mid-Holocene Period Research Articles

Geological and Hydrochemical Processes Driving Karst Development in Southeastern Riyadh, Central Saudi Arabia

This study investigates the processes leading to karst development in the southeastern part of Riyadh city extending up to Al Kharj. Numerous solution features such as sinkholes, collapsed dolines, and solution caverns are common in the area. The role of water in the development of the karst features was investigated using an integrated geological and hydrochemical approach. Geological investigations included the petrographic analysis of rock samples collected from zones of intense karstification with special emphasis on mineral dissolution. The study showed that the Sulaiy Formation is commonly fractured, brecciated, foliated, and contains numerous cavities, vugs, and openings. These features have formed by mineral dissolution by circulating groundwater, which has removed anhydrite beds from the underlying Arab–Hith sequence. Karstification likely started from the tectonically weak zones when there was more groundwater recharge. Studies show that during the early to mid-Holocene period, the climate in the Arabian Peninsula was humid, promoting groundwater recharge and subsequent mineral dissolution, though the process of karstification must have started much earlier. Hydrochemical findings reveal that mineral dissolution (halite and calcium sulfate) is the main process affecting groundwater chemistry. The Piper plot revealed two main hydrochemical facies: the (Ca2+ + Mg2+)–(Cl+ SO42−) Type (Type A) and the (Na+ + K+)–(SO42− + Cl) Type (Type B). Most of the samples belong to Type B, typical of groundwater facies affected by dissolution of halite and anhydrite mineral. The absence of the (Ca2+ + Mg2+)–(CO32− + HCO3−) type of groundwater facies indicates a lack of recent groundwater recharge and the removal of carbonate minerals from the system through precipitation, as evidenced by the saturation indices. Plots of the major ionic pairs (cations vs. anions) in groundwater indicate strong halite and gypsum/anhydrite dissolution. Of the three carbonate minerals, calcite has the highest average saturation index followed by aragonite and dolomite. This suggests significant past rock–water interaction leading to carbonate dissolution. Presently, any additional calcium or carbonate ions introduced into the water lead to calcite precipitation. The study indicates that the process of karst development may not be active today. Currently, groundwater chemistry is mainly influenced by rock–water interaction leading to gypsum/anhydrite dissolution, which has resulted in a high concentration of Na+, Ca2+, Cl− and SO42− ions in groundwater. The dissolution of gypsum and halite from the Hith Formation weakens the structural integrity of the overlying Sulaiy Formation, creating large underground cavities. These cavities increase the risk of roof collapse, leading to cover-collapse sinkholes as the roof becomes too thin to support the weight above.

Evaluating the vulnerability of Tetracentron sinense habitats to climate-induced latitudinal shifts.

Exploring the changing process of the geographical distribution pattern of Tetracentron sinense Oliv. and its main influencing factors since the last interglacial period can provide a scientific basis for the effective protection and management of the species. The MaxEnt model was used to construct the potential distribution areas of T. sinense in different periods such as the last interglacial (LIG), the last glacial maximum (LGM), the mid-Holocene (MID), and the current and future (2050s and 2070s). On the premise of discussing the influence of dominant environmental factors on its distribution model, the suitable area changes of T. sinense under different ecological climate situations were quantitatively analyzed. (1) The AUC and TSS values predicted by the optimized model were 0.959 and 0.835, respectively, indicating a good predictive effect by the MaxEnt model; the potential suitable areas for T. sinense in the current period are mainly located in Southwest China, which are wider compared to the actual habitats. (2) Jackknife testing showed that the lowest temperature in the coldest month (Bio6), elevation (Elev), seasonal variation coefficient of temperature (Bio4), and surface calcium carbonate content (T-CACO3) are the dominant environmental factors affecting the distribution of T. sinense. (3) From the last interglacial period to the current period, the total suitable area of T. sinense showed a decreasing trend; the distribution points of T. sinense populations in mid-Holocene period may be the origin of the postglacial population, and Southwest China may be its glacial biological refuge. (4) Compared with the current period, the total suitable area ranges of T. sinense in China in the 2050s and 2070s decreased, and the centroid location of its total fitness area all migrated to the northwest, with the largest migration distance in 2070s under the SSPs 7.0 climate scenario. Temperature was the principal factor influencing the geographical distribution of T. sinense. With global warming, the range of T. sinense suitable areas will show a shrinking trend, with a shift toward higher-latitude regions. Ex situ conservation measures could be taken to preserve its germplasm resources.

Half of the soil erosion in the Alps during the Holocene is explained by transient erosion crises as a consequence of rapid human land clearing

Human land use changes have altered soil erosion for millennia with extensive consequences on terrestrial and aquatic ecosystems as well as on biogeochemical cycles along the land-ocean continuum. Despite their great importance, past erosion trends have high uncertainties limiting quantitative estimates of long-term erosion dynamics. Here, we applied a new approach combining well-dated paleo-records of soil erosion from lake sediments and a spatially distributed semi-empirical model to simulate annual soil erosion in six lake watershed systems in the Northwestern Alps during the Holocene. Progressive and abrupt changes in soil erosion are detected in the six watersheds. Progressive erosion explains most of the soil exports observed during the Early to Mid-Holocene period (from 11,700 to 3000 cal. yr. BP), while transient erosion crises (i.e., periods of abrupt increase in the erosion rates spanning approximately 1000 ± 500 years) led to massive soil losses during the Late-Holocene period (from 3000 to 1000 cal. yr. BP). Our coupled approach of proxy-model reconstruction shows that the transient erosion crises represent the half of the total soil erosion exports during the Holocene. These estimates defy current representations of large-scale soil erosion during the Holocene that do not consider transient erosion crises, hence potentially underestimating the anthropogenic perturbation of lateral fluxes and fate along the land-ocean continuum. Our results further suggest that erosion and/or land cover proxies need to be consistently integrated into model approaches when attempting to estimate past variations in mass exports from terrestrial to aquatic ecosystems over centennial to millennial timescales.

Synchronizing the Western Gotland Basin (Baltic Sea) and Lake Kälksjön (central Sweden) sediment records using common cosmogenic radionuclide production variations

Multi-archive studies of climate events and archive-specific response times require synchronous time scales. Aligning common variations in the cosmogenic radionuclide production rate via curve fitting methods provides a tool for the continuous synchronization of natural environmental archives down to decadal precision. Based on this approach, we synchronize 10Be records from Western Gotland Basin (WGB, Baltic Sea) and Lake Kälksjön (KKJ, central Sweden) sediments to the 14C production time series from the IntCal20 calibration curve during the Mid-Holocene period ~6400 to 5200 a BP. Before the synchronization, we assess and reduce non-production variability in the 10Be records by using 10Be/9Be ratios and removing common variability with the TOC record from KKJ sediments based on regression analysis. The synchronizations to the IntCal20 14C production time scale suggest decadal to multi-decadal refinements of the WGB and KKJ chronologies. These refinements reduce the previously centennial chronological uncertainties of both archives to about ± 20 (WGB) and ±40 (KKJ) years. Combining proxy time series from the synchronized archives enables us to interpret a period of ventilation in the deep central Baltic Sea basins from ~6250 to 6000 a BP as possibly caused by inter-annual cooling reducing vertical water temperature gradients allowing deep water formation during exceptionally cold winters.

Asynchronous Holocene lake evolution in arid mid-latitude Asia is driven by glacial meltwater and variations in Westerlies and the East Asian summer monsoon

Understanding the mechanisms driving hydrological change in arid Central Asia over a range of time scales is crucial for making predictions for future changes in fragile desert-lake ecosystems. As of yet, the drivers of hydrological changes in lake systems of arid Central Asia over the Holocene remain largely unexplored. Aibi Lake, fed by rivers originating from the glaciated Tianshan Mountains and terminating in the arid Junggar Basin of northwestern China, presents a perfect natural laboratory to explore lake evolution in context to Holocene climate evolution in arid Central Asia. Here, a single-grain K-feldspar dating method was used to effectively date 20 paleolake shorelines with poorly bleached sediment to constrain lake level evolution over the past 18 k.y. Results indicate that Aibi Lake experienced a rapid increase in water levels, reaching a peak of ∼36 m during the early to mid-Holocene period (10−7 ka). Subsequently, the lake level may have shown a general decline during the middle Holocene (7−4 ka), with the lake reaching a low level of less than 10 m at ca. 4 ka. In the late Holocene, lake levels fluctuated by 10−30 m above modern levels during 4−1 ka, with generally low levels of <9 m after 1 ka. The evolution of Aibi Lake underlines a clear out-of-phase relationship between Central Asian lake evolution and Westerlies precipitation changes, where Holocene lake changes were instead more directly controlled by the flux of glacial meltwater from the Tianshan Mountains, driven by change in Northern Hemisphere summer insolation. Glacier meltwater, in combination with variable delivery of Westerlies and East Asian summer monsoon precipitation, are responsible for asynchronous lake evolution trends across Central to East Asia.

Mid-Holocene hydroclimatic change and hurricane activity in Central America recorded by an Isla de Mona Stalagmite

In recent years, Puerto Rico has been repeatedly hit by drought and hurricane, causing severe damage to the local society and economy. Therefore, understanding the region's climate variability and predicting extreme weather has become an important scientific problem. Cave stalagmites are widely recognized as high-quality terrestrial paleoclimate proxies due to their accurate dating and high resolution. In this study, we present a stalagmite-based multi-proxy reconstruction of hurricane and hydrological changes in Central America from the island of Isla de Mona, Puerto Rico, for the mid-Holocene period (4700–6260 a BP). Our data suggest a significant influence of solar activity on rainfall patterns in Central America via changes in the mean position of the Intertropical Convergence Zone (ITCZ). Our study further shows that El Niño may have played a role in influencing hurricane development at a decadal scale, and also found that the relationship of hurricane activities and El Niño intensity on the decadal and centennial scale is variable. The implications of our findings are crucial for informing contemporary climate models and enhancing our preparedness for potential future climate scenarios in the region.

Speleothem records from western Thailand indicate an early rapid shift of the Indian summer monsoon during the Younger Dryas termination

Mainland Southeast Asia experiences complex and variable hydroclimatic conditions, mainly due to its location at the intersection of Asian monsoon subsystems. Predicting future changes requires an in-depth understanding of paleoclimatic conditions that is currently hindered by a paucity of records in some regions. In this paper, we present the first speleothem stable isotope records from western Thailand detailing the Bølling-Allerød interstadial, Younger Dryas termination, and early- to mid-Holocene period. We find evidence of higher precipitation during the Bølling-Allerød (14,321–12,824 years before present (1950: BP)) compared to a Younger Dryas termination that starts 11,702–11,674 BP, has a rapid shift centered on 11,660–11,641 BP, and ends 11,603–11,589 BP. In addition, our records show Holocene monsoon intensity peaking at 8250 BP or before, a multi-millennia delay from the Northern Hemisphere summer insolation peak, followed by a trend to drier conditions until at least 750 BP. Assessment of the timing of the Younger Dryas termination in paleoclimate records across Southeast Asia reveals an earlier shift of the Indian Summer Monsoon to global climate shifts when compared to East Asian Summer Monsoon records. The causes of this are currently unknown. Some potentially important aspects include: an Indian Summer Monsoon influence on East Asian Summer Monsoon strength via the Indian Ocean Dipole climate pattern, the role of the Tibetan Plateau in monsoon dynamics, and exposure of the Sundaland shoreline. More high-resolution paleoclimate records, especially on the pathway of Indian Summer Monsoon to East Asian Summer Monsoon, are required for further discussion on the mechanisms controlling the differences between climate regimes.

The influence of climate oscillations and geological events on population differentiation of Camponotus japonicus in the Chinese mainland.

Camponotus japonicus (Hymenoptera: Formicidae) is an omnivorous social insect which builds sizable colonies in sparse woodlands or cropland and spreads across multiple climatic zones in the Chinese mainland. This study aims to reveal the role of climate changes and geological events in driving the genetic structure of social insect populations by investigating the phylogenetics and historical demography of C. japonicus in the Chinese mainland. Phylogenetic analyses were conducted based on the mitochondria DNA dataset using MrBayes and IQ-TREE. We constructed a haplotype network, calculated analyses of molecular variance, estimated the divergence time, and reconstructed the maximum clade credibility tree. Mismatch distribution and Bayesian skyline plots were used to infer historical population fluctuations. Additionally, ecological niche modeling was employed to predict the potential distribution of the species during the present, mid-holocene, and last glacial maximum periods in the Chinese mainland. The phylogenetic tree and median-joining network analyses support the presence of four distinct lineages in C. japonicus. These lineages exhibit significant genetic differentiation and limited gene flow. The divergence among the four lineages began in the early Pleistocene, approximately 1.41 million years ago (Ma). Subsequently, the central lineage diverged from both the northern and southern lineages around 1.16 Ma, while the northern and southern lineages diverged from each other at approximately 1.07 Ma. Population expansion was observed in the southern, central, and northern lineages prior to the last glacial maximum, while the Yunnan-Sichuan lineage experienced a slight increase in population size in more recent times. The predicted distribution of the species corresponds well with the actual distribution. Furthermore, the current suitable habitat areas in northern Xinjiang, southern Tibet, and the southeast coastal regions have significantly decreased compared to the last glacial maximum and the mid-holocene periods. Our results suggest that climate oscillations and geological events play an important role in driving genetic patterns and differentiation of C. japonicus. Mountain barriers isolate populations from each other, hinder the flow of genes, and effectively prevent the spread of this species. But at the same time, it also formed refugia at low altitudes areas such as Qinling-Bashan Mountains and Yanshan-Taihang Mountains and provide suitable habitats during glaciation. This study provides a good model for understanding how complex climate changes and geological events affect population genetic differentiation of social insects in the Chinese mainland.

Holocene extreme hydroclimate events in the Asian monsoon region were more frequent during cooler intervals

The areas affected by the East and South Asian monsoons contain almost half the world’s population. Understanding natural variability in these monsoons under warmer climates is critical for managing future changes. Here we present a high-resolution record of Holocene drought events derived from lake level changes in the South Asian monsoon region. By combining the published storm events in the East Asian monsoon region, we demonstrate that extreme hydroclimate events frequently occurred within a ca. 500-year cycle during the cool early-late Holocene, exhibiting a fierce Asian monsoon. In contrast, there were fewer extreme hydroclimate events during the warm mid-Holocene period. We propose that tropical temperatures and air-sea interaction in the Indo-Pacific Oceans are responsible for the occurrences of centennial-scale extreme events. Our findings suggest that tropical influences can module climate responses in monsoon regions, and the Asian monsoon may be more peaceful than hitherto expected under future global warming scenarios.

Specialized lithic technology from Gua Arca, Kangean Island, Indonesia

Stone artifacts are a common finding at prehistoric occupation cave sites in Indonesia. Flake tools with various key functions are one of the cultural markers of the pre-Neolithic period, frequently recovered in the context of assemblages of animal bones, bone tools, and shell artifacts. Recently, excavation at a new cave site on the small island of Kangean, unearthed an extensive set of stone tools. Our analysis of this assemblage of stone tools from Arca Cave site, Kangean Island, identified specific characteristics in typology, technology, and environmental context. Dating to at least 6,000years ago, the Kangean lithic assemblage is associated with the mid-Holocene period and possibly even earlier.

Archaeology of animate ancestors and entanglement at Mayarnjarn in the Wellington Range region, Northern Territory

ABSTRACTThe Wellington Range region, in far Northern Australia, provides a remarkable record of cultural encounter. Cathedral‐sized rock art galleries include contact imagery referencing Macassan and European visitors while lithic artefact assemblages echo social mobility between Indigenous groups occurring from at least the mid Holocene period. In this paper, we continue the trajectory of archaeological research in this region by examining community entanglement over the longue durée, focusing on the Mayarnjarn rock‐shelter complex. Specifically, and following advice from traditional custodians, the authors complement archaeological excavation results with reflections on interactions between Traditional Mawng speaking Owners and archaeologists occurring during the 2016 and 2018 field seasons. This paper provides a cultural chronology built around both OSL and radiocarbon dates, a first for the region, indicating site activities dating from the terminal Pleistocene. An increase in exotic artefacts and presence of paintings belonging to a pan‐Arnhem land rock art tradition suggests widening social networks during the Holocene. Insight into the nuanced nature of interactions, also the role of animate objects as relationship referents, emerge through ethnography and experience as the field season unfolds.

Landscape and Climate Changes in Southeastern Amazonia from Quaternary Records of Upland Lakes

The upland lakes (ULs) in Carajás, southeastern Amazonia, have been extensively studied with respect to their high-resolution structural geology, geomorphology, stratigraphy, multielement and isotope geochemistry, palynology and limnology. These studies have generated large multiproxy datasets, which were integrated in this review to explain the formation and evolution of the ULs. These ULs evolved during the Pliocene–Pleistocene periods through several episodes of a subsidence of the lateritic crust (canga) promoted by fault reactivation. The resulting ULs were filled under wet/dry and warm/cool paleoclimatic conditions during the Pleistocene period. The multielement geochemical signature indicates that the detrital sediments of these ULs were predominantly derived from weathered canga and ferruginous soils, while the sedimentary organic matter came from autochthonous (siliceous sponge spicules, algae, macrophytes) and allochthonous (C3/C4 canga and forest plants and freshwater dissolved organic carbon) sources. Modern pollen rain suggests that even small ULs can record both the influence of canga vegetation and forest signals; thus, they can serve as reliable sites to provide a record of vegetation history. The integrated data from the sedimentary cores indicate that the active ULs have never dried up during the last 50 ka cal BP. However, subaerial exposure occurred in filled ULs, such as the Tarzan mountain range during the Last Glacial Maximum (LGM) and the Bocaína and S11 mountain ranges in the mid-Holocene period, due to the drier conditions. Considering the organic proxies, the expansion of C4 plants has been observed in the S11 and Tarzan ULs during dry events. Extensive precipitation of siderite in UL deposits during the LGM indicated drier paleoenvironmental conditions, interrupting the predominantly wet conditions. However, there is no evidence of widespread forest replacement by savanna in the Carajás plateau of southeastern Amazonia during the late Pleistocene and Holocene.

Mechanisms for African easterly wave changes in simulations of the mid-Holocene

The mid-Holocene was a warm period with significantly amplified precipitation in North Africa, and a northward shifted Western African Monsoon during boreal summer. We conduct simulations for the pre-industrial and mid-Holocene periods to investigate the connection between summer rainfall variability and changes of African easterly waves (AEWs) during the mid-Holocene. Summer rainfall increases and migrates northward during the mid-Holocene, but the magnitude of change fails to reconcile the discrepancy with mid-Holocene proxy evidence, possibly due to no prescribed vegetation change in our simulations. The spectrum of summer rainfall over the Sahel and West Africa reveals enhanced synoptic time scale (3-to-6 days) variability during the mid-Holocene, which is consistent with the enhanced AEW activity influence. Specifically, the southern AEW track strengthens and migrates poleward during the mid-Holocene period, which modulates summer rainfall over the Sahel and West Africa. By comparison, the northern AEW track changes less and produces a minor contribution to rainfall changes in those regions. We find enhanced baroclinic and barotropic instabilities to promote the AEW activity during the mid-Holocene, with a doubling of the eddy kinetic energy of the meridional wind from that in PI, and baroclinic energy conversion plays a more important role. Stronger low-level meridional thermal gradients increase moisture flux from the Atlantic Ocean to inland.The amplified AEW activity, together with promoted moist convection and increased precipitation, results in a northern shift of the summer rainfall band during the mid-Holocene.

Predicting the Potential Distribution of the Endangered Plant Cremastra appendiculata (Orchidaceae) in China under Multiple Climate Change Scenarios

Cremastraappendiculata (Orchidaceae) is a perennial medicinal herb, which is included in the national second-class protected plant catalog in China. Due to the influences of climate change and anthropogenic activities, in conjunction with soaring commercial prices, the wild sources of C.appendiculata have been drastically reduced and are in danger of extinction. Consequently, it is important to predict the distribution of potentially suitable growth/propagation areas for C.appendiculata under the backdrop of climate change for its protection and sustainable use. For this study, an optimized maximum entropy model was employed to analyze the distribution patterns and changes of potentially suitable regions for C.appendiculata during different periods since the Last Glacial Maximum (LGM, 18–24 ka). Based on multiple climate change scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5), the distribution range of C. appendiculata was predicted for the 2050s (average for 2041–2060), 2070s (average for 2061–2080), and 2090s (average for 2081–2100). The results revealed that during the LGM period, the highly suitable growth area for C.appendiculata was 0.28 × 104 km2, which accounted for only 3.26% of the current highly suitable growth area. During the mid-Holocene (MH, 6 ka) period, the area of highly suitable regions increased to 8.38 × 104 km2, which accounted for 99.30% of the present highly suitable growth area. Further, the cumulative existing potentially suitable growth area for C. appendiculata is 213.9 × 104 km2, which accounts for 22.28% of China’s territory. Of these lands, the low, medium, and high suitable areas are 147.76 × 104 km2, 57.71 × 104 km2, and 8.44 × 104 km2, respectively. The highly suitable areas are primarily distributed across Sichuan, Gansu, Shaanxi, Chongqing, Guizhou, Hubei, and Anhui Provinces. Moreover, in the future the potentially suitable growth areas for C. appendiculata will decrease to varying degrees. Further, the results of this study found that the relatively low impact areas for C. appendiculata were mainly distributed across Shaanxi, Sichuan, Chongqing, and Guizhou Provinces. Centroid transfer analysis indicated that the center of potentially suitable growth areas for C.appendiculata shifted to the northwest in SSP2-4.5 and SSP3-7.0, while they initially shifted to the northwest and then to the southeast in SSP1-2.6 and SSP5-8.5.

Placing of the second oldest red ochre mine in mainland Europe, Lovas, Hungary, to human, paleoenvironmental and paleobiogeographic context

Although the 13.2–13.8 ky old Lovas red ochre mine, Central Transdanubia, Hungary is a very important Upper Palaeolithic archaeological site being the second oldest in mainland Europe, we have little knowledge of the conditions under which and how long the pits were cultivated and the post-mining sedimentation processes. The aim of the study was to study certain human circumstances of the mining activities, reveal the former ecological conditions which influenced the sedimentation processes and investigate how the changing climatic conditions led to the formation of the fossil macrofaunal assemblage of the archaeological site. The removal of ca. 25 m3 of pigment material from the pits was equivalent to a maximum of 8750–11042 transport occasions per person, although the pre-transport processing of the material could notably reduce the weight of the transportable pigment and the time demand. Based on the lower thermal comfort limit, mining activities could be performed predominantly in the summer months. In the relatively humid Bølling-Allerød period, the redeposition of the excavated barren material to the cavity could be rapid after the termination of the mining activity. In the Younger Dryas Stadial and the early Holocene, the recharge and covering of the former pits with sediment could be slow and it started to increase only in the mid-Holocene period. The modelling of the potential distribution range of five macrofaunal elements indicates that all the species occurred at the site in the Bølling-Allerød period in the wider environment of the Lovas red ochre mine. The reconstructed boreal forest biome in the time of cultivation of the mine can explain well the dominance of fossil elk bones found in the fossil assemblage.

Late quaternary evolution of lower Kaveri and adjoining river basins in Tamil Nadu, Southern India: A combined approach using remote sensing and optical dating of fluvial records

A drainage system responds swiftly on a regional or local scale to reveal the signature of neotectonic activities or any changes in climate. A few works in southern India have shown tectonic movements in terms of river and drainage response. The Gingee and the Vellar river basins (adjacent to the lower Kaveri Basin in Tamil Nadu) have been chosen for the present study. The morphometric analysis of the Gingee and the Vellar river basins and OSL dating of the sediments collected from the rivers' palaeochannels were carried out to achieve the proposed objectives. The study helped understand the role of climatic and tectonic elements in the evolution of the basins. The analysis indicates a regional scale-down warping shown by the southward tilting of the Gingee drainage systems and northward tilting of the Vellar drainage systems, strong asymmetry in some reaches (VRSB-II; III) and pronounced elongation of certain tributaries (GRSB-III; IV and VRSB-V). The Gingee River migrated clockwise (towards south) to its current position since the mid-Holocene period ∼3.5 ka, whereas the Vellar River shifted in an anti-clockwise (towards north) direction since 1.28 ka. This was the time when the study area experienced high precipitations. Also, these rivers are very coarse-grained bed load rivers found very shallow and thus, during heavy precipitation and discharges, prone to fill the channel quickly and shift the course. Luminescence ages of the paleochannels also suggest that both the rivers are migrating towards the central part with the same rate of ∼4.5 km/ka.

Late Quaternary changes in malaria-free areas in Papua New Guinea and the future perspectives

The New Guinea Highlands were among the first areas where agricultural societies developed about 9 kya. Even today, the highest human population densities can be found in the tropical highlands, those are the most important shelters for societies in this seriously malaria-affected equatorial area. In this study, the distribution and altitudinal patterns of Plasmodium vivax and Plasmodium falciparum malaria, as well as the potential generation numbers and the annual season lengths of the extrinsic transmission periods of the parasites were modelled for the Last Glacial Maximum, the Mid-Holocene Period, 1960–1990 and 2061–2080 in the Papua New Guinea Highland provinces. It was found that areas influenced by Plasmodium vivax malaria have always been larger than the endemic regions of Plasmodium falciparum. After the Last Glacial Period, the extension of the malaria-free areas decreased dramatically. It could trigger the development of agriculture in the highlands in the early Holocene due to the increasing population concentration in malaria-free areas. These malaria-free regions could be stable in the rest part of the Holocene, which could explain the high human genetic and cultural diversity of the New Guinea Highlands. Future models predict the disruption of this stability and the notable decrease of the malaria-free areas in the highlands, especially in the case of Plasmodium vivax malaria, but the upward move in the Plasmodium falciparum-endemic regions also seems to be notable. These changes can negatively affect the demographic stability and cultural complexity of the traditional highlander communities in Papua New Guinea.

Holocene variation in the Indian Summer Monsoon modulated by the tropical Indian Ocean sea-surface temperature mode

The evolution of the Indian Summer Monsoon (ISM) has been widely investigated owing to its significant climatic and socioeconomic influences. However, debates remain concerning the temporal variation during the Holocene and its driving mechanisms, particularly the potential contribution of sea-surface temperature (SST) in the tropical Indian Ocean (TIO). Here, we present a continuous sediment record covering the past 11.1 kyrs from the Beihai Wetland, southwestern China. The grain size, geochemical element composition and total organic carbon content (TOC) were analyzed and interpreted in terms of the sedimentary conditions, catchment erosion and regional climate variations. Higher detrital inputs and possibly high water levels were determined during the early to mid-Holocene period, suggesting strong catchment erosion under an intensified ISM. The maximum monsoon intensity appeared between 7.5 and 5.2 cal. kyr BP, which is broadly consistent with various ISM records. We propose that such mid-Holocene monsoon strengthening was primarily triggered by the TIO SST anomaly modes, i.e., the Indian Ocean Basin (IOB) mode and the Indian Ocean dipole (IOD) mode. Based on Holocene SST records from the TIO, a positive SST anomaly (positive IOB mode) and positive zonal SST anomaly gradient (positive IOD mode) may have occurred during the mid-Holocene, which jointly triggered intensification of the ISM. Our findings emphasize the significant contribution of the TIO in modulating the summer monsoon system. The abrupt increases in TOC content and median grain size indicate the formation of the current wetland system at approximately 5.2 cal. kyr BP following the decline in regional moisture as well as the retreat of the ISM. In addition, notable human impacts were determined during the last 800 years, as indicated by intensified catchment erosion in response to human-induced deforestation.

Loess soil distribution and properties in Mongolia

Loess and loess-like soil formations are distributed in 3 regions across Mongolia. The lower part of the Orkhon and Selenge river basin in North Mongolia is the main loess area and another two are located in east Mongolia, in the Onon and Ulz river basins and the Khalka Gol river area. Loess-like soil covers a total of 109,000 sq.km or 6.95 per cent of the territory of the country. Loess soil properties have been studied on the basis of 8 sections and 83 samples. Fine sand fraction is predominant in the loess granulometric composition and its mean value is 51.3 per cent, and silt content mean value is about 34.9 per cent. A typical loess is a non-stony silt or fine sand, but there are also gravel loess. The average stone gravel content in the loess sediments is 8.1 per cent, sandy loess doesn’t contain any stone, but coarse fragment is high (20.5 per cent) in gravel loess. There is higher sand content (57.0 per cent) in gravel loess as compared to sandy loess (47.4 per cent). Mongolian loess soil average calcium carbonate content is 2.9 per cent, and Organic Matter (0.93 per cent) is higher than Chinese loess (0.41 per cent). Using 14C isotope data analysis and sediment properties we have tried to define the loess stratigraphy. Lower base section of fine sand silty loess sediments or about 1-3 meter thick layers were mostly formed during the mid-Holocene (7.5-3.0 ka) period. Upper parts of silty loess or 1.0-0.7 meter top layers were accumulated in the late Holocene (3ka BP to present) period. Kastanozem topsoil humus horizon (15-30 cm) formation starts at 1.5-1.0 ka BP. Mid-Holocene period probably witnessed the most active loess accumulation with a warm and dry windy condition prevailing. Sandy loess with a thickness of 1-2 meters predominate in Mongolia, and in some places loess thickness reaches up to 20-30 meters.

Technology, subsistence strategies and diversity in South Sulawesi, Indonesia, during the Toalean Mid-Holocene period: recent advances in research

The central Indonesian island of Sulawesi has played an important role in modern and pre-modern human migration through the Southeast Asian island chain. Over the last two decades, archaeological excavations in South Sulawesi have provided new insights into the ancient human past of this region, in particular the extensive Mid-Holocene or ‘Toalean’ sites, as well as several significant Pleistocene-age discoveries. This paper assesses the latest research and what implications these works have for prior models of human prehistory in the region. We show that recent studies have revealed that Toalean-era toolmakers were able to adapt to different environments and raw material sources, but would also transport desired raw materials for production of certain artefact types. Early quarry sites have also been identified for the first time. In addition, new excavations have revealed complex tool forms in forested highland environments, previously thought to hold only sparse and elementary assemblages, allowing us to re-assess twentieth century models of Toalean cultural subgroups and distribution. The rich parietal art initially attributed to the Toalean has now been dated to the Late Pleistocene, roughly contemporaneous with the production of ‘portable art’ in this region, while lithic artefacts dated to between at least 194-118 thousand years ago at Talepu appear to predate modern Homo sapiens occupation. Two newly reported highland sites have also yielded rich and deeply stratified archaeological deposits. These may offer the best opportunity to test hypotheses such as the transitional ‘Ceramic Toalean’ contact phase, as site disturbance and subsistence have formerly compromised the stratigraphic integrity of most excavations. This review shows that, while much work is still needed particularly in obtaining a reliable body of well-stratified and reliable dates, recent research presents an image of early innovation in the region in the form of Late Pleistocene ‘art’ production and Mid-Holocene technological developments that are both earlier and more extensive that previously known.