The north-south migration of prevailing westerly system shapes the seasonality of modern precipitation in Arid Central Asia (ACA). The temperate continental climate with warm-season precipitation ...dominates the northern ACA and the Mediterranean climate with cold-season precipitation dominates the southern ACA. However, the north-south contrasts of precipitation/moisture for longer time scales remain unknown. In this study, we quantitatively reconstructed the precipitation sequence covering the past ~14.4 cal. kyr BP based on pollen data obtained from Shayan loess section in southern ACA using MAT (Modern Analogue Technique) method. Our reconstruction shows that the precipitation had an increasing trend from ~14.4 to ~8.2 cal. kyr BP and a decreasing trend from ~8.2 to ~1.5 cal. kyr BP with the past 1500 years being characterized by an averagely high precipitation. The precipitation trend in southern ACA was rather different from that in northern ACA where the precipitation has increased more or less constantly since the late deglaciation. The contrast between southern and northern ACA appears to have been associated with the south-north migration of westerlies that was accompanied with alterations of NAO (North Atlantic Oscillation) phases and also with changes in strengths of Siberian High and ENSO (El Nino-southern Oscillation).
•Pollen-based precipitation since ~14.4 cal. kyr BP was reconstructed using MAT method in southern ACA .•Last-deglacial precipitation trend in southern ACA was different from that in northern ACA.•Contrast between southern and northern ACA is associated with the westerlies, NAO phases, Siberian High and ENSO.
Based on 74 fossil pollen records and relative pollen productivity estimates for 29 plant taxa, we produced a quantitative reconstruction of regional vegetation change in North China over the past ...6,000 years, using the combined MAT-REVEALS approach. The results include the spatial dynamics of the five main land cover types (Pinus, coniferous trees excluding Pinus, deciduous trees, grassland and bare ground) for three time slices: 6 ka, 3 ka and 0.05 ka. From 6 ka to the present, the total vegetation cover decreased from 64% to 61% (i.e., bare ground increased from 36% to 39%), mainly because of decreases in the cover of deciduous trees (from 19% to 14%). At the same time, the cover of coniferous trees increased (from 10% to 14%), and that of herb plants was largely unchanged (from 34% to 33%). The vegetation cover was greater at high latitudes and altitudes than at lower latitudes and in lowland areas. On the regional scale, temperate coniferous forest with Larix and Betula was dominant in the Greater Khingan Mountains, while in the Changbai Mountains, deciduous forest (decreasing from 72% to 56%) gradually transitioned to coniferous-deciduous mixed forest (Pinus and coniferous trees increased from 1% to 18%). The deciduous forest was dominated by Quercus, Betula and Pinus and occurred mainly in the warm temperate mountains of North China, where the vegetation cover was relatively high before 3 ka (>70%), before decreasing substantially to 55% at 0.05 ka. Grassland with Artemisia and Poaceae was the main land cover type in the North China Plain and in the temperate steppe region where forest vegetation was relatively sparse. The spatial dynamics of the land cover types appear to have been affected by climate change; climatic cooling in the second half of the Holocene led to the southward migration of coniferous trees. At the same time, human activities were likely the cause of the reduction of the regional vegetation cover, especially the tree cover.
Climate, fire, and human activities strongly affected the development of vegetation communities during the Holocene, yet the relative importance of these individual factors remains unclear in many ...areas. This paper presents new multi-proxy records of environmental change for the Meshchera Lowlands (the central part of the East European Plain) during the Holocene. Changes in regional vegetation during the Mid- and Late Holocene were influenced by climate, fire regime and human impact, as indicated by pollen, plant macrofossil, charcoal and testate amoebae analysis from several peat cores, along with reconstruction of tree cover from pollen assemblages. Since 8500calyrBP, the vegetation history represented a series of consecutive phases of birch, birch-pine and pine-broadleaf forests, with introduction of spruce after 2500calyrBP. Maximal abundance of broadleaf tree species was detected from 4700 to 2000calyrBP. Vegetation dynamics were strongly influenced by human activity since 1400calyrBP. High fire frequency was recorded for the periods 8500–4500calyrBP and 3500–2000calyrBP, when the fire return interval varied from 40 to 80years. Since 2000calyrBP, the fire return period exceeded 500years suggesting a significant decline in fire frequency during the last two millennia.
•New data on the paleoenvironmental changes in the central European Russia are presented.•The first reconstructions of the Holocene fire frequencies in the Meshchera Lowlands•The Mid- and Late Holocene vegetation changes were mainly influenced by climate changes and fire regime.•Vegetation dynamics were strongly influenced by human activity since 1400calyrBP.•The fire frequencies was high during 8500–5000calyrBP and 3000–2000calyrBP and reduced during the last 2000calyrBP.
•Modern pollen assemblage data from South Korea reflected regional vegetation.•Reconstructed Tann may be influenced by KC intensity and the EAWM.•Reconstructed Pann is influenced by the EASM, ITCZ, ...and ENSO.•Centennial-scale oscillation indicated climate events in the southern South Korea.
The occurrence of extreme weather events in response to climate change has become a global concern. To prepare for the intensifying climate crisis, it is imperative to comprehend past extreme climate fluctuations, control factors, and triggers. In this study, we conducted a pollen-based quantitative reconstruction of the Northeast Asia paleohydroclimate. We collected 387 surface soil samples from 89 mountains in South Korea to produce a modern pollen assemblage dataset. As the dataset indicated that pollen samples from South Korea reflected the regional vegetation well, we applied a weighted modern pollen analogue technique to quantitatively reconstruct the mean annual temperature (Tann), annual precipitation (Pann), and summer precipitation (Psum) in the Gwangyang area. The reconstructed Tann increased by ca. 4000 cal BP and gradually decreased thereafter. Long-term Tann trends in the Gwangyang area, along the East Asian continental and Northwestern Pacific margins, appear to have been influenced by oceanic climate conditions, particularly the Kuroshio Current, whereas short-term trends were significantly correlated with the continental climate, the East Asian winter monsoon, and Bond events. Pann and Psum have gradually decreased during the Holocene, which is consistent with the induction of the East Asian summer monsoon by a northward shift of the Intertropical Convergence Zone. After ca. 5000 cal yr BP, the decrease in Pann slowed in association with strong typhoon activity of the El Niño–Southern Oscillation. Analysis of hydroclimate proxy data from southern South Korea revealed wet events at ca. 8900, 7800, 5900, 4500, 3200, 1900, and 1300 cal yr BP, and dry events at ca. 9300, 8200, 6200, 5200, 2800, 2200, and 1400 cal yr BP. Notably, we also confirmed the occurrence of a flooding event in southern South Korea at ca. 8900 cal yr BP.
Aim Our aims were to provide new pollen data for establishing a sub-continental surface pollen database (East Asian Pollen Database, EAPD) and to study relationships between vegetation and climate. ...Location The sample sites covered most regions of East Asia, including China, Mongolia, the Russian Far East, Vietnam, Cambodia and Thailand. Methods Data quality control procedures were applied, including taxonomic standardization, removal of duplicates, and adjustment of geographical coordinates. Vegetation types and climate parameters were assigned to each sample. Modern pollen distribution maps were drawn using circle scattergrams. The plots of pollen percentages versus climate variables allowed quantitative estimates of climate values. The modern analogue technique (MAT) was used to predict modern biomes and climate parameters. Results Pollen assemblages extracted from 2858 sites were used to model the geographical distribution of selected taxa and their relationships with climate. For most taxa, the reconstructed range fitted the observed geographical distribution rather well. Arboreal pollen (AP) and Pinus dominated the transition zone between forest and steppe. Use of the MAT revealed that the predicted and observed biomes matched in 71% of the cases. The warm temperate evergreen broadleaf forest had the best agreement between predictions and observations. Climate values reconstructed using MAT were highly correlated with observed values in January temperature. The correlation coefficient of the temperature variables ranged from 0.799 to 0.930 and was as high as 0.939 for precipitation. Main conclusions This paper documents a new modern pollen database for East Asia and makes the data readily available. The reconstructed biomes and climate variables are significantly correlated with the observed values, thus demonstrating the utility of the pollen database for future multiscale palaeoenvironmental studies.
To test the performance of dinoflagellate cyst based palaeoenvironmental reconstructions derived via the modern analogue technique (MAT) and a non-quantitative method, we have compared, ...reconstructions of mixed layer temperature, sea surface temperature and mixed layer salinity of a well dated site from the Gulf of Taranto, to instrumental data of air temperature, precipitation and river discharge. Two hypotheses are tested: the reconstructions of dinoflagellate cyst based MAT improve when a) a local reference dataset rather than an extra-regional reference dataset is used, b) the reference and downcore datasets are corrected for species specific preservation prior to analysis. This is achieved by executing four experiments based on different reference datasets 1) a North Atlantic dataset including all species, 2) a North Atlantic dataset including degradation resistant species, 3) a Mediterranean dataset including all species, 4) a Mediterranean dataset including degradation resistant species only.
We show that MAT based reconstructions improve when a local rather than an extra-regional reference dataset is used. Exclusively including species resistant to degradation improves the reconstruction if an extra-regional reference dataset is used, but leads to considerable loss of variability if the local reference dataset is used.
Both MAT-based and qualitative reconstructions correlate to instrumental data for industrial times. For pre-industrial times, MAT reconstructions of variability in temperature and salinity do not co-vary with variability in the instrumental data, whereas qualitative reconstructions provide a relatively good fit. We suggest this to be a result of the anthropogenic influence on coastal marine ecosystems existing today at the majority of the coastal sample sites in the reference dataset. As a result, conditions at these sites do not correspond to pre-industrial conditions. We advise users of dinoflagellate cyst transfer functions to pay more attention to this aspect.
•Regional reference data based MAT reconstructions are better than global based.•Excluding degradable species leads to loss of variability in the reconstructions.•MAT and qualitative reconstructions co-vary to instrumental data for industrial times.•MAT reconstructions do not co-vary to instrumental data for pre-industrial times.Coastal reference dataset samples do not represent pre-industrial conditions.
The Quaternary is well known for being a period of the geological record that saw significant and alternating climatic fluctuations. Here, we concentrate on the last 94 millennia that saw Australia ...and its surrounding seas undergo significant environmental changes. Importantly also it is during that this period of time includes the arrival and settlement of humans in Australia.
Following on from Marine Isotopic Stage 4 (MIS4) that saw, over the period of 71-59 ka BP, a significant eustatic sea level drop (∼100 m), low sea-surface temperatures as well as glacial conditions on land, Australia experienced wet conditions again, but eventually progressively entered into a glacial phase. By then, humans had arrived on this large continent and later the megafauna progressively became extinct. This paper describes in detail the climate over this period, based principally on the high-resolution record of two marine sediment cores located offshore of the southern Australian margin, and that are then compared with known events on land as well as other deep-sea cores. Particular emphasis is placed on the period that spans the Last Glacial Maximum (LGM), the extent of which thus far had been poorly defined in the Australian region. Emphasis is placed on the period from 34 to 14 ka to demonstrate that (1) the LGM, defined here as the period 24 to 18 ka, was not always extremely dry and cold, and (2) that people were able to live in inland Australia as water existed in places, despite generally cold conditions. We also show using a series of ten maps - at 2 ka intervals over the 34-14 ka period - the waxing and waning of oceanic fronts such as the Subtropical and Subantarctic Fronts, link sea-surface temperatures (SST) with periods of glacial expansion in the Australian Alps and Tasmania, as well as the South Island of New Zealand, and the extent of the Leeuwin Current down to south of Australia.
Aeolian dust was transported at sea over the main core site from ∼26 to 18 ka period, pointing to arid conditions in Australia, but this period was punctuated by two significant reductions in dust transport to both core sites, coinciding with a retreat of the Subantarctic Front away from the Australian southern coastline, and slight SST shifts for a few centuries at ∼24 and 22-21 ka BP. At the peak of the cold phase, from 23 to 18.4 ka, summer SST were of the order of 9 °C below that experienced during the middle of the Holocene at about 6 ka BP. A similar temperature drop was also experienced offshore the northwestern corner of Western Australia. Periglacial activity dates for the Australian mainland and Tasmania pool around ∼22 ka. On either side of the 24 ka event, the chain of lakes in the Willandra Lakes retained water and human activity was registered in the area. Elsewhere in Australia, water was present to sustain human populations during the cold and dry times. It is postulated here that northern Australia was at times quite wet, especially during MIS4.
The cessation of the LGM is set on 18.4 ka from offshore southern Australia as confirmed for the deep-sea cores by several proxies, and more likely at 18 ka inland. Finally, we document that it took two millennia for “glacial” conditions to end in the Australian region as registered in our deep-sea core records, well after the lowest global sea level ∼20.6 and 20 ka, respectively, started to rise.
There is also evidence of another very cold period determined on the Australian mainland, Tasmania and the South Island of New Zealand centred around 27 ka, after which time warmer conditions occurred before the start of the LGM. This is matched with our deep-sea records with very cold conditions and changes in oceanographic conditions.
•2 deep-sea cores provide information on the waxing and waning of oceanic fronts south of Australia.•The Last Glacial Maximum for the Australian region spans 24-18 ka.•10 maps detail conditions in the Australian region spaning the period 34–14 ka.•Environmental conditions for MIS2 & MIS4 are compared in great detail in the cores.•Australia was arid and cold during the LGM but there was water to support human occupation.
Dinocysts occur in a wide range of environmental conditions, including polar areas. We review here their use for the reconstruction of paleo sea ice cover in such environments. In the Arctic Ocean ...and subarctic seas characterized by dense sea ice cover, Islandinium minutum, Islandinium? cezare, Echinidinium karaense, Polykrikos sp. var. Arctic, Spiniferites elongatus–frigidus and Impagidinium pallidum are common and often occur with more cosmopolitan taxa such as Operculodinium centrocarpum sensu Wall & Dale, cyst of Pentapharsodinium dalei and Brigantedinium spp. Canonical correspondence analyses conducted on dinocyst assemblages illustrate relationships with sea surface parameters such as salinity, temperature, and sea ice cover. The application of the modern analogue technique permits quantitative reconstruction of past sea ice cover, which is expressed in terms of seasonal extent of sea ice cover (months per year with more than 50% of sea ice concentration) or mean annual sea ice concentration (in tenths). The accuracy of reconstructions or root mean square error of prediction (RMSEP) is ±1.1 over 10, which corresponds to perennial sea ice. Such an error is close to the interannual variability (standard deviation) of observed sea ice cover. Mismatch between the time interval of instrumental data used as reference (1953–2000) and the time interval represented by dinocyst populations in surface sediment samples, which may cover decades if not centuries, is another source of error. Despite uncertainties, dinocyst assemblages are useful for making quantitative reconstruction of seasonal sea ice cover.
•A novel strategy proposed to reconstruct the regional land-cover from pollen data.•The cover of bare ground was reconstructed as the main land cover type.•Actual plant cover and bare ground were ...reconstructed first-time using pollen data.•Fossil pollen percentages differ significantly from the reconstructed plant cover.
Fossil pollen data are essential for reconstructing ancient vegetation and land-cover changes. Sugita’s REVEALS model is the best method to estimate regional plant cover (in percentage cover) using pollen data from lakes. Such reconstructions imply that the sum of all plants’ cover is 100%. However, land cover is not always represented by vegetation alone, the area of bare ground can be significant in many types of biomes, e.g., in alpine or steppe regions. Here we define “total land cover” as the sum of vegetation cover (VegC) and bare ground (BareC). In this study, we use the relationship between tree pollen percentages and both tree cover (TreeC) and VegC (=TreeC + herb cover (HerbC)) based on a dataset of modern pollen assemblages and related total land cover. This relationship is applied to estimate past “actual” vegetation cover (a-VegC) from fossil pollen percentages using the Modern Analogue Technique (MAT). The REVEALS (RV) model can then be applied to the same fossil pollen records to estimate regional cover of individual plant taxa (RV PlantC; e.g., RV PinusC, etc.), total tree cover (RV-TreeC) and total herb cover (RV-HerbC). These cover values can then be converted into RV a-PlantC, RV a-TreeC and RV a-HerbC using the MAT-reconstructed a-VegC (e.g., RV PinusC × MAT a-VegC = RV a-PinusC; RV-TreeC × MAT a-VegC = RV a-TreeC, etc.). The results of leave-one-out cross-validation indicates that the MAT reconstructions using the modern pollen assemblages provide values of a-TreeC, a-HerbC and BareC mostly very similar to the modern vegetation data. We further tested the method using pollen assemblages from lake surface sediments of 11 lakes and the results also suggest a good performance of MAT-based reconstruction. We then applied the proposed method (MAT-REVEALS) to four Holocene pollen records available from the study area to evaluate the feasibility of the strategy to reconstruct past actual plant cover. The results suggest that the method provides plausible estimates of vegetation cover for the sub-regions within the study area. The results from Lake Daihai over the last 10,000 years BP are interpreted and discussed in more details to evaluate the effects of possible departures from the approach assumptions.
We present a calibration-set based on modern pollen and satellite-based Advanced Very High Resolution Radiometer (AVHRR) observations of woody cover (including needleleaved, broadleaved and total ...tree cover) in eastern continental Asia, which shows good performance under cross-validation with the modern analogue technique (all the coefficients of determination between observed and predicted values are greater than 0.65). The calibration-set is used to reconstruct woody cover from a taxonomically harmonized and temporally standardized fossil pollen dataset (including 274 cores) with 500-year resolution over the last 22 kyr. The spatial range of forest has not noticeably changed in eastern continental Asia during the last 22 kyr, although woody cover has, especially at the margin of the eastern Tibetan Plateau and in the forest-steppe transition area of north-central China. Vegetation was sparse during the LGM in the present forested regions, but woody cover increased markedly at the beginning of the Bølling/Allerød period (B/A; ca. 14.5 ka bp) and again at the beginning of the Holocene (ca. 11.5 ka bp), and is related to the enhanced strength of the East Asian Summer Monsoon. Forest flourished in the mid-Holocene (ca. 8 ka bp) possibly due to favourable climatic conditions. In contrast, cover was stable in southern China (high cover) and arid central Asia (very low cover) throughout the investigated period. Forest cover increased in the north-eastern part of China during the Holocene. Comparisons of these regional pollen-based results with simulated forest cover from runs of a global climate model (for 9, 6 and 0 ka bp (ECHAM5/JSBACH ∼1.125° spatial resolution)) reveal many similarities in temporal change. The Holocene woody cover history of eastern continental Asia is different from that of other regions, likely controlled by different climatic variables, i.e. moisture in eastern continental Asia; temperature in northern Eurasia and North America.
•A calibration-set for pollen and forest cover from China and Mongolia is introduced.•Forest cover changes show strong regional peculiarities in eastern continental Asia.•Forest cover has significantly changed in the forest-steppe transition areas.
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