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Abstract The South Atlantic Ocean is an important region for anthropogenic CO2(Canth) uptake and storage in the world ocean, yet is less studied. Here, after an extensive sensitivity test and method comparison, we applied an extended multiple linear regression method with six characteristic water masses to estimate Canthchange or increase (ΔCanth) between 1980s and 2010s in the South Atlantic Ocean using two meridional transects (A16S and A13.5) and one zonal transect (A10). Over a period of about 25 years, the basin‐wide ΔCanthwas 3.86 ± 0.14 Pg C decade−1. The two basins flanking the Mid‐Atlantic Ridge had different meridional patterns of ΔCanth, yielding an average depth‐integrated ΔCanthin the top 2000 m of 0.91 ± 0.25 mol m−2 yr−1along A16S on the west and 0.57 ± 0.22 mol m−2 yr−1along A13.5 on the east. The west‐east basin ΔCanthcontrasts were most prominent in the tropical region (0–20°S) in the Surface Water (SW), approximately from equator to 35°S in the Subantarctic Mode Water (Subantarctic Mode Water (SAMW)), and all latitudes in the Antarctic Intermediate Water (AAIW). Less ΔCanthin the eastern basin than the western basin was caused by weaker ventilation driven by SAMW and AAIW formation and subduction and stronger Antarctic Bottom Water (AABW) formation in the former than the latter. In addition to the spatial heterogeneity, Canthincrease rates accelerated from the 1990s to the 2000s, consistent with the overall increase in air‐sea CO2exchange in the South Atlantic Ocean.
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Changes in Oceanic Radiocarbon and CFCs Since the 1990s
Abstract Anthropogenic perturbations from fossil fuel burning, nuclear bomb testing, and chlorofluorocarbon (CFC) use have created useful transient tracers of ocean circulation. The atmospheric14C/C ratio (∆14C) peaked in the early 1960s and has decreased now to pre‐industrial levels, while atmospheric CFC‐11 and CFC‐12 concentrations peaked in the early 1990s and early 2000s, respectively, and have now decreased by 10%–20%. We present the first analysis of a decade of new observations (2007 to 2018–2019) and give a comprehensive overview of the changes in ocean ∆14C and CFC concentration since the WOCE surveys in the 1990s. Surface ocean ∆14C decreased at a nearly constant rate from the 1990–2010s (20‰/decade). In most of the surface ocean ∆14C is higher than in atmospheric CO2while in the interior ocean, only a few places are found to have increases in ∆14C, indicating that globally, oceanic bomb14C uptake has stopped and reversed. Decreases in surface ocean CFC‐11 started between the 1990 and 2000s, and CFC‐12 between the 2000–2010s. Strong coherence in model biases of decadal changes in all tracers in the Southern Ocean suggest ventilation of Antarctic Intermediate Water was enhanced from the 1990 to the 2000s, whereas ventilation of Subantarctic Mode Water was enhanced from the 2000 to the 2010s. The decrease in surface tracers globally between the 2000 and 2010s is consistently stronger in observations than in models, indicating a reduction in vertical transport and mixing due to stratification.
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- Award ID(s):
- 1924215
- PAR ID:
- 10549641
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 129
- Issue:
- 7
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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