|Title:||Inferring Histories of Accumulation, Ice Flow, and Ice Thickness from Internal Layers in Ice Sheets|
|Author:||Koutnik, M.R., Waddington, E.D., Conway, H. and Winebrenner, D.P.|
|Periodical:||American Geophysical Union, Fall Meeting 2007, abstract #C51A-0099|
Isochronous internal layers in ice sheets can be mapped with ice-penetrating radar. The shapes of these internal layers retain information about spatial and temporal patterns of accumulation and the history of ice flow. Deeper layers retain information from further in the past, but are more difficult to interpret because particles forming a deep layer have traveled through spatial and temporal gradients in accumulation and strain rate. To properly recover valuable information about the histories of ice dynamics and accumulation from deep internal layers, we solve an inverse problem. Solving this inverse problem uses an ice-sheet model in a new formulation, and recovers additional information from existing radar data. An inverse problem consists of a forward algorithm and an inverse algorithm. The forward algorithm makes a prediction of the data using a given set of model parameters, and the inverse algorithm adjusts the values of the unknown model parameters that control this prediction. Our forward algorithm calculates spatial and temporal gradients in ice temperature, ice thickness, and accumulation. Our inverse algorithm finds a spatially smooth accumulation history that also produces a prediction of the internal-layer architecture that fits the actual layer data within the uncertainties in the data. In addition to knowing the accumulation pattern, understanding past changes in ice thickness and the position of the ice divide are necessary to properly interpret an ice core. We are using radar data from central West Antarctica, near the upcoming West Antarctic Ice Sheet (WAIS) Divide ice core site, to infer the histories of accumulation and ice dynamics, and to support interpretation of this ice core. Radar data are also being collected over the Martian Polar Layered Deposits (PLD). Using synthetic layers, we have explored the feasibility of recovering accumulation patterns, and possibly accumulation rates on Mars. We present preliminary results for central West Antarctica, and for portions of the Martian North PLD.