EFFECTS OF ICE AND PERMAFROST ON DELTA DEPOSITIONAL PROCESSES: IMPLICATIONS FOR A WARMING ARCTIC (Invited Presentation)

River deltas create sedimentological records that help us interpret rates and mechanisms of sediment transport and local environmental conditions of the past. In the Arctic, ice and permafrost play a large role in governing depositional processes, but their influence is expected to decrease with warming temperatures. Here, we present results from numerical modeling of Arctic deltas aimed at understanding how ice and permafrost influence river delta dynamics and depositional patterns. Both ice and permafrost limit channel mobility, enhance overbank deposition, and roughen shorelines. Thick ice increases offshore channel incision and sediment delivery, resulting in an offshore-extending channel network and the creation of a subaqueous ramp nearshore. Permafrost stabilizes channels and focuses deposition near the channels, leading to enhanced channel levee development. Levee growth is further enhanced by overbank flooding due to ice-driven changes in water surface elevations. Overbank flooding leads to more extensive levees on deltas with both ice and permafrost compared to deltas with only permafrost. This limits channel infilling, helping to preserve abandoned channels on the delta plain. Ice can block smaller channels for much of the year, such that small channels are less geomorphically active than larger channels. Very resistant permafrost may damp this effect, as permafrost inhibits channel avulsion, resulting in fewer active channels on the delta plain that are capable of conveying river discharge to the coastal ocean. These results suggest that the loss of both ice and permafrost in a warming climate will increase lateral channel mobility, decrease the frequency of overbank flooding and therefore rates of delta plain aggradation, limit levee deposition, increase shoreline progradation rates, and decrease offshore transport of sediment.