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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-394
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-394
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Oct 2019

Submitted as: research article | 28 Oct 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Ocean Deoxygenation and Copepods: Coping with Oxygen Minimum Zone Variability

Karen F. Wishner1, Brad Seibel2, and Dawn Outram1 Karen F. Wishner et al.
  • 1Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA
  • 2College of Marine Science, University of South Florida, St. Petersburg, FL 33701, USA

Abstract. Increasing deoxygenation (loss of oxygen) of the ocean, including expansion of oxygen minimum zones (OMZs), is a potentially important consequence of global warming. We examined present day variability of vertical distributions of copepod species in the Eastern Tropical North Pacific (ETNP) living in locations with different water column oxygen profiles and OMZ intensity (lowest oxygen concentration and its vertical extent in a profile). Copepods and hydrographic data were collected in vertically-stratified day and night MOCNESS tows (0–1000 m) during 4 cruises over a decade (2007–2017) that sampled 4 ETNP locations: Costa Rica Dome, Tehuantepec Bowl, and 2 oceanic sites further north (21°–22° N) off Mexico. The sites had different vertical oxygen profiles: some with a shallow mixed layer, abrupt thermocline, and extensive very low oxygen OMZ core, and others with a more gradual vertical development of the OMZ (broad mixed layer and upper oxycline zone) and a less extensive OMZ core where oxygen was not as low. Copepod species (including examples from the genera Eucalanus, Pleuromamma, and Lucicutia) demonstrated different distributional strategies and physiologies associated with this variability. We identified sets of species that (1) changed their vertical distributions and depth of maximum abundance associated with the depth and intensity of the OMZ and its oxycline inflection points, (2) shifted their depth of diapause, (3) adjusted their diel vertical migration, especially the nighttime upper depth, or (4) expanded or contracted their depth range within the mixed layer and upper part of the thermocline in association with the thickness of the aerobic epipelagic zone (habitat compression concept).

The upper ocean to mesopelagic depth range encompasses a complex interwoven ecosystem characterized by intricate relationships among its inhabitants and their environment. It is a critically important zone for oceanic biogeochemical and export processes and hosts key food web components for commercial fisheries. Among the zooplankton, there will likely be winners and losers with increasing ocean deoxygenation as species cope with environmental change. Changes in individual copepod species abundances, vertical distributions, and life history strategies may create potential perturbations to these intricate food webs and processes. Present day variability provides a window into future scenarios and potential effects of deoxygenation.

Karen F. Wishner et al.
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Karen F. Wishner et al.
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Short summary
Increasing deoxygenation and oxygen minimum zone expansion are consequences of global warming. Copepod species had different vertical distribution strategies and physiologies associated with oxygen profile variability (0–1000 m). Species (1) changed vertical distributions and maximum abundance depth, (2) shifted diapause depth, (3) changed diel vertical migration depths, or (4) changed epipelagic depth range in the aerobic mixed layer. Present day variability helps predict future scenarios.
Increasing deoxygenation and oxygen minimum zone expansion are consequences of global warming....
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