MARS 511 Lab – Fall 2006
Oceanography of the Southern California Bight using CalCOFI Data
The California Cooperative Oceanic Fisheries Investigations program (CalCOFI) was established to
determine potential oceanographic contributions to the collapse of sardine stocks off the coast of California
during the 1940s. Although CalCOFI was not successful in preventing the demise of the sardine fishery, it was
extremely successful in establishing a comprehensive, long-term data set. An extensive series of oceanographic
and biological sampling cruises have been conducted for over 50 years, and these data now are available on the
CalCOFI website (www.calcofi.org).
The sampling grid (Figure 1) has included stations from the coastline offshore through the California
Current from Washington to the southern tip of Baja California. However, the Southern California Bight (SCB)
has received the most concentrated sampling. The SCB is defined by the California Current on the west and the
coastline of California and Baja California from Pt. Conception in the north to Punta Colnett in the south. We
will examine data from transect line 93 which begins near San Diego and extends west/southwest across the
California Current. A near shore station (93.26) will be compared with an offshore station in the California
Current (93.80) to look for geographic differences in hydrographic parameters, primary productivity, and
macrozooplankton biomass. We will investigate effects of El Niño at these two stations by examining results
from cruises in 1997-1999. A strong El Niño was recorded in early 1998 and followed by La Niña conditions in
1999. For more information on El Niño see www.pmel.noaa.gov/tao/elnino/nino-home.html.
Surface circulation in the SCB is dominated (except in the spring) by a large cyclonic gyre
(counterclockwise flow). This gyre is formed when a portion of the California Current is diverted toward the
coastline and then poleward as the Southern California Countercurrent (figure 2). Generally blocked by the
Channel Islands in the North, the Southern California Countercurrent merges with the California Current. The
California Current is broad and slow moving, and the volume of water it transports varies from year to year in
conjunction with global phenomena such as El Niño. Consequently, the strength of the Countercurrent varies as
well. Flow in the spring is more generally equatorward throughout the SCB. Smaller eddies form frequently in
the SCB and influence local conditions (seis.natsci.csulb.edu/bperry/scbweb/homepage.htm).
The net flow below both the California Current and the Southern California Countercurrent is poleward
and is known as the California Undercurrent. Water properties in the SCB are influenced by the mixture of the
Arctic (cold) California Current and the equatorial (warm) California Undercurrent. The relative influence of
each current varies geographically, seasonally and annually, and has a profound effect on the ecology of the
region.
Topography of the seafloor in the SCB is complex and comprised of an alternating series of deep basins
and ridges or islands (figure 3). Basins are characterized by hypoxic water masses because deep circulation is
blocked or restricted by sills and overlying waters are highly productive, contributing large amounts of detritus.
Decomposition of the detritus that sinks into the basins utilizes the low levels of oxygen provided by the source
waters. Turnover of water in the basins appears to be episodic and not annual, although occasionally rapid
when it occurs. Not only does this seafloor topography create a large diversity of benthic habitats in the SCB,
but it also influences surface water characteristics. Upwelling can be associated with flow near islands or
undersea ridges.
Using Explorer or another browser, go to the CalCOFI website (www.calcofi.org).
You can examine a map of the stations occupied by CalCOFI, read about its history and mission, and
compare the gear used in this program with what you will deploy on the R/V Sproul cruise.
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MARS 511 Lab - Fall 2006
Oceanography of the Southern California Bight using CalCOFI Data
I. Comparison of Onshore and Offshore Stations.
Select the CalCOFI Data tab and click the “Recent Data” label.
Click the “1990 to 1999” link.
From this page you will access hydrographic, primary productivity, and macrozooplankton data.
Additional information about the CalCOFI program can be found under the “Info” tab. Details of the methods
used to collect data and samples are under the “Cruises” tab.
Specific sampling dates are labeled with the year followed by the month (9702 = Feb. 1997). The month
of a specific station may not match the name of the cruise because many cruises began in one month and ended
in another.
Click on “1990s” and select 9702 from “Station Maps”. A map with CalCOFI cruise stations appears (same
as figure 1 in this document). We’re going to compare two sites: 93.80 near the inshore edge of the California
Current and 93.26 near shore.
Click on Station 93.26 on the "Clickable Stations map" for cruise 9702. Hydrographic data from this
station will appear. You can access a smaller set of hydrographic data (covering the euphotic zone) and
corresponding primary production data from the primary productivity link on the ‘Clickable stations map’.
These are the sources for the data provided to you in the accompanying Excel spreadsheet. It may be helpful to
return to the full hydrographic data set to help you interpret differences between the inshore and offshore
stations.
Open the Excel Spreadsheet of CalCOFI homework data. Use data from the Excel spreadsheet to make
depth profiles of Temperature, nitrate, and chl a. Place data from both 93.26 and 93.80 on each depth profile so
you can compare differences between these two sites. Use these depth profiles in addition to other data from
CalCOFI to answer the following questions. These questions don’t need to be answered explicitly; they are
intended to help you understand the data. THE HOMEWORK ASSIGNMENT IS IN SECTION III.
a) How do the depths selected for primary productivity measurements compare to the depth of the total
water column? What is the light level at the greatest depth selected for primary productivity?
b) Compare the mean uptake rate of 14C (mgCm-3 hr-1) at the surface between stations (= Net
Production). To calculate this number divide the mean uptake recorded at each depth by the
incubation time (hr). This allows you to compare the rates from different stations where the
productivity measurements were done for different lengths of time.
c) What is the uptake rate of 14C (mgCm-2 hr-1) integrated across the entire water column? To calculate
this number, divide the integrated uptake by the incubation time (hr). Why is the integrated value
reported as m-2 rather than as m-3 in the individual depth samples? How does this value compare
between the two stations?
d) What is the depth of maximum production at each site?
e) What is the depth of the chl a maximum at each site?
f) How does the position of the chl a maximum compare with the nitracline and pycnocline?
g) Does the depth of maximum production coincide with the depth of the chl a maximum? If not, why
are they different?
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MARS 511 Lab – Fall 2006
Oceanography of the Southern California Bight using CalCOFI Data
II. Effects of El Niño
The temperature effects of the 1998 El Niño were seen most strongly early in 1998. Toward the end of
the year hydrography had started to shift to La Niña conditions. To compare hydrographic and biological
responses to climate change, you will examine data collected in the same locations in January or February 1997,
1998, and 1999. Cruise 9901 covers a time period similar to that covered by the February samples in 9702 and
9802. Station 93.90 was used for Primary Productivity in 1999, so it will be substituted for Station 93.80 for the
offshore interannual comparison.
1. Construct depth profiles for Stations 93.26 and 93.80 (or 93.90) for Temperature, Nitrate, and chl a with all
three years represented on each depth profile. It may be easier to read these figures if 93.26 and 93.80(90) are
graphed separately.
2. Examine biomass of macrozooplankton at stations 93.26 and 93.80 over several years at the same season
(9702, 9802, 9901). Notice that plankton tows at each station were over variable depths and filtered different
volumes of water. Macrozooplankton biomass is expressed in the two far right columns as the volume (cm3) of
zooplankton in 1000 m3 sea water which allows comparison among tows. The 'small' macrozooplankton
sample is the total sample with any individual plankton over 5 ml in size removed (e.g. large jellyfish would be
removed). Your data set includes macrozooplankton biomass for sites of interest.
Make a simple table to compare the biomass among these years. All you need for the table is Cruise, Station,
Time of Day, Total Biomass (total cm3 per 1000m3 strained). The macrozooplankton data already have been
normalized for different volumes of water filtered. Think about the following questions as you look at the
table. THE WRITTEN ASSIGNMENT IS IN SECTION III.
a) Compare the volumes of macrozooplankton at stations 93.28 and 93.80. How does biomass vary at
these locations among years? What factors might explain this variability?
b) How does biomass of macrozooplankton compare to integrated primary productivity at these two
stations? Give a probable explanation for this relationship.
c) Were the samples from the two stations collected over the same depth range? How does the
sampling depth compare to total water column depth?
d) Was the sample taken at night or during the day? How might differences in sampling strategy
influence the results (e.g. time of day or differences in depth of sampling)?
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MARS 511 Lab - Fall 2006
Oceanography of the Southern California Bight using CalCOFI Data
III. Homework Report:
Write a brief paper (3-5 pages) describing major differences between onshore and offshore stations and
interannual variation in productivity. Supply the appropriate figures (not part of the page requirement) to
support your statements. The following are a few questions about some of the major relationships between
hydrographic data and productivity. Exploration of these relationships can provide important points for
discussion in your paper.
1. Comparison of Onshore and Offshore Stations.
What is the relationship of the chl a maximum to the nitracline and pycnocline?
Does the depth of maximum production coincide with the depth of the chl a max? Explain why or why
not.
How do the nitrate, chl a, and primary productivity profiles differ between Stations 93.26 and 93.80?
Explain. Be certain to convert the uptake measurements to uptake hr-1 according to the instructions in
Section I b,c before comparing years or stations.
2. Effects of El Niño
Turn in the answers and appropriate supporting figures to the following questions:
How do temperature and nitrate profiles vary among these years (1997-1999)?
Is the difference among years greater at Station 93.26 (onshore) or 93.80 (offshore)? Explain.
Compare primary productivity and chl a concentrations among these three years. Explain why you see
differences, if they exist. Be certain to convert the uptake measurements to uptake hr-1 according to the
instructions in Section I b,c before comparing years or stations.
How does macrozooplankton biomass vary among these years at the two stations? Does
macrozooplankton biomass appear to be correlated with primary production? Discuss.
Selected References:
Bograd, SJ; Digiacomo, PM; Durazo, R; Hayward, TL; and others. (2000) The state of the California Current,
1999-2000: Forward to a new regime? CalCOFI Reports 41:26-52.
Hayward, TL. (1997) Pacific Ocean climate change: Atmospheric forcing, ocean circulation and ecosystem
response. Trends in Ecology & Evolution 12:150-154.
Hayward, TL. (2000) El Nino 1997-98 in the coastal waters of Southern California: A timeline of events.
CalCOFI Reports 41:98-116.
Hayward, TL; Baumgartner, TR; Checkley, DM; Durazo, R; and others. (1999) The state of the California
Current in 1998-1999: Transition to cool-water conditions. CalCOFI Reports 40:29-62.
Lynn, RJ; Baumgartner, T; Garcia, J; Collins, CA; and others. (1998) The state of the California current, 19971998: Transition to El Nino conditions. CalCOFI Reports 39:25-49.
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MARS 511 Lab – Fall 2006
Oceanography of the Southern California Bight using CalCOFI Data
Figure 1.
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MARS 511 Lab - Fall 2006
Oceanography of the Southern California Bight using CalCOFI Data
Figure 2.
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MARS 511 Lab – Fall 2006
Oceanography of the Southern California Bight using CalCOFI Data
Figure 3.
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