Separating climatic and possible human impacts in the early Holocene: biotic response around the time of the 8200 cal. yr BP event

The early Holocene is characterised by rapid climate change events, which in the North Atlantic region are often associated with changes in thermohaline circulation. Superimposed on this in northwest Europe is localised evidence for human impact on the landscape, although separating climatic and anthropogenic mechanisms for environmental change is often difficult. Biotic and sedimentological evidence from a lacustrine sequence from the Inner Hebrides, Scotland, shows a considerable reduction in inferred local woodland centred upon 8250 cal. yr BP. These data correlate precisely with a distinctive rise in the charcoal:pollen ratio and hence suggest a possible Mesolithic human impact upon the vegetation around this time. A quantitative temperature reconstruction from chironomid analyses from the same sequence, supported by sedimentological data, indicates that the fall in arboreal pollen taxa occurred as climate warmed significantly during the early Holocene. This warming was followed by a significant cold event, with mean July temperatures reduced by 2°C, that lasted for at least 320 years ca. 7790–7470 cal. yr BP. Woodland recovered during this phase suggesting that the vegetation during the 8250 cal. yr BP interval was likely to have been responding to human activity, and not climate, and hence it is possible at specific sites to separate the influence of these key drivers of environmental change. Copyright © 2006 John Wiley & Sons, Ltd.     

Post‐glacial vegetation reconstruction and a possible 8200 cal. yr BP event from the low arctic of continental Nunavut,Canada

Climate models suggest that the global warming during the early to mid‐Holocene may have partly resulted from the northward advance of the northern treeline and subsequent reduction of the planetary albedo. We investigated the Holocene vegetation history of low arctic continental Nunavut, Canada, from a radiocarbon‐dated sediment core from TK‐2 Lake, a small‐lake ca. 200 km north of the limit of the forest‐tundra. The pollen and loss‐on‐ignition data indicate the presence of dwarf shrub tundra in the region since the beginning of organic sedimentation at ca. 9000 cal. yr BP with dominance of Betula, especially since 8700 cal. yr BP. At 8100–7900 cal. yr BP the dominance of the shrub tundra was punctuated by a transient decline of Betula and coincident increases of Ericaceae undiff., Vaccinium‐type, and Gramineae. This suggests an abrupt disturbance of the Betula glandulosa population, approximately simultaneously with the sudden 8200 cal. yr BP event in the North Atlantic. However, in the absence of other sites studied in the area, linkage to the 8200 cal. yr BP event remains tentative. The lack of any evidence of forest‐tundra in the region constrains the northern limit of the mid‐Holocene advance of the forest‐tundra boundary in central northern Canada. Consequently, our results show that the climate models imposing a mid‐Holocene advance of the limit of the forest‐tundra to the arctic coast of Canada may have overestimated the positive climatic feedback effects that can result from the replacement of tundra by the boreal forest. Copyright © 2003 John Wiley & Sons, Ltd.     

The Greenland 8200 cal. yr BP event detected in loss‐on‐ignition profiles in Norwegian lacustrine sediment sequences

High‐resolution loss‐on‐ignition analyses of lacustrine sediment cores from both proglacial and non‐glacial lakes in southern Norway have revealed a specific pattern characterised by a significant, two‐peaked reduction of the loss‐on‐ignition values in the basal half of the cores. In non‐glacier‐fed lakes, the loss‐on‐ignition variations are interpreted to reflect mainly lake productivity and hence variability in surface summer air temperature. Sediments deposited in proglacial lakes, however, reflect mainly the glacier activity in the lake catchment. Bulk AMS radiocarbon dates from the core sequences and the loss‐on‐ignition curve pattern suggest that this event correlates with the ‘8200 cal. yr BP event’ recorded in the GRIP and GISP2 Greenland ice‐cores, termed the Finse event in southern Norway. Copyright © 2001 John Wiley & Sons, Ltd.     

Climate forcing due to the 8200 cal yr BP event observed at Early Neolithic sites in the eastern Mediterranean

We explore the hypothesis that the abrupt drainage of Laurentide lakes and associated rapid switch of the North Atlantic thermohaline circulation 8200 yr ago had a catastrophic influence on Neolithic civilisation in large parts of southeastern Europe, Anatolia, Cyprus, and the Near East. The event at 8200 cal yr BP is observed in a large number of high-resolution climate proxies in the Northern Hemisphere, and in many cases corresponds to markedly cold and arid conditions. We identify the relevant archaeological levels of major Neolithic settlements in Central Anatolia, Cyprus, Greece and Bulgaria, and examine published stratigraphic, architectural, cultural and geoarchaeological studies for these sites. The specific archaeological events and processes we observe at a number of these sites during the study interval 8400–8000 cal yr BP lead us to refine some previously established Neolithisation models. The introduction of farming to South-East Europe occurs in all study regions (Thrace, Macedonia, Thessaly, Bulgaria) near 8200 cal yr BP. We observe major disruptions of Neolithic cultures in the Levant, North Syria, South-East Anatolia, Central Anatolia and Cyprus, at the same time. We conclude that the 8200 cal yr BP aridity event triggered the spread of early farmers, by different routes, out of West Asia and the Near East into Greece and Bulgaria.     

Late-Glacial and Holocene Record of Lake Levels of Mathews Pond and Whitehead Lake,Northern Maine,USA

Paleohydrology studies at Mathews Pond and Whitehead Lake in northern Maine revealed synchronous changes in lake levels from about 12,000 ¹⁴C yrs BP to the present. We analyzed gross sediment structure, organic and carbonate content, mineral grain size, and macrofossils of six cores from each of the two lakes, and obtained 72 radiocarbon dates. Interpretation of this paleo-environmental data suggests that the late-glacial and Younger Dryas climate was dry, and lake levels were low. Early Holocene lake levels were considerably higher but declined for an interval from about 8000 to 7200 ¹⁴C yrs BP. Sediment of both lakes contains evidence of a dry period at ∼7400 ¹⁴C yrs BP (8200 cal yr). Lake levels of both sites declined abruptly about 4800 ¹⁴C yrs BP and remained low until 3000 ¹⁴C yrs BP. Modern lake levels were achieved only within the past 600 years. The west-to-east, time-transgressive nature of lake-level changes from several sites across northeastern North America suggests periodic changes in atmospheric circulation patterns as a driving force behind observed moisture balance changes. Electronic supplementary material to this article is available at and accessible for authorized users.     

Vegetation responses to climatic variability in the Swiss Southern Alps during the Misox event at the early–mid Holocene transition

Sedimentary pollen, charcoal and plant macrofossil analyses with high resolution and precision suggest a strong shift in vegetation composition during the early to mid‐Holocene transition in the upper mountain belt. At Piano mire (1439 m above sea level (a.s.l.), Ticino, Switzerland) forests were dominated by Abies alba during the early Holocene (prior to ca. 8000 cal. a BP). Abrupt collapses of A. alba at ca. 7800–7400 cal. a BP enabled the expansion of the light‐demanding pioneer Betula. Afterwards A. alba populations regained their previous abundance in the forests. Within the dating uncertainties of our record we assume that a unique combination of wet and cold years between 8400 and 7500 cal. a BP led to repeated lethal disadvantages for Abies. Our record of Abies oscillations is in good biostratigraphic agreement with the record that has been used to define the Misox cold event (Pian di Signano, 1540 m a.s.l.), which has been previously correlated with the 8200 cal. a BP event. Given the age estimates of the Abies collapses in our well‐dated record, our results suggest that additional efforts are needed to understand the linkage between the Misox and the 8200 cal. a BP event. They imply a high sensitivity of mountain vegetation far below the tree line (～800 m) to Holocene climatic changes of about 2°C in annual air temperature. Copyright © 2010 John Wiley & Sons, Ltd.