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Glacimarine Sedimentation Notes

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Glacimarine Sedimentation Drewry 1986: Over 10% of world's oceans have glacimarine sediments forming in them. Why they are important. Dowdeswell 1987 - Model of sediment stores and processes in glaciomarine sedimentation. Four stages: sources, glaciology, oceanography, sediment reworking. Deposition directly from below grounding line or from the ice-front with melting and calving (Gilbert 1983). But away from immediate ice front, dominated by meltwater and ice-rafting processes which have quite different effects. Dowdeswell et. al. 1998 - Conceptual model of sedimentary processes. Continuum of changing environmental settings from Southeast Alaska to Eastern Antarctica. Meltwater Processes Meltstreams - release from meltwater portals or channels. For midlatitude + high-latitude temperate glaciers, discharges fluctuate significantly between summer and winter (low) due to re-establishment of channelized drainage in spring (Fountain + Walder 1998) Direct deposition from suspension. Rising in overflows as described by Powell 1990. ZFE  Established flow  Buoyant plumes. Almost always buoyant: Mulder &
Syvitski 1995 - 30/m^3. Settling according to Stokes' Law, exponential increases in time for larger particles (fine sand in 3 hours, silt in 3 years). Syvitski et. al. 1987: Settling (in fjords): Influenced by water body characteristics. Affected by tides, currents and waves. Tides and currents minimize stratification, enhance turnover: faster settling. Marine stratification breaks down in winter (Syvitski et. al. 1987). Flocculation -- bundling into aggregates. Includes zooplankton amalgamation into fecal pellets. This determines how far they are transported. Cowan et. al. 1999: Cyclic sedimentation from fluctuations in discharge, tides, marine productivity.
- Fine-grained and homogenous sediment. Powell 1990: Close to the ice-front direct deposition creating grounding-line fans, gravity flows.
- Powell & Domack 1995: Further away, fine grained muds, settling from suspension decaying exponentially with distance.
- Mugford & Dowdeswell 2010 modelling with SedPlume.
- The thin layers are particularly vulnerable to disturbance by bioturbation (burrowing by polcheates), or iceberg scouring, especially at ice-distal locations. Ice-Rafting Processes Icebergs - found in valley/outlet/surging/subpolar glaciers. Debris-rich unsorted till - 10-100m thick underneath Antarctic ice streams. Where this is released directly with minimal meltwater, creating grounding-line wedges. Dowdeswell & Murray 1990: Sediment amounts determined by distribution/concentration, calving rate, melting rate, temperature of water, and track of iceberg. These vary seasonally. Colder environments, tends to be thicker layers of basal sediments. Thomas & Connell 1985 - Release occurs through gradual melting - creating undermelt diamicton (sustained and gradual rain-out), and dropstones; Periodic roll-over and fragmentation - dump mounds. Contact deposits: direct melt-out from lodged iceberg. Iceberg-scouring can rework existing deposits. Extent of rafting depends on topgraphic characteristics. Where fjord topography constrains iceberg transport, or currents or water temperatures minimize transport or cause melting, ice-rafted debris is confined to fjords. Where icebergs are released from fjords or directly from outlet glaciers and ice streams they can be transported far into the sea. Sea ice (sikussak) traps icebergs. Thus marked by thick, unsorted sediment - unevenly distributed.

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