A rapid transition from ice covered CO 2 -rich waters to a biologically mediated CO 2 sink in the eastern Weddell Gyre

• Main Authors: Bakker, D. C. E., Hoppema, M., Schröder, M., Geibert, W., de Baar, H. J. W.
• Other Authors: School of Environmental Sciences Norwich, University of East Anglia Norwich (UEA), Department of Bentho-pelagic processes, Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung = Alfred Wegener Institute for Polar and Marine Research = Institut Alfred-Wegener pour la recherche polaire et marine (AWI), Helmholtz-Gemeinschaft = Helmholtz Association-Helmholtz-Gemeinschaft = Helmholtz Association, Royal Netherlands Institute for Sea Research (NIOZ)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: [PHYS.ASTR.CO]Physics [physics]/Astrophysics [astro-ph]/Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]; [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph]; [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Weddell; Weddell Sea; Sea ice
• Online Access: https://hal.science/hal-00297986; https://hal.science/hal-00297986/document; https://hal.science/hal-00297986/file/bgd-5-1205-2008.pdf

International audience Circumpolar Deep Water (CDW), locally called Warm Deep Water (WDW), enters the Weddell Gyre in the southeast, roughly at 25° E to 30° E. In December~2002 and January 2003} we studied the effect of entrainment of WDW on the fugacity of carbon dioxide (fCO 2 ) and dissolved inorganic carbon (DIC) in Weddell Sea surface waters. Ultimately the fCO 2 difference across the sea surface drives CO 2 air-sea fluxes. Deep CTD sections and surface transects of fCO 2 were made along the Prime Meridian, a northwest-southeast section, and along 17° E to 23° E during cruise ANT XX/2 on FS Polarstern . Upward movement and entrainment of WDW into the winter mixed layer had significantly increased DIC and fCO 2 below the sea ice along 0° W and 17° E to 23° E, notably in the southern Weddell Gyre. Nonetheless, the ice cover largely prevented outgassing of CO 2 to the atmosphere. During and upon melting of the ice, biological activity rapidly reduced surface water fCO 2 by up to 100 ?atm, thus creating a sink for atmospheric CO 2 . Despite the tendency of the surfacing WDW to cause CO 2 supersaturation, the Weddell Gyre may well be a CO 2 sink on an annual basis due to this effective mechanism involving ice cover and ensuing biological fCO 2 reduction. Dissolution of calcium carbonate (CaCO 3 ) in melting sea ice may also play a role in this rapid reduction of surface water fCO 2 . The CO 2 source tendency deriving from the upward movement of "pre-industrial" CDW is declining, as atmospheric CO 2 levels continue to increase, and thus the CO 2 sink of the Weddell Gyre will continue to increase as well (provided the upward movement of WDW does not change significantly).