Variations of the Indian summer monsoon over the last 30 000 years inferred from a pyrogenic carbon record from south‐west China

Abstract

The carbon isotope composition of pyrogenic carbon (d 13 C PyC ) can be used to identify changes in terrestrial vegetation and consequently climate. We analyzed the d 13 C PyC values in a continuous lacustrine sediment core from the south-east edge of the Qinghai-Tibetan Plateau that spans the last 30k cal a BP, to improve our understanding of changes in regional vegetation and the Indian summer monsoon (ISM) on centennial and millennial timescales. Our data show that a mixed C 3 /C 4 plant community and a dry climate prevailed from 30 to 14.6k cal a BP. Monsoonal precipitation abruptly increased at the glacial-Holocene transition, and C 3 plants growing under a humid climate dominated during the Holocene. Our record also reveals that ISM intensity decreased significantly during Heinrich Events and the Younger Dryas Chron. These findings suggest that changes in regional vegetation in south-west China are primarily controlled by ISM intensity, which in turn is related to solar insolation and high-latitude climate. This is the first d 13 C PyC record covering the last glacial maximum from the region, and provides insight into orbital-scale climate change and abrupt climate events that occurred in southwestern China's geological past.

Archaeal lipid-inferred paleohydrology and paleotemperature of Lake Chenghai during the Pleistocene–Holocene transition

“…Another possibility for the different H1 and YD lake-level variation is the sensitivity of the proxy to the lake level in the case of Lake Chenghai. The δ 18 O record of authigenic carbonates from Lake Chenghai and speleothem δ 18 O records in the ISM region suggest that the weakening of the ISM during the YD was less marked than that occurring during the H1 event, in turn suggesting that lake levels in southwest China may have been higher during the YD than the H1 event (Dykoski et al, 2005;Dutt et al, 2015;Kathayat et al, 2016;Sun et al, 2019;Zhang et al, 2019). For the %cren proxy, we note that the values are correlated to the logarithm of depth, suggesting that %cren may be less sensitive to water depth variation when the lake level is relatively high and more sensitive to water depth variation when the lake level is lower (Wang et al, 2019).…”

“…Over the past 2 decades, climate evolution in the ISM region since the Last Glacial Maximum has been reconstructed from various paleoclimatic archives, including speleothems and marine or lacustrine sediments (Dykoski et al, 2005;Rashid et al, 2007;Govil and Divakar Naidu, 2011;Saraswat et al, 2013;Contreras-Rosales et al, 2014;Q. Wang et al, 2014;Dutt et al, 2015;Wu et al, 2015;Kathayat et al, 2016;Zhang et al, 2017aZhang et al, , b, 2018Zhang et al, , 2019Li et al, 2018;Sun et al, 2019). These studies provide evidence of changes in ISM precipitation on orbital and millennial timescales, with a weakened ISM occurring dur-W. Sun et al: Archaeal lipid-inferred paleohydrology and paleotemperature of Lake Chenghai ing cold events and strengthened ISM occurring during warm intervals.…”

“…In addition to precipitation, temperature is an important climatic factor, due to its significant effects on evaporation and regional hydrological cycle. There remains a lack of quantitative reconstructions of terrestrial temperature from the ISM region (Shen et al, 2006;Zhang et al, 2017aZhang et al, , 2019Wu et al, 2018;Feng et al, 2019;Ning et al, 2019;Tian et al, 2019). During the last deglaciation-Holocene transition, the climate of high latitudes in the Northern Hemisphere is punctuated by three abrupt, millennial-scale events: the Heinrich 1 (H1) cold event, the Bølling-Allerød (BA) warm period and the Younger Dryas (YD) cooling (Alley and Clark, 1999).…”

“…These intervals are attributed to a variety of mechanisms including changes to orbitally controlled insolation, ice sheet extent, oceanic circulation and atmospheric greenhouse concentrations (Alley and Clark, 1999). The recent quantitative summer temperature proxy based on pollen and chironomids from southwest China has been developed to address the response of long-term temperature to the highlatitude climate changes (Zhang et al, 2017a(Zhang et al, , 2019Wu et al, 2018). However, the magnitude of these temperature variations is not consistent, and further studies are required.…”

“…The Lake Chenghai region is mainly affected by a warm-humid monsoonal airflow from the tropical Indian Ocean from June to September and by the southern branch of the Northern Hemisphere westerly jet between October and May (Wang and Dou, 1998). The mean annual air temperature (MAAT) is ∼ 14 • C, the mean annual precipitation is ∼ 660 mm with 80 % falling between June and September (the (2) Mawmluh Cave (Dutt et al, 2015); (3) Lake Ximenglongtan (Ning et al, 2019); (4) Lake Tengchongqinghai (Zhang et al, 2017b;Li et al, 2018;Tian et al, 2019); (5) Lake Tiancai (Zhang et al, 2017a(Zhang et al, , 2019; (6) Lake Lugu (Wang et al, 2014); (7) Lake Xingyun (Wu et al, 2015(Wu et al, , 2018; (8) Dongge Cave (Dykoski et al, 2005); (9) Nam Co (Günther et al, 2015); (10) Dangxiong Co (Ling et al, 2017); (11) Lake Yidun (Shen et al, 2006); (12) Lake Wuxu (Zhang et al, 2016); (13) Lake Muge (Ni et al, 2019). (b) The red triangle indicates the location of core CH2016 in Lake Chenghai, while green triangles indicate the locations of surface samples.…”