Oxygen Utilization and Downward Carbon Flux in an Oxygen-Depleted Eddy in the Eastern Tropical North Atlantic, supplement to: Fiedler, Björn; Grundle, Damian; Schütte, Florian; Karstensen, Johannes; Löscher, Carolin R; Hauss, Helena; Wagner, Hannes; Loginova, Alexandra; Kiko, Rainer; Silva, Pericles; Tanhua, Toste; Körtzinger, Arne (2016): Oxygen utilization and downward carbon flux in an oxygen-depleted eddy in the eastern tropical North Atlantic. Biogeosciences, 13(19), 5633-5647

DOI

The occurrence of mesoscale eddies that develop suboxic environments at shallow depth (about 40-100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, with the use of moorings, under water gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). During the survey the eddy core showed oxygen concentrations as low as 5 µmol kg-1 with a pH of around 7.6 at approximately 100 m depth. Correspondingly, the aragonite saturation level dropped to 1 at the same depth, thereby creating unfavorable conditions for calcifying organisms. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate organic matter and dissolved organic matter (POM and DOM), generally showed elevated concentrations in the surface mixed layer (0-70 m), with DOM also accumulating beneath the oxygen minimum. With the use of reference data from the upwelling region where these eddies are formed, the oxygen utilization rate was calculated by determining oxygen consumption through the remineralization of organic matter. Inside the core, we found these rates were almost 1 order of magnitude higher (apparent oxygen utilization rate (aOUR); 0.26 µmol kg-1 day-1) than typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC), were around 0.19 to 0.23 g C m-2 day-1 at 100 m depth, clearly exceeding fluxes typical for an oligotrophic open-ocean setting. The observations support the view that the oxygen-depleted eddies can be viewed as isolated, westwards propagating upwelling systems of their own, thereby represent re-occurring alien biogeochemical environments in the ETNA.

Identifier
DOI https://doi.org/10.1594/PANGAEA.865177
Related Identifier https://doi.org/10.5194/bg-13-5633-2016
Related Identifier https://doi.org/10.1594/PANGAEA.776961
Related Identifier https://doi.org/10.1594/PANGAEA.858255
Related Identifier https://doi.org/10.1594/PANGAEA.848614
Related Identifier https://doi.org/10.1594/PANGAEA.860480
Related Identifier https://doi.org/10.1594/PANGAEA.787808
Related Identifier https://doi.org/10.1594/PANGAEA.864810
Metadata Access https://ws.pangaea.de/oai/provider?verb=GetRecord&metadataPrefix=datacite4&identifier=oai:pangaea.de:doi:10.1594/PANGAEA.865177
Provenance
Creator Fiedler, Björn; Grundle, Damian; Schütte, Florian; Karstensen, Johannes; Löscher, Carolin R; Hauss, Helena; Wagner, Hannes; Loginova, Alexandra; Kiko, Rainer; Silva, P; Tanhua, Toste; Körtzinger, Arne
Publisher PANGAEA - Data Publisher for Earth & Environmental Science
Publication Year 2016
Funding Reference Seventh Framework Programme; Sixth Framework Programme; German Science Foundation
Rights Creative Commons Attribution 3.0 Unported
OpenAccess true
Representation
Language English
Resource Type Supplementary Collection of Datasets
Format application/zip
Size 2 datasets
Discipline Biogeochemistry
Spatial Coverage (-24.402W, 18.587S, -24.199E, 19.263N)
Temporal Coverage Begin 2014-03-06T05:09:00Z
Temporal Coverage End 2014-03-07T07:27:52Z