Quantitative reconstruction of precipitation changes on the NE Tibetan Plateau since the Last Glacial Maximum – extending the concept of pollen source-area to pollen-based climate reconstructions from large lakes

Abstract

Pollen records from large lakes have been used for quantitative palaeoclimate reconstruction but the influences that lake-size (as a result of species-specific variations in pollen dispersal patterns) and taphonomy have on these climatic signals have not previously been systematically investigated. We introduce the concept of pollen source-area to pollen-based climate calibration using the climate history of the north-eastern Tibetan Plateau as our study area. We present a pollen data-set collected from large lakes in the arid to semi-arid region of Central Asia. The influences that lake size and the inferred pollen source-areas have on pollen compositions have been investigated through comparisons with pollen assemblages in neighbouring lakes of various sizes. Modern pollen samples collected from different parts of Lake Donggi Cona (in the north-eastern part of the Tibetan Plateau) reveal variations in pollen assemblages within this large lake, which are interpreted in terms of the species-specific dispersal and depositional patterns for different types of pollen, and in terms of fluvial input components. We have estimated the pollen source-area for each lake individually and used this information to infer modern climate data with which to then develop a modern calibration data-set, using both the Multivariate Regression Tree (MRT) and Weighted-Averaging Partial Least Squares (WA-PLS) approaches. Fossil pollen data from Lake Donggi Cona have been used to reconstruct the climate history of the north-eastern part of the Tibetan Plateau since the Last Glacial Maximum (LGM). The mean annual precipitation was quantitatively reconstructed using WA-PLS: extremely dry conditions are found to have dominated the LGM, with annual precipitation of around 100 mm, which is only 32% of present-day precipitation. A gradually increasing trend in moisture conditions during the Late Glacial is terminated by an abrupt reversion to a dry phase that lasts for about 1000 yr and coincides with "Heinrich Event 1" in the northern Atlantic region. Subsequent periods corresponding to the Bølling/Allerød interstadial, with annual precipitation (<i>P</i>_ann) of about 350 mm, and the Younger Dryas event (about 270 mm <i>P</i>_ann) are followed by moist conditions in the early Holocene, with annual precipitation of up to 400 mm. A drier trend after 9 cal. ka BP is followed by a second wet phase in the middle Holocene, lasting until 4.5 cal. ka BP. Relatively steady conditions with only slight fluctuations then dominate the late Holocene, resulting in the present climatic conditions. The climate changes since the LGM have been primarily driven by deglaciation and fluctuations in the intensity of the Asian Summer Monsoon that resulted from changes in the Northern Hemisphere summer solar insolation, as well as from changes in the northern Atlantic climate through variations in the circulation patterns and intensity of the westerlies

Quantitative woody cover reconstructions from eastern continental Asia of the last 22 kyr reveal strong regional peculiarities

“…In this study, we added three new records with raw pollen percentage data: Lake Donggi Cona (35.5 N, 98.5 E, 4090 m a.s.l. ; Wang et al, 2014) from the eastern part of the Tibetan Plateau, Lake Sumxi Co (34.6 N, 84.2 E, 5059 m a.s.l. ; Campo and Gasse, 1993) from the western margin of the Tibetan Plateau, and Lake Bayan Nuur (90.9 N, 48.8 E, 1576 m a.s.l.…”

Lagged response of summer precipitation to insolation forcing on the northeastern Tibetan Plateau during the Holocene

“…In addition, there are a number of small lakes spread around the Qinghai Lake region, many of which have been studied in reconstructing the climatic and environmental changes over this area. We used pollen records from two of them-Dalianhai Lake (Cheng et al 2013) and Luanhaizi Lake (Herzschuh et al 2010;Wang et al 2014a).…”

“…However, significant discrepancies exist among different proxy records; in particular, pollen and ostracod oxygen isotope (δ 18 O) records indicate different periods for the climatic optimum during the Holocene (Lu et al 2010;. Pollen records from Qinghai Lake and the surrounding lakes of the northeastern Tibetan Plateau suggest a relatively dry early Holocene, with the wettest period spanning the middle Holocene, and then another dry period in the late Holocene Herzschuh et al 2010;Cheng et al 2013;Wang et al 2014a). Pollen-based moisture changes lag the Northern Hemisphere June insolation maxima by ~3 ka.…”

Quantitative reconstructions of mid- to late holocene climate and vegetation in the north-eastern altai mountains recorded in lake teletskoye

“…Pollen percentages were calculated on the basis of the total pollen sum. Only pollen taxa with a frequency of ≥ 0.5% in at least three samples were included in the numerical analyses (Wang et al, 2014) resulting in a reduction in the number of pollen taxa from 76 to 66.…”