Stable isotope and ostracode species assemblage evidence for lake level changes of Nam Co, southern Tibet, during the past 600 years

Ostracode species assemblages and stable oxygen and carbon isotopes of shells from two 210Pb-dated short cores of 78 cm and 47 cm length taken from Lake Nam Co, southern Tibet, provide information about lake level history of the past approximately 600 years at decadal resolution. A transfer function is applied to reconstruct paleo-water depths from modern ostracodes. Ostracode assemblages and isotope data from five species allow a subdivision into phases of lake level evolution. Before ∼1600 AD relatively low oxygen isotope values and high abundances of deep water (>30 m) ostracodes (i.e. ?Leucocythere dorsotuberosa, ?Leucocythere dorsotuberosa f. postilirata) suggest a lake level ∼10 m higher than today. Between ∼1600 AD and 1800 AD, more positive oxygen isotope values and higher abundances of shallow water ostracodes (i.e. Ilyocypris cf. mongolica, Candona xizangensis) suggest a lake level approximately 40 m below modern level. Between 1800 AD and ∼1920 AD oxygen isotopes are characterized by a trend to more negative values followed by a trend to more positive ones. These trends are interrupted by several short-term fluctuations but overall, oxygen isotope values suggest a drop in lake level. A clearer lake level picture is provided by species assemblages that suggest a continuously increasing lake level since 1900 AD. Precipitation data from meteorological stations nearby show an increase in precipitation in the last 30 years. The low lake level between 1600 AD and 1800 AD is contemporary to the Little Ice Age. During that cold period, meltwater input into the lake decreased. This underlines the sensitivity of the level of Lake Nam Co to temperature changes on the Tibetan Plateau.