On the glacial-interglacial variability of the Asian monsoon in speleothem δ ¹⁸ O records

Abstract

While Asian monsoon (AM) changes have been clearly captured in Chinese speleothem oxygen isotope (δ18O) records, the lack of glacial-interglacial variability in the records remains puzzling. Here, we report speleothem δ18O records from three locations along the trajectory of the Indian summer monsoon (ISM), a major branch of the AM, and characterize AM rainfall over the past 180,000 years. We have found that the records close to the monsoon moisture source show large glacial-interglacial variability, which then decreases landward. These changes likely reflect a stronger oxygen isotope fractionation associated with progressive rainout of AM moisture during glacial periods, possibly due to a larger temperature gradient and suppressed plant transpiration. We term this effect, which counteracts the forcing of glacial boundary conditions, the moisture transport pathway effect.

Paleoclimate Significance of Reconstructed Rainfall Isotope Changes in Asian Monsoon Region

“…The red star is the location of Lugu Lake (this study). The circles with letters or numbers inside are the locations of speleothem (blue) or marine (dark blue) records in the Indian summer monsoon region and speleothem (green) records in the East Asian summer monsoon region, including (b) Southeast Yunan (SEY) caves (G. Liu, Li, et al, 2020), (c) Xiaobailong Cave (Cai et al, 2015), (d) Coastal Bay of Bengal (CBoB) caves (G. Liu, Li, et al, 2020), (e) Mawmluh Cave (Dutt et al, 2015), (f) Bittoo Cave (Kathayat et al, 2016), (g) core SO188-342 KL in the northern Bay of Bengal (Contreras-Rosales et al, 2014), (h) core RC12-344 in the Andaman Sea (Rashid et al, 2007), (i) core SK218/1 in the western Bay of Bengal (Govil & Naidu, 2011), (1) Dongge Cave (Cheng et al, 2016), (2) Sanbao Cave (Cheng et al, 2016), (3) Hulu Cave (Cheng et al, 2016). clockwise east-to-west wind direction in the western Pacific Ocean (Figure 1a).…”

“…In the ISM region, some studies use the "amount effect" to interpret reconstructed changes in δ 18 Oc records based on modern observations, with lower δ 18 Oc values indicating more local or regional rainfall amount, and vice versa (Dansgaard, 1964;Cai et al, 2012;G. Liu, Li, et al, 2020).…”

“…Other studies argue that δ 18 Oc records inferred from China do not reflect changes in the amount of monsoon rainfall, due to the inconsistency between δ 18 Oc and other proxy‐based rainfall reconstructions from decadal to orbital timescales (Clemens et al., 2018; J. Liu et al., 2015; X. Liu, Liu, et al., 2020). In the Indian summer monsoon (ISM)—the tropical component of the ASM that originates from the Indian Ocean‒region (70–110°E, 10–30°N, after P. X. Wang et al., 2017), published δ 18 Oc records are not continuous in time or have large changes in sampling resolution over the late Quaternary (Dutt et al., 2015; Kathayat et al., 2016; G. Liu, Li, et al., 2020), probably due to the shortage of stable and continuous deposition of speleothems (Fleitmann et al., 2011). This hampers a better evaluation of relative changes in ISM intensity through time, and the comparison with other monsoon records.…”

Orbital-scale Asian summer monsoon variations: Paradox and exploration

“…But this hypothesis also needs to be tested by more sophisticated simulations. (3) Recently, Liu et al (2020a) found that speleothem δ 18 O records close to the ASM moisture source have a larger range of glacial-interglacial variability, which then decreases landward. It was then proposed that the moisture oxygen isotope fractionation during the transport from the ocean to the interior of the continent in the glacial period was significantly larger than in the interglacial period due to the larger temperature gradient and the weaker plant transpiration effect.…”

Determining key upstream rainout and convection zones affecting δ18O in water vapor and precipitation based on 8-year continuous observations in the East Asian Monsoon region

“…Our result is contrary to the conclusions of several previous studies in stalagmite δ 18 O records and isotope-embedded climate simulations in EAM region, which emphasize the role of upstream processes in the tropical Indian Ocean in depleting precipitation δ 18 O in the EAM region [16][17][60][61][62] . However, the significance of these processes in Indian Ocean on the EAM stalagmite δ 18 O is not supported by the notable difference of stalagmite δ 18 O records between the EAM and ISM regions in terms of phase, variation amplitude and pattern on the glacial-interglacial as well as shorter than millennial time scales 13,[63][64][65][66][67][68] . Therefore, our results could provide a new perspective for interpreting stalagmite δ 18 O records in EAM region.…”