Pavel E. Tarasov

2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia

Crater Core The high-northern latitudes of the Arctic have an important influence on climate and constitute a region with a unique array of complex feedbacks that make it difficult to understand the workings of its climate. Melles et al. (p. 315, published online 21 June) developed a 2.8-million-year record of Arctic climate, using a sediment core from a lake in northeastern Russia that was formed more than 3.5 million years ago by a meteorite impact. Pronounced glacial episodes began 2.6 million years ago but did not achieve orbital pacing for another 700,000 years. A sediment core from a Russian lake provides a high-latitude climate record where prior terrestrial records have been sparse. The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El’gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous “super interglacials” during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ~4° to 5°C and ~300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity.

A complete terrestrial radiocarbon record for 11.2 to 52.8 kyr B.P

Dating Carbon Radiocarbon dating is the best way to determine the age of samples that contain carbon and that are younger than ∼50,000 years, the limit of precision for the method. There are several factors that complicate such age determinations, however, some of the most important of which include variability of the 14C production in the atmosphere (which affects organic samples whose radiocarbon inventories are derived from atmospheric CO2), surface ocean reservoir effects (which affect marine samples that acquire their radiocarbon signatures from seawater), and variable dead carbon fraction effects (which affect speleothems that derive their carbon from groundwaters). Bronk Ramsey et al. (p. 370; see the Perspective by Reimer) avoid the need to make such assumptions, reporting the 14C results of sediments from Lake Suigetsu, Japan. Analysis of terrestrial plant macrofossils in annually layered datable sediments yielded a direct record of atmospheric radiocarbon for the entire measurable interval up to 52.8 thousand years ago. Radiocarbon measurements of samples from Lake Suigetsu, Japan, extend the 14C time scale back to more than 50,000 years ago. Radiocarbon (14C) provides a way to date material that contains carbon with an age up to ~50,000 years and is also an important tracer of the global carbon cycle. However, the lack of a comprehensive record reflecting atmospheric 14C prior to 12.5 thousand years before the present (kyr B.P.) has limited the application of radiocarbon dating of samples from the Last Glacial period. Here, we report 14C results from Lake Suigetsu, Japan (35°35′N, 135°53′E), which provide a comprehensive record of terrestrial radiocarbon to the present limit of the 14C method. The time scale we present in this work allows direct comparison of Lake Suigetsu paleoclimatic data with other terrestrial climatic records and gives information on the connection between global atmospheric and regional marine radiocarbon levels.

Vegetation dynamics of Mongolia.

Introduction to Studies on the Vegetation of Mongolia. Natural and Anthropogenic Factors and the Dynamics of Vegetation Distribution in Mongolia. 1.1. Introduction. 1.2. Natural Features of Mongolia. 1.3. Landscape-Ecological Regions. 1.4. Landscape and Ecological Factors of Vegetation Dynamics. 1.5. Conclusion. Late Quaternary Vegetation History of Mongolia. 2.1. Introduction. 2.2. An Overview of Previous Studies. 2.3. Data Used in this Study. 2.4. Regional Pollen Records from Individual Sites. 2.5. Holocene Changes in the Distribution of Tree and Shrub Taxa in Mongolia. 2.6. Spatial Reconstruction and Mapping of Mongolian Vegetation during the Last 15,000 Years. 2.7. General Discussion and Conclusions. Assessing Present-Day Plant Cover Dynamics. 3.1. Introduction. Modern Methods for Studying and Monitoring Plant Cover. 3.2. Mountain Plant Community Dynamics. 3.3. Plant Community Dynamics in Plains and Rocky Areas. 3.4. Dynamics of Water-Associated Vegetation. 3.5. Conclusions. Analysis of Present-Day Vegetation Dynamics. 4.1. Basic Changes in Vegetation. 4.2. Regressive Plant Community Successions. 4.3. Progressive Plant Community Regeneration. 4.4. Mapping Vegetation Dynamics. 4.5. Conclusions. Strategies for Nature Management and Vegetation Conservation. 5.1. Introduction. Methods for Vegetation Conservation. 5.2. Restoration and Conservation of Botanical Successions. 5.3. Systems for the Conservation of Botanical Diversity. 5.4. Conclusions. Summary Conclusions and Recommendations. References. Appendix 1. Appendix 2. Index.

Climate in northern Eurasia 6000 years ago reconstructed from pollen data

Using a climatic calibration based on the scores of the plant functional types (PFTs) calculated for 1245 surface pollen spectra, the climate at 6 ka BP has been reconstructed for a set of 116 pollen spectra from the former Soviet Union and Mongolia. The results are presented as maps of climatic anomalies and maps of probability classes showing the significance of these differences from the modern climate. The reconstructed patterns are spatially coherent, but have confidence levels that vary from region to region, due to the often-large error ranges. At 6 ka, the winters were more than 2oC warmer than today north of 50oN, with a high significance east of the Urals. Summers were also more than 2oC warmer than today with a high level of confidence north of the Polar Circle and in central Mongolia. In the mid-latitudes of Siberia, in northern Kazakhstan and around the Black and the Caspian seas, 6 ka summers were significantly cooler than today. The reconstructed moisture availability (ratio of actual to equilibrium evapotranspiration) was more than 10% higher than today in the Ukraine, southern Russia and northern Mongolia, and more than 10% lower than today in central Mongolia. This pattern corresponds partly with that of the water budget (annual precipitation minus evaporation) reconstructed from lake level records.

A method to determine warm and cool steppe biomes from pollen data; application to the Mediterranean and Kazakhstan regions

An objective method for the assignment of pollen spectra to appropriate biomes has been published recently. The aim of this paper is to improve the distinction between warm and cool steppes, thus refining vegetation and climate reconstruction, particularly during the Last Glacial Maximum. A set of modern pollen spectra from the Mediterranean and Kazakhstan regions, dominated today by open vegetation types, has been analysed statistically in order to relate pollen taxa abundances to warm acid cool grass/shrub plant functional types (PFTs). A statistical test using modern pollen data shows that the method is able to distinguish between cool and warm steppe biomes with a high degree of confidence. The method has been applied to two fossil pollen records. The results of this exercise showed that cool steppe dominated in central Greece between 18 000 and 13 000 yr BP, while in western Iran the vegetation was at the boundary between cool and warm steppes. These vegetation types were replaced by warm mixed forest in Greece and warm steppe in Iran after that time span

Seasonally specific responses of the East Asian monsoon to deglacial climate changes

The deglacial meltwater pulse in the North Atlantic that induced the Younger Dryas event also prompted climate cooling in East Asian monsoon regions such as Japan and coastal mid-latitude China. However, very little is understood about the mechanism that can transmit changes in the North Atlantic to the Far East. Here we show that the shutdown of the North Atlantic thermohaline circulation brought about significantly lower temperatures and higher precipitation in the Japanese winter, whereas the change in the Japanese summer climate was considerably smaller. The cooling of the Siberian air mass seems to have caused an increased pressure gradient between Siberia and the West Pacific in winter, intensifying the winter monsoon. The Mongolian high-pressure system and the westerly jet stream played an important role in the teleconnection. In contrast, the warming at the onset of the late glacial interstadial (GI-1; Bolling-Allerod) in the West Pacific did not have season-specific features, implying that the principal driving mechanism of this warming event may lie in a pan-hemispheric or global factor, such as insolation changes.

Regulation of the monsoon climate by two different orbital rhythms and forcing mechanisms

The East Asian monsoon is responsible for transferring huge amounts of heat and moisture between the land and the adjacent ocean. Significant changes in its capacity to do this will have direct impacts on regional climatic gradients and global atmospheric circulation. Determining the mechanisms that force long-term variation in monsoon behavior is therefore important for understanding global climate change. Competing theories vary in the degree of importance attached to glacial forcing, other orbital rhythms, and internal feedback mechanisms as primary drivers of change. There is, however, no convincing explanation as to why different proxy records from closely neighboring regions are tuned to different orbital rhythms. Here we present quantitative climatic reconstructions for the past 450 k.y. based on a long pollen record from Lake Biwa in Japan. The data suggest that continental and oceanic air mass temperatures respond predominantly to the 100 k.y. orbital rhythm, whereas the land-ocean temperature gradient and monsoon vigor oscillate mainly at the 23 k.y. insolation cycle. We suggest that the mechanisms for this behavior lie in the differential response of land and ocean to solar forcing, and conclude that the 100 k.y. signal dominates monsoon intensity only when the amplitude of solar forcing falls below a threshold level.

Comparison of modeled and reconstructed changes in forest cover through the past 8000 years: Eurasian perspective

Reproducing the tree cover changes throughout the Holocene is a challenge for land surface–atmosphere models. Here, results of a transient Holocene simulation of the coupled climate–carbon cycle model, CLIMBER2-LPJ, driven by changes in orbital forcing, are compared with pollen data and pollen-based reconstructions for several regions of Eurasia in terms of changes in tree fraction. The decline in tree fraction in the high latitudes suggested by data and model simulations is driven by a decrease in summer temperature over the Holocene. The cooler and drier trend at the eastern side of the Eurasian continent, in Mongolia and China, also led to a decrease in tree cover in both model and data. In contrast, the Holocene trend towards a cooler climate in the continental interior (Kazakhstan) is accompanied by an increase in woody cover. There a relatively small reduction in precipitation was likely compensated by lower evapotranspiration in comparison to the monsoon-affected regions. In general the model-data comparison demonstrates that climate-driven changes during the Holocene result in a non-homogeneous pattern of tree cover change across the Eurasian continent. For the Eifel region in Germany, the model suggests a relatively moist and cool climate and dense tree cover. The Holzmaar pollen record agrees with the model for the intervals 8–3 ka and 1.7–1.3 ka BP, but suggests great reduction of the tree cover 3–2 ka and after 1.3 ka BP, when highly developed settlements and agriculture spread in the region.

Atlantic to Urals - The Holocene climatic record of Mid-latitude Europe

The mid-latitude belt of Europe, broadly between 45o and 65o N, is probably the most intensively studied area of the PEPIII transect, but providing a synthesis of Holocene climatic change over this large and varied area is not easy. Ocean and ice core records provide a background scale of change to what was happening on the continent, but the tremendous events of the last glacial in these records have tended to obscure the importance of Holocene fluctuations. Temperature variations in the order of 1-2°C may appear as minor variations in an ice core record but such changes had effects on glaciers, lakes, treelines and bogs, and on people. The direct effects on humanity are moderated by the adaptability of societies, but there must have been some impact, especially on farming. In this paper we outline firstly the nature of the records, including such issues as their spatial and temporal resolution and the clarity of the climatic signal. We attempt to answer the key questions posed in this part of the PEPIII Science Plan by highlighting the evidence from key sites with high quality proxy records, rather than attempting to synthesize a Europe-wide picture, which would be premature, and needs further refinement of site chronologies. The stratigraphy of European peat bogs was one of the first proxy climate records, and was used in sub-dividing the Holocene. Recent development of more quantified analyses has revived the usefulness of the peat archive, and it seems that periods of wetter bog surfaces are most probably a reflection of secular summer temperature declines, and therefore evapotranspiration, rather than the irregular and rapid changes that characterise the precipitation record. Significant wet shifts occur in western European bogs at around 8200 - 7800, 4400 - 4000, 2800 - 2200, 1400 - 1300, and 1100 - 1000 cal. BP. Where the upper peat still exists the two phases of the Little Ice Age are often very marked, between AD 1300 - 1500 and especially AD 1650 - 1800. Periodicities of c. 1100, 600 and 200 years have been recognised. These peat data constitute valuable lowland records of change, reacting sensitively to climatic forcing in a way that established forests did not. Key sites include Mongan Bog, Ireland; Bolton Fell Moss and Walton Moss, England, and Dosenmoor, Germany. Further east and south than the north German coast the records become less sensitive, only reacting to major climatic deteriorations. Lake sediment records are valuable data sources, especially where the sediments are laminated. Lake Holzmaar, in western Germany, has provided a multi-proxy calendar-year dated lacustrine record which can be compared both with other precisely-dated lakes and with other proxy data. For example, data from Bussjosjon, southern Sweden, compare well with Holzmaar, showing synchronous early Holocene changes, stabilisation of environmental conditions around 10,000 cal. BP, and later anthropogenic/climate-induced increases of erosional processes around 2700 cal. BP. However, at Holzmaar there is no response to the 8200 year event because the closed deciduous forests operated as a buffer precluding increased erosion and sediment transfer. The glaciers and forest vegetation of the European Alps have been the source of many studies of climatic change. At the onset of the Holocene most Alpine glaciers retreated to historical dimensions, and it has been suggested that in the Eastern Swiss Alps there were no glaciers between 9400 and 3300 BP. Neoglaciation began around 3300 BP, reaching its maximum extent during the Little Ice Age, and in all eight synchronous Alpine ice advances have been detected and interpreted as the result of a 1°C temperature depression having a 1000-year periodicity. These data agree very well with North Atlantic Ice Rafted Debris (IRD) events and with the Holzmaar sedimentation rate record. The timberline represents the major ecotone in the Alps that reacts to climatic change, and recent research has emphasised the need for well-dated sites using pollen and macrofossil analyses in combination, as well as comparisons with other proxies in the Alpine and sub-Alpine region, such as oxygen isotope analyses of ostracode valves and lake level changes. The 8200 cal. BP event is reflected in various proxy records from the Alpine region and treeline studies indicate that Holocene summer temperature fluctuations had an amplitude of between ±0.5 to 1°C. Mid-latitude Europe is well represented in the European Pollen Database, with the zone between 5W-60°E and 45-60°N being characterized by 300 sites, but the number of sites and the data quality varies between the western and eastern part of this zone - the region east of 25°E has only 10 to 20 poorly dated sites. Several quantitative reconstructions of Holocene climate have been made, deriving curves of mean July and January temperatures and annual precipitation, as well as a recent reconstruction of climate patterns at 6000 BP, but the problems of coverage and chronology limits our ability to do precise interregional correlations and to discuss short-term climate events. Speleothems provide well-dated, precise multi-proxy records. Building upon the results from key Atlantic sites in Norway, Ireland and Scotland, future research has great potential to elucidate climatic change on meridional transects and to answer key questions involving the eastern extent of the influence of the Atlantic Ocean. Similarly, tree ring archives represent valuable high frequency, calendar dated proxy climate records, but they are few in number across the mid-latitude transect. It is clear that changes in the Atlantic Ocean can be detected in the climate over the European landmass, both in individual events such as that at 8200 cal.BP, and in cycles of change that may reflect IRD events and changes in the thermohaline circulation. Increasingly we are recognising that changes in solar activity have also had an impact. The Medieval Warm Period and the Little Ice Age are well expressed and well dated in a number of different proxy records. Future research needs to move to linking high quality data from key sites through more precise time control, as well as refining and standardising methods, both tasks for the new ESF-HOLIVAR programme.

Lateglacial and early-Holocene environments of Novaya Zemlya and the Kara Sea Region of the Russian Arctic

Pollen and radiocarbon data from Novaya Zemlya and the Kara Sea Region suggest that the hypo thetical Panarctic Ice Sheet (Denton and Hughes, 1981) never existed in this area, at least during the last 16 000 years. Lateglacial tundra environments were slightly cooler and drier than the present ones, but there were also warmer intervals such as the Allerød, which were rather favourable for vegetation development. Better conditions existed during the early Holocene, when warm Atlantic air masses and sea currents gradually penetrated eastwards to the Kara Region.