Abstract
Abstract. The appearance of phytoplankton blooms within sea ice cover is of high importance considering the upper ocean primary production that controls the biological pump, with implications for atmospheric CO2 and global climate. Satellite-derived chlorophyll a concentration showed unprecedented phytoplankton blooms in the Maud Rise polynya, Southern Ocean, with chlorophyll a reaching up to 4.67 mg m−3 during 2017. Multi-satellite data indicated that the bloom appeared for the first time since the entire mission records started in 1978. An Argo float located in the polynya edge provided evidence of bloom conditions in austral spring 2017 (chlorophyll a up to 5.47 mg m−3) compared to the preceding years with prevailing low chlorophyll a. The occurrence of bloom was associated with the supply of nutrients into the upper ocean through Ekman upwelling (driven by wind stress curl and cyclonic ocean eddies) and improved light conditions of up to 61.9 einstein m−2 d−1. The net primary production from the Aqua Moderate Resolution Imaging Spectroradiometer chlorophyll-based algorithm showed that the Maud Rise polynya was as productive as the Antarctic coastal polynyas, with carbon fixation rates reaching up to 415.08 mg C m−2 d−1. The study demonstrates how the phytoplankton in the Southern Ocean (specifically over the shallow bathymetric region) would likely respond in the future under warming climate conditions and continued melting of Antarctic sea ice.
Highlights
Antarctica sea ice moderately increased during the satellite era from 1979 to 2015, with regional heterogeneity that comprises both increasing and decreasing patterns in different sectors (Turner et al, 2017)
A large polynya was formed within the Maud Rise (MR) sea ice cover during September 2017, no phytoplankton bloom is observed in the satellite record
We have shown that the phytoplankton bloom occurred on the MR seamount during the appearance of the polynya in spring 2017
Summary
Antarctica sea ice moderately increased during the satellite era from 1979 to 2015, with regional heterogeneity that comprises both increasing and decreasing patterns in different sectors (Turner et al, 2017). Appearance of the polynyas plays an important role in the oceanic phytoplankton and primary production that control the biological pump of the ocean (Arrigo and Dijken, 2003; Shadwick et al, 2017), as well as being important for marine mammals and birds (Labrousse et al, 2018; Stirling, 1997), global heat and salt fluxes (Tamura et al, 2008), Antarctic bottom water properties (Zanowski et al, 2015), and atmospheric circulation (Weijer et al, 2017). In the background of HNLC, the occurrence of polynyas can enhance the chlorophyll a (chl a) concentration (a proxy for phytoplankton biomass) due to the in-
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