Investigating the role of ocean variability on recent polar ice sheet mass loss Ian Fenty Dimitris Menemenlis (JPL/Caltech) Eric Rignot (JPL/Caltech, UCI)

Compiled estimates of the polar ice sheet mass budgets indicate accelerating losses over the past two decades. Ice sheet mass losses may constitute half of observed sea level rise, with significant contributions from both the GrIs and the AIS (Church et al 2011, Rignot 2011) Compilation “The Copenhangen Diagnosis, 2009” Allison et al.

GRACE Mass Trend Adapted from figure courtesy of JPL GRACE team

Nioghalvfjerdsfjorden Zachariae Isstrøm Helheimgletscher Kangerlussuaq Gl. Annual mean ocean temperature at 200 m from 4 km ECCO model Northeast Greenland Southeast Greenland

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Cogley et al., 2011 Glossary of Glacier Mass Balance and Related Terms Total mass balance = SMB - D National Geographic Stock Components of glacier mass balance

The surface mass balance pattern indicates spatial heterogeneities within the ice sheet. In equilibrium, areas with net positive SMB (i.e., net accumulation) must be balanced by ice mass divergence and vice versa. Net surface mass gain: SE and NW Ice mass divergence via a network of small, fast outlet glaciers many of ultimately which terminate in the ocean (MtG or tidewater glaciers) Net surface mass loss: SW and N Ice mass convergence via a few broad, slow moving glaciers. Net Surface Mass Balance (Accumulation – Melt)

Summary Net mass losses in the GrIS since ~ mid 1990s Marine terminating glaciers have also accelerated and thinned Changes in the SMB alone are insufficient to explain losses of such magnitudes Instead, current hypotheses invoke enhanced melting at the ice-ocean interface. Observed ocean temperature and circulation patterns are broadly consistent with the timing and locations of observed glacial mass loss.