Nitrogen and carbon cycling in the North Sea and exchange with the North Atlantic-A model study, Part II: Carbon budget and fluxes

• Published in: Continental Shelf Research
• Main Authors: Kuhn, Wilfried, Paetsch, Johannes, Thomas, Helmuth, Borges, Alberto, Schiettecatte, Laure*-Sophie, Bozec, Yann, Prowe, A E Friederike
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon Press - An Imprint of Elsevier Science 2010
• Subjects: Ecosystem modeling; ECOHAM; HAMSOM; North Sea; Carbon budget; North Atlantic Oscillation; Continental shelf pump; CO2 uptake; Net ecosystem production; River loads; Stratification; Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; North Atlantic; North Atlantic oscillation
• Online Access: https://orbi.uliege.be/handle/2268/75315; https://orbi.uliege.be/bitstream/2268/75315/1/kuehn_et_al_2010.pdf; https://doi.org/10.1016/j.csr.2010.07.001

peer reviewed The 3-d coupled physical-biogeochemical model ECOHAM (version 3) was applied to the Northwest-European Shelf (47 degrees 41'-63 degrees 53'N, 15 degrees 5'W-13 degrees 55'E) for the years 1993-1996. Carbon fluxes were calculated for the years 1995 and 1996 for the inner shelf region, the North Sea (511,725 km(2)). This period was chosen because it corresponds to a shift from a very high winter-time North Atlantic Oscillation Index (NAOI) in 1994/1995, to an extremely low one in 1995/1996, with consequences for the North Sea physics and biogeochemistry. During the first half of 1996, the observed mean SST was about 1 degrees C lower than in 1995; in the southern part of the North Sea the difference was even larger (up to 3 degrees C). Due to a different wind regime, the normally prevailing anti-clockwise circulation, as found in winter 1995, was replaced by more complicated circulation patterns in winter 1996. Decreased precipitation over the drainage area of the continental rivers led to a reduction in the total (inorganic and organic) riverine carbon load to the North Sea from 476 Gmol C yr(-1) in 1995 to 340 Gmol C yr(-1) in 1996. In addition, the North Sea took up 503 Gmol C yr(-1) of CO2 from the atmosphere. According to our calculations, the North Sea was a sink for atmospheric CO2, at a rate of 0.98 mol C m(-2) yr(-1), for both years. The North Sea is divided into two sub-systems: the shallow southern North Sea (SNS; 190,765 km(2)) and the deeper northern North Sea (NNS; 320,960 km2). According to our findings the SNS is a net-autotrophic system (net ecosystem production NEP > 0) but released CO2 to the atmosphere: 159 Gmol C yr(-1) in 1995 and 59 Gmol C yr(-1) in 1996. There, the temperature-driven release of CO2 outcompetes the biological CO2 drawdown. In the NNS, where respiratory processes prevail (NEP < 0), 662 and 562 Gmol C yr(-1) were taken up from the atmosphere in 1995 and 1996. respectively. Stratification separates the productive, upper layer from the deeper layers of the ...