Abstract
We in this paper present a multi-proxy study of a 186-cm-long lacustrine sediment core (i.e., BY Core) obtained from the
Youerdusi Basin in the middle Tianshan Mountains in an attempt to disentangle the causal associations among climate
changes, ecological responses and hydrological variations. Palynological, assemblages and the associated biome scores
indicate that the upper limit of the forest zone was closer to the Youerdusi Basin with a larger wetland extent in the Youerdusi
Basin during the early part (i.e., from ~ 10.5 to ~ 5.8 cal. kyr BP) of the data-covering period (i.e., from ~ 10.5 to ~ 2.4 cal.
kyr BP). The upper limit of the forest zone was farther away from the Youerdusi Basin with a smaller wetland extent in the
Youerdusi Basin during the late part (i.e., from ~ 5.8 to ~ 2.4 cal. kyr BP). The changes of taiga biome score and the AP%
ratio indicate a persistent cooling trend during the data-covering period which is well corroborated by various proxy data
from nearby sites and the cooling trend is chronologically consistent with the trend of Northern Hemisphere temperature
anomalies that was interpreted to be a delayed response to the summer solar irradiance at 50° N. The tundra biome score
and the associated percentages of Cyperaceae in the Youerdusi Basin show two major stages of wetland extent variation.
The wetland extent variation in the Youerdusi Basin might have been controlled by precipitation and/or by glacier-melting
potential that was in turn controlled by both temperature and the extent of remained ice cover in higher elevations. The
δ13Corg values obtained from the BY Core indicate a wetting trend during the data-covering period which is reasonably corroborated
by various proxy data from nearby sites. We infer that the wetting trend was causally associated with the Holocene
increasing trend of the North Atlantic Ocean SST (sea surface temperature) and also with the Holocene increasing trend of
the westerlies’ intensity.
Keywords Pollen · Holocene · Tianshan mountains · Moisture · North Atlantic ocean
