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Antarctica is one of the most susceptible regions to climate change on Earth. Rising ocean temperatures, glacier melting, and disruptions of marine ecosystems make this polar region a focus of research on ecosystem transformation associated with ongoing climate change. Within the Antarctic ecosystem, diatoms, a key group of phytoplankton at the base of the marine food web, play a crucial role in maintaining marine ecosystem balance and functioning. Conventionally, fossil diatom assemblages have been investigated in marine sediment records to reconstruct paleoenvironmental conditions and understand climate change patterns of Antarctica. Recently, the application of ancient DNA techniques to ocean sediments (sedimentary ancient DNA, sed aDNA) has provided new insights into diatom community responses to environmental change over geological time scales. One benefit of sed aDNA analysis is that this technique can detect fragile diatom species that do not preserve well and are thus difficult to study via traditional microscopy techniques. In this paper, we review the importance of diatoms as indicators of Antarctic paleoenvironmental change, the novel use of diatom sed aDNA to assist Antarctic paleoenvironmental reconstruction, and the challenges and promises of using the sed aDNA approach. We propose that Fragilariopsis cylindrus , an extant polar diatom species, is an ideal model organism to study adaptation patterns of diatoms to changing climate due to its ecological success through time and the availability of whole-genome information for this species. Novel genetic information obtainable from ancient F. cylindrus, as well as other diatoms, will help us to better predict the evolutionary and adaptive dynamics of this important group of primary producers in the climatically vulnerable Antarctic region. • Climate change in Antarctica and the need to study this polar region. • Diatoms in Antarctic ecosystem and their role as paleoenvironmental indicators. • Using the novel technique of sedimentary ancient DNA (sed aDNA) in Antarctica. • Fragilariopsis cylindrus to study adaptation and evolution of diatoms in Antarctica. [ABSTRACT FROM AUTHOR]

This paper presents the first detailed paleoclimate reconstruction of the latest Antarctic isotope maximum (AIM4, ~ 33–29 ka cal. BP) at 52°S in continental southeastern Argentine Patagonia. High-resolution sedimentological and geochemical analyses of sediments from the maar lake Potrok Aike (PTA) reveal a decrease in the thickness of flood-induced turbidites and a series of wind burst deposits during AIM4, both pointing to increasingly drier conditions. This interpretation is also supported by a significant amount of runoff-driven micropumices incorporated within the sediments that suggests a lower lake level with canyons incising thick tephra deposits around the lake. Increased gustiness and/or dust availability in southeast Patagonia, together with intensified Antarctic circumpolar circulation in the Drake Passage, dust deposition in the Scotia Sea and in Antarctica ice shelf, are consistent with a southward shift of the Southern Westerly Winds (SWW) during the AIM4. In contrast to other warmer AIMs, the SWW during the AIM4 did not migrate far enough south to generate upwelling in the Southern Ocean and they did not reach 52°S in SE Patagonia, as revealed by unchanged values of the rock-magnetic proxy of wind intensity obtained from the same PTA core. Nevertheless, the SWW displacement during AIM4 imposed drier conditions at 52°S in southeast Patagonia likely by blocking precipitation from the Atlantic Ocean, in a way similar to modern seasonal variations and the other Antarctic warm events. [ABSTRACT FROM AUTHOR]

Abstract: We evaluate the opening of the Drake Passage (DP), between Antarctica and South America, and associated changes in ocean circulation as forcing factor for the onset of Antarctic glaciation near the Eocene–Oligocene transition (~34 million years ago). In this paper this hypothesis is tested through sensitivity experiments, using numerical models for the global ocean and atmosphere and for the Antarctic Ice Sheet. The response of the Antarctic continent to the opening of the DP and to the establishment of the Antarctic Circumpolar Current is examined. Two different climate states are reproduced with ocean gateway configurations similar to the Late Eocene and to the Late Oligocene, before and after the opening of the DP. A reduced southward heat flux and a decrease of surface temperature are found in the Antarctic realm when the DP is open. A more massive ice sheet develops on the continent in case of DP open compared to the configuration with closed DP. [Copyright &y& Elsevier]

Abstract: The question of whether Pliocene climate was warm enough to support a substantial vegetation cover on Antarctica is of great significance to the ongoing and controversial debate on the stability or dynamism of Antarctic ice sheets during warm periods with high atmospheric greenhouse gas concentrations. Here we present a systematic palynological comparison of pollen and dinoflagellate cyst assemblages from Early Pliocene diamictites and underlying late Cretaceous sediments collected from James Ross Island, northern Antarctic Peninsula. The diamictites are dated using a combination of 40Ar/39Ar and 87Sr/86Sr isotope ages on interbedded lavas and pristine bivalves. Well preserved pectinid shells and cheilostome bryozoans suggest that the palynomorph-bearing sediments were probably deposited during warmer Pliocene interglacials and later amalgamated into a diamictite formed by a major ice advance during cold glacial cycle. The palynological analyses presented herein do not identify any in-situ pollen and spores which indicate the presence of a substantial vegetation cover. Our study suggests a local (i.e. James Ross Island) provenance for most of the diamictites, whilst sediments from the western coast might have been delivered by ice sheets from the Antarctic Peninsula. Whilst the acritarch Leiosphaeridia might imply the presence of sea-ice and near-modern climate conditions during the Late Neogene, the presence of the dinoflagellate cyst Bitectatodinium tepikiense at one location suggests that sea surface temperatures might have been substantially warmer during some interglacials. The absence of in-situ pollen and spores in the James Ross Island diamictites cannot be taken as proof of non-existence of vegetation. However, the combined palynological and geological evidence presented in this paper makes the presence of a substantial Pliocene vegetation cover on James Ross Island unlikely and supports previous reconstructions of a permanent ice sheet on the Antarctic Peninsula throughout the Late Neogene. [Copyright &y& Elsevier]

Abstract: The stability of the Earth''s major ice sheets is a critical uncertainty in predictions of future climate and sea level change. One method of investigating the behaviour of the Greenland and the Antarctic ice sheets in a warmer-than-modern climate is to look back at past warm periods of Earth history, for example the Pliocene. This paper presents climate and ice sheet modelling results for the mid-Pliocene warm period (mPWP; 3.3 to 3.0million years ago), which has been identified as a key interval for understanding warmer-than-modern climates (). Using boundary conditions supplied by the United States Geological Survey PRISM Group (Pliocene Research, Interpretation and Synoptic Mapping), the Hadley Centre coupled ocean–atmosphere climate model (HadCM3) and the British Antarctic Survey Ice Sheet Model (BASISM), we show large reductions in the Greenland and East Antarctic Ice Sheets (GrIS and EAIS) compared to modern in standard mPWP experiments. We also present the first results illustrating the variability of the ice sheets due to realistic orbital forcing during the mid-Pliocene. While GrIS volumes are lower than modern under even the most extreme (cold) mid-Pliocene orbit (losing at least 35% of its ice mass), the EAIS can both grow and shrink, losing up to 20% or gaining up to 10% of its present-day volume. The changes in ice sheet volume incurred by altering orbital forcing alone means that global sea level can vary by more than 25m during the mid-Pliocene. However, we have also shown that the response of the ice sheets to mPWP orbital hemispheric forcing can be in anti-phase, whereby the greatest reductions in EAIS volume are concurrent with the smallest reductions of the GrIS. If this anti-phase relationship is in operation throughout the mPWP, then the total eustatic sea level response would be dampened compared to the ice sheet fluctuations that are theoretically possible. This suggests that maximum eustatic sea level rise does not correspond to orbital maxima, but occurs at times where the anti-phasing of Northern and Southern Hemisphere ice sheet retreat is minimised. [Copyright &y& Elsevier]

Abstract: A recent paper by De Deckker et al. (2010; Lead isotopic evidence for an Australian source of Aeolian dust to Antarctica at times over the last 170,000years, Palaeogeography, Palaeoclimatology, Palaeoecology, 285(3–4), 205–223) reports radiogenic isotope data of fluvial sediment samples from the Murray Darling Basin (MDB) in southeastern Australia. Some of these display Pb-isotope ratios similar to ancient, pre-industrial pollution dust retrieved from the EPICA Dome C ice core, Antarctica. The authors proposed that this result supports a dust provenance from the Darling sub-basin of the MDB. De Deckker et al. (2010) apparently did not appreciate the extent of anthropogenic Pb contamination of their potential Australian dust sources. In addition, they also neglected to analyze many of the other important Australian dust sources. By contrast, it is demonstrated here that the surface sediments are severely polluted, that other potential dust sources from Australia also need to be considered and that it is not possible to unequivocally distinguish Australian from South American dust using Pb-isotopes alone. [ABSTRACT FROM AUTHOR]

Abstract: A quantitative biochronological study by Cody et al. (2008) integrates comprehensive diatom biostratigraphy, magnetostratigraphy, and tephrostratigraphy from 32 Neogene sections around the Southern Ocean and Antarctic continental margin. A recent method, known as Constrained Optimization (CONOP), which can be viewed as a multidimensional version of graphic correlation, is applied to that very interesting database. The goal of the present paper is to discuss some theoretical aspects of quantitative biochronology and to compare the constrained optimization with the deterministic method called Unitary Associations (UAM), a graph theoretical model. We illustrate the fact that the UAM is an extremely powerful and unique theory allowing an in-depth analysis of the internal conflicting inter-taxon stratigraphic relationships, inherent to any complex biostratigraphical database. [Copyright &y& Elsevier]

Abstract: This paper reports and discusses the distribution, petrography and mineral chemistry of granule- to boulder-size clasts in the Early Pliocene to Quaternary sedimentary succession recovered by the CIROS-2 drill hole, located near the mouth of the Ferrar Glacier (McMurdo Sound). In the Pliocene interval (166.47–99.27 mbsf), Early Paleozoic basement granitoids (monzogranites and granodiorites) are most common, apart from the basal 13-m-thick diamictite unit, which is dominated by basalt clasts from the late Cenozoic McMurdo Volcanics. In the Pleistocene interval (99.27–0 mbsf) basement granitoids are also the most common, but are largely tonalities. Gabbros and dolerites of the Jurassic Ferrar Supergroup are a minor persistent component throughout the core. In contrast, basement metamorphic rocks and Beacon Supergroup sandstones are present only within the lowest part of the core, the former disappearing above ca. 70.20 mbsf, and the latter above ca. 99.30 mbsf. During Pliocene time, the clast assemblage is consistent with the main source of the detritus from basement rocks to the west, transported by an ancestral Ferrar Glacier through the Transantarctic Mountains, the basal basalts suggesting an invasion of Ross Sea ice into Ferrar Fjord from the south (in the area of Mount Discovery and Mount Morning volcanoes). The dominance of tonalite in Pleistocene clasts also suggests derivation from the coastal Blue Glacier area immediately to the south. The decrease in volcanic clasts from Late Pliocene time may relate to the final construction of the Mount Morning–Mount Discovery peninsula, which acted as a barrier to the northern movement of a grounded Ross Ice Shelf, whereas the appearance of the tonalite clasts suggests periods of ice flow from its present day provenance, the Blue Glacier–Miers Valley area, northward along the coast and then into Ferrar Fjord from the east. [Copyright &y& Elsevier]

Abstract: Many climatic proxy materials, such as ice cores, coastal and lacustrine sediments, and abandoned penguin rookeries, have been used to study palaeoclimatic changes and the palaeoenvironmental evolution of Antarctica. In this paper, we report another geological record-well preserved sedimentary sequences in the palaeo-notches in marine terraces of Fildes Peninsula, King George Island. Based upon grain size distribution and microtexture, geochemical element compositions, and radiocarbon dating, we identified the sediments in one palaeo-notch as lacustrine sediments, most likely deposited in a small palaeo-lake. From these data, we inferred that between 4000 and 3000 yr B.P. a moderate chemical weathering occurred and the climate was warmer and more humid than present, in good agreement with the findings from other climatic proxy materials. We believe that the sediments in palaeo-notches provide another reliable proxy material for studying the palaeoclimate and the palaeoenvironment in Antarctica. [Copyright &y& Elsevier]

This paper presents the results of the scanning electron microscopic (SEM) analysis of quartz grains from a selection of samples at Site 1166. Ocean Drilling Program Leg 188 drilled Site 1166 on the Prydz Bay continental shelf, Antarctica, to document onset and fluctuations of East-Antarctic glaciation. This site recovered Upper Pliocene–Holocene glacial sediments directly above Cretaceous through Lower Oligocene sediments recording the transition from preglacial to early glacial conditions. SEM analysis of quartz grains at Site 1166 was used to characterize the glacial and preglacial sediments by their diagnostic textures. Angular edges, edge abrasion as well as arcuate to straight steps, are the most frequent features in glacial deposits. The highest frequency of grains with round edges is present in Middle–Late Eocene fluvio–deltaic sands. However, angular outlines, fractured plates with subparallel linear fractures and edge abrasion indicating glacier influence are also present. Preglacial carbonaceous mudstone and laminated gray claystone show distinctive high relief quartz grains and some chemical weathering on grain surfaces. The results of the microtextural analysis of quartz grains are used to verify some critical periods of ice sheet evolution, such as the transition from the East Antarctic preglacial to glacial conditions on the continental shelf from Middle/Late Eocene to Late Eocene/Early Oligocene time. [Copyright &y& Elsevier]