Modeling the Effects of Sea Ice on Arctic Delta Evolution: A Case Study on the Colville Rive Delta, AK

Seasonal sea ice coverage significantly impacts Arctic delta morphology by limiting activity from wave and river influences and altering river-to-ocean sediment delivery. Furthermore, the presence of sea ice likely plays a major role in the formation of the broad subaqueous bench surrounding only Arctic deltas. Despite this important function, limited long-term morphologic modeling has been performed to understand the effects of sea ice on delta morphodynamics. To address this, a 1D long-term morphologic and hydrodynamic model was built in Delft3D-FLOW to simulate the temporal development of the Colville River Delta, AK during the dominant Arctic seasons: break-up/freshet, open-water, and freeze-up. The designed simulations focus on the deltaic clinoform (i.e., the cross-sectional view of a delta) and use a floating barge structure to mimic the effects of sea ice on surface waters. Long-term simulations show ice-affected deltas form a compound clinoform morphology, a coupled subaerial and subaqueous delta separated by a subaqueous platform that resembles the shallow bench observed offshore of Arctic deltas. The presence of nearshore sea ice and river forcing promoted sediment bypassing during break-up and were the key drivers behind bench formation. Additionally, a second depocenter formed during the open-water season that aided in outbuilding the subaerial delta and assisted in developing the compound clinoform morphology. Results produced from the long-term model were used to assess potential morphologic changes to Arctic deltas caused by seasonal sea ice decline. Modeled future simulations show Arctic deltas may lose the shallow bench feature on centennial timescales by (1) rapid sediment infill or (2) wave erosion. This study highlights the importance of sea ice on Arctic delta morphology and the potential morphologic transitions these high-latitude deltas may experience as the Arctic continues to warm.