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

As a component of the AMISOR (Amery Ice Shelf Ocean Research) project, meteoric and accreted marine ice cores were retrieved from the Amery Ice Shelf, East Antarctica.

During the 2001/02 and 2003/04 austral summers ice cores were obtained from the AM01 and AM01b sites; approximately 100 km from the shelf front. Further cores were obtained 70 km upstream, along the same flow line, at the AM04 site during 2005/2006. At these sites, the Amery Ice Shelf has a layered structure. The upper layer consists of meteoric ice, from local accumulation and ice entering the shelf through the Lambert Glacier drainage system. The bottom layer is accreted marine ice, over 200 m thick.

Crystal orientation fabric and grain size measurements are presented for meteoric and marine ice cores. Meteoric ice samples are characterized by grain areas >50 mm² and multiple- maxima crystal orientation fabrics. It is suggested that stress relaxation in ice flowing into the shelf from the Lambert Glacier drainage basin strongly influences the observed meteoric ice fabrics.

Vertical, large circle girdle orientation fabrics observed within the marine ice are influenced by the presence of brine and insoluble microparticle inclusions. Grain sizes in the marine ice are <10 mm² due to microparticles restricting grain growth. A strong single maximum fabric and layered, rectangular texture w as observed in the marine ice sample obtained closest to the ice shelf base. The fabric and texture of this sample are considered to be evidence for marine ice layer accumulation by frazil ice platelet accretion.