Icebergs, Ice Shelves and Sea Icebergs, Ice Shelves and Sea Ice: A ROMS Study of the Ice: A ROMS Study of the

Southwestern Ross Sea for Southwestern Ross Sea for 2001-20032001-2003

Michael S. DinnimanMichael S. DinnimanJohn M. KlinckJohn M. Klinck

Center for Coastal Physical Center for Coastal Physical OceanographyOceanography

Old Dominion UniversityOld Dominion University

Walker O. Smith, Jr.Walker O. Smith, Jr.Virginia Institute of Marine ScienceVirginia Institute of Marine Science

College of William and MaryCollege of William and Mary

Outline of PresentationOutline of Presentation

• Motivation for study• Describe circulation model and ice shelf modeling• Ross Ice Shelf basal melt• Changes in HSSW production• Iceberg effects in McMurdo Sound• 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• Development of high resolution (5 km) regional ocean circulation model to examine physical environment and marine ecosystems

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• Bathymetry from ETOP05 and BEDMAPBathymetry from ETOP05 and BEDMAP• Ice Cavities (Ice thickness from BEDMAP)Ice Cavities (Ice thickness from BEDMAP) - Mechanical and thermodynamic effects- Mechanical and thermodynamic effects• Includes macro-nutrients and nutrient Includes macro-nutrients and nutrient

uptakeuptake

Ice Shelf ModelingIce Shelf Modeling • PGF calculation assumes the ice shelf PGF calculation assumes the ice shelf

has no flexural rigidity and pressure at has no flexural rigidity and pressure at the base comes from the floating icethe base comes from the floating ice

• Thermodynamics: viscous sublayer Thermodynamics: viscous sublayer model:model:

Idealized Test Cases (ISOMIP: D. Holland et al.)

ROMS MOM2 – K. GrosfeldMICOM – D. Holland

Idealized Test Case: Start w/ uniform water at -1.9 C, 34.4 psu and integrate for 30 yrs.

All models have ~ 0.1 Sv. of overturning

Circulation Model Circulation Model (cont.)(cont.) • Imposed sea iceImposed sea ice - 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

• Bulk flux algorithm (COARE 2.0) for open Bulk flux algorithm (COARE 2.0) for open waterwater

• Daily wind stress and wind speed from a Daily wind stress and wind speed from a blend of QSCAT data and NCEP analysesblend of QSCAT data and NCEP analyses

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 and atmospheric climatologies of sea ice and atmospheric valuesvalues

• Three simulations continue from the spin up Three simulations continue from the spin up forced by daily winds for 9/2001 – 9/2003:forced by daily winds for 9/2001 – 9/2003:

- VARICE: Uses observed sea ice for 9/2001-- VARICE: Uses observed sea ice for 9/2001-9/20039/2003

- CLMICE: Uses climatological sea ice- CLMICE: Uses climatological sea ice - ICEBERG: VARICE + Stationary B-15A - ICEBERG: VARICE + Stationary B-15A

Mean annual average basal melt rate (2nd

year):

CLMICE: 14.0 cm/yrVARICE: 12.6 cm/yr

Climatology Datacourtesy of Chrissy Stoverand Alex Orsi

The difference insalt flux over timeis close to zero except for winter2002.

Even in winter 2002the difference inadvection is moreimportant than thevertical diffusion.

Ice Draft (No Iceberg) Ice Draft (Iceberg)

30m temp (1/22/02)VARICE

30m temp (1/22/02)ICEBERG

30m temp (1/17/03)CLMICE

30m temp (1/17/03)ICEBERG

Extra sea ice ineastern McMurdoin Feb. 2002, butmuch more in Feb.2003 even afterthe Ross Sea Polynya opened up

The iceberg blockedsome of the Ross SeaPolynya heat from entering McMurdoSound. However, abigger effect was thelimited opening of thepolynya in summer2002-2003 (due to C-19).

ConclusionsConclusions

• Interannual sea ice differences can have Interannual sea ice differences can have an effect on Ice Shelf Water and High an effect on Ice Shelf Water and High Salinity Shelf Water – implications for Salinity Shelf Water – implications for large-scale thermohaline circulationlarge-scale thermohaline circulation

• Icebergs B-15A and C-19 both had an Icebergs B-15A and C-19 both had an

effect on the advection of warm surface effect on the advection of warm surface water into McMurdo Sound – large water into McMurdo Sound – large icebergs can potentially greatly alter local icebergs can potentially greatly alter local environmental conditions and local environmental conditions and local ecosystemsecosystems

Future PlansFuture Plans

• TidesTides• Dynamic sea-ice (previous talk)Dynamic sea-ice (previous talk)• Bio-optical primary production modelBio-optical primary production model• Better bathymetryBetter bathymetry• AMPS forcingAMPS forcing

AcknowledgementsAcknowledgements

• BEDMAP data courtesy of the BEDMAP BEDMAP data courtesy of the BEDMAP consortiumconsortium

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

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

Annual average basal melt rate (cm/yr): CLMICE

Summer Average (20m, CLMICE)

Summer Average(20m, ICEBERG)