Evidence for cooler European summers during periods of changing meltwater flux to the North Atlantic
AUTOR(ES)
Heiri, Oliver
FONTE
National Academy of Sciences
RESUMO
We analyzed fossil chironomids (nonbiting midges) and pollen in two lake-sediment records to reconstruct and quantify Holocene summer-temperature fluctuations in the European Alps. Chironomid and pollen records indicate five centennial-scale cooling episodes during the early- and mid-Holocene. The strongest temperature declines of ≈1°C are inferred at ≈10,700–10,500 and 8,200–7,600 calibrated 14C years B.P., whereas other temperature fluctuations are of smaller amplitude. Two forcing mechanisms have been presented recently to explain centennial-scale climate variability in Europe during the early- and mid-Holocene, both involving changes in Atlantic thermohaline circulation. In the first mechanism, changes in meltwater flux from the North American continent to the North Atlantic are responsible for changes in the Atlantic thermohaline circulation, thereby affecting circum-Atlantic climate. In the second mechanism, solar variability is the cause of Holocene climatic fluctuations, possibly triggering changes in Atlantic thermohaline overturning. Within their dating uncertainty, the two major cooling periods in the European Alps are coeval with substantial changes in the routing of North American freshwater runoff to the North Atlantic, whereas quantitatively, our climatic reconstructions show a poor agreement with available records of past solar activity. Thus, our results suggest that, during the early- and mid-Holocene, freshwater-induced Atlantic circulation changes had stronger influence on Alpine summer temperatures than solar variability and that Holocene thermohaline circulation reductions have led to summer-temperature declines of up to 1°C in central Europe.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=524458Documentos Relacionados
- Meridional heat flux of the North Atlantic Ocean
- Evidence of Toscana Virus Variants Circulating in Tuscany, Italy, during the Summers of 1995 to 1997
- The North Atlantic Oscillation: Past, present, and future
- Adenosine 5′-Triphosphate Flux Through the North Inlet Marsh System †
- Reduction in Sink-Mobilizing Ability following Periods of High Carbon Flux 1