Penetration of monsoonal water vapour into arid central Asia during the Holocene: An isotopic perspective
Introduction
Atmospheric water vapour transport is a key process of the hydrological cycle (Bengtsson, 2010). Water vapour transport determines the distribution of precipitable water above the surface of the Earth, which therefore significantly influences global and regional precipitation distribution and variability (Ding and Wang, 2008). In addition, water vapour is an important greenhouse gas, which greatly affects global radiation balance (Bengtsson, 2010). Therefore, exploring water vapour transport is crucial to understand global and regional climate changes, especially precipitation changes.
Monsoon is referred to as the seasonally reversing winds accompanied by precipitation changes (Zhou and Zou, 2010). In summer, positive land–sea thermal contrast generates winds from ocean to land, carrying large amounts of water vapour from tropical oceans and bringing heavy rainfall to monsoon-influenced areas (Wang et al., 2008a). Hence, monsoonal water vapour transport is one of the most active components of the hydrological cycle. The Asian summer monsoon (ASM) is a major monsoon system, which includes two sub-monsoon systems: Indian summer monsoon (ISM) and East Asian summer monsoon (EASM). The ISM is a typically tropical monsoon, which is associated with intensive convective activity near the Bay of Bengal and Indian subcontinent (Wang and Fan, 1999). The EASM is a unique monsoon system with its sphere of influence extending from tropics to mid-latitudes (Wang et al., 2008a), which brings water vapour from the Pacific and Indian Oceans to East Asia (Ding and Wang, 2008). In addition, the ISM and EASM have been paid particular attention as their rainfall have a profound influence on the lives of billions of people in South Asia and East Asia. Therefore, a full understanding of the ASM behavior is essential for social development in these regions.
The ASM onset starts over the eastern Bay of Bengal in early May, followed by the onset over the South China Sea in mid-May, and then by the onset over southern China (Hainan and southern Guangdong) in late May. The ASM onset further occurs in southern India and southern China in early June, which then migrates north to central India and the Yangtze River Basin in mid-June, and finally reaches northern India and northern China in mid-July (Wang and LinHo, 2002). The ASM occurs primarily from May to September, although the summer monsoon completely finishes in November in southern India (Wang and LinHo, 2002). The migration of the EASM is in conjunction with the shift of the western Pacific subtropical high, which generates three distinct rainbands in southern China, the Yangtze River Basin, and northern China, respectively (Ding and Wang, 2008).
During the past decades, observations indicate that the EASM has undergone a significant weakening trend under the background of human-induced global warming (Liu et al., 2017, 2019b). However, the decadal variability of ISM precipitation is confusing during the past decades, showing divergent trends among different precipitation datasets (Walker et al., 2015). At an orbital timescale, proxy records reveal synchronous evolution of the EASM and ISM during the Holocene, showing a generally weakening strength of the monsoon (Cheng et al., 2016a; Fleitmann et al., 2003; Wang et al., 2008b). The recession of the ISM and EASM is mainly caused by reduced summer insolation (Cheng et al., 2016a). In addition to the monsoon strength, attention was paid to the geographical extent of the ISM and EASM. The ISM was suggested to have extended into the southwestern Tibetan Plateau during the early Holocene (Chen et al., 2020b). The EASM was considered to have stretched into arid central Asia during the early–middle Holocene (Morrill et al., 2003; Winkler and Wang, 1993). The intrusion of the EASM into arid central Asia during the early–middle Holocene was further supported by lower values in oxygen isotope ratios (δ18O) in the speleothem record from Kesang Cave in the central Tianshan Mountains, which are consistent with those in the EASM zone (Cheng et al., 2012, 2016b; Zhang et al., 2019a).
However, this interpretation of the δ18O in arid central Asia has been discussed in many other studies. Cai et al. (2017) interpreted the lower δ18O values of Kesang Cave as a result of increased precipitation with the water vapour transported by the westerlies from surrounding source regions during the early–middle Holocene. Rao et al. (2019) and Xu et al. (2019) indicated that δ18O in arid central Asia was controlled by the local hydrological cycle related to the runoff from surrounding mountain glaciers. Mountain glaciers have experienced a retreating trend in arid central Asia throughout the Holocene due to the long-term warming trend, leading to enriched 18O in water and hence in stalagmites during the late Holocene compared with the early Holocene.
In contrast, some other studies revealed a completely different moisture evolution history in arid central Asia with that in East Asia (Chen et al., 2015a, 2019). Many lake and loess records reconstruct a drier–than–present climate in arid central Asia during the early Holocene (Chen et al., 2016; Hong et al., 2014; Long et al., 2017; Wang and Feng, 2013; Xu et al., 2019). That is, arid central Asia was not controlled by the EASM during the early Holocene. The persistent drying trend in this area during the Holocene was dominated by westerly water vapour, which was jointly determined by the strength of the westerlies and the evaporation from the North Atlantic, the Mediterranean, Black, and Caspian Seas (Jin et al., 2012). Chen et al. (2019) therefore regarded this area as “westerlies Asia”, in order to distinguish it from the monsoon-influenced Asia.
In summary, there is still a lot of controversy about the water vapour sources for arid central Asia during the Holocene. A key debate is whether monsoonal water vapour could reach arid central Asia during the early–middle Holocene. To resolve this debate requires a tracer based on a clear physical process associated with the transport of monsoonal vapour water into arid central Asia. This study analyzed the present-day observed water vapour transport during the summer monsoon season (May to September) at a synoptic timescale, since synoptic-scale monsoonal water vapour towards arid central Asia has been detected by previous studies (Huang et al., 2015; Zhang and Jin, 2016). The relationship between observed precipitation δ18O and water vapour transport pathways, which is important for the understanding of factors influencing palaeoclimate archives (Breitenbach et al., 2010; Dayem et al., 2010; Yu et al., 2016), was further delineated. This study further took the difference in speleothem δ18O between Kesang Cave in the central Tianshan Mountains and Kinderlinskaya Cave in the southern Urals as a tracer to indicate the penetration of monsoonal water vapour into arid central Asia during the Holocene.
Section snippets
Regional setting and climatology
Arid central Asia constitutes the core area of Eurasia, spanning a vast territory roughly from the Caspian Sea (∼50° E) in the west to the western Hexi Corridor (∼95° E) in the east, and lies between the latitudes ∼36° N and ∼54° N (Fig. 1) (Chen et al., 2019). At present, annual precipitation is less than 400 mm in most area of arid central Asia, except in high-mountain regions (e.g., the Tianshan Mountains) (Fig. 2a). Most of the annual precipitation falls in winter
Holocene speleothem δ18O records
This study intends to explore the contribution of monsoonal water vapour to precipitation in arid central Asia during the Holocene based on spatial–temporal differences of δ18O variability from proxy records. There are many existing δ18O records in Eurasia spanning the Holocene, derived from speleothems (Cai et al., 2017; Cheng et al., 2012, 2016b; Comas-Bru et al., 2019, 2020; Kaushal et al., 2018; Liu et al., 2015a, 2019a; Zhang et al., 2019a), ice cores (Aizen et al., 2016), and lake
Comparisons of Holocene speleothem δ18O records between arid central Asia and other regions
At a seasonal timescale, the westerlies prevail in the southern Urals and arid central Asia throughout the year in present day (Fig. 3). Three records reveal a similar orbital-scale variability of speleothem δ18O in the westerly zone, showing a general enrichment of 18O during the Holocene (Fig. 5a-5c). However, there are significant differences in speleothem δ18O variations at a millennial timescale. During the early Holocene (11.5–9.3 ka BP), the δ18O values underwent a sharply increasing
Implication of δ18O difference between arid central Asia and the southern Urals
Arid central Asia shares a similar atmospheric circulation with the southern Urals, but has different atmospheric circulation with East Asia and India (Fig. 3). However, speleothem δ18O variability in arid central Asia behaves in a similar manner with that recorded in East Asia and India, but in a different manner with that recorded in the southern Urals during the Holocene (Fig. 5). So, what caused the δ18O differences between arid central Asia and the southern Urals during the Holocene?
Conclusions
Speleothem δ18O records in Eurasia reveal a similar evolution history at an orbital timescale during the Holocene, following Northern Hemisphere summer insolation. However, there exist remarkable differences at a millennial timescale. The differences might be caused by either local factors (e.g., local recycling) or large-scale circulation. Therefore, spatial–temporal variability of precipitation (speleothem) δ18O provides valuable information to study local or large-scale climate changes. This
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
JRA-55 Reanalysis data is provided by the Japan Meteorological Agency, Japan, from their website at https://jra.kishou.go.jp/JRA-55/index_en.html. NCEP Reanalysis data is provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html. ERA5 Reanalysis data is provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) from their website at //www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5
References (79)
- et al.
Persistent multidecadal power of the Indian summer monsoon
Earth Planet Sci. Lett.
(2010) - et al.
Strong influence of water vapor source dynamics on stable isotopes in precipitation observed in Southern Meghalaya, NE India
Earth Planet Sci. Lett.
(2010) - et al.
Holocene moisture changes in western China, central Asia, inferred from stalagmites
Quat. Sci. Rev.
(2017) - et al.
The variation of summer monsoon precipitation in central China since the last deglaciation
Earth Planet Sci. Lett.
(2010) - et al.
Westerlies Asia and monsoonal Asia: spatiotemporal differences in climate change and possible mechanisms on decadal to sub-orbital timescales
Earth Sci. Rev.
(2019) - et al.
A persistent Holocene wetting trend in arid central Asia, with wettest conditions in the late Holocene, revealed by multi-proxy analyses of loess-paleosol sequences in Xinjiang, China
Quat. Sci. Rev.
(2016) - et al.
Climate change, vegetation history, and landscape responses on the Tibetan Plateau during the Holocene: a comprehensive review
Quat. Sci. Rev.
(2020) - et al.
Relationship between sub-cloud secondary evaporation and stable isotopes in precipitation of Lanzhou and surrounding area
Quat. Int.
(2015) - et al.
Lessons learned from oxygen isotopes in modern precipitation applied to interpretation of speleothem records of paleoclimate from eastern Asia Katherine
Earth Planet Sci. Lett.
(2010) - et al.
Reconciliation of hydroclimate sequences from the Chinese loess plateau and low-latitude East Asian summer monsoon regions over the past 14,500 years
Palaeogeogr. Palaeoclimatol. Palaeoecol.
(2015)
A high-resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China
Earth Planet Sci. Lett.
Holocene East Asian summer monsoon records in northern China and their inconsistency with Chinese stalagmite δ18O records
Earth Sci. Rev.
Holocene moisture variations over the arid central Asia revealed by a comprehensive sand-dune record from the central Tian Shan, NW China
Quat. Sci. Rev.
Reconciling the ‘westerlies’ and ‘monsoon’ model: a new hypothesis for the Holocene moisture evolution of the Xinjiang region, NW China
Earth Sci. Rev.
Changes in dominant moisture sources and the consequences for hydroclimate on the northeastern Tibetan Plateau during the past 32 kyr
Quat. Sci. Rev.
Holocene moisture evolution across the Mongolian Plateau and its surrounding areas: a synthesis of climatic records
Earth Sci. Rev.
δ18O records in water vapor and an ice core from the eastern Pamir Plateau: implications for paleoclimate reconstructions
Earth Planet Sci. Lett.
The asian summer monsoon: teleconnections and forcing mechanisms—a review from Chinese speleothem δ18O records
Quaternary
East–west contrast of Northeast Asian summer precipitation during the Holocene
Global Planet. Change
Abrupt and moderate climate changes in the mid-latitudes of Asia during the Holocene
J. Glaciol.
Holocene warming in western continental Eurasia driven by glacial retreat and greenhouse forcing
Nat. Geosci.
Continuous measurements of atmospheric water vapour isotopes in western Siberia (Kourovka)
Atmos. Meas. Tech.
The global atmospheric water cycle
Environ. Res. Lett.
An abrupt shift in the Indian monsoon 4000 years ago
Increasing summer precipitation in arid Central Asia linked to the weakening of the East Asian summer monsoon in the recent decades
Int. J. Climatol.
East Asia summer monsoon precipitation variability since the last deglaciation
Sci. Rep.
A climatological northern boundary index for the East Asian summer monsoon and its interannual variability
Sci. China Earth Sci.
The Asian monsoon over the past 640,000 years and ice age terminations
Nature
Climate variations of Central Asia on orbital to millennial timescales
Sci. Rep.
The climate cyclicity in arid central Asia over the past 500,000 years
Geophys. Res. Lett.
Evaluating model outputs using integrated global speleothem records of climate change since the last glacial
Clim. Past
SISALv2: a comprehensive speleothem isotope database with multiple age-depth models
Earth Syst. Sci. Data Discuss.
ERA5: Fifth Generation of ECMWF Atmospheric Reanalyses of the Global Climate. Copernicus Climate Change Service Climate Data Store (CDS)
Stable isotopes in precipitation
Tellus
A study of rainy seasons in China
Meteorol. Atmos. Phys.
Holocene forcing of the Indian monsoon recorded in a stalagmite from Southern Oman
Science
Stable isotopes in atmospheric water vapor and applications to the hydrologic cycle
Rev. Geophys.
An Introduction to Dynamic Meteorology
Increasing summer rainfall in arid eastern-Central Asia over the past 8500 years
Sci. Rep.
Cited by (27)
Salinization mechanism of lakes and controls on organic matter enrichment: From present to deep-time records
2024, Earth-Science ReviewsInterannual variations in stable isotopes of atmospheric water in arid Central Asia due to changes in atmospheric circulation
2024, Global and Planetary ChangeRole of the tropical Indian Ocean in orbitally induced mid-Holocene precipitation variation in northwest China
2023, Quaternary Science ReviewsC<inf>4</inf> expansion of Central Asia in the middle Miocene linked to the strengthening Indian monsoon
2023, Global and Planetary ChangeObliquity forcing of lake-level changes and organic carbon burial during the Late Paleozoic Ice Age
2023, Global and Planetary Change