A diver inspecting a large barrel sponge while diving in McMurdo Sound's supercooled seawater. In the glare of the diver's flashlight you can see small ice crystals floating in the water column. These crystals sometimes appear when the seawater is slightly below its freezing point--a phenomenon unique to Antarctica's coastal areas. Seawater supercooling may increase the risk of freezing to the fishes and invertebrates.