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Characterizing the ecosystems' response to environmental changes on Tibetan Plateau (TP), as well as elucidating the regional disparities of these changes across the plateau's surface and its neighboring regions, holds significance for safeguarding the ecological security of Asia. Here, an improved pollen-based biomization procedure, incorporating weighted taxa, was conducted to illustrate the spatial and temporal differences of vegetation changes in TP, Xinjiang and southwestern China over the past 21,000 years. Results showed that the vegetation changes in TP and Xinjiang were characterized by alternations among herbaceous biomes, while the southwestern China were featured by changes among various woody biomes. Asynchronous vegetation change rates (ROCs) were discovered among TP, Xinjiang and southwestern China. The ROCs in TP were generally low during the Last Glacial Maximum but rose abruptly and peaked in the late deglacial period, whereas Xinjiang and southwestern China had high and increasing ROCs during Holocene. Those trajectories might relate to different sensitivities of vegetation to climate change and human disturbances. Habitat limitation on TP should be pretty intense during glacial period, leading to rapid vegetation establishment after glacier retreat. While in Xinjiang, water availability was the most obvious limitation, making the vegetation change sensitive to moisture and atmospheric CO 2 variations. The forest in Yunnan behaved the most stability but was characterized by vertical migration responding to deglacial warming. Holocene acceleration of ROCs aligned with intensified human activities in Xinjiang and southwestern China. To sum up, environmental conditions have been always important in determining post glacial vegetation changes in west China, but the ROCs were asynchronous due to different sensitivities of vegetation to climate change and human activity. Although the plateau's vegetation was quite stable during Holocene, the plateau terrestrial ecosystem may subject to increasing risk under accelerating global warming and intensifying human activities. • An improved taxa-weight biomization was conducted to reconstruct vegetation history in west China since 21ka BP. • Rate of change and random forest reveal vegetation dynamic and its main driving factors. • Different sensitivities of ecosystems to climate change and human activity caused the trajectories in vegetation change. [ABSTRACT FROM AUTHOR]

Pronounced changes in the deep Atlantic circulation occurred during glacial stages, which affected the global carbon distribution and the biogeochemical cycles of other elements. Previous studies demonstrated that oceanic mercury is sensitive to the same kind of processes that affect the carbon cycle in glacial-interglacial time scales. We used Hg isotopes to elucidate Hg cycling during the last two glacial-interglacial transitions in the subtropical western South Atlantic. Mass-dependent fractionation (MDF, δ202Hg) and mass-independent fractionation (MIF, Δ199Hg) show significant variations and shift toward higher and lower values during the penultimate and Last Glacial Maximum periods, respectively. δ202Hg variability is in-phase with periods of lower atmospheric CO2 and benthic δ13C, suggesting that MDF is affected by the same mechanisms that led to atmospheric CO2 drawdown during glacial stages. In contrast, terrestrial Hg input to our site, boosted by lower sea level and exposure of the continental shelf, dominates the Δ199Hg variability. [ABSTRACT FROM AUTHOR]

The deep ocean has long been recognized as the reservoir that stores the carbon dioxide (CO2) removed from the atmosphere during Pleistocene glacial periods. The removal of glacial atmospheric CO2 into the ocean is likely modulated by an increase in the degree of utilization of macronutrients at the sea surface and enhanced storage of respired CO2 in the deep ocean, known as enhanced efficiency of the biological pump. Enhanced biological pump efficiency during glacial periods is most easily documented in the deep ocean using proxies for oxygen concentrations, which are directly linked to respiratory CO2 levels. We document the enhanced storage of respired CO2 during the Last Glacial Maximum (LGM) in the Pacific Southern Ocean and deepest Equatorial Pacific using records of deglacial authigenic manganese, which form as relict peaks during increases in bottom water oxygen (BWO) concentration. These peaks are found at depths and regions where other oxygenation histories have been ambiguous, due to diagenetic alteration of authigenic uranium, another proxy for BWO. Our results require that the entirety of the abyssal Pacific below approximately 1,000 m was enriched in respired CO2 and depleted in oxygen during the LGM. The presence of authigenic Mn enrichment in the deep Equatorial Pacific for each of the last five deglaciations suggests that the storage of respired CO2 in the deep ocean is a ubiquitous feature of late-Pleistocene ice ages. [ABSTRACT FROM AUTHOR]

We reconstruct deep water‐mass salinities and spatial distributions in the western North Atlantic during the Last Glacial Maximum (LGM, 19–26 ka), a period when atmospheric CO2 was significantly lower than it is today. A reversal in the LGM Atlantic meridional bottom water salinity gradient has been hypothesized for several LGM water‐mass reconstructions. Such a reversal has the potential to influence climate, ocean circulation, and atmospheric CO2 by increasing the thermal energy and carbon storage capacity of the deep ocean. To test this hypothesis, we reconstructed LGM bottom water salinity based on sedimentary porewater chloride profiles in a north‐south transect of piston cores collected from the deep western North Atlantic. LGM bottom water salinity in the deep western North Atlantic determined by the density‐based method is 3.41–3.99 ± 0.15% higher than modern values at these sites. This increase is consistent with: (a) the 3.6% global average salinity change expected from eustatic sea level rise, (b) a northward expansion of southern sourced deep water, (c) shoaling of northern sourced deep water, and (d) a reversal of the Atlantic's north‐south deep water salinity gradient during the LGM. Plain Language Summary: Twenty thousand years ago, the atmosphere had a much lower temperature and contained less insulating carbon dioxide (CO2) gas than it did even before the human induced CO2 rise of the last centuries. Confirming if the carbon "missing" from the atmosphere 20,000 years ago was stored away in the deep ocean will help us predict where the carbon humans add to the atmosphere will end up over the next few millennia. We find the temperature and amount of salt (salinity) in today's waters by measuring them directly, but to find them in the past ocean we measure chemical compounds that are buried over time in the seafloor. In this study, we measure the density of water collected from the north Atlantic seafloor to estimate the past salinity. Our results support previous findings that 20,000 years ago the deep Atlantic was filled with more carbon‐rich water that sank from the surface in the Southern Ocean than in today's Atlantic, accounting for up to two‐thirds of the carbon "missing" from the atmosphere 20,000 years ago. Key Points: Paleosalinities of Last Glacial Maximum (19–26 ka) North Atlantic Bottom waters are 3.41–3.99 ± 0.15% higher than modern valuesNew paleosalinities support expansion of salty, southern sourced water displacing fresher, northern sourced water in the Last Glacial Maximum (LGM) deep AtlanticPaleosalinities are more precise when from porewater densities measured on ship from cores that span the LGM porewater chloride maximum [ABSTRACT FROM AUTHOR]

The upper end of the equilibrium climate sensitivity (ECS) has increased substantially in the latest Coupled Model Intercomparison Projects phase 6 with eight models (as of this writing) reporting an ECS > 5°C. The Community Earth System Model version 2 (CESM2) is one such high‐ECS model. Here we perform paleoclimate simulations of the Last Glacial Maximum (LGM) using CESM2 to examine whether its high ECS is realistic. We find that the simulated LGM global mean temperature decrease exceeds 11°C, greater than both the cooling estimated from proxies and simulated by an earlier model version (CESM1). The large LGM cooling in CESM2 is attributed to a strong shortwave cloud feedback in the newest atmosphere model. Our results indicate that the high ECS of CESM2 is incompatible with LGM constraints and that the projected future warming in CESM2, and models with a similarly high ECS, is thus likely too large. Plain Language Summary: Equilibrium climate sensitivity (ECS) is one of the most important metrics in climate science. It measures the amount of global warming over hundreds of years after a doubling of the atmospheric CO2 concentration. An ECS range of 1.5°C–4.5°C has been consistently supported by climate models over the past 40 years. However, this has changed in the latest generation of climate models with eight (as of this writing) showing an ECS > 5°C. Such a high ECS implies that future warming will be much greater than previously thought for the same amount of greenhouse gas emissions, making it more challenging for human and natural systems to adapt. This study examines whether the ECS in one "high‐ECS" model—Community Earth System Model version 2 (CESM2)—is realistic. Our approach is to perform a paleoclimate simulation of the culmination of the last glacial period, which was colder and had a lower atmospheric CO2 level than today. We find that the magnitude of cooling in the CESM2 simulation is much larger than supported by the observational evidence, indicating the model's ECS is too large. We further find that the high ECS of CESM2 is caused by the treatment of clouds in the model. Key Points: Community Earth System Model version 2 simulates an Last Glacial Maximum (LGM) global temperature at least 5°C colder than the proxy estimate, indicating its equilibrium climate sensitivity is too highThe large LGM cooling is caused by a strong shortwave cloud feedback in the new atmosphere modelThe shortwave cloud feedback in LGM simulations is connected to that in abrupt 4×CO2 simulations from the present‐day climate [ABSTRACT FROM AUTHOR]

Atmospheric carbon dioxide concentration (pCO2) varies by about 100ppm during glacial‐interglacial cycles. Previous studies suggest that the strongly stratified Southern Ocean at the Last Glacial Maximum increases the oceanic storage of carbon, but the glacial reduction of atmospheric pCO2 simulated by ocean general circulation models (OGCMs) does not reach 100ppm. One candidate for the underestimation is that carbonate compensation is not explicitly incorporated in the previous OGCM simulations. Therefore, we quantitatively evaluate the impact of carbonate compensation on the glacial atmospheric pCO2 by using an OGCM coupled with an ocean sediment model. As suggested by previous box model studies, our OGCM simulations show that the enhanced Southern Ocean stratification amplifies the decrease in atmospheric pCO2 due to carbonate compensation. Considering the enhanced stratification in the Southern Ocean, we obtain a 26‐ppm drawdown of atmospheric pCO2 by carbonate compensation, and the full reduction from our pre‐industrial simulation reaches 73ppm. Both the increase in ventilation ages in the deep Atlantic and Southern Oceans and the growth of export production in the subantarctic region reduce the bottom‐water carbonate ion and promote deposited carbonate dissolution. Consequently, a greater imbalance between the river inflow and burial loss of carbonate rises ocean alkalinity, lowering atmospheric pCO2. We suggest that the reproducibility of the Southern Ocean process is essential for controlling the magnitude of atmospheric pCO2 decline due to carbonate compensation. Key Points: A 73‐ppm reduction of atmospheric pCO2 is reproduced by an ocean general circulation model simulation including carbonate compensationDrop in atmospheric pCO2 due to carbonate compensation is linearly related to an imbalance between the river inflow and burial of carbonateWe show that enhanced stratification in the Southern Ocean amplifies the impact of carbonate compensation on atmospheric pCO2 [ABSTRACT FROM AUTHOR]

Substantial stratigraphic evidence from the Late Quaternary at orbital- and millennial‒scales indicates that the formation and evolution of aeolian‒sand landscapes results from the interaction between regional aeolian and fluvial‒lacustrine activity. In many deserts (sandy lands) across the planet, fluvial‒aeolian interplay at the glacial‒interglacial scale since the Late Quaternary has been responsive to monsoonal precipitation, and linked to atmospheric CO 2 and periodic variations in insolation. However, the patterns of fluvial‒aeolian interplay and their relationship with climate change are not always consistent over a given timescale during the Late Pleistocene. The paucity of studies on fluvial‒aeolian interplay in the Mu Us Desert (MUD) during the Last Glacial Period (LGP) hinders our understanding of the relationships between the dynamics of aeolian and fluvial‒lacustrine landscapes and their drivers. Here, based on a comprehensive field survey and stratigraphic dating of a typical fluvial‒aeolian sequence in the MUD, we synthesized the chronology of fluvial‒lacustrine and aeolian strata during the LGP. Our results show that extensive development of a fluvial‒lacustrine environment in the MUD during the LG mainly occurred during the late Last Glacial Maximum (LGMa, 20.1–18.4 ka BP) and Bølling/Allerød interstadial (14.8–12.6 ka BP), while thicker aeolian sands extensively accumulated during the Heinrich Stadial 2, Heinrich Stadial 1, and Younger Dryas periods. However, the development of fluvial‒lacustrine environments showed considerable spatial heterogeneity, mainly occurring on the southern and eastern margins of the desert, while they were extremely rare in the central and western parts of the desert owing to strong wind erosion. Comparisons with other high-resolution geological records from the Asian monsoon region reveal that the fluvial‒aeolian interplay in the MUD during the LGP was highly consistent with the evolution pattern of the East Asian summer monsoon (EASM) on the millennial‒centennial scale, and indicate that the development of fluvial‒lacustrine environments was mainly controlled by an increase in monsoonal precipitation during strengthening of the EASM. Consistency with other broad changes at high latitudes in the Northern Hemisphere suggests that fluvial‒aeolian interplay during the LGP in northern Chinese deserts, as represented by the MUD, was mainly controlled by changes in high-northern-latitude ice volume and the Atlantic Meridional Overturning Circulation. • Fluvial‒aeolian interplay during the Last Glacial Period in the Mu Us Desert is studied. • Regional fluvial‒aeolian interplay during the LGP is correlated with millennial-scale global climatic events. • Regional fluvial‒lacustrine environments mainly developed during the LGMa and B/A. • Fluvial‒lacustrine and aeolian processes during the LGP were mutually reinforcing and inhibiting. • High-northern-latitude forcing modulated millennial-scale fluvial‒aeolian interplay in the MUD during the LGP. [ABSTRACT FROM AUTHOR]

Abstract: Several lines of evidence have previously been used to suggest that ice retreat after the last glacial maximum (LGM) resulted in regionally-increased levels of volcanic activity. It has been proposed that this increase in volcanism was globally significant, forming a substantial component of the post-glacial rise in atmospheric CO2, and thereby contributing to climatic warming. However, as yet there has been no detailed investigation of activity in glaciated volcanic arcs following the LGM. Arc volcanism accounts for 90% of present-day subaerial volcanic eruptions. It is therefore important to constrain the impact of deglaciation on arc volcanoes, to understand fully the nature and magnitude of global-scale relationships between volcanism and glaciation. The first part of this paper examines the post-glacial explosive eruption history of the Andean southern volcanic zone (SVZ), a typical arc system, with additional data from the Kamchatka and Cascade arcs. In all cases, eruption rates in the early post-glacial period do not exceed those at later times at a statistically significant level. In part, the recognition and quantification of what may be small (i.e. less than a factor of two) increases in eruption rate is hindered by the size of our datasets. These datasets are limited to eruptions larger than 0.1km3, because deviations from power-law magnitude–frequency relationships indicate strong relative under-sampling at smaller eruption volumes. In the southern SVZ, where ice unloading was greatest, eruption frequency in the early post-glacial period is approximately twice that of the mid post-glacial period (although frequency increases again in the late post-glacial). A comparable pattern occurs in Kamchatka, but is not observed in the Cascade arc. The early post-glacial period also coincides with a small number of very large explosive eruptions from the most active volcanoes in the southern and central SVZ, consistent with enhanced ponding of magma during glaciation and release upon deglaciation. In comparison to non-arc settings, evidence of post-glacial increases in rates of arc volcanism is weak, and there is no need to invoke significantly increased melt production upon ice unloading, as occurred in areas such as Iceland. Non-arc volcanoes may therefore account for a relatively higher proportion of global volcanic emissions in the early post-glacial period than is suggested by the relative contributions of arc and non-arc settings at the present day. The second part of this paper critically examines global eruption records, in an effort to constrain global-scale changes in volcanic output since the LGM. Accurate interpretation of these records relies on correcting both temporal and spatial variability in eruption recording. In particular, very low recording rates, which also vary spatially by over two orders of magnitude, prevent precise, and possibly even accurate, quantitative analysis. For example, if we assume record completeness for the past century, the number of known eruptions (volcanic explosivity index≥2) from some low-latitude regions, such as Indonesia, is approximately 1 in 20,000 (0.005%) for the period 5–20ka. There is a need for more regional-scale studies of past volcanism in such regions, where current data are extremely sparse. We attempt to correct for recording biases, and suggest a maximum two-fold (but potentially much less) increase in global eruption rates, relative to the present day, between 13 and 7ka. Although volcanism may have been an important source of CO2 in the early Holocene, it is unlikely to have been a dominant control on changes in atmospheric CO2 after the LGM. [Copyright &y& Elsevier]

Abstract: Using the Earth system model of intermediate complexity Bern3D, we transiently simulate changes in atmospheric CO2 and climate over the Last Glacial–Interglacial cycle. A third of the glacial–interglacial atmospheric CO2 change can be explained by relatively well-established forcings such as temperature, salinity, a shallowing and weakening of the Atlantic Meridional Overturning Circulation, iron fertilization of the marine biosphere by aeolian dust input and land carbon inventory changes. A 10% increase in the oceanic phosphate inventory decreases atmospheric CO2 by 50 ppmv during the glaciation, however due to the long residence time of phosphorus in the ocean and the long time scales of ocean–sediment interactions it only contributes to a 5 ppmv increase between 20 and 0 ka B.P. The enhanced surface nutrient utilisation simulated as a result of a greater oceanic phosphate inventory leads to a good representation of glacial export production and δ13CO2 changes, lending support to this hypothesis. A deepening of particulate organic matter remineralization can effectively lower pCO2 during the glaciation, however it leads to a significant increase in deep and to changes in export production in poor agreement with paleo-proxies. Finally the parametrization of brine rejection around Antarctica could lead to 10–20 ppmv change in pCO2, but its timing casts doubt onto its effectiveness in forcing CO2 variations over the Last Glacial–Interglacial cycle. The results highlight the importance of a transient, 3-dimensional setting for the interpretation of proxy records. [Copyright &y& Elsevier]

Mountain glacier records offer important constraints on the timing and magnitude of climate variability during the last glacial cycle. Existing moraine chronologies from the central Southern Alps indicate maximum ice extent was achieved during marine isotope stages 3–4, followed by repeated advances of similar, but gradually declining extent during marine isotope stage 2, until onset of the glacial termination. Questions remain over the precise role of climate in driving these changes, as most existing moraine chronologies come from large, complex former valley glacier systems, where non-climatic influences such as changing bed topography and proglacial lake formation may have influenced glacier length changes. Here we address this problem via a new cosmogenic 10Be chronology and equilibrium line altitude reconstruction from a cirque glacier situated in Fiordland, New Zealand. Our chronology shows moraine deposition at 32 ± 11 ka, 18.7 ± 0.2 ka, 18.1 ± 0.1 ka, and c. 17.2 ± 0.3 ka. The simple geometry of the former glacier supports the role of climate in driving a net decline of regional ice volume during marine isotope stages 3–2. Close spacing and good preservation of the 19–17 ka moraines permits 2D glacier reconstruction which suggests the equilibrium line altitude remained depressed by c.1130 m (equivalent to 5.8 ± 0.6 °C colder than present) during this interval. Onset of warming after 17.2 ± 0.2 ka is consistent with climate proxy evidence for a sustained southward shift in the southern westerly winds, which may have promoted deglaciation via shifting ocean currents and promoting increases in atmospheric carbon dioxide. • Moraine ages from southern New Zealand constrain ice extent during last glacial. • Equilibrium line altitude was 1100 m lower than present at the Last Glacial Maximum. • Regional air temperatures remained depressed by c. 6 °C until 17 ka. [ABSTRACT FROM AUTHOR]

[Display omitted] • Millennial-scale climate variability in the Bay of Bengal is reconstructed by TEX 86. • Warming trend during millennial-scale cold events is revealed in the northern Indian Ocean. • Atmospheric CO 2 force SST change during the millennial-scale cold events over the past 40 kyr. To better understand the process of hydrographic and temperature changes in the Indian Ocean, we present Glycerol dialkyl glycerol tetraether data on core BoB-56 from the Bay of Bengal to reconstruct the sea surface temperature (SST) variability during the last glaciation. The results indicate that the TEX 86 -derived SST ranged from 22.00 to 28.30 °C with several fluctuations since 40 ka BP and that the evolution pattern matched well with the marine isotope stage (MIS). During MIS 3, the SST kept around 24.60 °C with some small amplitudes. The SST showed more significant fluctuations during MIS 2 and increased gradually with a ~3 °C cooling during the Last Glacial Maximum (LGM). After the Younger Dryas (YD) stage, Holocene SST values exhibited miniscule variations. During the last glaciation climate variability process, the cold signals of the YD and Heinrich events were recorded well in our core SST series, revealing a regional response to global climate changes. The warming trend during these millennial-scale cold events in the northern Indian Ocean was also identified, and SST increased in the range of 2 °C. A comparison of SST records and atmospheric CO 2 concentration shows that the warming process during the YD, LGM, and Heinrich (1–4) events matched the gradual increase in atmospheric CO 2 concentration in the northern Indian Ocean. Hence, this study implies millennial-scale hydroclimate change linked with atmospheric CO 2 forcing that could improve our knowledge of the role of atmospheric CO 2 in triggering abrupt Indian Ocean climate changes. [ABSTRACT FROM AUTHOR]