Initial borehole results from the Amery Ice Shelf hot-water drilling project

Abstract

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.

Meteoric and marine ice crystal orientation fabrics from the Amery Ice Shelf, East Antarctica

“…Figure 3 provides a schematic illustration of the ice-shelf thickness profile and structure along the AM04-AM01 flowline and indicates a horizon within the marine ice layer, referred to as the hydraulic connection depth. Marine ice below this depth has a sufficient concentration of interconnected brine-filled pores and channels to maintain a hydraulic connection to the underlying ocean (Craven and others, 2004). At AM01 the measured total ice thickness is 479 m, with a hydraulic connection noted at a drill depth of 376 m, suggesting the lower 103 m of marine ice is permeable (Craven and others, 2004).…”

“…Particulate inclusions, present variously in linear, planar and random dispersions, have been observed in all Amery Ice Shelf marine ice cores from the G1, AM01/AM01b and AM04 borehole sites (Wakahama, 1974;Craven and others, 2004Craven and others, , 2005Craven and others, , 2009). Roberts and others (2007) report that particulate inclusions from the AM01 cores comprised approximately two-thirds lithogenic and one-third biogenic material, although it is reasonable to expect these proportions to vary throughout the marine ice layer due to spatial and temporal variability in the accretion process and biological activity beneath the Amery Ice Shelf and in Prydz Bay, north of the ice shelf.…”

“…At AM01 the hot-water drill coring barrel was used to retrieve ice cores at 240 m depth within the meteoric ice and depths of 290, 360 and 390 m within the marine ice layer (Craven and others, 2004). Figure 3 provides a schematic illustration of the ice-shelf thickness profile and structure along the AM04-AM01 flowline and indicates a horizon within the marine ice layer, referred to as the hydraulic connection depth.…”

History of benthic colonisation beneath the Amery Ice Shelf, East Antarctica

“…During the austral summer of 2003-2004 a hot water drill was used to create a 400 mm access hole through the 480 m thick Amery Ice Shelf (Craven et al 2004). A purpose built slim line gravity corer, 12 cm in diameter, was lowered through the access hole to collect a 47 cm long sediment core at Site AM01b (69°26' S, 71°27' E) beneath the Amery Ice Shelf (for further details see Hemer et al in press).…”

Platelet ice attachment to instrument strings beneath the Amery Ice Shelf, East Antarctica

“…Between 2001 and 2010 the Amery Ice Shelf Ocean Research (AMISOR) project (Craven and others, 2004) established a network of six hot-water drilled boreholes through the Amery Ice Shelf (Fig. 1).…”