The influence of 14C reservoir age on interpretation of paleolimnological records from the Tibetan Plateau

There is a great deal of controversy regarding the fate of glaciers and ice fields on the Tibetan Plateau in the face of continued anthropogenic global warming. Paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the Tibetan Plateau to changing conditions. Specifically, the numerous lakes distributed across the Tibetan Plateau can provide high-resolution (spatial and temporal) climate reconstructions to investigate past changes in the climate system. In this paper, we review the primary limitation to exploiting these valuable paleoclimate archives: errors in radiocarbon-based age models. We review the techniques that have been used to estimate 14C reservoir ages on the Tibetan Plateau and compile the published 14C reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties. Using site-specific evaluations of Bangong Co and Lake Qinghai, we demonstrate that 14C age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records. We also examine 14C-induced uncertainties in the spatial climatic response on the Tibetan Plateau to (1) the termination of the Last Glacial Maximum and (2) the Holocene Thermal Maximum. We conclude with recommendations for reducing uncertainties in future lake-based paleoclimate studies on the Tibetan Plateau

Centennial-scale compound-specific hydrogen isotope record of Pleistocene–Holocene climate transition from southern New England

Northeastern North America experienced major climate shifts during the Pleistocene –Holocene transition. However, there have been no high-resolution isotopic records of climate change from this region. Here, we present a centennial-scale record of climate change during the transition based on D/H ratios of behenic acid (C22 nacid) or dDBA from a sediment core in Blood Pond, Massachusetts. Surface calibrations from a transect of 19 lakes in eastern North America show that dDBA values track mean annual atmospheric temperature variations. The abrupt climate events observed in Blood Pond records show remarkable similarity with Greenland ice core d18O records during the Pleistocene. During the early Holocene, the northeastern North America dDBA record was more variable than Greenland, possibly due to the close proximity of the Laurentide ice sheet, and impact of freshwater outbursts as the ice sheet rapidly retreated. Citation: Hou, J., Y. Huang, W. W. Oswald, D. R. Foster, and B. Shuman (2007), Centennialscale compound-specific hydrogen isotope record of Pleistocene–Holocene climate transition from southern New EnglandOrganismic and Evolutionary Biolog

A 2540-year record of moisture variations derived from lacustrine sediment (Sasikul Lake) on the Pamir Plateau

Although the Pamir Plateau is an ideal place to investigate paleo-environmental changes in the westerlies-dominated high Central Asia, there are only few Holocene records from this region. We present a sub-centennially resolved lacustrine record of moisture variations from Sasikul Lake, central Pamir Plateau, based on geochemical, sedimentological, and mineralogical proxies. Our results show that generally dry conditions at Sasikul Lake during the past 2540 years were interrupted by a pronounced wet period between ad 1550 and 1900, corresponding to the ‘Little Ice Age’ (LIA). More negative values of carbonate δ18O, lower total inorganic carbon (TIC), and sand content during LIA all indicate a relatively wet period with higher lake level. Higher TIC during the ‘Medieval Warm Period’ (MWP; ad 950–1200) reveals a lower lake level relative to the LIA. Low δ18O during this time is probably attributed to changes in the isotopic composition of input water and/or upstream moisture sources. The significant increase in detrital minerals and decrease in carbonate during the LIA provide further evidence for higher allochthonous input during the wet period at Sasikul Lake. The inferred moisture variations are consistent with existing records from regions of the northern Tibetan Plateau and Central Asia that are also influenced by the westerlies, but out-ofphase with those records from the Asian monsoon region, indicating that moisture variations at Sasikul Lake were mainly influenced by the strength and trajectories of the westerlies. The inferred water level at Sasikul Lake decreased significantly during the first half of the 20th century, and then increased in recent decades. This is consistent with the increase in lake area derived from satellite images and the monitoring data of large lake-level changes in Central Asia

Large Holocene summer temperature oscillations and impact on the peopling of the northeastern Tibetan Plateau

Summer temperatures on the Tibetan Plateau (TP) significantly affect stability of glaciers that provide steady water resources to nearly half of the world population. However, lack of reliable, long-term proxy records greatly impedes understanding of regional temperature sensitivity to climate forcings. Here we present a 16ka long, alkenone-based summer temperature record from Lake Qinghai, northeastern TP that demonstrates major regional temperature response to changes in summer insolation and Atlantic Meridional Overturning Circulation during the Holocene and late glacial. Importantly, we find a period of sustained summer temperature decline (>4 degrees C) between 5 and 3.5ka, which coincides with expansion of Barents Sea ice coverage and is likely driven by intensification of the Westerlies. This unusually long and pronounced regional cooling event likely delayed permanent human settlements on the high-altitude regions (>3000m) of the TP by at least 500years

Paleoclimatic fluctuations inferred from leaf wax n-alkane records in Central Tibet in the late Oligocene to early Miocene

Climatic variations and their forcing mechanisms in Tibet are highly significant for understanding the environmental effects of the Tibetan Plateau through its controlling on atmospheric circulation. Here we present new leaf wax n-alkanes from Cenozoic lacustrine sediments in the Lunpola Basin of central Tibet to constrain long-term paleoclimatic changes. Our results suggest that the paleoclimate from the late Oligocene to early Miocene was generally stable, but tending slightly towards cold-dry from 25.5 to 23.2 Ma, followed by a trend towards warm-humid between 23.2 and 21.7 Ma, and finally by a more arid and highly oscillating climate after 21.7 Ma. Our results compare favorably with the proxies of marine delta O-18 records, which suggests that the general long-term trend since the late Oligocene has been a response to global temperature variations. Moreover, spectral analysis of delta C-13(31) and delta H-2(31) data reveals that relative humidity exhibits similar to 400 kyr cycles, controlled mainly by periodic changes in global ice volumes

Quantitative estimates of Holocene glacier meltwater variations on the Western Tibetan Plateau

Knowledge of the alpine glacier meltwater variations is fundamental prerequisite for understanding glacier dynamics and assessing the availability of freshwater resources. Glaciers on the Tibetan Plateau (TP) are sources of water for most major Asian rivers, but their melting history remains unclear, preventing in-depth understanding of their mechanisms. Here, we propose the authigenic carbonate delta O-18 from glacial lakes as a quantitative proxy to estimate variations of glacier meltwater. In the Western Kunlun Mountain, 6 18 0 record at Guozha Co indicates that maximum glacier meltwater (-28.62 +/- 25.76 Gt) occurred at 9.5-8.5 ka BP, and minimum glacier meltwater (24.53 +/- 25.02 Gt) at 1.3-0.5 ka BP. Nearly 20% of regional glaciers melted from the Early to Late Holocene, likely controlled by the summer temperature and accumulation of melting potential estimated by positive degree-day. Based on the projected temperature, this study suggests the TP glaciers likely face severe threats at the current rates of global warming. (C) 2021 Elsevier B.V. All rights reserved

A 2540-year record of moisture variations derived from lacustrine sediment (Sasikul Lake) on the Pamir Plateau

Although the Pamir Plateau is an ideal place to investigate paleo-environmental changes in the westerlies-dominated high Central Asia, there are only few Holocene records from this region. We present a sub-centennially resolved lacustrine record of moisture variations from Sasikul Lake, central Pamir Plateau, based on geochemical, sedimentological, and mineralogical proxies. Our results show that generally dry conditions at Sasikul Lake during the past 2540 years were interrupted by a pronounced wet period between ad 1550 and 1900, corresponding to the ‘Little Ice Age’ (LIA). More negative values of carbonate δ18O, lower total inorganic carbon (TIC), and sand content during LIA all indicate a relatively wet period with higher lake level. Higher TIC during the ‘Medieval Warm Period’ (MWP; ad 950–1200) reveals a lower lake level relative to the LIA. Low δ18O during this time is probably attributed to changes in the isotopic composition of input water and/or upstream moisture sources. The significant increase in detrital minerals and decrease in carbonate during the LIA provide further evidence for higher allochthonous input during the wet period at Sasikul Lake. The inferred moisture variations are consistent with existing records from regions of the northern Tibetan Plateau and Central Asia that are also influenced by the westerlies, but out-ofphase with those records from the Asian monsoon region, indicating that moisture variations at Sasikul Lake were mainly influenced by the strength and trajectories of the westerlies. The inferred water level at Sasikul Lake decreased significantly during the first half of the 20th century, and then increased in recent decades. This is consistent with the increase in lake area derived from satellite images and the monitoring data of large lake-level changes in Central Asia