The 8.2 ka event and early-mid Holocene forest, fires, and flooding in the Central Ebro Desert, NE Spain

The impact of the 8.2 ka cooling event during the Early–Mid Holocene has not been widely observed in Southern Europe, which in contrast to Northern Europe, was already experiencing a cooler than present climate at this time. Multi-proxy analysis of sediment cores from two closed-basin saline lakes in the Central Ebro Desert (NE Spain) has allowed us to investigate the impact of climatic changes around the time of this event in more detail. Long-term changes in climate between the Early and Mid Holocene indicate a shift in winter to a more positive NAO, resulting in declining lake levels in one lake sensitive to winter groundwater recharge, and cooler winter temperatures reconstructed from pollen–climate analysis. Reconstructed summer temperatures also declined over this period while annual precipitation and forest cover increased, interpreted as a result of enhanced convection-driven summer precipitation association with a northward displacement of the sub-tropical high pressure. Around 8.2 ka, a marked increase in fire frequency is shown between ca 8.8 and 8.0 ka BP, along with an expansion of fire-tolerant evergreen oak and peak in water levels in a second storm run-off fed lake. A maximum in fire intensity occurred with the deposition of a charcoal layer at both lake sites dated to 8150±130 and 8285±135 cal BP, respectively. The increase in fire is largely attributed to a temporary return southward of the summer sub-tropical high pressure over the Mediterranean, which not only increased summer aridity, but also caused a contradictory regional warming before Hemispheric cooling set in.

The climate of Europe during the Holocene: a gridded pollen-based reconstruction and its multi-proxy evaluation

Pamela Collins, Basil Andrew Stansfield Davis, Jed Oliver Kaplan

We present a new gridded climate reconstruction for Europe for the last 12,000 years based on pollen data. The reconstruction is an update of Davis et al. (2003) using the same methodology, but with a greatly expanded fossil and surface-sample dataset and more rigorous quality-control. The modern pollen dataset has been increased by more than 80%, and the fossil pollen dataset by more than 50%, representing almost 60,000 individual pollen samples. The climate parameters reconstructed include summer/winter and annual temperatures and precipitation, as well as a measure of moisture balance, and growing degree-days above 5 degrees C. Confidence limits were established for the reconstruction based on transfer function and interpolation uncertainties. The reconstruction takes account of post-glacial isostatic readjustment which resulted in a potential warming bias of up to +1-2 degrees C for parts of Fennoscandia in the early Holocene, as well as changes in palaeogeography resulting from decaying ice sheets and rising post-glacial sea-levels. This new dataset has been evaluated against previously published independent quantitative climate reconstructions from a variety of archives on a site-by-site basis across Europe. The results of this comparison are generally very good; only chironomid-based reconstructions showed substantial differences with our values. Our reconstruction is available for download as gridded maps throughout the Holocene on a 1000-year time-step. The gridded format makes our reconstructions suitable for comparison with climate model output and for other applications such as vegetation and land-use modelling. Our new climate reconstruction suggests that warming in Europe during the mid-Holocene was greater in winter than in summer, an apparent paradox that is not consistent with current climate model simulations and traditional interpretations of Milankovitch theory. (C) 2015 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2015

Holocene climate, environment and cultural change in the circum-Mediterranean region

Basil Andrew Stansfield Davis

This book provides a major synthesis of evidence for past climate variability at the regional and continental scale across Europe and Africa. It focuses on two complementary time-scales, the Holocene (approximately the last 11,500 years) and the last glacial-interglacial cycle (approximately the last 130,000 years). An overview of the climate system of the past has never been attempted before on this scale, and, as such, the volume represents a benchmark for future research. It is written by an expert group of climate change scientists and presents an insight into past climate variability that challenges climatologists who seek to explain climate dynamics of the past and provides climate modellers with a work of reference for data-model comparison. The book is an advanced but very readable text essential for all students and scientists interested in global environmental change.

Springer2004

Climate change and Arctic ecosystems: 2. Modeling, paleodata-model comparisons, and future projections

Jed Oliver Kaplan

Large variations in the composition, structure, and function of Arctic ecosystems are determined by climatic gradients, especially of growing-season warmth, soil moisture, and snow cover. A unified circumpolar classification recognizing five types of tundra was developed. The geographic distributions of vegetation types north of 55degreesN, including the position of the forest limit and the distributions of the tundra types, could be predicted from climatology using a small set of plant functional types embedded in the biogeochemistry-biogeography model BIOME4. Several palaeoclimate simulations for the last glacial maximum (LGM) and mid-Holocene were used to explore the possibility of simulating past vegetation patterns, which are independently known based on pollen data. The broad outlines of observed changes in vegetation were captured. LGM simulations showed the major reduction of forest, the great extension of graminoid and forb tundra, and the restriction of low- and high-shrub tundra (although not all models produced sufficiently dry conditions to mimic the full observed change). Mid-Holocene simulations reproduced the contrast between northward forest extension in western and central Siberia and stability of the forest limit in Beringia. Projection of the effect of a continued exponential increase in atmospheric CO2 concentration, based on a transient ocean-atmosphere simulation including sulfate aerosol effects, suggests a potential for larger changes in Arctic ecosystems during the 21st century than have occurred between mid-Holocene and present. Simulated physiological effects of the CO2 increase (to >700 ppm) at high latitudes were slight compared with the effects of the change in climate.

2003

The climate of Europe during the Holocene: a gridded pollen-based reconstruction and its multi-proxy evaluation

Pamela Collins, Basil Andrew Stansfield Davis, Jed Oliver Kaplan

Pergamon-Elsevier Science Ltd2015