Ice break-up on southern Lake Baikal and its relationship to local and regional air temperatures in Siberia and to the North Atlantic Oscillation

The calendar date of ice break-up on southern Lake Baikal has been recorded uninterruptedly since 1869. A strong trend to earlier thawing up to around 1920 (1 d per 3.3 yr) is followed by the lack of any significant trend the reafter. For the period 1931-1994, the timing of break-up is related to loc al surface air temperatures integrated over periods of 1-3 months. Although highest unimodal correlations an with the 3-month mean air temperature, a bimodal relationship between break-up and air temperature exists at shorter integration times, with break-up date being related not only to the air te mperature prevailing during thawing (April) but also to that prevailing dur ing the time of ice formation, when air temperatures are lowest (February). High-frequency (interannual) fluctuations in the timing of break-up appear to be influenced mainly by the air temperatures prevailing during thawing, and low-frequency (interdecadal) fluctuations by those prevailing during i ce formation. Whereas correlations with April air temperatures are always significant, th ose with February air temperatures an only significant during the latter pa rt of this century, i.e., after cessation of the tendency toward earlier th awing. The high correlation between break-up date and integrated air temper ature is not merely local but extends over most of Siberia and parts of nor thern China. Because air temperatures in Siberia contain a strong winter NA O (North Atlantic Oscillation) signal, so does the Lake Baikal break-up dat e, with up to 14% of the variance in the observed date of break-up being ex plained by the seasonal NAO index from January to March. As in the case of the air temperature data, a significant NAO signal in the break-up date can be detected only during the latter part of this century, implying that the influence of the NAO on the thawing of Lake Baikal during the early part o f this century was probably negligible.