The sea-floor morphological features and sedimentary cover on the shelves of the northern Trinity Peninsula, Antarctica, result from glaciomarine processes. Roughness of the sea floor is apparent at scales from kilometre-wide Glacial troughs to metre-wide iceberg scours. The sedimentary cover is unequally distributed, with a preference for sheltered areas and sea-floor depressions where deposition obeys local controlling factors. An uppermost draping layer caused by settling of fine particles was observed in several of the studied settings. Large parts of the shelves are devoid of sediments, and there the sea floor shows widespread, mostly relict evidence of Glacial erosion. The observed sea-floor morphologies and sedimentary cover highlight the return to grade of the shelves from the northern Trinity Peninsula region.

High-resolution Bottom Parametric Source profiles have revealed details of the sedimentary structure of the upper 150 ms of the sediment drifts off the Pacific margin of Graham Land, Antarctic Peninsula. These profiles show that the dominant process is hemipelagic sedimentation, although instability processes are also important, as shown by the widespread presence of transparent, chaotic and semi-transparent acoustic facies. These new data are relevant to the evaluation of the palaeoenvironmental potential of the sediment drifts and show that the amount of remobilised sediment is significant in some of the drifts.

Sediments from the Antarctic continental margin may provide detailed palaeoenvironmental records for Antarctic shelf waters during the late Quaternary. Here we present results from a palaeoenvironmental study of two sediment cores recovered from the continental shelf off Mac. Robertson Land, East Antarctica. These gravity cores were collected approximately 90 km apart from locations on the inner and outer shelf. Both cores are apparently undisturbed sequences of diatom ooze mixed with fine, quartz-rich sand. Core stratigraphies have been established from radiocarbon analyses of bulk organic carbon. Down-core geochemical determinations include the lithogenic components AÍ and Fe, biogenic components opal and organic carbon, and palaco-redox proxies Mn, Mo and U. We use the geochemical data to infer past variations in the deposition of biogenic and lithogenic materials, and the radiocarbon dates to estimate average sediment accumulation rates. The Holocene record of the outer-shelf core suggests three episodes of enhanced diatom export production at about 1.8, 3.8 and 5.5 ka BP, as well as less pronounced bloom episodes which occurred over a shorter period. Average sediment accumulation rates at this location range from 13.7 cm ka−1 in the late Pleistocene early Holocene to 82 cm ka−1 in the late Holocene, and suggest that the inferred episodes of enhanced biogenic production lasted 100-1000 years. in contrast, data for the inner-shelf core suggest that there has been a roughly constant proportion of biogenic and lithogenic material accumulating during the middle to late Holocene, with a greater proportion of biogenic material relative to the outer shelf. Notably, there is an approximately 7-fold increase in average sediment accumulation rate (from 24.5 to 179 cm ka−1) at this inner-shelf location between the middle and late Holocene, with roughly comparable increases in the mass accumulation rates of both biogenic and lithogenic material. This may represent changes in sediment transport processes, or reflect real increases in pelagic sedimentation in this region during the Holocene. Our results suggest quite different sedimentation regimes in these two shelf locations during the middle to late Holocene.

Based on sedimenlological and micropaleontological work on three sediment cores collected at about 167° Ε in the western Ross Sea, Antarctica, and accelerator mass spectrometer l4C ages of organic carbon, we have reconstructed environmental changes in the area during the late Quaternary. Since 38 ka BP at latest, this area was a marine environment with low productivity. A grounded ice sheet advanced and loaded the sediments before about 30-25 ka BP. After 25 ka BP, the southernmost site (76°46'S) was covered by floating ice (shelf ice), preventing deposition of coarse terrigenous materials and maintaining a supply of diatom tests and organic carbon until 20 ka BP. The northernmost site (74°33'S) was in a marine environment with a moderate productivity influenced by shelf ice/ice sheet after about 20 ka BP. Since about 10 ka BP, a sedimentary environment similar to the present-day one has prevailed over this area.

We document the similarity of depositional facies occurring in gravity cores recovered from two disjunct regions of the Antarctic continental shelf: the Ross Sea and the MaC. Robertson shelf. The facies sequence model is represented in two cores, one collected during the 1995-1 cruise of the R/V Nathaniel R. Palmer (core NBP95 TC-18) and the other collected by the RSV Aurora Australis during cruise 149 in 1995 (core 149 39GC38). Both cores show a succession of facies indicative of ice-shelf retreat during the late-Pleistocene to Holocene transition. Distinct lithofacies range in thickness from a few tens of cm to 1 m and consist of (from bottom to top) a coarse, granulated sandy mud; laminated silt and clay; structureless silly clay; poorly sorted sandy siliceous mud; and siliceous mud and ooze. These facies represent the passage of distinct depositional regimes across the core sites, including sub-ice shelf beneath a basal debris zone; sub-ice shell distal to a debris zone; calving-line transition; and open marine. This facies model represents an advance in our understanding of Glacial marine stratigraphy for the Antarctic continental shelf and will provide the basis for more realistic palaeoglacial reconstructions.

Quaternary deposits in six sediment cores from the Scotia Sea, Antarctica, were examined for the presence of volcanic ash layers. The cores were recovered from water depths of 3369-4025 m. Altogether, 23 ash layers were found, 18 of which have been investigated by electron-probe microanalysis. Deception Island is identified as the source of all the ash layers analyzed. The upper ash layer in each core can be correlated across all six cores, over a distance of -100 km, on the basis of its unusual bimodal composition, major oxide geochemistry and stratigraphie position. Two other ash layers can also be correlated between several of the cores.

The southern Prince Albert Mountains, between David and Mawson Glaciers (75°30' to 76°S) in Victoria Land, Antarctica, comprise a series of nunataks with elevations ranging from 800m near the coast to 2300 m ~130 km inland. Geochemical and grain-size analyses of tills from these nunataks reveal three major groups of deposits:

• (1) coarse to medium sandy tills, found on Glaciolly streamlined summit plateaus of Kirk-pat rick Basalt above 2000 ma.s.l.., with geochemical compositions very similar to those of the underlying jurassic Kirkpatrick Basalt;

• (2) bimodal silty and sanely tills of the Sirius Group with Ferrar/Beacon-dominated geochemical compositions, at elevations of 1300-1600 m a.s.l. on striated summit plateaus and high-elevation terraces;

• (3) fine-grained tills with high SiO2 contents from ice-cored moraines at the lee sides of large nunataks.

The geochemical composition of sandy tills from the highest summit plateaus suggests that valleys had not yet cut through the Kirkpatrick Basalt and into Beacon and Ferrar rocks at the time of deposition. These tills represent a phase of temperate glaciation prior to deposition of diatom-bearing Sirius Group tills. The latter were deposited after a first phase of landscape dissection as inferred from geochemical data. The fine-grained ice-cored moraines are late-Pleistocene basal tills.

The presence of pre-Pliocene Glacial deposits on high mountain summits in the Prince Albert Mountains has implications for the interpretation of high-elevation Sirius Group sediments in other areas of the Transantarctic Mountains. It is possible that the “Sirius debate” has its origin in interpretations of both thin, barren pre-Pliocene deposits on high mountain summits and thick sequences of diatom-bearing deposits in valleys elsewhere in the Transantarctic Mountains. Both types of deposits are associated with the Sirius Group, but they belong to separate Glacial episodes.

The fluctuation of the East Antarctic ice-shect (EAIS) margin and relative sea-level change since the last glaciation are discussed from the stratigraphy and TAMS 14C ages of raised beach deposits in the northern part of the Soya Coast.The beach deposits reveal two marine sediment layers with in situ fossil shells of Laternula elliptica, and an interbedded fluvial sediment layer. The l4C ages of fossils in the lower, older marine beds ranged from 36 to 43 ka, and in the upper, younger beds from 4.9 to 5.2 ka without reservoir correction. Neither marine layers nor in situ fossil shells were disturbed by ice-sheet loading or scouring. The interbedded fluvial sediments appear to have been deposited by a stronger fluvial process than present meltwater activity in the area. These facts lead us to the following conclusions: (1) marine transgression occurred during the last interstadial around 40 ka or the Last Intcrglacial, and in the Holocene around 5 ka: (2) the EATS possibly retreated from the northern Sôya Coast prior to the Last Glaciol Maximum (LGM); (3) the fluvial process may have occurred during a period of low sea level which may have been a warmer period than the present, probably during the late-Glaciol to postglaciol age; and (4) the EAIS did not rcadvance over these sediments during or since the LGM.

Determining past sea-ice distribution is an important goal of paleocean-ographers. Here, we present a possible approach to determining past sea-ice distribution in the Southern Ocean during the Last Glaciol Maximum (LGM). Diatoms are the prin-cipal opal-forming organisms south of the Antarctic Polar Front; their productivity is partly mediated by the presence/absence of sea ice. We reasoned that there should be good coherence between percentage biogenic opal in surface sediments and percentage annual sea-ice cover. This hypothesis was tested by comparing percentage biogenic opal in surface sediments against modern-day sea-ice cover in surface waters directly above each core site. The chronology for each core was determined by various means (biostratigraphy, 14C age dating, and carbonate and opal stratigraphy). With the resulting curve we estimate that yearly concentration of sea ice can be determined to within 30%. Using these data, we estimated percentage sea-ice cover during the LGM for a number of sediment sites (50-66°S) from the Southern Ocean. Core sites now beneath 100% open water witnessed some 25-60% sea ice during the LGM, while core sites presently beneath sea ice during half of the year witnessed more than 75% sea-ice cover during the LGM.

Evidence from the Ross embayment, Antarctica, suggests an abrupt cooling and a concomitant increase in sea-ice cover at about 6000 BP (6 ka). Stable-isotope (δD) concentrations in the Taylor Dome ice core, at the western edge of the Ross embayment, decline rapidly after 6 ka, and continue to decline through the late Holocene. Methanesulfonic acid concentrations at Taylor Dome show opposite trends to δD Sediment cores from the western Ross Sea show a percentage minimum for the sea-ice diatom Fragilariopsis curta between 9 and 6 ka, whenTaylor Dome δD values are highest, followed by an increase through the late Holocene. Radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the Ross embayment ceased at about 6 ka, coincident with the environmental changes inferred from the sediment and ice-core records. The similarity in timing suggests an important role for climate in controlling the evolution of ice-shelf margins following the end of the last glaciation.

The potential effect of meltwater input from the Antarctic ice sheet is studied in sensitivity experiments with an ocean general circulation model coupled to an energy-balance model of the atmosphere. The effect is generally a reduction of surface salinity and deep convection in The Southern Ocean, associated with surface cooling. There is an accompanying, delayed intensification of the overturning in the Northern Hemisphere, leading to warmer conditions over both the North Atlantic and North Pacific With a sufficiently large meltwater pulse it is possible to trigger switches between different steady states of the ocean's thermohaline circulation, which differ mainly in the formation rates of North Atlantic Deep Water. Thus a transient perturbation in the Southern Ocean can lead to long-term climate changes in both hemispheres. The model reacts morè sensitively to melt water input into theWeddell Sea than into the Ross Sea.

A study of the δD and δ18O composition of ice formed at or near the grounding line was undertaken in Terra Nova Bay, East Antarctica. The results indicate that a double-diffusion mechanism is responsible for freezing at the grounding line in areas sheltered from the sub-ice cavity circulation. Freezing at the grounding line is unlikely to be prevalent today, but the situation may have been different in the past when the ice reached the outer limit of the continental shelf and there was no sub-ice cavity. The implications for sediment export in the polar oceans are explained.

Traditional models of Glaciol isostasy, derived predominantly for studying the response of the earth to the retreat of Northern Hemisphere ice sheets since the last ICC age, use earth models which assume constant lithospheric thickness. For Antarctica, where the continent below the ice sheet is two separate land masses differing in geological form, the assumption thai a uniform lithosphere can explain isostatic bchavioitr is questionable. Here, a method to calculate the glacio-isostatic adjustment of the continent with a laterally varying lithospheric thickness IS presented. The method is then used in a time-dependent ice-sheet model to model the isostatic response of the continent when the ice sheet passes through a Glaciol/interglacial transition. Various relations bet ween the “crustal thickness” beneath Antarctica, derived from seismic data, and the “lithospheric thickness” estimate used in glacio-isostatic calculations are assumed in a sensitivity study. Using the simplest relationships between crustal and lithospheric thickness, the greatest sensitivity of the ice sheet to the crustal structure of Antarctica is not in the interior but at coastal locations, particularly near the major ice shelves. During periods of ice-sheet advance the grounding-line migration of the shelves varies according to the depression of the earth peripheral to the ice sheet. The peripheral depression depends on the regional elasticity of the lithosphere which is controlled by the lithospheric thickness. Therefore the capacity for the ice sheet to advance varies with the regional thickness of the crust.

In the reconstruction of the Glaciol history of ice-covered areas, ice-sheet dynamics — translating the climatic signal to glacier variations — is often disregarded. in this paper an experimental framework, based on ice-sheet modeling, is presented to determine possible glacier transfer functions linking the climatic signal to the proxy record of Glaciol-geological observations. Applied to a flowline through a marginal mountain range in Dronning Maud Land, Antarctica, it provides a better insight into the Glaciol history of the last 200000 years. With respect to the different combinations of boundary conditions, at least two scenarios were obtained for the Glaciol history in the vicinity of the mountain range. While inland of the mountains and near the coast the response to the climatic signal is more or less similar for both scenarios, with in the mountain range a large difference was found, depending on the choice of boundary conditions. This aberrant behavior of the ice sheet near mountain ranges is an important element in the interpretation of the Glaciol-geological proxy record as a function of the climatic signal. The reason for the different response patterns encountered in the mountain area is primarily related to the sensitive interplay between surface mass balance and thermomechanical properties of the glacier.

The Dome Fuji Project is a comprehensive study of present and past glaeiological/climatological features of the Antarctic ice sheet in east Dronning Maud Land. Field observations on a 100U km traverse route from the coast to Dome Fuji slum changes in various glaciological parameters with surface elevation and distance from the coast. Deep ice-core drilling at Dome Fuji was started in August 1995 and reached a depth of 2503.52 m in December 1996. in situ core analyses revealed 25 visible tephra layers and a number of distinct cloudy bands in the ice.

An ice core to 2503.52 m depth was drilled during 1995 and 1996 at 77°19′01″S, 39°42′12″ E (3810 m a.s.l.), at the summit of Dome Fuji, East Antarctica. Climatic and environmental conditions were observed at the coring site throughout the 2 years of wintering operation. Meteorological and glaciological observations made clear the present surface processes of mass balance. The chemistry of the surface snow layers was observed for investigation of the atmospheric environment reflected in snow deposits.

Core analyses have been carried out in Japan. Permeability and density measurements show that air bubbles are completely closed off by densification processes at about 98 m depth. The vertical profile of δ18O suggests that the core covers two warm stages and one cold stage from the surface down to 1800 m depth. The transition from the cold to the warm period affects the vertical distribution of ice-crystal size. The chemical constituents in the ice core show large differences between warm and cold periods. A depth–age relationship is presented and a study made of palaeoclimatic and core signals.

An investigation of crystal-size and microparticle variations has been carried out for the 1196 m ice core retrieved from Dome Summit South (DSS) near the summit of Law Dome, East Antarctica. Results show that for ice deposited during the Holocenr (depth <1103 m), microparticle concentrations are low. Variations of crystal size with in the Holocenc ice are due to growth with time at a temperature-dependent rate, and recrystallisation as a consequence of the ice flow. in the DSS ice core the highest microparticle concentration occurs close to the depth (1133 M) at which oxygen isotope ratios exhibit the greatest negative values, i.e. the Last Glaciol Maximum (LGM). Also at this depth, crystal size reduces sharply from a general crystal growth trend above to near minimum core values below. For ice originating during the LGM, the concentration of particles is an order of magnitude greater than the mean Holocene concentration. Laboratory annealing tests at -1 °C confirm the retarded crystal growth in the high-microparlicle-concent ration ice.

The isotopic composition of Pb and the concentrations of Pb, Ba and Bi wert- measured in selected ice-core samples from Law Dome, East Antarctica, to a depth of 1196 m. The range of concentrat ions found in decontaminated ice was 0.03-1.5 pgg−1 for Pb, 0.9-6.1 pgg−1 for Ba and 0.4 17 fgg −1 for Bi, excluding the deepest sample which contained ~1 pjpm of rock dust. The abundances of all four stable lead isotopes were measured and gave 206Pb/207Pb ratios up to ~1.23. Avalue of 208Pb/207Pb= 2.78 was measured in the deepest sample and is consistent with reported Pb isotope ratios of Antarctic gran-ulites. Although the element concentrations in some samples were lower than have been reported elsewhere, geochemkal and isotopic evidence indicated that a number of samples were contaminated with Pb not present in the original ice. However, it appears that the technical skills now available are approaching the level where careful sample selection, decontamination and analysis can yield accurate results for the concentration and isotopic composition of Pb in Earth's purest naturally occurring ice.

During the ninth Italian Antarctic Expedition, a 22 m deep firn core was drilled on the Hercules Névé (ΗΝ) in the Transantarctic Mountains, northern Victoria Land, Antarctica, The continuous dust record from HN, spanning 70 years from 1927 to 1994, displays sharp differences between the upper 15.5 m and the bottom part. The background of dust concentration in the upper part is quite homogeneous, with values around 6.5 x 103 particles g −1 of water, and some peaks reaching maximum values of 1.0-1.5 x 104 particles g−1 of water. in this part the volume-size distribution of particles shows a relative maximum around 0.9 μm while a second maximum occurs for particles larger than 12 μm . The larger particles are likely to have a local origin, while the small-size component may be representative of long-range transport dust. Below 15.5 m the record shows higher values in both background and peak concentration, with mean values of 1.6 x 104 particles g−1. The volume-size distribution changes from 0.9 to 1.5μm in parallel with the increase of dust concentration. The dust record suggests significant increases in concentration for the periods 1932-42 and 1951-64. It suggests some correlations with precipitation anomalies over South America and indirectly supports the hypothesis that small-sized dust at HN may originate from South America.

Antarctic radio-echo sounding (RES) data at 60 MHz have been used to determine an independent stratigraphy for the ice core at Vostok station, based on internal radio-echo layering. A-scope RES data allow the amplitude of reflected electromagnetic (e/m) waves to be measured and, by accounting fur geometric spreading and absorption losses of the e/m wave, power reflection coefficients (PRCs) to be calculated. This information is compared with time-continuous Z-scope RES data in order to trace continuous e/m reflectors across the ice sheet. Internal ice-sheet horizons deeper than 800 m are caused by layers of ice that possess distinctly different dielectric properties (i.e. acidic layers) compared with ice above and/or below. Comparison of four PRC samples, located ~ 5 km from Vostok station, revealed five distinct internal reflections between 1000 and 2200 m. Z-scope data from directly over the Vostok station site show the same five prominent internal radio-echo layers. The depth-related radio-echo signals were then compared with chemical records from the Vostok ice core, including the H2SO4 signal, a major component of which is derived from volcanic events. From this procedure, internal radio-echo reflectors and Vostok ice-core acid measurements were correlated. Avery good match was made between Z-scope and ice-core data. However, vertical offsets observed between A-scope-derived RES layers and peaks in the chemical signal of up to 100 m are probably due to the general Inkling of the ice-sheet layering between the core site and the RES flight-line. We conclude that 60 MHz RES layering may be regarded as a stratigraphy independent of palaeoclimate, and may be used to correlate other deep Southern Hemisphere ice cores.