Effects of Ice and Permafrost on Delta Channel Dynamics and Morphology

Wednesday, December 12, 2018 - 08:00
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All deltas are influenced to varying degrees by rivers, waves, and tides. Arctic deltas, however, are also affected by permafrost and ice cover. The lack of direct observations of how ice and permafrost influence coastal sediment transport, channel dynamics, and delta morphology limits our ability to understand Arctic delta dynamics and potential response to climate change. Permafrost alters sediment erodibility and fast-ice cover constricts flow underneath the ice, introducing friction and resistance to flow. Previous research incorporating these effects into a reduced complexity model of delta formation (DeltaRCM) suggests that ice or permafrost presence reduces channel mobility, altering deltaic sediment retention and depositional patterns. While this research considered ice and permafrost separately, results suggested that ice might have a greater effect on delta morphology and dynamics than permafrost. Building on this research, we use DeltaRCM to explore the combined effects of ice thickness and permafrost erodibility on delta dynamics and morphology. Delta characteristics change with increasing ice thickness, regardless of permafrost erodibility. Shoreline roughness and offshore deposition increase with ice thickness, and delta area decreases. Similarly, delta morphodynamics change with with permafrost erodibility regardless of ice thickness. Shoreline rugosity and area of open water on the delta (e.g. lakes, abandoned channels) decreases with increasing permafrost erodibility. Both ice and permafrost decrease channel mobility to a comparable degree. However, ice thickness appears to have a stronger effect on depositional patterns such as progradation rate, shoreline rugosity, and offshore and overbank deposition. These results suggest that permafrost thaw and ice retreat in a warming climate may result in deltas with more dynamic channel networks. Ice retreat may have additional implications for storage and fluxes of water and sediment through Arctic deltas.

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