A ten-year time series from
Monterey Bay, California: Seasonal, interannual and long-term patterns
F. P. Chavez, R. P. Michisaki, G. E. Friederich,
J. T. Pennington, B. Schlining, C. Fayos, P. Walz, C. Sakamoto, R. Hopcroft, R. Kudela, C.
Castro, E. Mauri, and K. R. Buck
Figure 1. An AVHRR image of sea surface temperature (SST) overlaid with
the Monterey Bay coastline and locations of the major stations. This view is
from April 1995 and shows a plume of cold upwelled water (blue and pink regions)
orignating north of Santa Cruz and travelling south across the mouth of Monterey
Bay. Upwelling usually occurs in the spring. Click on the image for an
enlarged view (54k).
The coastal ocean off western North America has received considerable
oceanographic study because of its fisheries and proximity to large human populations. The
oceanography of this region is strongly influenced by the process of coastal upwelling. In
general, coastal upwelling occurs along eastern ocean margins when equatorward winds act
in combination with the Coriolis force to move surface waters offshore, drawing deeper
water to the surface. This upwelled water occurs as a cool band along the
coast, typically 10s of km broad, separated from warmer offshore waters by a
variable series of fronts, plumes and eddies which can extend >100 km offshore.
Upwelled water is nutrient-rich, and supports high levels of phytoplankton and higher
trophic level. In the northeast Pacific, coastal upwelling occurs seasonally.
Monterey Bay, the site of the present study (herein MB), is a deep
(>1000 m), non-estuarine embayment in central California broadly open to the coastal
ocean (Fig. 1). Its oceanography has received considerable study (physical oceanography
reviewed by Breaker and Broenkow, 1994). Skogsberg (1936) and Skogsberg and Phelps (1946)
defined three oceanographic periods still in common use: (1) a spring/summer
upwelling season; (2) a summer/fall oceanic season; and (3) a
winter Davidson Current season, characterized by a low thermal gradient water
column to 100 m. In 1989 the Monterey Bay Aquarium Research Institute (MBARI) began an
intensive study of the coastal upwelling system of central California (Chavez 1996)
incorporating biweekly to monthly ship expeditions together with continuous observations
from strategically placed moored platforms (Chavez et al., 1997). The purpose of
this presentation is to describe the seasonal, interannual and long-term trends in
environmental (winds, currents, temperature, salinity), chemical (nutrients) and
biological (chlorophyll, primary production, phytoplankton taxonomic groups) for MB. In
addition AVHRR and SeaWiFS images are included to provide spatial context.
Aboard our research vessel the R/V Point Lobos, time series measurements have
been collected on a continuing series of twice monthly day cruises since 1989, switching
to monthly cruises in 1994. From 1989 to 1998 a total of 206 cruises have been completed,
collecting samples from over 600 stations. Three major station are routinely
sampled: inshore station C1, mid-bay station H3 (a California Cooperative of Fisheries,
CalCOFI, station) later changed to the Mooring 1 site, and an outer bay station at Mooring
2 (see Figure 1). Several other stations were sampled including minor coastal
station 'H1', outer bay station 'C7', and sections of CalCOFI Line 67. Augmenting this
time series are data from the "Shift-Up", "Coastal Ocean Processes",
"Pegasus", and "Studies of Ecological and Chemical RespoSses to
Environmental Trends" (SECRET) projects, see Table 1 below.
||Number of major station casts
|Monterey Bay Time Series
|Coastal Ocean Processes
Biological, chemical, and physical measurements were collected using a conductivity,
temperature, and depth rosette (CTD), see Table 2. The CTD utilized was either a
Sea-Bird 19 or 911 Plus CTD mounted in a General Oceanics 12 bottle rosette with 5 liter
Niskin bottles fitted with silicon O-rings. Profiling data was collected on the
downcast where conductivity, temperature and depth data were collected at 24 Hz and
processed with modified Sea-Bird software that bins the data to 1 meter intervals.
Additionally the CTD has been outfitted with auxiliary sensors, a downwelling cosine
Photosynthetically Active Radiance (PAR) (Licor QCP 200) and a SeaTech fluorometer and
transmissometer. Water samples were collected on the upcast at the nominal depths of
0m, 5m, 10m, 20m, 40m, 60m, 80m, 100m, 150m and 200m.
|Phytoplankton Protist Carbon (痢 l-1)
||Total Carbon Dioxide
|Chlorophyll (痢 l-1)
|Phaeopigments (痢 l-1)
|Carbon Uptake (mg m-3)
||PAR Cosine (湲 m-2 s-2)
||PAR 4pi (湲 m-2 s-2)
Table 2. Samples collected from shipboard CTD for the time series study.
Next: Methods and Materials
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