1. NASA ROSES – Interdisciplinary Research in Earth Science (IDS) Linking Greenland ice sheet mass loss to decadal circulation changes in the ocean and atmosphere Patrick Heimbach *, MIT Gordon Hamilton *, U. Maine Eric Larour *, JPL Dimitris Menemenlis *, JPL An T. Nguyen *, MIT Fiammetta Straneo *, WHOI Ian Fenty, JPL Eric Rignot, UC Irvine *: Co-PI’s

2. Rationale: Widespread retreat, thinning, acceleration of Greenland’s marine-terminating outlet glaciers over the last decade

3. Causes? Not well understood! Primary mechanisms suggested: –Increased submarine melting at the ice/ocean interface –Reduction or weakening of the ice mélange –Increased crevassing and structural weakening of the glacier from surface warming and melt Climatic drivers: –atmospheric: large-scale atmos. circulation shifts surface warming subglacial discharge of surface melt water –oceanic: ocean warming large-scale ocean circulation shifts

4. Proposed work ASTE as baseline for circum-Greenland circulation variability –assess residual misfits in target region Through hierarchy of nestings: ECCO v4 (LLC90) -> ASTE (LLC270) -> IDS-Greenland (LLC2160), produce solution that is: –very well constrained by observations at open boundaries –produces mesoscale variability for study region of interest Coupling of circum-Greenland circulation to fjord circulation, and thermodynamic terminus melting For two process regions connect to ice sheet model ISSM Work with observationalists (ocean/fjord & outlet glaciers)

5. A focus: Circum-Greenland ocean circulation variability Hakkinen & Rhines (2004)

6. A focus: Circum-Greenland ocean circulation variability Initial study by Rignot, Fenty, et al., Annals Glaciol., 2012

7. Rationale for nested approach non-optimized optimized Solutions from decadal adjoint-based optimized state estimates are highly appropriate for use as initial and boundary conditions in higher-res. estimates.

8. New grids From 1 o (~ 100 km) to 1/48 o (~1 km)

9. Glacier/fjord types e.g.: Helheim Glacier/ Sermilik Fjord e.g.: 79North

10. Initial process study - Sermilik Fjord (NSF-funded) Straneo et al. (2010) AW July 2008 Sept. 2008 Three main water masses in fjord: 1.Fresh, cold, light Polar Waters (PW) 2.Salty, warm, dense Atlantic Waters (AW) 3.Glacial Meltwater (GM) See also: Motyka et al. (2003/11); Rignot et al. (2010)

11. Initial process study - Sermilik Fjord (NSF-funded) Xu et al. 2012, Sciascia et al. (submitted 2012) Mean submarine melt rate as function of subglacial discharge (melt water from glacier surface which drains to the glacier’s bed and discharges at the glacier terminus) Three dynamical regimes MITgcm 1D plume model Jenkins (2011) (rescaled) typical discharge rates for Sermilik Fjord line plume theory: Q ~ B 1/3 z, with B = g’ Q sg / L

12. Initial process study: East Greenland Spill Jet Magaldi et al. (2011)

13. Second study site: 79North 1 km bathymetry See Seroussi et al., GRL, 2011 for glacier modeling of 79North

14. Advertisement (sneak-preview!) An international workshop on ice sheet/ocean/atmosphere interactions in Greenland: Challenges to improving observations, process understanding and modeling Date: June 3-7, 2013 Location: Beverly (near Boston) MA, USA http://www.usclivar.org/meetings/griso-workshop