The impact of subsurface water from the central Weddell Sea on the global abyssal carbon sequestration

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Hoppema, M. , Fahrbach, E. , Bellerby, R. G. J. and Baar, H. J. W. d. (2004): The impact of subsurface water from the central Weddell Sea on the global abyssal carbon sequestration , EGU 1st General Assembly, 25-30 Apr, Nice, France. .
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We investigated the intermediate water mass of the central Weddell Gyre using TCO2 and oxygen data of FS Polarstern cruises. This water mass, designated as Central Intermediate Water (CIW), is enriched in CO2 and depleted in O2 relative to its source water due to biological degradation. CO2 enrichment and O2 depletion were quantified. The O2 depletion inventory was greater than that of TCO2 enrichment, which is in line with a biological origin of the signal. Because subsurface remineralization in the central Weddell Gyre is restricted to the CIW, the export production estimate from previous work has been applied to compute the renewal time of CIW from these inventories. A renewal time of only three years was found. From renewal time and volume of the CIW, a transport velocity (renewal rate) of 6-7 Sv was obtained. Of this, only 1-2 Sv is upwelled into the surface layer. The remaining 5-6 Sv CIW is exported to the abyssal Antarctic Circumpolar Current to the north. Results of water mass age and transport rate have thus been obtained using a method based on biogeochemical parameters. The mechanism of lateral transport of remineralized carbon from the subsurface Weddell Sea into the abyssal world oceans is presented and its impact is quantified. This shallow, CO2-charged water stands in isopycnal contact with the abyssal world ocean waters to the north of the subpolar Weddell Sea. Via isopycnal water transport, remineralized CO2 is transferred and sequestered in the deep sea. The amount involved is 1.9 1013 g C/yr, which is equal to 6% of the currently estimated world-wide natural CO2 sequestration in the abyssal oceans. It constitutes an important component of the lower limb of the global oceanic carbon cycle and is likely to play a significant role on the glacial-interglacial time scale. During a glacial period, reduced CO2 transport via the CIW would tend to increase the atmospheric partial pressure of CO2 as opposed to the generally decreasing pCO2 trend.

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