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1.
We present a relative sea-level (RSL) history, constrained by AMS radiocarbon-dated marine-freshwater transitions in isolation basins from a site adjacent to the Lambert Glacier, East Antarctica. The RSL data suggest an initial ice retreat between c. 15,370 and 12,660 cal yr B.P.. Within this period, meltwater pulse IA (mwp IA, between c. 14,600-14,200 and 14,100-13,700 cal yr B.P.) occurred; an exceptionally large ice melting event, inferred from far-field sea-level records. The RSL curve shows a pronounced highstand of approximately 8 m between c. 7570-7270 and 7250-6950 cal yr B.P. that is consistent with the timing of the RSL highstand in the nearby Vestfold Hills. This is followed by a fall in RSL to the present. In contrast to previous findings, the isolation of the lakes in the Larsemann Hills postdates the isolation of lakes with similar sill heights in the Vestfold Hills. An increase in RSL fall during the late Holocene may record a decline in the rate of isostatic uplift in the Larsemann Hills between c. 7250-6950 and 2847-2509 cal yr B.P., that occurred in response to a documented mid-Holocene glacier readvance followed by a late-Holocene retreat.  相似文献   
2.
Decadal–centennial‐scale climate variability in coastal Antarctica remains poorly understood due to the limited number of highly resolved, well‐dated records. We present a 900‐year, decadal‐scale reconstruction based on sedimentary diatoms from Lake Abi in Lützow–Holm Bay, East Antarctica. Hydrological change is inferred from diatom ecological preferences in conjunction with an existing regional training set and implies that lake water specific conductivity, depth and nitrogen availability are the key drivers of diatom assemblage change. Lake Abi underwent a series of subtle environmental changes related to these environmental variables, possibly driven by changes in catchment snow melt and the duration of seasonal ice cover. Ordination is used to trace the major patterns of change in the diatom community, with notable shifts identified between 470 and 400 and at ～350 cal a BP (where present = CE 1950). The frequency of environmental variability at Lake Abi is broadly consistent with a record of the Interdecadal Pacific Oscillation during the last millennium, but contrasts with the apparent climate stability elsewhere in eastern Antarctica. Further research is required to constrain the limnological and ecological responses of lakes in coastal Antarctica to obtain more rigorous palaeoclimate reconstructions from these sites of immense potential.  相似文献   
3.
George VI Ice Shelf is the largest ice shelf on the western side of the Antarctic Peninsula and its northern margin marks the southern most latitudinal limit of recent ice shelf retreat. As part of a project to reconstruct the long-term (Holocene) history of George VI Ice Shelf we studied two epishelf lakes impounded by the ice shelf at Ablation Point, on the east coast of Alexander Island. These lakes, Moutonnée and Ablation, are stratified water bodies with a lower marine layer and an upper freshwater layer. To determine if their sediment records could be used to detect past changes in the presence or absence of the ice shelf it was necessary to describe their present-day limnology and sedimentology. We measured water column chemistry and sampled the water column and sediments of the lakes along vertical and horizontal transects. We analysed these samples for diatoms, stable isotopes (δ18O, δ2H, δ13CDIC, δ13Corg), geochemistry (TOC, TN, C/N ratios) and physical sedimentology (grain-size). This was supplemented by chemical and biological reference data from the catchments. Results showed that the water columns of both lakes are nutrient limited and deficient in phytoplankton. Benthic productivity is low and decreases with depth. Comparison of water column chemistry with an earlier survey shows a net increase in the thickness of the freshwater layer in Moutonnée Lake between 1973 and 2001, which could indicate that George VI Ice Shelf has thinned during this period. However, a similar trend was not observed in Ablation Lake (5 km to the north) and an alternative explanation is that the changes are a seasonal phenomena. Data from the surface sediment transects identified a number of proxies that respond to the present day stratification of the water column including diatom species composition, stable isotopes and geochemistry, particularly in Moutonnée Lake. Collectively these data have been used to develop a conceptual model for determining past ice shelf configuration in epishelf lakes. Specifically, periods of past ice shelf loss, and the removal of the ice dam, would see the present stratified epishelf lake replaced by a marine embayment. It is suggested that this change would leave a clear signature in the lake sediment record, notably the deposition of an exclusively marine biological assemblage, increased ice rafted debris and δ13Corg values that are indicative of marine derived organic matter. These authors contributed equally to this work  相似文献   
4.
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5.
The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice‐covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedimentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene climate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold conditions are inferred from high lake‐water salinities, and low water levels and an extended duration of nearshore sea‐ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stratified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea‐ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea‐ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice‐core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long‐term climate change on the terrestrial environment. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
6.
Direct exploration of subglacial lakes buried deep under the Antarctic Ice Sheet has yet to be achieved. However, at retreating margins of the ice sheet, there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered. One of these lakes, Hodgson Lake (72°00.549′S, 068°27.708′W) has emerged from under more than 297–465 m of glacial ice during the last few thousand years. This paper presents data from a multidisciplinary investigation of the palaeolimnology of this lake through a study of a 3.8 m sediment core extracted at a depth of 93.4 m below the ice surface. The core was dated using a combination of radiocarbon, optically stimulated luminescence, and relative palaeomagnetic intensity dating incorporated into a chronological model. Stratigraphic analyses included magnetic susceptibility, clast provenance, organic content, carbonate composition, siliceous microfossils, isotope and biogeochemical markers. Based on the chronological model we provisionally assign a well-defined magnetic polarity reversal event at ca 165 cm in the lake sediments to the Mono Lake excursion (ca 30–34 ka), whilst OSL measurements suggest that material incorporated into the basal sediments might date to 93 ± 9 ka. Four stratigraphic zones (A–D) were identified in the sedimentological data. The chronological model suggests that zones A–C were deposited between Marine Isotope Stages 5–2 and zone A during Stage 1, the Holocene. The palaeolimnological record tracks changes in the subglacial depositional environment linked principally to changing glacier dynamics and mass transport and indirectly to climate change. The sediment composition in zones A–C consists of fine-grained sediments together with sands, gravels and small clasts. There is no evidence of overriding glaciers being in contact with the bed reworking the stratigraphy or removing this sediment. This suggests that the lake existed in a subglacial cavity beneath overriding LGM ice. In zone D there is a transition to finer grained sediments characteristic of lower energy delivery coupled with a minor increase in the organic content attributed either to increases in allochthonous organic material being delivered from the deglaciating catchment, a minor increase in within-lake production or to an analytical artefact associated with an increase in the clay fraction. Evidence of biological activity is sparse. Total organic carbon varies from 0.2 to 0.6%, and cannot be unequivocally linked to in situ biological activity as comparisons of δ13C and C/N values with local reference data suggest that much of it is derived from the incorporation of carbon in catchment soils and gravels and possibly old CO2 in meteoric ice. We use the data from this study to provide guidelines for the study of deep continental subglacial lakes including establishing sediment geochronologies, determining the extent to which subglacial sediments might provide a record of glaciological and environmental change and a brief review of methods to use in the search for life.  相似文献   
7.
The recent disintegration of Antarctic Peninsula ice shelves, and the associated accelerated discharge and retreat of continental glaciers, has highlighted the necessity of quantifying the current rate of Antarctic ice mass loss and the regional contributions to future sea-level rise. Observations of present day ice mass change need to be corrected for ongoing glacial isostatic adjustment, a process which must be constrained by geological data. However, there are relatively little geological data on the geometry, volume and melt history of the Antarctic Peninsula Ice Sheet (APIS) after Termination 1, and during the Holocene so the glacial isostatic correction remains poorly constrained. To address this we provide field constraints on the timing and rate of APIS deglaciation, and changes in relative sea-level (RSL) for the north-eastern Antarctic Peninsula based on geomorphological evidence of former marine limits, and radiocarbon-dated marine-freshwater transitions from a series of isolation basins at different altitudes on Beak Island. Relative sea-level fell from a maximum of c. 15 m above present at c. 8000 cal yr BP, at a rate of 3.91 mm yr?1 declining to c. 2.11 mm yr?1 between c. 6900–2900 cal yr BP, 1.63 mm yr?1 between c. 2900–1800 cal yr BP, and finally to 0.29 mm yr?1 during the last c. 1800 years. The new Beak Island RSL curve improves the spatial coverage of RSL data in the Antarctic. It is in broad agreement with some glacio-isostatic adjustment models applied to this location, and with work undertaken elsewhere on the Antarctic Peninsula. These geological and RSL constraints from Beak Island imply significant thinning of the north-eastern APIS by the early Holocene. Further, they provide key data for the glacial isostatic correction required by satellite-derived gravity measurements of contemporary ice mass loss, which can be used to better assess the future contribution of the APIS to rising sea-levels.  相似文献   
8.
Despite the dominance of cyanobacteria in polar freshwater aquatic ecosystems, little is known about their past biodiversity and response to climate and environmental changes. We explored the use of light microscopy of microfossils, high performance liquid chromatography of the fossil pigment composition and denaturing gradient gel electrophoresis of fossil 16S rRNA genes to study past and present-day differences in cyanobacterial community structure in response to climate changes in two adjacent maritime Antarctic lakes with contrasting depths (4 and 26 m) and light climates. Light microscopy was of limited use because of degradation of cell structures. Fossil cyanobacterial pigment concentrations were below the detection limits of our method in several sediment samples in the deep lake, but abundant and diverse in the sediment core from the shallow pond, probably as a consequence of increased light availability and/or a more diverse and abundant benthic cyanobacterial flora. Total carotenoid and chlorophyll concentrations were highest in both lakes between ca. 2,950 and 1,800 cal yr BP, which coincides with the late Holocene climate optimum recognised elsewhere in maritime Antarctica. Cyanobacterial molecular diversity was higher in the top few centimeters of the sediments in both lakes. In deeper sediments, the taxonomic turnover of cyanobacteria appeared to be relatively small in response to past climate anomalies in both lakes, underscoring the broad tolerance of cyanobacteria to environmental variability. This, however, may in part be explained by the low taxonomic resolution obtained with the relatively conserved 16S rRNA gene and/or the preferential preservation of particular taxa. Our results highlight the potential of fossil DNA in lake sediments to study colonization and succession dynamics of lacustrine cyanobacteria and warrant further investigation of the factors that affect preservation of cyanobacterial DNA.  相似文献   
9.
The West Antarctic Peninsula is one of the fastest warming regions on Earth. Faster glacier retreat and related calving events lead to more frequent iceberg scouring, fresh water input and higher sediment loads, which in turn affect shallow water benthic marine assemblages in coastal regions. In addition, ice retreat creates new benthic substrates for colonization. We investigated three size classes of benthic biota (microbenthos, meiofauna and macrofauna) at three sites in Potter Cove (King George Island, West Antarctic Peninsula) situated at similar water depths but experiencing different disturbance regimes related to glacier retreat. Our results revealed the presence of a patchy distribution of highly divergent benthic assemblages within a relatively small area (about 1 km2). In areas with frequent ice scouring and higher sediment accumulation rates, an assemblage mainly dominated by macrobenthic scavengers (such as the polychaete Barrukia cristata), vagile organisms and younger individuals of sessile species (such as the bivalve Yoldia eightsi) was found. Macrofauna were low in abundance and very patchily distributed in recently ice‐free areas close to the glacier, whereas the pioneer nematode genus Microlaimus reached a higher relative abundance in these newly exposed sites. The most diverse and abundant macrofaunal assemblage was found in areas most remote from recent glacier influence. By contrast, the meiofauna showed relatively low densities in these areas. The three benthic size classes appeared to respond in different ways to disturbances likely related to ice retreat, suggesting that the capacity to adapt and colonize habitats is dependent on both body size and specific life traits. We predict that, under continued deglaciation, more diverse, but less patchy, benthic assemblages will become established in areas out of reach of glacier‐related disturbance.  相似文献   
10.
In this paper we present geological evidence from the Larsemann Hills (Lambert Glacier – Amery Ice Shelf region, East Antarctica) of marine sediments at an altitude of c. 8 m a.s.l., as revealed by diatom, pigment and geochemical proxies in a lake sediment core. The sediments yielded radiocarbon dates between c. 26 650 and 28 750 14C yr BP (31 366–33 228 cal yr BP). This information can be used to constrain relative sea level adjacent to the Lambert Glacier at the end of Marine Isotope Stage 3. These data are compared with the age and altitude of Marine Isotope Stage 3 marine deposits elsewhere in East Antarctica and discussed with reference to late Quaternary ice sheet history and eustatic sea-level change.  相似文献   
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