Size Matters: Variation in Phytoplankton Biovolume Observed in Remote Sensing Imagery Across a Putative Nutrient Gradient Nearshore to Offshore of Southern California

Abstract:

Eastern boundary currents are characterized by strong wind-driven upwelling and high nutrient flux to the surface nearshore, and sometimes with weaker wind-curl stress upwelling and lower nutrient flux to the surface offshore. Prior studies have described a nutrient gradient caused between stronger coastal upwelling and weaker, offshore wind-stress upwelling within the California Current System (CCS). This nutrient gradient, in turn, causes a gradient between ecosystem regimes as it relates to phytoplankton community structure. Our study asks following questions: How does phytoplankton biodiversity vary perpendicular to shore, across a nutrient gradient, from a coastal upwelling to a wind-stress curl upwelling region? and how well can remotely sensed images portray this PSC distribution? Using mooring, shipboard (CalCOFI dataset), and satellite remote sensing observations (Aqua-MODIS) we evaluate the mesoscale-submesoscale variability of phytoplankton size class (PSC) distribution along the coast of southern California. The 18 year lifespan of MODIS makes it possible to observe changes in PSC during El Niño, La Niña, and neutral years. A number of different PSC algorithms will be evaluated with MODIS imagery and compared with in situ (CalCOFI) datasets. We anticipate our findings will show matchups between in situ data and remotely sensed data supporting a PSC gradient between onshore and offshore upwelling systems. Given that different phytoplankton size classes support different trophic systems, our results have the potential to support the use of remote sensing observations to project shifts within higher trophic levels.