Reply to comment on 'Oxygen budget of a perennially ice-covered Antarctic lake'

Top (Top et al. 1983, 1985) has found that in laboratory-grown ice and in Arctic ice floes 50% of the gas is retained in the ice upon freezing. As Top points out in his comment, Bari and Hallett (1974), whom we cite in Wharton et al. (1986), actually discussed how and when the ice-rejected dissolved gas gets back into the ice. We did not misquote this reference. Careful examination of the Bari and Hallett paper will reveal that in their experiments “bubbles cease abruptly” at freezing rates below about 3 pm sl. The freezing rate of the ice in the Antarctic lakes is estimated to be 30 cm yrl which corresponds to 0.009 pm s-l, well below the limit of bubble formation. The rate of freezing is an important variable in the exclusion of gas when water freezes. Hence, we do not expect a significant amount of gas to be retained in the Antarctic lake ice. This is consistent with observations of the ice cover. The results from laboratory experiments and Arctic floes reported by Top are not relevant since much higher freezing rates occur in these relatively thin ice environments. Indeed, the thick, stable, perennial ice cover of an Antarctic lake is unique in nature. Therefore, it is not too surprising that Arctic experience led Top to an incorrect conclusion. In conclusion, we feel that our original assumption of 100% exclusion is indeed representative of the conditions in the Antarctic lake. Top’s other comments are based on his incorrect estimate of the gas retention and hence do not apply.