Direct observation of increasing CO2 in the Weddell Gyre along the Prime Meridian during 1973-2008

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Van Heuven, S. M. A. C., Hoppema, Mario, Huhn, O., Slagter, H. A., De Baar, H. J. W.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2011
• Subjects: Southern Ocean; Weddell Sea
• Online Access: https://epic.awi.de/id/eprint/21209/; http://www.sciencedirect.com/science/article/pii/S096706451100213X; https://hdl.handle.net/10013/epic.38240

The World Ocean takes up a large portion of the anthropogenic CO2 (Cant) emitted into the atmosphere. Determining the resulting increase in dissolved inorganic carbon (CT, expressed in µmol kg-1) is challenging, particularly in the subsurface and deep Southern Ocean where the time rate of change of CT (in µmol kg−1 decade−1) is often expected to be low. We present a determination of this time trend of CT in a dataset of measurements that spans 35 years, comprising 10 cruises in the 1973-2008 period along the 0º-meridian in the Weddell Gyre. The inclusion of many cruises aims to generate results that are more robust than may be obtained by taking the difference between only one pair of cruises, each of which may suffer from errors in accuracy. To further improve consistency between cruises, data were adjusted in order to obtain time-invariant values of CT (and other relevant parameters) over the 35 years in the least ventilated local water body, this comprising the deeper Warm Deep Water (WDW) and upper Weddell Sea Deep Water (WSDW). It is assumed that this normalization procedure will allow trends in CT in the more intensely ventilated water masses to be more clearly observed. Time trends were determined directly in measurements of CT, and alternatively in back-calculated values of preformed CT (CT0; i.e., the CT of the water at the time that it lost contact with the atmosphere). The determined time trends may be attributed to a combination of natural variability (in hydrography or biogeochemistry) and increased uptake of anthropogenic CO2 from the atmosphere. In order to separate these natural and anthropogenic components, an analysis of the residuals of a multivariate linear regression (MLR), involving the complete time series of all 10 cruises, was additionally performed. This approach is referred to as the Time Series Residuals (TSR) approach. Using the direct method, the time trends of CT in the WSDW are quite small and non-significant at +0.176±0.321 µmol kg−1 decade−1 . On the other hand, the measured ...