Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka bp

Recent global warming is pronounced in high-latitude regions (e.g. northern Asia), and will cause the vegetation to change. Future vegetation trends (e.g. the “arctic greening”) will feed back into atmospheric circulation and the global climate system. Understanding the nature and causes of past vegetation changes is important for predicting the composition and distribution of future vegetation communities. Fossil pollen records from 468 sites in northern and eastern Asia were biomised at selected times between 40 cal ka bp and today. Biomes were also simulated using a climate-driven biome model and results from the two approaches compared in order to help understand the mechanisms behind the observed vegetation changes. The consistent biome results inferred by both approaches reveal that long-term and broad-scale vegetation patterns reflect global to hemispheric-scale climate changes. Forest biomes increase around the beginning of the late deglaciation, become more widespread during the early and middle Holocene, and decrease in the late Holocene in fringe areas of the Asian Summer Monsoon. At the southern and southwestern margins of the taiga, forest increases in the early Holocene and shows notable species succession, which may have been caused by winter warming at ca. 7 cal ka bp. At the northeastern taiga margin (central Yakutia and northeastern Siberia), shrub expansion during the last deglaciation appears to prevent the permafrost from thawing and hinders the northward expansion of evergreen needle-leaved species until ca. 7 cal ka bp. The vegetation climate disequilibrium during the early Holocene in the taiga-tundra transition zone suggests that projected climate warming will not cause a northward expansion of evergreen needle-leaved species

Measurement of the photon beam asymmetry in γ⃗p→K+Σ0 at Eγ = 8.5 GeV

We report measurements of the photon beam asymmetry Σ for the reaction γ⃗p→K+Σ0 (1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected by using a linearly polarized photon beam in the energy range of 8.2–8.8 GeV incident on a liquid hydrogen target. The beam asymmetry Σ was measured as a function of the Mandelstam variable t , and a single value of Σ was extracted for events produced in the u channel. These are the first exclusive measurements of the photon beam asymmetry Σ for the reaction in this energy range. For the t channel, the measured beam asymmetry is close to unity over the t range studied, − t = ( 0.1 – 1.4 ) ( GeV / c ) 2 , with an average value of Σ = 1.00 ± 0.05 . This agrees with theoretical models that describe the reaction via the natural-parity exchange of the K ∗ (892) Regge trajectory. A value of Σ = 0.41 ± 0.09 is obtained for the u channel integrated up to − u = 2.0 ( GeV / c ) 2

A late Quaternary pollen dataset from eastern continental Asia for vegetation and climate reconstructions: Set up and evaluation

A total of 271 pollen records were selected from a large collection of both raw and digitized pollen spectra from eastern continental Asia (70°−135°E and 18°−55°N). Following pollen percentage recalculations, taxonomic homogenization, and age–depth model revision, the pollen spectra were interpolated at a 500-year resolution and a taxonomically harmonized and temporally standardized fossil pollen dataset established with 226 pollen taxa, covering the last 22 cal ka. Of the 271 pollen records, 85% were published since 1990, with reliable chronologies and high temporal resolutions; of these, 50% have raw data with complete pollen assemblages, ensuring the quality of this dataset. The pollen records available for each 500-year time slice are well distributed over all main vegetation types and climatic zones of the study area, making their pollen spectra suitable for paleovegetation and paleoclimate research. Such a dataset can be used as an example for the development of similar datasets for other regions of the world

Last Glacial Maximum climate of the former Soviet Union and Mongolia reconstructed from pollen and plant macrofossil data

International audienceAn improved concept of the best analogues method was used to reconstruct the Last Glacial Maximum (LGM) climate from a set of botanical records from the former Soviet Union and Mongolia. Terrestrial pollen and macrofossil taxa were grouped into broad classes - plant functional types (PFTs), defined by the ecological and climatic parameters used in the BIOME1 model. PFT scores were then calibrated in terms of modern climate using 1245 surface pollen spectra from Eurasia and North America. In contrast to individual taxa, which exhibit great variability and may not be present in the palaeoassemblages, even in suitable climates, PFTs are more characteristic of the vegetation types. The modified method thus allows climate reconstruction at time intervals with partial direct analogues of modern vegetation (e.g. the LGM). At 18 kBP, mean temperatures were 20-29 degrees C colder than today in winter and 5-11 degrees C colder in summer in European Russia and Ukraine. Sites from western Georgia show negative, but moderate temperature anomalies compared to today: 8-11 degrees C in January and 5-7 degrees C in July. LGM winters were 7-15 degrees C colder and summers were 1-7 degrees C colder in Siberia and Mongolia. Annual precipitation sums were 50-750 mm lower than today across northern Eurasia, suggesting a weakening of the Atlantic and Pacific influences. Reconstructed drought index shows much drier LGM conditions in northern and mid-latitude Russia, but similar to or slightly wetter than today around the Black Sea and in Mongolia, suggesting compensation of precipitation losses by lower-than-present evaporation

Palaeovegetation in China during the late Quaternary: Biome reconstructions based on a global scheme of plant functional types

Two previous reconstructions of palaeovegetation across the whole of China were performed using a simple classification of plant functional types (PFTs). Now a more explicit, global PFT classification scheme has been developed, and a substantial number of additional pollen records have become available. Here we apply the global scheme of PFTs to a comprehensive set of pollen records available from China to test the applicability of the global scheme of PFTs in China, and to obtain a well-founded reconstruction of changing palaeovegetation patterns. A total of 806 pollen surface samples, 188 mid-Holocene (MH, 6000 14C yr BP) and 50 last glacial maximum (LGM, 18,000 14C yr BP) pollen records were used to reconstruct vegetation patterns in China, based on a new global classification system of PFTs and a standard numerical technique for biome assignment (biomization). The biome reconstruction based on pollen surface samples showed convincing agreement with present potential natural vegetation. Coherent patterns of change in biome distribution between MH, LGM and present are observed. In the MH, cold and cool-temperate evergreen needleleaf forests and mixed forests, temperate deciduous broadleaf forest, and warm-temperate evergreen broadleaf and mixed forest in eastern China were shifted northward by 200–500 km. Cold-deciduous forest in northeastern China was replaced by cold evergreen needleleaf forest while in central northern China, cold-deciduous forest was present at some sites now occupied by temperate grassland and desert. The forest–grassland boundary was 200–300 km west of its present position. Temperate xerophytic shrubland, temperate grassland and desert covered a large area on the Tibetan Plateau, but the area of tundra was reduced. Treeline was 300–500 m higher than present in Tibet. These changes imply generally warmer winters, longer growing seasons and more precipitation during the MH. Westward shifts of the forest–shrubland–grassland and grassland–desert boundaries imply greater moisture availability in the MH, consistent with a stronger summer monsoon. During the LGM, in contrast, cold-deciduous forest, cool-temperate evergreen needleleaf forest, cool mixed forests, warm-temperate evergreen broadleaf and mixed forest in eastern China were displaced to the south by 300–1000 km, while temperate deciduous broadleaf forest, pure warm-temperate evergreen forest, tropical semi-evergreen and evergreen broadleaf forests were restricted or absent from the mainland of southern China, implying colder winters than present. Strong shifts of temperate xerophytic shrubland, temperate grassland and desert to the south and east in northern and western China and on the Tibetan Plateau imply drier conditions than present

Transient simulation of the last glacial inception. Part II: Sensitivity and feedback analysis

The sensitivity of the last glacial-inception (around 115 kyr BP, 115,000 years before present) to different feedback mechanisms has been analysed by using the Earth system model of intermediate complexity CLIMBER-2. CLIMBER-2 includes dynamic modules of the atmosphere, ocean, terrestrial biosphere and inland ice, the last of which was added recently by utilising the three-dimensonal polythermal ice-sheet model SICOPOLIS. We performed a set of transient experiments starting at the middle of the Eemiam interglacial and ran the model for 26,000 years with time-dependent orbital forcing and observed changes in atmospheric CO2 concentration (CO2 forcing). The role of vegetation and ocean feedback, CO2 forcing, mineral dust, thermohaline circulation and orbital insolation were closely investigated. In our model, glacial inception, as a bifurcation in the climate system, appears in nearly all sensitivity runs including a run with constant atmospheric CO2 concentration of 280 ppmv, a typical interglacial value, and simulations with prescribed present-day sea-surface temperatures or vegetation cover—although the rate of the growth of ice-sheets growth is smaller than in the case of the fully interactive model. Only if we run the fully interactive model with constant present-day insolation and apply present-day CO2 forcing does no glacial inception appear at all. This implies that, within our model, the orbital forcing alone is sufficient to trigger the interglacial–glacial transition, while vegetation, ocean and atmospheric CO2 concentration only provide additional, although important, positive feedbacks. In addition, we found that possible reorganisations of the thermohaline circulation influence the distribution of inland ic

Last glacial maximum biomes reconstructed from pollen and plant macrofossil data from northern Eurasia

International audiencePollen and plant macrofossil data from northern Eurasia were used to reconstruct the vegetation of the last glacial maximum (LGM: 18,000 +/- 2000 C-14 yr BP) using an objective quantitative method for interpreting pollen data in terms of the biomes they represent (Prentice Et al., 1996). The results confirm previous qualitative vegetation reconstructions at the LGM but provide a more comprehensive analysis of the data. Tundra dominated a large area of northern Eurasia (north of 57 degreesN) to the west, south and east of the Scandinavian ice sheet at the LGM. Steppe-like vegetation was reconstructed in the latitudinal band from western Ukraine, where temperate deciduous forests grow today, to western Siberia, where taiga and cold deciduous forests grow today. The reconstruction shows that steppe graded into tundra in Siberia, which is not the case today. Taiga grew on the northern coast of the Sea of Azov, about 1500 km south of its present limit in European Russia. In contrast, taiga was reconstructed only slightly south of its southern limit today in south-western Siberia. Broadleaved trees were confined to small refuges, e.g. on the eastern coast of the Black Sea, where cool mixed forest was reconstructed from the LGM data. Cool conifer forests in western Georgia were reconstructed as growing more than 1000 m lower than they grow today. The few scattered sites with LGM data from the Tien-Shan Mountains and from northern Mongolia yielded biome reconstructions of steppe and taiga, which are the biomes growing there today