A STUDY OF BRASH ICE IN THE PROXIMAL MARINE ZONE OF A SUBPOLAR TIDEWATER GLACIER

Intermittent calving of tidewater Maar Glacier into Arthur Harbor (Anv ers Island, Antarctic Peninsula) produces mainly brash ice (fragments <2 m in diameter). To assess the potential role of brash ice in the se award transport of glacigenic sediment in this subpolar region, measur ements were made of (1) brash melt rates under laboratory and field co nditions and (2) size distributions of freshly calved brash. In consta nt-temperature (1 degrees C) laboratory runs, melt rates for similarly shaped bergs increased significantly with relative flow velocity and were also greater for bergs containing fractures or air bubbles. Under held conditions, brash bergs subjected to rough open water were obser ved to melt approximately 20 times faster (range = 12-26) than those l ocked in densely packed jams protected from wave and current action. P ublished melt-rate equations developed for deep-draft or still-water b ergs greatly underestimate melt rates for brash in rough sea surfaces. Size-frequency distributions (by weight) of four 102 m(2) samples of dense brash are closely approximated by Rosin-probability distribution s. For an average population of freshly calved brash subjected to mean open-water melt rates observed in Arthur Harbor, over 90% of the berg s will completely melt within 24 hours. Consequently, little brash esc apes the proximal marine zone, and most debris rafted by such bergs is probably deposited within a few hundred meters of the glacier terminu s.