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Discussion papers | Copyright
https://doi.org/10.5194/os-2017-89
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Oct 2017

Research article | 24 Oct 2017

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Ocean Science (OS).

Turbulence and hypoxia contribute to dense zooplankton scattering layers in Patagonian Fjord System

Iván Pérez-Santos1,2, Leonardo Castro2,3, Nicolás Mayorga1, Lauren Ross4, Luis Cubillos2,3, Mariano Gutierrez5, Edwin Niklitschek1, Eduardo Escalona2, Nicolás Alegría6, and Giovanni Daneri2,7 Iván Pérez-Santos et al.
  • 1Centro i~mar, Universidad de Los Lagos, Puerto Montt, Chile
  • 2COPAS Sur-Austral, Universidad de Concepción, Campus Concepción, Víctor Lamas 1290, Casilla 160-C, código postal: 4070043, Concepción, Chile
  • 3Departamento de Oceanografía, Universidad de Concepción, Campus Concepción, Víctor Lamas 1290, Casilla 160-C, código postal: 4070043, Concepción, Chile
  • 4Department of Civil and Environmental Engineering, University of Maine, 5711 Boardman Hall, Orono, ME 04469-5711
  • 5Universidad Nacional Federico Villareal, Facultad de Oceanografía, Pesquerías y Ciencias Alimentarias, Calle Francia 726, Miraflores, Lima, Perú
  • 6Instituto de Investigaciones Pesqueras, Talcahuano, Chile
  • 7Centro de Investigaciones en Ecosistemas de la Patagonia (CIEP), Coyhaique, Chile

Abstract. The Puyuhuapi Fjord is an atypical fjord, with two mouths, located in northern Patagonia (44.7°S). One mouth lies to the south, close to the Pacific Ocean, whilst the second connects with the Jacaf Channel to the north where a shallow sill inhibits deep water ventilation contributing to the hypoxic conditions below ~100m depth. Acoustic Doppler Current Profiler moorings, scientific echo sounder transects, and in-situ abundance measurements were used to study zooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel. The acoustic records and in-situ zooplankton data revealed diel vertical migrations of siphonophores, euphausiids and copepods. A dense layer of zooplankton was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic layer (~100m), which acted as a physic-chemical barrier to the distribution and migration of the zooplankton. Aggregations of zooplankton and fishes were generally more abundant around the sill in Jacaf Channel than anywhere within Puyuhuapi Fjord. In particular, zooplanktons were distributed throughout the entire water column to ~200m depth, with no evidence of a hypoxic boundary. Turbulence measurements taken near the sill in the Jacaf Channel indicated high turbulent kinetic energy dissipation rates (ε ~10−4Wkg−1) and vertical diapycnal eddy diffusivity (Kρ ~10−2m2s−1) values. These elevated vertical mixing ensures that the water column well oxygenated and promotes zooplanktons aggregation. The sill region represents a major topographic contrast between the two fjords, and we suggest that this is an feature for future research on carbon export and fluxes in these fjords.

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Iván Pérez-Santos et al.
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Short summary
Fjord systems play an important role in primary production and carbon export. Acoustic, hydrographic and in-situ abundance measurements were used to study zooplankton assemblages at 44.7° S. Diel vertical migration of zooplankton stopped at the hypoxic boundary layer and apparently did not tolerate the hypoxia conditions. Turbulence appears to be the oceanographic process that contributes to the vertical mixing around sill, helping to the interchange of nutrient, feeding and carbon export.
Fjord systems play an important role in primary production and carbon export. Acoustic,...
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