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- Title
A short-term sink for atmospheric CO<sub>2</sub> in subtropical mode water of the North Atlantic Ocean.
- Authors
Bates, Nicholas R.; Pequignet, A. Christine; Johnson, Rodney J.; Gruber, Nicolas
- Abstract
Large-scale features of ocean circulation, such as deep water formation in the northern North Atlantic Ocean, are known to regulate the long-term physical uptake of CO[sub 2] from the atmosphere by moving CO[sub 2]-laden surface waters into the deep ocean. But the importance of CO[sub 2] uptake into water masses that ventilate shallower ocean depths, such as subtropical mode waters of the subtropical gyres, are poorly quantified. Here we report that, between 1988 and 2001, dissolved CO[sub 2] concentrations in subtropical mode waters of the North Atlantic have increased at a rate twice that expected from these waters keeping in equilibrium with increasing atmospheric CO[sub 2]. This accounts for an extra ∼0.4-2.8 Pg C (1Pg = 10[sup 15] g) over this period (that is, about 0.03-0.24 PgCyr[sup -1]), equivalent to ∼3-10% of the current net annual ocean uptake of CO[sub 2] (ref. 3). We suggest that the lack of strong winter mixing events, to greater than 300 m in depth, in recent decades is responsible for this accumulation, which would otherwise disturb the mode water layer and liberate accumulated CO[sub 2] back to the atmosphere. However, future dimate variability (which influences subtropical mode water formation) and changes in the North Atlantic Oscillation (leading to a return of deep winter mixing events) may reduce CO[sub 2] accumulation in subtropical mode waters. We therefore conclude that, although CO[sub 2] uptake by subtropical mode waters in the North Atlantic—and possibly elsewhere—does not always represent a long-term CO[sub 2] sink, the phenomenon is likely to contribute substantially to interannual variability in oceanic CO[sub 2] uptake.
- Publication
Nature, 2002, Vol 420, Issue 6915, p489
- ISSN
0028-0836
- Publication type
Academic Journal
- DOI
10.1038/nature01253