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Reconstruction of past accumulation rates from internal layers around Kohnen station (Antarctica)

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Citation:
Sacchettini, M. , Parrenin, F. , Eisen, O. and Steinhage, D. (2006): Reconstruction of past accumulation rates from internal layers around Kohnen station (Antarctica) , International Symposium on Cryospheric Indicators of Global Climate Change,Cambridge, EnglandAugust 2006. .
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Abstract:

Reconstruction of past accumulation rates above ice sheets are useful to 1) date ice cores and interpret their paleoclimatic data 2) constrain past boundary conditions of 3D ice sheet models and 3) compare with accumulation measurements for recent periods.Ice cores can help reconstruct accumulation rates in the past, but only for a given location. On the contrary, internal layers traced by radio echo sounding of the ice sheets, and assumed to be isochronous layers, provide a way to infer past accumulation rates on large areas. To form an isochronous layer, a paleo surface of the ice sheet is advected horizontally and thinned vertically. The reconstruction of past accumulation rates from isochrones thus requires a flow model to correct for these effects, and this flow model has to be used in an inverse mode.Here, we apply such a method to a radio echo sounding profile near Kohnen station. The flow model used is a 2D1/2 model along a flow line, with prescribed surface elevation and velocity profile. The inverse method is based on a Newton algorithm and will be fully described. We show that for non shallow isochrones, the knowledge of the flow parameters is required to invert for accumulation rates. For example, there is no simple relationship between the elevation of the subglacial bedrock and the elevation of the isochrones along our profile. For this reason, we try to reconstruct an "effective bedrock elevation" along the flow line, which is the bedrock elevation that produces similar isochrones geometries in our model. This step being made, we show our reconstructions of spatial variations of accumulation along the profile at different periods of time.

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