Published by Copernicus Publications on behalf of the European Geosciences Union. 484M.-J. Gaillard et al.: Holocene land-cover reconstructions for studies on land cover-climate feedbacks Abstract. The major objectives of this paper are: (1) to review the pros and cons of the scenarios of past anthropogenic land cover change (ALCC) developed during the last ten years, (2) to discuss issues related to pollen-based reconstruction of the past land-cover and introduce a new method, REVEALS (Regional Estimates of VEgetation Abundance from Large Sites), to infer long-term records of past landcover from pollen data, (3) to present a new project (LAND-CLIM: LAND cover -CLIMate interactions in NW Europe during the Holocene) currently underway, and show preliminary results of REVEALS reconstructions of the regional land-cover in the Czech Republic for five selected time windows of the Holocene, and (4) to discuss the implications and future directions in climate and vegetation/land-cover modeling, and in the assessment of the effects of human-induced changes in land-cover on the regional climate through altered feedbacks. The existing ALCC scenarios show large discrepancies between them, and few cover time periods older than AD 800. When these scenarios are used to assess the impact of human land-use on climate, contrasting results are obtained. It emphasizes the need for methods such as the REVEALS model-based land-cover reconstructions. They might help to fine-tune descriptions of past landcover and lead to a better understanding of how long-term changes in ALCC might have influenced climate. The RE-VEALS model is demonstrated to provide better estimates of the regional vegetation/land-cover changes than the traditional use of pollen percentages. This will achieve a robust assessment of land cover at regional-to continental-spatial scale throughout the Holocene. We present maps of RE-VEALS estimates for the percentage cover of 10 plant functional types (PFTs) at 200 BP and 6000 BP, and of the two open-land PFTs "grassland" and "agricultural land" at five time-windows from 6000 BP to recent time. The LAND-CLIM results are expected to provide crucial data to reassess ALCC estimates for a better understanding of the land suface-atmosphere interactions.

The Earth's biota originated and developed to its current complex state through interacting with multilevel physical forcing of our planet's climate and near and outer space phenomena. In the present study, we focus on the time scale of hundreds to thousands of years in the most recent time interval-the Holocene. Using a pollen paleocommunity dataset from southern Lithuania (Čepkeliai bog) and applying spectral analysis techniques, we tested this record for the presence of statistically significant cyclicities, which can be observed in past solar activity. The time series of non-metric multidimensional scaling (NMDS) scores, which in our case are assumed to reflect temperature variations, and Tsallis entropy-related community compositional diversity estimates q* revealed the presence of cycles on several time scales. The most consistent periodicities are characterized by periods lasting between 201 and 240 years, which is very close to the DeVries solar cycles (208 years). A shorter-term periodicity of 176 years was detected in the NMDS scores that can be putatively linked to the subharmonics of the Gleissberg solar cycle. In addition, periodicities of ≈3,760 and ≈1,880 years were found in both parameters. These periodic patterns could be explained either as originating as a harmonic nonlinear response to precession forcing, or as resulting from the long-term solar activity quasicycles that were reported in previous studies of solar activity proxies. Solar activity patterns, which are mostly determined by the highly complicated magnetohydrodynamics in its interior, have a major influence on decadal to (at least) millennial variability in weather, climate and biota 1,2. The primary evidence for the persistence of cyclic variation in solar activity over short time periods comes from direct satellite multispectral and visible light observations using telescopes 2-4. Long-term observations of the Sun's activity, including cyclic patterns, are mostly determined through studying fluctuations in cosmogenic 10 Be isotopes and Δ 14 C isotopic ratios, whose production is regulated by the combined effects of the Earth's and the Sun's magnetic fields on low-to-moderate energy cosmic rays flux into the atmosphere 5,6. Recently, nitrate (NO 3 −) concentrations in Antarctic glacier ice was suggested as an additional direct index of solar activity 7. Analyses of these direct proxies, besides the very well-known 11-year cycles, have most frequently revealed the presence of so-called DeVries (~208-year) and Gleissberg (~80-to 90-year) cycles, as well as longer cycles that modulate shorter-term periodicities 8,9. The effects of solar forcing as determined from paleoclimatic and paleobiological proxies are multifaceted and variable in magnitude and effect type. Long-term solar activity was implicated in modulating the winter precipitation patterns, and thus the glacier expansion and contraction dynamics, during the Holocene in Alaska, northwest North America and the tropical Andes 10-13. Strong support for the existence of 11-year s...

No abstract

No abstract

A reconstructed pattern of Lateglacial and Holocene hydrological changes in the area of the former lakes Dūbas, Pelesa and Matara is presented. The investigated basin is situated in southeastern Lithuania, beyond the marginal ridge of the Weichselian Glaciation, on the margin of the sandy plain that is the watershed between the Ūla and Katra rivers. Pollen analysis, radiocarbon dating, loss-on-ignition measurements and GIS-based simulation of water level fluctuations have been applied in order to obtain new information on the development of the Ūla–Katra watershed area. The results of multiproxy investigations revealed the history of the development and extinction of Dūbas, Pelesa and Matara lakes. A single basin, covering a large part of the study area, had formed after the retreat of the continental ice sheet from southeastern Lithuania. This basin was divided into three separate lakes during the Allerød Interstadial as a result of a drop in water level. Blocking of the drainage by aeolian sediments around the early Boreal caused another rise in the water-table and the successive merging of the separate lakes. Probably as a result of river capture, the single lake was drained abruptly after c. 2000 years. Another river-capture event in the 19th century caused abrupt drainage of the study area, which led to the final extinction of the three lakes.