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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 (2016): Oxygen Utilization and Downward Carbon Flux in an Oxygen-Depleted Eddy in the Eastern Tropical North Atlantic. PANGAEA,, 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,

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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.
Related to:
Bange, Hermann Werner (2012): Hydrochemistry measured on water bottle samples during POSEIDON cruise POS399 in June 2010. PANGAEA,
Krahmann, Gerd (2016): Physical oceanography during METEOR cruise M105. PANGAEA,
Krahmann, Gerd; Dengler, Marcus; Thomsen, Soeren (2016): Physical oceanography during METEOR cruise M107. PANGAEA,
Tanhua, Toste (2016): Hydrochemistry of water samples during METEOR cruise M105. PANGAEA,
German Science Foundation (DFG), grant/award no. 27542298: Climate - Biogeochemistry Interactions in the Tropical Ocean
Seventh Framework Programme (FP7), grant/award no. 264879: Changes in the carbon uptake and emissions by oceans in a changing climate
Sixth Framework Programme (FP6), grant/award no. 511176: Marine carbon sources and sinks assessment
Median Latitude: 18.892513 * Median Longitude: -24.328921 * South-bound Latitude: 18.587500 * West-bound Longitude: -24.401733 * North-bound Latitude: 19.262933 * East-bound Longitude: -24.199350
Date/Time Start: 2014-03-06T05:09:00 * Date/Time End: 2014-03-07T07:27:52
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Datasets listed in this publication series

  1. Fiedler, B (2016): Hydrochemistry of water samples during ISLANDIA cruise ISL_00314.
  2. Fiedler, B (2016): Physical oceanography during ISLANDIA cruise ISL_00314.