The ocean in the global carbon budget, 1959–2024: sink fractions, emissions cointegration, acidification, heat content and Arctic sea ice
Küresel karbon bütçesinde okyanus, 1959–2024: yutak payları, emisyonlarla eşbütünleşme, asitlenme, ısı içeriği ve Arktik deniz buzu
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Abstract
The ocean absorbs about a quarter of anthropogenic CO₂ emissions and most of the excess heat of the climate system, while becoming more acidic. We combined the Global Carbon Budget 2025 (GCB) with four independent observational records, Mauna Loa atmospheric CO₂, surface pH at Station ALOHA, upper-ocean heat content and September Arctic sea-ice extent, all retrieved live from the open GOMD platform by a notebook that stops when a series is missing. The GCB series close exactly: fossil and land-use emissions equal atmospheric growth plus ocean, land and cement-carbonation sinks plus the budget imbalance in every year (maximum residual below 0.001 GtC per year). In 2020–2024, fossil emissions averaged 10.17 GtC per year, land-use emissions 1.27, atmospheric growth 5.70, the ocean sink 3.24 and the land sink 2.35 GtC per year. The ocean took up 28.3% of total emissions, compared with 25.9% in the 1960s; the ocean-sink fraction increased by 0.0043 per decade (p = 0.007) and the airborne fraction by 0.016 per decade (p = 0.044). Total emissions and the ocean sink are cointegrated (slope 0.288, ADF = −3.63). Annual mean CO₂ at Mauna Loa rose from 315.98 ppm in 1959 to 427.35 ppm in 2025, with a record increase of 3.52 ppm in 2024; converted to carbon mass, its growth correlates with the GCB atmospheric term at r = 0.88. Surface pH at Station ALOHA decreased by 0.0195 units per decade (1988–2024) and correlated with Mauna Loa CO₂ at r = −0.98. Upper-ocean (0–700 m) heat content increased by 5.38 × 10²² J per decade since 1979, and September Arctic sea-ice extent decreased by 0.74 million km² per decade, with a change point in 2001. The independent records are mutually consistent and reproduce published budget values.
Keywords
Global carbon budget; Ocean carbon sink; Airborne fraction; Ocean acidification; Mauna Loa; Station ALOHA; Ocean heat content; Arctic sea ice; Cointegration
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