Cal Years Research Articles

Long-term latitudinal effects of precipitation change in global monsoon regions

Global paleomonsoon precipitation evolution is confined to asynchronous responses to global monsoons to shared forcings, including summer insolation, sea surface temperature, atmospheric circulation coupling, and ocean circulation. However, most studies are based on conclusions drawn from single or a few discrete records or deduced from top-down climate models, which limits our ability to understand the latitudinal effect of monsoon precipitation. In particular, precipitation is a locally constrained climate factor. Here, we present a comprehensive assessment of global monsoon precipitation over the last 12,000 cal year BP based on modern observations, paleoclimate simulations, paleoclimate records, and monsoon precipitation reconstructions over the past 12,000 cal year BP based on a bottom-up algorithm called climate field reconstruction approaches. The results show that the middle latitude monsoon precipitation is in line with the evolution of the insolation and significant long-term decreasing (increasing) trends in low latitude monsoon precipitation have not occurred over the last 12,000 years BP. For modern monsoon evolution, the monsoon precipitation also changes along the meridional direction, with overall decreasing precipitation in the global monsoon region and increasing precipitation in the monsoon margin area. Monsoon systems at different latitudes all record eight Holocene weak precipitation events, including the Younger Dryas (12,900 cal year BP to 11,700 cal year BP), which can be considered a strong effect caused by a significant reduction or collapse of a meridional ocean circulation system, namely, the Atlantic Meridional Overturning Circulation. Moreover, the low- and middle-latitude monsoon precipitation lags by approximately 2,000 years behind the onset of North Atlantic warming. Taken together, our findings provide important insights into the latitudinal effect of monsoon precipitation at different locations.

Palaeoclimatic variability during last eight millennia from a morainal lake in Zanskar, northwest Himalaya, India

Centennial–scale palaeoenvironmental variability has been deduced during past eight millennia using multi–proxy study (textural analysis, environmental magnetic parameters, stable carbon isotopes, palynofacies and elemental concentration), from Khangok–Padam in Zanskar Valley, northwest Himalaya. The multi–proxy record from this morainal lake spanning last ~8200 cal years BP has revealed four hydroclimatic phases. The overall progressively improving hydroclimatic trend is indicated by multi proxy study: sediment size/texture (as a proxy for the energy condition and depositional environment), mineral magnetism (proxy for sediment flux or lithogenic input and lithologic variation), carbon isotope signature (δ13Corg) preserved in organic constituents of sediments (a proxy for palaeovegetation and climate change), elemental geochemistry (proxy for weathering and erosion) and selected samples for palynofacies data (a proxy for changes in biological organic matter). This improving hydroclimatic trend is however punctuated by an abrupt wet spell at ~6200–5200 cal years BP and relatively drier climate during the Little Ice Age between 1400 and 1900 CE. The main driving force implicated for the changes are seen to be the solar output variations. The area lying in a transitional climatic zone of NW Himalaya shows no emphatic record of the events like the 4200 cal. years BP, 2600 cal. years BP and Holocene Climatic Optima. Contrary to the earlier studies in the region (e.g., Tsokar and TsoMorari), our results show an improving hydroclimatic condition in this transition climatic zone between the Indian Summer Monsoon dominated Higher and westerly dominated Trans Himalaya.

System responses to Holocene relative sea-level rise and sediment supply in a macrotidal estuary

Estuaries are at the interface of marine and terrestrial systems and as such, are subject to environmental change arising from multiple driving mechanisms, with the interplay between the dominant controls varying spatially and temporally. Relative sea-level (RSL) change and sediment supply can play a significant role in driving environmental change. This study examines the relative influence of these drivers during the Holocene. Biostratigraphic records and RSL data are presented from two locations in the inner portion and upper reaches of the macrotidal Humber Estuary, eastern England. The results provide a new terrestrial limiting point and six sea-level index points, two of which at c. 1500 cal years BP provide the youngest sea-level index points for the inner estuary. An early-mid Holocene tidal lagoon system, that lacks modern equivalent, is recorded at one site. The results indicate a shift in the dominance of RSL rise driving the early Holocene creation of wetlands, to sediment supply dominating changes in the mid-late Holocene against the backdrop of a reduced rate of RSL rise, with a submergence of wetlands evident after c. 4000 cal years BP. The persistence of fen carr evident between c. 6800 and 5500 cal years BP suggests stability and resilience of the peatland system to continuing RSL rise. As rates of contemporary RSL rise increase, combined with climate and human impacts on the landscape, the drivers of change in these type of estuary systems will shift, with the records providing analogues of potential system responses that can help inform coastal management strategies.

Seeds of Coronilla talaverae (Fabaceae), an endemic endangered species, in Argaric Early Bronze Age levels of Punta de Gavilanes (Mazarrón, Spain)

Punta de Gavilanes (Mazarrón Bay, Spain) was occupied from third millennium cal BC to the first century BC. Overall, the archaeobotanical remains suggest that agriculture and gathering coexisted in the site since the beginning of the occupation of the site. Depending on the sea level variation, the site passed from island in the middle Holocene to peninsula in the late Holocene. Seeds from this archaeological site associated with radiocarbon dates of ≈ 4200 and ≈ 1500 cal years BP include specimens of eight species of shrubs and trees, of which a winter flowering shrub (Coronilla talaverae Lahora and Sánchez-Gómez), is an endangered species that no longer occurs on Punta de Gavilanes area. The seeds of this endemic Coronilla species are associated with materials dated ≈ 3900 cal years BP in a Bronze Age cultural context. The vanished species was presumably locally exterminated by human alteration of its natural habitat or because of environmental changes. The species of Coronilla identified from Punta de Gavilanes is known from relatively distant seashore areas. This endangered species could be effectively preserved by reintroduction to areas that it occupied prior to human alteration, in particular Punta de los Gavilanes.

Fillings And Late Holocene Palaeoenvironments Of The Palustrine Depressions Of The Lopé National Park, Middle Ogooué Valley In Gabon

This work is devoted to the study of fillings and late Holocene palaeoenvironments of two marshes located in the savannas of the northern part of Lopé National Park in Gabon. Sedimentological and geochemical analyzes associated with 14C dating were performed on the sedimentary deposits of Yao and Vitex marshes. The results obtained were compared with these of the sedimentary core of the Lopé 2 marsh, previously analysed. All of these data show that the active filling of these marshes was carried out synchronously. The small variation observed are linked to specific physical characters to each of the marshes. This filling began between 2300 and 2000 cal years BP in all of the marshes. It started at the beginning of the humid climatic phase which followed the climatic pejoration recognized throughout the area of Atlantic Central Africa between 2500 and 2000 years BP. During this humid climatic phase, the rains were abundant and regular and the depressions were filled with sediments which are very rich coarse detrital elements from the erosion of slopes. The marshes and its banks were covered with sparse vegetation. Subsequently the sediments gradually become depleted in coarse detrital materials and enriched with organic constituents. This evolution would indicate a gradual reduction in erosion linked to the densification of the vegetation cover on the slopes. It is mostly related to the development of vegetation in the marshy basins. This development of the vegetation and the conservation of the organic matter of the marshes are due to the perennial flooding of the palustrine depressions.

Morphometric affinities and direct radiocarbon dating of the Toca dos Coqueiros’ skull (Serra da Capivara, Brazil)

The biological variation of the earliest skeletons of South America has been intensely debated for the last two centuries. One of the major research constraints has been the limited number of available samples dating to the early Holocene. We here present the first direct radiocarbon-date for the early Holocene human skeleton from Toca dos Coqueiros (Serra da Capivara, Brazil), also known as “Zuzu” (8640 ± 30 BP; 9526–9681 cal years BP). We performed craniometric analyses using exclusively samples from Brazil, to revisit the sex of the skeleton, and to discuss the evolutionary processes involved in the occupation of the continent. The sex of the individual was estimated as a female when compared to late and early Holocene individuals, but as a male when compared only to the early Holocene series. We also found that Zuzu presents the strongest differences with the late Holocene Guajajara individuals, located nearby, and the strongest similarities with the early Holocene series from Lagoa Santa, attesting for solid biological affinities among early Holocene individuals from Brazil, as well as a moderate level of morphological variation among them. This suggests that the early individuals were part of the same heterogeneous lineage, possibly a different one from which late Holocene populations diverged.

Forest Fire History in Amazonia Inferred From Intensive Soil Charcoal Sampling and Radiocarbon Dating

Fire has a historical role in tropical forests related to past climate and ancient land use spanning the Holocene; however, it is unclear from charcoal records how fire varied at different spatiotemporal scales and what sampling strategies are required to determine fire history and their effects. We evaluated fire variation in structurally intact, terra-firme Amazon forests, by intensive soil charcoal sampling from three replicate soil pits in sites in Guyana and northern and southern Peru. We used radiocarbon (14C) measurement to assess (1) locally, how the timing of fires represented in our sample varied across the surface of forest plots and with soil depth, (2) basin-wide, how the age of fires varies across climate and environmental gradients, and (3) how many samples are appropriate when applying the 14C approach to assess the date of last fire. Considering all 14C dates (n = 33), the most recent fires occurred at a similar time at each of the three sites (median ages: 728–851 cal years BP), indicating that in terms of fire disturbance at least, these forests could be considered old-growth. The number of unique fire events ranged from 1 to 4 per pit and from 4 to 6 per site. Based upon our sampling strategy, the N-Peru site—with the highest annual precipitation—had the most fire events. Median fire return intervals varied from 455 to 2,950 cal years BP among sites. Based on available dates, at least three samples (1 from the top of each of 3 pits) are required for the sampling to have a reasonable likelihood of capturing the most recent fire for forests with no history of a recent fire. The maximum fire return interval for two sites was shorter than the time since the last fire, suggesting that over the past ∼800 years these forests have undergone a longer fire-free period than the past 2,000–3,500 years. Our analysis from terra-firme forest soils helps to improve understanding of changes in fire regime, information necessary to evaluate post-fire legacies on modern vegetation and soil and to calibrate models to predict forest response to fire under climate change.

Structure and Composition of Rhodolith Beds from the Sergipe-Alagoas Basin (NE Brazil, Southwestern Atlantic)

Rhodolith beds are biogenic benthic habitats mainly formed by unattached, non-geniculate coralline algae, which can be inhabited by many associated species. The Brazilian continental shelf encompasses the largest continuous rhodolith bed in the world. This study was based on samples obtained from seven sites and videos taken by a Remotely Operated Vehicle (ROV) at four transects off the Sergipe-Alagoas Coast on the northeast Brazilian shelf. ROV operations and bottom trawl sampling revealed the occurrence of rhodolith beds between 25 and 54 m depths. At the shallower depths, fruticose (branching) rhodoliths (maërl) appear in troughs of ripples, and other non-branching rhodoliths occur associated with corals and sponge patches surrounded by bioclastic sand. Rhodoliths also occur in patches from 30 to 39 m depth; some are fused, forming larger, complex tridimensional structures. At deeper depths, from 40 to 54 m, the abundance of rhodoliths increases and occur associated with fleshy macroalgae on a smooth seafloor; some rhodoliths are fused into complex structures, locally some are fruticose (maërl), and others are partially buried by fine-grained sediment. The collected rhodoliths vary from fruticose in two sites to encrusting to lumpy, concentric and boxwork nodules in the rest; their size ranges from small (<1.5 cm) to large (~6 cm) and are mostly sub-spheroidal to spheroidal. A total of 16 red algal morpho-taxa were identified in the study sites. Two phases of growth can be distinguished in some rhodoliths by changes in color. The brownish inner cores yielded ages of 1600–1850 cal years before the present, whereas outer layers were much younger (180–50 years BP old). Growth layers appeared to have been separated by a long period of burial in the seafloor sediment. Other rhodoliths have ages of hundreds of years.

Traces of a prehistoric and potentially tsunamigenic mass movement in the sediments of Lake Thun (Switzerland)

Mass movements constitute major natural hazards in the Alpine realm. When triggered on slopes adjacent to lakes, these mass movements can generate tsunami-like waves that may cause additional damage along the shore. For hazard assessment, knowledge about the occurrence, the trigger and the geomechanical and hydrogeological mechanisms of these mass movements is necessary. For reconstructing mass movements that occurred in or adjacent to lakes, the lakes’s sedimentary record can be used as an archive. Here, we present a prehistorical mass-movement event, of which the traces were found in an alpine lake, Lake Thun, in central Switzerland. The mass movement is identified by large blocks on the bathymetric map, a chaotic to transparent facies on the reflection seismic profiles, and by a mixture of deformed lake sediments and sandy organic-rich layers in the sediment-core record. The event is dated at 2642–2407 cal year BP. With an estimated volume of ~ 20 × 106 m3 it might have generated a wave with an initial amplitude of > 30 m. In addition to this prehistorical event, two younger deposits were identified in the sedimentary record. One could be dated at 1523–1361 cal year BP and thus can be potentially related to an event in 598/599 AD documented in historical reports. The youngest deposit is dated at 304–151 cal year BP (1646–1799 AD) and is interpreted to be related to the artificial Kander river deviation into Lake Thun (1714 AD).

Late Holocene sediment accumulation on emergent reef platforms: Human presence in a dynamic and unstable sedimentary environment in the equatorial western Pacific

A transect of pits across the island of Teiro on the atoll of Abaiang in the Gilbert Islands of the equatorial Pacific exposes a sequence of washover deposits overlying the reef platform. Each washover event appears to have truncated the existing sediment surface and contributed to the initiation and the vertical and lateral build-up of the island.Burnt material towards the base of the washover sequence has yielded an age of c. 1100–1000 cal years. This is suggestive of a recent date for the formation of the island, supporting the thesis that atoll islands are a product of sediment accumulation consequent upon the sea-level fall of the last few millennia. This created some of the last land masses on Earth on which human settlement is possible.The burnt material appears to be the product of human activity and is thus indicative of human arrival on Abaiang by c. 1100 cal BP. As elsewhere in the Gilberts, the earliest evidence for a human presence overlaps or postdates the c. 2000–1900 cal BP age for the start of falling sea-levels. This exposed the atolls to subaerial conditions and provided new land for human occupation.The presence of anthropogenic material towards the base of the washover sequence is indicative of a human presence on the island long before it approached a state of relative stability and during a period of repeated disruption by coastal inundation and sediment accumulation.

Human practices behind the aquatic and terrestrial ecological decoupling to climate change in the tropical Andes

Anthropogenic climate change and landscape alteration are two of the most important threats to the terrestrial and aquatic ecosystems of the tropical Americas, thus jeopardizing water and soil resources for millions of people in the Andean nations. Understanding how aquatic ecosystems will respond to anthropogenic stressors and accelerated warming requires shifting from short-term and static to long-term, dynamic characterizations of human-terrestrial-aquatic relationships. Here we use sediment records from Lake Llaviucu, a tropical mountain Andean lake long accessed by Indigenous and post-European societies, and hypothesize that under natural historical conditions (i.e., low human pressure) vegetation and aquatic ecosystems' responses to change are coupled through indirect climate influences—that is, past climate-driven vegetation changes dictated limnological trajectories. We used a multi-proxy paleoecological approach including drivers of terrestrial vegetation change (pollen), soil erosion (Titanium), human activity (agropastoralism indicators), and aquatic responses (diatoms) to estimate assemblage-wide rates of change and model their synchronous and asynchronous (lagged) relationships using Generalized Additive Models. Assemblage-wide rate of change results showed that between ca. 3000 and 400 calibrated years before present (cal years BP) terrestrial vegetation, agropastoralism and diatoms fluctuated along their mean regimes of rate of change without consistent periods of synchronous rapid change. In contrast, positive lagged relationships (i.e., asynchrony) between climate-driven terrestrial pollen changes and diatom responses (i.e., asynchrony) were in operation until ca. 750 cal years BP. Thereafter, positive lagged relationships between agropastoralism and diatom rates of changes dictated the lake trajectory, reflecting the primary control of human practices over the aquatic ecosystem prior European occupation. We interpret that shifts in Indigenous practices (e.g., valley terracing) curtailed nutrient inputs into the lake decoupling the links between climate-driven vegetation changes and the aquatic community. Our results demonstrate how rates of change of anthropogenic and climatic influences can guide dynamic ecological baselines for managing water ecosystem services in the Andes.

A 12,000 kyr paleohydroclimate record in the southeastern, U.S.A based on deuterium from bat guano

The southeastern United States endures environmental change from human population increase, climate change, and land-use alterations creating the need to understand baseline conditions and environmental patterns prior to human impacts. While paleoenvironmental data can be reconstructed from a variety of archives (e.g., lake sediments, tree rings, speleothems), some geographic areas contain fewer such records. One archive capable of recording moisture regimes and other paleoenvironmental changes over millennia but has received little attention relative to other climate proxies is bat guano deposits in cave systems. Bat guano deposits are found in many cave environments in the southeastern United States and can be used as an archive of paleoenvironmental data including precipitation, vegetation, and aspects associated with the ecology of bats. Here, we present a 12,000-year record of paleoenvironmental change based on δ2H stable isotopes in a guano core collected from Cave Springs Cave in Alabama, USA. Results suggest distinct shifts in moisture with dryer conditions during the early Holocene/late Pleistocene (12,200–9500 cal year BP) (δ2H values − 86.82 to −-77.70), wetter conditions during the middle Holocene (9300–3900 cal year BP) (δ2H values − 125.74 to − 80.63), roughly coinciding with the Holocene Climatic Optimum event time interval (9000–5000 cal year BP). During the last 4000 years, conditions in the region shifted in the southeastern United States region becoming dryer once again. Climate inferences based on guano δ2H are consistent with the role of atmospheric moisture on regional vegetation changes suggested by previous pollen records obtained from lake sediment cores. This study suggests bat guano δ2H may be a reliable method to provide a long-term paleoclimate record.

Reconstruction of the coastline of the Barents sea (the Kola Peninsula) during the Late Glacial and Holocene

Abstract. Comprehensive studies (lithological and micropaleontological) of bottom sedi ments from nine lakes at the Teriberka Village (the Kola Peninsula, Northwestern Russia) were carried out. The sediments formed after an isolation from the sea was dated. Based on these new data, a preliminary sea-level curve for the study area was constructed. The sea-level curve indicates several phases evolution of the Kola coast during the Late Glacial and Holocene. Rapid drop (~40 mm per year) of a sea-level was occurred ca. 11,500 cal. years BP. The sea level gradually elevated between ca. 11,000 and 7,600 cal. years BP (the Tapes transgression). Science ca. 7,300 cal years BP, the sea level slowly decreases by 2 3 mm per year.

Mid- to Late Holocene (5200–980 cal YR BP) paleoenvironmental dynamics in the Ilha Grande, Brazil, assessed by terrestrial and marine microfossils

Ilha Grande is a Brazilian island that has a high vegetal biodiversity with a well-documented prehistoric human occupation but has few paleoenvironmental studies developed in this area. In view of this, multiproxy analysis of lagoonal sediments including radiocarbon dating were carried out on a 139 cm-long continental sediment core. The aim of our study was to recognise and explain environmental dynamics in this region during the Holocene (∼5200 cal yr BP). The palynomorphs indicate the continuous presence of Atlantic Forest under humid conditions during the last Holocene sea-level highstand, after 5200 cal yr BP. A phase of low palynomorph concentrations was followed by a marked increase in palynomorph accumulation and diversity which may be linked to the subsequent drop of the sea-level. Dinoflagellate cysts showed a higher accumulation at the base of the sediment core. The high accumulation of charcoal particles identified between approximately 3700 and 3000 cal years BP might indicate human activity related to the long-lasting bonfires kept burning by the inhabitants of the archaeological site of Ilhote do Leste.

Mid-Late Holocene Sub-Millennial Scale Inverse Trends of South Asian Summer and Winter Monsoons in Sri Lanka

The South Asian Monsoon (SAM) brings precipitation crucial for agriculture across the densely populated region of South Asia. Identifying the key long-term drivers of the SAM is essential to improve the predictability of future monsoonal trends in the context of current global climate scenarios and increasingly frequent drought and flooding events in this part of the world. Here, we reconstruct ∼6000 years of climatic and environmental history of the South Asian summer monsoon-fed Bolgoda South Lake and the Horton Plains, and the winter monsoon-fed Panama lagoon, in Sri Lanka to better understand monsoonal operation over this island and its connection to broader climate systems. Multiple proxies (diagnostic biomarkers, hydrogen and carbon isotopes of individual n-alkane, grain size, and Zr/Rb elemental ratio) indicate a sub-millennial scale decreasing trend of summer monsoon rainfall in the wet zone of Sri Lanka alongside an increasing trend of winter monsoon rainfall in the dry zone during the last ∼6000 years. We also observed multi-centennial scale arid events in the Bolgoda South Lake and Horton Plains records at ∼3,500 and ∼1,000 cal years BP. Inverse monsoonal behavior during the mid- and late Holocene seems to be led by the southward migration of the mean latitudinal position of ITCZ, induced by varying solar energy distribution between the Northern and Southern hemispheres due to Earth’s processional cycle. Our observations are broadly supported by existing paleoclimatic records from the Indian sub-continent, but abrupt arid phases are asynchronous in the regional records. In addition, these short-term arid conditions do not show systematic correlations with the different modes of climate variables known to have teleconnections with the Indian Ocean monsoon.

Historia de la vegetación del sitio Huapilacuy II durante el Holoceno Medio a partir del análisis polínico y de macrofósiles vegetales, Isla Grande de Chiloé, Chile

This study examines the new fossiliferous site Huapilacuy II of Mid-Holocene age (7,344±51-6,865±58 cal years BP.) located in the northwestern coast of the Isla Grande de Chiloé. This area was not affected by the successive Pleistocene glaciations, and therefore it presents a biogeographic relevance as a potential area of refugia and stability for the vegetation. The presence of plant macrofossils contained in a sedimentary sequence of ca. 300 cm thick, confers a special interest to the site, due to the scarce information available on this type of indicator in paleoenvironmental studies of southern Chile. Additionally, several pollen-based reconstructions from the southern Lake District of Chile (40-44˚ S), document the Holocene sequence of recolonization by the different temperate rainforests types that today occupy this region, although there are non-Holocene records for the Pacific coast of the region. The aim of this study is to reconstruct the local environmental conditions and paleoecology based on the stratigraphic context and the analysis of plant macrofossils at the site Huapilacuy II. In addition, based on the pollen analysis of the deposit, we provide new information to reconstruct the regional characteristics of the vegetation during the Middle-Holocene. In particular, the plant macrofossil record of marsh species contained in the sediments of the lower section of the studied sedimentary sequence, together with the pollen analysis of the same sequence, document a first phase of plant colonization at 7,344±51 cal yrs. BP, with predominance of Poaceae, ferns, and trees with regeneration capacity in open areas, such as Embothrium coccineum and Drimys winteri. The analysis of leaf macrofossils and palynomorphs recovered from several intercalated layers, from the middle section of the sedimentary sequence, show the local and regional development of dense and very humid forests dominated by Aextoxicon punctatum, associated with several species of Myrtaceae. The presence of soil moisture indicator species, such as Luma chequen, Myrceugenia sp. and Myrtaceae Blepharocalyx-type is consistent with the sedimentary environment and the local development of swamp or riverine forests. This hygrophile forest environment is also consistent with the assemblage of fossil mosses, dominated by species that grow today in dense closed-canopy forests, such as Weymouthia, Ptychomnium, Rigodium, Porothamnium and Eucamptodon.
 The regional correlation of the pollen spectra from Huapilacuy II and other records from the Lake District allows us to establish latitudinal and longitudinal differences of tree composition in the temperate-rainforests that expanded during the Early to Mid-Holocene. In particular, this study established for the northwestern coast of the Isla Grande de Chiloé the presence of the coastal association of the valdivian forest (As. Lapagerio-Aextoxiconetum), currently distributed along the Chilean coastline between 30˚- 43˚S. In contrast, the Valdivian associations recorded in other areas of the region exhibit the dominance of Eucryphia cordifolia, Caldcluvia paniculata, Weinmannia trichosperma and different species of Nothofagus. Despite the differences in tree composition, the fossil bryophyte species recorded in several of the sites compared are common with those reported for Huapilacuy II, thus showing the wide ecological range of Chilean bryophytes associated with closed-canopy temperate-rainforests.

New insights into the geological evolution of palaeorivers and their relationship to the Indus Civilization and Early Historic settlements on the plains of Haryana, NW India

Abstract The Quaternary sediments and landscapes of the plains of northwestern Haryana and the ancient settlement mounds distributed across them have great potential to reveal the history of the evolution and disappearance of palaeorivers and their relationship to the Indus Civilization and Early Historic periods in NW India. There are numerous palaeochannels in Haryana, and their distribution and burial in the subsurface creates difficulties for accessing the archives and proxies necessary for developing insight into the timing of river flow and shift, and its relationship to settled populations. This paper investigates the deep and shallow subsurface sedimentary lithology of an area around Sirsa that is close to the course of the modern Ghagghar River. The paper presents additional age constraints provided by dates from the site at Rakhigarhi and examines a sedimentary substrate of a new archaeological mound situated on a palaeochannel identified at a mound near Dhir village. New AMS radiocarbon dates of drifted charcoal from natural and cultural strata suggest human activity and/or natural burning in this region as early as 10 405–10 190 cal years BP (8455–8240 cal years BC). The substrate sediments recorded at the Dhir mound indicate flooding events after the urban phase of the Indus Civilization.

Radiocarbon dating of a composite multi-period debris cone stratigraphy in the Lochan na Lairige, Ben Lawers

An early stage in formation of a composite debris cone in the glacial trough of the Lochan na Lairige, on Ben Lawers, is 14 C dated to 6398–6225 cal years BP. A large proportion of the debris cone comprises a structureless gravel with boulders, possibly deposited in a single event. Blanket peat formed on the debris cone surface at 3820–3496 cal years BP. Sediment slurries are recorded across the peat after this time, at c . 3950– c . 3100, c . 2000 and c . 1400 cal years BP, and at c . 1200– c . 1100 cal years BP. They were much less significant events. They can be related to periods of higher effective precipitation in the region.

Evidence of the Early Holocene eruptive activity of Volcán de Colima and the 8.2 kyr global climatic event in lacustrine sediments from a debris avalanche-dammed lake

Abstract Volcán de Colima, one of the most active volcanoes in Mexico, experienced at least nine flank failures during the last 30 000 years, with catastrophic effects on the environment that implies the formation of temporary dams where lacustrine sediments accumulated for hundreds of years. These lacustrine sequences preserve an exceptional record from which to reconstruct the effect of subsequent volcanic eruptions and, eventually, contemporary environmental and climatic conditions. Here we analyse an Early Holocene lacustrine sequence, named ‘Gypsum King’, which accumulated in a short-lived temporary lake, likely formed by emplacement of the 10 755–11 230 cal years BP Mesa-Yerbabuena debris avalanche. Through detailed analysis of the 1.8 m thick lacustrine sequence ( 14 C ages, sulfur content, grain size), it was possible to identify the 8.2 kyr global climate event and better constrain the Early Holocene main sub-plinian to plinian eruptions of Volcán de Colima. The results presented here highlight the potential to explore sulfur content and abrupt change in grain size in lacustrine sediments as additional proxies to better constrain eruptive phases in volcanic environments. Finally, the Gypsum King sequence provides the first evidence of the 8.2 kyr global climate event along the Eastern tropical Pacific Coast.

Environmental change and the timing of the settlement of the Bronze Age Andronovo culture, in far northwest Xinjiang, China

The relationships between societal and environmental changes have long attracted strong interest amongst scientists. Each of these systems has their own internal dynamics such as the adaptability and social systems built by people; and the feedbacks and controls on environmental systems. North west Xinjiang presents a challenging topographic and climate setting for people. Yet existing evidence shows Bronze Age populations settled into the Bortala Valley as early as the third millennium BCE. The harshness of the region provides a test case for exploring how environmental changes and societal changes may have intertwined. Near the town of Wenquan there is an extensive wetland which contains a sedimentary record covering the last 10,400 years. The early to mid-Holocene is marked by desert and a lake at Wenquan, but there is little evidence for human activity. By 4500 cal year BP the climate became more humid and soon peak humidity occurred when a regional steppe was developed and small numbers of trees were present on the mountains, also the lake shallowed to become a marsh and peatland. The uplands saw a slight increase in tree cover after this, probably as a result of moisture increase due to some cooling. Later changes in the archaeological record seem to be independent of the timing of any environmental changes, and human impacts on the wetland were small until historical times. In short, the major change from desert to steppe may have enabled people to settle the region, but later changes in the environment were too small to be revealed in the Wenquan sediment data, with the adaptability of societies overcoming any environmental challenges and with land-use practices being too small or localized to impact the palaeoenvironmental record.