Using DIC‐δ¹³C Pair to Constrain Anthropogenic Carbon Increase in the Southeastern Atlantic Ocean Over the Most Recent Decade (2010–2020)

Abstract The southeastern Atlantic Ocean is a crucial yet understudied region for the ocean absorption of anthropogenic carbon (C anth ). Data from the A12 (2020) and A13.5 (2010) cruises offer an opportunity to examine changes in dissolved inorganic carbon (DIC), its stable isotope (δ 13 C), and C anth over the past decade within a limited region (1∼3°E, 32∼42°S). For the decade of 2010–2020, C anth invasion was observed from the sea surface down to 1,200 m based on both DIC and δ 13 C data. The mean C anth increase rate (1.08 ± 0.26 mol m −2 yr −1 ) during this period accelerated from 0.87 ± 0.05 mol m −2 yr −1 during the previous period (1983/84–2010). The δ 13 C‐based C anth increase closely matches the DIC‐based estimation below 500 m but is 26% higher in the upper ocean. This discrepancy is likely due to δ 13 C's longer air‐sea exchange timescale, seasonal variability in the upper ocean, and the chosen ratio of anthropogenically induced changes in δ 13 C and DIC. Finally, column inventory changes based on the two methods also exhibit very similar mean C anth uptake rates. The paired DIC concentration and stable isotope dataset may enhance our ability to constrain C anth accumulation and its controlling mechanisms in the ocean.