Holocene hydrological and climatic change on the northern Mongolian Plateau based on multi-proxy records from Lake Gun Nuur

A multi-proxy study including analyses of δ ¹³C _org for the lake sediment core GN-02 and grain size, TOC, CaCO ₃ content, δ ¹³C _carb and δ ¹⁸O _carb of bulk carbonate, and the mineralogy of the parallel core GN-04 from Gun Nuur was performed to reconstruct the Holocene hydrology and climate on the northern Mongolian Plateau. The chronology was established using 40 ¹⁴C dates of bulk organic matter in addition to nine previously published radiocarbon dates for core GN-02, and further five ¹⁴C dates for the new core GN-04. A lake reservoir effect of 1060 ¹⁴Cyears was determined as the intercept of the high-resolution GN-02 age-depth model at the modern sediment surface. The size of the reservoir effect is supported by the age of the core-top sample (1200±40 ¹⁴Cyears) and the determined difference between a wood-derived radiocarbon age from the GN-02 core base and the age-model inferred age for bulk organic matter at the same stratigraphic level (1000 ¹⁴Cyears).Low lake level and prevailing aeolian sediment deposition at Gun Nuur under dry conditions were recorded during the earliest Holocene (> 10,800-10,300. cal a BP). Gun Nuur expanded under significantly wetter conditions between 10,300 and 7000. cal a BP. Unstable climate conditions existed in the mid Holocene (7000-2500. cal a BP) and three periods of low lake-levels and significantly drier conditions were recorded between 7000-5700, 4100-3600 and 3000-2500. cal a BP. Intermediate lake levels were inferred for the intervening periods. Around 2500. cal a BP, the climate change and wetter conditions were established again. As a consequence, the lake level of Gun Nuur rose again due to higher effective moisture and the relatively wet present conditions were achieved ca. 1600. cal a BP. Our results suggest that the initial Holocene climate change on the northern Mongolian Plateau was not accompanied by a rapid increase in precipitation as on the Tibetan Plateau. The establishment of wetter conditions in northern Mongolia lagged behind the early Holocene moisture increase on the Tibetan Plateau by ca. 1000. years. Subsiding dry air in the north of the Tibetan Plateau resulted from the strengthened summer monsoon on the Tibetan Plateau during the period of maximum summer insolation and probably inhibited a significant precipitation increase in Mongolia. The significant moisture increase in the Gun Nuur region at ca. 10.3. cal. ka BP is probably not related to the northward shift of the present summer monsoon boundary or the moisture delivery from the northern Atlantic through the westerlies. Instead, water from melting snow, ice and frozen ground and the generation of precipitation from the local recycling of moisture are discussed as possible moisture source for the early onset of wetter conditions on the Mongolian Plateau.