Search

The seasonal rainfall regime is a key factor control on local ecological and social processes and is commonly thought to be stable under long‐term climate changes. Here we present a unique high‐resolution rainfall record from the Thai‐Malay Peninsula, combined with a state‐of‐the‐art transient climate simulation, demonstrating a fundamental rainfall regime shift from summer to winter during the Holocene. Transient model simulation and new sensitivity experiments further reveal that westward migration of the boundary between summer and winter rainfall regimes results in a summer to winter rainfall regime shift forced by distinct changes in summer and winter monsoons. Our findings suggest that the seasonal rainfall regime could be unstable under climate change around the boundaries of rainfall regimes in the tropics and possibly worldwide, which might be more critical for shaping both past and future ecological environments. Plain Language Summary: The observed seasonal rainfall regime, which varies over time, challenges the assumption of stable seasonal patterns in reconstructions of paleorainfall, suggesting that a reappraisal of the understanding of past ecological‐social changes with respect to rainfall may be needed. In this study, we have used a high‐resolution rainfall record from the Thai–Malay Peninsula and a state‐of‐the‐art transient paleoclimate simulation to describe a novel summer to winter rainfall regime shift during the Holocene era in the tropics, which may apply to regime‐boundary regions worldwide and thus provide a new perspective on dramatic ecological and social changes recorded around regime boundary regions for both past and future studies. Key Points: A unique rainfall record in the Thai‐Malay and a transient simulation suggest a summer to winter rainfall regime shift during the HoloceneTransient paleoclimate simulation simulation reveals that this shift was caused by westward migration of the boundary between summer and winter rainfall regimesThis regime shift could occur in regions around the boundaries of rainfall regimes in the tropics and possibly worldwide [ABSTRACT FROM AUTHOR]

Abstract: The δ18O values of marine benthic foraminifera indicate a long-term cooling through the middle and late Eocene around the globe. During the same time period, the India–Asia plate collision and the Pacific–Asia plate convergence must have significantly affected East Asia, especially East China. In this context, the evolving pattern of vegetation in East Asia and its controlling factor remains uncertain. In this study, 19 published Paleogene pollen records with independent age control in China were compiled and analyzed. The results indicate that the tropical and subtropical taxa and their percentages increased from the Late Paleocene to the Early Eocene, implying a warming trend in East Asia. From the Middle to the Late Eocene, the tropical and subtropical taxa and their percentages decreased continuously, showing a stepwise cooling. The most dramatic changes in vegetation occurred from the Late Eocene to the Early Oligocene in China, which is characterized by universal increase in coniferous pollen. This evolution trend of palynoflora in China appears well consistent with the δ18O curve of marine benthic foraminifera, revealing that global climate made a major contribution to changes in East-Asian vegetation during the Paleogene. It is noteworthy that from the Late Paleocene to the Early Oligocene East China was always wetter than West China so that broadleaf trees could bloom and develop continuously in East China. Influenced by the India–Asia plate collision and the Pacific–Asia plate convergence, the extensional basins in East China developed significantly during the Paleogene, and provided favorable locations and adequate moisture for the continuous development of broadleaf trees in East China. [Copyright &y& Elsevier]

Abstract: The vegetation on the northeastern margin of the Tibetan Plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive. Pollen samples from the Fanjiaping Loess section in Lanzhou on the western Chinese Loess Plateau (CLP) were analyzed in conjunction with OSL dating. The results indicate that pollen zone B (60.6–46.0 ka, correlative to the early MIS 3) had the greatest abundances of Cupressaceae, Tsuga, Gramineae and Cyperaceae of the entire section, suggesting a warm phase during the last glacial period. These pollen taxa decreased significantly in abundance in the zones C (46.0–39.0 ka) and D (39.0–27.0 ka), reflecting a substantial climate cooling from the middle MIS 3 to MIS 2. These results correlate with climate records from the South China Sea, the CLP, Baikal Lake, North America, North Atlantic Ocean and other regions, and probably correspond with the decline of northern high-latitude insolation and the increase of global ice volume from 50 to 20 ka. In particular, arboreal pollen, fern spore and algae abundances declined sharply since ∼40 ka, while shrub and herb pollen reached the highest abundances. Conifer pollen Picea and Abies abundance also rose markedly and increased up the section. This implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since ∼40 ka. The decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a ‘snow/ice/albedo’ feedback, which would result in less climate sensitivity to radiative forcing. Meanwhile, vegetation decline in the Northern Hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling, enhancing the growth of polar ice sheets since 40 ka. The development of polar ice sheets increased the polar-to-equator temperature and pressure gradients, strengthening the westerlies and supplying plenty of moisture to Northwest China during 40–30 ka. Lake sediments developed widely on the Tibetan Plateau during 40–30 ka, probably related to an increase in the seasonality of middle-to-low latitude insolation which caused an enhancement of glacier melting on the Plateau. [Copyright &y& Elsevier]

Abstract: Intense tectonic movement occurred along the northeastern margin of the Tibetan Plateau 3–4Ma. During the same time period, global climate changed from a period of stability to a period of frequent and abrupt changes, which prevented fluvial and glacial systems from establishing a state of equilibrium. Thus, it is difficult to directly attribute the 3–4Ma coarse-grained sediment accumulation in East Asia to climate change or tectonic activity. This study compares Late Cenozoic multi-proxy records from the Chinese Loess Plateau (CLP) to the low-latitude grain size, sea level and benthic δ 18O records from the South China Sea (SCS) and the high latitude grain-size record from Lake Baikal. All records suggest a steady and persistent cooling since ~4Ma, which correlates well with those cooling records from other regions around the world. This coincided in timing with the modeling results that the closure of the Central American Seaway (CAS) initiated strengthening of Atlantic meridional overturning circulation between 4.8 and 4.0Ma which led to both warming of the Northern Hemisphere (NH) and cooling of the Southern Hemisphere (SH). Cooling of the SH would induce a marked development of the Antarctic ice sheets at ~4Ma, pushing the Intertropical Convergence Zone (ITCZ) northward. This was superimposed on warming of the NH and brought more precipitation to the middle latitudes of the NH, resulting in increases in coarse-grained sediments in the Sikouzi section from the western CLP since 4.2Ma. Notably, the absence of coarse-grained sedimentation in the Sikouzi section during 3.0-2.1Ma and the gradual decrease in coarse-grained peaks since 2.1Ma reflected by the Sikouzi grain-size record probably resulted from stepwise increase in the NH ice volume pushing the ITCZ southward. On the other hand, development of the Antarctic ice sheets would induce global cooling and enhancement of physical weathering, initiating increases in sedimentation rates as well as increases in grain size from Lake Baikal to the CLP to the SCS. Therefore the closure of the CAS during 4.8–4.0Ma and its influence on ocean heat transport was possibly the major forcing factor for global cooling since 4Ma. A persistent and steady cooling during 4–3Ma probably made a significant contribution to the establishment of the NH ice sheets at 2.75Ma ago. [Copyright &y& Elsevier]

Global climate shifted to markedly warmer interglacial conditions across the "mid-Brunhes transition" (MBT, ~400 ka). However, a global MBT synthesis that spans marine and terrestrial evidence remains elusive, which limits our understanding of the role of the MBT in mid-Pleistocene human evolution. We synthesize Asian precipitation reconstructions within a context of global palaeoclimatic records and find that the MBT occurred in two stages. First, stronger warming of northern hemisphere continents, weaker southern hemisphere warming, and related more extensive northward displacement of the intertropical convergence zone (ITCZ) during interglacial marine isotope stage (MIS) 13 intensified and expanded precipitation in Asian monsoon regions and in other widespread northern hemisphere regions, with accompanying carbon reservoir changes featuring globally high marine benthic δ13C values because of vegetation expansion at ~500 ka. Subdued southern hemisphere warming and northward ITCZ displacement decreased southern hemisphere precipitation simultaneously during MIS 13. Second, a shift to globally warmer interglacials at ~400 ka, with elevated atmospheric CO 2 concentrations, smaller ice volume, and higher sea level resulted in sustained high interglacial precipitation in East Asia from MIS 11 onward and sustained high marine benthic δ13C values during MIS 11. We also synthesize palaeoanthropological data and find that the climate and ecosystem changes across the MBT coincided with the timing of human lineage diversification, including the emergence of Neanderthals and Denisovans in Eurasia and Homo sapiens in Africa, and their potential coexistence with H. heidelbergensis , H. erectus , H. floresiensis , H. naledi , and other Homo archaics. The timing of the MBT also coincided with novel hominin behavioural developments, including fire control and the transition from handaxe industries to more versatile Levallois techniques. Combined with environmental theories of human evolution, this chronological coincidence suggests a potential link between mid-Pleistocene environmental changes and human evolution. [ABSTRACT FROM AUTHOR]

Hydroclimatic variations in central Asia are widely recognized to be tele-connected with the North Atlantic climate via the mid-latitude Westerlies. However, the long-term hydroclimatic variation and its response to North Atlantic climate changes are not fully understood. Here we report multi-decadal and centennial hydroclimatic variations in central Asia during the late Holocene using high-resolution oxygen and carbon isotopes of bulk carbonate from a remote hydrologically closed alpine lake in Tianshan Mountains, northwestern China. The hydroclimatic variations inferred from the covariance between δ18O carb and δ13C carb and published multi-proxy in the Lake Sayram together agree well with the records from the central Asia, showing enhanced effective moisture at the intervals of 4000-3780, 3590-3210, 2800-2160, 1700-1370 and 890-280 cal yr BP during the negative phase of North Atlantic Oscillation (NAO). Comparison with European hydroclimatic changes on centennial scale, our records not only provide valuable insight into the hydroclimatic variations in central Asia, but also indicate all broadly contemporaneous changes with that of southern Europe whereas antiphase with that of northern Europe. We then conclude that the observed antiphase hydroclimatic pattern between northern Europe and southern Europe-central Asia on centennial time scale during the late Holocene were persistently controlled by the north-south migration of mid-latitude Westerlies and changes of NAO phase in response to solar irradiance forcing. However, further research is necessary to fully disentangle the natural and anthropogenic forcing mechanisms for enhanced effect moisture and/or precipitation in central Asia. • Paired δ18O carb and δ13C carb revealed enhanced effective moisture during the negative phase of NAO. • The hydroclimate in central Asia were contemporaneous with that of S Europe whereas antiphase with that of N Europe. • The hydroclimate in central Asia were contemporaneous with that of S Europe whereas antiphase with that of N Europe. [ABSTRACT FROM AUTHOR]