• The low grazing indices and the high diatom biomass observed in the NAP suggest that the diatom bloom was in a fast sinking process.
• Observations corroborate the concept that highly productive Antarctic coastal marine ecosystems are effective biological carbon pump systems.
• This scenario represents a low energy input from the primary producers to the classic short diatom–krill–whale Antarctic food chain.
Dynamics of an intense diatom bloom in the Northern Antarctic Peninsula, February 2016
Abstract - https://doi.org/10.1002/lno.11437
Diatoms are considered the main base of the Southern Ocean food web as they are responsible for more than 85% of its annual primary production and play a crucial role in the Antarctic trophic structure and in the biogeochemical cycles. Within this context, an intense diatom bloom reaching > 45 mg m−3 of chlorophyll a was registered in the Northern Antarctic Peninsula (NAP) during a late summer study in February 2016. Given that nutrient concentrations and grazing activities were not identified here as limiting factors on the bloom development, the aim of this study was to evaluate the effect of water column structure (stability and upper mixed layer depth) on the phytoplankton biomass and composition in the NAP. The diatom bloom, mainly composed by the large centric Odontella weissflogii (mostly > 70 μm in length), was associated with a local ocean carbon dioxide uptake that reached values greater than −60 mmol m−2 d−1. We hypothesize that the presence of a vertically large water column stability barrier, just below the pycnocline, was the main driver allowing for the development of the intense diatom bloom, particularly in the Gerlache Strait. Contrarily, a shift from diatoms to dinoflagellates (mainly Gymnodiniales < 20 μm) was observed associated with conditions of a highly stable thin layer. The results suggest that a large fraction of this intense diatom bloom is in fast sinking process, associated with low grazing pressure, showing a crucial role of diatoms for the efficiency of the biological carbon pump in this region.
Fig. 1. Study area and stations’ locations during 2016 in the late austral summer cruise. Hydrographic stations positions are marked by circles, squares, and triangles, indicating zones characterized by Gerlache, Bellingshausen, and Bransfield surface waters, respectively. Labeled stations with “x” indicate locations where high-resolution vertical pigments’ profiles are available. The bathymetry is represented by the color scale bar on the right. An inset map in the upper left corner shows a larger area that pinpoints where the main map is located. The abbreviations are as follows: AI, Anvers Island; AP, Antarctic Peninsula; BI, Brabant Island; SSI, South Shetland Islands.