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 Bussjösjön, 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.