What factors determine the temporal long-term changes in pigment-based coccolithophores in the North Pacific subtropical gyre?

Coccolithophores, ocean’s dominant calcifying phytoplankton, are known to be vulnerable to ocean acidification, resulting from increased uptake of anthropogenic carbon in the upper ocean. Recently, some studies reported a basin-scale long-term increase in coccolithophore abundance with positive correlation to increased carbon contents in the upper mixed layer of North Atlantic subtropical gyre. This result is generally contrast to the present knowledge. However, a research question on how the North Pacific subtropical gyre (NPSG) has responded to the condition has not yet been investigated. Here, using Hawaii Ocean Time-series monthly dataset observed at Station ALOHA (22°45’N, 158°W) for the periods of 1988−2017, we (1) present temporal long-term trend of pigment-based coccolithophore abundance (i.e., 19’hexanoyloxyfucoxanthin pigment concentrations; hereafter 19’-hex), (2) investigate the environmental variables (physical-biogeochemical-climate) governing the temporal trend of 19’-hex in the NPSG, and (3) discuss mechanisms driving the difference between two basins.