Drainage mass balance constraints on tidal modulation of ice stream and outlet glacier dynamics
Abstract
Tides exert first order control of outlet glacier and ice stream dynamics at the grounding line. Tides amplify mixing of subglacial discharge, enhance ice melt, mix effluent subglacial discharge, cause changes in buoyant load along the grounding line, and alter sliding at the base of the ice sheet. These effects and responses are often tuned to the locally dominant tidal amplitude and frequency. In large embayments the effects vary laterally with the tidal currents, but for smaller fjords, the tide acts as a more simple local forcing. One of the strongest and most interesting effects is on ice discharge. Observations have shown that ice discharge can be tidally modulated on semidiurnal, diurnal, and fortnightly timescales. However, the distance of response of the outlet varies widely: from essentially zero distance to 10s or even 100s of kilometers. Hypotheses have related this to shear margin strength or basal dynamics. Here, we look at coupled models of basal hydrology to understand how the response distance could be dictated by catchment properties. Initial results showed that the compressibility of the system is key to understand the upstream dissipation, but there is also a subtle but important mass balance of the basal hydrology that suppresses the response distance and potentially lessens tidal effects. For Antarctica, the upstream mass balance is dominated by basal melting, primarily through geothermal heating but also from frictional heat generated from sliding. This means that the response distance is relatively fixed over a tidal cycle. Conversely, Greenland is much more complicated with strong variations in surface meltwater flux that feeds into a basal system despite smaller lateral effects. This basal system then changes fjord dynamics on diurnal timescales so that the response and forcing are nonlinearly coupled. This nonlinear coupling means that the response distance can vary widely in Greenland based on hydrology alone. Our results show how tidal modulation can yield widely different behaviors in glacial drainages with well-developed basal hydrology.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.C33A0768C
- Keywords:
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- 0726 Ice sheets;
- CRYOSPHEREDE: 0774 Dynamics;
- CRYOSPHEREDE: 0776 Glaciology;
- CRYOSPHEREDE: 0790 Weathering;
- CRYOSPHERE