Variability of nutrients and carbon dioxide in the Antarctic Intermediate Water between 1990 and 2014 |
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| Authors: | Essowè Panassa J Magdalena Santana-Casiano Melchor González-Dávila Mario Hoppema Steven MAC van Heuven Christoph Völker Dieter Wolf-Gladrow Judith Hauck |
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| Institution: | 1.Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research,Bremerhaven,Germany;2.Instituto de Oceanografía y Cambio Global. Universidad de Las Palmas de Gran Canaria,Las Palmas de Gran Canaria,Spain;3.Royal Netherlands Institute for Sea Research,Den Burg,The Netherlands |
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| Abstract: | Antarctic Intermediate Water (AAIW) formation constitutes an important mechanism for the export of macronutrients out of the Southern Ocean that fuels primary production in low latitudes. We used quality-controlled gridded data from five hydrographic cruises between 1990 and 2014 to examine decadal variability in nutrients and dissolved inorganic carbon (DIC) in the AAIW (neutral density range 27 < γ n <? 27.4) along the Prime Meridian. Significant positive trends were found in DIC (0.70 ± 0.4 μmol kg??1 year??1) and nitrate (0.08 ± 0.06 μ mol kg??1 year??1) along with decreasing trends in temperature (??0.015 ± 0.01°C year??1) and salinity (??0.003 ± 0.002 year??1) in the AAIW. Accompanying this is an increase in apparent oxygen utilization (AOU, 0.16 ± 0.07 μ mol kg??1 year??1). We estimated that 75% of the DIC change has an anthropogenic origin. The remainder of the trends support a scenario of a strengthening of the upper-ocean overturning circulation in the Atlantic sector of the Southern Ocean in response to the positive trend in the Southern Annular Mode. A decrease in net primary productivity (more nutrients unutilized) in the source waters of the AAIW could have contributed as well but cannot fully explain all observed changes. |
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