Modeling the Effect of Basal Ice Accretion Growth and Decay on Ice Sheet Isochrone Architecture
Abstract
Large-scale anomalous plume like features, rising from the bed, have recently been observed in radio echo sounding data in both Antarctica and Greenland. For Antarctica they have been hypothesized to be produced by subglacial ice accretion, whereas in Greenland the process of layer folding due to variations in ice rheology has been proposed as an additional explanation. Here we use a 3-D time-dependent model capable of calculating tracers and isochrone layers within the ice, in order to explore the genesis and evolution of accretion features. We find that with basal accretion alone we are able to reproduce similar features that are very similar as observed both in Greenland and Antarctica. The basal accretion leads to an accretion plume, which is initially rising due to small/neglectable horizontal flow components and pushing up the meteoric ice layers above. When the horizontal flow component is larger than the vertical flow component the accreted plume is deflected downstream, leading to folds in both the accreted layers and the neighboring meteoric ice layers. The inferred basal accretion rates are of the order of magnitude of surface accumulation rates. We find that such a simple process as basal accretion can produce very complex features in the lower part of the ice column such as folds and age inversions. Additionally, when we stop basal accretion new folds develop in the lowest part of the ice column. The modeled isochrone architectures resemble the observed features in the Greenland radar data. Potentially this mechanism of growing and decaying accretion features could explain some of the folds found in the lowest part of the Greenland ice cores. This combined approach of observation and modeling allows determination of whether such an accretion process is actively happening and its age relative to the average accumulation rates; besides, it gives us an insight about the timing of changes in basal conditions. Considering the spatial extents of such features, they may provide a significant, but currently neglected, contribution for the mass balance of an ice sheet.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.C33E..02L
- Keywords:
-
- 0726 CRYOSPHERE / Ice sheets;
- 0774 CRYOSPHERE / Dynamics;
- 0798 CRYOSPHERE / Modeling