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Icebergs, Ice Shelves and Sea Ice: A ROMS Study of the Southwestern Ross Sea for 2001-2003

Icebergs, Ice Shelves and Sea Ice: A ROMS Study of the Southwestern Ross Sea for 2001-2003. Michael S. Dinniman John M. Klinck Center for Coastal Physical Oceanography Old Dominion University Walker O. Smith, Jr. Virginia Institute of Marine Science College of William and Mary.

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Icebergs, Ice Shelves and Sea Ice: A ROMS Study of the Southwestern Ross Sea for 2001-2003

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  1. Icebergs, Ice Shelves and Sea Ice: A ROMS Study of the Southwestern Ross Sea for 2001-2003 Michael S. Dinniman John M. Klinck Center for Coastal Physical Oceanography Old Dominion University Walker O. Smith, Jr. Virginia Institute of Marine Science College of William and Mary

  2. Outline 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

  3. Motivation • 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

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

  5. Ross Sea Model • ROMS (Regional Ocean Modeling System) - Free surface, hydrostatic, primitive equation ocean general circulation model in terrain-following coordinates • 5 km grid spacing, 24 vertical levels • Bathymetry from ETOP05 and BEDMAP • Ice Cavities (Ice thickness from BEDMAP) - Mechanical and thermodynamic effects • Includes macro-nutrients and nutrient uptake

  6. Ice Shelf Modeling • PGF calculation assumes the ice shelf has no flexural rigidity and pressure at the base comes from the floating ice • Thermodynamics: viscous sublayer model:

  7. Idealized Test Cases (ISOMIP: D. Holland et al.) ROMS MICOM – D. Holland MOM2 – K. Grosfeld 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

  8. Circulation Model (cont.) • Imposed sea ice - 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 • Bulk flux algorithm (COARE 2.0) for open water • Daily wind stress and wind speed from a blend of QSCAT data and NCEP analyses

  9. 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 and atmospheric values • Three simulations continue from the spin up forced by daily winds for 9/2001 – 9/2003: - VARICE: Uses observed sea ice for 9/2001-9/2003 - CLMICE: Uses climatological sea ice - ICEBERG: VARICE + Stationary B-15A

  10. Mean annual average basal melt rate (2nd year): CLMICE: 14.0 cm/yr VARICE: 12.6 cm/yr

  11. Climatology Data courtesy of Chrissy Stover and Alex Orsi

  12. The difference in salt flux over time is close to zero except for winter 2002. Even in winter 2002 the difference in advection is more important than the vertical diffusion.

  13. Ice Draft (No Iceberg) Ice Draft (Iceberg)

  14. 30m temp (1/22/02) ICEBERG 30m temp (1/22/02) VARICE

  15. 30m temp (1/17/03) ICEBERG 30m temp (1/17/03) CLMICE

  16. Extra sea ice in eastern McMurdo in Feb. 2002, but much more in Feb. 2003 even after the Ross Sea Polynya opened up

  17. The iceberg blocked some of the Ross Sea Polynya heat from entering McMurdo Sound. However, a bigger effect was the limited opening of the polynya in summer 2002-2003 (due to C-19).

  18. Conclusions • Interannual sea ice differences can have an effect on Ice Shelf Water and High Salinity Shelf Water – implications for large-scale thermohaline circulation • Icebergs B-15A and C-19 both had an effect on the advection of warm surface water into McMurdo Sound – large icebergs can potentially greatly alter local environmental conditions and local ecosystems

  19. Future Plans • Tides • Dynamic sea-ice (previous talk) • Bio-optical primary production model • Better bathymetry • AMPS forcing

  20. Acknowledgements • BEDMAP data courtesy of the BEDMAP consortium • Computer facilities and support provided by the Center for Coastal Physical Oceanography • Financial support from the U.S. National Science Foundation (OPP-03-37247).

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

  22. Summer Average (20m, CLMICE) Summer Average (20m, ICEBERG)

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