Extensive nitrogen loss from permeable sediments off North-West Africa.

Sokoll, Sarah, Lavik, Gaute, Sommer, Stefan, Goldhammer, Tobias, Kuypers, Marcel M. M. and Holtappels, Moritz (2016) Extensive nitrogen loss from permeable sediments off North-West Africa. Open Access Journal of Geophysical Research: Biogeosciences, 121 (4). pp. 1144-1157. DOI 10.1002/2015JG003298.

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Abstract

The upwelling area off North-West Africa is characterized by high export production, high nitrate and low oxygen concentration in bottom waters. The underlying sediment consists of sands that cover most of the continental shelf. Due to their permeability sands allow for fast advective pore water transport and can exhibit high rates of nitrogen (N) loss via denitrification as reported for anthropogenically eutrophied regions. However, N loss from sands underlying naturally eutrophied waters is not well studied, and in particular, N loss from the North-West African shelf is poorly constrained. During two research cruises in April/May 2010/2011, sediment was sampled along the North-West African shelf and volumetric denitrification rates were measured in sediment layers down to 8 cm depth using slurry incubations with 15N-labeled nitrate. Areal N loss was calculated by integrating volumetric rates down to the nitrate penetration depth derived from pore water profiles. Areal N loss was neither correlated with water depth nor with bottom water concentrations of nitrate and oxygen but was strongly dependent on sediment grain size and permeability. The derived empirical relation between benthic N loss and grains size suggests that pore water advection is an important regulating parameter for benthic denitrification in sands and further allowed extrapolating rates to an area of 53,000 km2 using detailed sediment maps. Denitrification from this region amounts to 995 kt yr-1 (average 3.6 mmol m-2 d-1) which is 4 times higher than previous estimates based on diffusive pore water transport. Sandy sediments cover 50-60% of the continental shelf and thus may contribute significantly to the global benthic N loss.

Document Type: Article
Additional Information: The data used are listed in the references, tables, and at: www. pangaea.de - WOS:000378702800008
Keywords: Denitrification; N loss; permeable sediments; sand; upwelling; RV Poseidon; POS398; RV Maria S. Merian; MSM17/4
Research affiliation: OceanRep > SFB 754 > B6
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 754 > B4
OceanRep > SFB 754
AWI
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1002/2015JG003298
ISSN: 2169-8953
Projects: SFB754
Expeditions/Models/Experiments:
Date Deposited: 10 Jun 2016 07:45
Last Modified: 01 Feb 2019 15:02
URI: http://oceanrep.geomar.de/id/eprint/33056

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