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. Antarctic Bottom Water (AABW) is known as a long-term sink for anthropogenicCO 2 ( Cant ), but the sink is hardly quantified because of thescarcity of observations, specifically at an interannual scale. Wepresent in this paper an original dataset combining 40 years ofcarbonate system observations in the Indian sector of the Southern Ocean(Enderby Basin) to evaluate and interpret the interannual variability of Cant in the AABW. This investigation is based on regular observationscollected at the same location (63 ∘  E–56.5 ∘  S) in theframework of the French observatory OISO from 1998 to 2018 extended byGEOSECS and INDIGO observations (1978, 1985 and 1987). At this location the main sources of AABW sampled is the low-salinity CapeDarnley Bottom Water (CDBW) and the Weddell Sea Deep Water (WSDW). Ourcalculations reveal that Cant concentrations increased significantly inthe AABW, from an average concentration of 7  µ mol kg −1 calculated for the period 1978–1987 to an average concentration of 13  µ mol kg −1 for the period 2010–2018. This is comparable toprevious estimates in other Southern Ocean (SO) basins, with the exceptionof bottom water close to formation sites where Cant concentrations are about twice as large. Our analysis shows that totalcarbon ( CT ) and Cant increasing rates in the AABW are about thesame over the period 1978–2018, and we conclude that the long-term change in CT is mainly due to the uptake of Cant in the different formationregions. This is, however, modulated by significant interannual tomulti-annual variability associated with variations in hydrographic(potential temperature, Θ ; salinity, S ) and biogeochemical ( CT ; totalalkalinity, AT ; dissolved oxygen, O 2 ) properties. A surprisingresult is the apparent stability of Cant concentrations in recent yearsdespite the increase in CT and the gradual acceleration of atmosphericCO 2 . The interannual variability at play in AABW needs to be carefullyconsidered in the extrapolated estimation of Cant sequestration basedon sparse observations over several years.

ocean science

Variability and stability of anthropogenic CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in Antarctic Bottom Water observed in the Indian sector of the Southern Ocean, 1978–2018