Tidal forcing of the flow of West Antarctic ice streams

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The goal of the Tides Experiment is to understand the recently-observed tidal-forcing of the ice streams of West Antarctica. Sparse observations of ice streams B and D suggest that the tides beneath the Ross Ice Shelf play a significant role in modulating the speed and possibly direction of flow of these ice streams. We will deploy arrays of GPS receivers and seismometers to better understand this phenomenon.

Current Status

Deployment maps showing our 2003 set of sites on various background maps.

PDF of the Support Information Package (SIP)

Scientific Motivation

The West Antarctic Ice Sheet (WAIS) is a marine ice sheet, grounded below sea level and potentially unstable in reponse to sea-level rise and/or climate warming. The flowof this ice sheet is variable on timescales ranging from centuries to millenia. The future of this ice sheet is a topic of considerable debate.

The ice streams of the Ross Sea Embayment (A--F) drain the interior West Antarctic Ice Sheet by rapidly moving vast quantities of ice to the calving front of the Ross Ice Shelf. These ice streams are key factors in any discussion of WAIS stability because they are strongly out of balance. Understanding the role of the ice streams as buffers between the interior ice and the floating ice shelves is crucial to any attempt at modeling the WAIS system and predicting the future of the ice sheet. These ice streams have been shown to have highly variably flow speeds (and directions) at time scales as short as a single day. Previous results have shown that the motion is tidally forced, but the mechanism in unclear. Bindschadler et al., in press, show one kind of behavior (stick-slip motion with a 24 hour periodicity on a slip-doublet, and the peaks of the doublet are separated by six hours) Anandakrishnan et al., in press, Anandakrishnan and Alley, 1997, show a more-linear-viscous response to the tidal forcing (high tide slows flow, and vice versa, with the slowdown propagating upstream at O(m/s)).

This figure illustrates the curious behavior of the near-grounding-line motion of ice streams B (upper panel) and D (lower panel). The upper panel shows the very jerky motion where the ice sits still for a long time (that is the small knot of points) and then jumps forward very quickly (that is the straight lines) to a new fixed position (that is the next knot). By contrast, ice stream D speeds way up and slows way down (top curve in the lower panel) and also sways side to side (middle curve in the lower panel) in response to the tide (bottom curve in lower panel). Click on the image for a PDF version.

Details

GPS: Trimble dual-frequency receivers provided by UNAVCO.
20 dual-frequency receivers deployed on ice streams B, C, and D, as well as on some of the inter-stream ridges and on the floating ice.Used to determine elevation and ice flow speeds.
Seismics: short period geophones and recorders, provided by IRIS/PASSCAL Instrument Center.
40 2-Hz geophones will be deployed in a number of mini-arrays (4 stations in a square around a GPS site) to help locate the stick-slip events.

Links

Info for IO-205 Project Participants such as how to fill out the RPSC forms and how and when to ship boxes South.

Some of my own links (Linux, glaciology, seismology, news, etc.)

Night/Day Terminator

Today's terminator at Byrd Surface Camp at noon. Click for a larger image. Image courtesy of the xearth program

Sridhar Anandakrishnan <sak@essc.psu.edu>

Last modified: Fri Apr 11 13:36:16 EDT 2003