Circumpolar connections between Antarctic krill ( Euphausia superba Dana) populations: Investigating the roles of ocean and sea ice transport

S.E Thorpe,E.J Murphy,J.L Watkins

doi:10.1016/j.dsr.2007.01.008

S.E Thorpe, E.J Murphy + Show 1 more

Open Access

https://doi.org/10.1016/j.dsr.2007.01.008

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Abstract

Antarctic krill, Euphausia superba Dana, has a heterogeneous circumpolar distribution in the Southern Ocean. Krill have a close association with sea ice which provides access to a critical food source and shelter, particularly in the early life stages. Advective modelling of transport pathways of krill have until now been on regional scales and have not taken explicit account of sea ice. Here we present Lagrangian modelling studies at the circumpolar scale that include interaction with sea ice. The advection scheme uses ocean velocity output from the Ocean Circulation and Climate Advanced Modelling (OCCAM) project model together with satellite-derived sea ice motion vectors to examine the potential roles of the ocean and sea ice in maintaining the observed circumpolar krill distribution. We show that the Antarctic Coastal Current is likely to be important in generating the large-scale distribution and that sea ice motion can substantially modify the ocean transport pathways, enhancing retention or dispersal depending upon location. Within the major krill region of the Scotia Sea, the effect of temporal variability in both the ocean and sea ice velocity fields is examined. Variability in sea ice motion increases variability of influx to South Georgia, at times concentrating the influx into pulses of arrival. This variability has implications for the ecosystem around the island. The inclusion of sea ice motion leads to the identification of source regions for the South Georgia krill populations additional to those identified when only ocean motion is considered. This study indicates that the circumpolar oceanic circulation and interaction with sea ice is important in determining the large-scale distribution of krill and its associated variability.

Highlights

Zooplankton are major grazers of phytoplankton and have an important role in determining the fate of carbon fixed in the upper ocean (Banse, 1995)
To examine the mean ocean circulation simulated by Ocean Circulation and Climate Advanced Modelling project (OCCAM), particles were tracked in the climatological velocity fields for 10 years [Fig. 2(a)]
Westward sea ice motion close to the continent is connected to eastward motion associated with the ACC by areas of northward sea ice movement, from the main coastal embayments of the Weddell and Ross Seas and Prydz Bay

Summary

Introduction

Zooplankton are major grazers of phytoplankton and have an important role in determining the fate of carbon fixed in the upper ocean (Banse, 1995). Within ocean ecosystem models developed for analysing carbon budgets, zooplankton are often represented as single compartments with no structure based on the model of Fasham et al (1990). This may be sufficient to represent small, fast growing microzooplankton Popova et al, 2002), but is not a realistic representation for zooplankton that have complex life cycles, live 1, 2 or more years and may undergo vertical migrations of over 1000 m and horizontal movements of over 1000 km For such species more complex models are required that consider the changes in biological–physical process interactions during development. Developing more realistic models for other ocean ecosystems that include the life-cycles of key zooplankton species and their interactions with the physical environment is a key goal of global ocean ecosystem research

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