Cross Shelf Processes
Oceanographic Transport and Cross Shelf Processes
To determine how oceanographic processes influence material transport to and from the kelp forest ecosystem, we conducted seasonal channel-wide cruises that surveyed hydrographic and biological parameters between 2000 and 2006. During each cruise, an undulating towed vehicle called a Scanfish was deployed to obtain high resolution, two-dimensional maps of temperature, salinity, beam attenuation at 660 nm (a measure of water turbidity), and chlorophyll from the surface to ~ 100 meters depth. A set of cross-channel transects of CTD (conductivity, temperature and depth) surveys along the Scanfish tracks provided vertical profiles of the same water properties measured by the Scanfish, but from the surface to the sea floor. Additional parameters such as nutrient and particle concentrations were derived from bottle samples obtained during the CTD surveys. Depth profiles of primary production were also measured to assess the magnitudes of phytoplankton and macrophyte production. Other instruments attached to the CTD measured optical properties used to characterize the particle fields and dissolved components of the water column. Spatial variation in currents was measured continuously during the cruises with a ship-board ADCP. The data from these cruises provides a valuable measure of the "background state" of the Channel with respect to seawater temperature, salinity, nutrient concentration, phytoplankton biomass, and primary productivity. Characterizing the seasonal patterns in these properties, as well as changes at shorter time scales will help us to assess the role of "open channel" nutrient delivery to kelp forest reefs, and to adequately compare it to nutrient subsidies from terrestrial sources.
Analyses of data from the sixteen SBC-LTER cruises is a major focus of current research designed to improve our understanding of oceanic and cross-shelf processes that transport materials to and from kelp forests in the Santa Barbara Channel. We are using data analysis procedures to visualize and quantify sub-surface property distributions obtained from the extensive suite of shipboard, moored, and land-based instrumentation. Particular attention is being given to processing acoustic Doppler current profiler (ADCP) data, which are critical for understanding the role of ocean currents in structuring density, nutrient, and phytoplankton distributions offshore of the kelp forests. We are also making substantial progress in interpreting patterns of phytoplankton primary productivity obtained during the cruises.