Sediment Content in Antarctic Iceberg Fragments Sufficient to Sink the Ice

Iceberg fragments recovered from the sea floor near Swift Glacier, Antarctica, contained sufficient sediment to sink the ice. Sediment concentrations in the samples would have caused them to settle at 0.13 to 0.35 m/s through the water column. Impact with the sea floor would significantly turbate soft sediments. Unlike sediment dumped from icebergs, the stratigraphy of the frozen sediments created by glacial processes may be preserved in the marine sedimentary record after melting of the ice. Negatively buoyant berg fragments may be common in polar regions, and when driven by currents may scour the sea floor up and down slopes unlike floating ice.Des fragments d’icebergs recueillis sur le fond océanique, près du glacier de Swift, en Antarctique, contenaient suffisamment de sédiments pour couler à une vitesse de 0,13 à 0,35 m/s. La collision de tels fragments avec le plancher marin entraînerait un brassage important des sédiments mous. Au contraire de celle de sédiments délestés par les icebergs, la stratigraphie de ces sédiments gelés résultant de processus glaciaires peut être préservée au sein des dépôts marins après la fonte des fragments de glace dans lesquels ils sont emprisonnés. Ces fragments, dont la densité est supérieure à celle de l’eau, pourraient être communs dans les régions polaires et causer, sous l’action des courants, un labourage ascendant et descendant des pentes des fonds marins, contrairement aux glaces flottantes

Magnetic stratigraphy and sedimentology of Holocene glacial marine deposits in the Palmer Deep, Bellingshausen Sea, Antarctica: implications for climate change? Marine Geology 152

Abstract The Palmer Deep is a closed bathymetric depression on the Antarctic Peninsula continental shelf. It contains three separate sub-basins. These basins lie along a northeast-southwest axis with water depths ranging from >1400 m to the southwest (Basins II and III) to just over 1000 m to the northeast (Basin I). Six sediment piston cores were collected from the study region; these cores clearly demonstrate the varied sediment character for each basin. Sediments in Basin I are laminated and thinly bedded consisting of diatomaceous, pelagic=hemipelagic sediments, siliciclastic, terrigenous sediments, and ice rafted, hemipelagic sediments. In concurrence with other investigators, we propose that these laminations and thin beds represent climatically forced productivity cycles. Basin II and Basin III sediments alternate between pelagic=hemipelagic units and bio-siliceous mud turbidites. Correlations between cores are based on their remarkable magnetic susceptibility (MS) records which indicate alternating biogenic (low MS) and siliciclastic (high MS) dominated sedimentation; the bio-siliceous mud turbidites are characterized by intermediate to low MS values. Cores taken from within the main axis of the basins are expanded ultra-high resolution sections. A core collected on the sill between Basins II and III represents a condensed sediment section and may contain a complete Holocene record of changing paleoenvironments, one that records the transition from a glacial, ice shelf environment to an open marine, Holocene environment. A sharp drop in magnetic susceptibility at mid-core is a common sedimentological feature of each basin. Presently, we favor a climate change hypothesis for this magnetic lithostratigraphic transition which may reflect the termination of the Holocene Hypsithermal and a marked change in productivity dated ca. 2500 years BP

Stratigraphic signature of the late Palaeozoic Ice Age in the Parmeener Supergroup of Tasmania, SE Australia, and inter-regional comparisons

Recent research in eastern Australia has established that rather than being a single, long-lived epoch, the late Palaeozoic Ice Age comprised a series of glacial intervals each 1–8 million years in duration, separated by non-glacial intervals of comparable duration. In order to test whether the glacial events recognized in New South Wales and Queensland have broader extent, we conducted a reappraisal of the Parmeener Supergroup of Tasmania, southeast Australia. A facies analysis of the Pennsylvanian to Permian section was carried out, allowing rationalization of the succession into four recurrent facies associations: a) glacigenic facies association, restricted to the basal Pennsylvanian/earliest Permian Wynyard Formation and correlatives, b) glacially/cold climate-influenced to open marine shelf facies association, which accounts for large parts of the Permian succession, c) deltaic facies association, which specifically describes the Lower Permian “Lower Freshwater Sequence” interval, and d) fluvial to estuarine facies association, which specifically addresses the Upper Permian Cygnet Coal Measures and correlatives. Indicators of sediment accumulation under glacial influence and cold climate are restricted to four discrete stratigraphic intervals, all of which indicate that glaciation was temperate in nature. The lowermost of these, incorporating the basal Wynyard Formation and its correlatives, and overlying Woody Island Formation, shows evidence of proximal glacial influence (subglacial, grounding-line fan and ?fjordal facies), and is likely a composite of one or more Pennsylvanian glacial event(s) and an earliest Permian (Asselian) glacial. The second, of late Sakmarian to early Artinskian age, comprises an initial more proximal ice-influenced section and an overlying more distal ice-influenced interval. The third (Kungurian to Roadian) and fourth (Capitanian) intervals are both distal glacimarine records. The four intervals are of comparable age to glacials P1–P4, respectively, recognized in New South Wales and Queensland (notwithstanding apparent discrepancies of \u3c 2 million years in age), and display similar facies characteristics and vertical contrasts to those intervals. Accordingly, it is concluded that the late Palaeozoic stratigraphy of Tasmania preserves a glacial/cold climate record correlatable to that of mainland eastern Australia, lending support to the hypothesis that these events were widespread across this portion of Gondwana

A new US polar research vessel for the twenty-first century

Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 3 (2012): 204-207, doi:10.5670/oceanog.2012.96.Scientific and political interests at the poles are significant and rapidly increasing, driven in part by the effects of climate change and emerging geopolitical realities. The polar regions provide important services to global ecosystems and humankind, ranging from food and energy to freshwater and biodiversity. Yet the poles are experiencing changes at rates that far outpace the rest of the planet. Coastal Arctic communities are impacted by climate change through coastal erosion, sea level rise, ice loss, and altered marine food webs, threatening the future of their subsistence lifestyle. Climate change has dramatically increased the melt rate of ice sheets and glaciers at both poles and has the potential to significantly raise sea level worldwide. Oil and gas drilling as well as transportation in the Arctic have reached all-time high levels, in part because of reduced sea ice cover. Tourism is a growing industry at both poles, bringing more than 20,000 tourists each year to the western Antarctic Peninsula alone. The collateral effects of human activities include the potential for pollution of the marine environment, particularly through spills of hydrocarbons. Our ability to understand the effects of such activities and mishaps is limited, particularly in ice-covered areas during winter

A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20ka, 15ka, 10ka and 5ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorit. © 2014 The Authors

Record of Holocene Palaeoclimate Change Along the Antarctic Peninsula: Evidence from Glacial Marine Sediments, Lallemand Fjord

In light of recent warming and environmental changes observed on the Antarctic Peninsula, an increased knowledge of regional palaeoclimatic trends may provide an improved understanding of the expected response of the Antarctic glacial, oceanic and biotic systems to continued warming. Sedimentologic and geochemical analyses of a 5.5 m long, high-resolution sediment core (PD92 GC-1), collected in Lallemand Fjord, represent the most detailed record of Holocene climate change, to date, in Antarctica. Grain size, smear slide analysis, magnetic susceptibility and total organic carbon content (TOC) were measured. One radiocarbon date establishes a chtonology for the base of the core. Correlation with the upper portion of core GC-1 with other cores collected in the fjord is based upon carbon stratigraphy, nine radiocarbon analyses and 2lOPb data. Deglaciation of Lallemand Fjord is believed to have occurred prior to 8000 yr BP, followed by a period of open marine conditions with variable extent of sea ice (variable TOC content) between 8000 and 2700 14C yr BP. A climatic optimum is recognised between 4200 and 2700 yr BP. Around 2700 yr BP, a decrease in TOC and diatom abundance reflects the formation of more extensive and seasonally persistent sea (fast) ice. The Muller Ice Shelf, now present in the fjord, advanced approximately 400 years ago, coincident with the Little Ice Age. These results indicate environmental variability throughout the Holocene that was consistent across most portions of the maritime Antarctic Peninsula. Surprisingly, the timing of climate transitions correlates with Northern Hemisphere T-Events and ice-core data from Greenland, indicating the possibility of coherent climate variability in the Holocene, at least for the high latitudes