Our working group consists mainly of phytoplankton ecologists who wish to understand the fundamental question: what controls phytoplankton growth and distribution in the ocean? More specifically, how do the multiple interactions of light, macro- and micronutrients and phytoplankton physiology determine the rates, processes, and patterns we observe in the marine environment? Oceanography is rapidly moving away from observational science towards an understanding of underlying mechanistic processes at all scales, in part because of the wealth of revolutionary new technological and scientific advances such as ocean color from satellite sensors (Figure 1). Our approach is to combine a suite of 3 tools: (1) remotely sensed data from moorings and satellites in combination with biological models; (2) novel bio-optical methods assaying phytoplankton physiology; and (3) the refinement of stable and radio-tracer isotopes. By integrating these methods, we can begin to use ocean color to answer important ecological questions.

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Figure 2: Phytoplankton - Coccolithophorids

Data from several Earth observing satellite-based sensors aid researchers in their study of ocean productivity, color, and conditions. These include the Sea viewing Wide Field of view Sensor (SeaWiFs), the Moderate-resolution Imaging Spectroradiometer (MODIS), and the Advanced Very High Resolution Radiometer (AVHRR). While SeaWiFs and MODIS deliver scientists spectacular imagery and data of ocean pigments, the AVHRR sensor provides measurements of ocean meteorological conditions such as sea surface temperature (SST). SST helps researchers monitor ocean water conditions at varying levels of phytoplankton productivity throughout the year. (top)

Phytoplankton Ecology

The name "Phytoplankton", refers to the group of microscopic plants that float with ocean currents in the photic zone, the upper layer of the ocean in which light penetrates allowing photosynthesis to occur. Phytoplankton levels in the ocean vary with the supply of nutrients at any given time, and experience rapid blooms of productivity during periods of upwelling of oceanic deepwater. These upwelling periods are vertical movements of water that create a stirring action, delivering nutrients to the surface mixed layer and regulating water temperature. Upwelling in the coastal region is driven by Ekman transport, a circulatory action in which surface waters move perpendicular to the dominant wind direction. In the case of Northern Hemisphere waters off the coast of California, coastal surface waters are moved offshore (upwelling) by the dominant North-westerly winds. Upwelling waters are rich in nutrients derived from decomposing organic matter and compounds exchanged in the atmospheric-oceanic boundary layer that has settled into the deeper waters.

Nutrients that control the intensity of Phytoplankton blooms are primarily composed of carbon in the form of dissolved inorganic carbon (as HCO3). Other nutrients such as nitrogen (N), usually in the form of nitrate (NO3) or Ammonia (NH4, and phosphorus as phosphate (PO4). P and N are typically referred to as "limiting nutrients" as their availability in minimal amounts will be the first nutrients to cause a limitation in productivity. The supply of phosphorus to waters in the productive zone is approximately a tenth of the amount of carbon, some of which is from atmospheric inputs, but most carbon is already present in seawater. P and N supplies increase or decrease in concentration as upwelling strength fluctuates. The most common species of phytoplankton indigenous to productive coastal waters waters of California are Coccolithophorids (Fig. 2), small platy organisms composed of calcium carbonate.
References 1, 2
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Research Projects

There are a number of current projects focusing on the study of biological productivity of phytoplankton in the coastal regions of Central and Northern California. Brief descriptions of the projects follow:

• ECOHAB: Within the Monterey Bay region, there are several funded groups working closely together on the Pseudo-nitzschia/domoic acid complex. We (myself and William Cochlan, SFSU) are funded to develop in the field and laboratory an understanding of how Si, N, C, and light interact physiologically to trigger DA production. Colleagues at MBARI (C. Scholin), UCSC (D. Garrison, M. Silver, J. Goldman, E. Rue), U. Maine (M. Wells), and MLML (G.J. Smith) are working on related aspects, ranging from the role of metal availability, including iron, to the transfer of toxin through the marine food web. Some preliminary data from our collaborators at MBARI can be found here.

• NASA projects: A physiological model of nitrogen utilization by natural phytoplankton assemblages which can predict new production in coastal waters using remotely sensed data (AVHRR and ocean color data) or moorings is being developed as part of NASA grant NAG5-6563. As part of the EPA funded Coastal Intensive Sites Network (CISNet; NASA grant NAG5-7632), we are also developing regional algorithms (pigments, CDOM, sediments, new production) along a gradient of water conditions, from the blue-water stations occupied off central California to the turbid waters of San Pablo Bay. Remote sensing and bio-optical data for this project are located here.

• CoOP: As part of an NSF-sponsored Coastal Ocean Projects program (CoOP), we have just begun a 5-year study of coastal productivity (The Role of Wind Driven Transport in Shelf Productivity, or WEST). We have proposed to study the 3-dimensional wind-driven circulation of water concurrently with size-structured distributions of phytoplankton and zooplankton species in this multi-institution, multi-investigator program. Further, we proposed to study the key physical and biological processes that control primary production, zooplankton population responses, and offshore transport of plankton and nutrients over the strongly wind-driven shelf and slope off Bodega Bay. This program has 3 field years, with a combination of instrumented moorings and cruises, followed by two years of data assimilation and development of a coupled physical-biological model. We are responsible for the bio-optical component and shipboard process studies, and is developing regional algorithms for new and primary production. Remote sensing and bio-optical data for this project are located here.

• A partnership with the California Coastal Ocean Observing System (CalCOOS) is also in progress. CalCOOS is a multi-institution research group dedicated to resource observation and support of resource management and emergency response. The group has a dedicated focus on the complex biological processes and meteorological conditions that affect the California coastal region.
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