Variability in diatom contributions to biomass, organic matter production and export across a frontal gradient in the California Current Ecosystem

© 2015. American Geophysical Union. All Rights Reserved. In the offshore waters of Southern California, submesoscale processes associated with fronts may stimulate phytoplankton blooms and lead to biomass shifts at multiple trophic levels. Here we report the results of a study on the cycling of biogenic silica (bSiO 2 ) with estimates of the contributions of diatoms to primary and new production in water masses adjacent to (i.e., coastal or oceanic) and within an offshore front in the Southern California Current Ecosystem (CCE). The coastal and oceanic water were sampled in cyclonic and anticyclonic e ddies, respectively, with the frontal water being an interaction region between the eddy types. Concentrations of bSiO 2 varied by 25-fold across the front, with concentrations in frontal waters 20-25% of those in coastal waters. Rates of biogenic silica production spanned an equally large range, with rates within the frontal region that were half those in the coastal regions. Contributions of diatoms to primary and new production were disproportionately higher than their contribution to autotrophic biomass in all areas, ranging from 5-8%, 19-30%, and 32-43% for both processes in the oceanic, frontal and coastal waters, respectively. Across the frontal area, diatoms could account for < 1.0%, 6-8%, and 44-72% of organic matter export in the oceanic, frontal and coastal waters, respectively. The results suggest that the regions of frontal interactions between eddies in the southern CCE can account for variability in diatom biomass, productivity and export over very short spatial scales that is comparable to the variability observed across the Pacific basin