| Summary: | 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 thereafter. For the period 1931-1994, the timing of break-up is related to local 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 temperature prevailing during thawing (April) but also to that prevailing during 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 ice formation. Whereas correlations with April air temperatures are always significant, those with February air temperatures an only significant during the latter part of this century, i.e., after cessation of the tendency toward earlier thawing. The high correlation between break-up date and integrated air temperature is not merely local but extends over most of Siberia and parts of northern China. Because air temperatures in Siberia contain a strong winter NAO (North Atlantic Oscillation) signal, so does the Lake Baikal break-up date, with up to 14% of the variance in the observed date of break-up being explained 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 of this century was probably negligible.
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