East Asian summer monsoon variability during Marine Isotope Stage 5 based on speleothem δ18O records from Wanxiang Cave, central China

Abstract

Speleothems from Wanxiang Cave, China (33°19′ N, 105°00′ E), located near the northern limit of the East Asian summer monsoon, provide high-resolution records of paleomonsoon variability. We present a simple model for interpreting δ 18 O shifts in speleothems from this region in which the δ 18 O of speleothem calcite is inversely related to monsoon intensity. In contrast to observations at higher latitudes, atmospheric temperature has little effect on δ 18 O of precipitation near Wanxiang Cave. Furthermore, the temperature dependence of calcite-water δ 18 O fractionation acts in the opposite sense, most likely canceling out the effect of local temperature variations on speleothem δ 18 O. Given this, the maximum δ 18 O shift that could occur due only to changes in the composition of the oceanic source region, the amount of rainfall, and the amount of evaporation between full glacial conditions with a weak summer monsoon and full interglacial conditions with a strong summer monsoon is 5.5‰. Accordingly, it is necessary to invoke changes in past atmospheric circulation patterns and in the ratio of summer to winter precipitation to explain the nearly 7‰ range observed in fossil Wanxiang Cave speleothems. Two stalagmites, WXSM 51 and WXSM 52, exhibit more positive δ 18 O during stadial periods (marine isotope stages [MIS] 8, 6, 5d, 5b, and 2) than during interstadial periods (MIS 9, 5a, 5c, 5e). Thus, East Asian summer monsoon intensity is generally decreased during globally cooler periods and increased during globally warmer periods. We present detailed δ 18 O records from MIS 5a-5b and 5c-5d. During the MIS 5d-5c transition, summer monsoon intensity increased steadily from 117.6 ka, with a peak in intensity occurring at 106.8 ka, concurrent with Greenland Interstadial 24. During the MIS 5b-5a transition, monsoon intensity increased abruptly at about 85.7 ka, when δ 18 O decreased by approximately 4‰ in 200 years. Monsoon variability, inferred from the MIS 5c-5d and MIS 5a-5b records, closely coincides with global climate changes observed in the GISP2, Vostok, and SPECMAP records, and with the Northern Hemisphere insolation curve. This suggests that East Asian summer monsoon intensity varies in phase with global climate fluctuations and is largely controlled by variations in Northern Hemisphere incident solar radiation. The MIS 5a-5b and 5c-5d paleomonsoon records from Wanxiang Cave also agree well with other records of Asian monsoon variability indicating that δ 18 O of speleothems from Wanxiang Cave is a valid proxy for past changes in monsoon intensity.

Roles of forest bioproductivity, transpiration and fire in a nine-year record of cave dripwater chemistry from southwest Australia

“…Speleothem trace element records serve as proxies for diverse information including recharge (McMillan et al, 2005;McDonald et al, 2004;Johnson et al, 2006;Tremaine and Froelich, 2013), soil and bedrock weathering (Musgrove and Banner, 2004;Hori et al, 2014;Rutlidge et al, 2014), aerosol flux , organic matter composition and flux (Hartland et al, 2012) and cave PCO 2 (Wynn et al, 2014a;Treble et al, 2015). These records are readily obtained at high resolution (seasonal or better) using laser ablation, secondary ionisation mass spectrometry (SIMS) or synchrotron instruments (Fairchild and Treble, 2009).…”

High regional climate sensitivity over continental China constrained by glacial-recent changes in temperature and the hydrological cycle

“…O records, for example, there are possible contributions of temperature, precipitation at the site or along air mass trajectories, an altered balance between winter and summer monsoon intensity, changing frontal systems and water vapor sources, humidity effects, and kinetic isotope fractionations (1,(12)(13)(14)(15). Therefore, quantitative constraints on terrestrial climate changes from thermodynamically based proxies are limited, yet are crucial for constraining the sensitivity of this region and others to future climate forcing (16,17).…”

Implications of stalagmite density for past climate change: An example from stalagmite growth during the last deglaciation from Wanxiang Cave, western Loess Plateau

“…Important breakthroughs have also been made in the relationships between Asian monsoon changes and longevity of past Chinese dynasties, as well as the impacts of human activity on the Asian monsoon [8]. Stable oxygen and carbon isotopes were often affected by isotopic fractionation, overlapping of precipitation and temperature effects and other environmental factors [17,18]. Diagenetic processes (micritization and neomorphism) sometimes modify stalagmite isotope and trace element records [19].…”