Seasonal Variations in the Small Phytoplankton Contribution to the Total Primary Production in the Amundsen Sea, Antarctica

Abstract

The importance of small phytoplankton in warming and strati？ed water conditions has beenemphasized, but little information on the small phytoplankton contribution is currently available in theSouthern Ocean. In this study, we analyzed temporal variations in the carbon uptake rates of large and smallphytoplankton and the small phytoplankton contributions to the total primary production. The data werecollected in the Amundsen Sea polynya region using three different ？eld observations (early January,January？February, and February？March) from 2012 to 2016. The total primary production in the polynyaregion decreased from 0.84 ± 0.18 g C·m？2·day？1in early January to 0.19 ± 0.04 g C·m？2·day？1inFebruary？March, which is typical of the seasonal variation in the primary production of phytoplankton inthe Amundsen Sea. In contrast, the small phytoplankton contributions to the total carbon uptake ratesincreased considerably from early January (14.9 ± 8.4%) to February？March (50.8 ± 18.4%) in the polynyaregion. This substantial increase of small phytoplankton contribution was not caused by increasing biomassand the speci？c uptake rates of small phytoplankton, but rather by seasonally declining biomass and thespeci？c uptake rates of large phytoplankton during the study period. The overall contribution (25.5 ± 15.7%)of small phytoplankton to the primary production in the polynya region based on the three different timeobservations is signi？cantly higher than the previous result (14.9 ± 8.4%) based on one time observation.Therefore, a seasonal variation in the small phytoplankton contribution in the Amundsen Sea should beconsidered in further studies.