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OC3570 Operational Oceanography & Meteorology

“Interpretation of June 2008 conditions along CalCOFI Line-67 by using Climatology”

LT Dimitrios Alevras Hellenic Navy

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I. Introduction

In the late 1940s following heavy fishing during WW II, sardine landings in CA were

in decline and the California Division of Fish and Game, California Academy of

Sciences, Scripps Institute of Oceanography & U.S. Fish and Wildlife Service joined

forces to develop the California Cooperative Sardine Research Program.

The goal was to understand the physical and biological components of the marine

ecosystem as they affected sardine stocks. Before goal was achieved however, the

sardines vanished.

In 1953 the program was scaled-back and renamed the “California Cooperative

Oceanic Fisheries Investigations” (CalCOFI) program. This program conducts quarterly

survey cruises on a fixed station grid as depicted in Figure (1).

The CalCOFI Line 67 is located within and offshore (SW) of Monterey Bay as

presented in Figure (2). One of these cruises conducted by the R/V POINT SUR during

June of 2008 (22-27) as illustrated in Figure (3).

II. Purpose

The purpose of this project is the interpretation of the June 2008 conditions along

CalCOFI Line-67 by using Climatology.

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III. Procedure

CTD and ADCP data were attained along CalCOFI line 67 aboard the R/V POINT

SUR from June 22-27, 2008. Locations of CTD stations are depicted in Figure (3). Data

were acquired at each station using a Sea-Bird Electronics, Inc. CTD, which provided

continuous measurements of conductivity (which provided salinity), temperature and

pressure. All CTD casts were taken to a pressure of 1000 dbar. The vessel mounted

ADCP measured currents along the ship’s track. The conditions during the cruise are

presented by using:

- Wind field plots,

- T-S diagrams,

- Diagrams of Salinity & Temperature by using Principal Component Analysis

(PCA) (or Proper Orthogonal Decomposition (POD)),

- Geostrophic velocity plots, and

- Plots of Density Anomaly, Temperature, Density and Dissolved Oxygen

Distribution.

All climatology data were provided by the NOAA and the PACific Ocean Observing

System.

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IV. Climate Conditions

The climate conditions that are pertinent to the cruise measurements and the area of

CalCOFI line 67 are the ensuing:

(a) Temperature & Salinity:

The plot of Figure (4) (provided by the Monterey Bay Aquarium Research Institute)

presents the sea surface temperatures (SST) at 1M station (Monterey Bay). It shows that

during last June, SST was one of the colder. Figure (5) (provided by Bill Peterson,

NOAA) presents the SST and salinity averaged from May to September at Newport,

Oregon since CTD data collection began in 1997. Since temperature and salinity through

June 08 averaged 07.31 C and 33.91 respectively, is another evident that last June was

one of the colder than any summer. Figure (6) (provided by NOAA) depicts the SST and

SST anomaly during last June at the area of interest. The explanation for those cold

temperatures could be the strong winds observed in June. Figure (7) (provided by NOAA

Coastwatch) shows strong southeastward winds, especially along the CalCOFI line 67

area.

(b) Upwelling conditions:

The monthly coastal upwelling index (Figure (8) provided by NOAA, NMFS)

demonstrated upwelling favorable conditions during last June. By combining this with

the previous Figure (7) it is obvious that strong southeastward, upwelling favorable, wind

stress occurred along the coast in the area of interest.

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(c) El Nino Southern Oscillation (ENSO):

Figure (9) (provided by NOAA) presents the Upper Ocean Conditions (Ocean Nino

Indexes, the Upper-Ocean Heat Anomalies and the Thermo cline slope indexes) since

1950 as a function of time in the equatorial Pacific. The Oceanic Nino Index (ONI) is

based on SST departures from average in the Nino 3.4 region (Figure (10)) and is a

principal measure for monitoring, assessing and predicting ENSO. The monthly thermo

cline slope index represents the difference in anomalous depth of the 020 C isotherm

between west and east Pacific. By comparing the top two panels we can observe that heat

anomalies are greater (least) prior to and during the early stages of El Nino (La Nina)

episode. Thus by comparing the first and the third panels we can discern that the slope of

the oceanic thermo cline is least (greatest) during El Nino (La Nina) episodes. The

current values of the upper-ocean heat anomalies (slightly positive) and the thermo cline

slope index (near zero) during last June indicate neutral conditions and specific, a

transition from La Nina to El Nino episode.

V. Cruise Results

The wind field diagrams (Figures (11) to (13)) depicts the strong southeastward winds

that took place along the coast in the area of interest during last June.

Figures (14) and (15) presents the first two principal components (PC) for the Salinity

(var: 61.5% ) while Figures (16) and (17) the equivalent for the sea surface temperature

(var: 64.9% ). The divergence of the PC amplitudes from the mean values is consistent

with the fact that last June was one of the colder summer months.

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Figure (18) presents the geostrophic velocity along CalCOFI line 67 as a function of

distance from the coast. Positive values represent equatorward flows while negative

values poleward. Both California Current (CC) and California Undercurrent (CUC) are

evident. The CC is a surface (0-300 m deep) current, which carries colder, fresher

subarctic water equatorward throughout the year with average speeds generally less than

25 cm s-1 (Reid and Schwartzlose, 1962). Thus, the CC is denoted by a low salinity, low

temperature core which usually lies between 300-400 km offshore (Lynn and Simpson,

1987). It is evident from this plot that the location of the CC is closer that normal to the

shore (120 to 140 km). The CUC flows poleward over the continental slope from Baja to

at least 050 N with a relatively narrow width between 10-40 km (Hickey, 1998). The

CUC has its origin in the eastern equatorial Pacific, and is identified by its warm, saline,

oxygen and nutrient-poor signature. Hickey (1979) concluded that the location, strength

and core depth show considerable seasonal variability and can be related to the seasonal

variability in wind stress and curl of the wind stress.

The T-S diagrams of Figures (19) and (20) depicts the cooler, saline, surface water that

is most likely associated with the coastal upwelling, and the equatorward flow of cool,

fresh, arctic water which characterizes the CC. There is a distinct separation between the

two water masses. The cool, fresher waters of the CC can be distinguished from the

warmer, saline waters of the CUC. This separation becomes apparent below ~100 dbar

(or ~100 C).

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Figures (21) and (22) presents the Temperature and Salinity Anomalies plots

respectively. In these plots again are noticeable:

- The cooler, saline surface water of the coastal upwelling

- The equatorward flow of cool, fresh arctic waters (CC) at a distance of 120 to 140

km from the coast

- Well mixing conditions at the surface which are evidence of the strong winds

Figures (23) to (26) present the Density Anomaly, Dissolved Oxygen, Temperature

and Salinity Distribution as a function of distance from the coast and of depth. For better

representation we are focusing at the upper 200 dbars. In these plots the CC, which is

characterized by a low salinity, low temperature core, and the CUC which is identified by

its saline, oxygen-poor signature are evident. The well mixing conditions attributable to

the strong wind stress are also noticeable.

VI. Conclusions

The CTD data and the geostrophic velocity field were in general concurrence. All

cruise data showed that due to the strong winds, we had well mixing conditions and very

cold sea temperatures. The location of the California Current and the California Under

Current was evident at cruise data and specifically the location of the CC was closer to

the coast than normal. All cruise data were in agreement with the upwelling favorable

conditions. With the exception of the cold sea temperatures and the location of the CC,

generally, the cruise data were consistent with the Climate Conditions.

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Figure (1)

Figure (2)

: CalCofi line 67

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11 22334466

8855

77991100 1111

1122

11331144

CCTTDD

Figure (4)

Figure (5)

Figure (3)

: June 2008

: June 2008

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Figure (6)

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Figure (7)

Figure (8)

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Figure (9)

Figure (10)

June 2008

: La Nina : El Nino

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Figure (11)

Figure (12) Figure (13)

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Distance from H3, km

Pre

ssur

e, d

bar

Zscore of T90 Mode 2, %var= 14.3

-150 -100 -50 0-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

1998 2000 2002 2004 2006 2008

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

PC

am

plitu

de

timeDistance from H3, km

Pre

ssur

e, d

bar

Zscore of T90 Mode 1, %var= 50.6

-150 -100 -50 0-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

-5

-4

-3

-2

-1

0

1998 2000 2002 2004 2006 2008

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

PC

am

plitu

de

time

Distance from H3, km

Pre

ssur

e, d

bar

Zscore of Salinity Mode 2, %var= 20.4

-150 -100 -50 0-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

-0.6

-0.4

-0.2

0

0.2

0.4

1998 2000 2002 2004 2006 2008

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

PC

am

plitu

de

timeDistance from H3, km

Pre

ssur

e, d

bar

Zscore of Salinity Mode 1, %var= 41.8

-150 -100 -50 0-1000

-900

-800

-700

-600

-500

-400

-300

-200

-100

0

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

1998 2000 2002 2004 2006 2008

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

PC

am

plitu

de

time

Figure (14) Figure (15)

Figure (16) Figure (17)

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Figure (18)

Figure (19) Figure (20)

CC

CUC

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Figure (21) Figure (22)

CUC

CC

Well mixing conditions

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Figure (23) Figure (24)

Figure (25) Figure (26)

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VII. References

- Collins, C.A., R.G. Paquette and S.R. Ramp, 1996b. Annual Variability of ocean

currents at 350 m depth over the continental slope off Point Sur, California. CalCOFI

rep., 37, 257-263.

- Hickey, B., .Coastal Oceanography of Western North America from the Tip of Baja

California to Vancouver Island; Coastal Segment. in The Sea, Robinson, A.R., and

Brink, K. H., pp 12,947-12,966, 1998.

- Graphs of Upwelling Indices over the last 18 months (http://www.pfel.noaa.gov/

products/PFEL/modeled/indices/upwelling/NA/daily_upwell_graphs.html)

- Lynn, R.J., and J.J. Simpson, 1987. The California Current System: The seasonal

variability of its physical characteristics, J. Geophys. Res., 92, 12,947-12,966

- Neander D.O. (LCDR, NOAA), 2001The California Current System: Comparison of

Geostrophic Currents, ADCP Currents and Satellite Altimetry

- Pacific Coast Ocean Observing System,2008/Climatic and Ecological Conditions in the

California Current LME for April to June 2008 /

(http://pacoos.org/QuarterlyUpdate_Climatic/AprMayJun08.pdf)

- Pennington J.T., Michisaki R., Johnston D., Chavez F.P., Ocean observing in the

Monterey Bay National Marine Sanctuary: CalCOFI and the MBARI time series

A Report to the Sanctuary Integrated Monitoring Network (SIMoN), March 7, 2007

- Pickard, G.L., and W.J. Emery, 1982. Descriptive Physical Oceanography; An

Introduction, 5th Ed., pp 64-65, Butterworth/Heinemann.