Silicon and nitrogen cycling in the upwelling area off Peru: A dual isotope approach

Grasse, Patricia, Ryabenko, Evgenia, Ehlert, Claudia, Altabet, Mark A. and Frank, Martin (2016) Silicon and nitrogen cycling in the upwelling area off Peru: A dual isotope approach Limnology and Oceanography, 61 (5). pp. 1661-1676. DOI 10.1002/lno.10324.

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Abstract

We present a comparison of the dissolved stable isotope composition of silicate (δ30Si(OH)4) and nitrate (δ15 inline image) to investigate the biogeochemical processes controlling nutrient cycling in the upwelling area off Peru, where one of the globally largest Oxygen Minimum Zones (OMZs) is located. Besides strong upwelling of nutrient rich waters mainly favoring diatom growth, an anticyclonic eddy influenced the study area. We observe a tight coupling between the silicon (Si) and nitrogen (N) cycles in the study area. Waters on the shelf showed high Si(OH)4 concentrations accompanied by diminished inline image concentration as a consequence of intense remineralization, high Si fluxes from the shelf sediments, and N-loss processes such as anammox/denitrification within the OMZ. Correspondingly, the surface waters show low δ30Si(OH)4 values (+2‰) due to low Si utilization but relatively high δ15 inline image (+13‰) values due to upwelling of waters influenced by N-loss processes. In contrast, as a consequence of the deepening of the thermocline in the eddy center, a pronounced Si(OH)4 depletion led to the highest δ30Si(OH)4 values (+3.7‰) accompanied by high δ15 inline image values (+16‰). In the eddy center, high inline image: Si(OH)4 ratios favored the growth of non-siliceous organisms (Synechococcus). Our data show that upwelling processes and the presence of eddies play important roles controlling the nutrient cycles and therefore also exert a major influence on the phytoplankton communities in the Peruvian Upwelling. Our findings also show that the combined approach of δ30Si(OH)4 and δ15 inline image can improve our understanding of paleo records as it can help to disentangle utilization and N-loss processes.

Document Type: Article
Additional Information: WOS:000383621800009
Keywords: silicon isotopes, nitrogen isotopes, Oxygen Minimum Zone, Peruvian Upwelling
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Kiel University
Refereed: Yes
DOI etc.: 10.1002/lno.10324
ISSN: 0024-3590
Date Deposited: 04 Aug 2016 12:13
Last Modified: 03 May 2017 12:28
URI: http://eprints.uni-kiel.de/id/eprint/33523

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