A new approach for reconstructing Holocene temperatures from a multi-species long chain alkenone record from Lake Qinghai on the northeastern Tibetan Plateau

The extent of unsaturation in long chain alkenones (LCKs) in lakes has potential for quantitatively indicating paleotemperature in terrigenous environments. However, the traditional temperature proxies derived from marine LCKs may not be able to address the problem related to the prevalent species effect, which restricts the application of LCKs in lacustrine studies. In our LCK record from the northeastern Tibetan Plateau, C-37/C-38 differences revealed that the LCK producer species in Lake Qinghai may have changed during the Holocene. This possible species effect may have caused inconsistency between the U-37(K') and U-37(K) records. Therefore, we formulated a new proxy, U-37(Ks), with a parameter "s" to indicate the different exponential response in LCK unsaturation to temperature change in multiple species. Our U-37(Ks)-derived temperature time series resembles the general temperature trends of the Northern Hemisphere on a millennial scale, while exhibiting several apparent cold events, especially at ca. 9 ka. The result shows that the Holocene optimum in Lake Qinghai was interrupted by cold events in the early Holocene. This could be a result of a weak Asia summer monsoon and cold air transmission in the North Atlantic. (C) 2015 Elsevier Ltd. All rights reserved.