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 variabilityHakkinen & Rhines (2004)

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.

New grids

From

1o (~ 100 km)

to

1/48o (~1 km)

Glacier/fjordtypes

e.g.:Helheim Glacier/Sermilik Fjord

e.g.:79North

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

Initial process study: East Greenland Spill Jet

Magaldi et al. (2011)

Second study site: 79North

1 km bathymetry

See Seroussi et al., GRL, 2011for glacier modeling of 79North

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An international workshop on ice sheet/ocean/atmosphere interactions

in Greenland: Challenges to improving observations, process understanding and modeling

Date: June 3-7, 2013Location: Beverly (near Boston) MA, USA

http://www.usclivar.org/meetings/griso-workshop