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1971

A study of mean monthly thermal conditions and inferred currents in Monterey Bay.

Lammers, Lennis Larry

Monterey, California. Naval Postgraduate School http://ndl.handle.net/10945/15924

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CONDITIONS AND INFERRED CURRENTS

IN MONTEREY BAY

by

Lennis Larry Lammers

Thesis Advisor: DAs, besser

June i971

A STUDY OF MEAN MONTHLY THERMAL

2d for public rnclease; distribution unlimcted. THESIS oii

L2555

T139379

A Study of Mean Monthly Thermal

Conditions and Inferred Currents in Monterey Bay

by

Lennis Larry Lammers Lieutenant Commander, United States Navy B.S., United States Naval Academy, 1960

Submitted in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE IN OCEANOGRAPHY

from the

NAVAL POSTGRADUATE SCHOOL June 1971

Pei FE

WA Y i I !

MONTER:

ABSTRACT

Temperature data, collected over the past 40 years ewas compiled and averaged in the first known study of mean ther- mal conditions throughout the waters of Monterey Bay. The following results were obtained:

(1) The distribution of mean sea surface temperature in the Bay was obtained by calculating mean monthly values at selected grid points and drawing isotherms,

| (2) Progressive warming of the upper 100m was observed to occur in a nearly linear fashion with time, resulting in

a maximum temperature increase of :.8°C over the 29 year

eimcerval from 1931 to 1960. This implies that the in-

molotty OL UPWELLING 1s aiso CoCrcasing 2th camo:

(3) Geographic variations in the rates of upwelling and downwelling, causing a relatively "'warm tongue" along Ge Callyol axis, appeared to be a major element iniluencing the dynamics of the Bay, and

(4) Mean currents were inferred from the copoe eapiies of mean TOR isothermal surfaces. Limited comparisons of mieminterred flow to past measured currents were very el- couraging and tended to support the feasibility of such an inference in the shallow waters and irregular topography of

Monterey Bay.

We

el.

ie.

TABLE SOP MCON GEN TS

INTRODUCTION ------------------------------------ 10 A. THERMAL CONDITIONS IN MONTEREY BAY ---------- 10 B. CURRENTS IN MONTEREY BAY -------------------- 1

dei MPOx t ANCE veie Scie = aos i ae ila:

2. Why Little is Known Concerning Distribu-

tion of Bay Currents -------------------- ll 3. The Feasibility of Approximating Mean Currents by the Geostrophic Approach ---- qa a, Ihe Gtascical Geostropimc i iletiod aa b. Approximations Derived from the CaS Sa Game ME WiNO Ca ae iS Ge OB SECT DV a 14 D. ORGANIZING AND USING THE DATA --------------- 15 VALIDITY OF THE COMPUTED MEAN MONTHLY TEMPERA- TURES MAND SENS TITES)) =o 992-29 = 2922-2 ee i A. TIME RANGE OF DATA ---------------3-- -3----s-- My B. POSITIONING OF STATIONS --------------------- We GC. UsSteor TREE DIFFERENT DATA, COREEGR IO OCS TES IS) 09 = ES 20 DS GEOGRAPHIC DISTRIBUGMRONS OF DAdAy = acre aes Ze THERMAL CONDITIONS ------------------------------ 26 No Isis ANNUAL THERMAL CYCLE IN MONTEREY DAY ees ie lWe anyon REG ON Ss sis Ss Sis a ae ie eee aS do ekheVUpwe Lling Pe riOg! 9 >— >> eee 23 be Thes"Oceanitc Period %--- =>]. aan 24 e. ‘The “"Davadson Current Period: --— 24 2. the Regions of the Shallows)-—_._-_-- 24

THE VARIATIONS IN INTENSITY OF (URWETIN Galea

COMPARISON OF THE ANNUAL THERMAL CYCLE IN THE BAY TO THAT OF AN OFFSHORE LOCATION -----

1. Mixing in the Upper Layers ---=------_-.-. 2. Upwelling ------------------------------- PROGRESSIVE WARMING -------------------------

THE DISTRIBUTION OF MEAN MONTHLY SEA SURFACE VEMPERATURED IN MONTEREY BAY Se ee =e eee

1. Description of Figures ------------------ D>. IDSeSrcueeuiemn c2--0e- 252s Seosceesssesseusees

a. The Annual Cycle of Mean Sea Surface Temperature -------------------------

(1) Upwelling ----------------------

(2) The Variation in Mean Air Tem- De PascU tC ee ee

bh. Horizontal Sea Surface Temperature Gradients ---------------------------

3. Summary ---------------------------------

USE OF ISOTHERMAL SURFACES AS INDICATORS OF MEAN CURRENT -------- ec rrr rcr rr r rrrrrree

POoolieen GEINERALING FORGES goo [a ae

1. Offshore Currents --------------rcrcr cre a. The California Current --------------

b. The Davidson Current ----------------

3. Tides -------------- error rrr re Weep ve ling === 32322-9922

VERIFYING THE CORRELATION BETWEEN ISOTHERMAL AND ISOPYCNAL SURFACES ----------------------

PORTRAYAL OF THE ISOTHERMAL, SURFACES ae

1. Selecting the Isothermal Surface for Portrayal ------------------ rrr rere

Zi

28 28 28 Zo

TN 29 SZ

32

52

yA

53

5S

a

DeSe ripe res of Figures ------------------

D. MEAN CURRENTS INDICATED By [HE TSO LIER Ae SURFACES ---------------- eee oe re ree ee eee

L.

2. Annual Variations of Mean Flow in the Bay ------------ oe --------- ee a. November to February ---------------- b. February to April ------------------- c. August to October ------------------- d. Octobers= 22> 9-2] = eee e. April-to August --------------------- E. COMPARISONS OF INFERRED MEAN CURRENT TO PREVIOUSLY MEASURED CURRENTS ---------------- 1. March ----------------------------------- 2, July ------------------------------------ 3. August ---------------------------------- aneeeie@Kay S 16.6 ok. Modeunenonee --------- b. Stoddard's Drogue Study ------------- 4. September ------------------------------- S. October ----------------->- 1S io eee eee | Gee UNovenber <=-=++2 sees = 222 ee F. SUMMARY -------- cern ccc ccc mr cr rr rrr rrr rere V. CONCLUSIONS AND RECOMMENDATIONS ----------------- A. CONCLUSIONS ----------------c-ccc rrr crc rere B. RECOMMENDATIONS -----------------rcrr rrr clr ree APPENDIX A: Data Sources -------------cccfrrc ct lero APPENDIX B: Computer Dees Mave Ofe Data. =<- 22a APPENDIX C: List of Figures ------------------------->-

Intensities of Mean Flow in the Bay and Offshore --------------------------------

COMPUTER: PROGRAMS 333 = cee ee 127

LIST OF REFERENCES =222—2 22-2 o == a eee 159 INITIAL DISTRIBUTION DIST —-32>42 222 eee 161 FORM DDALAT 3. @ 22-2 Ses Se eee ree ee ee 164

Lisl, OF TABLES

The Range in the Total Number of Temperatures Averaged to Compute the Means for Blocks in the Bay -- c+ -- - eee OS Se = ee aa

Listing of Specific Data Contained on Computer Master Tape, NPS 306 ----------------------------

The Station Title Record -----=<=------2--o2-- =e The Station Data Record. 2 ao sae a aeele Soe ree ere

Definition of Computer Variables in the Final Output of Program Number 11 ---------------------

a0. ee

Zi.

BS

14.

i eae

Gr

ey.

18.

ED SU bor ier

Computer Grid System Used in Monterey Bay -==s2=5 75 The Initial Computer Grid System ---------------- 76 Location of Major Data Sources ------------------ Ta Annual Mean Temperature Cycle by Skogsberg ------ 78 Annual Mean Temperature Cycle by Bolin ---------- 73 Aniicdietean lenperatiune Gy c¢lesBased om CalCOF I

SURV CN Supe P= 8 SI 80 The Progressive Warming of Bay Waters ----~------- 81

Standard Deviation of Temperature for Selected Blocks as a Function of Time -------------------- 82

Standard Deviation of Temperature for Selected

Blocxs as a Function of Depth ------------------- 83 The Annual Mean Temperature Cycle at Block 19 --- 84 The Annual Mean Temperature Cycle at Block 3 ---- 85

Vertical Mean Temperature Sections S-1 and S-2 for the Month of November ----------------------- 86

The Geographic Regions of the Bay (as Defined by Author) -----------------+-+cr er -------- ------------e 87

The Annual Cycles of Mean Sea Surface Temperature Tae very = oma) low ReC1 Ons 0 meene Bi dyiee eee 88

The Annual Mean Temperature Cycles at Blocks 1 and 5 ------- 2-2 enon nn nn ee eee eee- 89

The Annual Cycles of Mean Sea-Surface Tempera- ture in Relatively Deeper Regions of the Shallows ----------------------------------- re 90

The Annual Mean Temperature Cycles at Blocks 2 aime; @ 3966656665665 55 5565 5556556556 65 56555 Sees 91

Typical Annual Mean Temperature Cycles of a Canyon versus an Offshore Station --------------- 92

Dipping of the Isotherms Across the Canyon in : Webel 2 ee SSS = = 5 Sa oe Ss Se SS 8 Ss ee Be ea eee 93

19-30. Distribution of the Mean Monthly Sea Surface

Temperature for January Through December ------- 94 hos oe Intensities of Mean Flow in the Bay and

Offshore ------------e- ere - ree ee ee nner ee 106 SZ. The Annual Mean Density Gyeleswapeocl cee a 107

Blocks ---- rrr rrr err rrr rr rr rr rr re eee ce eee Er - The Annual Mean Temperature Versus Density

Cycles at Block 13 .=3=-~ = -site2 ~-92 ee 108 34-48. Topographies of Selected Mean Isothermal Sur-

faces for January Through December ------------- VOS Sl zs 49. Commari sons soc interred Ciimuents tours et

Measured Currents in August -------------------- 124 50. Comparison of Inferred Currents to Past

Measured Currents in November Using the Plotted

Position of the 12°C Isothermal Surface -------- EZ) Sl. Conpawesen ot InternedsCurreiless eomudse

Measured Currents in November Using a Trans-

fated Position of the 12°C lsothenmalesurtaccm= eee

I. INTRODUCTION

Monterey Bay 1S a large, semi-elliptiecabeindemeaeuen in the California coastline separated into nearly equal halves by a deep submarine canyon ‘Figure 1).! The outer extremity of the Bay may be defined by a line joining Point

Soamtca Cruz to the north and Point Pinos to the sowuen-

A. THERMAL CONDITIONS IN MONTEREY BAY

-everal Studies Mave Deen conducted of Lhermaleonaa. fons a& specific locations in Monterey Bay. The most ex- Bemsive were those by Skogsberg [1936] and Bolin [1964]; both spanning five year periods. Skogsberg studied the memenern portion of the Bay from 1929-1935 and Bolin re- searched conditions at a station in the Monterey Submarine Canyon (see Appendix A). Although these studies well de- fined the thermal conditions for a portion of the Bay, ap- parently no one had investigated the Bay as a whole.

As discussed in Appendix A, the author compiled a considerable amount of temperature (and some salinity) data covering the period of time from Skogsberg's study until the present. As outlined by the author's objectives (Para- graph C), this data was utilized to study mean monthly ther- mal conditions throughout the Bay and to investigate the possible relationship between the thermal conditions and

timerecated mean currents.

1 Pl Ereures will be found in Appendix

10

Ba CURRENTS IN MONTEREY BAY le Lipion Galee

The distribution of current in Monterey Bay is virtually unknown but there is little doubt of its great importance in determining the ecological future of the area. Pollutants, transported by the currents, are scattered freely along the beaches in the form of sewage and general rubbish. Less evident is the adverse effect on marine life Smeated by the discharge of industrial pollutants into the Tie CuULrentES not only distribute “harmful” pol imtameam nue also serve to maintain the chemical and thermal balance

Meeessary tO support marine life.

Ze Why Little is Known Concerning Distribut tommeireeay

Cie mes

The well establisned currents of the open oceans meeetreclatively strong and unchanging with time (e€.¢., the See Streame and the offshore California Current) and hence; mreir general movements are fairly well understood= Monterey imeem oeing enclosed on three sidés, presents a diiferent Situation. The Bay currents are weak and variable and their mean flow is aimost completely disguised by the effects of iveal windss tides, topography, and) seasonal changes in the offshore currents.

Past Current studies in the Bay have beemmered limited nature, both in time and in geographical coverage. They have contributed towards an understanding of ''short term" currents (such as those resulting £xen the tides) but

too few cbservations have peen made to be of much use in

ce

describing the mean flow. In time, and with many addi- tional current observations, a study of the combined ef-

fects could prove to be of great value.

3. The Feasibility of Approximating Mean Currents by the Geostrophic Approach

Indirect approximations of current using the geo- erophic theory may be divided into two categories: mite Classical use of the géostrophic method, and (2) ap- proximations derived from the classical method.

dene Cllasstewe Geostroephice Meriod

Basically, flow obtained by classical applica- Pmionmen the geostrophic method 1s that which results from the balancing of the Coriolis force and the pressure force between two points on a surface of variable elevation, ivewmann and Pierson [19660j| discuss the theory in their nigel entitied, Principles of Physical Oceanography). Com- pecea elevation of the sea surface at a given location in the ocean is represented by a term called the "dynamic height,’’ a relative parameter based on the density of sea water at the location and referred to an assumed level-of- no-motion. A high value of density (usually colder watery Meuetas a lower dynamic height and conversely. By geo- Strophic theory, the circulation in the Northern Hemisphere is counterclockwise about locations of lower dynamic height (depressed surfaces) and clockwise about locations of higher dynamic heights (elevated surfaces). The level-of-no-motion

mothe depth of water (as best can be ascertained) where

eZ

absolute current vellocity equals zéro and Thicwan om eo a. One Ble Gre iels Nese finale I Sion.

Accurate representation of the mean current based on the classical geostrophic method thus requires two prerequisites; (1) a knowledge of mean temperature and salinity (to obtain mean density) of the water column at weveral well spaced locations in the area of interest, sand (2) a level-of-no-motion everywhere shallower than the depth of the bottom (otherwise, there is no reference ex- eam. the bottom itself from which to compute true velocity) . fimealiy, of course, wind driven and tidal currents are Weomected in computing means.

Dew CouOxImaeTonseVUerived fromthe Classica Method

Several approximations to the classical ap- meoach have been used in relatively deep waters with con- Siderable success. Barker and Denham [1970] used the weassical method to plot geopotential topographies (Sur- faces of equal dynamic height) for various levels-of-no- motion off the northeast coast of New Zealand. The close Somnelation between the shapes of the topographies sug- gested that broad current patterns could be approximated without using an accurate level-of-no-motion. Duncan and Nell [1969] demonstrated that isopycnal (equal density) surfaces were closely related to current patterns in their study off the ape Coast. Drift cards were employed ete measure general current trends and were coun to follow the

momycnal contours as predicted by geostrophieytmegy itor

ILS

the Southern Hemisphere. Leipper [19/70] demonsteatedmen a temperature data alone could be used to approximate cur- rent in th® Gulf of Mexico. “Monthly topographwecmoieen 22°C isothermal surface were constructed by him from data eollected on various cruises during the perrod 1965-locGce ihe current was found to closely follow thescontours mean: mm a direction placing colder waters to the left of the flow. These results were verified by geostrophic flows com- puted at various locations in the Gulf. This approach is based on the assumption that temperature changes are di- Rectiy proportional to density changes throughout the water column, and thus isothermal surfaces may be considered in place of isopycnal surfaces.

Application of any of the above approximations to the shallow waters and irregular topography of Monterey may WOuld be a considerable extension of usual practice. However, the theory of geostrophic flow does not depend on the depth of water, therefore, geostrophic methods might be useful in indicating broad current patterns in the shallow meters of the Bay. Considerable temperature data was com- piled for Monterey Bay in this study (see Appendix A). The author used this data to investigate the feasibility of relating mean currents to mean isothermal surfaces in a

manner similar to that of Leipper.

ee OBJECTIVES

The objectives of this study are to:

14

ae i aan

1. Compile” temperature and salinity datammemonpre. mens @ecanographic studies condueted in Monterey Baye

2. Conduct a study of the distribution of mean monthly memperature in Monterey Bay and construct charts of the mean menthly distribution of sea surface temperature,

5. Investigate the feasibility sor anterrence meaneceur- rents from the topographies of mean isothermal surfaces, and A. Prepare a computer program for the continuing

meorage and retrieval of oceanographic data collected in

Monterey Bay.

D. ORGANIZING AND JUSING THE DATA

The IBM 360 computer at the Postgraduate School was used to compile the temperature data and to compute monthly averages (as discussed in Appendix B). A grid system, dividing the Bay into 19 blocks, 4mi by 4mi in dimensions, maeused to segregate the temperature data (Figure 1). The mmenor's initial grid system covered a larger area (Figure 2) memcaining 39 blocks, but only the numbered blocks held Significant data. The mean temperature of a given block, mased on the averaging of all temperatures compiled for that miteek, WaS assumed to be effectively located at its center.

mie temperature data was compiled over the 40 year merervyal from 1929 through 1968. Temperatures collected by feeerecliable methods were combined in the averaging process (although the computer program did allow for data to be

maenieved by type, 1.e., Nansen, XBT, BT).

rS

The risks inherent in the "lumping" together of all types of temperature data spanning a 40 year interval and further reducing data from 4mi by 4mni blocks to represent points in their centers were fully realized. This lumping was essential due to the erratic distribution of data within the Bay and also because no reasonaily short time span held enough data to support this study. The errors introduced

Ib the above procedures are discussed in Chapter II.

16

Hi. VALIDITY OF THE COMPUTED MEAN MONTHIY UEMPERA ies (AND DENSITIES) A discussion of the questions raised in the Introduc- tion involving the method of computing mean monthly temper- atures is considered necessary before an appraisal of the

results (Chapters III and IV) can be made.

A. TIME RANGE OF DATA

Data from three separate time intervals within the previously mentioned 40 year time span was averaged and Compared to determine the degree of consistency of thermal Sonditions relative to the progression of time. Three Bay studies (as referenced in Appendix A) were used: (1)

Wes «ss ae ANAN TNF FN foON N ae Galea in BRugsverg (13929-1533), (2) Bolin (1951-1655)

ee

| tnd > aila mS)

(ae

CalCOFI surveys (1954-1967).*% The time intervals between midpoints (mean years) of the studies were 22 years from skogsberg to Bolin and 7 years from Bolin to CalCOFI, with a total time interval of 29 vears (1931 co 1900)

ice anntal thermal cyclegmot the thinee perweds (Cane ures 4-6) were generally similar in shape with upwelling noticeable from the surface to 500m (as characterized by the humps in the isotherms during the months of April @eeeugh June). A consistent feature over the 29 year in-

terval was the apparent weakening in intensity of upwelling

2

Pie TwOCednoeraphte Staltons: USC Cm Mmuncs Cm cimmaare Suraine enown in Figure 3. Skogsberg's station is denoted by "C", Bolin's by "B" and CalCOFI by a square numbered "5". It is meted that the three stations are contained within a radius fa two mi.

17

with time. The 9°C isotherms from all three studies are plotted in Figure 4 to wdemonstrate sie entre cea oon Served that the depths of the 9°C asothermms were relatively mmose together during the winter momens. | Dunringe=ene re. meaander of the year (especially noticeable in May) the 9°C isotherms were observed to deviate from one ancther. The deviation followed a consistent pattern with the 9°C iso- therm of the earliest study (Skogsberg in 1931) at the shallowest depth and the 9°C isotherms of the later two meudies at greater depths as time progressed. This “£lat- tening out" of the 9°C isotherm with time could indicate a weakening in intensity of upwelling.

A general warming with time was also observed to occur momoughout the waters of the Bay. Figure 6A depicts the Menperature increase (AT) observed to occur over the period from 1931 (Skogsberg's mean) to 1960 (CalCOFI's mean) at memccted depths throughout the year. The curves represent meme variation of AT for each month and for depths from the emrtace to 500m. Figure 6A shows that the maximum tempere- ume increase occurred at depths £rom the surface to 100m fea during the period from October to December. At depths trom 2Z00-500m, AT cycled between positive and negative values throughout the year; however, AT was always positive (temperature increase) in the months of May, June, September, and October.

The consistently positive values of AT in May and June for depths from the surface to 500m might be another indica-

men Chat upwelling was decreasing in intensity (with time)

18

throughout this region, since the warming in May and June mould also indicate a ftlattéming ouWt of thewisothkerms.

The reasons for the maximum temperature increase during the Memths of October to December are unknown. It could be re- Mated to changes in the "Oceanic Period," or possibly, to memocs in the transiftien period between the antluecnce of the California and Davidson current systems.

In sunmary, the general warming of the water column etn time was observed to be consistent in the upper 100m (by the similarity in the shape of the AT curves in Figure 6A at these depths). At depths below 200m, the consistency was not as good (as observed by the AT curves cycling be- Bween positive and negative values); however, the total meamec of AT was only 0.5°C in the deeper waters.

the maximum temperature increase over the 29 year interval was 1.8°C (the 50m curve in November from Figure my resulting in about 1/15th of a degree C increase per year. This small annual temperature change, along with meee general similarity of the curves (as observed in Fig- mimes 4-6) was considered to represent consistent behaviour meen time. Jt was concluded that the author's method of averaging temperature values was jUS tated lias provided

meeragces that were representative of the overall period.

B. POSITIONING OF STATIONS The computer grid system was based on the assumption meat all temperature values found in a given block were lo-

Sacred at its center. The grid system was initially positioned

19

so as to minimize the distance of known oceanographic sta- tions from grid centers. The maximum deviation from such centers was 1.6 mi. Data was assumed to be scattered

memdomly around™the centers of the blocks in the grid sys-

tem.

ie. MWiSE ObevHREE DIEEERENT SDATA TCOREECI ION SYSTEMS

The data was collected by Nansen, BT, and XBT devices. Several papers have been written concerning system errors meemiiar to each. The magnitude of the errors in the BT's and XBT's are apparently undeterminable.

lemrmvesticate “the Sienitrveance Of poss#ple system mors, the standard deviations (oc) of temperature (and density) values were included in the computer output. (X fama) represented the interval containime 672 of all values averaged for a given mean oor

Standard deviations of mean monthly sea surface temper- memre versus time (by months) were plotted for selected mocks. Figure 7 (Block 13) represented the worst condi- tion found. The larger standard deviation at Ju ls was not mepresentative; the consistent features of all graphs were: (1) minimum values of standard deviation for the month of January, and (2) the relatively small variation of the fmerues throughout the year.

Plots of standard deviation versus depth (Figure §8) were = 6 CONnsiSteme.. Values of standard deviation halved

within 30-40m of the surface, reached values of 0.5°C anywhere

from 50-275m and then linearly decreased to minimun valucs of

20

fel-0.2°C an deeper waters. The decredsem@or swandard devia- meron with increasing depth of water and Tis practreal ly invariable value (0.1-0.2°C) below 800m, where the data was Exclusively from Nansen casts, indieéated that seasonal changes were mainly responsible for variations in mean

mmperatures. System errors were thus neglected.

D. GEOGRAPHIC DISTRIBUTION OF DATA

ine 5800 oGeanographic Stations wsed Tnethts crud, m25,100 temperatures) were erratically distributed through- Sethe blocks in the computer grid system (Figure 2). Meecks 1-6, 13, 20, and 21S contained the major portion of me data (10-85 surface temperatures per block per month) and thus were given major consideration in the analysis. The remainder of the blocks contained random amounts of mma, except for Blocks 17 and 19 which generally contained 5-6 values per month each.

micaGily, the Dilgeks containing relatively tew. tcneera- mmmes {less than 10 per month) would yield less reliable averages than blocks with many values. Choosing a minimum mmmer Of temperature values to achieve relatively accurate mean monthly temperatures was based on a study of continuity Metween weak blocks (with less than 10 temperatures per Mmemth at a given depth) and strong blocks (more than 10 tem- peratures).

epayeine Ct MU seemed temper atlt cme, ClLCs ic amemon tilly temperature sections, and standard deviation versus time and depth were drawn for weak Blocks 8, 17, and 19 and for strong BWocks 1-6 and 13. The annual mean temperature cycles of tne

Jad

weak blocks compared closely to those of the strong blocks. This comparison was well represented by Block 19 (Figure 9) and Block 3 (Figure 10).

Further continue. in data, betneen weak sandese won blocks was demonstrated by Figure 11, showing the thermal Seructures of two vertical sections {see Figure 12 for lo- meron of sections), one oriented north to south connecting Bwocks 1, 2, 17, and 5 (S-1) and the other oriented along the Monterey Submarine Canyon axis (S-2) connecting Blocks mee 5, 17, and 19. The isotherms were smooth and continuous meethe upper and lower waters for both sections throughout the year. In depths from 50-100m, the isotherms were smooth and continuous along section S-2. Along section S-1 the iso- mierms were occasionally depressed at Block 17. The depres- eon Of isotherms at Block 17 in section S-1 and lack of depression for the same block in section S-2 will be shown Memee consistent in Chapter III, paragraph B.

Pamally, the standard deviations of mean monthly tem- Mmematures versus time and depth were comparable for all Blocks, weak or strong (Figure 7 and 8 were representative).

The continuity exhibited in the vertical sections be- tween adjacent weak and strong blocks (and within the blocks femeeime progressed) supported the limited use made of the weak blocks for constructing mean monthly isothermal sur- maces in Chapters III and IV. As the isothermal surfaces mee prepared, the weak blocks demonstrated further consis- Bemey of data, especially Blocks 8, 17, and 19. Examples of

mes are noted in Chapter IV.

Zz

III. THERMAL CONDITIONS

A. THE ANNUAL THERMAL CYCLE IN MONTEREY BAY The "S-phase" annuiaigethermal cy cle yoceurr ings es ee me Jocations in Monterey Bay has been described by Skogsberg [1936], Bolin [1964] and others. The following discussion considers the variation in mean thermal conditions relative to various geographic locations throughout the Bay, a sub- fect apparently not previously dealt with. Figure 12 depicts three geographic regions in the Bay Meee the author will refer to in’ this Chapter. The choice of the 50 fathom curve as a dividing line was arbitrary, but gave the desired sectioning. ae une Canvone re Sance=solin descrimped tne thermal conere rons or mee Canyon region a detailed account will not be repeated Mere owever, a briet description of the ‘phases’ will be necessary for later comparisons. ao they Upwelling Pewrod, | Conmoniy "cons dered temepan Lrem mid- anuary to memeenber, the Upwelling Period is characterized by the rising of the deep, colder waters. As found in this study Mmreure 10), the cold waters began their upward movement in mid-January from depths as great as 700m (however, the move- ments were minimal below 300m). The maximum rate of rise occurred between February and March and the peak was found

in April or May when the 11°C water nearly reached the

ZS

Puxrtace. Although upwelling reached its peakwlater at mucater depths, None was obServedearter July.

The descent (downwelling) of the cold waters generally commenced in June and was apparent until late November at greater depths.

pemee the Oceeanne, PC amoac

This#peried is econmenl seonsideredmtemeceur muring September and October and is well defined by the mary vertical temperature gradients at depths from the Surtace to about 100m.

ee.) ine “Davidson Cumment Period”

In November the south-moving California Cur- rent is displaced by the north-moving Davidson Current along mee coast. The influx of warmer waters into the Bay re- meets in a weakening of the vertical temperature gradients ome a resulting well-mixed layer of water from the surface memabout SOm. The northerly flow continues until mid- January when the California Current again predominates and mee’ 5-phase'' annual cycle commences again.

wee thesRegions of the Shallowom see Fipure 12)

The annual thermal cycle in the Shallows was simi- lar to that in the Canyon Region with two noteworthy ex @eptions:

PEnctewenesvely Shallow rep1omns at the extreme northern and southern ends of the Bay possessed unique pomual thermal cycles at depths from the surface to 10m. Referring to Figure 13, the annual cycle of the surface

Bemperature in the Canyon (Block 3) showed a clear decrease

24

in temperature from January until early May and then a steady increase until late September (this was typical for all the deep water areas). The annual cycles of surface temperature for the very shallow waters (Blocks 1 and 5) showed no similar decrease in late winter but rather a mreeady increase from mid-January until late September (Figures 13 and 14). This steady temperature increase, unique for the shallow water regions (less than 75m), was probably due to greater heating of the water column from bottom reflection and the insolation of nearby land masses. mais greater heating of the shallow areas is clearly shown in the distribution of mean monthly sea surface temperatures @s will be discussed in paragraph E (Figures 19-30). The relatively deep regions of the Shallows areas (Blocks 2 and ay) exhibited a very slight amount of cooling from January leer! May, but not nearly as much as did the canyon Region Mec Figures 15 and 16). The second exception is discussed

below.

B THE VARIATIONS IN INTENSITY OF UPWELLING

In studying the various graphs constructed for the mmalysis of thermal conditions, the author came upon a Peature which could be an important element in the dynamics of the Bay in general. Figure 17 is introduced to show the months of the maximum rates of upwelling and downwelling during the eee Ilivsoyete eiloye Oe elie eunugiliZl ences sie levels

Shows maximum rates of upwelling from February to March, and

ZS

maximum rates of downwelling (or heating) from July to Prieust (note the slopes of the 10°C and 11 © iserheris)©

Vertical temperatune, section 5-1 (Seemmieiie sh mo ienis @ strange dipping of the isotherms at Block 17 for all of the above mentioned months (Figure i8 is representative). meock 17 was a weak block (less than 10 temperatures per memth) and thus the dipping was suspected. To attempt to mercy the dipping of isotherms in the Canyon, two addi- Meonal sections were constructed (see Figure 12 for loca- mrons), both running across the Canvon axis (as did section meee Section S-3 connected Blocks 2, 3, and 4, and sec- meron S-4 connected Blocks 2, 3, and 6 (emphasis is placed Saethe fact that sections S-3 and S-4 contained only strong blocks with greater than 20 temperatures per month each).° The results are clearly illustrated in Figure 18 which shows ferked dipping of the isotherms across the Canyon axis in mime sections. This results in a relatively warm tongue mene the Canyon axis for the months of maximum rates of up- welling and downwelling.

The dipping of the isotherms across the Canyon axis Mould have been caused by the up-slope entry of the cold up- Memling waters into the regions of the Shallows. During February and March, when upwelling rates are highest, the

cold waters are ascending from depths down to 300m. As the

Table V lists the number of temperatures compiled for mae Various blocks of the computer grid system.

26

cold, dense water spreads to the Canyon walls, its hori- zontal movement is interrupted, and thus it is accelerated up the walis and into the shallower adj 2cecnt reviuonse Bonversely, in July and August, when downwelling rates are meehest, the cold waters are descending from the near- mmerace regions. Their rates of descent are accelerated mito the Canyon since the deepening topography offers no mesistance to their sinking. The transition period (from April to June) between upwelling and downwelling showed no dipping of isotherms across the Canyon.

No dipping of isotherms was observed along the Canyon mers, this would be as expected since the depth of water feeome the axis (section S-2) was everywhere deeper than 500m mans affording no bottom influence unon the cold upwelling meee rs.

mie annual mean temperature cycles of the relatively deep regions (Figure 16) and the very shallow regions (Fig- Mee 14) of the Shallows further demonstrated the up-slope surge idea. During the months of highest up/downwelling mires, Blocks 2 and 4 (adjacent to the Canyon) exhibited somewhat stronger upwelling (greater slopes of the 10°C amd 11°C isotherms) than did Blocks 1 and 5 which were at the extreme northern and southern ends of the Bay. It thus mepeared that the cold up-surging waters might have lost some of their momentum by the time they reached the very

m@eallow regions of Blocks 1 and 5.

Lg

OF COMPARISON OF THE ANNUAL THERMAL CYCLE IN THE BAY | TO: THAT OF ANSOFP SHORES LOCA LI OM

Block 20, located 2Z2>mi west-soutawes Guo fence a Migure 2) was compared to Block 3 in the Canyon. Figure 17 demonstrated two broad differences between the thermal Sonditions of the two locations.

ioe MixXIne anenevpoen: Layers

The offshore station exhibited generally warmer Surface waters throughout the year and better mixing of the upper waters (0-50m) from January to April. At onset of Mme "Oceanic Period" in September, the offshore and Bay Meations both exhibited maximum vertical temperature gradi- mcs.

At the close of the "Oceanic Period" in November, the Bay station exhibited somewhat better mixing than did Meeeottshore station, maintaining its more uniform surface femeers until January. The weakening of the vertical tem- perature gradients in the Bay (as described by Bolin) was mesumed to be the result of the influx of warm waters Drought into the Bay by the north-flowing Davidson Current Mmring the period of November through January). The more uniform mixing of the Bay waters might have been due to a meeater influence by the Davidson Current nearshore.

2. Upwelling

Upwe Ding 2S=Gonsrdered to Tesult trom Ene nor theniy winds deflecting the surface waters to the right and away mom the coast, allowing the deeper cold waters to rise. The

mieensity of upwelling should then decrease as the distance

Zo

meethe coast increases, Figure 17 demonstuagecamenaueenns was indeed the case, Block 20 showing less intense upwelling

maaan Block 3.

DD, PROGRESSIVE WARMING

Chapter II, paragraph A, contains a discussion of the meogressive warming found for the entire water column in mie bay over the 29 year interval from 1931 to 1960. It em@ould be noted that Bolin [1964] found an opposite indica- mmo Of progressive cooling from 1951-1955. He investigated mre “previous and subsequent" sea surface temperatures taken at selected locations along the west coast of North America mie round that the years of his study were all relatively cool and that 1955 had the minimum temperature in a "long- memm trend." In Chapter II, evidence was presented indica- ting continual progressive warming over the 29 year interval noted above. It thus appears that the cooling observed by Bolin was a short-term cycle. 2 mie DISTRIBUTION OF MEAN MONTHLY SEA SURFACE TEMPERATURE

IN MONTEREY BAY

mecires 19-50 depict the distumeution Of mean mone, Sea surface. temperature in Monterey Bay.

Mec seh ptton Cb Figunes

Mie Sets sowed alUrCOm@conesene ll wumemGeltc ms

Or their respective blocks) served as the points from which Pecherms were drawn. The values of mean monthly tempera- mre are directly below the points. Table I lists the total

mumbecr of temperature measurements per block per month (at

29

mpl I. Ine Range in the Total Number o@ @iempemauumes

Averaged to Compute the Means for Blocks in ie Bay, |

MeOCKk DEPTH RANGE OF TOTAL TEMPERATURES PER MONIR AT 0%q@ SOn nO. (m ) J lp M A M J J A 9 O N D

it 0 65 ~62. 62 65, 64. 615567 65 00) 0 Zee 50 0 0 0 0 0 il 0 0 0 0 it 0

2 0 62 64 64 67 64 61 68 65 61 68 70 67 50 Se 8 ) 8 op) 6 SS thee 6s

3 0 79 79 79 84 77 69 84 81 77 83 94 85 50 MOS 2) Ae BUS 25 eee 2 OR 3p 2G

4 0 om) OS We N22 72 1s Se 1a Se ty 0 50 A) 2 19 es IS AO Os Bie ie 26° 28 Zi

5 0 65 66 67 67 63 60 68 64 63 70 69 68 50.00 == ------- DEPTH OF WATER LESS THAN 50m ---------

6 0 69 60 64 70 66 62 69 65 60 67 70 68

50 s) 6 6 8 6 7 Li 6 2 8 fi

i 0 0 0 0 0 0 il 0 0 5 Z il 0 50 0 0 0 0 0 0 0 0 2 1 1 0 8 0 1 es, 0 dl ee 9 6 5 Z i 8 5 > 0 gly =a 0 9 8 h 5 5 Z 7 8 5 3 0 Loy LANA 25S AIT 2S 22. LI ee Ss eee 50 LL ek. bac 25. Zin eo oe Ze Ze oe ee | ec 16 0 Z 0 0 2 0 4 il 0 oe i) 1 Ih SUE er ae DEPTH OF WAR eos Dn AN SSO > sereaeene ie} 0 4 18 4 4 5 S 5 5 6 5 6 4 50 4 18 4 4 5 5 5 5 6 5 6 4 WO 0 4 4 4 s 4 5 4A 5 4 5 6 4 50 4 4 4 3 4 3 A 5 4 I 6 + 20 0 ES 2 2S hey 8) S > 6 5 5 50 10 3 Z 12 8 ive 5 § 6 5 3 J F M A M J J A S O N D

mere 1: Blocks 9-11, 14, and 18 seldom contained data.

mec 2: Block 20 (see Figure 3) is located 22 mi offshore.

50

the surface and 50m) that were used to compute the mean temperatures. Mean temperatures are not listed (or used) mi the figures if less than four values were available

mer averaging. Dashed lines represent probable extensions me the isotherms.

Tne cirele in the Upper vricht hand cConiensoreceaen mesure displays the local mean wind condition (taken from meme. ©. Naval Oceanographic Office "Pilot Charts,” series H.O. 1401) and the mean offshore currents (taken meom the U. S. Naval Oceanographic Office Publication H.O. 570). The local mean winds are shown as a series of ar- mews (fine lines) that fly with the winds. The lengths of Maye arrows represent the percentages of the month that winds were from the directions shown (the percentage shown for the longest arrow serves as a reference). The number of mms Ol a given arrow defines the wind force by the

meautrort Scale, as shown below:

Number of Tails Mean Wind Force (kt)

0 Le 4-6