Variability of North Sea pH and CO2in response to North Atlantic Oscillation forcing.

Salt, Lesley A., Thomas, Helmuth, Prowe, A.E. Friederike , Borges, Alberto V., Bozec, Yann and de Baar, Hein J. W. (2013) Variability of North Sea pH and CO2in response to North Atlantic Oscillation forcing. Open Access Journal of Geophysical Research: Biogeosciences, 118 (4). pp. 1584-1592. DOI 10.1002/2013JG002306.

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High biological activity causes a distinct seasonality of surface water pH in the North Sea, which is a strong sink for atmospheric CO2 via an effective shelf pump. The intimate connection between the North Sea and the North Atlantic Ocean suggests that the variability of the CO2 system of the North Atlantic Ocean may, in part, be responsible for the observed variability of pH and CO2 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 CO2 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 CO2 (pCO2) 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 CO2 system with consideration of the NAO state.

Document Type: Article
Additional Information: WOS:000329871400020
Keywords: carbon; North Sea; NAO; pH
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1002/2013JG002306
ISSN: 2169-8953
Projects: CARBOOCEAN, Future Ocean
Date Deposited: 13 Jan 2014 08:45
Last Modified: 06 Feb 2018 14:07

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