Sediment inclusions in Alaskan coastal sea ice: Spatial distribution, interannual variability, and entrainment requirements

Abstract

We investigated the spatial characteristics of sedimentary inclusions and elucidated processes controlling their spatial and temporal variability in the fast ice cover of the shallow-marine environment of Elson Lagoon near Barrow, Alaska. This was accomplished by examining the frazil ice layer of sea-ice cores representing the 1998, 1999, and 2000 fall freeze-up periods and comparing the results with a sediment resuspension model. Sediments occur exclusively as aggregates of clay to fine-silt sized particles that were confined to brine inclusions in the frazil ice. The average cross-sectional area of these aggregates is positively correlated with sediment concentration of the frazil ice (R2 = 0.82, P < 0.01). The minimum distance between neighboring aggregates (nearest-neighbor distance) is negatively correlated with sediment concentration (R2 = 0.78, P < 0.01). However, little correlation exists between the number of aggregates and sediment concentration. Sediment concentrations ranged from 24 to 1470 mg L-1 and sediment loads ranged from 2 g m-2 to 384 g m-2, with 1998 and 2000 sediment loads being one to two orders of magnitude smaller than 1999 sediment loads. Similarly, the potential for bottom-sediment resuspension was greater in 1999 than in 1998 and 2000 by more than a factor of two. Resuspension potential is controlled spatially by the local bathymetry and interannually by wind velocity and fetch. At submeter scales, increases in bottom sediment resuspension result in greater sea-ice sediment concentrations, larger aggregates, and smaller nearest-neighbor distances.