THE EFFECT OF GLACIAL RETREAT ON FJORD DEPOSITIONAL REGIMES, TAAN FIORD, ICY BAY, ALASKA

Taan Fiord is an arm of Icy Bay that was once fully occupied by Tyndall Glacier with as much as 400 m of vertical ice accumulation. Since 1961, Tyndall Glacier has retreated 17 km and has deposited up to 90 m of sediment within the fjord basin. These high-level short-term sedimentation rates are potentially the result of high angle fjord wall failure, glacial outwash, and alluvial sedimentation.

Recently acquired multi-channel seismic (MCS) and multibeam bathymetry data in Taan Fiord image basin deposition from the glacier face to the bay mouth, encompassing the recent 60 years of retreat. MCS profiles across Taan Fiord exhibit large changes in depth to acoustic basement, which in most cases we interpret to be due to moraine distribution. Additionally, sediment overlying the moraines varies greatly across the fjord in thickness, seismic character, and depositional geometry.

Previous studies indicate that fjord depositional regimes are location dependent. We observe spatially influenced stratigraphic variations in our MCS profiles, which could correlate to differences in depositional environments. We hypothesize that we can distinguish alluvial deposits from glacial outwash and submarine landslides by defining seismic character from deposits primarily influenced by each depositional regime, and use these deposits to reconstruct the history of sedimentation in Taan Fiord since the most recent glacial withdrawal. In this regard, the Taan Fiord sediments can provide insight into the processes associated with recent glacial retreats, and show the impact of rapidly changing climate on a modern temperate glacial system.