[1] This study uses seismic receiver functions, surface wave phase velocities, and airborne gravity measurements to investigate the structure of the Transantarctic Mountains (TAM) and adjacent regions of the Ross Sea (RS) and East Antarctica (EA). Forty-one broadband seismometers deployed during the Transantarctic Mountain Seismic Experiment provide new insight into the differences between the TAM, RS, and EA crust and mantle. Combined receiver function and phase velocity inversion with niching genetic algorithms produces accurate crustal and upper mantle seismic velocity models. The crustal thickness increases from 20 ± 2 km in the RS to a maximum of 40 ± 2 km beneath the crest of the TAM at 110 ± 10 km inland. Farther inland, the crust of EA is uniformly 35 ± 3 km thick over a lateral distance greater than 1300 km. Upper mantle shear wave velocities vary from 4.5 km s À1 beneath EA to 4.2 km s À1beneath RS, with a transition between the two at 100 ± 50 km inland near the crest of the TAM. The $5 km thick crustal root beneath the TAM has an insufficient buoyant load to explain the entire TAM uplift, suggesting some portion of the uplift may result from flexure associated with a buoyant thermal load in the mantle beneath the edge of the TAM lithosphere.

[1] The flow velocity of ice stream D, West Antarctica has been measured to vary by a factor of three over the course of a day. These fluctuations are measured at the grounding line as well as upstream of the grounding line in the ice plain of ice stream D. The diurnal velocity fluctations appear to be driven by the tide beneath the Ross Ice Shelf. These results suggest that there is significant, and heretofore poorly understood, influence of the ocean tide and of the ice shelf on the dynamics of ice stream flow.

The last glacial period exhibited abrupt Dansgaard-Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeoclimate archives. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard-Oeschger cycle and vice versa, suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw. Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision. Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 ± 92 years (2σ) for Dansgaard-Oeschger events, including the Bølling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 ± 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard-Oeschger dynamics.

The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

The WAIS (West Antarctic Ice Sheet) Divide deep ice core was recently completed to a total depth of 3405 m, ending 50 m above the bed. Investigation of the visual stratigraphy and grain characteristics indicates that the ice column at the drilling location is undisturbed by any large-scale overturning or discontinuity. The climate record developed from this core is therefore likely to be continuous and robust. Measured grain-growth rates, recrystallization characteristics, and grain-size response at climate transitions fit within current understanding. Significant impurity control on grain size is indicated from correlation analysis between impurity loading and grain size. Bubble-number densities and bubble sizes and shapes are presented through the full extent of the bubbly ice. Where bubble elongation is observed, the direction of elongation is preferentially parallel to the trace of the basal (0001) plane. Preferred crystallographic orientation of grains is present in the shallowest samples measured, and increases with depth, progressing to a vertical-girdle pattern that tightens to a vertical single-maximum fabric. This single-maximum fabric switches into multiple maxima as the grain size increases rapidly in the deepest, warmest ice. A strong dependence of the fabric on the impurity-mediated grain size is apparent in the deepest samples.