Production and Export of High Salinity Shelf Water in a Model of the Ross Sea Michael S. Dinniman Y. Sinan Hüsrevoğlu John M. Klinck Center for Coastal Physical Oceanography Old Dominion University

Outline of Presentation Motivation for model Description of circulation model High Salinity Shelf Water on the shelf High Salinity Shelf Water at the NW shelf break Conclusions

Motivation Large interannual variability in the observed sea ice recently ( ) at least partially due to several large icebergs (C-19 and B-15) Difficult to model with dynamic sea ice model => imposed sea ice model Also interested in dynamics of polynyas (and their effect on water masses) => dynamic sea ice model Development of high resolution (5 km) regional ocean circulation model to examine physical environment and marine ecosystems during this period

Image courtesy of AMRC – U. Wisc. (Jan 2003)

Ross Sea Model ROMS (Regional Ocean Modeling System) ROMS (Regional Ocean Modeling System) - Free surface, hydrostatic, primitive equation ocean general circulation model in terrain-following coordinates - Free surface, hydrostatic, primitive equation ocean general circulation model in terrain-following coordinates 5 km grid spacing, 24 vertical levels 5 km grid spacing, 24 vertical levels Quadratic bottom stress (3 x ) Quadratic bottom stress (3 x ) Small (tracers 5.0 m 2 /s, momentum 0.1 m 2 /s) horizontal mixing on geopotential surfaces Small (tracers 5.0 m 2 /s, momentum 0.1 m 2 /s) horizontal mixing on geopotential surfaces KPP vertical mixing (including surface boundary layer, but not bottom boundary layer) KPP vertical mixing (including surface boundary layer, but not bottom boundary layer)

Ross Sea Model (cont.) Original bathymetry from ETOPO5 and BEDMAP (new bathymetry, including Davey data, in testing) Original bathymetry from ETOPO5 and BEDMAP (new bathymetry, including Davey data, in testing) Ice Cavities (Ice thickness from BEDMAP) Ice Cavities (Ice thickness from BEDMAP) - Mechanical and thermodynamic effects - Mechanical and thermodynamic effects Daily winds Daily winds - Blend of QSCAT data/NCEP reanalyses - Blend of QSCAT data/NCEP reanalyses - ECMWF reanalyses (ERA-40) - ECMWF reanalyses (ERA-40) - AMPS analyses and forecasts - AMPS analyses and forecasts No tides No tides Includes macro-nutrients and nutrient uptake Includes macro-nutrients and nutrient uptake

Sea Ice Imposed sea ice Imposed sea ice - Easier, will represent coastal polynyas, gets ice correct in presence of icebergs - Easier, will represent coastal polynyas, gets ice correct in presence of icebergs - Set model ice concentration to SSM/I 25km data - Set model ice concentration to SSM/I 25km data - Heat and salt fluxes computed from thermodynamic calculation of ice freezing or melting, but ice is not accumulated or transported - Heat and salt fluxes computed from thermodynamic calculation of ice freezing or melting, but ice is not accumulated or transported Dynamic sea ice model Dynamic sea ice model - CICE 3.1 (Hunke and Dukowicz, 1997;2002) - CICE 3.1 (Hunke and Dukowicz, 1997;2002) - 5 ice categories with 4 layers in each - 5 ice categories with 4 layers in each - One snow layer for each ice category - One snow layer for each ice category - Elastic-Viscous-Plastic rheology - Elastic-Viscous-Plastic rheology - Coupled to ROMS with WRF I/O API MCT - Coupled to ROMS with WRF I/O API MCT

Experiments Model is initialized in mid-September and spun up for 6 years with a 2-year repeating cycle of daily winds and monthly climatologies of sea ice Model is initialized in mid-September and spun up for 6 years with a 2-year repeating cycle of daily winds and monthly climatologies of sea ice Three simulations continue from the spin up forced by daily winds for at least two years Three simulations continue from the spin up forced by daily winds for at least two years - IICE: Imposed sea ice and daily winds from QSCAT/NCEP - IICE: Imposed sea ice and daily winds from QSCAT/NCEP - DICE: Dynamic sea ice and daily winds from ERA-40 - DICE: Dynamic sea ice and daily winds from ERA-40 - DICE+: Dynamic sea ice, winds from ERA-40 and AWS winds around Terra Nova Bay - DICE+: Dynamic sea ice, winds from ERA-40 and AWS winds around Terra Nova Bay

Salinity cross section: IICE experiment and climatology (climatology courtesy Chrissy Wiederwohl and Alex Orsi)

TNB polynya is formed and maintained by persistent westerly katabatic winds which average 13 m/s and are stable tens of kms offshore (Bromwich and Kurtz, 1984).

Annual Average Wind Stress AWS (DICE+)ECMWF (DICE)

DICE IICE DICE+ Clim 300m mean salinity

High Salinity Shelf Water (S > 34.65, T < -0.5, z < 200m) flux off the entire continental shelf (IICE case) QSCAT/NCEP winds: 1.01 Sv. AMPS winds: 1.41 Sv.

300 m flow Annual average velocity (IICE) Bottom layer flow

IICE: Bottom Salinity 2 – 2.5d timescale for downslope events Does not directly correlate with local winds Dynamical cause?

Sigma-Θ cross section

IICE + Tides: Bottom Salinity

Conclusions The model creates plenty of HSSW on the western continental shelf and transports this to the shelf break The model creates plenty of HSSW on the western continental shelf and transports this to the shelf break - Wind (and bathymetry) details matter - Wind (and bathymetry) details matter Even without tides, we do get pulses of high salinity water to go down the NW shelf break Even without tides, we do get pulses of high salinity water to go down the NW shelf break - Dynamics and accuracy of this remain to be studied - Dynamics and accuracy of this remain to be studied Model may be a useful tool for studying Antarctic overflows Model may be a useful tool for studying Antarctic overflows

Acknowledgements BEDMAP data courtesy of the BEDMAP consortium BEDMAP data courtesy of the BEDMAP consortium AMPS winds courtesy of John Cassano AMPS winds courtesy of John Cassano Computer facilities and support provided by the Center for Coastal Physical Oceanography Computer facilities and support provided by the Center for Coastal Physical Oceanography Financial support from the U.S. National Science Foundation (OPP ). Financial support from the U.S. National Science Foundation (OPP ).

ETOPO5 bathymetryDAVEY bathymetry

VARICE windsAMPS winds Antarctic Mesoscale Prediction System (AMPS): Real-time forecast system for Antarctic (30 km resolution)