Lake Hovsgol at 51°N in NW Mongolia is located in a rift basin with a small confined catchment.This lake serves as a sensitive “water gauge” in a region dominated by westerly atmospheric circulation in summer and by the Siberian(Asiatic) High pressure system in winter.Unlike most lakes in the region,Hovsgol remained relatively deep during the last glacial-interglacial transition,preserving a continuous record of finely-laminated sediments.Unlike in the neighboring Lake Baikal,sediments of Lake Hovsgol from the last glacial-interglacial transition contain both endogenic carbonates and ostracod shells.As a result,these sediments represent the first regional paleoclimate archive suitable for a study of past changes in the oxygen isotope composition of lake waters from δ~(18)O of carbonates deposited in a stable deepwater lacustrine setting.Here we present a synthesis of Lake Hovsgol data on changes in lake level,hydrologic budget and carbonate oxygen isotope composition to arrive at a new understanding of changes in westerly atmospheric circulation over continental interior of Asian during the past 25 cal ka.We show that the dramatic lowstand of the lake on the order of ~200 m dates back to 22 cal ka BP,i.e.,pre-dates the interval typically recognized as last glacial maximum(LGM).Since this major lowstand event,the lake level was rising more or less steadily with an intermediate lowstand on the order of ~100 m at 16 cal ka BP.This positive trend in the hydrologic balance during deglaciation is consistent with the mineralogy of endogenic carbonates from X-ray diffraction analysis:the abundance of Mg-calcite and the content of Mg in calcite steadily decreased in Hovsgol sediments since the last glacial.Stable isotope analysis of carbonates in Lake Hovsgol lowstand facies shows that oxygen isotope ratios of lake water were not controlled by either evaporative enrichment in the closed basin or by the hypothesized input of glacial meltwater.Instead,changes in the composition of atmospheric precipitation appear to be the main control on the δ~(18)O ratios of lake water.Thus,Lake Hovsgol carbonates for the first time offer regional proxy records for past changes in the amount and composition of westerly atmospheric precipitation.Current radiocarbon age models suggest that certain mismatches may exist between the timing of Lake Hovsgol δ~(18)O signals of enhanced regional precipitation from warmer air masses and the timing of temperature variations in Greenland and the timing of the rapid changes in SE Asian monsoon.The reconstruction of the hydrologic balance of the basin from sediment lithology and carbonate mineralogy coupled with oxygen isotope records of Lake Hovsgol help better explain the regional liistory of late Pleistocene glaciation and constrain the source of moisture for the postglacial lake level rise in a number of smaller lake basins in continental Asia. Lake Hovsgol at 51 ° N in NW Mongolia is located in a rift basin with a small confined catchment. This lake serves as a sensitive “water gauge” in a region dominated by westerly atmospheric circulation in summer and by the Siberian (Asiatic) High pressure system in winter.Unlike most lakes in the region, Hovsgol silent relatively deep during the last glacial-interglacial transition, preserving a continuous record of finely-laminated sediments .Unlike in the Lake Baikal, sediments of Lake Hovsgol from the last glacial -interglacial transition contain both endogenic carbonates and ostracod shells. As a result, these sediments represent the first regional paleoclimate archive suitable for a study of past changes in the oxygen isotope composition of lake waters from δ ~ (18) O of carbonates deposited in a stable deepwater lacustrine setting. Here we present a synthesis of Lake Hovsgol data on changes in lake level, hydrologic budget and carbonate oxygen isotope composition to arrive at a new understanding of changes in westerly atmospheric circulation over continental interior of Asian during the past 25 cal ka.We show that the dramatic lowstand of the lake on the order of ~ 200 m dates back to 22 cal ka BP, ie, pre-dates the Since this major lowstand event, the lake level was rising more or less steadily with an intermediate lowstand on the order of ~ 100 m at 16 cal ka BP. This positive trend in the hydrologic balance during deglaciation is consistent with the mineralogy of endogenic carbonates from X-ray diffraction analysis: the abundance of Mg-calcite and the content of Mg in calcite steadily decreased in Hovsgol sediments since the last glacial. Table isotope analysis of carbonates in Lake Hovsgol lowstand facies shows that oxygen isotope ratios of lake water were not controlled by either evaporative enrichment in the closed basin or by the hypothesized input of glacial meltwater. Instead, changes in the compos ition of atmospheric precipitation appear to be the main control on the δ ~ (18) O ratios of lake water. Lake, Lake Hovsgol carbonates for the first time offer offer proxy records for past changes in the amount and composition of westerly atmospheric precipitation. Current radiocarbon age models suggest that certain mismatches may exist between the timing of Lake Hovsgol δ ~ (18) O signals of enhanced regional precipitation from warmer air masses and the timing of temperature variations in Greenland and the timing of the rapid changes in SE Asian monsoon. The reconstruction of the hydrologic balance of the basin from sediment lithology and carbonate mineralogy coupled with oxygen isotope records of Lake Hovsgol help better explain the regional liistory of late Pleistocene glaciation and constrain the source of moisture for the postglacial lake level rise in a number of smaller lake basins in continental asia.