Mounting evidence from models and geological data implies that the Antarctic Ice Sheet may behave in an unstable manner and retreat rapidly in response to a warming climate, which is a key factor motivating efforts to improve estimates of Antarctic ice volume contributions to future sea-level rise. Here, we review Antarctic cooling history since peak temperatures of the Middle Eocene Climatic Optimum (approx. 50 Ma) to provide a framework for future initiatives to recover sediment cores from subglacial lakes and sedimentary basins in Antarctica's continental interior. While the existing inventory of cores has yielded important insights into the biotic and climatic evolution of Antarctica, strata have numerous and often lengthy time breaks, providing a framework of ‘snapshots’ through time. Further cores, and more work on existing cores, are needed to reconcile Antarctic records with the more continuous ‘far-field’ records documenting the evolution of global ice volume and deep-sea temperature. To achieve this, we argue for an integrated portfolio of drilling and coring missions that encompasses existing methodologies using ship- and sea-ice-/ice-shelf-based drilling platforms as well as recently developed seafloor-based drilling and subglacial access systems. We conclude by reviewing key technological issues that will need to be overcome.

This chapter contains sections titled: Introduction Geological Setting Regional Stratigraphy Age and Correlation with Ciros-1 Geological Map and Cross-Section Comparison with Sequences of Similar Age In New Zealand Summary

The first oceanographic data from beneath the McMurdo Ice Shelf, Antarctica, are presented here with synchronous observations from southern McMurdo Sound. Multilevel current profiles at three sites over spring tide revealed primarily K1 diurnal tides with net transport from McMurdo Sound into the basin beneath the McMurdo Ice Shelf. The time series in southern McMurdo Sound captured the 14 day tidal phase shift and showed that transport into the subice shelf cavity was even greater over neap tide, with average transport ∼1.8 Sv. McMurdo Sound sea ice cover during this period was the heaviest in 25 years of satellite record and was associated with the proximity of two massive icebergs, B‐15a and C‐19. The warmest waters observed beneath the ice shelf were set at the surface freezing temperature, probably through recent interaction with this extensive sea ice cover. Observed ranges of temperature and salinity were narrowed to the extent that neither Antarctic Surface Water nor High Salinity Shelf Water were observed beneath the ice shelf. We anticipate that in years with more typical summer sea ice cover surface waters swept beneath the ice shelf will be significantly warmer, having even greater potential for basal melt near the ice shelf front. Our observations also exhibit some of the interactions particular to the subice shelf ocean environment. These include occurrence of platelet ice in ice shelf meltwater, boundary layer friction effects from the ice cover on the ocean, and tidal currents driving enhanced melting near the ice shelf front.

Because of the paucity of exposed rock, the direct physical record of Antarctic Cenozoic glacial history has become known only recently and then largely from offshore shelf basins through seismic surveys and drilling. The number of holes on the continental shelf has been small and largely confined to three areas (McMurdo Sound, Prydz Bay, and Antarctic Peninsula), but even in McMurdo Sound, where Oligocene and early Miocene strata are well cored, the late Cenozoic is poorly known and dated. The latest Antarctic geological drilling program, ANDRILL, successfully cored a 1285-m-long record of climate history spanning the last 13 m.y. from subsea-floor sediment beneath the McMurdo Ice Shelf (MIS), using drilling systems specially developed for operating through ice shelves. The cores provide the most complete Antarctic record to date of ice-sheet and climate fluctuations for this period of Earth's history. The >60 cycles of advance and retreat of the grounded ice margin preserved in the AND-1B record the evolution of the Antarctic ice sheet since a profound global cooling step in deep-sea oxygen isotope records ~14 m.y.a. A feature of particular interest is a ~90-m-thick interval of diatomite deposited during the warm Pliocene and representing an extended period (~200,000 years) of locally open water, high phytoplankton productivity, and retreat of the glaciers on land.

AbstractAn updated compilation of published and new data of major-ion (Ca, Cl, K, Mg, Na, NO3, SO4) and methylsulfonate (MS) concentrations in snow from 520 Antarctic sites is provided by the national ITASE (International Trans-Antarctic Scientific Expedition) programmes of Australia, Brazil, China, Germany, Italy, Japan, Korea, New Zealand, Norway, the United Kingdom, the United States and the national Antarctic programme of Finland. The comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across Antarctica and exhibit distinct geographical patterns. The Antarctic-wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples. This paper aims to initiate data compilation and administration in order to provide a framework for facilitation of Antarctic-wide snow chemistry discussions across all ITASE nations and other contributing groups. The data are made available through the ITASE web page (http://www2.umaine.edu/itase/content/syngroups/snowchem.html) and will be updated with new data as they are provided. In addition, recommendations for future research efforts are summarized.

It is known from small sets of tide gauges that sub‐surface pressure (sea level corrected for the inverse barometer effect) around Antarctica varies coherently around about half of the continent, and that this coherent signal is related to atmospheric forcing in the form of the Antarctic Oscillation, or Southern Hemisphere Annular Mode. We here confirm that this coherence extends to a more extensive network of tide gauges, and to parts of the continental shelf far from the shore, as measured by bottom pressure gauges. We use time series from an eddy‐permitting ocean model with realistic forcing to relate the coherent mode to fluctuations in transport through Drake Passage, and confirm, using a 1° resolution barotropic model, that the fluctuations are predominantly due to barotropic dynamics, although baroclinic dynamics are expected to play an increasing role at interannual timescales.

Data from a new sea-level recorder station at Scott Base on Ross Island and from a longestablished sea-level recorder at Cape Roberts are analysed for tides and storm surge. Tides are primarily diurnal and their amplitude reduces to almost zero every 13.66 days, corresponding to the Moon's crossing of the equator. Global tide models are shown to give a poor fit with observations in Ross Sea, and although a local tide model gives a better fit for phase, the amplitudes are still not accurate. The only atmospheric tide that is significant is the semidiurnal solar tide whose amplitude is much larger than empirical models predict. Storm surge can be largely explained by changes in atmospheric pressure. Significant storm surge events are infrequent compared to locations at lower latitudes.

We present the first dedicated study of the thermal properties of perennially frozen, ice‐cemented, subsurface Dry Valley permafrost. From time series analysis of 14 months' temperature measurements, we resolve depth and seasonal variations in the thermal properties at two nearby sites at Table Mountain with different origin, composition, and polygonal ground patterning. We determine apparent thermal diffusivity (ATD) profiles directly from thermistor array measurements at 13.5‐cm‐depth intervals and 4‐hour time intervals in the top 2 m. We treat the system as purely conductive year round due to the cold temperatures and compare the performance of several common analysis schemes with a graphical finite difference method that we present in detail. This comparison is facilitated by one site showing strong depth variations including an abrupt twofold increase in ATD across a sharp compositional boundary. We characterize the composition of the inhomogeneous ground from recovered cores and estimate an ice‐fraction‐dependent heat capacity in the range C = 1.7 ± 0.1 to 1.8 ± 0.1 MJ m−3 °C−1. We calculate apparent thermal conductivity profiles that correlate very well with the core compositions. The conductivity generally lies in the range 2.5 ± 0.5 W m−1 °C−1 but is as high as 4.1 ± 0.4 W m−1 °C−1 for a quartose Sirius sandstone unit at one site. The seasonal variation in the ATD is consistent with its expected temperature dependence.

Downwasting has altered the morphology of the terminus region of the Tasman Glacier between 1971 and 1993. Rapid melting began in the late 1960s in a few isolated melt ponds in the centre and in a small elongated lakelet at the eastern lateral moraine. These ponds and lakes grew rapidly in size during the 1970s and coalesced to form a large melt lake by about 1990. This melting has led to a disintegration of the entire terminus region, and now occurs as far as 3 km upstream from the old terminus. The main front of the glacier has retreated c. 1.5 km since 1982. The breaking up of the glacier has been accelerated by the onset of iceberg calving-a process which probably started in 1991. The icebergs can have volumes of several millions of cubic metres before they break up into smaller ice masses that melt slowly during the summer. A temperature survey has shown that the melt lake is almost isothermal (0.3-0.5 degrees C). A poorly understood convection mechanism prevents suspended silt from settling and causes the uniform grey colour of the lake (here called ''Tasman Lake'').Gravity surveys in 1971/72 and in 1982 revealed that the average thickness of the glacier was between 150 and 200 m over the large (almost 2 km(2)) area now occupied by the melt lake. The bottom level of the glacier was close to 600 m a.s.l.; this level has been confirmed by recent radar soundings and bathymetric surveys. The present lake level stands at 727 m a.s.l. The surveys demonstrate how the terminus region of the largest New Zealand glacier has disintegrated over the past 22 years.

Marine-ending glaciers may retreat with global warming as sea level rises by ocean thermal expansion. If the sea floor rises by sediment accumulation, then glaciers may not feel the effect of sea level rise. A submersible ROV and other techniques have been used to collect data from temperate and polar glaciers to compare sediment production and mass balance of their grounding-line systems. Temperature Alaskan valley glaciers flow at about 0.2--2 km/a and have high volumes of supraglacial, englacial and subglacial debris. However, most sediment contributed to the base of their tidewater cliffs comes from subglacial streams or squeezing out subglacial sediment and pushing it with other marine sediment into a morainal bank. Blue Glacier, a thin, locally fed polar glacier in Antarctica, flows slowly and has minimal glacial debris. The grounding-line system at the tidewater cliff is a morainal bank that forms solely by pushing of marine sediment. An Antarctic polar outlet glacier, Mackay Glacier, terminating as a floating glacier-tongue, has similar volumes of basal debris to Alaskan temperature glaciers and flows at 250 m/a. However, no subglacial streams issued from Mackay's grounding line and all sedimentation was by rockfall and grainfall rainout from seawater undermelt of the tongue. Amore » grounding-line wedge of glacimarine diamicton is deposited over subglacial (lodgement ) till. Although Antarctic grounding-line accumulation rates are three orders of magnitude smaller than Alaskan rates, both are capable of compensating for predicted rises in sea level by thermal heating from global warming.« less