Cold intrusions in Lake Baikal: Direct observational evidence for deep-water renewal

Abstract

We studied cold, deep‐water intrusions in the South Basin of Lake Baikal on the basis of 2 yr of data (December 1995‐November 1997) from near‐bottom and near‐surface thermistor strings, monthly conductivity‐temperature‐depth (CTD) profiles, and a near‐bottom current meter, all collected near the South Basin maximum depth of 1,461 m. The data show intrusions into the greatest depths with temperatures of 0.08–0.20°C below ambient (~3.33 to ~3.38°C at maximum depth). The intrusions were observed three times per year between January and June, when surface water is always cooler than deep water, with durations of a few (at least 1–3) days. The estimated water input ranged from 1 to 10 km3 per event, and the annually accumulated volume was estimated to be 10–30 km3, which is significantly less than the steady‐state indirect estimates of 30–70 km3 yr−1 to the permanently stratified deep water (depth ≫ 300 m). This indicates that not all of the cold intrusions reach the deepest area. Because the cooling of the near‐bottom waters was not accompanied by a significant increase in ion or particle content and because deep sediment traps did not contain significant enrichments of minerogenic particles, we concluded that Selenga River inflow is not a possible source of the cold intrusions. Two CTD profiles in June 1996 and 1997 showed lower temperature throughout the deep water, as expected from thermobaric instabilities. The required downwelling is definitely not occurring in the pelagic interior but most probably by near‐coast counterclockwise currents. The source of the regularly occurring deep intrusions is clearly cold surface water, but the actual mechanism is uncertain.

Spatial analysis of ice phenology trends across the Laurentian Great Lakes region during a recent warming period

“…Therefore, lake-specific factors that influence the amount of heat in the lake (e.g., lake volume) and the rate at which heat is lost to cooler air (e.g., depth, surface area and exposure to wind ;Hutchinson 1957) affect the timing of ice formation (Assel andHerche 1998, 2000). In large lakes, the depth of convective mixing can be much shallower than the maximum or mean depth, allowing ice formation to occur despite the existence of permanently stratified deep water (e.g., Lake Baikal; Wuest et al 2005).…”

Stratification of very deep, thermally stratified lakes

“…In two cases, i.e. Crater Lake in Oregon, USA Collier, 1995, Crawford 2005) and Lake Baikal, Siberia, Russia , Imboden and Wüest 1995, Wüest et al 2005, the stratification and 45 the deep water renewal had been investigated in detail, though many more such lakes are known (Boehrer and Schultze 2008, see above).…”

On contribution of horizontal and intra-layer convection to the formation of the Baltic Sea cold intermediate layer

“…We may only suggest that the cold bottom intrusions observed in Lake Baikal (Wüest et al, 2005), are formed this way: the authors relate the phenomenon with the spring thermal bar, and point out that "the source of the regularly occurring deep intrusions is clearly cold surface water, but the actual mechanism is uncertain".…”

“…10), thus providing conditions for the sort of thermobaric instability. This kind of instability was shown to be the reason for the formation of 120 m -thick homogeneous layer around meso-thermal maximum in Lake Baikal (Wüest, et al, 2005). In fresh-water Baikal, however, the Tmd varies with depth due to the pressure solely, whilst in the Baltic both pressure and salinity contribute to the Tmd variations with the depth.…”

“…Sharing features with the oceanic "winter cascading from the shelf" (e.g., Killworth, 1977;Jacobs and Ivey, 1998), the cascading in the Baltic Sea is more complicated because twice per year the water temperature crosses the temperature of maximum density (Tmd), which never happens in saline oceanic water. At the same time, similar to fresh-water Lake Baikal, deep waters in the Baltic remain always above the Tmd due to their higher salinity, whilst the upper layer is cooled down to the freezing point (Shimaraev and Granin, 1991;Wüest et al, 2005). In spite of all the differences, application of knowledge about oceanic and lake processes can shed some light onto the situation in the Baltic Sea.…”