Coastal upwelling off Peru and Mauritania inferred from helium isotope disequilibrium.

Steinfeldt, R., Sültenfuß, J., Dengler, Marcus , Fischer, Tim and Rhein, Monika (2015) Coastal upwelling off Peru and Mauritania inferred from helium isotope disequilibrium. Open Access Biogeosciences (BG), 12 . pp. 7519-7533. DOI 10.5194/bg-12-7519-2015.

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Abstract

Upwelling is an important process, bringing gases and nutrients into the ocean mixed layer. The upwelling velocities, however, are too small to be measured directly. Here we use the surface disequilibrium of the 3He / 4He ratio measured in two coastal upwelling regions off Peru in the Pacific ocean and off Mauritania in the Atlantic ocean to calculate the regional distribution of vertical velocities. To also account for the fluxes by diapycnal mixing, microstructure-based observations of the vertical diffusivity have been performed on all four cruises analysed in this study. The upwelling velocities in the coastal regions vary between 1.1 ± 0.3 × 10−5 and 2.8 ± 1.5 × 10−5 m s−1 for all cruises. Vertical velocities are also inferred from the divergence of the wind-driven Ekman transport. In the coastal regimes, both methods agree within the error range. Further offshore, the helium-derived vertical velocity still reaches 1 × 10−5 m s−1, whereas the wind-driven upwelling from Ekman suction is smaller by up to 1 order of magnitude. One reason for this difference is ascribed to eddy-induced upwelling. Both advective and diffusive nutrient fluxes into the mixed layer are calculated based on the helium-derived vertical velocities and the vertical diffusivities. The advective part of these fluxes makes up at about 50 % of the total. The nutrient flux into the mixed layer in the coastal upwelling regimes is equivalent to a net community production (NCP) of 1.3 ± 0.3 g C m2 d−1 off Peru and 1.6–2.1 ± 0.5 g C m2 d−1 off Mauritania.

Document Type: Article
Additional Information: WOS:000367350700009
Keywords: ATA_IFMGEOMAR/3; POSEIDON; POS347; METEOR; M68; M91; L'Atalante
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
Refereed: Yes
Open Access Journal?: Yes
Publisher: Copernicus Publications (EGU)
Projects: SOPRAN
Expeditions/Models/Experiments:
Date Deposited: 01 Oct 2015 13:06
Last Modified: 22 Jan 2016 08:33
URI: https://oceanrep.geomar.de/id/eprint/29867

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