Geoökologisches Kolloquium SS 2005

All lecture dates

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Dr. Denis-Didier Rousseau
Institut des Sciences de l\'Evolution (UMR CNRS 5554) Université Montpellier II und Alexander-von Humboldt Preisträger am LS Geomorphologie der UBT
Tuesday, 24.05.2005 18:15 H6

Pollen transport in the Arctic: evidences of a late spring long distance transport with changing trajectories and implication to paleoreconstructions

Tracing modern atmosphere dynamics is important to constrain models used for past climate reconstruction. The main types of tracers of arctic air masses are chemical and show different patterns. Dust in the ice at the summit of the Greenland ice cap has been shown, through isotope analyses, to be originated from Chinese deserts, mostly the Takla Makan and Gobi. Conversely, the chemical composition of the aerosols reaching the summit of the ice cap associated with backward air masses trajectories points to source areas in North America, Europe and Asia. A total of four pollen traps have been displayed on both coasts of Greenland during the last years in order to assess long distance transport in the Arctic domain and to identify potential vegetation source areas associated with air mass pathways. The on going EPILOBE project, monitoring the pollen transport to the Greenland coast, is based on four stations where filters are trapping all year long the pollen grains present in the air. A first record of long distance pollen transport to southern Greenland, at Narsarsuaq, have been observed in 2002 through the capture of pollen grains from trees, hickory and hemlock, oak, beech, hornbeam, walnut, growing in North America. This transport was in agreement with the dates of pollen production measured in southern Canada in the Toronto area, at the northern range of the common distribution of these trees. The pattern of the transport had been described by using the HYSPLIT application from NOAA, which allows determining backward trajectories.
A new transport to Narsarsuaq has been observed in the filters exposed in Narsarsuaq at about the same timing than in 2003. The filters exposed during weeks 21 (20 - 26 May) and 22 (27 May - 2 June) indicate the occurrence in the Greenland air of pollen grains from trees, which again are better growing in eastern North America. Despite the plants already observed in 2002, which absolutely indicate North America as a potential source of the pollen, other trees, also growing in eastern North America have been noticed. These are poplar, yew, ash, plane tree, and spruce. The backward air trajectories, computed by the HYSPLIT application for the concerned weeks, show mostly a similar pattern for most of the transport over the Great Lakes area. It appears then that a regular pattern of air masses responsible for the transport of pollen grains from North America to Greenland should be constant, as already described for anthropogenic pollutants.
Another pollen trap was installed on the sea ice during the ice-sea drift expedition from North Pole of French explorer Dr. Jean-Louis Etienne in 2002. The results show two different patterns within an interval of two weeks. Until now the use of pollen as an air mass tracer had not yet been investigated. Here we show that first evidence pollen represents a biological alternative to understand both present and past air mass dynamics in the Arctic and its associated relationship with biosphere changes.


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