Abstract
The early Holocene cooling, which occurred around 8200 calendar years before present, was a prominent abrupt event around the north Atlantic region. Here, we investigate the timing, duration, magnitude and regional coherence of the event as expressed in carbonate oxygen-isotope records from three lakes on northwest Europe's Atlantic margin in western Ireland, namely Loch Avolla, Loch Gealáin and Lough Corrib. An abrupt negative oxygen-isotope excursion lasted about 200 years. Comparison of records from three sites suggests that the excursion was primarily the result of a reduction of the oxygen-isotope values of precipitation, which was likely caused by lowered air temperatures, possibly coupled with a change in atmospheric circulation. Comparison of records from two of the lakes (Loch Avolla and Loch Gealáin), which have differing bathymetries, further suggests a reduction in evaporative loss of lake water during the cooling episode. Comparison of climate model experiments with lake-sediment isotope data indicates that effective moisture may have increased along this part of the northeast Atlantic seaboard during the 8200-year climatic event, as lower evaporation compensated for reduced precipitation.
Highlights
The early Holocene cooling event that occurred around 8200 years BP has become a major research focus for palaeoclimatologists concerned with rapid climate change
The primary trigger for the 8200 year cooling is thought to be the catastrophic drainage of glacial Lakes Agassiz and Ojibway; large water bodies that accumulated over North America to the south of the waning Laurentide ice sheet during the late glacial and early Holocene (Barber et al, 1999)
The À0.9‰ shift in d18Op during the 8200-year event inferred from the carbonate isotope records agrees well with the shift seen in the model runs (À0.8‰) and is very consistent with geographical patterns presented in Daley et al (2011): the results from the three sites studied here are very coherent
Summary
The early Holocene cooling event that occurred around 8200 years BP has become a major research focus for palaeoclimatologists concerned with rapid climate change. The primary trigger for the 8200 year cooling is thought to be the catastrophic drainage of glacial Lakes Agassiz and Ojibway; large water bodies that accumulated over North America to the south of the waning Laurentide ice sheet during the late glacial and early Holocene (Barber et al, 1999). There is some evidence to suggest that the freshwater outburst occurred in two discrete events rather than as a single episode (Clarke et al, 2004; Hillaire-Marcel et al, 2007), it is clear that a large amount of fresh water was discharged into the North Atlantic over a very short time prior to 8000 years ago. Whilst freshwater forcing is seen as the major trigger for the 8200-
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