Taxonomic variability of phytoplankton and relationship with production of CDOM in the polynya of the Amundsen Sea, Antarctica

Abstract

To evaluate the relationship between the phytoplankton composition and the CDOM production in the Amundsen Sea, we examined the taxonomic variability of phytoplankton, nutrients and chromophoric dissolved organic matter (CDOM) participating in two research cruises, ANA02C (February, 2012) and ANA04B (January, 2014). For both cruises, the peak concentrations of chlorophyll a (Chl-α) were measured in the Amundsen Sea Polynya (ASP) where the average Chl-α concentration was 2.31 μg L^-1 ( 71.01 μg L^-1) in February 2012 and 3.92 μg L^-1 ( 73.14 μg L^-1) in January 2014. The major phyto- plankton groups were diatoms and prymnesiophytes, while the minor groups were cryptophytes, chlorophytes, dinophytes, chrysophytes and cyanophytes. The phytoplankton compositions in the sea ice zone (SIZ), the ASP and ice shelf (IS) was distinct. The predominance of <em>Phaeocystis antarctica</em> (<em>P. ant</em>- arctica) (70-90%) was observed at all stations, except in the SIZ in January 2014. While the CDOM concentrations (a355) ranged from 0.07 to 0.98 m^-1 , the average values of a355 of the euphotic layer in the ASP was 0.51 m^-1 ( 7 0.19 m^-1 ), which was much higher than any other region of the Southern Ocean. CDOM showed strong correlation with Chl-a but no relationship with salinity, which implies that bio-logical processes were the main source of CDOM. Among the major phytoplankton taxa, <em>P. antarctica</em> was confirmed as the most important contributor to the production of CDOM, according to the high corre-lation between marker pigment (hex-fuco) and CDOM. The unusually high CDOM in the ASP is expected to give as impact on the environment in various aspects. As a nature of CDOM, absorption of solar radiation at the surface can result in the increase of sea surface temperature (SSTs), which will accelerate the ice melting. Also the photo-oxidation of CDOM can serve as a feedback to increasing atmospheric CO₂ concentrations after peak bloom in austral summer.