Variability of North Sea pH and CO sub(2) in response to North Atlantic Oscillation forcing

High biological activity causes a distinct seasonality of surface water pH in the North Sea, which is a strong sink for atmospheric CO sub(2) via an effective shelf pump. The intimate connection between the North Sea and the North Atlantic Ocean suggests that the variability of the CO sub(2) system...

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Bibliographic Details
Published in:Journal of geophysical research. Biogeosciences 2013-12, Vol.118 (4), p.1584-1592
Main Authors: Salt, Lesley A, Thomas, Helmuth, Prowe, AEFriederike, Borges, Alberto V, Bozec, Yann, Baar, Hein JW
Format: Article
Language:English
Subjects:
Atlantic Ocean
Carbon dioxide
Marine
North Atlantic oscillation
North Sea
Partial pressure
Pumps
Shelves
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Summary:High biological activity causes a distinct seasonality of surface water pH in the North Sea, which is a strong sink for atmospheric CO sub(2) via an effective shelf pump. The intimate connection between the North Sea and the North Atlantic Ocean suggests that the variability of the CO sub(2) system of the North Atlantic Ocean may, in part, be responsible for the observed variability of pH and CO sub(2) in the North Sea. In this work, we demonstrate the role of the North Atlantic Oscillation (NAO), the dominant climate mode for the North Atlantic, in governing this variability. Based on three extensive observational records covering the relevant levels of the NAO index, we provide evidence that the North Sea pH and CO sub(2) system strongly responds to external and internal expressions of the NAO. Under positive NAO, the higher rates of inflow of water from the North Atlantic Ocean and the Baltic outflow lead to a strengthened north-south biogeochemical divide. The limited mixing between the north and south leads to a steeper gradient in pH and partial pressure of CO sub(2) (pCO sub(2)) between the two regions in the productive period. This is exacerbated further when coinciding with higher sea surface temperature, which concentrates the net community production in the north through shallower stratification. These effects can be obscured by changing properties of the constituent North Sea water masses, which are also influenced by NAO. Our results highlight the importance of examining interannual trends in the North Sea CO sub(2) system with consideration of the NAO state. Key Points * The North Sea shelf pump is affected by the North Atlantic Oscillation * Variability in the water mass composition of the North Sea impacts pH * The North Sea carbon system responds to forcing on different time scales
ISSN:2169-8953
2169-8961
DOI:10.1002/2013JG002306