Roosevelt Island – a good place for an ice coreProgress on the RICE Project – Roosevelt Island Climate and Evolution

An international ice coring project on Roosevelt Island in the eastern Ross Sea. Partners from NZ, US, Denmark, UK, Italy, Australia, Germany & China

H. Conway, N. Bertler, D. Dahl-Jensen, A. Pyne, R.C. Hindmarsh, E. Brook, E.D. Waddington, R.L. Hawley, J. Fitzpatrick, S. Kipfstuhl and the RICE Team

NSF-OPP

BAS, USGS, AWI

LGM reconstruction of Ross Sea Sector (adapted from Denton and

Hughes, 2002), constrained by marine data and the geologic record from the TAM in the western Ross Sea.

No geologic dipsticks in the eastern Ross Sea; an ice thickness history is needed to constrain the LGM ice volume

Reconstruction has +500m of ice over running the Island.

MotivationEstablish histories of climate and ice thickness in the eastern Ross Sea

- focus here on the ice-thickness history through the Holocene

1. Help constrain ice volume in the Ross Embayment during the LGM

2. Holocene deglaciation of the Ross Embayment

• two grounding line retreat scenarios, both consistent with geologic data from E. Antarctic outlet glaciers• constraints from the east are also needed

(adapted from Conway et al, 1999)

• coastal dome (bounded to the north by the Bay of Whales)

• rises about 500m above the ice shelf

• about 100 by 60km

• drilling at the northern summit, which is just 4m higher than the southern summit

• a 2-D ridge

Image, from T. Scambos, T. Haran & M. Fahnestock, derived using the Bamber DEM (combines ICESat and radar altimetry); quantitative slope information added using multiple MODIS images.

N

Roosevelt Island today - geometry

• ice thickness h=745m thick at summit; accumulation rate b=0.18m/yr

• characteristic timescale h/b ~4kyr

• A single, well developed stack of Raymond bumps beneath the divide

Roosevelt Island today – radar-detected stratigraphy

Interpretation

Bump-amplitude profile fitted with Dansgaard-Johnson parameterization (Conway et al, 1999) indicates:• not in steady state; thinning of ~ 0.09m/yr for more than 3kyr

• no significant divide migration over past 3kyr• divide-type flow started ~3kyr BP

Interpretation

Matching the bumps with fully coupled thermo-mechanical dynamic model gives similar timing of events (Martin et al., 2006). In addition, they showed:• relatively high power (n=4) rheology needed to match the data (or alternatively, complex variations in grain size or ice fabric; but need an ice core for validation)

• not possible to match the surface profile (but they did not have information about the asymmetric bed topography)

The architecture of the Raymond stack only gives histories back 3-4kyr

- extracting histories farther back in time requires dated layers.

REMINDER: not just climate histories recorded in ice sheets, but also histories of ice dynamics (thinning/thickening)

• in steady state, annual layers get thinner

• layers get thinner even faster when entire ice sheet is also stretched and thinned

• that is, for an accumulation rate history b(t), and past ice dynamics, represented by

thinning function (t)), thickness of a layer at time t is: t(t)b(t)

• a transient ice-flow model needed to investigate possible combinations of (t) and b(t) that are reasonable and match the layer-thickness data, t

Range of depth-age and layer thickness-age relationships expected for Roosevelt Island

- dates needed to constrain the modeled layer-thickness history

Results using a prescribed accumulation history, with thickness histories: 300m thinning since 3kyr BP (red dash-dot line); 600m thinning since 14kyr (black solid line); 1000m thinning since 14kyr.

dates are on the way….

• a new NZ drill (a clone of the Hans Tausen drill) is on site

• trench dug, drill setup

• 130m core recovered is in NZ

• upper borehole cased and fluid filled

• all equipment on site; expect to complete drilling to the bed this coming season

Ice core measurements• visual stratigraphy• ECM• trapped gases (methane)

• stable isotopes• chemistry• MSA• volcanic horizons• black carbon• ice fabric

Borehole measurements• temperature • optical stratigraphy• sonic velocity

Additional measurements

1. Direct measurements of vertical velocity using phase-sensitive radar (Corr et al., 2002; Gillet-Chaulet et al., 2011)

• first measurements made in 2010-11• repeat measurements planned 2012-13

Additional measurements

2. Flux divergence from surface velocity field (142 poles), and radar-detected ice thickness

• use the measurements to calculate spatial patterns of thickness change

3. Map accumulation pattern by tracking radar layers between dated short cores

• first measurements in 2010-11• repeat measurements in 2011-12• repeat measurements planned 2012-13

Summary

Ice-core data

Improved climate and ice sheet

histories

Inverse methods with ice dynamics

Geophysical data

More next year ….. thank you

Camp from space, January 16, 2012