| Radar
evidence for stability of the Ross/Amundsen ice flow divide of the West
Antarctic ice sheet.
David
L. Morse, Donald D. Blankenship Edwin
D. Waddington The marine-based West Antarctic ice sheet is likely the dominant contributor to past and possibly future rapid sea level changes. West Antarctic ice primarily flows westward to the Ross Sea, northward to the Amundsen Sea, and eastward to the Weddell Sea. Observations of dramatic thinning at the grounding lines of the Pine Island and Thwaites glaciers suggest that presently the Amundsen Sea catchment may be well out of balance. The Ross Sea catchment is currently in balance to within measurement uncertainty, although its grounding line has retreated by approximately 1000 km since the last glacial maximum, approximately 15,000 years ago. Such large-scale changes of the ice sheet margin configuration may also be expressed by movement of the divide that separates the flow of ice into these two catchments. Recovering a history of any such divide migration through the Holocene may shed light on the Ross-side retreat history, or alternatively, a recently activated migration may provide information about the current Amundsen Sea catchment imbalance. Ross/Amundsen flow divide migration is of particular interest since this is the site chosen for the second WAISCORES deep ice core. During
1999/2000, we conducted a series of airborne radar surveys of the Ross/Amundsen
flow divide region with the objective of detecting stratigraphy patterns
indicative of flow divide migration. The surveys consisted of continuous
radar profiles along 12 curvilinear paths that follow local ice flow direction
while maintaining constant terrain clearance. Such along-flow surveys
facilitate flow-band modeling studies for quantitative determination of
divide stability and or migration. Each of these approximately 120 km
long lines were surveyed twice, once with equipment parameters set to
optimize maximum ice penetration (for deep layer and bed detection) and
once with settings to optimize near-surface resolution of stratigraphy
(for enhanced temporal resolution). Imaged stratigraphy in the upper half
of the ice column gives a record of the flow divide position over the
past approximately 4 ka. We will discuss this evidence for relative stability
of the divide position and its implications for post-glacial retreat of
the West Antarctic ice sheet. |