HR: 1340h
AN: GC43A-0951 [WITHDRAWN]    [Abstracts]
TI: Changes in the Subduction of Southern Ocean Water Masses in ten IPCC Models
AU: * Downes, S M
EM: s.downes@utas.edu.au
AF: Institute of Antarctic & Southern Ocean Studies, University of Tasmania, Private Bag 77, Hobart, TAS 7001, Australia
AU: * Downes, S M
EM: s.downes@utas.edu.au
AF: Antarctic Climate and Ecosystems CRC, Univeristy of Tasmania, Private Bag 80, Hobart, TAS 7001, Australia
AU: Bindoff, N L
EM: N.Bindoff@utas.edu.au
AF: Institute of Antarctic & Southern Ocean Studies, University of Tasmania, Private Bag 77, Hobart, TAS 7001, Australia
AU: Bindoff, N L
EM: N.Bindoff@utas.edu.au
AF: Antarctic Climate and Ecosystems CRC, Univeristy of Tasmania, Private Bag 80, Hobart, TAS 7001, Australia
AU: Bindoff, N L
EM: N.Bindoff@utas.edu.au
AF: CSIRO Marine and Atmospheric Research, Hobart Tasmania, Castray Esplanade, Hobart, TAS 7000, Australia
AU: Rintoul, S R
EM: steve.rintoul@csiro.au
AF: Antarctic Climate and Ecosystems CRC, Univeristy of Tasmania, Private Bag 80, Hobart, TAS 7001, Australia
AU: Rintoul, S R
EM: steve.rintoul@csiro.au
AF: CSIRO Marine and Atmospheric Research, Hobart Tasmania, Castray Esplanade, Hobart, TAS 7000, Australia
AB: The Southern Ocean's Subantarctic Mode and Antarctic Intermediate water masses dominate the oceanic uptake of anthropogenic CO₂ and store heat, freshwater and dissolved gases. We analyse the ocean's response to changes in surface forcing using two different methods and across ten models from the IPCC Fourth Assessment Report. We compare the 1950's 20^th century mean climate and the 2090s A2 scenario, where CO₂ concentration reaches 860 ppm by the year 2100. Subduction rates are analysed on density surfaces (which evolve with time) and on surfaces that are fixed in time, defined by the position of density surfaces in the 1950s. We diagnose the subduction and entrainment rates of mode and intermediate water masses on both surfaces. The model means show a decrease in the subduction rates resulting from warming and freshening at the ocean's surface in the South-east Indian and Pacific Oceans. A corresponding cooling and freshening is found on density surfaces within the ocean interior in these two water masses (upper 1500 m) and compare well with observations. There is a gain in the net surface buoyancy flux at mode water densities due to the increased northward Ekman transport. The surface buoyancy flux decrease at intermediate water densities is dominated by warmer surface waters and to a lesser extent by the surface heat fluxes and through increases in the vertical stratification below the mixed layer. Our multi-model analysis shows a decrease in the renewal rates of Southern Ocean water masses and hence affecting the uptake of anthropogenic CO₂.
DE: 0399 General or miscellaneous
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting