Reconstruction Of Past Climate Research Articles

Phytolith based paleoecological reconstruction from a loess-paleosol sequence in the Kashmir Himalaya, India

The temporal vegetation development provides vital information for understanding past climatic changes. In this study, we reconstruct vegetation dynamics from the last glacial period using phytoliths as a proxy from the Wanihama loess-paleosol sequence (LPS) near Srinagar in Kashmir Himalaya, India. Different phytolith assemblages and indices (Ic and Iw) revealed a series of warm and cold events documented in the LPS. The data indicate the predominance of broad-leaved and sparse conifer vegetation from ca. 42 ka to 39 ka, suggesting a comparatively warm and humid climate. After ca. 39 ka, conifers and grasses increased, indicating a transition to a cold climate. The cold climate, intervened by a short stadial, continued until ca. 31 ka with the predominance of conifers, grasses, and sedges. Subsequently, three other cold events were noted until ca. 14 ka, which resulted in vegetation disappearance and a substantial decrease in phytolith count. These cold events roughly coincide with the climatic instability in the Atlantic Ocean that caused severe cooling at high northern latitudes and likely impacted the Asian climate. Phytolith assemblages showed an overall increasing proportion of C4 grasses towards the top of the LPS, suggesting warm and dry climatic conditions. We also correlated the phytolith-based vegetation reconstruction with other paleoenvironmental proxies recorded from the same section, as well as with the last glacial climatic changes documented in different regions, to determine the reliability of phytoliths in LPSs as a proxy for past vegetation and climate reconstruction in the Kashmir Himalaya.

Distribution of branched glycerol dialkyl glycerol tetraether (brGDGT) lipids from soils and sediments from the same watershed are distinct regionally (central Chile) but not globally

Quantitative reconstructions of past continental climates are vital for understanding contemporary and past climate change. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are unique bacterial lipids that have been proposed as universal paleothermometers due to their correlation with temperature in modern settings. Thus, brGDGTs may serve as a crucial paleotemperature proxy for understanding past climate variations and improving regional climate projections, especially in critical but under constrained regions. That said, complications can arise in their application due to varying source contributions (e.g., soils vs. peats vs. lacustrine). As such, this study investigates brGDGT distributions in Chilean lake surface sediments and corresponding watershed soils to determine the source of brGDGTs to lake sediments. Global datasets of brGDGTs in lake sediments and soils were additionally compiled for comparison. Distinct brGDGT distributions in Chilean lakes and soils indicate minimal bias from soil inputs to the lacustrine sediments as well as in situ lacustrine production of brGDGTs, which supports the use of brGDGTs in lake sediments as reliable paleotemperature proxies in the region. The ΣIIIa/ΣIIa ratio, initially promising as a brGDGT source indicator in marine settings, shows global complexities in lacustrine settings, challenging the establishment of universal thresholds for source apportionment. That said, we show that the ratio can be successfully applied in Chilean lake surface sediments. Direct comparisons with watershed soils and further research are crucial for discerning brGDGT sources in lake sediments and improving paleotemperature reconstructions on regional and global scales moving forward. Overall, this study contributes valuable insights into brGDGT variability, essential for accurate paleoreconstructions.

Open paleoenvironment and dry climate in south India immediately before the Youngest Toba Tuff eruption (~75 ka) are suggested by Vondrichnus structures at the Jwalapuram locality, Jurreru valley

Abstract The Younger Toba Tuff (YTT) eruption is regarded as one of the largest of its time and possibly responsible for changing past climate and vegetation from C3 to C4 in the Indian subcontinent. A paleosol constituting a Toba pre-tephra horizon at the Jwalapuram locality, exhibits the preservation of biogenic structures identified as Vondrichnus planoglobus and Vondrichnus obovatus. This study investigated their paleoecological and paleoenvironmental significance. These structures are hard and compact, rounded to sub-rounded, spherical to sub-spherical bodies with empty chambers, surrounded by carbonate layers, and preserved in close proximity to termite pipes and nests and rhizolith structures. Their occurrence in the Jwalapuram area is significant, as the locality has been well documented as suitable for reconstruction of past climate and vegetation in light of the impact of the YTT eruption. Based on the present findings, we assume that the investigated locality would likely have an insect population and bush to scrub vegetation, indicating a dry environment immediately before the YTT eruption.

Reconstructing colonization dynamics to establish how human activities transformed island biodiversity

Drivers and dynamics of initial human migrations across individual islands and archipelagos are poorly understood, hampering assessments of subsequent modification of island biodiversity. We developed and tested a new statistical-simulation approach for reconstructing the pattern and pace of human migration across islands at high spatiotemporal resolutions. Using Polynesian colonisation of New Zealand as an example, we show that process-explicit models, informed by archaeological records and spatiotemporal reconstructions of past climates and environments, can provide new and important insights into the patterns and mechanisms of arrival and establishment of people on islands. We find that colonisation of New Zealand required there to have been a single founding population of approximately 500 people, arriving between 1233 and 1257 AD, settling multiple areas, and expanding rapidly over both North and South Islands. These verified spatiotemporal reconstructions of colonisation dynamics provide new opportunities to explore more extensively the potential ecological impacts of human colonisation on New Zealand’s native biota and ecosystems.

A global compilation of diatom silica oxygen isotope records from lake sediment – trends and implications for climate reconstruction

Abstract. Oxygen isotopes in biogenic silica (δ18OBSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy-model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (Tair), atmospheric circulation patterns, hydrological changes, and lake evaporation. While every lake has its own local set of drivers of δ18O variability, here we explore the extent to which regional or even global signals emerge from a series of paleoenvironmental records. This study provides a comprehensive compilation and combined statistical evaluation of the existing lake sediment δ18OBSi records, largely missing in other summary publications (i.e. PAGES network). For this purpose, we have identified and compiled 71 down-core records published to date and complemented these datasets with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution, ranging from decadal-scale records covering the past 150 years to records with multi-millennial-scale resolution spanning glacial–interglacial cycles. The best coverage in number of records (N = 37) and data points (N = 2112) is available for Northern Hemispheric (NH) extratropical regions throughout the Holocene (roughly corresponding to Marine Isotope Stage 1; MIS 1). To address the different variabilities and temporal offsets, records were brought to a common temporal resolution by binning and subsequently filtered for hydrologically open lakes with lake water residence times < 100 years. For mid- to high-latitude (> 45° N) lakes, we find common δ18OBSi patterns among the lake records during both the Holocene and Common Era (CE). These include maxima and minima corresponding to known climate episodes, such as the Holocene Thermal Maximum (HTM), Neoglacial Cooling, Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). These patterns are in line with long-term air temperature changes supported by previously published climate reconstructions from other archives, as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratropical lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) timescales despite stemming from different lakes in different geographic locations and hence constitute a valuable proxy for past climate reconstructions.

The Extraordinary March 2022 East Antarctica “Heat” Wave. Part II: Impacts on the Antarctic Ice Sheet

Abstract Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) that caused these record-shattering temperature anomalies. Here, we continue our large collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt that was recorded along coastal areas, but this was outweighed by widespread high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Last, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea ice extent. Significance Statement Using our diverse collective expertise, we explored the impacts from the March 2022 heat wave and atmospheric river across East Antarctica. One key takeaway is that the Antarctic cryosphere is highly sensitive to meteorological extremes originating from the midlatitudes and subtropics. Despite the large positive temperature anomalies driven from strong downward longwave radiation, this event led to huge amounts of snowfall across the Antarctic interior desert. The isotopes in this snow of warm airmass origin will likely be detectable in future ice cores and potentially distort past climate reconstructions. Even measurements of space activity were affected. Also, the swells generated from this storm helped to trigger the final collapse of an already critically unstable Conger Ice Shelf while further degrading sea ice coverage.

Anion elements incorporation into corals skeletons: Experimental approach for biomineralization and paleo-proxies.

The elemental composition of coral skeletons provides important information for palaeoceanographic reconstructions and coral biomineralization. Partition of anions and their stable isotopes in coral skeleton enables the reconstruction of past seawater carbonate chemistry, paleo-CO2, and past climates. Here, we investigated the partition of B, S, As, Br, I, and Mo into the skeletons of two corals, Acropora cervicornis and Pocillopora damicornis, as a function of calcium and carbonate concentrations.* Anion-to-calcium ratio in the corals (An/CaCoral) were correlated with the equivalent ratios in the culturing seawater (An/CO32-SW). Negative intercepts of these relationships suggest a higher CO32- concentration in the coral extracellular calcifying fluid (ECF) relative to seawater, from which the skeleton precipitates. The enrichment factor of CO32- at the ECF was 2.5 for A. cervicornis and 1.9 for P. damicornis, consistent with their relative calcification rates. The CO32-ECF concentrations thus calculated are similar to those proposed by previous studies based on B/Ca coupled with δ11B, as well as by direct measurements using microsensors and fluorescent dyes. Rayleigh fractionation modeling demonstrates a uniform Ca utilization at various CaSW concentrations, providing further evidence that coral calcification occurs directly from a semiclosed seawater reservoir as reported previously. The partition coefficients reported in this study for B, S, As, Br, I, and Mo open up wide possibilities for past ocean chemistry reconstructions based on Br having long residence time (~160 Ma) in the ocean. Other elements like S, Mo, B, as well as pCO2 may also be calculated based on these elements in fossil coral.

Quantitative pollen-based paleoclimate reconstructions for the past 18.5 ka in southwestern Yunnan Province, China

Quantitative reconstruction of past climate plays an important role in understanding global and regional climate changes and validating climate models. Although some important progress has been made in quantitative paleoclimate reconstructions based on terrestrial records in the Indian summer monsoon region, high-resolution quantitative studies spanning the last ∼20 ka are still relatively sparse with differing results. This study presents high-resolution quantitative variations in mean temperature of the coldest month (MTCM, the first controlling factor of the regional vegetation), mean annual temperature (MAT, the second controlling factor), and mean annual precipitation (MAP) from Lake Tengchongqinghai in southwestern China, based on an updated modern pollen dataset and the fossil pollen record spanning the last 18.5 ka. The results show that temperature and precipitation increased gradually from 18.5 ka, and peaked from 7.2 to 4.5 ka when MAT was on average 1.0 °C higher than the modern observational value (14.5 °C), corresponding to the mid-Holocene thermal maximum (HTM), and then decreased gradually. The total reconstructed ranges are between −2.2 and 9.2 °C for MTCM, 7.7 and 17.2 °C for MAT, and 840 and 1300 mm for MAP. On top of this overall climate trend, seven abrupt cold and dry events were detected during the periods of 16.2–14.8 ka, 12.8–11.5 ka, ∼11.1 ka, 9.1–8.4 ka, ∼7.7 ka, 4.3–3.7 ka, and 0.68–0.009 ka (1270–1950 CE). The results of this quantitative reconstruction were validated by both statistical and ecological evaluations. We conclude that the trend of climatic change since 18.5 ka in this study area was primarily driven by June, July, August, and September solar insolation and changes in radiative forcing and greenhouse gas concentrations. The abrupt changes may be caused by changes in the Atlantic meridional overturning circulation, solar activity, the position of the Intertropical Convergence Zone, and volcanic activity.

Palynological response deduced through spatially distinct surface samples to reconstruct palaeoecology and palaeoclimate of the Barak Valley, Assam (Indo-Burma region), northeast India

Establishing modern pollen analogues under various vegetation types in a location is necessary without which it is difficult to accurately interpret fossil pollen assemblages in any region in terms of the past environment and palaeoclimate. We have analysed the modern pollen dataset of 30 surface soil and sediment samples from the forested, cropland, wetland and river sites of the Karimganj District in south Assam, to comprehend the connection between the recent pollen assemblage and the vegetation patterns in the Barak Valley. The overall pollen data reflect the tropical moist deciduous and semi-evergreen forest comprising Syzygium, Schleichera, Terminalia, Lagerstroemia, Duabanga, Sapotaceae, Ilex, Mesua and Schima under a warm and humid climate in response to rainfall variations in the region. The presence of Euphorbiaceae and Convolvulaceae inferred high monsoonal activity in and around the region. A robust relationship between local herbaceous vegetation and pollen was observed. The steady occurrence of cereal pollen (average 18.67%) along with other cultural pollen taxa like Brassicaceae, Coriandrum and Solanaceae illustrate intense agricultural activity around the valley areas. Multivariate principal component analysis (PCA) and box plot were applied to the quantified data obtained from pollen frequency analyses of the surface samples which clearly revealed a significant variation and similarity in vegetation types. Thus, an attempt has been commenced to precisely observe the behavioural pattern of modern pollen deposition in a varied depositional setting, which could, in turn, help in assessing the expanse of agricultural practices and the depth of deterioration of pristine forests and surrounding areas. This modern training dataset could also help in the precise reconstruction of past climate and vegetation shifts in the Barak Valley region. A correlation of regional palynodata with other regions of the Indian subcontinent and Indo-Burma will also be assessed for better interpretation.

Branched GDGT-based temperature calibrations from Central European lakes

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are common in lake sediments, where they are frequently employed to infer mean annual air temperatures (MAAT) or air temperatures of months above freezing (MAF) using the MBT'5Me lipid paleothermometer. The reliable reconstruction of such temperatures, however, requires robust calibration functions. Here, we investigated brGDGT distributions in surface sediments from 41 freshwater lakes located along an altitudinal gradient across the Alps (Central Europe) and spanning a MAAT range from 1.3 to 12.9 °C. Linear regression analysis demonstrates that fractional abundances of brGDGTs are strongly correlated with MAAT and MAF allowing to establish regional MBT'5Me-based transfer functions: MAAT (°C) = −2.19 + 31.91 × MBT'5Me (r2 = 0.72; RMSE = 1.51 °C) and MAF (°C) = 4.81 + 15.64 × MBT'5Me (r2 = 0.64, RMSE = 0.92 °C). Stepwise forward selection yielded the following, alternate temperature calibrations: MAAT (°C) = 7.11 + 67.66 × Ib – 13.54 × IIIa (r2 = 0.72; RMSE = 1.47 °C) and MAF (°C) = 5.19 + 16.22 × Ia (r2 = 0.66; RMSE = 0.98 °C). Our results demonstrate that the above calibration functions allow precise temperature reconstructions using lacustrine sediment records. However, our data also show that high-altitude lakes are more prone to warm bias and that lakes characterized by comparatively high abundances of 6-methyl brGDGTs show aberrant behaviors with temperature offsets up to ∼7 °C. Determining the IR6Me, as an independent control complementary to the MBT'5Me, is thus essential to validate the robustness of brGDGT-based temperature reconstructions of past climates. A cut-off value of 0.50 for the IR6Me is here proposed, after which MBT'5Me-reconstructed MAATs from lacustrine archives should be regarded as unreliable.

Climatically induced anomalies in tree-ring structure of Abies pindrow (Royal ex D. Don) and Taxus baccata (L.) growing in Hindu-Kush mountainous region of Pakistan

Dendroclimatic potential from Abies pindrow Royal ex D. Don. (fir) and Taxus baccata L. (yew) was investigated by developing four different types of tree-ring width chronologies (by ARSTAN program) in a mixed broadleaf forest of Kalam, KP, Pakistan. Firstly, measured tree-ring width series were cross-dated and identified the best and least (cross-matched with master plot) samples with the most applied Skeleton Plot Model (SPM) method alongside checking the quality through statistical program (COFECHA). Tree-ring attributes (age, growth rate and earlywood and latewood) were also measured with maximum age (677 years) was observed in fir plant and maximum growth rate (6.096 mm year−1) in yew plant with clear demarcations of earlywood and latewood formation. Yew trees were observed to be more sensitive species towards climatic variations (expressed population signal = 0.945, mean sensitivity = 0.321 and signal to noise ratio = 3.214) while fir trees were comparatively less affected by climatic alterations of the study site (expressed population signal = 0.954, mean sensitivity = 0.314 and signal to noise ratio = 2.453). Correlation between tree-ring series of T. baccata with the master series was found to be more significant as compared to A. pindrow after developing series plots of both the species by using package dplR in R. Potential ecological and anatomical explanations for these results were also discussed. Sensitivity of samples showed good climatic signals which are valuable for dendroclimatic growth response investigations leading to reconstruction of past climate as well as possible future climate predictions.

Integration of direct radiocarbon dating, genetic studies and taxonomy of small mammals to investigate the chronology of past climatic oscillations: The Last Glacial Maximum sequence of Grotta della Ferrovia (Fabriano, Italy)

The recent developments in palaeoecological reconstruction methods, collagen extraction of small bone samples and ancient DNA analyses led us to test new approaches to enhance the chronological resolution of past climate reconstructions inferred from small mammal assemblages.Grotta della Ferrovia (Fabriano, Ancona, Italy, 40°25′36″N, 13°0′11″E, 215 m a.s.l.) is a small cave that opens on the southern bank of the Esino river, around 45 km west of Ancona. Discovered in 1966, it is famous among scholars because it is the first locality where the fossil birch mouse was recorded in Italy and because of the remarkable archaeological lithic evidence assemblage found in the cave related to the Late Epigravettian. Across the small mammal sequence, distributed into seven layers (from GDF7 to GDF2), two main phases can be recognized: in the first phase, from GDF7 to GDF5, Microtus arvalis is dominant over Microtus agrestis, in a poorly diversified assemblage. The sequence gradually changes in GDF4 and a second phase can be observed in GDF3 and GDF2, where Apodemus gr. sylvaticus-flavicollis dominates, but combined with a higher number of taxa. From GDF7 to GDF3, few individuals of Sicista cf. subtilis and Alexandromys oeconomus are recorded. Environmental and climatic reconstructions calculated with the Habitat Weighting and the Bioclimatic methods show a dominance of open meadows (GDF7 to GDF4) that were gradually replaced by closed or semi-closed forests (GDF3 and GDF2) in a context of gradually increasing temperature, shifting from a cold phase to conditions similar to the current ones in the area.Direct radiocarbon dates on 18 rodent bones and aDNA analyses on three Microtus arvalis teeth helped us to better understand the significance of the oscillation inferred from the small mammal sequences. A robust series of nine radiocarbon measurements from GDF7 to GDF5 shows that this part of the sequence accumulated between ∼24,600–19,600 cal BP (95.4% probability), which includes the final phases of the Last Glacial Maximum (LGM). The ancient DNA from Microtus arvalis confirmed the chronological framework and the presence of italic populations in this area during the LGM, similar to the slightly more ancient Grotta del Sambuco on the western side of the central Peninsula. The small mammal radiocarbon dates from GDF4 and above are less consistent with their stratigraphic position, probably related to post-depositional disturbance of the sediments, but suggest that the last part of the sequence accumulated during the Late Glacial.Our results show that it is now possible to validate and enhance paleoclimatic and paleoenvironment inferences from small mammal sequence studies with direct radiocarbon dates and ancient DNA analyses, using these integrated methods as a high resolution tool for studying the past.

Proxy Archives Based on Marine Calcifying Organisms and the Role of Process-Based Biomineralization Concepts

Proxy archives based on marine calcifying organisms and their element and isotope signatures represent valuable tools in the reconstruction of past climates. Despite the fact that the underlying biomineralization processes behind the measured signatures are poorly understood, these tools work remarkably well. However, even though they work well many researchers felt the need to decipher the “black box” and understand the processes leading to the measured signatures. In this paper we assess how far we have come in understanding the biomineralization processes underpinning proxy signatures derived from marine calcifying organisms and how this understanding improved the way we use these proxy archives today. Biomineralization in the context of proxy research is an interdisciplinary field and cross-discipline communication can be challenging due to a lack of background in foreign disciplines. This often leads to misunderstanding and over- (or under-) estimation of certain concepts/methods/data. We, therefore, present a concise introduction to the topic, clarifying key concepts and their applicability to proxy interpretation.

Seasonal Variations in Triple Oxygen Isotope Ratios of Precipitation in the Western and Central United States.

Triple oxygen isotope ratios offer new opportunities to improve reconstructions of past climate by quantifying evaporation, relative humidity, and diagenesis in geologic archives. However, the utility of in paleoclimate applications is hampered by a limited understanding of how precipitation values vary across time and space. To improve applications of , we present , d-excess, and data from 26 precipitation sites in the western and central United States and three streams from the Willamette River Basin in western Oregon. In this data set, we find that precipitation tracks evaporation but appears insensitive to many controls that govern variation in , including Rayleigh distillation, elevation, latitude, longitude, and local precipitation amount. Seasonality has a large effect on variation in the data set and we observe higher seasonally amount-weighted average precipitation values in the winter (40 ± 15 per meg [± standard deviation]) than in the summer (18 ± 18 per meg). This seasonal precipitation variability likely arises from a combination of sub-cloud evaporation, atmospheric mixing, moisture recycling, sublimation, and/or relative humidity, but the data set is not well suited to quantitatively assess isotopic variability associated with each of these processes. The seasonal pattern, which is absent in d-excess and opposite in sign from , appears in other data sets globally; it showcases the influence of seasonality on values of precipitation and highlights the need for further systematic studies to understand variation in values of precipitation.

Subfossil Insect Collections From the Arctic of Northeast Asia and Northwest North America

Subfossil insects (mostly beetles) are common in the Late Cenozoic terrestrial loose deposits of the Arctic. The best-studied areas are those regions that remained ice-free during the Pleistocene — in Alaska and Yukon, northeast Siberia, and west Chukotka. Tertiary subfossil insects have been found in Alaska, Yukon, Canadian Northwest Territories, and Greenland. The northernmost sites (above 75°N) are Ellesmere and Meighen Islands in Canada, Kap Kobenhavn in Greenland, and Faddeyevsky and Navaya Sibir’ Islands in Siberia. Collections from North America and Russia are housed in research institutions such as The Geological Survey of Canada (GSC) in Ottawa, University of Alberta (UofA) in Edmonton, Paleontological Institute (PIN) in Moscow, and Institute of Plant and Animal Ecology in Yekaterinburg; collections from Greenland are housed in the Zoological Museum, University of Copenhagen. The collections are mainly used for research purposes, including reconstruction of past climate and environment, stratigraphy, origin of local faunas, and ecosystems of the past. A few extinct species have been described from the late Neogene and early Quaternary.

Revisiting the Holocene global temperature conundrum.

Recent global temperature reconstructions for the current interglacial period (the Holocene, beginning 11,700 years ago) have generated contrasting trends. This Review examines evidence from indicators and drivers of global change, as inferred from proxy records and simulated by climate models, to evaluate whether anthropogenic global warming was preceded by a long-term warming trend or by global cooling. Multimillennial-scale cooling before industrialization requires extra climate forcing and major climate feedbacks that are not well represented in most climate models at present. Conversely, global warming before industrialization challenges proxy-based reconstructions of past climate. The resolution of this conundrum has implications for contextualizing post-industrial warming and for understanding climate sensitivity to several forcings and their attendant feedbacks, including greenhouse gases. From a large variety of available evidence, we find support for a relatively mild millennial-scale global thermal maximum during the mid-Holocene, but more research is needed to firmly resolve the conundrum and to advance our understanding of slow-moving climate variability.

Pleistocene megafaunal extinction in the grasslands of Junín‐Peru

AbstractAimTo determine the timing of megafaunal extinction in the high plains of Peru and also to determine if the timing was delayed in grasslands compared with previously published forested settings to dissociate the effects of succession from human or climatic impacts.LocationThe Junín Plateau, Peru.TaxonFlowering plants and Ascomycetes.MethodsThe sediments used in this analysis were collected from the edge of Lake Junín, Peru. Eleven ages derived from 14C accelerator mass spectrometry provide a chronology. We provide a paleoecological reconstruction of past climate and vegetation change, fire history and megafaunal herbivore presence from c. 20,000–7000 years ago based on fossil pollen, charcoal and Sporormiella spores. Data were analysed using multivariate analysis and Bayesian change point analysis.ResultsMegafaunal populations appear to have been positively impacted by dry climatic oscillations until c. 15,200 years ago. A reduction in Sporormiella abundance between 13,000 and 12,300 years before the present coincides with increased charcoal abundance and is identified as the period of megafaunal population collapse leading to extinction. The timing of the extinction does not differ substantially from that observed in wooded Andean settings.Main ConclusionThe timing of the collapse of megafaunal populations in high grasslands was very similar to that of lower, now‐forested settings. Upticks in fire activity, during what is generally seen to be a wet period, formed the backdrop to extinction and are strongly associated with human activity.

No changes in overall AMOC strength in interglacial PMIP4 time slices

Abstract. The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism of poleward heat transport and an important part of the global climate system. How it responded to past changes in forcing, such as those experienced during Quaternary interglacials, is an intriguing and open question. Previous modelling studies suggest an enhanced AMOC in the mid-Holocene compared to the preindustrial period. In earlier simulations from the Palaeoclimate Modelling Intercomparison Project (PMIP), this arose from feedbacks between sea ice and AMOC changes, which were dependent on resolution. Here we present an initial analysis of recently available PMIP4 simulations for three experiments representing different interglacial conditions – one 127 000 years ago within the Last Interglacial (127 ka, called lig127k), one in the middle of the Holocene (midHolocene, 6 ka), and a preindustrial control simulation (piControl, 1850 CE). Both lig127k and midHolocene have altered orbital configurations compared to piControl. The ensemble mean of the PMIP4 models shows the strength of the AMOC does not markedly change between the midHolocene and piControl experiments or between the lig127k and piControl experiments. Therefore, it appears orbital forcing itself does not alter the overall AMOC. We further investigate the coherency of the forced response in AMOC across the two interglacials, along with the strength of the signal, using eight PMIP4 models which performed both interglacial experiments. Only two models show a stronger change with the stronger forcing, but those models disagree on the direction of the change. We propose that the strong signals in these two models are caused by a combination of forcing and the internal variability. After investigating the AMOC changes in the interglacials, we further explored the impact of AMOC on the climate system, especially on the changes in the simulated surface temperature and precipitation. After identifying the AMOC's fingerprint on the surface temperature and rainfall, we demonstrate that only a small percentage of the simulated surface climate changes could be attributed to the AMOC. Proxy records of sedimentary Pa/Th ratio during the two interglacial periods both show a similar AMOC strength compared to the preindustrial, which fits nicely with the simulated results. Although the overall AMOC strength shows minimal changes, future work is required to explore whether this occurs through compensating variations in the different components of AMOC (such as Iceland–Scotland overflow water). This line of evidence cautions against interpreting reconstructions of past interglacial climate as being driven by AMOC, outside of abrupt events.

Climate and fire drivers of forest composition and openness in the Changbai Mountains since the Late Glacial

Ongoing climate changes have a direct impact on forest growth; they also affect natural fire regimes, with further implications for forest composition. Understanding of how these will affect forests on decadal-to-centennial timescales is limited. Here we use reconstructions of past vegetation, fire regimes and climate during the Holocene to examine the relative importance of changes in climate and fire regimes for the abundance of key tree species in northeastern China. We reconstructed vegetation changes and fire regimes based on pollen and charcoal records from Gushantun peatland. We then used generalized linear modelling to investigate the impact of reconstructed changes in summer temperature, annual precipitation, background levels of fire, fire frequency and fire magnitude to identify the drivers of decadal-to-centennial changes in forest openness and composition. Changes in climate and fire regimes have independent impacts on the abundance of the key tree taxa. Climate variables are generally more important than fire variables in determining the abundance of individual taxa. Precipitation is the only determinant of forest openness, but summer temperature is more important than precipitation for individual tree taxa with warmer summers causing a decrease in cold-tolerant conifers and an increase in warmth-demanding broadleaved trees. Both background level and fire frequency have negative relationships with the abundance of most tree taxa; only Pinus increases as fire frequency increases. The magnitude of individual fires does not have a significant impact on species abundance on this timescale. Both climate and fire regime characteristics must be considered to understand changes in forest composition on the decadal-to-centennial timescale. There are differences, both in sign and magnitude, in the response of individual tree species to individual drivers.

New perspectives on historical climatology

AbstractHistorical climatology is an interdisciplinary field of research encompassing the reconstruction of past climate and weather from written sources and artifacts, as well the application of climate reconstructions to the study of human history. Historical climatology has grown in recent years, and this growth has brought both insights and challenges. Research has expanded into new regions and periods and diversified into novel sources, methods, and interdisciplinary collaborations. At the same time, the heterogeneity of evidence and approaches has complicated the integration of multiple climate and weather reconstructions. Moreover, the diversity of disciplinary perspectives, terminologies, and perspectives can create miscommunication among scholars in the field, particularly on issues of historical knowledge and causation. Innovative approaches in the field, including Bayesian methods, may help address these challenges.This article is categorized under: Climate, History, Society, Culture > Disciplinary Perspectives Climate, History, Society, Culture > World Historical Perspectives Assessing Impacts of Climate Change > Representing Uncertainty The Social Status of Climate Change Knowledge > Knowledge and Practice