176 resultados para historical records


Relevância:

20.00% 20.00%

Publicador:

Resumo:

The Northern Hemisphere cooling event 8200 years ago is believed to represent the last known major freshwater pulse into the North Atlantic as a result of the final collapse of the North American Laurentide ice sheet. This pulse of water is generally believed to have occurred independently of orbital variations and provides an analogue for predicted increases in high-latitude precipitation and ice melt as a result of anthropogenically driven future climate change. The precise timing, duration and magnitude of this event, however, are uncertain, with suggestions that the 100-yr meltwater cooling formed part of a longer-term cold period in the early Holocene. Here we undertook a multiproxy, high-resolution investigation of a peat sequence at Dooagh, Achill Island, on the west coast of Ireland, to determine whether the 8200-year cold event impacted upon the terrestrial vegetation immediately downwind of the proposed changes in the North Atlantic. We find clear evidence for an oscillation in the early Holocene using various measures of pollen, indicating a disruption in the vegetation leading to a grassland-dominated landscape, most probably driven by changes in precipitation rather than temperature. Radiocarbon dating was extremely problematic, however, with bulk peat samples systematically too young for the North Atlantic event, suggesting significant contamination from downward root penetration. The sustained disruption to vegetation over hundreds of years at Dooagh indicates the landscape was impacted by a long-term cooling event in the early Holocene, and not the single century length 8200-year meltwater event proposed in many other records in the North Atlantic region.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The Northern Ireland Hare Survey documented the distribution of the Irish Hare (Lepus timidus hibernicus). Historical game bag records and other, more contemporary, records of hare distribution were examined. These data indicate how numbers of L t. hibernicus may have changed over the last 140 years. The results of the Northern Ireland Hare Survey suggested that L. t. hibernicus was widespread throughout Northern Ireland. Current average densities are no more than 0.65 hares/km(2). Game bag records indicate that hare densities may have been much higher in the past, with a maximum of 138 hares/km(2) recorded on Crom Estate, Co. Fermanagh, in 1864. Evidence from hare distribution recorded during the Northern Ireland Rabbit Survey indicates that hare numbers declined between 1984 and 1994. Evidence from all sources suggests that L. t. hibernicus has declined in abundance substantially, with present total population estimates for Northern Ireland ranging from 8250 to 21000 individuals. Flushing data indicate that rushes and hedgerows are important diurnal resting areas for hares. While the principal reason for the decline in numbers of L. t. hibernicus in Northern Ireland is not clear, more species-rich pasture and provision of areas of cover, such as rushes, may arrest further declines, or indeed promote numbers of hares, particularly in lowland areas.