Summary
Hot water drilling of the Amery Ice Shelf conducted as a component of the AMISOR (Amery Ice Shelf Ocean Research) project to enable access the underlying ocean cavity has allowed limited retrieval of ice cores using a hot water coring barrel. During the 2001/02 and 2003/04 field seasons ice cores were obtained from the AM01 and AM01b drill sites, with further cores obtained from the AMO4 site during 2005/06. In both locations the ice shelf is characterised by a three layered structure. The upper layer consists of ice formed by local accumulation of snow on the ice shelf itself and is not described here. The middle layer is meteoric (continental) ice entering the Amery Ice Shelf through the Lambert glacier system and the bottom layer consists of marine ice accreted onto the ice shelf base. We present crystal orientation and size measurements for meteoric and marine ice samples obtained from the AM01 and AM04 drill sites. For the meteoric ice samples obtained 20 and 45 m above the meteoric-marine ice interface at the AM01 and AM04 sites respectively, the crystal orientation fabric and grain size are compared to expected patterns based on interpretation of satellite derived ice shelf strain rates and historical Amery Ice Shelf core data. Previous analysis of Amery Ice Shelf marine ice (Craven et al 2005) from below the hydraulic connection depth at the AM01 site indicates crystal sizes and orientation consistent with conditions during formation, with no indication of crystallographic modification by in-situ deformation resulting from large scale ice shelf dynamics. We compare this observation to the current data for AM01 and AM04 marine ice samples obtained higher in the marine ice layer, at depths ranging from above the hydraulic connection to within 5 m of the meteoric-marine ice interface. Evidence for changes in marine ice crystallography induced by ice shelf dynamics is discussed with particular reference to distributions of crystal orientation and grain size and the influence of marine debris in controlling grain size.