Production and Export of High Production and Export of High Salinity Shelf Water in a Model Salinity Shelf Water in a Model

of the Ross Seaof the Ross Sea

Michael S. DinnimanMichael S. DinnimanY. Sinan HüsrevoğluY. Sinan Hüsrevoğlu

John M. KlinckJohn M. KlinckCenter for Coastal Physical Center for Coastal Physical

OceanographyOceanographyOld Dominion UniversityOld Dominion University

Outline of PresentationOutline 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

MotivationMotivation• Large interannual variability in the observed sea ice recently (2001-2003) 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 ModelRoss Sea Model

• ROMS (Regional Ocean Modeling System)ROMS (Regional Ocean Modeling System)

- - Free surface, hydrostatic, primitive equation Free surface, hydrostatic, primitive equation ocean general circulation model in terrain-ocean general circulation model in terrain-following coordinatesfollowing coordinates

• 5 km grid spacing, 24 vertical levels5 km grid spacing, 24 vertical levels

• Quadratic bottom stress (3 x 10Quadratic bottom stress (3 x 10-3-3))

• Small (tracers 5.0 mSmall (tracers 5.0 m22/s, momentum 0.1 /s, momentum 0.1 mm22/s) horizontal mixing on geopotential /s) horizontal mixing on geopotential surfacessurfaces

• KPP vertical mixing (including surface KPP vertical mixing (including surface boundary layer, but not bottom boundary boundary layer, but not bottom boundary layer)layer)

Ross Sea Model Ross Sea Model (cont.)(cont.)

• Original bathymetry from ETOPO5 and Original bathymetry from ETOPO5 and BEDMAP (new bathymetry, including BEDMAP (new bathymetry, including Davey data, in testing)Davey data, in testing)

• Ice Cavities (Ice thickness from BEDMAP)Ice Cavities (Ice thickness from BEDMAP)

- - Mechanical and thermodynamic effectsMechanical and thermodynamic effects

• Daily windsDaily 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 tidesNo tides• Includes macro-nutrients and nutrient Includes macro-nutrients and nutrient

uptakeuptake

Sea IceSea Ice

• Imposed sea iceImposed sea ice - - Easier, will represent coastal polynyas, gets ice Easier, will represent coastal polynyas, gets ice

correct in presence of icebergscorrect 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 - Heat and salt fluxes computed from

thermodynamic calculation of ice freezing or thermodynamic calculation of ice freezing or melting, but ice is not accumulated or melting, but ice is not accumulated or transportedtransported

• Dynamic sea ice modelDynamic 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

ExperimentsExperiments

• Model is initialized in mid-September and Model is initialized in mid-September and spun up for 6 years with a 2-year repeating spun up for 6 years with a 2-year repeating cycle of daily winds and monthly cycle of daily winds and monthly climatologies of sea ice climatologies of sea ice

• Three simulations continue from the spin up Three simulations continue from the spin up forced by daily winds for at least two yearsforced by daily winds for at least two years

- IICE: Imposed sea ice and daily winds from - IICE: Imposed sea ice and daily winds from QSCAT/NCEPQSCAT/NCEP

- DICE: Dynamic sea ice and daily winds from - DICE: Dynamic sea ice and daily winds from ERA-40ERA-40

- DICE+: Dynamic sea ice, winds from ERA-40 - DICE+: Dynamic sea ice, winds from ERA-40 and AWS winds around Terra Nova Bayand AWS winds around Terra Nova Bay

Salinity cross section:IICE experiment and climatology (climatologycourtesy ChrissyWiederwohl and AlexOrsi)

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 StressAnnual Average Wind Stress

2000

2001

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

ConclusionsConclusions

• The model creates plenty of HSSW on the The model creates plenty of HSSW on the western continental shelf and transports this western continental shelf and transports this to the shelf breakto the shelf break

- Wind (and bathymetry) details matter- Wind (and bathymetry) details matter

• Even without tides, we do get pulses of high Even without tides, we do get pulses of high salinity water to go down the NW shelf salinity water to go down the NW shelf breakbreak

- Dynamics and accuracy of this remain to be - Dynamics and accuracy of this remain to be studiedstudied

• Model may be a useful tool for studying Model may be a useful tool for studying Antarctic overflowsAntarctic overflows

AcknowledgementsAcknowledgements

• BEDMAP data courtesy of the BEDMAP data courtesy of the BEDMAP consortiumBEDMAP consortium

• AMPS winds courtesy of John CassanoAMPS winds courtesy of John Cassano

• Computer facilities and support Computer facilities and support provided by the Center for Coastal provided by the Center for Coastal Physical OceanographyPhysical Oceanography

• Financial support from the U.S. Financial support from the U.S. National Science Foundation (OPP-National Science Foundation (OPP-03-37247).03-37247).

ETOPO5 bathymetry DAVEY bathymetry

VARICE winds AMPS winds

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