Mass, nutrients and oxygen budgets for the North Eastern Atlantic Ocean

Abstract

Abstract. A surface to bottom North-East Atlantic Ocean budget for mass, nutrients (nitrate and phosphate) and oxygen is determined using an optimization method based on climatological data from the World Ocean Atlas 2009 and three surveys of the OVIDE transect (from Greenland to Portugal). Budgets are derived for two communicating boxes representing the North Eastern European Basin (NEEB) and the Irminger Sea. For the NEEB (Irminger) box, it is found that 30% of the mass import (export) across the OVIDE section reach (originate from) the Nordic Seas while 70% is redistributed between both boxes through the Reykjanes Ridge (9.3±0.7×109 kg s−1). Net biological source/sink terms of nitrate point to both the Irminger and NEEB boxes as net organic matter production sites (consumming nitrate at a rate of −7.8±6.5 kmol s−1 and −8.4±6.6 kmol s−1 respectively). Using a standard Redfield ratio of C:N =106:16, nitrate consumption rates indicate that about 40 TgC yr−1 of carbon is fixed by organic matter production between the OVIDE transect and the Greenland-Scotland Ridge. Nutrients fluxes also induce a net biological production of oxygen of 73±60 kmol s−1 and 79±62 kmol s−1 in the Irminger and NEEB boxes which points to the region as being autotrophic. Air-sea oxygen fluxes show an oceanic oxygen uptake in the two regions (264±66 kmol s−1 in the north and 443±70 kmol s−1 in the south), dominated by the abiotic component. The abiotic flux is partitionned into a mixing and a thermal components. It is found that the Irminger Sea oceanic oxygen uptake is driven by an air-sea heat flux cooling increasing the ocean surface oxygen solubility. Over the North Eastern European Basin the mixing component is about half the thermal flux, presumably because of the oxygen minimum in the subtropical thermocline.