Spatial and Temporal Variability of Coccolithophore Blooms in the Eastern Bering Sea

Abstract

Coccolithophores are a widespread group of marine phytoplankton that produce plates of calcium carbonate that cover their cells. Large blooms of coccolithophores may significantly influence the biogeochemical properties of the ocean and atmosphere and trophic dynamics of the marine ecosystem. Because of the important implications of coccolithophore blooms, their timely monitoring and reporting is necessary for ecosystem management. To communicate with ecosystem management stakeholders, we developed an annual Coccolithophore Bloom Index (CBI) for the eastern Bering Sea shelf using satellite ocean color data. Comparisons between in situ and satellite data and the CBI (years 1997–2017) were used to examine the hypotheses regarding environmental influences on interannual bloom variability. A significant nonlinear relationship with summer stratification was found: the CBI was higher during years with either very low or very high stratification. In addition, while the blooms usually occurred over the middle shelf (50- to 100-m depth), more of the bloom was located over the shallow (30–50 m) inner shelf when stratification was low. Spatial correspondence between nutrient concentrations (nitrate and ammonium) and the areal extent of the coccolithophore bloom provides tantalizing but nonconclusive evidence that nutrient availability plays a role in bloom formation and location.