Hidden biosphere in an oxygen-deficient Atlantic open ocean eddy: future implications of ocean deoxygenation on primary production in the eastern tropical North Atlantic.

Löscher, Carolin, Fischer, M. A., Neulinger, Sven, Fiedler, Björn, Philippi, M., Schütte, Florian, Singh, Arvind, Hauss, Helena , Karstensen, Johannes , Körtzinger, Arne, Künzel, S. and Schmitz, Ruth A. (2015) Hidden biosphere in an oxygen-deficient Atlantic open ocean eddy: future implications of ocean deoxygenation on primary production in the eastern tropical North Atlantic. Open Access Biogeosciences (BG), 12 (16). pp. 7467-7482. DOI 10.5194/bg-12-7467-2015.

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Abstract

The eastern tropical North Atlantic (ETNA) is characterized by a highly productive coastal upwelling system and a moderate oxygen minimum zone with lowest open ocean oxygen (O2) concentrations of around 40 μmol kg−1. Only recently, the discovery of re-occurring mesoscale eddies with sometimes close to anoxic O2 concentrations (<1 μmol kg−1) and located just below the mixed layer challenged our understanding of O2 distribution and biogeochemical processes in this area.

Here, we present the first metagenomic dataset from a deoxygenated anticyclonic modewater eddy in the open waters of the ETNA. In the eddy, we observed a significantly lower bacterial diversity compared to surrounding waters, along with a significant community shift. We detected enhanced primary productivity in the surface layer of the eddy indicated by elevated chlorophyll concentrations and increased carbon uptake rates up to three times as high as in surrounding waters. Carbon uptake below the euphotic zone correlated to the presence of a specific high-light ecotype of Prochlorococcus, which is usually underrepresented in the ETNA. Our combined data indicate that high primary production in the eddy fuels export production and the presence of a specific microbial community responsible for enhanced respiration at shallow depths, below the mixed layer base. Progressively decreasing O2 concentrations in the eddy were found to promote transcription of the key gene for denitrification, nirS, in the O2-depleted core waters. This process is usually absent from the open ETNA waters.

In the light of future ocean deoxygenation our results show exemplarily that even distinct events of anoxia have the potential to alter microbial community structures and with that critically impact primary productivity and biogeochemical processes of oceanic water bodies.

Document Type: Article
Additional Information: WOS:000367350700006
Keywords: R.V. Islandia Expedition; R.V. Meteor; M105
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence > FO-R07
OceanRep > The Future Ocean - Cluster of Excellence > FO-R09
OceanRep > SFB 754 > B4
OceanRep > SFB 754
OceanRep > The Future Ocean - Cluster of Excellence > FO-R03
OceanRep > SFB 754 > A4
OceanRep > The Future Ocean - Cluster of Excellence > FO-R10
OceanRep > SFB 754 > B8
Kiel University
OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > SFB 754 > B9
OceanRep > The Future Ocean - Cluster of Excellence > FO-R06
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-12-7467-2015
ISSN: 1726-4170
Related URLs:
Projects: CVOO, Future Ocean, SFB754, SOPRAN
Expeditions/Models/Experiments:
Date Deposited: 07 Dec 2015 13:47
Last Modified: 11 Dec 2018 10:02
URI: http://oceanrep.geomar.de/id/eprint/30429

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