Orbital-scale Asian summer monsoon variations: Paradox and exploration

Abstract

The Asian summer monsoon (ASM) is a vast climate system, whose variability is critical to the livelihoods of billions of people across the Asian continent. During the past half-century, much progress has been made in understanding variations on a wide range of timescales, yet several significant issues remain unresolved. Of note are two long-standing problems concerning orbital-scale variations of the ASM. (1) Chinese loess magnetic susceptibility records show a persistent glacial-interglacial dominated~100 kyr (thousand years) periodicity, while the cave oxygen-isotope (δ 18 O) records reveal periodicity in an almost pure precession band (~20 kyr periodicity)-the "Chinese 100 kyr problem". (2) ASM records from the Arabian Sea and other oceans surrounding the Asian continent show a significant lag of 8-10 kyr to Northern Hemisphere summer insolation (NHSI), whereas the Asian cave δ 18 O records follow NHSI without a significant lag-a discrepancy termed the "sea-land precession-phase paradox". How can we reconcile these differences? Recent and more refined model simulations now provide spatial patterns of rainfall and wind across the precession cycle, revealing distinct regional divergences in the ASM domain, which can well explain a large portion of the disparities between the loess, marine, and cave proxy records. Overall, we also find that the loess, marine, and cave records are indeed complementary rather than incompatible, with each record preferentially describing a certain aspect of ASM dynamics. Our study provides new insight into the understanding of different hydroclimatic proxies and largely reconciles the "Chinese 100 kyr problem" and "sea-land precession-phase paradox".

Color Reflectance of Coastal Sediments in the South Bohai Sea and its Implication to Orbital Forcing of East Asian Summer Monsoon

“…Overall, although the uncertainties in monsoonal proxies cannot be excluded in this study, the Bohai records likely fill the gap between the new hypothesis of Cheng et al (2021) and the diverse periodicities of monsoon proxies, supporting that different archives preferentially record a certain aspect of the EASM. Moreover, the difference between the two Bohai records responding to the EASM might highlight a distinct role of precession and eccentricity cycles, which are worth of further investigation in future.…”

“…The Asian Monsoon plays a critical role in transporting large quantities of heat and moisture to the East Asia, the most populated region on the Earth (Zhang et al, 2008;Tan et al, 2021), and their evolution has been attracting a great amount of research attentions from geological records to numerical modeling (Jiang and Lang, 2010;Shi et al, 2012;Wang et al, 2014;Shi et al, 2019;Cheng et al, 2021). These geological records include loess deposits Guo et al, 2002;Sun et al, 2019), speleothem records (Wang et al, 2001;Cheng et al, 2009;Cheng et al, 2016), and marine and lacustrine sediments (Tian et al, 2008;Clemens et al, 2018;Yi et al, 2018;Chen et al, 2020;Xu et al, 2021).…”

“…Besides of these two scenarios, the dominant obliquity band in the Chinese loess plateau and non-precession component in the EASM variability in marine sediments at IODP U1429 site are also proposed (Li et al, 2017;Clemens et al, 2018), inferring a more complex response of the EASM to orbital forcing. To reconcile these hypotheses, Cheng et al (2021) suggested that different archives preferentially record a certain aspect of the EASM and spatial patterns of rainfall and wind across the precession cycle may be the major reason producing distinct regional divergences. However, testifying this new hypothesis is not easy, because the former requires a profile with a multiple dominance of eccentricity, obliquity, and precession cycles, or at least an equilibrium between them, while the later needs a full-cover study in the monsoon domain.…”

Seasonal and Inter-Annual Variations of Stable Isotopic Characteristics of Rainfall and Cave Water in Shennong Cave, Southeast China, and Its Paleoclimatic Implication

“…However, the significance of δ 18 O C has long been debated. For example, on orbital timescales, the Asian summer monsoon intensity inferred from Chinese speleothem δ 18 O C records show a significant precession signal and closely follow Northern Hemisphere summer insolation (NHSI) (Wang et al, 2008;Cai et al, 2015;Tan et al, 2015;Cheng et al, 2016;Kathayat et al, 2016;Tan et al, 2018;Cheng et al, 2021), while the Arabian Sea marine multi-proxy records indicate that the Asian summer monsoon intensity lags NHSI ∼8 ka (Clemens et al, 2010;Clemens et al, 2018). Clemens et al (2010) attributed this discrepancy to the comprehensive influence of the moisture source and moisture transport pathway on speleothem δ 18 O C .…”

“…Clemens et al (2010) attributed this discrepancy to the comprehensive influence of the moisture source and moisture transport pathway on speleothem δ 18 O C . Recently, Cheng et al (2021) and Zhang et al (2021) point out that a coherent orbital-scale speleothem δ 18 O C variability across most Asian monsoon regions (except southeastern China) indeed stems from the NHSI-forced changes in overall monsoon intensity; speleothem and marine records are complementary rather than incompatible, and each record reflects a certain aspect of Asian monsoon dynamics. Speleothem δ 18 O C records in southeastern China are rather distinct and should not be linked directly to the overall monsoon intensity due to its distinct precipitation seasonality (Zhang et al, 2020;Zhang et al, 2021).…”