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Marine sedimentation at a calving glacier margin

¹ Department of Geological Sciences, Rutgers University, New Brunswick, New Jersey 08903, USA
² Department of Geosciences, University of Nebraska, Lincoln, Nebraska 68588-0340, USA

A 2-month study at a subpolar, tidewater glacier was conducted at Anvers Island, Antarctic Peninsula (lat 64°S), to improve understanding of sedimentary processes and associated deposits in glacial marine settings. Data collected in the ice-proximal environment were (1) brash ice-size distribution and melt rates to assess sediment source and transport mechanisms; (2) conductivity-temperature-turbidity-depth (CTTD) profiles, water samples, and sediment-trap catches to study processes and patterns of sediment dispersal; (3) bottom cores and grabs to document recent glacial marine sedimentation; and (4) remotely operated vehicle video surveys of the ice terminus and sea bottom to obtain images of physical and biological processes. The water column is stratified and a halocline occurs at 20–30 m. Water temperature ranged from –1 to 1.6 °C, salinity was 32–34, and suspended solids were 3–5 mg/l well above the bottom. Ephemeral turbid horizons contain 8–15 mg/l suspended solids; rare surface plumes and a quasipermanent turbid layer produced by resuspension during calving events reach 25–35 mg/l. Meltwater drains from the glacier surface, but no subglacial meltwater was detected directly entering the sea. The most important sources of sediment appear to be the direct melting of the submerged ice front and melting of calved glacial ice. Most fragments of floating ice melt within 1 km of the ice front. Some sediment may be contributed as low-density (1.1 g/cm³) algae-bound sediment pellets by meltwater streams draining the ablating ice surface. Sediment enters the stratified water column and is moved by tidal and wind-driven circulation. Marine sedimentation rates are low (3 mm/yr) relative to depth of bioturbation, resulting in unstratified sandy mud with dispersed clasts.

Key Words: algae • Antarctic Peninsula • glacio-marine sedimentation • icebergs • ice rafting

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