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A real-time video camera probe was deployed in a hot-water drilled borehole through the Amery Ice Shelf, East Antarctica, where a total ice thickness of 480 m included at least 200 m of basal marine ice. Down-looking and side-looking digital video footage showed a striking transition from white bubbly meteoric ice above to dark marine ice below, but the transition was neither microscopically sharp nor flat, indicating the uneven nature (at centimetre scale) of the ice-shelf base upstream where the marine ice first started to accrete. Marine ice features were imaged including platelet structures, cell inclusions, entrained particles, and the interface with sea water at the base. The cells are assumed to be entrained sea water, and were present throughout the lower 100-150 m of the marine ice column, becoming larger and more prevalent as the lower surface was approached until, near the base, they became channels large enough that the camera field of view could not contain them. Platelets in the marine ice at depth appeared to be as large as 1-2 cm in diameter. Particles were visible in the borehole meltwater; probably marine and mineral particles liberated by the drill, but their distribution varied with depth.

The Amery Ice Shelf Ocean Research (AMISOR) project aims to examine and quantify processes involved in the interaction between the ice shelf, the interior grounded ice and the oceanic water masses that circulate beneath it. Two boreholes were melted through the shelf, within 100 km of the calving front, to access the ocean cavity. One (AM02) was at a site where it was believed that basal melt was occurring, and the other (AM01) was in a region with accreted marine ice. At both sites the summertime ocean structure revealed meltwater-modified boundary layers up to 100 m thick immediately beneath the shelf. Salinity and temperature data in the upper cavity at AM02 showed a strong seasonal cycle as a result of a combination of ice-shelf basal melt, and the intrusion of ocean water masses modified by sea-ice processes in Prydz Bay. At AM01, a 200m thick layer of marine ice underlay the meteoric ice, and showed an increase in salinity and decrease in stable-isotope fractionation with depth. The lowest 100m of marine ice was highly permeable, with a rectangular banded textural facies. Other preliminary results from this study are also reported.

ABSTRACT. The temperature profile in the 1200 m deep Dome Summit South (DSS) borehole near the summit of Law Dome, Antarctica, was measured in 1996, 3 years after the termination of the deep drilling.The temperature profile contains information on past surface temperature over the last 4 ka. This temperature history is determined by the use of a Monte Carlo inverse method in which no constraints are placed on the unknown temperature history and no solution is assumed to be unique. The temperature history is obtained from a selection of equally well-fitting solutions by a statistical treatment.The results show that solutions covering the last 4 ka have a well-developed central value, a most likely temperature history. The temperature record has two well-developed minima at AD1250 and 1850. From 1850 to the present, temperatures have gradually increased by 0.7 K. The reconstructed temperatures are compared with the stable oxygen isotope ( IV y) from the DSS ice core. TEMPERATURE PROFILE FROM LAW DOMEIn 1993 the glaciology group of the Australian Antarctic Division completed the drilling of a 1200 m deep ice core to bedrock 4.68 km south-southwest of the highest point on the Law Dome ice cap (66³46 H S,112³48 H E;1370 m a.s.l.) (Morgan and others, 1997). In 1996 a temperature profile was inferred from measurements every 10^20 m in the deep borehole, with a measuring accuracy of 0.02 K (Van Ommen and others, 1999). Temperature measurements in the top 50 m are from the cased part of the deep borehole, above the liquid level, and they are disturbed and influenced by the temperature and pressure conditions in the building constructed over the borehole. They do not represent the undisturbed firn and ice temperatures.In 1997, temperatures were measured in a 270 m deep dry borehole drilled 80 m south of the deep borehole (Van Ommen and others, 1999). These temperatures have an accuracy of 0.05 K, but are believed to be a better representation of the undisturbed firn and ice temperatures than those from shallow depths in the deep borehole. The two temperature profiles were combined in such a way that the shallow borehole profile was used down to 50 m, the depth zone between 50 and 270 m was used to align the two profiles, and the temperatures from the deep borehole were used below 50 m. The combined temperature profile (Fig. 1a, solid curve) is used to reconstruct the past temperature history. A study of the noise in the data (Fig. 1b) clearly shows the increased errors in the measurements from the shallow borehole. Below 750 m depth, convection cells in the borehole liquid are seen to appear. Temperature excursions in the profile due to these cells increase as the temperature gradient increases (Gundestrup, 1989; Gundestrup and others, 1994; Gundestrup and Clow, 1997).The convection cells are smoothed out before the reconstruction of the past temperatures is attempted, as they do not represent ice temperatures.A temperature profile assuming steady-state conditions and the present-day ice-sheet configuration (accumula...

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