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| Titel |
The mechanisms of North Atlantic CO2 uptake in a large Earth System Model ensemble |
| VerfasserIn |
P. R. Halloran, B. B. B. Booth, C. D. Jones, F. H. Lambert, D. J. McNeall, I. J. Totterdell, C. Völker |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 14 ; Nr. 12, no. 14 (2015-07-30), S.4497-4508 |
| Datensatznummer |
250118041
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| Publikation (Nr.) |
 copernicus.org/bg-12-4497-2015.pdf |
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| Zusammenfassung |
| The oceans currently take up around a quarter of the carbon dioxide (CO2)
emitted by human activity. While stored in the ocean, this CO2 is not
influencing Earth's radiation budget; the ocean CO2 sink therefore plays
an important role in mitigating global warming. CO2 uptake by the oceans
is heterogeneous, with the subpolar North Atlantic being the strongest CO2
sink region. Observations over the last 2 decades have indicated that
CO2 uptake by the subpolar North Atlantic sink can vary rapidly. Given the
importance of this sink and its apparent variability, it is critical that we
understand the mechanisms behind its operation. Here we explore the combined
natural and anthropogenic subpolar North Atlantic CO2 uptake across a
large ensemble of Earth System Model simulations, and find that models show a
peak in sink strength around the middle of the century after which CO2
uptake begins to decline. We identify different drivers of change on
interannual and multidecadal timescales. Short-term variability appears to be
driven by fluctuations in regional seawater temperature and alkalinity,
whereas the longer-term evolution throughout the coming century is largely
occurring through a counterintuitive response to rising atmospheric CO2
concentrations. At high atmospheric CO2 concentrations the contrasting
Revelle factors between the low latitude water and the subpolar gyre,
combined with the transport of surface waters from the low latitudes to the
subpolar gyre, means that the subpolar CO2 uptake capacity is largely
satisfied from its southern boundary rather than through air–sea CO2 flux.
Our findings indicate that: (i) we can explain the mechanisms of subpolar
North Atlantic CO2 uptake variability across a broad range of Earth System
Models; (ii) a focus on understanding the mechanisms behind contemporary
variability may not directly tell us about how the sink will change in the
future; (iii) to identify long-term change in the North Atlantic CO2 sink
we should focus observational resources on monitoring lower latitude as well
as the subpolar seawater CO2; (iv) recent observations of a weakening
subpolar North Atlantic CO2 sink may suggest that the sink strength has
peaked and is in long-term decline. |
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