Two Production Stages of Coccolithophores in Winter as Revealed by Sediment Traps in the Northern South China Sea

摘要

Coccolithophores, originating in the Late Triassic, are one of the most successful marine calcifying algae living in modern oceans. Coccoliths are the calcareous fossil remnants left in marine sediments after coccolithophores die. These calcite scales record the conditions of the surface ocean (e.g., primary productivity, seawater temperature, and carbonate chemistry) and are expected to be a promising subject in paleoceanographic and paleoclimatic studies. Hence, a comprehensive understanding of the ecology and phenology of living coccolithophores, as well as their interactions with other plankton groups, is needed to develop better constraints on their uses in paleoenvironmental studies. Here we show modern coccolithophore production through the coccolith fluxes from sediment traps at a ~500-m water depth from 2013 to 2015 in the northern South China Sea. In addition to the expected seasonality of the coccolithophore production that occurs during winter seasons due to the strong water mixing induced by monsoon winds, a two-stage mode for the coccolithophore production is also recognized in relatively "coastal" waters. The first stage includes the production of Gephyrocapsa oceanica in December, when the macronutrient inventory is built, and the second stage describes the growth of Emiliania huxleyi in late February with the depletion of silicate nutrients. This two-stage mode originates from subtle differences in the nutrient assimilation ability between the two species. In addition, coccolithophore production is significantly influenced by the decadal oceanic events (i.e., El Ni?o) in the northern South China Sea.