Mass, nutrient and oxygen budgets for the northeastern Atlantic Ocean

[摘要] The northeast Atlantic is a key horizontal and vertical crossroads regionfor the meridional overturning circulation, but basic nutrient and oxygenfluxes are still poorly constrained by observations in the region. A surfaceto bottom northeast Atlantic Ocean budget for mass, nutrients (nitrate andphosphate) and oxygen is determined using an optimization method based onthree surveys of the OVIDE transect (from Greenland to Portugal) completedwith the World Ocean Atlas 2009. Budgets are derived for two communicatingboxes representing the northeastern European basin (NEEB) and the IrmingerSea.

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% are redistributed between both boxes through the ReykjanesRidge (9.3 ± 0.7 × 10⁹ kg s⁻¹).

Net biological source/sink terms of nitrate point to both the Irminger andNEEB boxes as net organic matter production sites (consuming nitrate at arate of –7.8 ± 6.5 kmol s⁻¹ and–8.4 ± 6.6 kmol s⁻¹, respectively). Using a standard Redfieldratio of C : N = 106 : 16, nitrate consumption rates indicate that about40 TgC yr⁻¹ of carbon is fixed by organic matter productionbetween the OVIDE transect and the Greenland–Scotland Ridge. Nutrient fluxesalso induce a net biological production of oxygen of73 ± 60 kmol s⁻¹ and 79 ± 62 kmol s⁻¹ in theIrminger and NEEB boxes, which points to the region as being autotrophic.

The abiotic air–sea oxygen flux leads to an oceanic oxygen uptake in the tworegions (264 ± 66 kmol s⁻¹ in the north and443 ± 70 kmol s⁻¹ in the south). The abiotic flux ispartitioned into a mixing and a thermal component. It is found that theIrminger Sea oceanic oxygen uptake is driven by an air–sea heat flux coolingincreasing the ocean surface oxygen solubility. Over the northeasternEuropean basin the mixing component is about half the thermal flux,presumably because of the oxygen minimum in the subtropical thermocline.

[学科分类] 地球化学与岩石