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:	R. F. Flynn, T. G. Bornman, J. M. Burger, S. Smith, K. A. M. Spence, S. E. Fawcett
Formato:	article
Lenguaje:	EN
Publicado:	Copernicus Publications 2021
Materias:	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5
Acceso en línea:	https://doaj.org/article/2b2436c900474c63ac7d41810a8cc7c9
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spelling	oai:doaj.org-article:2b2436c900474c63ac7d41810a8cc7c92021-11-24T11:12:27ZSummertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf10.5194/bg-18-6031-20211726-41701726-4189https://doaj.org/article/2b2436c900474c63ac7d41810a8cc7c92021-11-01T00:00:00Zhttps://bg.copernicus.org/articles/18/6031/2021/bg-18-6031-2021.pdfhttps://doaj.org/toc/1726-4170https://doaj.org/toc/1726-4189<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>R. F. FlynnT. G. BornmanT. G. BornmanJ. M. BurgerS. SmithK. A. M. SpenceS. E. FawcettS. E. FawcettCopernicus PublicationsarticleEcologyQH540-549.5LifeQH501-531GeologyQE1-996.5ENBiogeosciences, Vol 18, Pp 6031-6059 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5
spellingShingle	Ecology QH540-549.5 Life QH501-531 Geology QE1-996.5 R. F. Flynn T. G. Bornman T. G. Bornman J. M. Burger S. Smith K. A. M. Spence S. E. Fawcett S. E. Fawcett Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf
description	<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>
format	article
author	R. F. Flynn T. G. Bornman T. G. Bornman J. M. Burger S. Smith K. A. M. Spence S. E. Fawcett S. E. Fawcett
author_facet	R. F. Flynn T. G. Bornman T. G. Bornman J. M. Burger S. Smith K. A. M. Spence S. E. Fawcett S. E. Fawcett
author_sort	R. F. Flynn
title	Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf
title_short	Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf
title_full	Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf
title_fullStr	Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf
title_full_unstemmed	Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf
title_sort	summertime productivity and carbon export potential in the weddell sea, with a focus on the waters adjacent to larsen c ice shelf
publisher	Copernicus Publications
publishDate	2021
url	https://doaj.org/article/2b2436c900474c63ac7d41810a8cc7c9
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Summertime productivity and carbon export potential in the Weddell Sea, with a focus on the waters adjacent to Larsen C Ice Shelf

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