Modern Sediment Yields from Tidewater Glaciers: Coupling Climate and Erosion

The massive glacimarine sedimentary sequences found on continental shelves from the Antarctic to the high Artic contain a complex history of Quaternary climate change that reflect climate-driven changes in sediment yields from adjacent glaciers and ice sheets. To unlock this climate history from the glacial sedimentary record, one must look to modern glacimarine environments, which provide a wealth of stratigraphic data useful in unraveling the climate-dependent efficiency of glaciers in denuding the landscape and in delivering sediment to the ocean margins.

Fjords are particularly effective sediment traps for the sediment produced by glaciers, as the sediments deposited within the basins behind moraines or shoals have little opportunity for removal except by glacial readvance. Fjords therefore contain complete sequences of glacially-derived sediment, from which we can assess the relationship of sediment production by glaciers to the extent of glacial cover and to changes in mass balance, and hence to changes in climate.

The total sediment budgets imaged in recently deglaciated fjords in Alaska and Patagonia were combined with simple numerical models of proglacial sedimentation and of ice mass budgets to calculate the sediment flux as a function of time and ice dynamics from five retreating, temperate tidewater glaciers. The glacial erosion rates inferred from these sediment budgets are some of the highest reported erosion rates worldwide, averaging between 16-40 mm/a over the past 50 years. These erosion rates also scale with retreat rates, implying that most contemporary sediment yield data from retreating glaciers correspond to recent erosion rates that exceed long-term rates by a factor of 3.5 ± 1.5. For these tidewater glaciers, the drastic retreat and drawdown of ice since the end of the Little Ice Age are linked to unusually rapid calving and ice motion, which are conducive to unusually rapid erosion.