ÉTUDE EN LIGNE SUR ISOCÈLE DE LA DÉSINTÉGRATION 186Tl → 186Hg

L'étude de la décroissance 186Tl → 186Hg a été entreprise à l'aide du séparateur en ligne Isocèle. Les niveaux 0+2 et 2+2 sont proposés à très basse énergie. Un schéma de niveaux partiel est discuté dans le cadre des modèles existants

The Effects of Flowline Length Evolution on Chemistry-Delta O-18 Profiles from Penny Ice Cap, Baffin Island, Canada

The isotopic and chemical signatures for ice-age and Holocene ice from Summit, Greenland and Penny Ice Cap, Baffin Island, Canada, arc compared. The usual pattern of low delta(18)O, high Ca2+ and high Cl- is presented in the Summit records, but Penny Ice Cap has lower than present Cl- in its ice-age ice. A simple extension of the Hansson model (Hansson, 1994) is developed and used to simulate these signatures. The low ice-age Cl- from Penny Ice Cap is explained by having the ice-age ice originating many thousands of km inland near the centre of the Laurentide ice sheet and much further from the marine sources. Summit\u27s flowlines all start close to the present site. The Penny Ice Cap early-Holocene delta(18)O\u27s had to be corrected to offset the Laurentide meltwater distortion. The analysis suggests that presently the Summit and Penny Ice Cap marine impurity originates about,500 km away, and that presently Penny Ice Cap receives a significant amount of local continental impurity

Variability and change in the Canadian cryosphere

Abstract During the International Polar Year (IPY), comprehensive observational research programs were undertaken to increase our understanding of the Canadian polar cryosphere response to a changing climate. Cryospheric components considered were snow, permafrost, sea ice, freshwater ice, glaciers and ice shelves. Enhancement of conventional observing systems and retrieval algorithms for satellite measurements facilitated development of a snapshot of current cryospheric conditions, providing a baseline against which future change can be assessed. Key findings include: 1. surface air temperatures across the Canadian Arctic exhibit a warming trend in all seasons over the past 40 years. A consistent pan-cryospheric response to these warming temperatures is evident through the analysis of multi-decadal datasets; 2. in recent years (including the IPY period) a higher rate of change was observed compared to previous decades including warming permafrost, reduction in snow cover extent and duration, reduction in summer sea ice extent, increased mass loss from glaciers, and thinning and break-up of the remaining Canadian ice shelves. These changes illustrate both a reduction in the spatial extent and mass of the cryosphere and an increase in the temporal persistence of melt related parameters. The observed changes in the cryosphere have important implications for human activity including the close ties of northerners to the land, access to northern regions for natural resource development, and the integrity of northern infrastructure

ÉTUDE EN LIGNE SUR ISOCÈLE DE LA DÉSINTÉGRATION 186Tl → 186Hg

L'étude de la décroissance 186Tl → 186Hg a été entreprise à l'aide du séparateur en ligne Isocèle. Les niveaux 0+2 et 2+2 sont proposés à très basse énergie. Un schéma de niveaux partiel est discuté dans le cadre des modèles existants.We have studied the 186Tl → 186Hg decay by means of the Isocele on-line isotope separator. The 0+2 and 2+2 levels are proposed at a low excitation energy. A partial level scheme is being discussed in the framework of available models

Penny Ice Cap Cores, Baffin Island, Canada, and the Wisconsinan Foxe Dome Connection: Two States of Hudson Bay Ice Cover

Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (d18O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in d18O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM d18O values suggest thick ice frozen to the bed of Hudson Bay