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The extent of multi-year sea ice impacts climate processes worldwide, such as ocean-atmosphere carbon dioxide exchange and deep ocean current formation. Reconstructing these processes in the past, and assessing the distribution of ecologically and climatically significant features, such as polynas, requires recognition of sediments deposited under multi-year sea ice, but little is known about their characteristics. Textural analysis of subaerial and sea floor sediment in Explorers Cove, McMurdo Sound, at the mouth of Taylor Valley, Antarctica, augmented with observations of sedimentary structures and faunal components, elucidates how sediment is transported to the sea floor and allows characterization of the deposits. Comparison of grain-size characteristics of subaerial (moraine, delta and sea-ice surface) sediment and sea floor sediment from short cores taken at depths of 7 to 25 m indicates that the likely source of the moderately to poorly sorted sea floor sand is deltaic sediment; small glacial meltwater streams have built deltas since Taylor Valley became ice-free ca 7000 years ago. Windblown sediment accumulating on the multi-year sea ice close to the coast typically is coarser grained than sediment on the sea floor; this suggests that the transport of sediment through the ice to the sea floor is not the predominant mode of sediment transfer. However, supra-sea-ice sediment does move to the sea floor through local fractures. The rate of sedimentation under multi-year sea ice is low because of limited stream flow and biogenic sedimentation; the ice cover inhibits primary productivity and dampens waves, precluding physical re-suspension. The upper centimetres of sea floor sediment are churned by epifaunal scallops and brittle stars that leave no telltale biogenic structures and whose calcite ossicles and shells may be poorly preserved. The resulting deposits under multi-year sea ice are poorly sorted, massive sand that provides little evidence of the bioturbators that have masked the indicators of the original physical depositional processes. [ABSTRACT FROM AUTHOR]

Abstract: Aeolian sediment accumulates on the surface of annual sea ice in Southern McMurdo Sound (SMS). It is sourced from ice-free areas around the sound and is released from the sea ice during annual melting and sinks to the sea floor. However, the volume, composition and contribution to overall sedimentation in the region have not previously been quantified. Here, we present the results of a systematic, quantitative field study of aeolian sediment on the surface of sea ice in SMS carried out during the drilling of the ANDRILL 2-2A drillhole during the austral summer of 2007. Our results reveal a surprisingly large volume of aeolian sediment (between 7.8 and 24.0 tonnes of aeolian sediment per km2) forming an elongate lobe extending north from the McMurdo Ice Shelf onto the sea ice surface. Detailed particle size analysis reveals distinctive fine sand and silt modes that progressively fine down wind, suggesting that the sediment is transported under two distinct wind transport processes. XRF grain composition analysis indicates that the material is predominantly volcanic and is sourced primarily from a large area of loose debris on the surface of the McMurdo Ice shelf. Comparison with modern sediment recovered from the sea floor shows a remarkable similarity in grain size distributions and suggests that the sea floor is dominated by aeolian sediment that has settled through the water column. Our calculations indicate that this process produces a sea floor sedimentation rate of up to 1.53 cm/ky in the local area. This new dataset quantifies the aeolian sediment flux in SMS and highlights the contribution of aeolian deposition to the modern sedimentary record in SMS. Furthermore, it draws attention to the recently demonstrated link between iron-bearing aeolian sediment release from sea ice and the triggering of phytoplankton blooms each spring. [Copyright &y& Elsevier]