86 Paleoclimatology/Paleoceanography (Posters) II

PALYNOLOGICAL INDICES IDENTIFY MID TO LATE HOLOCENE CHANGES IN MOISTURE AVAILABILITY AT LAKES TELMEN AND DOOD, NORTHERN MONGOLIA

Paper number: 86-16
Program: Technical Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Comparison of palynological and sedimentological data from cores of lakes Telmen and Dood, in north-central Mongolia, reveals significant regional coherence with respect to Late Holocene changes in moisture availability. Telmen is a saline, closed basin lake that occupies an intermountain depression between the Hangai and Bulnay ranges. Although this basin has been covered by steppe vegetation for the past ~7000 years, a semi-quantitative pollen index based on the ratio of characteristic dry steppe taxa (Artemisia and Chenopodiaceae) to common meadow-steppe and forest-steppe taxa of the family Poaceae permits identification of humid and arid intervals. Correspondence between low values of this palynological index, intervals of laminated sediments, flooding, and lake highstands validates use of the index as a proxy for moisture availability in the Telmen region. Maximum humidity is recorded between ~4060-1650 14C yr B.P.

Dood is a fresh water oligotrophic lake located on the floor of the extensional Darhad Basin, approximately 300 km north of Lake Telmen. This basin lies within the transition zone between forest-steppe ecosystems to the south and boreal forest to the north. Consequently, changes in moisture availability can be detected using the more conventional steppe/forest index, based on the ratio of herb pollen to arboreal pollen. Low values of the steppe/forest index are correlative with sedimentological properties indicative of humid climate conditions. Maximum humidity is recorded between the base of the core, ~3800 14C yr B.P., and ~2900 14C yr B.P. Cores from both lakes record additional humid intervals that encompass the Medieval Warm Epoch and the last centuries of the Little Ice Age.

Whereas comparison with published lake status records reveals broad coherence between northern lakes Telmen, Dood, and Hubsugul, the majority of Mongolian lakes record increasingly arid conditions after 6000 yr B.P. These data suggest that changes in atmospheric circulation may be more significant than temperature changes driven by solar insolation in determining regional water budgets throughout central and northern Mongolia.