Estimating the storage of anthropogenic carbon in the subtropical Indian Ocean: a comparison of five different approaches

Type Article
Date 2009-04-27
Language English
Author(s) Alvarez M.1, Lo Monaco C.2, Tanhua T.3, Yool A.4, Oschlies A.3, Bullister J. L.5, Goyet C.6, Metzl N.2, Touratier F.6, McDonagh E.4, Bryden H. L.4
Affiliation(s) 1 : CSIC UIB, IMEDEA, Esporles 07190, Spain.
2 : Univ Paris 06, LOCEA IPSL, F-75252 Paris, France.
3 : IFM GEOMAR, D-24105 Kiel, Germany.
4 : NOCS, Southampton SO14 3ZH, Hants, England.
5 : NOAA, Pacific Marine Environm Lab, Seattle, WA 98115 USA.
6 : Univ Perpignan, IMAGES, F-66860 Perpignan, France.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2009-04-27 , Vol. 6 , N. 4 , P. 681-703
DOI 10.5194/bg-6-681-2009
WOS© Times Cited 34
Abstract The subtropical Indian Ocean along 32 degrees S was for the first time simultaneously sampled in 2002 for inorganic carbon and transient tracers. The vertical distribution and inventory of anthropogenic carbon (CANT) from five different methods: four data-base methods (Delta C*, TrOCA, TTD and IPSL) and a simulation from the OCCAM model are compared and discussed along with the observed CFC-12 and CCl4 distributions. In the surface layer, where carbon-based methods are uncertain, TTD and OCCAM yield the same result (7 +/- 0.2 molC m(-2)), helping to specify the surface CANT inventory. Below the mixed-layer, the comparison suggests that CANT penetrates deeper and more uniformly into the Antarctic Intermediate Water layer limit than estimated from the much utilized Delta C* method. Significant CFC-12 and CCl4 values are detected in bottom waters, associated with Antarctic Bottom Water. In this layer, except for Delta C* and OCCAM, the other methods detect significant CANT values. Consequently, the lowest inventory is calculated using the Delta C* method (24 +/- 2 molC m(-2)) or OCCAM (24.4 +/- 2.8 molC m(-2)) while TrOCA, TTD, and IPSL lead to higher inventories (28.1 +/- 2.2, 28.9 +/- 2.3 and 30.8 +/- 2.5 molC m(-2) respectively). Overall and despite the uncertainties each method is evaluated using its relationship with tracers and the knowledge about water masses in the subtropical Indian Ocean. Along 32 degrees S our best estimate for the mean CANT specific inventory is 28 +/- 2 molC m(-2). Comparison exercises for data-based CANT methods along with time-series or repeat sections analysis should help to identify strengths and caveats in the CANT methods and to better constrain model simulations.
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Alvarez M., Lo Monaco C., Tanhua T., Yool A., Oschlies A., Bullister J. L., Goyet C., Metzl N., Touratier F., McDonagh E., Bryden H. L. (2009). Estimating the storage of anthropogenic carbon in the subtropical Indian Ocean: a comparison of five different approaches. Biogeosciences, 6(4), 681-703. Publisher's official version : https://doi.org/10.5194/bg-6-681-2009 , Open Access version : https://archimer.ifremer.fr/doc/00218/32916/