Ice-flow history of Thwaites Glacier, West Antarctica
Participants:Ginny Catania (PI), University of Texas at Austin
Joe MacGregor, University of Texas at Austin
Donald Blankenship, University of Texas at Austin
Howard Conway (Co-PI), University of Washington
Funding agency: NSF June 2008 - June 2011
Project Goals:
This
project has a sharply focused scientific goal: to understand the response of
Thwaites Glacier
to recent changes at its grounding line within the context of any possible long-term variability in
mass balance. To this end we concentrate on understanding the controls on fast glacier flow in this
area and search for evidence which allows us to quantify the effect of recent changes in elevation
and grounding line retreat on margin position within the context of longer time-scale retreat. Our
plan is to work with data from groups that have previously visited the region (UTIG and ITASE,
Figure 2) and those that are planning upcoming surveys (PSU/CReSIS) to collect the appropriate
data needed for analysis which allows us to test the following hypotheses related to our goal:
Margin migration: Observed changes in grounding line position and ice sheet elevation of Thwaites
Glacier have forced outward migration of its lateral margins over the past few decades indicating
that the basal boundary conditions that permit fast flow are not fixed in space and
time.
Past variability: The divide between Thwaites and Pine Island Glaciers (Figure 2) contains
stratigraphy indicating that bounding glaciers have been active but fixed spatially for several
millenia.
Controls on fast flow: A layer of deformable, wet till (as measured by increased bed reflectivity)
underlies the fast-moving trunk regions of Thwaites Glacier but not beneath the slow-moving
ridge between Thwaites and Pine Island Glacier. This wet till permits fast flow within the
trunk region.
to recent changes at its grounding line within the context of any possible long-term variability in
mass balance. To this end we concentrate on understanding the controls on fast glacier flow in this
area and search for evidence which allows us to quantify the effect of recent changes in elevation
and grounding line retreat on margin position within the context of longer time-scale retreat. Our
plan is to work with data from groups that have previously visited the region (UTIG and ITASE,
Figure 2) and those that are planning upcoming surveys (PSU/CReSIS) to collect the appropriate
data needed for analysis which allows us to test the following hypotheses related to our goal:
Margin migration: Observed changes in grounding line position and ice sheet elevation of Thwaites
Glacier have forced outward migration of its lateral margins over the past few decades indicating
that the basal boundary conditions that permit fast flow are not fixed in space and
time.
Past variability: The divide between Thwaites and Pine Island Glaciers (Figure 2) contains
stratigraphy indicating that bounding glaciers have been active but fixed spatially for several
millenia.
Controls on fast flow: A layer of deformable, wet till (as measured by increased bed reflectivity)
underlies the fast-moving trunk regions of Thwaites Glacier but not beneath the slow-moving
ridge between Thwaites and Pine Island Glacier. This wet till permits fast flow within the
trunk region.
Existing data for Thwaites (TG) and Pine Island (PIG) glaciers overlying velocity derived from InSAR (Thomas and others, 2004) and AVHRR data from NSIDC. Completed airborne geophysics surveys from UTIG (green) and BAS (blue). Drainage boundaries (black lines), the ITASE route (red dashed line) and ice core sites (red-black circles) are as shown. Grey box indicates the region show in Figure 3). Inset shows survey location in context of Antarctica.
To test these hypotheses we propose to analyze detailed ice-penetrating radar data across the
Thwaites Glacier margins and into the slow moving region between Thwaites and Pine Island
glaciers (Figure 3) in collaboration with CReSIS scientists who will be acquiring data in this
region during the 2008/09 and 2009/10 Antarctic field seasons (see letter of support from Sridhar
Anandakrishnan). Ice-penetrating radar of ice sheets continues to yield crucial information from
analysis of ice thickness, internal layer geometry and basal properties. In particular, the geometry
of internal layers provides insight into the flow history of ice sheets (Nereson and others, 1998;
Jacobel and others, 2000; Conway and others, 2002; Siegert and others, 2004; Catania and others,
2006a) and is a useful tool in ice flow model calibration (Wang and others, 2002). In addition,
ice-penetrating radar is particularly well-suited for profiling and mapping bed conditions using
changes in bed return amplitude to discern melted from frozen bed conditions (e.g., Bogorodsky
and others, 1985).
