A High Resolution Coupled Sea-Ice/Ocean Model for the Antarctic Peninsula Region Michael S. Dinniman John M. Klinck Center for Coastal Physical Oceanography Old Dominion University See also (poster this evening): West Antarctic Peninsula Circulation and Implications for Biological Production: Andrea Piñones et al. Good morning. I’d like to present some work we’re doing with a coupled sea-ice/ocean model for the Antarctic Peninsula Region

Outline of Presentation Introduction and Model Description Ice Shelf Modeling Sea Ice Modeling Cross-shelf Transport Future plans Conclusions

Research Questions What is the magnitude and extent of cross-shelf exchange? What is the structure of the circulation on the WAP shelf? What are the circulation dynamics that drive the coastal current? Which physical processes are responsible for exchanges across the permanent pycnocline? What processes control sea ice in the region? This model was funded to help answer questions on how the circulation affects ecosystems in the Southern Ocean GLOBEC region. Five research questions from the proposal…how can the model help answer these? What do we need in a circ. model to help answer?

Antarctic Peninsula Model ROMS: 4 km horizontal resolution, 24 levels Ice shelves (mechanical and thermodynamic) Imposed sea ice or dynamic sea ice model Bathymetry: ETOPO2v2 + WHOI SOGLOBEC region + Padman grid + BEDMAP + Maslanyj Open boundaries: T + S set to SODA, barotropic V relaxed to SODA, baroclinic V pure radiation Daily wind forcing from a blend of QSCAT data and NCEP reanalyses or Antarctic Mesoscale Prediction System (AMPS) winds Other atmospheric parameters from several sources (including AMPS) ROMS: Regional Ocean Modeling System: hydrostatic finite difference OGCM with a terrain following vertical coordinate. Need to define two bathymetric surfaces now w/ the ice shelves. SODA: 1958-2001 Ocean Reanalysis (uses 0.25x0.4 deg version of POP). Note that this model is still under development.

Mention ice shelves. Kept Larsen B because we’re supposed to run this during the SOGLOBEC field season.

Ice Shelf Modeling Ice Shelf basal melt can add large amounts of freshwater to the system (George VI estimated basal melt: 2-5 m/yr) Ice Shelf does not change in time in model Three equation viscous sub-layer model for heat and salt fluxes (Holland and Jenkins 1999) PGF calculation assumes the ice shelf has no flexural rigidity and pressure at the base comes from the floating ice Had to put ice shelves in because GVI has massive melt (2-5 m/yr) which leads to a large amount of fresh water from the north end of ice cavity flowing out into MB, which could effect the circulation in the area we care about. 3 eqn’s: conservation of heat, conservation of salt, freezing point dependence on salt and pressure. No flexural rigidity assumption is fine except w/i a few km of the coast. Assumes viscous sub-layer is at freezing. Can have fancy physics in the transfer coeffs. Three eqns. can be solved simultaneously

Model average velocity Melting leads to freshwater in the sfc. coming out on the left side. Explain bottom velocities (zero line, color contours, relative velocity from geostrophy and estimate of absolute velocity from inversion of tracer conservation equations). Just say this is an estimate of total (not relative) velocity. Model average velocity (net through flow: 0.09 Sv.) Potter and Paren (top,1985) and Jenkins and Jacobs (bottom, 2008, net S to N through flow 0.17-0.27 Sv.)

Sea Ice Modeling Budgell (2005) model (built into ROMS) - Thermodynamics based on Mellor and Kantha (1989) with two ice layers, a snow layer, surface melt ponds and a molecular sub layer at the ice/ocean interface - Dynamics based on an elastic-viscous-plastic rheology after Hunke and Dukowicz (1997) and Hunke (2001) Los Alamos CICE available, but not using yet due to time constraints CICE is much more complicated thermodynamically (has several ice classes), but the dynamics are similar. Sinan has it working for the Ross, but it just about doubles the time. Budgell’s model is only ~20% more expensive since it’s less complicated and integrated into the code.

Model daily ice concentration (12/24/03 – 5/23/04) Put movie here. We don’t have tides, so the sloshing around on several day time scales is in response to the wind.

model ice concentration SSM/I ice concentration January 2001 January 2002 The seasonal cycle of the sea ice is determined thermodynamically, but the winds are very important in making interannual changes. In this simulation, all the forcing is climatological EXCEPT the winds…we can capture the interannual variability pretty well here (w/ just winds). model ice concentration SSM/I ice concentration

Maximum temperature below 200 m from observations. Klinck et al., 2004 One of the things we want to look at is cross shelf exchange. Maximum temperature below 200 m from observations. Klinck et al., 2004 Trajectories of model floats released along the shelf break to show cross- shelf exchange. Piñones et al., poster this evening

Future Plans Validation of this model 1 km nested model in MB CICE sea ice model? Bathymetry: new Smith and Sandwell, other updates? Different atmospheric forcing experiments Lower trophic level ecosystem model Lower trophic level model will have functional groups of phytoplankton (akin to NEMURO)

Conclusions Model is still a work in progress Several model features appear to be working well - George VI Ice Shelf and supply of fresh water to Marguerite Bay - Sea ice model and interannual variability of ice concentration Model should be a useful tool for studying effects of circulation on ecosystems in the region

Acknowledgements AMPS winds courtesy of John Cassano (U. Colorado) Computer facilities and support provided by the Center for Coastal Physical Oceanography Financial support from the U.S. National Science Foundation (ANT-0523172)

Based on Smith and Sandwell Tom Bollmer may be interested in this (if he doesn’t know about it already). Bathy is key. ETOPO2 is the background for the WHOI, ESR and ODU stuff. I think I’m going to do at least one more update of the bathymetry. Look at 72S transition, Ronne entrance, Weddell slope. Based on Smith and Sandwell (v8.2, only north of 72S) Smith andSandwell (v 9.2)

Much warmer water entering the ice shelf cavity than Ross => Much greater melting: 2.1 m/yr (Potter and Paren, 1985) 2.8 m/yr (Corr et al., 2002) 3.1-4.8 m/yr (Jenkins and Jacobs,2008) We’re primarily looking at GVI right now as a source of fresh water for our simulation. The melting here is so large that we have to be more careful than for the Ross model. Note the melting is very inhomogeneous Model average basal melt under GVI: 6.2 m/yr Jenkins and Jacobs, 2008

Model average velocity 50m below surface (free surface or ice shelf) Note: This is distance below surface (whether free surface or ice). Shallow flow to the left. Deep flow: in in the north on the right, in on the left in the south (hence high melting along northern edge). Model average velocity 50m below surface (free surface or ice shelf) Model average velocity 400m below surface (free surface or ice shelf)

AMPS Forcing Antarctic Mesoscale Prediction System: Quasi-Operational atmospheric forecast system in use for the Antarctic Currently based on PMM5, but transitioning to WRF We have an archive of analyses and forecasts from 30km grid for 2001-2005 (but much of our model domain not covered before 11/02)

Model ice concentration: AMPS winds QSCAT/NCEP winds Model ice concentration: October 2004 We figured the AMPS winds would be better everywhere, but it’s not that simple. Sea ice can actually be a good marker for wind effects and here, even though the ice edge is pretty much the same, the concentrations are much better with the blended winds. Note the only difference between the two simulations here was the winds. SSM/I: October 2004

QSCAT/NCEP winds AMPS winds Note: AMPS winds “feel” the mountain chain better, but the blended winds (esp. beyond the ice edge) are based on real data. QSCAT/NCEP winds AMPS winds

Xie and Arkin Precipitation AMPS Precipitation (9/03-9/05, m/yr) Xie and Arkin Precipitation (m/yr)

Summer surface velocity Original forcing Summer surface velocity These are from runs with imposed sea ice and the AMPS run is still going on as we speak. Both simulations have a coastal current in the fall, but the new forcing starts one in the summer, has a better cyclonic flow around MB and has a better current along the shelf break. Summer surface velocity Original forcing Summer surface velocity AMPS forcing

Model ice concentration: AMPS winds QSCAT/NCEP winds Model ice concentration: November 2004 SSM/I: November 2004

Model ice concentration: AMPS winds QSCAT/NCEP winds Model ice concentration: February 2005 SSM/I: February 2005