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Cited by 105Marine and coastal ecosystemsOceanographic and Atmospheric ProcessesMarine Biology and Ecology Research

Open ocean dead zones in the tropical North Atlantic Ocean.

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Karstensen, J., Fiedler, B., Schütte, F., Brandt, P., Körtzinger, A., Fischer, G., Zantopp, R., Hahn, J. +2 more·2015·Biogeosciences
DOI 10.5194/bg-12-2597-2015

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Abstract

Abstract. Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg−1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg−1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day−1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

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  • Oxygen can drop to zero in closed mesoscale eddy cores in the eastern tropical North Atlantic, substantially lower than the average value of 40 μmol kg-1.

    “Oxygen can drop to zero in these eddies (Karstensen et al., 2015), substantially lower than the average value of 40 µmol kg -1 .”

    From The tropical atlantic observing system (2019) · cites this paper as Karstensen et al., 2015

    The Abstract reports oxygen below 2 µmol kg⁻¹, lowest at eddy centres, and §3.1 describes the measured level as close to the threshold for anoxia—not zero. The Abstract and §3.1 also describe about 40 µmol kg⁻¹ as the region’s usual lower limit, rather than its average. (LLM, conf=0.88)

    Experimental — accuracy not yet measured

  • In the eastern tropical Atlantic, estimates of the biological pump and its dependence on oxygen availability are complicated by the presence of mesoscale eddies, which contain shallow (40-100 m) suboxic environments.

    “In the eastern tropical Atlantic, estimates of the biological pump and its dependence on oxygen availability are complicated by the presence of mesoscale eddies, which contain shallow (40-100 m) suboxic environments (Karstensen et al., 2015).”

    From The tropical atlantic observing system (2019) · cites this paper as Karstensen et al., 2015

    The Introduction reports extremely low oxygen in mesoscale eddies in the eastern tropical North Atlantic, and §3.1 places one low-oxygen eddy core around 70 m depth. Section 3.4 links sinking particles to oxygen consumption, but does not establish that eddies complicate estimates of the biological pump or its dependence on oxygen availability; it says the available data cannot be used to estimate productivity. Page numbers were not provided in our copy. (LLM, conf=0.85)

    Experimental — accuracy not yet measured

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Authors
Karstensen, J., Fiedler, B., Schütte, F., Brandt, P., Körtzinger, A., Fischer, G., Zantopp, R., Hahn, J., Visbeck, M., & Wallace, D.
Affiliations
  • GEOMAR Helmholtz Centre for Ocean Research Kiel (DE)
  • University of Bremen (DE)
Corresponding author
Karstensen, J.
ORCID
Venue
Biogeosciences
Publisher
Copernicus GmbH
Published
2015-04-30
Volume
12
Issue
8
Pages
2597-2605
ISSN
  • 1726-4170 (ISSN-L)
  • 1726-4189
DOI
10.5194/bg-12-2597-2015
OpenAlex
W2078401285
Cited by
105
References
39
Citations by year
2026: 3 · 2025: 10 · 2024: 5 · 2023: 6 · 2022: 7 · 2021: 13 · 2020: 8 · 2019: 8 · 2018: 12 · 2017: 10 · 2016: 16 · 2015: 7
FWCI
12.49
Type
journal article
Language
en
Open access
Licence
Locations
  • Biogeosciences (publishedVersion, cc-by)
  • Helmholtz Centre for Ocean Research Kiel (GEOMAR) (acceptedVersion, other-oa)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • Seventh Framework Programme (312463)
  • Bundesministerium für Bildung und Forschung (AWA 01DG12073E)
  • Deutsche Forschungsgemeinschaft (SFB 754)
  • European Commission (264879)
Topics
  • Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine and coastal ecosystems
  • Physical Sciences › Earth and Planetary Sciences › Oceanography › Oceanographic and Atmospheric Processes
  • Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine Biology and Ecology Research
Keywords
tropical North Atlantic, ocean eddies, cyclonic eddies, anticyclonic eddies, euphotic zone, eddy propagation, diurnal vertical migration, zooplankton, West African coast, mixed layer

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