Processes of deep-water renewal in Lake Baikal

Abstract

Deep-water renewal in Lake Baikal (Siberia), the world s deepest lake and largest lake by volume, is relatively fast. Water age calculated from tritium and helium as well as from chlorofluorocarbons does not exceed 19 yr. Relative saturation of dissolved oxygen typically exceeds 80%. The equation of state of Baikal water was determined including the effect-of dissolved ions and silicic acid. Based on nearly 600 CTD profiles taken between 1993 and 1995, two mechanisms of deep-water mixing were identified. (1) In spring, cold and relatively saline water from the Selenga, the major inflow to the lake, forms a density plume that reaches the bottom of the central basin during April and early May. Due to entrainment of lake water the plume transports about 125 km3 of water per year to the deepest part of the basin. Later in spring, the river water forms the thermal bar observed along the eastern shore. There are indications that parts of the Selenga are also plunging to the deep part of the southern basin. (2) At Academician Ridge, separating the cold and saline water of the central basin from the warmer and slightly less saline water of the northern basin, horizontal mixing results in a water mass that can sink on either side of the sill. Whereas in the central basin the water mass stays at intermediate depth, in the northern basin it sinks to the deepest part. More detailed data are needed to quantify this density flux. No indication of a wind-induced thermobaric instability was found.