A rapid transition from ice covered CO2–rich waters to a biologically mediated CO2 sink in the eastern Weddell Gyre

• Published in: Biogeosciences
• Main Authors: Bakker, D. C. E., Hoppema, M., Schröder, M., Geibert, W., Baar, H. J. W.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Weddell; Weddell Sea; Sea ice
• Online Access: https://doi.org/10.5194/bg-5-1373-2008; https://www.biogeosciences.net/5/1373/2008/

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 air-sea fluxes of CO 2 . 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 μatm, 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 play a minor role in this rapid reduction of surface water fCO 2 .