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The Strengthening East Australian Current, its eddies and biological effects - an introduction and overview

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Suthers, IM and Young, JW and Baird, ME and Roughan, M and Everett, JD and Brassington, GB and Byrne, M and Condie, SA and Hartog, JR and Hobday, AJ and Holbrook, NJ and Malcolm, HA and Oke, PR and Thompson, PA and Ridgway, KR and Hassler, CS (2011) The Strengthening East Australian Current, its eddies and biological effects - an introduction and overview. Deep-Sea Research, Part 2: Topical Studies in Oceanography, 58 (5). pp. 538-546. ISSN 0967-0645

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Abstract

The poleward flowing East Australian Current (EAC) is characterised by its separation from the coast, 100–200 nautical miles north of Sydney,to form the eastward flowing Tasman Front and a southward flowing eddyfield. The separation zone greatly influences coastal ecosystems for the relatively narrow continental shelf(only15–50kmwide),particularly between 32–341S. In this region the continental shelf has a marked shift in the seasonal temperature-salinity relationship and elevated surface nitrate concentrations.This current parallels the portion of the coast where Australia’s population is concentrated and has a long history of scientific research. However,understanding of physical and biological processes driven by the EAC,particularly in linking circulation to ecosystems,is limited.In this special issue of 16 papers on the EAC,we examine the effects of climatic wind-stress forced ocean dynamics on EAC transport variability and coastal sealevel,from ENSO to multi-decadal timescales; eddy formation and structure;fine scale connectivity and larval retention.Comparisons with the poleward-flowing Leeuwin Current on Australia’s west coast show differences in ecosystem productivity that can be attributed to the under lying physics in each region. On average there is double the chlorophyll a concentration on the east coast than the west.In comparison to the Leeuwin, the EAC may have less local retention of larvae and act as a partial barrier to on shore transport,which may also be related to the local spawning and early life history of small pelagicfishoneach coast.Inter- annual variations in the EAC transport produce a detectable sea-level signal in Sydney Harbour,which could provide a useful fisheries index as does the Fremantle sea level and Leeuwin Current relationship. The EAC’s eddy structure and formation by the EAC are examined. A particular cold-coreeddy is shown to have a ‘tilt’ towards the coast,and that during a rotation the flow of particles may rise up to the euphotic zone and then down beneath.In a warm-coreeddy,surface floodingis shown to produce a new shallower surface mixed layer and promote algal growth.An assessment of plankton data from 1938–1942 showed that the local, synoptic conditions had to be incorporated before any comparison with the present. The reare useful relationships of water mass characteristics in the Tasman Sea and separation zone with larval fish diversity and abundance,as well as with long-line fisheries.These fisheries-pelagic habitat relationships are invaluable for fisheries management,as well as for climate change assessments. There is further need to examine the EAC influence on rainfall,storm activity, dust deposition, and on the movements by fish,sharks and whales. The Australian Integrated Marine Observing System (IMOS)has provided new infrastructure to determine the changing behaviour of the EAC and its bio-physical interaction with the coasts and estuaries. The forecasting and hindcasting capability developed under the Blue link project has provided a new tool for data synthesis and dynamical analysis. The impact of a strengthening EAC and how it influences the livelihoods of over half the Australian population, from Brisbane to Sydney, Hobart and Melbourne, is just being realised.

Item Type: Article
Keywords: East Australian Current; Leeuwin Current; Ecosystem; Separation zone; Finding Nemo; Tasman Front; Integrated Marine Observing System; Bluelink; Mesoscale variation; Eddy; Climatology
Journal or Publication Title: Deep-Sea Research, Part 2: Topical Studies in Oceanography
Page Range: pp. 538-546
ISSN: 0967-0645
Identification Number - DOI: 10.1016/j.dsr2.2010.09.029
Additional Information: The definitive version is available at http://www.sciencedirect.com
Date Deposited: 07 Oct 2011 01:28
Last Modified: 18 Nov 2014 04:22
URI: http://eprints.utas.edu.au/id/eprint/11885
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