Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf
<p>The Weddell Sea represents a point of origin in the Southern Ocean where globally important water masses form. Biological activities in Weddell Sea surface waters thus affect large-scale ocean biogeochemistry. During January–February 2019, we measured net primary production (NPP), nitrogen...
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| Autores principales: | , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/2b2436c900474c63ac7d41810a8cc7c9 |
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| Sumario: | <p>The Weddell Sea represents a point of origin in the Southern Ocean where
globally important water masses form. Biological activities in Weddell Sea
surface waters thus affect large-scale ocean biogeochemistry. During
January–February 2019, we measured net primary production (NPP), nitrogen
(nitrate, ammonium, urea) uptake, and nitrification in the western Weddell
Sea at the Antarctic Peninsula (AP) and Larsen C Ice Shelf (LCIS), in the
southwestern Weddell Gyre (WG), and at Fimbul Ice Shelf (FIS) in the
south-eastern Weddell Sea. The highest average rates of NPP and greatest
nutrient drawdown occurred at LCIS. Here, the phytoplankton community was
dominated by colonial <i>Phaeocystis antarctica</i>, with diatoms increasing in abundance later in the
season as sea ice melted. At the other stations, NPP was variable, and
diatoms known to enhance carbon export (e.g. <i>Thalassiosira</i> spp.) were dominant. Euphotic
zone nitrification was always below detection, such that nitrate uptake
could be used as a proxy for carbon export potential, which was highest in
absolute terms at LCIS and the AP. Surprisingly, the highest <span class="inline-formula"><i>f</i></span> ratios
occurred near FIS rather than LCIS (average of <span class="inline-formula">0.73±0.09</span> versus <span class="inline-formula">0.47±0.08</span>). We attribute this unexpected result to partial ammonium
inhibition of nitrate uptake at LCIS (where ammonium concentrations were <span class="inline-formula">0.6±0.4</span> <span class="inline-formula">µM</span>, versus <span class="inline-formula">0.05±0.1</span> <span class="inline-formula">µM</span> at FIS), with elevated
ammonium resulting from increased heterotrophy following the accumulation of
nitrate-fuelled phytoplankton biomass in early summer. Across the Weddell
Sea, carbon export appears to be controlled by a combination of physical,
chemical, and biological factors, with the highest potential export flux
occurring at the ice shelves and lowest in the central WG.</p> |
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