Phenological pattern of coccolithophore blooms in global shelf regions

Coccolithophores are one of the most abundant and widely distributed phytoplankton in the ocean. Their coccoliths production is not only a dominant source of biogenic CaCO₃, but also bestow coccolithophores distinguishable optical properties. Thus, coccolithophore blooms can be detected in most water conditions by spaceborne sensors. The role of such blooms has been proved to be significant in estimation of CaCO₃ budget, shifts of the air-ocean CO₂ balance and paths of carbon export. Most coccolithophore blooms has been observed along shelf regions while shows an obvious seasonal pattern. To quantify this seasonal variability, particulate inorganic carbon and chlorophyll data are usually considered to indicate coccolithophores’ dynamic. However, current methods are limited to retrieve calcite concentration in low level and can fail under turbid hydrological water conditions, particularly in shelf seas. It’s partly attributed to a sequential succession of blooms of other phytoplankton community and suspension of sediment from sea floor and river discharge. In this study, calcite concentration is used as an indication of coccolithophores’ biomass production. As one key point to study phenology is determining the onset and end time points of blooms, an optical model is proposed to separate coccolithophore calcite from other particulate matters. Through tracking the change of calcite concentration, the whole process of blooms including formation, developing and fading is described. By calculating the average phenological parameters of coccolithophore blooms during decades, it can provide valuable insight of the marine phytoplankton community response to climate change.