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A 150‐ to 220‐year lag between abrupt Greenland warming and maximum Antarctic warming characterizes past glacial Dansgaard‐Oeschger events. In a modeling study, we investigate how the cross‐equatorial oceanic heat transport (COHT) might drive this phasing during an abrupt Northern Hemisphere (NH) warming. We use the MITgcm in an idealized continental configuration with two ocean basins, one wider, one narrower, under glacial‐like conditions with sea ice reaching midlatitudes. An exaggerated eccentricity‐related solar radiation anomaly is imposed over 100 years to trigger an abrupt NH warming and sea‐ice melting. The Hadley circulation shifts northward in response, weakening the NH trade winds, subtropical cells, and COHT in both ocean basins. This induces heat convergence in the Southern Hemisphere (SH) ocean subsurface, from where upward heat release melts sea ice and warms SH high latitudes. Although the small‐basin meridional overturning circulation also weakens, driven by NH ice melting, it contributes at most one‐third to the total COHT anomaly, hence playing a subsidiary role in the SH and NH initial warming. Switching off the forcing cools the NH; yet heat release continues from the SH ocean subsurface via isopycnal advection‐diffusion and vertical mixing, driving further sea ice melting and high latitude warming for ~50–70 more years. A phasing in polar temperatures resembling reconstructions thus emerges, linked to changes in the subtropical cells' COHT, and SH ocean heat storage and surface fluxes. Our results highlight the potential role of the atmosphere circulation and wind‐driven global ocean circulation in the NH–SH phasing seen in DO events. Key Points: Polar temperature phasing linked to changes in cross‐equatorial ocean heat transport and Southern Ocean heat storage in MITgcmCross‐equatorial ocean heat transport mainly driven by subtropical cell weakening due to northward ITCZ shift; smaller role of AMOCMaximum warming in the South delayed with respect to the North due to subsurface heat release and ice melting [ABSTRACT FROM AUTHOR]

There is a growing appreciation of the uncertainties in the estimation of snow‐melt and glacier‐melt as a result of climate change in high elevation catchments. Through a detailed examination of three hydrological models in two catchments, and interpretation of results from previous studies, we observed that many variations in estimated streamflow could be explained by the selection of a best parameter set from the possible good model parameters. The importance of understanding changing glacial dynamics is critically important for our study areas in the Upper Indus Basin where Pakistan's policymakers are planning infrastructure to meet the future energy and water needs of hundreds of millions of people downstream. Yet, the effect of climate on glacial runoff and climate on snowmelt runoff is poorly understood. With the HBV model, for example, we estimated glacial melt as between 56% and 89% for the Hunza catchment. When rainfall was a scaled parameter, the models estimated glacial melt as between 20% and 100% of streamflow. These parameter sets produced wildly different projections of future climate for RCP8.5 scenarios in 2046–2075 compared to 1976–2005. Assuming no glacial shrinkage, for one climate projection, we found that the choice among good parameter sets resulted in projected values of future streamflow across a range from +54% to +125%. Parameter selection was the most significant source of uncertainty in the glaciated catchment and amplified climate model uncertainty, whereas climate model choice was more important in the rainfall dominated catchment. Although the study focuses on Pakistan, the overall conclusions are instructive for other similar regions in the world. We suggest that modellers of glaciated catchments should present results from at least the book‐ends: models with low sensitivity to ice‐melt and models with high sensitivity to ice‐melt. This would reduce confusion among decision makers when they are faced with similar contrasting results. [ABSTRACT FROM AUTHOR]

The article informs on the emergence of an equatorial mode of climate variability in the Indian Ocean (IO). It mentions that simulations indicate that under greenhouse warming and Last Glacial Maximum conditions, the IO can exhibit increased sea surface temperature variability in the eastern equatorial IO.

Some lateral moraines contain a rich record of Holocene glacial expansion. Previous workers have used such evidence to document glacial fluctuations in western Canada, Alaska, and the U.S. Pacific Northwest, but similar studies in Patagonia are uncommon. Here we report on the late Holocene behavior of Stoppani Glacier, a 75 km2 glacier sourced in the Cordillera Darwin, southernmost Patagonia. Based on radiocarbon-dated wood and organic material contained in the glacier's northeast lateral moraine, we infer that Stoppani Glacier advanced shortly before 3.8–3.6, at 3.2–2.8, 2.3–2.1, and 0.3–0.2, and possibly sometime before 1.4–1.3 and 0.8–0.7 cal ka BP. These advances culminated at 0.3–0.2 cal ka BP, when the glacier constructed a prominent end moraine, marking its greatest extent of the past 4000 years. Although the timing of several of the advances overlap with the age range of glacial expansion recognized elsewhere in Patagonia, some do not. Asynchronous behavior observed in the glacial record may arise from the type of evidence (e.g., lateral stratigraphy vs. end moraine) used to document glacial fluctuations or variations in climate or glacial response times. A significant difference between the Stoppani record and some other Patagonian records is that the former indicates general expansion of ice over the last 4000 years, whereas the latter indicate a net decrease in extent over that period. [ABSTRACT FROM AUTHOR]

Peatlands are an essential part of the terrestrial carbon cycle and the climate system. Understanding their history is key to understand future and past land-atmosphere carbon fluxes. We performed transient simulations over the past 22 000 years with a dynamic global peat and vegetation model forced by Earth System Model climate output, thereby complementing data-based reconstructions for peatlands. Our novel results demonstrate a highly dynamic evolution with concomitant gains and losses of active peatland areas. Modelled gross area changes exceed net changes several fold, while net peat area increases by 60 % over the deglaciation. Peatlands expand to higher northern latitudes in response to warmer and wetter conditions and retreating ice sheets and are partly lost in mid-latitude regions. In the tropics peatlands are partly lost due to flooding of continental shelves and regained by non-linear interactions between temperature, precipitation and CO2. Large north-south shifts of tropical peatlands are driven by shifts in the position of the Inter Tropical Convergence Zone associated with the abrupt climate events of the glacial termination. Time slice simulations for the Last Glacial Maximum (LGM) demonstrate large uncertainties in modelled peatland extent (global range: 1.5 to 3.4 Mkm2) stemming from uncertainties in climate forcing. Net uptake of atmospheric CO2 through peatlands, modelled at 350 GtC since the LGM, includes decay from former peatlands. Carbon uptake would be misestimated, in particular during periods of rapid climate change and subsequent peatland area shifts, when considering only changes in the area of currently active peatlands. Our study highlights the dynamic nature of peatland distribution and calls for an improved understanding of former peatlands to better constrain peat carbon sources and sinks. [ABSTRACT FROM AUTHOR]

The uncertain response of marine terminating outlet glaciers to climate change at time scales beyond short-term observation limits models of future sea level rise. At temperate tidewater margins, abundant subglacial meltwater forms morainal banks (marine shoals) or ice-contact deltas that reduce water depth, stabilizing grounding lines and slowing or reversing glacial retreat. Here we present a radiocarbon-dated record from Integrated Ocean Drilling Program (IODP) Site U1421 that tracks the terminus of the largest Alaskan Cordilleran Ice Sheet outlet glacier during Last Glacial Maximum climate transitions. Sedimentation rates, ice-rafted debris, and microfossil and biogeochemical proxies, show repeated abrupt collapses and slow advances typical of the tidewater glacier cycle observed in modern systems. When global sea level rise exceeded the local rate of bank building, the cycle of readvances stopped leading to irreversible retreat. These results support theory that suggests sediment dynamics can control tidewater terminus position on an open shelf under temperate conditions delaying climate-driven retreat. Tidewater glaciers in fjords can advance/retreat independent of climate due to stabilization by sediments at their termini. We show that an Alaskan paleo-ice stream behaved similarly on an open shelf, suggesting that increased sediment flux may delay catastrophic retreat of outlet glaciers in a warming world. [ABSTRACT FROM AUTHOR]

We investigated two stalagmites from the Saripa Cave and Bumi Cave in southern Sulawesi, Indonesia, using high-precision U-series dating and high-resolution trace element and C-O-Sr isotope analysis. The growth record (from 10.4 ± 0.1 ka to 77.4 ± 0.9 ka) of the Saripa Cave stalagmite (SR04-ST3) is fragmented with two major (at the top: 10.4-11.6 ka and middle: 43.8-44.7 ka sections of the stalagmite) and some short (middle and bottom sections) growth phases, interrupted by long-lasting growth hiatuses. Both the timing of the growth phases and the δ18O values for different growth phases are correlated with those of cold/dry (~22 ka and 43.8-44.7 ka) and wet/warm periods (e.g., Greenland Interstadials 12, 14, and 21) in the northern hemisphere speleothem records, displaying both anti-phase and in-phase relationships with the northern hemisphere records. This observation is unique in the Western Pacific tropical region, mostly likely because the Saripa Cave is located within the region of the latitudinally migrating Intertropical Convergence Zone (ITCZ), whereby the rainfall seasons may have changed through time depending on the mean latitude of the ITCZ. The Saripa Cave stalagmite contains textural laminae, which are here interpreted as a record of rapid environmental changes, possibly caused by volcanic eruptions at around 22.55 ka and 44.73 ka BP. The Bumi Cave record (stalagmite BC-09-3-C), on the other hand, presents very little variation in stable isotope and trace element compositions between 26.8 ka and 18.5 ka and does not seem to be influenced by any possible volcanic activity. More detailed future studies investigating millimeter- to submillimeter-scale geochemical time-series constrained by accurate ages in speleothems can be useful in unfolding the effects of eruptions and provide parallel records of climate and sudden environmental changes. [ABSTRACT FROM AUTHOR]

Many stable isotope paleoaltimetry studies have focused on paleoelevation reconstructions of orogenic plateaus such as the Tibetan or Andean Plateaus. We address the opportunities and challenges of applying stable isotope paleoaltimetry to "smaller" orogens. We do this using a high‐resolution isotope tracking general circulation model (ECHAM5‐wiso) and explore the precipitation δ18O (δ18Op) signal of Cenozoic paleoclimate and topographic change in the European Alps. Results predict a maximum δ18Op change of 4–5‰ (relative to present day) during topographic development of the Alps. This signal of topographic change has the same magnitude as changes in δ18Op values resulting from Pliocene and Last Glacial Maximum global climatic change. Despite the similar magnitude of the isotopic signals resulting from topographic and paleoclimate changes, their spatial patterns across central Europe differ. Our results suggest that an integration of paleoclimate modeling, multiproxy approaches, and low‐elevation reference proxy records distal from an orogen improve topographic reconstructions. Plain Language Summary: Here we use a climate model with water isotopes implemented to explore the maximum precipitation isotopic signal of Cenozoic topographic and paleoclimate change in the European Alps. Our results show that the impact of topography change has the same magnitude as changes in the isotopic composition of local precipitation resulting from Pliocene and Last Glacial Maximum global climatic change. Key Points: High‐resolution isotope tracking general circulation model (ECHAM5‐wiso) is used to explore changes in past oxygen isotope ratios in precipitation in the AlpsModel‐simulated isotopic signals of topographic change and difference between glacials and interglacials show the same magnitudeLow‐elevation proxy records improve reconstructions of paleotopography by reducing long‐term climate change bias [ABSTRACT FROM AUTHOR]

In addressing the controversial issues of the Late Pleistocene paleogeography of the Caspian basin, an important role is given to the results of the spore-pollen analysis and based on them reconstructions of climate and vegetation changes in the Northern Caspian region during the development of the Early Khvalynian transgression. In this paper we present the main results of the palynological study of deposits (chocolate clays and the overlying and underlying layers from the Srednyaya Akhtuba section) of maximum stage of the Early Khvalynian transgression; the materials are illustrated by pollen diagram with the data of spore-pollen analysis and the detailed list of palynoflora recovered from the studied Lower Khvalynian sequences, and complemented with photographs of pollen belonging to the principal autochtonous taxa and, for comparison, to some redeposited palynomorphs. Palynological materials indicate subaqual (brackish marine and freshwater) sedimentation of the sediments studied in periglacial landscapes and, for the most part, under very harsh climatic conditions. The performed climate-stratigraphic reconstructions do not contradict the data of absolute dating on the accumulation of the studied deposits during the Late Valdai (Ostashkov) late Glacial period. During this interval in the territory of the study area, plant communities of the glacial climate — tundra-steppe, periglacial forest-steppe, periglacial steppe, periglacial parklands and periglacial forests — were developed. The widespread occurrence in the composition of the periglacial vegetation cover of the studied region of the yernik formations from Betula nana and shrub communities from Betula fruticosa , B. nana , Alnaster fruticosus , Juniperus , etc. testifies to the severe climatic conditions and, possibly, the existence of sporadic permafrost in the cold stages (stadials) of the Ostashkov Late Glacial period. [ABSTRACT FROM AUTHOR]

Aim: To investigate cerrado responses to glacial–interglacial climate change and the potential for connective rain forest corridors between the Atlantic Coastal Forest and Amazonian rain forest. Location: The crater lake of Serra Negra (18 °S, 46 °W) in Minas Gerais, Brazil. Taxon: 117 fossil pollen types, 22 non‐pollen palynomorphs were documented. Methods: We recovered 7.82 m of sediment from the lake, and analysed fossil pollen at 62 depth intervals throughout the core. We derived a chronology based on radiocarbon dating with simple rate extrapolation to the base of the core. Results: The c. 90,000‐year fossil record showed a trend towards cooler climates at the Last Glacial Maximum (LGM), but interstadial warming coupled with reduced evaporative stress allowed the expansion of woodlands under cool, moist conditions. Cool‐adapted trees were most abundant between c. 67,000 and 48,000 years ago. A cool cerrado‐like environment marked full glacial conditions between c. 48,000 and 34,000 years ago. The peak of the LGM between c. 34,000 and 17,000 years ago is inferred to have been dry as no sediment accumulated in the system. Main conclusions: Expanded ranges of cold‐tolerant forest taxa led to establishment of a series of assemblages without modern analogue. A system characteristic of modern cerrado was rare in the history of this site. Multiple forest expansions were observed, each differing in composition. The periods of forest abundance at Serra Negra were not temporally aligned with forest expansion in the Atlantic Coastal Forest, and did not provide a continuous corridor of similar forest that connected the cerrado to the Atlantic Coastal Forest. [ABSTRACT FROM AUTHOR]

We present a new global reconstruction of seasonal climates at the Last Glacial Maximum (LGM, 21 000 years BP) made using 3-D variational data assimilation with pollen-based site reconstructions of six climate variables and the ensemble average of the PMIP3—CMIP5 simulations as a prior (initial estimate of LGM climate). We assume that the correlation matrix of the uncertainties in the prior is both spatially and temporally Gaussian, in order to produce a climate reconstruction that is smoothed both from month to month and from grid cell to grid cell. The pollen-based reconstructions include mean annual temperature (MAT), mean temperature of the coldest month (MTCO), mean temperature of the warmest month (MTWA), growing season warmth as measured by growing degree days above a baseline of 5 ∘ C (GDD 5), mean annual precipitation (MAP), and a moisture index (MI), which is the ratio of MAP to mean annual potential evapotranspiration. Different variables are reconstructed at different sites, but our approach both preserves seasonal relationships and allows a more complete set of seasonal climate variables to be derived at each location. We further account for the ecophysiological effects of low atmospheric carbon dioxide concentration on vegetation in making reconstructions of MAP and MI. This adjustment results in the reconstruction of wetter climates than might otherwise be inferred from the vegetation composition. Finally, by comparing the uncertainty contribution to the final reconstruction, we provide confidence intervals on these reconstructions and delimit geographical regions for which the palaeodata provide no information to constrain the climate reconstructions. The new reconstructions will provide a benchmark created using clear and defined mathematical procedures that can be used for evaluation of the PMIP4–CMIP6 entry-card LGM simulations and are available at 10.17864/1947.244 (Cleator et al., 2020b). [ABSTRACT FROM AUTHOR]

Weddell Sea-derived Antarctic Bottom Water (AABW) is one of the most important deep water masses in the Southern Hemisphere occupying large portions of the deep Southern Ocean (SO) today. While substantial changes in SO-overturning circulation were previously suggested, the state of Weddell Sea AABW export during glacial climates remains poorly understood. Here we report seawater-derived Nd and Pb isotope records that provide evidence for the absence of Weddell Sea-derived AABW in the Atlantic sector of the SO during the last two glacial maxima. Increasing delivery of Antarctic Pb to regions outside the Weddell Sea traced SO frontal displacements during both glacial terminations. The export of Weddell Sea-derived AABW resumed late during glacial terminations, coinciding with the last major atmospheric CO2 rise in the transition to the Holocene and the Eemian. Our new records lend strong support for a previously inferred AABW overturning stagnation event during the peak Eemian interglacial. The Southern Ocean plays a key role in glacial-interglacial transitions and today, Weddell Sea derived Antarctic Bottom Water is one of the most important deep water masses. New records show that in contrast to today, no Weddell Sea water was exported during the last two glacial maxima, providing new insights towards the condition of Antarctic Bottom Water formation in extreme climate states. [ABSTRACT FROM AUTHOR]

Glacier recession is a globally occurring trend. Although a rich body of work has documented glacial response to climate warming, few studies have assessed vegetation cover change in recently deglaciated areas, especially using geospatial technologies. Here, vegetation change at two glacier forefronts in Glacier National Park, Montana, U.S.A. was quantified through remote sensing analysis, fieldwork validation, and statistical modeling. Specifically, we assessed the spatial and temporal patterns of landcover change at the two glacier forefronts in Glacier National Park and determined the role of selected biophysical terrain factors (elevation, slope, aspect, solar radiation, flow accumulation, topographic wetness index, and surficial geology) on vegetation change (from non-vegetated to vegetated cover) at the deglaciated areas. Landsat imagery of the study locations in 1991, 2003, and 2015 were classified and validated using visual interpretation. Model results revealed geographic differences in biophysical correlates of vegetation change between the study areas, suggesting that terrain variation is a key factor affecting spatial-temporal patterns of vegetation change. At Jackson Glacier forefront, increases in vegetation over some portion or all of the study period were negatively associated with elevation, slope angle, and consolidated bedrock. At Grinnell Glacier forefront, increases in vegetation associated negatively with elevation and positively with solar radiation. Integrated geospatial and field approaches to the study of vegetation change in recently deglaciated terrain are recommended to understand and monitor processes and patterns of ongoing habitat change in rapidly changing mountain environments. [ABSTRACT FROM AUTHOR]

Climate change and glacial retreat are changing the runoff behavior of Alpine springs and streams. For example, in the extremely dry and hot summer of 2018, many springs used for drinking water supply lost up to 50 percent of their average discharge; a few springs have even run dry. In order to ensure drinking water supply in the future, springs featuring large and constantly sufficient discharge rates will have to be identified and tapped. A case study was undertaken at the Tuxbachquelle because catchment area and temporal variation of physicochemical and hydrochemical properties were previously unknown. Tracer tests with uranine proved a hydraulic connection between this karst spring and a stream a few kilometers uphill. At low runoff, uranine needed about 4½ hours from the sink to the spring, whereas at high runoff more than four days was required. It became evident that discharge, electrical conductivity, temperature, and turbidity of the Tuxbachquelle respond within a few hours to precipitation events. The water quality and an examination of the water balance resulted in a significantly larger catchment area. It is assumed that widely karstified calcite marble subterraneously drains a considerable part of the Tuxertal (Tux Valley), including some active rock glaciers. [ABSTRACT FROM AUTHOR]

Changeover from a glacial to an interglacial climate is considered as transitional between two stable modes. Palaeoceanographic reconstructions using the polar foraminifera Neogloboquadrina pachyderma highlight the retreat of the Polar Front during the last deglaciation in terms of both its decreasing abundance and stable oxygen isotope values (δ18O) in sediment cores. While conventional isotope analysis of pooled N. pachyderma and G. bulloides shells shows a warming trend concurrent with the retreating ice, new single-shell measurements reveal that this trend is composed of two isotopically different populations that are morphologically indistinguishable. Using modern time series as analogues for interpreting downcore data, glacial productivity in the mid-North Atlantic appears limited to a single maximum in late summer, followed by the melting of drifting icebergs and winter sea ice. Despite collapsing ice sheets and global warming during the deglaciation, a second "warm" population of N. pachyderma appears in a bimodal seasonal succession, separated by the subpolar G. bulloides. This represents a shift in the timing of the main plankton bloom from late to early summer in a "deglacial" intermediate mode that persisted from the glacial maximum until the start of the Holocene. When seawater temperatures exceeded the threshold values, first the "cold" (glacial) then the "warm" (deglacial) populations of N. pachyderma disappeared, whilst G. bulloides with a greater tolerance to higher temperatures persisted throughout the Holocene to the present day in the midlatitude North Atlantic. Single-specimen δ18O of polar N. pachyderma reveals a steeper rate of ocean warming during the last deglaciation than appears from conventional pooled δ18O average values. [ABSTRACT FROM AUTHOR]

This paper investigates the correlation between climate, environment and human land use in the Westernmost Mediterranean on both sides of the Strait of Gibraltar during the Late Glacial. Using a multi-proxy approach on a sample of 300 sites from the Solutrean and Magdalenian of the Iberian Peninsula and from the Iberomaurusian in Morocco, we find evidence for significant changes in settlement patterns and site density after the Last Glacial Maximum. In Southern Iberia, during Heinrich Stadial 1, hyperarid zones expanded drastically from the south-eastern coast to the West through the Interior. This aridification process heavily affected Magdalenian settlement in the South and caused a strong decline of hunter-gatherer population. Southern Iberia during Heinrich Stadial 1 turned out to be a high-risk environment when compared to Northern Iberia. At the same time, the Late Iberomaurusian of Morocco, although considered to be situated in a high-risk environment as well, experiences an increase of sites and expansion of settlement area. [ABSTRACT FROM AUTHOR]

Aim: Understanding the drivers of speciation within islands is key to explain the high levels of invertebrate diversification and endemism often observed within islands. Here, we propose an insular topoclimate model for Quaternary diversification (ITQD), and test the general prediction that, within a radially eroded conical island, glacial climate conditions facilitate the divergence of populations within species across valleys. Location: Gran Canaria, Canary Islands. Taxon: The Laparocerus tessellatus beetle species complex (Coleoptera, Curculionidae). Methods: We characterize individual‐level genomic relationships using single nucleotide polymorphisms produced by double‐digest restriction site associated DNA sequencing (ddRAD‐seq). A range of parameter values were explored in order to filter our data. We assess individual relatedness, species boundaries, demographic history and spatial patterns of connectivity. Results: The total number of ddRAD‐seq loci per sample ranges from 4,576 to 512, with 11.12% and 4.84% of missing data respectively, depending on the filtering parameter combination. We consistently infer four genetically distinct ancestral populations and two presumed cases of admixture, one of which is largely restricted to high altitudes. Bayes factor delimitation support the hypothesis of four species, which is consistent with the four inferred ancestral gene pools. Landscape resistance analyses identified genomic relatedness among individuals in two out of the four inferred species to be best explained by annual precipitation during the last glacial maximum rather than geographic distance. Main conclusions: Our data reveal a complex speciation history involving population isolation and admixture, with broad support for the ITQD model here proposed. We suggest that further studies are needed to test the generality of our model, and enrich our understanding of the evolutionary process in island invertebrates. Our results demonstrate the power of ddRAD‐seq data to provide a detailed understanding of the temporal and spatial dynamics of insular biodiversity. [ABSTRACT FROM AUTHOR]

Dual proxies were used to estimate paleo sea surface temperatures (SST) for the Bay of Plenty, north of New Zealand. U37K′ and Mg/Ca in the planktonic foraminifera Globogerina bulloides reconstruct SST for the growth seasons for the organisms they are based upon. U37K′ SST (summer) were consistently ~ 3.5 °C warmer than Mg/Ca (spring), suggesting that Bay of Plenty SST during the last glacial maximum (LGM) was 17.3 °C in summer and 13.8 °C in spring. Combining these results with published data based on the same proxies from other sites around New Zealand shows cooling of 3–4 °C in both seasons at all sites in the LGM relative to the Holocene. This indicates that overall, glacial surface water cooling was similar in subtropical and subpolar waters in both spring and summer. This contrasts with published foraminiferal assemblage reconstructions suggesting greater subantarctic cooling during the LGM. Deglacial warming across the region was characterized by changes in both seasonal and latitudinal temperature differences. Warming began in subtropical waters at ~21 ka, ~ 1.5 ka earlier than in subantarctic water. In the Bay of Plenty, the seasons maintained a consistent offset, while in Hawke Bay, springs stayed cold while summers warmed until after the Antarctic Cold Reversal. In contrast, subantarctic spring SST warmed rapidly, causing temperature differences to decrease between the Chatham Rise (subantarctic) and subtropical sites, possibly caused by shifting westerly winds. The use of multiple proxies enhances our understanding by adding a seasonal component to the glacial story of climate change in the southwest Pacific Ocean. Key Points: Alkenone and foraminiferal Mg/Ca provide seasonal temperature reconstructions for late winter/early spring versus summer in the New Zealand areaSea surface temperatures were 3–4 °C cooler in both seasons during the last glaciation in both subtropical and subantarctic watersSignificant changes in seasonality and latitudinal gradients in SST were only seen during the deglaciation from 35 to 45°S around New Zealand [ABSTRACT FROM AUTHOR]

Effectively identifying the genetic structure and related factors of a species can facilitate understanding the evolutionary history of the species. Phylogeographic patterns and genetic data are essential in investigating the species historical processes and diversification that response to environmental, climatic and geological influences. In this study, Specific Length Amplified Fragment Sequencing (SLAF-seq) data and ecological niche models (ENMs) are combined to identify the genetic structure and demographic modeling of Quercus spinosa , and evaluate the impacts of historical range shifts, climatic variation, and landscape factors on this species. The population topology and genetic divergence of the Cenozoic were inferred by a site frequency spectrum based composite-likelihood approach which is a novel strategy for maximizing the utility of linked SLAF markers. The overall genetic structure using model-based and model-free clustering methods was consistently identified as two geographically distinct genetic clusters. A deep divergence between two natural lineages (i.e., a western Himalaya-Hengduan Mountains lineage and an eastern Qin-ling Mountains lineage) was observed. The demographic modeling and Niche reconstruction indicated that the two groups were diverged in the late Miocene and then presented as two distinct genetic lineages. With the Quaternary glacial climate fluctuation, two groups had continuous asymmetrical secondary contact and gene exchange in the Sichuan Basin during the last glacial maximum. Besides, a significant relationship between genetic distance and geography in all individuals was identified by the Mantel test. Overall, this study 1) contributes to a better understanding of the role played by Quaternary climatic fluctuation in the present-day distributions of Q. spinosa ; 2) provides a comprehensive view of the genome-wide variation of sclerophyllous forests in ecological adaptive evolution; 3) indicates that dispersal limitation and ecological divergence contribute to the genome-wide differentiation of Q. spinosa , which supports a hypothesis that complex geography and climatic changes strongly influence the evolutionary origin and history of the species. [ABSTRACT FROM AUTHOR]

Pollen analysis of pond and spring deposits at the Aubrey Clovis site in North Texas provides a 1300-year record of late glacial grassland vegetation from 17,200 to 15,900 cal years BP. Forty-six pollen taxa are identified in the well-preserved assemblages. The late glacial pollen record at the Aubrey site represents three environments: upland, riparian, and lacustrine-wetland. The pond-related sediments are dominated by 80% Poaceae pollen, an unusually high amount in pollen records; the spring tufa sediments are dominated by Cyperaceae. Cattail (Typha latifolia) and other wetland plants, including green algae Botryococcus, Pediastrum , and Chara were present. The riparian habitat of the wide late glacial alluvial valley had alder (Alnus), willow (Salix), cottonwood (Populus), and water elm (Planera aquatica). The upland vegetation was a treeless grassland with comparatively high amounts of Asteraceae-type pollen; it is therefore called the aster prairie. Quercus, Juniperus , Carya , Ulmus , Ambrosia , and Chenopodiaceae pollen are much less abundant than found in modern grassland pollen records. Small amounts of Artemisia , Pinus , and Picea pollen are present, a consequence of long-distance transport. Regional late glacial cool-wet climate produced moist prairie soils. The Cross Timbers oak forest that occurs near the site today had not yet formed. Dissimilarity analysis of the pollen data shows that the late glacial aster prairie has no analog with modern shortgrass, mixed-grass, or tallgrass prairies. In contrast, a favorable analog exists with fossil pollen data from a lower zone at Patschke Bog, central Texas, and Muscotah Marsh, northeastern Kansas, indicating that a grassland characterized by high amounts of Asteraceae pollen formed a unique late glacial vegetation type in the region, earlier in Texas and later in Kansas. Because of its chronology and location in the eastern Great Plains, the late glacial aster prairie may be ancestral to the modern tallgrass prairie. • The late glacial aster prairie has no analog with modern tallgrass, mixed-grass, or short grass prairies. • The treeless condition of the aster prairie is supported by the absence of bark beetles and other tree-dwelling insects. • The late glacial climate was cooler than today, based on associated insects and mollusks. [ABSTRACT FROM AUTHOR]

Beetles of the family Tenebrionidae, particularly those of the subfamily Pimeliinae, are highly diverse and abundant in desert ecosystems. The sensitivity of the many wingless species to geographical and ecological isolation makes them ideal candidates for studying effects of climatological and/or geophysical changes on organismal diversity. Our study focuses on Brinckia , the only genus of the subtribe Hypomelina adapted to coastal sand dune hummocks (nabkhas) and restricted to that environment along the Namib Desert and the transitional Namib south of the Orange River. Today, Brinckia appear to be common along the coast, albeit with different species, wherever the absence of shifting sand dunes enables the beach hummocks to form, mainly around Salsola and Zygophyllum species. Therefore, past diversification can probably be directly attributed to temporary extinctions of this habitat in certain coastal regions. The presumed center of origin and diversification of Brinckia is on the Gariep Karoo coastline between Port Nolloth and Lüderitz. Our molecular phylogenetic analysis suggests that the first split within Brinckia occurred ∼2.3 Ma, i.e., relatively recently, and may be associated with aridification that occurred at that time due to global climate change. However, subsequent speciation is more likely the result of the emergence of extensive dune fields, which may have been responsible for temporary habitat degradation in the supralittoral zone. More recent, recurrent and ongoing diversification since the mid-Pleistocene transition, as observed for tenebrionids along the coast of the Atacama and Peruvian deserts, is not typical of Brinckia and supports the stability of their coastal habitat despite glacial climate oscillations. [Display omitted] • Brinckia is adapted and restricted to beach hummocks along the Namib coastline. • The supposed center of origin and diversification is in the Gariep Karoo. • The first split 2.3 Ma might be related to aridification due to global climate change. • Further splits could be related to local habitat degradation from shifting sand dunes. [ABSTRACT FROM AUTHOR]

The Indian summer monsoon (ISM) is a significant component of global climate and plays a key role in transporting heat and moisture from tropical oceans to the Indian subcontinent. The ISM has a critical role in ecosystem functioning as well as the development of regional agriculture and societies. However, it is difficult to ascertain the extent to which these two drivers interact and impact regional biogeochemistry from contemporary process studies because of the widespread human footprint, and millennial-scale ISM dynamics remain poorly understood over the last 20,000 years. Here we used high-resolution diatoms from alpine lakes at different elevations in the southwest monsoon region to reconstruct summer temperature and environmental variability since the Last Glacial Maximum (LGM). By comparing with other proxy-based temperature reconstructions of the Tibetan Plateau and the monsoon proxy records from South Asia, we found a 3–6 °C warming trend and ISM strengthening since the LGM. Our results indicate that summer temperature began to increase since 17.5 cal. kyr BP, marking the onset of deglacial warming. During the early to middle Holocene, the climate clearly warmed and then decreased afterward. The maximum warm interval occurred during the mid-Holocene, which followed changes in Northern Hemisphere summer insolation. Additionally, examinations of fossil diatom assemblages revealed that changes in compositions were closely linked with global and Indian monsoon climate changes on glacial and interglacial time scales. The abrupt temperature increases from extreme cold to warm transition during the Late-glacial/Holocene boundary (∼3 °C) are strongly associated with regional replacement of major biotic species compositions. The presence of biotic transition and the increased rate of temperature increase during the Late-glacial/Holocene transition confirm the importance of climate change in restructuring biological communities. This suggests that biotic structures necessary to survive such rapid climate regime were susceptible to impacts of the speed and magnitude of temperature change in monsoon region. • Composite mean July temperature inferred by diatoms from multiple lakes and comparison with palaeoclimatic bio-proxies. • Quantitative estimates show a regionally coherent Holocene maximum warmth over the southeastern Tibetan Plateau. • Temperature increases by ca. 1.5–3.4 °C since the Holocene represent a first threshold in ecosystem responses to climate warming [ABSTRACT FROM AUTHOR]

Southern Africa's Greater Cape Floristic Region (GCFR) – a hotspot of biological diversity and palaeo-anthropological evidence for modern human evolution – is a climatically complex region where broad climatic gradients influence the relative importance of plant photosynthetic types in local vegetation. This mix of photosynthetic pathways imprint an isotopic signature on palaeo-records, thereby allowing for the reconstruction of historical climate and vegetation. Here, we use vegetation plot data, coupled with the photosynthetic-type affinities of plant genera, to relate their relative cover to bioclimatic drivers and use these to create spatial distribution models of C 3 and C 4 grasses and CAM shrubs across the contemporary GCFR. We then use palaeodistribution modelling, drawing on downscaled climate models for the Last Glacial Maximum (LGM), to hindcast the LGM distributions of photosynthetic types for the GCFR and its then-exposed offshore areas. In addition, we construct a model to account for the effect of lower atmospheric CO 2 concentration ([CO 2 ]) during the LGM on the competitive interactions between C 3 and C 4 grasses and use this model to hindcast relative C 4 -grass cover across the glacial-era GCFR. Our palaeodistribution models suggest that, even though there were some reductions in CAM cover and shifts in C 3 -/C 4 -dominated grass layers between the LGM and Holocene, these were mostly localised, with changes at the regional scale being relatively muted. For C 3 /C 4 grasses, distributional shifts were even more subtle once sub-ambient glacial [CO 2 ] was accounted for. Our hindcasts of glacial, [CO 2 ]-adjusted grass cover show agreements and inconsistencies with various sedimentary and herbivore-diet records in the palaeo-archive: both lines of evidence suggest the dominance of C 3 species in the strongly winter-rainfall western GCFR; in the eastern GCFR, with muted rainfall seasonality, hindcasts of relative C 3 :C 4 cover and δ13C signals from palaeo-records vary, with greater disparities between them. The lack of significant upheavals in the distribution of photosynthetic types suggests that the GCFR presented a relatively stable and dependable resourcescape for hunter-gatherer populations through the glacial–interglacial cycle of the LGM–Holocene transition. Our maps of relative C 3 -/C 4 -grass and CAM-shrub cover provide a reasonable surrogate for relative biomass of different photosynthetic types in local vegetation at a landscape scale and depict an independent estimate of carbon isoscapes across the GCFR – under both an interglacial (Holocene) and glacial (terminal Pleistocene) climate – against which palaeo-records can be assessed. • Spatial models of relative cover of CAM shrubs and C 3 /C 4 grasses under current and LGM climates • Spatial model of relative C 4 -grass cover under LGM climate and atmospheric CO 2 concentration ([CO 2 ]) • Muted changes in distribution of photosynthetic types through LGM–Holocene transition • Distributional shifts for C 4 grasses more subtle when sub-ambient glacial [CO 2 ] is accounted for • Maps of CAM-shrub and C 3 -/C 4 -grass cover can be used to assess palaeo-records of carbon isoscapes [ABSTRACT FROM AUTHOR]

The article discusses need for satellite-based real-time monitoring for Himalayan glacial catchments. It mentions increasing temperatures and human interventions have added stress on the region's hydrological sensitivity and have increased the risks of major flood events; and Glacial lake areas are affected by the regional rainfall.

(B) El Capitan Cave speleothem EC-16-5-F carbon and oxygen isotope record. Finally, in Figure 3b the blue and red lines representing the El Capitan Cave speleothem EC-16-5-F carbon and oxygen isotope record are incorrect. [Extracted from the article]

The late Pennsylvanian of Atlantic Canada records a major transition in the evolution of fossil plants. This transition, broadly characterized by the replacement of the arborescent Lycopsida (giant club mosses) and Cordaitales (early gymnosperms) by Mariattales (tree ferns) and Coniferales (early modern conifers), has been known globally as the "Carboniferous Rainforest Collapse", and is commonly associated with widespread aridification amid fluctuations between glacial and interglacial climate regimes. In recent years it has become apparent that there are significant regional differences in the tempo of floral turnover, while studies of single locality sequences have revealed significant cyclical changes in plant community composition over short timescales. What remains unclear is the specific tempo of floral turnover within Atlantic Canada. This study explores the transition in fossil plant community structure at the regional scale, focusing on the late Pennsylvanian localities from Nova Scotia, New Brunswick, and Prince Edward Island. Fossil macrofloral occurrence data were compiled from museum repositories and records from the published literature, representing plant fossil occurrences spanning the middle Bashkirian through the end of the Kasimovian. Species and genus presences and absences were used to conduct multivariate analyses of similarity between localities. Preliminary results show a gradual shift in species composition over time, with the greatest degree of turnover occurring in the late Moscovian. Conversely, analysis of community composition at the genus level revealed little change in composition between time bins, but an increase in variance between sites within time bins. These results indicate that the shift in palaeofloral community composition in Atlantic Canada may be best described as a gradual increase in the breadth of uniquely composed communities as opposed to a turnover pulse, as assemblages similar in composition to those of the middle Bashkirian persist throughout the studied interval. [ABSTRACT FROM AUTHOR]

High latitude deep water upwelling has the potential to control global climate over glacial timescales through the biological pump and ocean-atmosphere CO 2 exchange. However, there is currently a lack of continuous long nutrient upwelling records with which to assess this mechanism. Here we present geochemical proxy records for nutrient upwelling and glacial North Pacific Intermediate Water (GNPIW) formation in the Bering Sea over the past 850 kyr, which demonstrates that glacial periods were characterised by reduced nutrient upwelling, when global atmospheric CO 2 and temperature were also lowered. We suggest that glacial expansion of sea ice in the Bering Sea, and the simultaneous expansion of low nutrient GNPIW, inhibited vertical mixing and nutrient supply across the subarctic Pacific Ocean. Our findings lend support to the suggestion that high latitude sea ice and the resultant intermediate water formation, modulated deep water upwelling and ocean-atmosphere CO 2 exchange on glacial-interglacial timescales. • Increased Bering Sea sea ice caused expansion of intermediate water in glacials. • Intermediate water expansion inhibited deep water nutrient supply to surface waters. • Region contributed to global ocean-air CO 2 exchange on glacial timescales. • Tight correlation between subarctic nutrient upwelling and global CO 2. [ABSTRACT FROM AUTHOR]

This study evaluates paleoclimate sensitivity over the past 800,000 years from proxy-based reconstructions of changes in global temperature, ice sheets and sea level, vegetation, dust, and greenhouse gases. This analysis uses statistical methods that are not biased by the variable (heteroscedastic) uncertainty in the reconstructions, and applies a Monte Carlo-style probabilistic framework to quantify several sources of measurement and structural uncertainty. Not addressing the heteroscedastic uncertainty would result in regression results that underestimate paleoclimate sensitivity by over 30%, and not using a probabilistic framework could underestimate the credible interval by fivefold. A comparison of changes in global temperature (ΔT) and changes in radiative forcing from greenhouse gases, ice sheets, dust, and vegetation (ΔR[GHG,LI,AE,VG]) over the past 800 kyr finds that the two are closely coupled across glacial cycles with a correlation of 0.81 (0.6 to 0.9, 95% credible interval). The variation of ΔT with ΔR over the past 800 kyr is non-linear, with lower correlation and lower responsiveness at colder temperatures. The paleoclimate sensitivity parameter estimates (S[GHG,LI,AE,VG]) are 0.84 °C/W/m2 (0.20 to 1.9 °C/W/m2, 95% interval) for interglacial periods and intermediate glacial climates and 0.53 °C/W/m2 (0.08 to 1.5 °C/W/m2, 95% interval) for full glacial climates, 37% lower at the median. The estimates of S[GHG,LI,AE,VG] and the pattern of state dependence are similar across glacial cycles over the past 800 kyr. This analysis explicitly includes several sources of uncertainty and is still able to provide a strong upper bound for the paleoclimate sensitivity parameter for interglacial periods and intermediate glacial climates: over 1.5 °C/W/m2 is < 10% probability, 1.7 °C/W/m2 is < 5% probability, and over 1.9 °C/W/m2 is < 2.5% probability. [ABSTRACT FROM AUTHOR]

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We analyzed the single‐grain mineralogical composition of aeolian dust transported to central East Antarctica for provenance purposes. Comparison with data from the last glacial period shows for the first time disappearance of carbonates during the Holocene related to sea level rise and suppressed deflation from the Argentinean continental shelf, exposed during Marine Isotope Stage 2. Zeolites, related to alteration of volcanic glass in the subglacial/periglacial environment of Patagonia, show a similar behavior. The remaining minerals, remarkably similar between the two climatic periods, are compatible with a Pampean and Patagonian provenance, but Holocene data show a more pronounced volcanic and metamorphic imprint and presence of minerals related to warm climate weathering environments compatible with an additional contribution from subtropical latitudes of South America. These results do not imply a major large‐scale reorganization of atmospheric circulation after the last climatic transition. Plain Language Summary: Aeolian mineral dust particles transported through the atmosphere from the austral continents to the Antarctic ice sheet represent a tracer of atmospheric circulation and transport, as well as being a source of information about environmental conditions within dust source regions. Many lines of evidence suggest that central East Antarctic dust is sourced from South America during the last glacial period, whereas there is not a general consensus about dust provenance during the Holocene. A major limitation to this problem is represented by the extremely low dust concentration in Antarctic ice during interglacials. In this study, we analyzed the single‐grain mineralogy of more than 2,300 mineral dust particles transported by winds to Dome C during four different time windows within the Holocene, the current interglacial. Comparing results with those obtained from dust deposited during the last glacial period, we observe that some minerals that are typically associated to glacial climate conditions in Patagonia almost disappear during Holocene, while the remaining minerals are compatible with a South American provenance in both climate periods. Data thus suggest that the dominant atmospheric circulation patterns did not experience a significant change with climate. However, data suggest an additional contribution from subtropical South American latitudes during Holocene. Key Points: The mineralogy of more than 2,300 aeolian dust particles windblown to central East Antarctica (Dome C) during the Holocene was identifiedDisappearance of carbonate dust during the Holocene relates to sea level rise and suppressed deflation from the Argentinean shelfAeolian dust suggests Pampean and Patagonian provenance in the Holocene and a lower latitude contribution, without major circulation changes [ABSTRACT FROM AUTHOR]

Differentiating thermokarst basin sediments with respect to the involved processes and environmental conditions is an important tool to understand permafrost landscape dynamics and scenarios and future trajectories in a warming Arctic and Subarctic. Thermokarst basin deposits have complex sedimentary structures due to the variability of Yedoma source sediments, reworking during the Late Glacial to Holocene climate changes, and different stages of thermokarst history. Here we reconstruct the dynamic growth of thermokarst lakes and basins and related changes of depositional conditions preserved in sediment sequences using a combination of biogeochemical data and robust grain-size endmember analysis (rEMMA). This multi-proxy approach is used on 10 sediment cores (each 300–400 cm deep) from two key thermokarst sites to distinguish four time slices that describe the Holocene thermokarst (lake) basin evolution in Central Yakutia (CY). Biogeochemical proxies and rEMMA reveal fine-grained sedimentation with rather high lake levels and/or reducing conditions, and coarse-grained sedimentation with rather shallow lake levels and/or oxidizing (i.e. terrestrial) conditions in relation to distal and proximal depositional and post-sedimentary conditions. Statistical analysis suggests that the biogeochemical parameters are almost independent of thermokarst deposit sedimentology. Thus, the biogeochemical parameters are considered as signals of secondary (post-sedimentary) reworking. The rEMMA results are clearly reflecting grain-size variations and depositional conditions. This indicates small-scale varying depositional environments, frequently changing lake levels, and predominantly lateral expansion at the edges of rapidly growing small thermokarst lakes and basins. These small bodies finally coalesced, forming the large thermokarst basins we see today in CY. Considering previous paleoenvironmental reconstructions in Siberia, we show the initiation of thaw and subsidence during the Late Glacial to Holocene transition between about 11 and 9 cal kyrs BP, intensive and extensive thermokarst activity for the Holocene Thermal Maximum (HTM) at about 7 to 5 cal kyrs BP, severely fluctuating water levels and further lateral basin growth between 3.5 cal kyrs BP and 1.5 cal kyrs BP, and the cessation of thermokarst activity and extensive frost-induced processes (i.e. permafrost aggradation) after about 1.5 cal kyrs BP. However, gradual permafrost warming over recent decades, in addition to human impacts, has led to renewed high rates of subsidence and abrupt, rapid CY thermokarst processes. • Small thermokarst lakes and basins grew rapidly during the Holocene Thermal Maximum. • Short-term phases of forcing climate lead to very active thermokarst processes. • Endmember analysis reveals different depositional environments in growing lakes. • Distal and proximal depositional and post-sedimentary conditions are differentiated. • Sedimentological and biogeochemical characteristics are weakly correlated. [ABSTRACT FROM AUTHOR]

The age model of the western Bering Sea core 85 KL was modified through correlation of new and earlier-measured productivity proxies with the Chinese interstadials described by δ18O records of Hulu and Sanbao caves and the relative paleointensity events in the studied core with those in the dated records. Resulted sequence of millennial scale Bering Sea Interstadials recorded by abrupt productivity risings was established during the penultimate glacial consistently with the Chinese interstadials and Antarctica isotope maxima. The pattern of the frequency and amplitude of the millennial productivity/climate variability in the Bering Sea during the penultimate glacial resembles that initially depicted in the δ18O of Chinese cave stalagmites and is quite similar to one of the Dansgaard–Oeschger cycles during last glacial, except for their terminations. Contrary to well-pronounced interstadial A.1 during termination TI, an interstadial B.1 over the TII has lower duration and therefore is weakly observed in Antarctic temperature changes. Our results provide robust evidence that the bipolar seesaw mechanisms of millennial climate changes in the Northern and Southern Hemispheres were similar during the last and penultimate glacials. [ABSTRACT FROM AUTHOR]

Ocean currents are an important driver of evolution for sea‐dispersed plants, enabling them to maintain reciprocal gene flow via sea‐dispersed diaspores and obtain wide distribution ranges. Although geographic barriers are known to be the primary factors shaping present genetic structure of sea‐dispersed plants, cryptic barriers which form clear genetic structure within oceanic regions are poorly understood. To test the presence of a cryptic barrier, we conducted a phylogeographic study together with past demographic inference for a widespread sea‐dispersed plant, Vigna marina, using 308 individuals collected from the entire Indo‐West Pacific (IWP) region. Chloroplast DNA variation showed strong genetic structure that separated populations into three groups: North Pacific (NP), South Pacific (SP) and Indian Ocean (IN) (F′CT among groups = 0.954–1.000). According to the Approximate Bayesian computation inference, splitting time between NP and SP was approximately 20,200 years (95%HPD, 4,530–95,400) before present. Moreover, a signal of recent population expansion was detected in the NP group. This study clearly showed the presence of a cryptic barrier in the West Pacific region of the distributional range of V. marina. The locations of the cryptic barrier observed in V. marina corresponded to the genetic breaks found in other plants, suggesting the presence of a common cryptic barrier for sea‐dispersed plants. Demographic inference suggested that genetic structure related to this cryptic barrier has been present since the last glacial maximum and may reflect patterns of past population expansion from refugia. [ABSTRACT FROM AUTHOR]

To better understand what determines the Last Glacial Maximum (LGM) cold and dry climate, a suite of numerical experiments with the Nanjing University of Information Science and Technology Earth System Model version 1 are conducted to assess the relative contributions of individual external forcings, including greenhouse gases (GHGs), ice sheets (IS), land-sea configuration (LSC) and the Earth's orbital parameters, and the contribution of their combination in the LGM mean climate change. Results of the single-forcing sensitivity experiments not only reveal spatial patterns of temperature and precipitation changes that are different from today's climate, but also shed light on understanding the underlying processes through which each forcing contributes to the formation of the LGM climate. The full forcing experiment simulates a 5.3 K global cooling and an 11.8% reduction of the global mean precipitation, thus yielding a hydrological sensitivity of 2.2% K−1, which is larger than that caused by the present-day GHG forcing. The excessive hydrological sensitivity is primarily attributed to the land-sea configuration change, since its dynamic factor (circulation change) amplifies the precipitation reduction at the tropical convergence zones over both hemispheres. The GHG forcing is the largest contributor to the tropical cooling, whereas ice sheets are responsible for the large hemispheric temperature asymmetry and meridional gradients of the zonal mean temperature change during the LGM period. The LGM precipitation is characterized by decreased precipitation over the Indo-Pacific Ocean and a salient wave train pattern over the Northern Hemisphere (NH). The GHG and LSC forcings are the major contributors to the former since they can change the Indo-Pacific sea surface temperature and the associated Walker circulation, while ice sheets lead to the wave train pattern over the NH by changing the North Atlantic jet stream/storminess and shifting the Intertropical Convergence Zone southward. The climate responses to the LGM forcings are nonlinear. The nonlinearity mainly comes from the overlapping effects induced by the IS and LSC forcings. [ABSTRACT FROM AUTHOR]

Understanding the transition of biosphere‐atmosphere carbon exchange between glacial and interglacial climates can constrain uncertainties in its future projections. Using an individual‐based dynamic vegetation model, we simulate vegetation distribution and terrestrial carbon cycling in past cold and warm climates and elucidate the forcing effects of temperature, precipitation, atmospheric CO2 concentration (pCO2), and landmass. Results are consistent with proxy reconstructions and reveal that the vegetation extent is mainly determined by temperature anomalies, especially in a cold climate, while precipitation forcing effects on global‐scale vegetation patterns are marginal. The pCO2 change controls the global carbon balance with the fertilization effect of higher pCO2 linking to higher vegetation coverage, an enhanced terrestrial carbon sink, and increased terrestrial carbon storage. Our results indicate carbon transfer from ocean and permafrost/peat to the biosphere and atmosphere and highlight the importance of forest expansion as a driver of terrestrial ecosystem carbon stock from cold to warm climates. Plain Language Summary: The terrestrial biosphere plays a key role in mitigating climate change by sequestering the anthropogenic carbon emissions in the atmosphere. The projected change in biosphere‐atmosphere carbon exchange remains highly uncertain due to competing effects of elevated CO2 concentration and the accompanying climate forcing. Studying how the carbon balance changed in the past cold and warm climate transitions can help to constrain these uncertainties. Here we perform dynamic vegetation model simulations to reproduce the vegetation patterns and terrestrial carbon variations in these climate states, which are consistent with paleo‐vegetation and carbon cycle‐related reconstructions. We further investigate separately the climate forcing effects (precipitation, temperature, and CO2 concentration) and take into account the different land‐sea distributions. We conclude that global vegetation distribution is mainly determined by temperature anomalies rather than precipitation anomalies. Furthermore, the forest expansion from the cold to warm climate state, mainly driven by CO2 fertilization effect, contributes the most to an increased terrestrial ecosystem carbon stock. Key Points: Vegetation pattern and terrestrial carbon cycling in past cold and warm climates are simulated consistently by a dynamic vegetation modelThe glacial‐interglacial temperature changes have larger influences on the global vegetation extent than precipitation anomaliesThe CO2 concentration, by affecting forest coverage through the fertilization effect, dominates the changes of terrestrial carbon stock [ABSTRACT FROM AUTHOR]

The present-day ocean ventilation in the Arctic Mediterranean (Nordic Seas and Arctic Ocean), via transformation of northward inflowing warm Atlantic surface water into cold deep water, affects regional climate, atmospheric circulation and carbon storage in the deep ocean. Here we study the glacial evolution of the Arctic Mediterranean circulation and its influence on glacial climate using radiocarbon reservoir-age reconstructions on deep-sea cores from the Fram Strait that cover the late glacial period (33,000–20,000 yr ago; 33–20 ka). Our results show high Benthic-Planktic 14C age differences of ∼1500 14C years 33–26.5 ka suggesting significant water column stratification between ∼100–2600 m water depth, and reduction and/or shoaling of deep-water formation. This phase was followed by break-up of the stratification during the Last Glacial Maximum (LGM; 26–20 ka), with Benthic-Planktic 14C age differences of ∼250 14C years, likely due to enhanced upwelling. These ocean circulation changes potentially contributed to the final intensification phase of glaciation via positive cryosphere-atmosphere-ocean circulation-carbon cycle feedbacks. Our data also do not support 'extreme aging' of >6000 14C years in the deep Arctic Mediterranean, and appear to rule out the proposed outflow of very old Arctic Ocean water to the Nordic Seas during the LGM and to the subpolar North Atlantic Ocean during the deglacial period. • Strong ocean stratification in the Fram Strait during the late glacial (33–26 ka). • Breakup of ocean stratification during the LGM (26–20 ka) due to enhanced upwelling. • No extreme aging of >6000 yr in the Arctic Mediterranean as previously suggested. [ABSTRACT FROM AUTHOR]

In this paper, fluvial deposits of Middle Pleistocene age in the mountain‐foreland area of southern Poland (Eastern Sudetes and Western Carpathians) are studied in order to document the evolution of fluvial systems during the coldest stages of glacial periods when the Scandinavian Ice Sheet advanced far to the south. The focus is on fluvial response to climate change and glacial impact on river system behaviour. Also considered is the tectonic uplift of the mountain part of river catchments and its potential influence on the style of fluvial sedimentation in the fore‐mountain area. Three drainage basins that were active during the Elsterian and Saalian glaciations are investigated. Facies analyses are carried out on thick successions of braided river deposits covered with till or glaciolacustrine sediments, which result in a reconstruction of the fluvial activity synchronous with the ice‐sheet advance. The results suggest that fluvial activity declined prior to ice‐sheet advance into the fore‐mountain area. This climatically induced change is directly recorded in alluvial successions by upward‐decreasing bed thicknesses and grain sizes. River longitudinal profiles were shortened in front of the advancing ice sheet. The base level of the studied rivers, created by the ice‐sheet margin, rose in parallel with glacial advance. As a result, the successive reaches of rivers (degradational, transitional, aggradational) underwent shortening and moved upstream within the catchments. Moreover, tectonically induced local increases of river slopes may have influenced the depositional processes. [ABSTRACT FROM AUTHOR]

The cycling of climate into and out of glacial states in response to orbital forcing illustrates the important role of feedbacks in the Earth system. In this contribution, the Geophysical Fluid Dynamics Laboratory coupled ocean‐atmosphere model is used to qualitatively assess how changes in the Earth's precessional parameters may have impacted Atlantic Meridional Ocean Circulation and Southern Ocean dynamics. The Southern Ocean region responds to precessional forcing similar to that of the Last Glacial Maximum with a slight shift in maximum average annual wind stress, a reduction in austral winter wind stress, and an increase in austral winter sea ice. During austral summer, stratification and wind stress increase, Changes in the temperature and density of the North Atlantic lead to a decrease in Atlantic Meridional Overturning Circulation. Together these changes contribute to aging of the global deep ocean, except around Antarctica where enhanced local convection decreases the age of upwelling waters. These circulation changes may have implications for a precessionally driven feedback that contributes to enhanced storage of CO2 in the deep ocean and a reduction in atmospheric CO2. Plain Language Summary: The Earth has cycled into and out of ice ages over last 2.6 million years. The precise factors that cause these changes in climate are not fully understood. The correspondence between the Earth's climate and the Earth's position in space suggests that there is a connection between the two. In this work we use a fully coupled global climate model to explore whether the season during which Earth is closest to the Sun has an impact on ocean circulation. We use two model runs, one having the Earth in a northern hemisphere winter perihelion (close pass) position and another placing the Earth in a northern hemisphere summer perihelion. We find that the northern hemisphere winter perihelion position is associated with changes in Southern Ocean circulation that include an increase in upwelling and a decrease in the age of the upwelled water. We also find that deep ocean circulation in the Atlantic Ocean decreases and that global ocean deep waters increase in age. The observed changes are consistent with the idea that a Northern Hemisphere winter perihelion position may contribute to glacial interglacial climate change and a drawdown of atmospheric CO2. Key Points: Precessional forcing that places the Earth at a boreal winter perihelion position causes an increase in wind stress and Ekman upwelling during austral summer/fall and a decrease during austral winter/spring in the high‐latitude Southern OceanGlobal deepwater age responds to a boreal winter perihelion position by increasing ~200 yearsAtlantic Meridional Overturning Circulation decreases in response to a boreal winter perihelion position. Southern Ocean ventilation increases [ABSTRACT FROM AUTHOR]

The relationship between soil formation and sedimentation on the floodplain of the Utyaganka River (the Ural River basin) in the Arkaim Reserve (Chelyabinsk oblast, Southern Ural, Russia) was studied. Pedological, palynological, and mineralogical research methods were applied, and 15 radiocarbon dates of soil humus and sediments were obtained. The thickness of the Holocene sediments on the low floodplain is 4–5 m. Their top 1.5-m-thick layer formed in the recent 2000 yr contains three buried (partially superposed) soils formed at the mean rate of 13.3 cm/100 yr. Alluvial soddy soils with solonetzic and salinity features reflect intensive anthropogenic erosion in the river basin and characterize the Little Ice Age and the dry and warm Viking Age. At the depth of 1.5–5 m, there are up to five buried soils separated from one another by alluvium layers; they were formed in the period of 12 000–2000 BP at the rate of 1.9–3.1 cm/100 yr. Among them, the soils that developed 4200–2000 BP are characterized by varying humus content and solonetzicity; they are enriched with carbonates and reflect sharp fluctuations in atmospheric moistening against the background of dominating arid and continental climate. The soils formed 5500–4200 BP are gleyed, moderately humified, and calcareous; they testify to a more humid and warm climate than now. This period was characterized by the maximal area of forests (the pollen of tree species reaches 67%). The period of 8000–5500 BP was specified by warm and dry climate, which is indicated by soil properties and palynological data (15% of tree pollen). Soils formed 9500–8000 BP on stony proluvium-alluvium are eroded mucky gley soils; they reflect sharp fluctuations of the climate at the end of the glacial epoch. Floods were probably accompanied not only by alluvium accumulation but also by regular erosion of the surface and a decrease in the thickness of the humus horizon. This resulted in the renewal of soils and slowed down the increase in the thickness of humus horizon and in the intensity of alluvium accumulation. The average portion of humified soil layers reaches 26% of the total thickness of alluvial sediments. [ABSTRACT FROM AUTHOR]

• A multi-biomarker record from Lake Elsinore, CA sediment core spans 32–9 ka. • Deglacial warming and storm-track shifts are consistent with prior studies nearby. • Plant wax hydrogen isotopes indicate storm-track changes during the last glacial. • Lipids show temperatures varied during the last glacial, including extreme warmth. Reconstructions of past hydroclimate provide a means to understand precipitation responses to global ocean-atmosphere climate dynamics beyond the scope of that in the instrumental record. Late glacial climate was characterized by abrupt variability in ice and ocean dynamics, however the implications for hydroclimate are not as well known. Here we present organic geochemical proxy evidence for precipitation isotopes based on plant leaf wax hydrogen isotopic compositions (δ D wax) and temperature proxy evidence based upon the branched glycerol dialkyl glycerol tetraethers (brGDGTs), that derive from the membrane lipids of bacteria, each extracted from a sedimentary archive in Lake Elsinore, California spanning 32–9 ka. We add proxy evidence for vegetation and salinity from additional biomarker analyses and compare to prior pollen and sedimentological evidence from the same core. Our record indicates a strong deglacial warming of 10 °C in Lake Elsinore (beginning at 14.5 ka) that accompanied a D-enrichment of precipitation of +90‰ and more C 4 vegetation (12–10 ka), after a cold, wet and C 3 -dominated phase (20–14.5 ka), indicating winter-dominated precipitation during the Last Glacial Maximum and Heinrich Stadial 1. During the late glacial (32–20 ka) we find abrupt variability, with precipitation isotopic shifts (∼70‰) that are independent of temperature swings implicating changes in storm track, rather than local temperature as drivers of the precipitation isotope signal. Temperature is however not irrelevant for hydroclimate: we find extreme warmth at 29.4 ka and 26.8 ka, the latter coincident with existing reports of an extended dry period (27.5–25.5 ka), suggesting a long hot and dry interlude during the generally cooler glacial period. We compare δ D wax with speleothem δ 18 O from Nevada, also within the winter-dominated precipitation region. Our results corroborate the Last Glacial Maximum and deglacial signals, and fill gaps revealing storm-track instability from 32–20 ka, however the pacing and magnitude of the biomarker signals merit cautious interpretation. [ABSTRACT FROM AUTHOR]

The most pronounced mode of climate variability during the last glacial period are the so-called Dansgaard–Oeschger events. There is no consensus of the underlying dynamical mechanism of these abrupt climate changes and they are elusive in most simulations of state-of-the-art coupled climate models. There has been significant debate over whether the climate system is exhibiting self-sustained oscillations with vastly varying periods across these events, or rather noise-induced jumps in between two quasi-stable regimes. In previous studies, statistical model comparison has been employed to the NGRIP ice core record from Greenland in order to compare different classes of stochastic dynamical systems, representing different dynamical paradigms. Such model comparison studies typically rely on accurately reproducing the observed records. We aim to avoid this due to the large amount of stochasticity and uncertainty both on long and short time scales in the record. Instead, we focus on the most important qualitative features of the data, as captured by summary statistics. These are computed from the distributions of waiting times in between events and residence times in warm and cold regimes, as well as the stationary density and the autocorrelation function. We perform Bayesian inference and model comparison experiments based solely on these summary statistics via Approximate Bayesian Computation. This yields an alternative approach to existing studies that helps to reconcile and synthesize insights from Bayesian model comparison and qualitative statistical analysis. [ABSTRACT FROM AUTHOR]

Hydrogen isotope ratios of long‐chain alkenones (δ2HC37 ratios) have been shown to correlate with salinity in several culture studies. However, it is uncertain how applicable the δ2HC37‐salinity relationship is to reconstruct past salinity. The δ2HC37 ratios were measured on sediments from a drill core (ODP site 1234) at the Chilean Margin covering the last ~150 kyr. High δ2HC37 values corresponded to glacial time periods and interglacial periods are characterized by lower δ2HC37 values, aligning with δ18O ratios measured on planktonic foraminifera from the same core. Effects of parameters such as species composition, the δ2H‐δ18O relationship used for ice volume corrections, and nutrient‐ or light‐controlled growth rate, did not appear to significantly alter δ2HC37 ratios at ODP 1234. We used linear regression equations from batch culture experiments, marine surface sediments, and suspended particulate organic matter to quantitatively characterize salinity changes over the last ~150 kyr at ODP 1234. However, most of these equations yielded larger salinity shifts than previously suggested, a phenomenon also observed for other δ2HC37 records. This suggests that the paleosensitivity of δ2HC37 ratios to salinity was larger in the geologic record than has been observed in any modern environment or laboratory settings, or that glacial to interglacial salinity shifts might have been larger than currently believed. Key Points: Hydrogen isotope ratios of long‐chain alkenones track glacial to interglacial climate changesSensitivity of hydrogen isotope ratios of alkenones to salinity is larger in paleosettings than observed in cultures or modern environments [ABSTRACT FROM AUTHOR]

The optical properties of atmospheric secondary brown carbon (BrC) aerosol are poorly understood because of its chemical complexity, and this has hampered quantitative assessments of the impacts of this light‐absorbing material on glaciers on the Tibetan Plateau. For this study, a statistical approach was developed to investigate BrC light absorption over the southeastern margin of the Tibetan Plateau. Secondary sources for BrC were more important for absorption than primary ones. A diurnal cycle in secondary BrC absorption was explained by the formation of light‐absorbing chromophores by photochemical oxidation after sunrise followed by photobleaching of the chromophores under the more oxidizing conditions as the day progressed. Multimethod analyses showed that biomass burning in northern Burma and along the Sino‐Burmese border was the most important source for the secondary BrC. The mean integrated simple forcing efficiency was 79 W/g, indicating that secondary BrC can cause substantial radiative effects. Plain Language Summary: A statistical approach was developed to evaluate light absorption by secondary brown carbon (BrC) aerosol particles. We characterized the diurnal cycle of secondary BrC over the southeastern margin of Tibetan Plateau, identified likely pollution sources, and estimated its radiative effects. To our knowledge, this is the first time that light absorption from primary versus secondary BrC has been evaluated. This approach should be useful for further improving models and accurately evaluating the effects of BrC on glacial recession on the Tibetan Plateau. Key Points: A statistical approach was developed to investigate secondary brown carbon (BrC) absorption over the southeastern Tibetan PlateauSecondary sources were the major contributors to the BrC light absorptionLong‐range transport of biomass‐burning products was an important source for secondary BrC [ABSTRACT FROM AUTHOR]