On the Estimation of Zooplankton-Mediated Active Fluxes in Oxygen Minimum Zone Regions.

Kiko, Rainer and Hauss, Helena (2019) On the Estimation of Zooplankton-Mediated Active Fluxes in Oxygen Minimum Zone Regions. Open Access Frontiers in Marine Science, 6 . Art.Nr. 741. DOI 10.3389/fmars.2019.00741.

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Abstract

In the Peruvian upwelling system, the mesopelagic oxygen minimum zone (OMZ) is the main vertically structuring feature of the pelagic habitat. Several zooplankton and nekton species undertake diel vertical migrations (DVMs) into anoxic depths. It has been argued that these migrations contribute substantially to the oxygen consumption and release of dissolved compounds (in particular ammonium) in subsurface waters. However, metabolic suppression as a response to low ambient oxygen partial pressure (pO2) has not been accounted for in these estimates. Here, we present estimates of zooplankton- and nekton-mediated oxygen consumption and ammonium release based on vertically stratified net hauls (day/night, upper 1,000 m). Samples were scanned, followed by image analysis and size-/taxon-specific estimation of metabolic rates of all identified organisms as a function of their biomass as well as ambient temperature and pO2. The main crustacean migrants were euphausiids (mainly E. mucronata) on offshore stations and the commercially exploited squat lobster Pleuroncodes monodon on the upper shelf, where it often undertakes migration to the seafloor during the day. Correction for metabolic suppression results in a substantial reduction of both respiration and ammonium excretion within the OMZ core. Ignoring this mechanism leads to a 10-fold higher estimate of DVM-mediated active export of carbon by respiration to below 100 m depth at deep-water stations. The DVM-mediated release of ammonium by euphausiids into the 200–400 m depth layer ranges between 0 and 36.81 μmol NH4 m−2 d−1, which is insufficient to balance published estimates of ammonium uptake rates due to anammox. It seems critical to account for the modulation of zooplankton metabolic activity at low oxygen in order to correctly represent the contribution of migrating species to the biological pump.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-OEB Ökosystembiologie des Ozeans
OceanRep > SFB 754
OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-B Experimental Ecology - Benthic Ecology
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.3389/fmars.2019.00741
ISSN: 2296-7745
Projects: SFB754
Expeditions/Models/Experiments:
Date Deposited: 13 Dec 2019 08:01
Last Modified: 27 Mar 2020 09:08
URI: http://oceanrep.geomar.de/id/eprint/48434

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