Release of an ice-active substance by Antarctic sea ice diatoms

Interstitial water from the diatom-rich ice platelet layer in McMurdo Sound, Antarctica contains a macromolecular, ice-active substance (IAS) that, at in situ concentrations, causes dense pitting on the basal surfaces of growing ice platelets. In this respect, it resembles several fish antifreezes that also cause pitting on ice surfaces, but unlike the antifreezes, it does not lower the freezing point. The IAS appeared to be released by diatoms, as extracts from the diatoms contained IAS, while seawater from a diatom-free area did not. No evidence of IAS was found in several species of temperate water diatoms. The ice-pitting activity of the IAS was destroyed by proteases and by incubation at 40° C, but not by periodate oxidation, or by incubation with galactosidase or endonuclease. Thus, activity appears to arise from a protein or protein component, and not from carbohydrate or nucleic acids. Potential roles of the IAS in the sea ice community are discussed.