Variability of nutrients and carbon dioxide in the Antarctic Intermediate Water between 1990 and 2014

• Published in: Ocean Dynamics
• Main Authors: Panassa, Essowe, Santana-Casiano, J. M., González Dávila, Melchor, Hoppema, Mario, Van Heuven, S. M. A. C., Völker, Christoph, Wolf-Gladrow, Dieter, Hauck, Judith
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: SPRINGER HEIDELBERG 2018
• Subjects: Antarc*; Antarctic; Southern Ocean
• Online Access: https://epic.awi.de/id/eprint/46651/; https://epic.awi.de/id/eprint/46651/1/Panassa2018.pdf; https://hdl.handle.net/10013/epic.a9ae3742-5335-4d9b-bb7a-293eaac95f33

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.