Summary
I discuss 300-400 MHz ground-penetrating radar (GPR) profiles of sea ice in McMurdo Sound, Antarctica. I recorded them in mid October, 2005 when ice temperature could have eliminated most brine in the ice and allowed the bottom to be profiled. The transects total 8 kIn and extend from near McMurdo Station to the transition onto the ice shelf. Horizons showing continuous and intermittent stratification occur throughout the ice. Their phases indicate both relatively low and high permittivity layers, which are probably caused by variations in porosity and brine volume. The deepest horizon consistently occurs at about 2.5-3 m depth, which is the thickness expected for this ice, but it is of the wrong polarity and too weak to be from seawater. Consequently, this depth may be a minimum value. A profile segment over the transition to the glacial ice of the McMurdo Ice Shelf shows the onset of the well known brine layer, and it has the correct strength and polarity. The brine layer within the glacial fim appears to be directly fed from a layer within the sea ice and not from the bottom. However, this seems unlikely because of such a limited supply of brine needed to feed the immense extent of the brine layer. Therefore, it may be either an intermittent connection until the sea ice is released, or there may have been a separation between the glacial and the sea ice that allowed sea water to rise to this layer.