Anchor ice, seabed freezing, and sediment dynamics in shallow Arctic Seas

Abstract

Diving investigations confirm previous circumstantial evidence of seafloor freezing and anchor ice accretion during freeze‐up storms in the Alaskan Beaufort Sea. These related bottom types were found to be continuous from shore to 2‐m depth and spotty to 4.5‐m depth. Spotty anchor ice occurred as pillow‐shaped crystal aggregates on buried slabs of frozen sand surrounded by unfrozen sand. Considerations of required conditions for ice bonding and anchor ice growth allows regional extrapolation and suggests the possibility of anchor ice growth out to 20‐m depth, the estimated maximum depth of supercooling during fall storms. Anchor ice and seabed freezing apparently do not develop during a calm freeze‐up. Because of the abrupt growth of anchor ice during a freezing storm and its release soon after formation of a surface ice cover, this ice type has not been documented before. The concretelike nature of frozen bottom, where present, should prohibit sediment transport by any conceivable wave or current regime during the freezing storm. But elsewhere, particularly where the bonded crust is broken by grounded ice, anchor ice lifts coarse material off the bottom and incorporates it into the ice canopy, thereby leading to significant ice rafting of shallow shelf sediment and likely sediment loss to the deep sea.

Variability in Arctic sea ice optical properties

“…It is possible that the particles were trapped during the normal ice growth and the change in physical structure is related to metamorphism of the ice by localized heating because of the higher absorption by the particles [Fritsen et al, 1992;Zeebe et al, 1996]. The small crystals observed may also be related to a freezing mechanism such as a sub-ice frazil layer [Dieckmann et al, 1986] or buoyant anchor ice [Reimnitz et al, 1987] that brought the particles to the ice surface. Regardless of the mechanism, the relationship between ice structure and absorbing inclusions is important for improving our understanding of the light field associated with sea ice.…”

Unraveling Sediment Transport Along Glaciated Margins (the Northwestern Nordic Seas) Using Quantitative X-Ray Diffraction of Bulk (< 2mm) Sediment

“…1) (Eggertsson, 1993;Dyke et al, 1997;Tremblay et al, 1997). Sediments in the sea ice "…contain on average more than 94% silt and clay" (Dethleff and Kuhlmann, 2010), and the process of sediment entrainment in sea ice (Reimnitz et al, 1987;Darby, 2003;Dethleff and Kuhlmann, 2009) results in an enhancement of the fine-fractions relative to sediments on the sea floor. Dethleff and Kuhlmann (2010) were able to distinguish between eastern (Kara Sea) and and western (Laptev Sea) sources based on clay mineralogy.…”

Transformation of terrestrial organic matter along thermokarst-affected permafrost coasts in the Arctic

“…Depending on the oxygen availability, terrestrially derived OM from the slump can be stabilized and preserved for longer time scales in marine sediments under anaerobic conditions (Walter et al, 2007). However, all marine sediments and OC in the water column at water depths less than 30 m can be affected by wave erosion, resuspension or ice-scouring, and thus long-term accumulation of OM may be limited Macdonald et al, 2015;Reimnitz et al, 1987;Vonk et al, 2012). Further offshore, the contribution of autochtonous sources increases gradually along the narrow shelf and towards the Alaskan Beaufort Sea and Chukchi Sea, where autochtonous production dominates (Naidu et al, 2000).…”