
(a)
/
oL_j
(0
j FM AM
STAGE
F-'--- I
S
0
N
D
S
0
N
U
- 2 F4
3'-1
U,
0
z
.0
-j
0
z
(/)
£JCL L/ELET
0
Figure LL
(a) Monthly totals of precipitation (1957-4959)
on the west coast of Vancouver Island
(Bamfield, B.C.)
(Fig. 1).
(b) Mean monthly hours of bright sunshine on
the west coast of Vancouver Island (ucluelet, B.C.)
(Fig. 1).
(After climatological Atlas of Cari,ada,
1953, National Research Council of Canada).
8
From the insolation cycle and from the heat budget studies
cited, it has been inferred that, in the coastal waters, there is
a net heat gain in aue.r from insolation and net Iat loss in
winter from evaporation, beck radiation, and conduction.
heat is transferred to the depths mainly by turbulence.
Wind
causes the mixing downward of heat increments which, through con-
vection, result in
thermocline
structures. The depth to waich the
therniocline extends indicates the limit of downward heat transfer.
The process of thermocline
formation has been discussed by Defant
(2, p. 121-2), as well, as many others. Figure 2 ahows the mixed
upper zone,
thermocline,
and lower zone
structures.
During periods of heat loss at the surface, due to the
processes mentioned above, wind mixing results in convective
cooling throughout the wiudmixed layer.
C.
Wind and its contribution to
structure
In winter the winds blow predominantly from the southeast; in
eurmer, predominantly from the northwest
(u-,
p. 62) (Fig. 5).
The effectiveness of wind mixing is determined
by the balance
between the wind-generated turbulence and the stability of the
water mass.
Sverdrup,
The general aspects of this have been discussed by
j (10, p. k96-8).
Wind-induced divergence and convergence are formidable factors
in some coastal regions (10,
p. 500-502).
When northwest
winds
drive surface waters seaward from a western coast, and estuarine
J
I
FM AM J
I
A
J
I
S
N
I
I
p......
ES TE VA N P0/NT
6000
SE
A'
4000-
\
I'
\\
:''
2:
i957--.--
6000-
/958
/
\
/
\
/959.-.
\!
V
N
STAGE N I
2 _ l
!--
3
N
4 -1
N
-1
11,000
E
I.-
/
I,'
'I)
5-
10,000
9000
8000
j
7000
-
/
\
I-
,,,
5000r
M
Figure 5.
A
M
P JAS
Winds along the west coast of Vancouver Island
(Estevan Point, B.C.) (Fig. 1).
(Upper). Components of wind mileage resolved
from the southeast and northwest (1957-1959),
by months.
(Lower) Total wind mileage (1957-1959), by
months.
10
discharge is not capable of replenishing it, divergence results
(Fig. 6).
The
ament of deep water to the surface along the
coast has been termed "upwelling" by Sverdrup (9, p. 155)
divergence system
The
has also been named as the cause of the cool
tomperatures along this coast in suimiiei(7, p. 135).
III.
The Model
A.
Stage 1 (December
through March)
During this period, the winds are predominantly from the
southeast
and the monthly wind mileages are maximum (Fig. 5).
Precipitation (Fig. 4 a) and the corresponding runoff through
local estuaries (Fig. 3) are also at their annual maximum.
1.
Salinity
An example of observed salinity data is shown in Fig. 7.
In the shallow water, the salinity structure is strongly developed
only near the shore. In the oceanic part of the region the waters
are isohaline to at least 50 in depth. The isohalines slope downward toward the shore, particularly in the inshore region.
The force of the wind results
entire oceanic and
in deep mixing throughout the
coastal region except
near shore where the
large coastal discharge provides continuous renews 1 of brackish
water and large stability. An onshore moveinent produced by the
strong southeast winds confines the brackish discharge from local
estuaries (e.g. Barkley Sound) to a narrow, northward flowing,
11
NCSTHWEST
0
0
WINDS
0
-- 1ND DR. EV SURFACE TRANSPORT
0
OFFSHORE -
0
/
of
DIVERGENCE
SOUTHEAST
WINDS
- WIND DRIVEN SURFAOE TRANSPORT - ONSHORE
I
CONVERGENCE
Figure 6.
Conditions of divergence and convergence in
British Columbia coastal waters.
NAUTICAL MILES FROM SHORE
0
50
2. 6
:.
100
I.-
SALINITY (%)
I
0
I5O
N
200 -
FEBRUARY 9, 1960
N
C".
250
-V.
-L
I
Figure 7.
Ecarnple of salinity structure in a section seaward of Amphitrite
Point, B.C.
(Fig. 1) during stage 1.
.1,)
alonshore stream (1, p. 9L7; 4, p. 86).
The relative intensities
of wind and discharge determine the width of
the brachish coastal
water belt.
An idealized model of the type of salinity distribetion and
plots of structures in the section are shown in Fig. 8
a and
structures obserwd in each part of the section are shown tn
Fig. 9.
The isoha line
50 to 70
in
oceanic upper zone (OU) in the slope region is
deep with a characteristic range of salinity 32.2 to
32.6 o/oo, The oceanic halocline extends below this in two
distinct sections (OH1 and 0112) (Figs. 8 a, 9 a i) to about 200 m
depth.
At this limit
the salinity becomes 33.8 to 33.9
0/00.
In
this paper, the oceanic halocline will be considered as a single
feature (OH).
The oceanic lower zone (OL) lies below the halo-
dine, and in it the salinity increases slightly toward the sea
bottom.
Normally, (Fig. 7) the shelf is a transition region containing
a modified coastal upper zone (mcU) (Fig. 8 a), and a modified
coastal halocline (inCH) extending to the bottom (Fig. 9 b ii).
This is indicated in plot II (Fig. 8 a). The salinity is 31 to
32 0/00
to
in the upper zone, and increases in the haloeline
to 32.2
32.6 0/00.
At tines there has been evidence of low salinity coastal
waters in the oceanic upper zone over the edge of the continental
shelf (Fig. 9 a Li). Such a condition seems likely to be
14
POST!ONS
3/o/OrnCU
ou
53
'N.
:f
orncH
/1
OH2
STAGE
I
DECEM3ER through MARCH
o
33B/59 o
OL
SALINITY(%0)
0
'\.
T"°°
N ot
L
°
/.
o
°7O/8.O
200 -
/
STAGEI
DECE BER through MARCH
/1::
250 70
80
0
0.0
7(
8
90C
0.0 7.0
8.0
QO
I0
'E2it±'7
(b.)
Figure 8.
Model of structure and distribution in a vertical
plane seaward of Amphitrite Point, B.C. (Fig. 1)
and plots of structures showing ranges of values
at positions I, II, and III (Fig. 1).
(a) Salinity, Stage 1.
(b) Temperature, Stage 1.
15
E
Ui
0
(a)POSITION I (SLOPE)
o
1°C 7O
.0
S%030
3?0
90
1°C 70
Iq.o
3.0
S% 30.0
5C
I0(
E
FEBRUARY 27,196/
1°C 79
S°J 319
U
0
8.p
90
3.0
s% 28.0
(j)
9.0
T°C 7.p
C
(b)POSTION
3.0
31.0
330
89
(j)
99
29.0
9.0
3Q.O
MARCH 8,196/
5C
JANUAR//2,/960
9.0
1?
3.0
0
IOC
9.0
LJANUARY /1,196/
T°C 70
(0
89
S%39.0
80
(ii)
9p
310
I00
?°
3.
(ii)
II (S1ELF)
5C
DECEMBER 5,1958
(iii)
(c)POSLTION flI (INSHORE)
Figure 9.
Examples of data in: (a) position I, (b) position II,
and (c) position III during Stage 1 (Fig. 8).
'C
associated with the infrequent periods of off-chore flow created
by northwesterly windc. Alsc there are timec when the oceanic
upper zone may intrude over the continental shelf because of the
conwrgencc uiecbanisi a ociate with strong southeasterly winds.
When this occurs the water over the continental shelf becomes
homcgenous (Fig. 9 b 1).
Plot III (Fig. 6 a) and Fig. 9 c sh
the large range of
values and structures to be found in the inshore coastal (C)
atcrs. continual rep1enishzent of the brackish water from
estuarine discharge (Fig. 3) usually intains the structure in
which the salinity increases with depth, despite w5.nd and tidal
mixing. A mixed upper zone, sporadically created by the wind, uy
be present. Surface salinities range from 27 to 31 o/o while
near the bottom the values range from 30 to
31 0/00.
2. Temperature
During this period winds are strong (Fig. 5), insolation is
minimum (Fig.
L
b), and surface cooling is maxivu'. The conse-
quences are indicated in the examples of observed data shown in
Figures 10 and 11.
In both figures, surface temperatures are low.
However, inshore stability has inhibited mixing over the shelf so
that temperatures decrease shoreward.
In both figures, the iaotherms ilope downward to the coast.
Figure 10 indicates this most clearly. First, the isotherms slope
more steeply and more definitely downward toward the coast.
Second, the more stable coastal water is confined more closely to
NAUTICAL MILES FROM SHORE
50
25
0
E
I
I-
w
a
'1u.f'
Figure 10.
Example of temperature, Stage 1.
I.-.
-.4
ii:i
NAUIICAL MILLS -U
,rIvr
84
C)
I0.
200
250
Mu FR
ThIITIrftI
FROM SHORE
0
50
33 4______________________
4?
33.6
4?
..
I
I-
w
a.
a
[.SALI N
33.9 -------------- -.
ITY (%o)
APRIL 6-8, 1959
Figure 11 (upper).
Example of temperature, Stage 1
Figure 12 (lower).
Example of salinity, Stage 2.
19
the shore
and the
well-mixed oceanic upper zone dominates the
slope region and seaward.
The idealized model of temperature
dietribetion
in
the
seaward
section, and "plots" of the structures are shn in Figure 8 b, and
structures observed in each part of the section are shown in
Figure 9.
In the slope and offshore part there is an isothermal upper
zone, more
then 50 in
(Fig. 9 a i).
deep, coincident with the salinity upper zone
The temperatures range from 8.5° to 9.8° C.
Doe
(3, p. 12) found that surface temperatures decreased to seaward
from this region in winter.
At the bottom of the upper zone there
is frequently a temperature maximum (Fig. 10) which is considered
a transient feature, although it is recurrent. Below this zone
(Plot I, Fig. 8 b)
the temperatures decrease uniformly with depth
to values between 7° and 8° C at 200
in
depth.
tn the shelf and inshore parts of the section the structures
are isothermal or increase with depth. It appears that the positive
temperature structure is the more common.
The temperature of the bottom
waters is at its annual maximum
during this season. It is reasoned that this water is the remnant
of upper zone oceanic water which
seasons. During the winter
it
was warmed during
the previous
is conveyed shoreward and depressed
by the convergence mechanism, and partly cooled.
It is overlaid
by estuarine-diecharge waters which are stable because of their low
salinity, and
colder because they
are subject to surface cooling.
20
Plot II
(Fig. 8 b) shows
in Fig. 9 b ii.
the general structure, which is
The upper zone (0-30 m
7° C when estuarine water is
range from 8.5' to 9.8' C.
exemplified
depth) may be as cold as
present. More frequently the values
Bottom temperatures range from 9° to
100 C.
In the inshore waters (Plot III, Fig. 8 b) a wide range of
temperature structures may be found.
The waters may be isothermal,
or positive or negative therzaoclines may exist, depending on the
properties of the brackish eatuarine
examples in Fig. 9 c).
that is present (see
In this part of the region the range of
to
temperature at the surface is 7°
to
discharge
100 C and at
the
bottom is 8.5°
950 c
B.
Stage
2 (March through April)
During this period the coastal runoff (Fig. 3) is less than
during Stage 1 and insolation (Fig. 4 b) increases.
Wind velocities
(Fig. 5) are still large but the direction is variable because this
is a period of change from dominant southeast to northwest winds.
This results in a
surface
1.
relaxation of the
chanism and allows
waters to extend seaward.
Salinity
An example of the observed
Fig. 12.
convergence
salinity
structure is shown in
The winter accumulation of brackish coastal (C) water
spreads seaward over the oceanic (0) water previously present.
event may occur in varying degrees depending on the
This
nature of the
2].
wind and the amount of coastal water.
northwest and southeast
discharges
from the
estuaries may
of brackish
lated pools
winds and
Alternating periods of
periodic, tidal-controlled,
result in the formation of iso-
water in this region (k, p. 67 and 71).
During this period the isohalines still bend downward, toward
the coast, particularly in the shelf part of
oceanic part
the slope is much less
In the
the section.
than during the winter.
The model of salinity distribution and structures (plots) is
shown in Fig. 13 a, and structures observed in the
of the
several
parts
section are shown in Fig. 1k.
In the oceanic
and slope parts of the section the three salinity
zones are apparent and are
values as in Stage 1
75 a depth and is
defined by
The oceanic upper zone (OU) extends to a bout
continuous over the
balocline extends to
the structure and range of
shelf. Below this
about 175 a depth.
the oceanic
This rise from the depth
(200 a) found in Stage 1 is attributed to the relaxation of the
winter
convergence mechanism.
In this Stage 2, the coastal waters (CU and CR) may extend
further
seaward and
and slope parts of
override the oceanic upper zone in the shelf
the section.
This coastal water
contains a
shallow (10 a) homogeneous upper zone (CU) and a haloclthe (CR)
which extends
in
Plots I
to about 30 a depth.
and II, there may
Thus, as shown by the
structures
exist one halocline (OR) or two halo-
dines (OR and CR) in the slope
part (Fig. 1k a ii and a i), and
one halocline (CU) over the shelf (Fig. 1k b). The coastal
features
22
POSITIONS
2/3260O6E;0
I
0
OH
STAGE 2
MARCH through MAY
I-
0
w
0
0
)
(Thi
/c
SALftflTY
IC,
' ,o.
3%.
34
3%..
39
23
3%.
10_i
50 -
100-
2:
o
t
1OoRE
5/95
)
85/9.5
-:
,-,
80/10.0
0
o
0
1'sTAG2
C)
E
I5O
MARCH through APRIL
0
L.a
_:zo,e.o_
TEMPERATURE
30L
7
$
19C1
(C)
8
rc.
IC-
r.
30-
Figure 13. Model of structure (Fig. 1).
(a) Salinity, Stage 2.
(b) Temperature, Stage 2.
3
23
C;,
C)
0C)
E
I-
a-
w
C)
F]
(a) POSTON I (SLOPE)
T(°C)
8
10
31
C),
C)
33
3.2
;
T(CC) 7
9
SC%o)3
29
9
Q
3
31
C)
8, /959
Lu
C)
)0
(I)
4p.rf/ 8, /959
tp
(1)
e
tj
C)
C)
29
O
9
30
4-
C)
E
I
I-
3-
[gcrci 28, /96/
Lu
ci
(11)
C)
K
r May
/4, /960
(ii) -
(c)POSITiON III (INSHORE)
(b)POSTON II (SHELF)
Figure 14.
Examples of data during Stage 2 (Fig. 13).
214
are superimposed on the oceanic upper zone (CU) water and separate
Because of this and tidal mixing
it from surface wind influence.
with the less saline coastal waters this lower (CU) water loses its
homogeneity (Fig. 114 b i and ii).
Plot III (Fig. 13 a) show8 the low
eurface waters (27 to
salinities in
the inshore
Below this, coastal halocline (CII)
3]. o/oo).
water extends to the bottom. The inflow of brackish
estuarine
(runoff) water maintains the intense shallow halocline (Fig.
2.
114 c).
Temperature
During these months the insolation (Fig.
gradually.
The heating and cooling
14
b) increases
processes are
nearly in
balance
(12, p. 1107) and there is no appreciable change occuring in the
thermal structure.
An example of observed temperature structure is shown in
Fig. 15.
In general the
upper
The model of temperature
is shown in Fig. 13 b
and
waters are isothermal.
distribution and structure (plots)
the structures
observed
in the several
parts of the section are shown in Fig. 114.
In the slope part (Plot I, Fig. 13 b) the isothermal upper
zone reaches
oceanic upper
its
maximum depth (about 75
salinity
zone (OU, Fig.
tures range from 8.5' to 9.5' C.
decreases uniformly
to 7
in) coincident
13 a).
with the
Upper zone
tempera-
Below this the temperature
to 8' C at about 200 in
dthe
It will be noted that the Stage 2 temperature model (Fig. 13 b)
is shorter by one month than the Stage 2 salinity model (Fig. 13 a).
25
NAUTICAL MILES FROM SHORE
40
20
60
=
e
0
SO
/
2 IOC
C
S
2
I-
50
:
N /:..
TEMPERATURE(°C)
MARCH 27-28, 1961
/
250
60
C
NAUTICAL MILES FROM SHORE
40
20
----.:
50
[
:
32q
_3.Q_.
---- .-.--.
.3Z.8
-.
0
:
N.
.: .:N.
/ AJSHOR
--
33.4
.:
I0(
/.: :..
I50[
SAUNITY (%)
/:.
F/
2O
JUNE 9, 1960
Figure 15 (upper).
Examples of temperature, Stage 2.
Figure 16 (lower).
Examples of salinity, Stage 3.
26
It is felt that while the shelf salinity structure
undergoes
marked changes during this period, the temperature
structure remains
quite similar
to
that shown in Stage 1 through April. Apparently,
relative temperature homogeneity
salinity water that flows
Inshore,
seaward
the temperature
is achieved in the head of lower
in this stage (e.g. Fig. 1k a i).
structure is more closely associated
with the salinity structure (Fig. 14 c). Doubtless the stability
inherent in the salinity structure prevents the downward dissipation
of heat
Bence, any temperature increase, slight
conserved in the upper
C.
though
it is, is
10 to 20 m of depth.
Stage 3 (May through July)
During this period the large mainland rivers are in freahet
(Fig. 3 b) due to the melting snow in the mountains. This reaches
the region as an increased outflow of brackish water from Juan de
Puce Strait
(Fig. 1).
A lesser contribution of
runoff comes from
the secondary maximum of local eatuarine outflow (Pig. 3 a), which
is also due to snow storage.
During this period the predominant winds are moderate
from
the
northwest (Fig. 5). Bence the convergence mechanism is fully
relaxed, and some instances of divergence may be expected.
I. Salinity
An example of observed salinity structure is shown in Fig. 16.
Here there is a marked shallow halocline lying horizontally.
Obviously the water above this balocline is coastal water which
27
extends seaward beyond the continental slope. Iidiately below
this shallow balocline to 75 a depth, the isobalines are inclined
downward toward the coast, particularly over the shelf. Below 75 a
depth, in the offshore part the isohalines are inclined upward
toward the continental slope.
The presence of a well defined
brackish
evidence that the estuarine mechanism
upper zone is sufficient
(15, p. 267; 16, p.
52M) is
now an important feature in the behaviour of these coastal waters.
The model of
salinity distribution and structure (plots) are
shown in Fig. 17 a, and the structures observed in the several parts
of the section are shown in Fig. 18.
Coaa ta 1 water (CU and CR) frequently extends seaward of
the
continental slope and occupies most of the depth of the oceanic
upper zone (0U) (Plot I - dashed lines) (Fig. 18 a i).
There is a shallow upper zone (CU) 10 to 20 a deep extending
from the inshore part of the section seaward of the shelf. At any
position it is vertically isobaline (Fig. 18) due to normal wind
mixing, but its salinity increases to seaward, as shown in the
figures, due to entrainment (15, p. 526). The coastal halocline
(CR) is continuous through the three parts of the section. In the
elope and shelf parts
it extends to 30 to kO a depth, and is limited
by salinity 32.2 to 32.6 0/00.
In the slope part of the section
this is underlaid by the remnants of the oceanic upper zone (OU)
which separates the coastal and oceanic haloclines (Fig. 18 ai).
If the coastal water does
not
extend into the oceanic part of
28
PosIT!o:s
1.
CU -20/3/0
20/?22
T/0
5
rn
250/3/0
-1.
1
5O
H
ooL/.'..
°
STACI3
MAY thrcgh JULY
SALNTY (%)
200r
24
(a)
75/85o
/
/4..
200 -
ST3E3
JULY
6.5/Z5
TEMPERATURE (°C)
25O
50
/
(b)
Figure 17.
Model of structure (Fig. 1).
(a) Salinity, Stage 3.
(b) Temperature, Stage 3.
29
T(°C)6 7 8
3
i
a
34
F
I)
:
:
/
L-
\
/
CL
I?
J
\
/
L5L
2 3
U
32
2OC
2cc-
250
JUNE /G:, 150
JULY 23, /958
(a) POSTON I (SLOPE)
T(°C)
sç%3p
9
(9
32
3;(
3
'?
'9
3
'!
0S(%
50
,'AY4,/95O
-
JUNE /6,1950
T(°C)
I':
S('3l
9
(p
32
SJ29
5?
(I)
,I
33
'?
l
34
10
(j)
(2
II
p
3
32
__.r'
( JUNE6,/950
Sc
r
Io0
0
JULY23, /958
(
'
\
)
(b)POSmON II (sHaF)
(C) POSTON
Figure 18.
P1 (NSHOrE')
Examples of data during Stage 3 (Fig. 17).
30
the section (Plot
I) (flg. 18 a ii) then
occupies the upper 50 m of depth.
oceanic upper (OU) water
In any case, below the layer of
oceanic upper zone (OU) water, the oceanic halocline (OH) extends
down to about 150 m depth.
Its lower limit is marked by salinity
33,7-33.9 o/oo. The rise of this oceanic balocline (OH) towards
and onto the shelf is attributed primarily to the entrainnt
mechanism associated with the brackish upper
of moderate
zone.
The condition
winds, predominantly from the northwest, allows the
convergence mechanism to relax, bet may not be sufficient to create
a divergence system.
During this season it is mest probable that coastal (C) rather
than
oceanic (0) water occurs in the upper 40 m over the shelf part
of the section (Fig. 17 a, Plot II). Below this, oceanic halocline
(OH) water extends to the bottom. The lack of residual oceanic
upper zone (017) water between the two haloclines (Plot II, Fig. 17 a,
and Fig. 18 b) indicates that it must have lest its
identity through mixing.
homogeneous
By reason of the overlying coastal water,
the 017 water is no longer influenced by the thorough-mixing effect
of the wind. Hence, a velocity shear between it and the oceanic
halocline (OH) below, is sufficient
to cause mixing and the entrain-
ment upward of Oil water (the necessity for such velocity shear is
discussed by ¶rully, (15, p. 271)).
Hence, the
rise of the oceanic
halocline onto the shelf during this stage is probably
not due to
the divergence process, a mechanism not likely to be effective until
the northwest winds become more prevalent.
There is no reason, of
31
course, why the OU water in the shelf region is not mixed upward
into the coastal halocline water.
Both mechanisms must be expected
to occur, their relative effectiveness being dependent upon the
relative velocity shears involved.
Inshore (Plot III, l?ig. 17 a) the eoaatal upper zone (CU) and
halocline (CID occupy the whole depth.
vident1y the vo1ur
of
estuarine discharge is sufficient to dominate this part of the
section at this time of year.
The haloclina here may be generated
by lateral entrainment (16, p. 526) or from points of local upwelling
in the vicinity (13, p. k03).
In any case, oceanic halocline (011)
water is seldom found inshore during this period.
2.
Temperature
During May through July, insolation (Fig.
maximum in this region.
An isothermal upper
b) and heating are
temperature zone is
formed to the depth of local wind mixing. This depth is limited
by the pycnocline
inherent in the halocline. In this upper zone
the temperature increases progressively.
Hence, the
thermocline
associated with the haloclthe grows Lu magnitude during the period.
temperature of
Below this the
the water is
not affected by local
surface heating.
Examples of observed
Figs. 19 and 20.
coincident with
temperature structure are shown in
Here the temperature structure is
the salinity
distinct and
structure (Fig. 16).
The model of temperature distribution and structure (plots)
is shown in Fig. 17 b and the
structures observed in the several
32
UTICAL MILES FROI CCE
LJ
1
i
-
---
(
-
ICQr
_SdE1..
'
o
..
UflL
i
JUNE
6, 93O
fti
:rcco,i&
rUTC.L. MILES FRO? SIWE
o
(_T,
o
SHELF
2.
TEMPERATURE (DC)
/
JULY 22, 958
10
'.)
Figure 19 (upper). Example of temperature, Stage 3.
Figure 20 (lowar). Example of temperature, Stage 3.
33
parts of the system are shown in Fig. 18.
When oceanic (CU) water is dominant
in the offshore
part of
the region (Fig. 18 a ii) the upper temperature zone is 10 to 20 m
deep and the the rmocline extends to about 60 m depth.
However, if
coastal (CU and CR) waters extend beyond the continental a lope prior
to the development of the temperature structures, these structures
are coincident with the salinity structures (Fig. 18 a i).
In this region at this time there is usually a considerable
temperature gradient in the oceanic halocline (Fig. 18 a) which
constitutes a secondary thermocline (Plot I, Fig. 17 b) between
35 and 75 m depth.
It may be recalled that during Stages 1 and 2 the winter windinduced convergence system was dominant.
system has relaxed.
During this Stage 3, that
Coincidentally, there is a marked decrease in
the eub-thermocline temperatures in the slope part of the region
(Position I) as shown in Fig. 21 a, although there is very little
change in the salinity (Fig. 21 b). This is also shown in the
annual cycles of temperature and salinity in Fig. 22. Evidently
there is a change of water mass. The temperature-salinity relations
at Position I and at two positions to seaward, during Stage 2,
are
shown in Fig. 21 c. The water of a given salinity becomes cooler
to seaward. Also water at a given depth becomes cooler and less
saline to seaward. These features were also noted by Doe (3, p.
10-il). Figure 21 d allows comparison of the temperature-salinity
relations at Position
I during
Stages 2 and 3. These confirm that
3L.
0
STAGE 2
(5p4l 8,1959)
1_'ST(1GE
50
3
(Jane 14,1959)
ETU(C)
i5c-
1
L059
/
(c
2C
ib
TEMPERATURE (CC)
SALJN (TV (%.)
POSITION I (Slope 004 Fig. I)
Sw3rd of
s. I.
2 (Aprtl 8, 1959)
seoword
of Po,.
-
/
\
(i
Li
l.9
119
143
C-)
G7
Li
50
116
Li
Li
I
I.
lx
STAGE 3 (Jone
lOt
\23
175
2(10
70
lx
Li
Li
I
TEMPERATURE-SAL/N
TO SEAWARD
85
TEMPERATURE- SALINITY
STAG'ES 283
STAGE 2
/959
231
APRIL 6-8,
(c)
33
SAUNITY (%.)
Figure 21.
:34
o
246
POSITION!
32
196
(d)
33
SAL(NITY (%.)
34
(a, b) Examples of temperature and salinity structures
at position I (Fig. 1) during Stage 2 and Stage 3.
(c) Temperature-salinity relations during Stage 2 at
position I and at two locations seaward of position I.
These show the water mass differences with distance
seaward.
Depth values are in metres.
(d) Temperature-salinity relations during Stage 2 and
Stage 3 at position I (diagrams a, b).
These show the
water mass change with time.
35
4 JASON D
-T
I
I
I
PO7?! 2
i
- 0rnercs
A-2.3fflfrO$
30'
4..
3
z
-J
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Cu
/.A/'
Oç
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7',
2
32
CL
4
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FI1 A
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STAGE
OL
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"-'...
7 A"..
..'..---
A4"'...
-,A
I-
A)..'
---'
A
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A-75J
A
A
--
5I
4
0
-'',-
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C-.
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A
A A
STLCE
A
M A M 4
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£
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Cd)
U.
100 mct-c3
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___.__. -;--.;...
0
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.0
"'
-----
-'
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.A-.----
A
II,
r
kL
0 4 F M A M 4 4 A $ 0 N D 4
Figure 22.
A
A - 200 ntrcA
A
"'
N.
A.'' A
04 Ft.A PJJ AS ON 04
Temperature and salinity values observed from 1957
through 1961 at position I (see Fig.
1).
36
there baa been a marked change of temperature at this position
during the interval, but little change in salinity.
Comparing the
diagrams 21 c and 21 d it is evident that the water observed at
Position I during Stage 3 is similar to the water found 120 miles
to seaward during Stage 2. ividently this water has moved shore-
ward during the interval. This moven*nt and the associated rise
of the isopleths is believed to be associated with the convergence
"relaxation," and/or the beginning of wind-induced divergence during
this period.
Over the continental shelf (Plot II, Fig. 17 b) the upper zone
and shallow (seasonal) thermocline are coincident with the haline
CR and CU zones (Fig,
18 b).
The
intensity of the pycnocline
inherent in the halocline restricts the downward transfer of heat.
As a result the surface waters are usually warmer in the shelf
in the slope and oceanic parts of the section (Fig. 20).
However,
it appears that as this stage develops, the thermal influence
density becomes greater
than the
than
on
haline influence on density and
dominates the stability of the composite pycnocline. The drop in
temperature values in the zone
below the seasonal
be attributed to surface effects,
hence it
thermocline cannot
must be associated with
the migration of cooler, deeper water onto the shelf. This was
discussed in the preceding section on salinity.
Inshore, the thermal structure is similar to that over the
shelf (Plot III, Fig. 17 b). The therznocline may extend to near
the bottom or it may be more intense in the upper 10-20 m depth
(Fig. 18 c).
37
D.
Stage
ti.
(July through October)
During this period, precipitation (Fig.
14
a), land drainage
from coastal and mainland rivers (Fig. 3), and hence estuarine
discharge are low or minimal. Insolation (Fig.
14
b) wanes and the
rate of heat gain decreases rapidly. During most of the period
the winds are predominantly from the northwest and their strength
is less than the annual average (Fig. 5). They induce a dominant
weak divergence aieclianism.
Localized upwelling oecur (13, p. 1403;
p. 72). In October, at the end of the period the occurrence of
southeast wind increases so that their frequency is about the aan
£4,
as the
1.
northwest winds.
Salinity
Figure 23 shows an example of observed salinity distribution
in the
section. Lack of appreciable dilution from land drainage
and wind-induced offshore transport of surface water (divergence)
result in dissipation of coastal waters, increased salinity in the
upper zone, and weakening of the coastal halocline.
In the oceanic and shelf parts of the region
are inclined
upward toward the coast.
the isohalines
They are inclined downward
in the inshore part. This is attributed to the wind induced
divergence situation over the outer shelf.
The model of salinity
shown in Fig.
the
211.
distribution
and structure (plots) is
and observed structures in the several parts of
section are shown in Fig. 25.
0
60
40
NAUTICAL MILES
FRO1i
-
SHORE
20
0
50
S1UNt t Y ()
I5O ,,,
/
200 -
j<.
,,<'
_-
'7
-,
2O
Figure 23.
/
ooio: 9H0, 1960
/
Example of salinity, Stage
-
LI.
39
-.
I
22
6
cj
POS1TIOt'S
i:i
"
C U
3/O/322
'-2O/32.6
C
'30:VJ/5
-
°
STAGE 4
°
1
jULY throwjh OCTOCER-
a-
o
o
/1
32%.
I
31%,
34
33
SiLI TV%)
4
33
32
30%.
32
33
1
(a)
u
0
____
//O//5O-
l50
-
200
-
JULY throuh OCTOBER
o
65/75
TEMPEATURE(°C)
g'c
0
4
16
6
8
0
2
14'C
8'C
10
(b)
Figure 2'-!..
structure (Fig. 1).
(a) Salinity, Stage 4.
Model o
(b) Temperature, Stage 14.
2
14
Ll.O
'IC)3
I2
2
34
33
5:L
I(cc
J
S%3l
32
33
50-.
-
:c
I
Ii
1L
/
/
230H
OCTOBER 2,
1
/57
250OCTO2ER 9, /960
(iI)
(a)F3STON I (SLOPE)
T(°C) 8
10
S%)3I
32
33
dIlLY !.2. 1957
10C
T°C)
8
0
12
If
'0
i(°C)
34
(I)
14
S(%Y3O
TC)
0
12
14
32
31
33
JULY /2, /957
p
S(%)so
I
I
1
3!
II
32
33
C
TC)
(11)1
0
oCro&R 2, /957
S%c30
p
3!
12
32
( IY
l
33
OCTOBER 2, /957_H
(b)POSITON
(SHELF)
50
r
oc TOL7? 9, /950
(II
(c)POSITION In (INSHORE)
Figure 25.
Examples of data during Stage 4 (Fig. 24).
41
During this period the occurrence of distinctive coastal
The oceanic structure
(CU and CR) water beyond the shelf is rare.
(Plot 1) contains a shallow (20 in) upper zone (OU), a halocltne
extending to about 150 a depth, and a lower zone.
The shallowness of the upper zone (OU) is attributed to the
divergence
situation which dissipates the surface water seaward,
and induces uprising of the deeper watets.
Because the winds are
not steady these conditions are variable.
Their correlation with
the wind cannot be estimated at the present time, because the lag
of the sea after the wind is not known.
Over the continental shelf (Plot II, Fig. 24)
upper zone (CU)
is
about 15 a deep (Fig. 25 b).
the coastal
Below it the
coastal halocline (CR) extends to 20 to 30 a depth.
Oceanic
upper zone (OU) water does not occur over the shelf at this time.
Rather,
the oceanic halocline (OR) exists below the coastal
Frequent by the demarcation becomes indistinct
ha bc line (Cli) war
as indicated by the ranges of salinity values and the structures
(Fig. 25 b). In these cases
the
halocline is
very nearly continuous
through the CR and OH zones (Plot II, Fig. 24 a).
Inshore (Plot III, Fig. 211. a) the upper zone (CU) is about
10 a deep.
Although oceanic haloclina (OR) water may penetrate
this far inshore, below 30 a depth, the general case shows that the
coastal halocline
(CR) La continuous to the bottom, with an in-
tensification in its upper portion.
It is observed
that the isoha lines are inclined downward toward
L2
the shore in
of the
the shelf and
isohalines
inshore parts of the section. The crest
occurs over the outer shelf. It is reasoned that
the upward inclination would be continuous to the surface or the
shore, as they are off the California coast (10, p. 500-2) if part
of the demand for divergence water were
discharge.
not
provided by estuarine
In California there is virtually no land drainage in
summer, end the northwest trade winds blow predominantly.
The
divergence situation becomes fully developed and creates a demand
for replacement water along the coast which can only
be
satisfied
by upwel].ing from the depths (10, p. 725). Northward from the
Columbia River there is considerable estuarine discharge, even
durir this "dry" season. Also the wind directions are variable,
eithough they are predominantly from the northwest.
ilence the
divergence situation is rarely, if ever, fully developed, and part
of the demand for replacement water is met by estuarine discharge.
The crest of the inclined isoha lines marks the division between the
shoreward part of the section where the demand is met by estuarine
discharge, and the seaward part where the major contribution is from
the underlying waters.
2.
Temperature
Figure 26 shows an example of observed temperature distribution
in the section. The surface temperature increases from the shore
to a maximum seaward of the continental slope. The seasonal thermo-
dine is continuous and increases in magnitude to seaward.
Below
this there is considerable temperature structure in which gradient
60
40
NAUTICAL MILES FROM
SHORE
20
()
-
/.
50
100
E
iEMPERATURE(°()
IaJ50
rTr2 o_J
'1
Figure 26.
I%J,
izi'i
4:.
Example of temperature, Stage 4.
and the inclination of the isotherins are coincident with the haline
structure.
The model of temperature distribution and structure (plots) is
shown in Fig.
2L1
b and the observed structures in the several parts
of the section are shown in Fig. 25.
The waters are wartiest (12° to 16° C) in the offshore upper
zone which extends to about 20 m depth (Fig. 23).
In the oceanic
and slope part of the section, the seasonal thermocline occurs in
two segments (Plot I, Fig. 2k; Fig. 25 a). The more intense thermoclj.ne extends to 35
Tfl
about the same as during Stage 3. This shallow
thermocline is not as intense in the shelf region because of the
movement of surface-warmed waters seaward. The deeper thermoeline
is more intense than in Stage 3 due to the divergence mechanism at
the edge of the slope region. Over the shelf, it blends in with
the lower halocline, continuous to the bottom due to the rise of
isotberms up onto the shelf from the sub-thermocline oceanic water
(see Fig. 6 - divergence).
Over the shelf the bottom of the upper thermocline extends to
about 30 m depth early in this Stage (July). Later (October) it
rises to about 20 m depth.
(Compare Figs. 25 b I and b ii). This
rise is believed to indicate an increase of divergence between the
periods of observation.
Inshore, the 11 to 15° C upper zone is about 10 m deep (Fig.
25 c) or non-existent. The thermocline coincides with the halocline
with occasional intensification in the upper 20 at depth (Plot III,
Fig. 214
b).
L5
through December)
. Stage 5 (October
During this period
runoff
from the mainland sources is small
(Fig. 3 b) but the period of increased runoff from local
(Fig. 3 a) is
(Fig. k a).
associated with
estuaries
the maximum coastal precipitation
The winds are predominantly southeast and of moderate
intensity (Fig. 5).
I.
Salinity
Two examples of salinity structure in the section are shom
in Fig. 27 and 28. Ia general the near
to seaward in a
vertically isohaline
is moderate structure.
surface salinity increases
In one set of deta the isohalines are in-
parts of the section.
dined slightly downward to the coast in all
In
the other they are slightly peaked
continental shelf,
Below this there
upper zone.
over the outer
reminiscent of the Stage 4
limit of the
structure, but much
less marked. Evidently the oceanographic ichanism is
between
divergence and
convergence, neither
The model of salinity distribution
shown in Fig. 29
a and some
examples of
alternating
becoming fully developed.
and structure (plots) is
oheerved
structure in
the
several parts of the section are shown in Fig. 30.
During this stage
the oceanic upper zone (01.1) deepens to
40 m (Plot I, Fig. 29 a; Fig. 30 a).
This results in an intensifi-
cation of the top of the oceanic halocline (OH).
to about 180 in due to
the
In the shelf part of
about
Its base descends
advent of convergence.
the region (Plot II, Fig. 29
5; Fig. 30 b)
46
NAUTILAL MLES FROM SHORE
20
40
0
100
E
I
I-
Q 50
w
2m
N.4UTICAL
40
M;LES
20
2
FROM SHORE
-3
0
'-2.Q
/NSH0
100
0
0
IQ.
w
0
___33.9
/
SAUNITY
NOVEMBER 27, 1959
:
2
25cL
I
Figure 27 (upper).
Example of salinity, Stage 5.
Figure 28 (lower).
Example of salinity, Stage 5.
47
POSTONS
STGE5
H
OCTOBER through DECEMBER
E 150;
38/33 9 _2______-_------1:.
D200
0
SALINTY(%)
OL/c1:
250
3%.
3%.
E\\\L±NN
4
3)
2c0-
34
33
31%.
30
3
80-
in
90//tO 0
50
50//tO 0
0
75/5 5-0
00
0
STCE 5
0
gH5O
0
F-
o
a
OCTOBER through DECEMBER-
Ui
-6.5/O- 0
TEMPERATURE (°C)
II
7
8
9
0
8
I,C
9
0
10-
Figure 29. yodel of structure (Fig. 1).
(a) Salinity, Stage 5.
(b) Temperature, Stage 5.
iC
c
o
6
_____.L...i._J._
0
19
_;_J_33
34
'
4
)
L
4;
H
IOC
-
/
c)
I
I
aw
a
//
200
/
230-
230
NOVEMBER 26, /D59
DEC&IISER 5.
/958
()
I,1.
jI 3
a)P3STON I (SLO9E)
19
S1i
tO
32
4
3
41)
.J4.
4-
0 __
50
5C
I-,f
S.°630
NOVEMBER 25. /957
(I)
TC) a
]
S(%0)31
I
t
I
32
.__I_It
315
I
32
_L/.J_i
33
r
NOLIEMBER 25, /957
tC)
I
12
II
31
I s(%,
0
12
Ii
0r2
t
a-
50,
(I)
t:0VE/18ER 2
a
U-i
T(°C)
5C
/959
10
12
/2
2k
ri
IOOj DECEMBER I, /960
(b) POSITIO3 U (SHELF)
OEcE7BER I, /960
(c)?O3I
Figure 30.
C.. )
1?[ CSHOE)
Examples cf data during Stage 5 (Fig. 29).
£19
the coastal upper zone (CU) becomes 20 to 30
It may, or
deep.
m
may no; cover the whole shelf but never extends into the slope part
of the section. It is slightly more saline than in Stage
LI,
probably
due to deeper mixing. The haloc].ine lies between 25 and 35 m depth.
Inehore
(Plot III, Fig. 29 a; Fig. 30 c) the coastal upper
zone (CU) is 10 to 30 in
deep, and below it the halocline (CR) extends
to the bottom.
2.
Temperature
During this period, insolation decreases (Fig.
£1.
b) and cooling
becomes the dominant process in the heat budget. The theriuocline
decays, sinks and is compressed as heat is lost from the sea surface.
Surface waters become colder than the underlying waters, and convec-
tive sinking (and mixing) occur unless prevented by haline stability.
Fig. 31 shows an example of temperature structure in the section
during this stage. There i. a deep upper zone with evidence of
large temperature inversions, a 1 though stability is ma inta med by the
salinity structure. Below this, there is an intense thermocline,
slightly inclined toward the continental shelf.
The model of temperature distribution and structure is shown
in Fig. 29 b and examples of observed structure in the several parts
of the section are shown in Fig. 30.
In the offshore part there is an isothermal zone, coincident
with the salinity upper zone (0(1), to about
110
in
depth.
zone ama 11 temperature inve ra ions near the surface
decaying thermocline extends down to about 75
in
In this
are common.
The
depth. The deepening
N\UTICAL MILES FROM
40
0
20
SHORE
[i
__
50
- -1
c
- -
84
::...
IOO
:
Q)
E
I
ft
0
EMP EAT'JRE (°c)
-
N
S
200-
/
NO\!EMDER 25-26, I57
250
Figure 31.
Exnmple of temperature, Stage 5.
0
5].
of the base of the thermocline, and the slightly warmer temperatures
at 200
rn
compared to Stage 14, signify the relaxation of the summer
divergence condition.
This is confirmed by the rise of temperatures
in the sub-ha iodine water shown in Fig. 22.
Over the shelf (Plot II, Pig. 29 b; Fig. 30 b)
layer may be deeper than the haline upper zone (CU).
the isothermal
This suggests
that the source waters have similar temperatures at thi, time, or
that the surface waters have been cooled to the same temperature as
the waters in the halocline.
A variety of temperature structures way be found next to the
coast.
Depending on the relative influences of wind, surface cooling,
and the temperatures of the estuarine and oceanic waters, the
structure may be negative, is othe rma 1, or pos it ive.
IV.
Summary
It has been shown that the waters over the continental she if
and slope, west of Vancouver Island, contain structural features
which can be related to general meteorological conditione.
On the
basis of seasonal climate, the observed changes in structure have
been used to define five main divisions or stages in the chain of
oceanographic events.
Although it has been shown that short-term
variability La considerable, the large scale characteristics of each
stage are intended to provide a basis for research on a finer scale.
As it stands, the model with ita relatively large, yet definitive,
ranges of values for the basic properties may prove to be of value
52
to workers interested in just such ranges (e.g. fisheries biologists).
It is of interest to note that Pickard has found a relationship
between the maximum densities throughout the near-shore vertical
column (taken
densities
from the ranges given in the model) and the maximum
found in the west coast
of Vancouver Island
inlets (8).
His plot of inlet density maxima versus sill-depth contains values
which are less than or almost equal to the plot
of the maximum
densities versus depth for the coastal
He postulates that
the inlets
serve as a "memory"
region.
of maximum
near-shore
densities and
concludes that the extreme values suggested by the model "-- are
probably typical of long term
conditions."
53
V.
1.
Bibliography
F. 0. The effect of the prevailing winds on the
inshore water masses of the 1ecate Strait region, B. C.
Barber1
Journal of the Fisheries Research Board of Canada lk:9145
952.
1957.
2.
Defant, Albert. Physical oceanography. Vol. 1.
3.
Doe, L. A. E. Offshore waters of the Canadian Pacific coast.
Journal of the Fisheries Research Board of Canada 12:1-341.
Pergamon, 1961.
729 p.
New York,
1955.
14.
Lane, R. K. A review of the temperature and salinity
structures in the approaches to Vancouver Island, British
Columbia. Journal of the Fisheries Research Board of
Canada 19:14591.
1962.
5.
National Research Council of Canada. Climatological atlas
of Canada, prepared by Morley K. Thomas. Ottawa, 1953. 195 p.
6.
Pacific Oceanographic Group. Fisheries Research Board of
Canada. Data records. Nanaimo, 1957-1961. (MS Report Series
(Oceanographic and Limnological) no. 16, 17, 23, 29, 36, '13,
JIB, 52, 541, 58, 63, 67, 68, 70, 76, 82, 83, 8k, 91, 914.).
117,
7.
Pickard, 0. L, and D. C. McLeod. Seasonal variation of the
temperature and salinity of surface waters of the British
Columbia coast. Journal of the Fisheries Research Board of
Canada 10:1251145.
8.
9.
Pickard, 0. L.
1953.
Oceanographic characteristics of inlets of
Vancouver Is land, British Columbia. Journal of the Fisheries
Research Board of Canada (in press).
Swrdrup, H. U.
On
the process of upwelling. Journal of
Marine Research 1:155-1614.
1938.
10.
Sverdrup, H. U., M. W. Johnson, and R. U. Fleming. The
oceans. Englewood Cliffs, N. J., Prentice-Hall, 19142. 1087 p.
11.
Tabata, S. Neat budget of the water in the vicinity of
Triple Island, British Columbia. Journal of the Fisheries
Research Board of Canada
15:1429.451.
1958.
54
12.
Temporal changes of salinity, temperature, and
dissolved oxygen content of the water at Station "P" in the
northeast Pacific Ocean, and sou* of their determining
factors. Journal of the Fisheries Research Board of Canada
Tabata S.
18:10731124.
13.
1961.
Tully J. P. Surface non-tidal currents in the approaches to
Juan de Fuca Strait. Journal of the Fisheries Research Board
of Canada 5:398-409.
114.
Oceanography and prediction of pulpmill pollution in
Alberni Inlet. Bulletin of the Fisheries Research Board of
Canada 83: 169 p.
15.
1942.
1949.
the behavior of fresh water entering the sea.
______.
Notes
16.
______.
On structure, entrainnt, and transport in estuarine
17.
Tully, J. P., and F. G. Barber. An estuarine analogy in the
sub-Arctic Pacific Ocean. Journal of the Fisheries Research
on
In: Proceedings of the Seventh Pacific Science Congress,
Aukland and Christchurch, New Zealand. 1949. Vol. 3.
Wellington, R. E. Owen, 1952. p. 267-289.
embaymenta.
Journal of Marine Research 17:523-535.
Board of Canada 17:91-112.
18.
Waldichuk, N.
1958.
1960.
Physical oceanography of the Strait of Georgia,
British Columbia. Journal of the Fisheries Research Board of
Canada 14:321486. 1957.