Long-term trends and anthropogenic forcing of surface ocean carbon storage and acidification

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Oct 15, 2025, 2:14:35 PM (5 days ago) Oct 15
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https://www.sciencedirect.com/science/article/abs/pii/S0141113625006634

Authors: Wei-Bo Chen

11 October 2025


Abstract
This study investigates long-term trends and anthropogenic influences on surface ocean carbon storage and acidification across the global ocean during 1985–2022, using a high-resolution (0.25° × 0.25°) product reconstructed by a neural-network framework from the Copernicus Marine Service. Global and regional trends in dissolved inorganic carbon (DIC), total alkalinity (TA), pH, surface partial pressure of CO2 (spCO2), and air–sea CO2 flux (fgCO2) were quantified using linear regression, Mann–Kendall tests, and Sen's slope estimator. Results reveal a significant global DIC increase of 0.75 ± 0.015 μmol kg−1 yr−1, corresponding to an annual carbon sink of ∼2.0 PgC yr−1, alongside a pH decline of −0.00164 ± 0.000034 units yr−1, indicating intensified acidification. The fgCO2 rose from 0.32 to 0.72 mol C m−2 yr−1, reflecting a strengthened carbon sink (from 1.2 to 2.6 PgC yr−1), with a temporary decline during 2021–2022 linked to reduced emissions during the COVID-19 pandemic. Spatial analyses highlight pronounced DIC and fgCO2 increases in the North Atlantic and Southern Ocean, contrasted by persistent CO2 outgassing in equatorial regions. Spearman's rank correlations and Bai–Perron breakpoint analyses identify structural shifts in carbon dynamics, particularly in 1997–1998 and 2012–2013, associated with accelerated anthropogenic forcing. Declining TA:DIC ratios signal a weakening of oceanic buffering capacity, raising concerns about the future efficiency of marine carbon sequestration. These findings underscore the ocean's critical role in mitigating atmospheric CO2, while revealing its increasing vulnerability to sustained anthropogenic pressures.

Source: ScienceDirect 
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