Reliability of phytoliths for reconstructing vegetation dynamics in northeast China

<p>  Phytolith provides a new preconstruction and interpretation of palaeovegetation in either forest or grassland regions. In particular, the phytolith reliability records in both vegetation types should be assessed when they are employed on palaeovegetation reconstruction in north temperate region. Yet this issue has not been clearly investigated. Being two vegetation types (including forest and grassland) in northeast China (NE China) where it is an integrated physical geography unit, they provide some crucial references regarding the phytolith reliability. Thus, we firstly focused the study site of NE China to collect 108 topsoil samples from five dominant community types in forest region and 154 topsoil samples from four dominant community types in grassland region, respectively, to their phytolith assemblages. This study was to establish the reference databases of modern soil phytolith to demonstrate their record reliability. These phytolith data thus better serve palaeovegetation reconstruction in sedimentary sequences using their corresponding vegetation types in two selected regions.</p><p>    Analytical results showed that topsoil phytolith assemblages and their phytolith indices (Iw, Ic and W/G) varied substantially with different vegetation types in NE China; phytolith indices were also variations aligned with vegetation compositions. These finding suggest that phytolith is a reliable proxy using reconstructing palaeovegetation.</p><p>  The palaeovegetation reconstruction based on these phytolith reference databases indicated that NE China had experienced substantial vegetation changes since the late-glacial period. Community types in forest region may have experienced a succession sequence from the open Larix mixed forest to the open woodland, then turning to the closed broadleaf forest, and finally to the closed Pinus koraiensis mixed forest. In particular, we found that vegetation types in grassland region was dominated by a flourish C3 grass steppe since late-glacial period, with a total coverage higher than 50%. The coverage of C3 grass and C4 grass were higher than 25% and 16%, respectively.</p><p>  The palaeovegetation interpretation using these phytolith reference databases since the late-glacial period were consistent with that reconstructed using pollen assemblages in the same stratigraphic profile, confirming the phytolith reliability for reconstructing vegetation type and community type in the NE China. Phytolith record analysis also provided some detailed vegetation information such as the vegetation composition of the understory and Larix abundance in forest region, and the proportion of C3/C4 grass, their biomass and community coverage in grassland region.</p><p>  Thus, this study demonstrates the phytolith reliability to provide new perspectives on palaeovegetation reconstruction in northern temperate regions. Furthermore, this finding acts as a potential reference for exploring the relationship between phytolith and (palaeo)vegetation in other temperate regions.</p><p>(Supported by the National Natural Science Foundation of China (Grant No.41971100,41771214 )</p>

Deglaciation of the central sector of the Cordilleran Ice Sheet in northern British Columbia

<p>The Cordilleran Ice Sheet (CIS) repeatedly covered western Canada during the Pleistocene and attained a volume and area similar to that of the present-day Greenland Ice Sheet at the Last Glacial Maximum. Numerical modelling studies of the CIS during the last glacial-interglacial cycle indicate the central sector of this ice sheet, located in mountainous northern British Columbia, played an important role during both the advance and retreat phases. Additionally, the models indicate that the rapid climate oscillations at the end of the Pleistocene had a dramatic effect on the CIS. The abrupt warming at the onset of the Bølling-Allerød caused significant thinning of the ice sheet, resulting in a fifty percent reduction in mass, while the subsequent cooling caused the expansion of alpine glaciers across the former central sector of the CIS. However, the mountainous terrain and remote location have thus far impeded our understanding of this important region of the CIS, and the ice sheet configuration during the Late Glacial remains poorly constrained. </p><p>Here we use the glacial landform record to reconstruct the deglaciation dynamics of the central sector of the CIS during the Late Pleistocene climate reversals. Numerous high elevation meltwater channels suggests the early emergence of mountain peaks above the ice sheet and the configuration of ice marginal landforms, particularly lateral meltwater channels, eskers, kame terraces and ice-contact deltas, allows the westward retreat of the ice margin to be traced towards ice dispersal centres in the Skeena and Coast mountains. Hundreds of arcuate, sharp-crested terminal moraines delineate the extent of alpine glaciers, ice caps and ice fields that regrew on mountain peaks above the CIS and numerical dating indicates that this readvance occurred during the Late Glacial period. Additionally, at some locations, cross-cutting relationships preserve the interaction of the local readvance glaciers with the trunk glaciers of the CIS, allowing the extent of the central sector of the CIS during the Late Glacial period to be reconstructed for the first time.  </p>

Inferring population histories for ancient genomes using genome-wide genealogies

Ancient genomes anchor genealogies in directly observed historical genetic variation, and contextualise ancestral lineages with archaeological insights into their geography and lifestyles. We introduce an extension of the Relate algorithm to incorporate ancient genomes and reconstruct the joint genealogies of 14 previously published high-coverage ancients and 278 present-day individuals of the Simons Genome Diversity Project. As the majority of ancient genomes are of lower coverage and cannot be directly built into genealogies, we additionally present a fast and scalable method, Colate, for inferring coalescence rates between low-coverage genomes without requiring phasing or imputation. Our method leverages sharing patterns of mutations dated using a genealogy to construct a likelihood, which is maximised using an expectation-maximisation algorithm. We apply Colate to 430 ancient human shotgun genomes of >0.5x mean coverage. Using Relate and Colate, we characterise dynamic population structure, such as repeated partial population replacements in Ireland, and gene-flow between early farmer and European hunter-gatherer groups. We further show that the previously reported increase in the TCC/TTC mutation rate, which is strongest in West Eurasians among present-day people, was already widespread across West Eurasia in the Late Glacial Period ~10k - 15k years ago, is strongest in Neolithic and Anatolian farmers, and is remarkably well predicted by the coalescence rates between other genomes and a 10,000-year-old Anatolian individual. This suggests that the driver of this signal originated in ancestors of ancient Anatolia >14k years ago, but was already absent by the Mesolithic and may indicate a genetic link between the Near East and European hunter-gatherer groups in the Late Paleolithic.

Jura glacial lakes: a paleoclimatic and paleoenvironmental evolution since the Late Glacial Period.

<p>During the retreat of a Würm ice sheet, numerous glacial paleolakes took place in the Swiss and French Jura. Two sites were investigated: the Amburnex Valley site (Switzerland), which evolved in well-developed peatland and the Lake Val (France), which is still persisted as a lacustrine system. During the Late Glacial period, both sites were glacial lakes characterized by a significant accumulation of lacustrine sediments.</p><p>Using a multiproxy approach, this project aims to reconstruct the paleoclimatic and the paleoenvironmental evolution recorded in lacustrine sediments and peatbog deposits since the last 13’000 years.</p><p>The Amburnex core (7m) exhibit a basal morainic deposit from the Würm period, overlain by three meters of lacustrine deposits and four meters of peatland deposits. The Lake Val core (4.5m) consists of the same lithological succession.</p><p>A multiproxy approach based on palynological analyses, grain-size analyses, mineralogical analyses (XRD) and geochemical analyses (TOC, Nitrogen, Phosphorus and Mercury contents; major and trace elements; organic carbon isotopes) have been used to characterize the hydrological and climatic fluctuations, the trophic level and the origin of organic matter in order to reconstruct the paleoenvironmental and paleoclimatic evolution of this area.</p><p>In the Amburnex site, the Bølling-Allerød, the Younger Dryas and the beginning of the Preboreal period have been recognized by palynological analyses and confirmed by carbon 14 dating. During the Oldest Dryas, oligotrophic conditions took place as suggested by the very low concentrations in nitrogen and organic matter. Then, during the warmer Bølling period, an enrichment in total organic carbon (TOC) associated with a decrease in phosphorus content are observed, implying the development of eutrophic conditions and maybe phosphorus recycling. Later in the Allerød period, low TOC and phosphorus contents, associated with varved carbonate deposits, indicate a return to more oligotrophic conditions. New organic matter enrichments are observed in the interval corresponding to the colder Younger Dryas period. These trends are quite consistent with those observed in the Lake Val and reflect significant changes in runoff and nutrient inputs at least at regional scale.</p>

History of Vegetation of Ulyanovsk City and Its Surroundings

The vegetation evolution on the modern territory of the Ulyanovsk City and its surroundings, beginning from the late glacial period, can be presented as follows. 11,000– 10,300 years ago: a “tundra-steppe” with wormwood-mazy, horsetail, fern, shrubbygreen-green communities. 10,300–9,500 years ago: wormwood-haze-cenotic cenoses, isolated islets of sparse pine forests. 9,500–8,500 years ago: sagebrush-cerebral, cereal steppes and pine forests. 8,500–8,000 years ago: turf-grass, grass-meadow-grass meadow steppes and pine forests. 8,000–6,000 years ago: forbred-cereal, less often turfgrass meadow steppes, birch, and birch-pine forests, the appearance of deciduous species. 6,000–4,500 years ago: pine-broad-leaved, broad-leaved forests, mixed-grassgrass meadow steppes, and the maximum afforestation. 4,500–3,200 years ago: broadleaved, pine-broadleaf forests, and the appearance of agrocenoses. 3200–2500 years ago: pine, pine-birch forests, reduction of broad-leaved species, the expansion of turfgrass steppes and agrocenoses. 2,500–700 years ago: the emergence of secondary forests and meadow steppes (fescue, wormwood-cereal), the expansion of agrocenoses. 700–350 years ago: pine, pine-birch, pine-broadleaf forests, reduction of agrocenoses. 350 years ago till the present time: a sharp decline in forests, the predomination of secondary pine, broad-leaved, small-leaved, mixed forests and secondary meadow steppes, the expansion of agrocenoses and residential areas. Thus, the vegetation of the territory of the Ulyanovsk City and its environs since the late glacial period varied from the steppe one (11,000–8,000 years ago) to the forest-steppe one (8,000–700 years ago) and again to the steppe one (700 years ago – modern time). The least afforestation of the territory was observed from 11,000 to 9,500 years ago (3–4%) and from 350 years ago to the present (6–7%). The greatest afforestation of the forest-steppe was from 6,000 to 3,200 years ago, when the forest-to-steppe ratio was equal.