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NASA ROSES – Interdisciplinary Research in Earth Science (IDS)
Linking Greenland ice sheet mass loss to decadalcirculation changes in the ocean and atmosphere
Patrick Heimbach*, MITGordon Hamilton*, U. Maine
Eric Larour*, JPLDimitris Menemenlis*, JPL
An T. Nguyen*, MITFiammetta Straneo*, WHOI
Ian Fenty, JPL Eric Rignot, UC Irvine
*: Co-PI’s
Rationale: Widespread retreat, thinning, acceleration of Greenland’s marine-terminating outlet glaciers over the last decade
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
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)
A focus: Circum-Greenland ocean circulation variabilityInitial study by Rignot, Fenty, et al., Annals Glaciol., 2012
Rationale for nested approach
non-optimized
optimized
Solutions from decadaladjoint-based optimizedstate estimates arehighly appropriate for useas initial and boundaryconditions in higher-res.estimates.
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)
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 modelJenkins (2011)
(rescaled)typical discharge ratesfor Sermilik Fjord
line plume theory: Q ~ B1/3 z, with B = g’ Qsg / L
Second study site: 79North
1 km bathymetry
See Seroussi et al., GRL, 2011for glacier modeling of 79North