Environmental Forcings on the Remotely Sensed Phytoplankton Bloom Phenology in the Central Ross Sea Polynya

We investigated the interannual variability of the phytoplankton bloom in the central Ross Sea Polynya derived from the annual phenology metrics of the bloom based on ocean color satellite measurements obtained between 2002 and 2017. The phenology metrics determined by the adjusted Gaussian fitting method include the bloom amplitude (BA), bloom initiation timing (BIT), and bloom peak timing (BPT). We found the following results for three phenology metrics. The BA tended to increase since 2002, probably related to the formation of open water area by the atmospheric circulation changes on the synoptic scale over the Ross Sea. The significant sea ice loss trend due to the changing winds over the entire southern coast of the Ross Sea was found. Continuous winds in widened open water can move surface water masses more easily along the wind direction, transferring water masses or chlorophyll pigments themselves accordingly. This process has led to the recent intense bloom in the central Ross Sea Polynya. The interannual variability of the BIT is a function of the sea surface temperature in November and wind speed in October, implying that there is a strong association between ice drift and melting, which can be primarily related to the onset of the polynya expansion. Although there was no direct factor to the BPT, it was somewhat related to the BIT and BA. In other words, the environmental factors forming the BIT and BA might have indirectly influenced the BPT, suggesting that early polynya and large biomass could lead to promoting the bloom decay.