Tidal-induced mixing and diapycnal nutrient fluxes in the Mauritanian upwelling region.

Schafstall, Jens, Dengler, Marcus , Brandt, Peter and Bange, Hermann W. (2010) Tidal-induced mixing and diapycnal nutrient fluxes in the Mauritanian upwelling region. Open Access Journal of Geophysical Research: Oceans, 115 (C10). C10014. DOI 10.1029/2009JC005940.

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Abstract

The Mauritanian coastal area is one of the most biologically productive upwelling regions in the world ocean. Shipboard observations carried out during maximum upwelling season and short-term moored observations are used to investigate diapycnal mixing processes and to quantify diapycnal fluxes of nutrients. The observations indicate strong tide-topography interactions that are favored by near-critical angles occurring on large parts of the continental slope. Moored velocity observations reveal the existence of highly nonlinear internal waves and bores and levels of internal wave spectra are strongly elevated near the buoyancy frequency. Dissipation rates of turbulent kinetic energy at the slope and shelf determined from microstructure measurements in the upper 200 m averages to ɛ = 5 × 10−8 W kg−1. Particularly elevated dissipation rates were found at the continental slope close to the shelf break, being enhanced by a factor of 100 to 1000 compared to dissipation rates farther offshore. Vertically integrated dissipation rates per unit volume are strongest at the upper continental slope reaching values of up to 30 mW m−2. A comparison of fine-scale parameterizations of turbulent dissipation rates for shelf regions and the open ocean to the measured dissipation rates indicates deficiencies in reproducing the observations. Diapycnal nitrate fluxes above the continental slope at the base of the mixed layer yielding a mean value of 12 × 10−2 μmol m−2 s−1 are amongst the largest published to date. However, they seem to only represent a minor contribution (10% to 25%) to the net community production in the upwelling region.

Document Type: Article
Additional Information: 10.1029/2009jc005940
Keywords: Oceanography; Chemistry; Mauritanian upwelling region; INTERNAL SOLITARY WAVES; NEW-ENGLAND SHELF; CONTINENTAL-SHELF; MICROSTRUCTURE MEASUREMENTS; VELOCITY MICROSTRUCTURE; TURBULENT DISSIPATION; NORTH-ATLANTIC; ENERGY; TIDES; GENERATION; POSEIDON ; POS347 ; POS348 ; METEOR ; M68/3
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1029/2009JC005940
ISSN: 2169-9275
Projects: SOPRAN, Future Ocean
Expeditions/Models/Experiments:
Date Deposited: 12 Oct 2010 10:02
Last Modified: 16 Jan 2018 12:38
URI: http://oceanrep.geomar.de/id/eprint/9876

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