CURRENT NEWS

Kerguelen Axis 2015-16

Marine science activities in support of research and observing of marine ecosystems in the vicinity of the Kerguelen Axis during 2015-16 austral summer

A.J. Constable1,2, S. Aoki11, S. Blain4, A. Bowie2,3, P. Boyd2,3, Z. Chase3, S. Corney2, C. Cotté4,5, M. Cox1,2, L. Clarke2, B. Deagle1,2, M. Double1,2, H. Doyle2, L. Emmerson1,2, M. Hindell2,3, T. Holmes2,3,S. Kawaguchi1,2, M. Kawai6, P. Koubbi4,5, E. Laurenceau2, A. Macdonald9, C. LoMonaco4, A. McMinn2,3, J. Melbourne-Thomas1,2, M. Moteki6, I. Obernosterer4T. Odate7, H. Perez-Tribouilliers3, H. Phillips2,3, L. Ratnarajah2,3S. Rintoul2,8, C. Schallenberg2, C. Southwell1,2, K. Swadling2,3, K. Takahashi7, L. Talley10, B. Tilbrook2,8, R. Trebilco2, M. Tonnard2,3T.W. Trull2,8, P. van der Merwe2A. Walters3, D. Welsford1,2, K. Westwood1,2, B. Wojtasiewicz8, K. Wuttig2,8.

The Southern Ocean is one of the most rapidly changing environments on Earth. Key questions for understanding the consequences of change in the region include: (i) Will southward movement of the ocean fronts, as well as the extent of winter sea ice, give rise to a contraction in the northern range of polar species such as Antarctic krill?  (ii) How will productivity of the region change as a result of changing attributes of physical habitats in areas of iron supply?  (iii) What factors might give rise to a shift from a krill-based food web to a food web based on copepods and fish?  These questions are central to management of fisheries and conservation in the region.  Important to managers is the question on how to most efficiently monitor the ecosystem to determine whether such changes are arising or may arise in the near future.  This last question is central to developing biological capability within the Southern Ocean Observing System.

Drivers of food webs in the Southern Ocean include bottom topography, the Antarctic Circumpolar Current (ACC), its associated fronts including its southern boundary, coastal currents and gyres, seasonal extent of sea ice, and locations of primary production, which are often associated with hot spots of iron supply.  Our ability to answer the questions above will be determined, in part, by our ability to assess the relative importance of these drivers in Southern Ocean ecosystems.

The Kerguelen Plateau and its associated marine food webs, including those near the Antarctic continent, form an axis in the Indian Sector of known high productivity.  Unlike many other regions of the Southern Ocean, the Kerguelen Axis (Figure 1) is a place where environmental drivers of the ecosystem can be differentiated from one another. A marine science program over the southern area of the Kerguelen Plateau will be undertaken by the RV Aurora Australis in January-February 2016 by a number of Australian researchers from the Australian Antarctic Division, CSIRO, Institute of Marine and Antarctic Studies, Antarctic Climate and Ecosystems Cooperative Research Centre and the Gateway Research Partnership (orange track Figure 1).  This program will use CTD and trace metal casts along with float deployments for physical, biogeochemical and microbial sampling.  Biota will be sampled by using underway active acoustics, a continuous plankton recorder, Rectangular Midwater Trawls and International Young Gadoid Pelagic Trawls with depth stratified codends.  The three main aims are to determine the northern limit of Antarctic krill distribution, the relative importance of different environmental drivers of that distribution, and the relative importance of copepods and mesopelagic fish in different habitats for the pelagic food web within this region.  The program will also provide a basis for determining the supply of iron to the biogeochemical cycles supported in this region and for assessing Antarctic Bottom Water and its flow up the eastern margin of the Kerguelen Plateau, around the Australian Antarctic Basin.  In addition to these goals, the data collected will provide a foundation for identifying ecosystem essential ocean variables (eEOVs) for measuring ecosystem change in the region.

Five other marine science voyages will occur in the Indian Sector of the Southern Ocean in the same time frame as the RV Aurora Australis voyage (Figure 1).  They will provide an excellent opportunity to enhance the physical, biogeochemical, active acoustic, and biological sampling.  These other voyages include the RV Investigator (Australia – oceanography, biogeochemistry, acoustics, continuous plankton recorder, plankton), RV Umitaka Maru (Japan - oceanography, continuous plankton recorder), RV Hakuho Maru (Japan - physical oceanography), RV Marion Dufresne (France – physical oceanography, biogeochemistry, acoustics, continuous plankton recorder) and RV Roger Revelle (USA – physical and biogeochemical oceanography).  More than 25 profiling floats will be deployed on the various voyages, including 17 biogeochemical floats deployed as part of the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) program. The combined datasets will provide a unique multi-disciplinary snapshot of the physical, chemical and biological state of the Kerguelen Axis region.  Comparison of these observations with past and future measurements will allow an assessment of change throughout the full ocean depth.

Data from this research will be synthesised and published in a series of special issues.  The data will be made available through various portals; including the SOOS portal.  The results from the RV Aurora Australis voyage will be made available through the Australian Antarctic Data Centre and, combined with the data from the RV Investigator, through the Integrated Marine Observing System.  The conclusions of this research, including efficient designs for biological observing in the Indian Sector of the Southern Ocean, will be presented to the 2018 Conference on Marine Ecosystem Assessments of the Southern Ocean.

Figure 1: Map showing the Kerguelen Axis in the Indian Sector of the Southern Ocean.  Tracks of vessels undertaking marine science in the region in January-March 2016 are shown. Highlighted features include the Southern Boundary of the Antarctic Circumpolar Current (SB-ACC), the Southern ACC Front (SACCF), the Polar Front (PF), the SubAntarctic Front (SAF), the Sub-Tropical Front (STF) and the northern extent of winter sea ice in October 2015.  Grid is at 10 longitude and 10 degrees latitude.  Vertical meridian is 80°E.  Visible latitude over Antarctica is 70°S.  Sources of data are: Bathymetry - Amante, C. and B.W. Eakins, 2009. ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. NOAA Technical Memorandum NESDIS NGDC-24. National Geophysical Data Center, NOAA. [accessed 2015-07-27].  Max Sea Ice edge (15% concentration) - Monthly maximum compiled from daily October sea ice concentration maps, days "2015-10-09", "2015-10-14" were removed to avoid artefacts. Maslanik, J. and J. Stroeve. 1999, updated daily. Near-Real-Time DMSP SSMIS Daily Polar Gridded Sea Ice Concentrations, Version 1. [Near-real-time Southern Hemisphere, October 2015]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. [accessed November 2015].  Fronts - Orsi, Alejandro H., Thomas Whitworth, and Worth D. Nowlin. "On the meridional extent and fronts of the Antarctic Circumpolar Current." Deep Sea Research Part I: Oceanographic Research Papers 42.5 (1995): 641-673.  Ice shelves and Antarctic continent - Antarctic Digital Database, V6 (supplied by AADC)

 

Acknowledgements

We would like to acknowledge and thank many people for their assistance in preparing for this program, including Rob King, Phil Boxall, Lloyd Symons, Rick van den Enden, Andrew Cawthorn, Michael Sumner, Diana Davies, Ruth Eriksen, Tim Lamb and many others in the Australian Antarctic Division (Australian Department of Environment), Antarctic Climate and Ecosystems Cooperative Research Centre, the Antarctic Gateway Partnership (a Special Research Initiative of the Australian Research Council).

1 Australian Antarctic Division, Kingston, Tasmania, Australia.

2 Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart Tasmania, Australia.

3 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia.

4 Université Pierre et Marie Curie, Paris, France.

5 Muséum National d'Histoire Naturelle, Paris, France.

6 Tokyo University of Marine Science and Technology, Tokyo, Japan.

7. National Institute for Polar Research, Tokyo, Japan.

8 CSIRO Oceans and Atmosphere, Hobart, Tasmania, Australia.

9 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA

10 Scripps Institution of Oceanography, La Jolla, California, USA

11Institute of Low Temperature Science, Hokkaido University, Japan

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