Observation and modeling of platelet ice fabricin McMurdo Sound, Antarctica

摘要

During the annual growth of landfast ice in McMurdo Sound, Antarctica, an episodicflux of platelet ice crystals from the ocean contributes to the build up of a porous subiceplatelet layer, which is steadily incorporated into the sea ice cover as it thickens overwinter. In November 2007, we examined the spatial variability of these processes bycollecting sea ice cores, with simultaneous oceanographic observations, along an east-westtransect in the sound. Previously identified draped and bladed platelet ice types wereobserved. In addition, we identify resumed columnar growth which appears to be a resultof geometric selection from the subice platelet layer after the arrival of new plateletcrystals from the ocean has ceased. A numerical model of mechanical platelet iceprocesses is developed that predicts crystal texture and c axis distributions, producingvirtual incorporated platelet ice with known growth history. This model demonstrates howa disordered subice platelet layer arises from an initially flat interface and suggests thatsuch a layer is more likely to form later in the growth season. The model also suggestshow the grain boundary density in incorporated platelet ice responds to changes in the fluxof loose platelet crystals from the ocean. Application of this result to our 2007 platelet iceobservations indicates that sea ice in western McMurdo Sound is subject to larger andmore persistent platelet fluxes than the ice in the east. This is consistent with the pattern ofin situ supercooling just beneath the ocean surface.