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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Apr 2019

Research article | 23 Apr 2019

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

Zooplankton diel vertical migration and downward C into the Oxygen Minimum Zone in the highly productive upwelling region off Northern Chile

Pritha Tutasi1,3,4 and Ruben Escribano2,3 Pritha Tutasi and Ruben Escribano
  • 1Doctoral Program of Oceanography, Universidad de Concepción, Chile
  • 2Department of Oceanography and Instituto Milenio de Oceanografía (IMO), Facultad de Ciencias Naturales y Oceanográficas, Chile
  • 3Universidad de Concepción, Concepción, P.O. BOx 160 C, Chile
  • 4Dirección de Oceanografía Naval, Instituto Oceanográfico de la Armada (INOCAR), Guayaquil, Ecuador

Abstract. The daily vertical movement of zooplankton, known as diel vertical migration (DVM), can enhance the vertical flux of carbon (C) and so contributing to the functioning of the biological pump. The magnitude and efficiency of this active transport of C may depend on the size and taxonomic structure of the migrant zooplankton. However, the impact that a variable community structure can have on zooplankton-mediated downward C has not been properly addressed. This taxonomic effect may become critically important in highly productive eastern boundary upwelling systems (EBUS), where zooplankton biomass becomes aggregated in the coastal zone, but comprised by a highly variable community structure (size-composition). In these systems, presence of a subsurface oxygen minimum zone (OMZ) can impose an additional constraint to vertical migration and so influencing the downward C export. Here, we address these issues based on a high-resolution zooplankton sampling at three stations off northern Chile (20°S−30°S) during November 2015. Automated analysis of zooplankton composition and taxa-structured biomass allowed us to estimate daily migrant biomass by taxa, amplitude of migration and daily rate of migration, defined as the daily exchange of biomass between the upper mixed layer and below the thermocline. We found that high biomass aggregates above the oxycline, associated with more oxygenated surface waters and this condition was more evident upon a more intense OMZ. Some taxa however, were found closely associated with the OMZ. We found that most taxa were able to perform DVM in the upwelling zone withstanding severe hypoxia. Even, several strong migrants, such as copepods Eucalanidae and Euphausiids, can exhibit a large migration amplitude (~500 m), remaining either temporarily or permanently during the day or night condition within the core of the OMZ and so contributing to the release of C below the thermocline. Our estimates of DVM-mediated C flux showed that migrant biomass (5099 ± 2701 mg C m−2d−1) may contribute with about 678 ± 465 mg C m−2d−1 to the OMZ system through respiration, mortality, and production of fecal pellets, implying the existence of a very efficient mechanism to incorporate freshly produced C into the OMZ. This downward C by zooplankton is however strongly depending on taxonomic structure due to variable migration amplitude and behavior affecting the daily rate of diel vertical migration.

Pritha Tutasi and Ruben Escribano
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Status: open (until 04 Jun 2019)
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Pritha Tutasi and Ruben Escribano
Pritha Tutasi and Ruben Escribano
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Short summary
Vertical migration of zooplankton has rarely been studied under the effect of a variable community structure which depending on the behavior and size of its groups can strongly alter the magnitude of C being actively taken to depth by migrants. Here, we address this issue in a highly productive upwelling system where a high amount of zooplankton can daily move below the mixed layer despite presence of an extremely low-oxygen water and so contributing to a significant export of C to depth.
Vertical migration of zooplankton has rarely been studied under the effect of a variable...