Showing papers by "Hubertus Fischer published in 1995"

Glacio-meteorological and isotopic studies along the EGIG line, central Greenland

Abstract: The geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements in 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from −31.6°C at Dome GRIP (3230 m a.s.l.) to −11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.s.l. and −18°C at T05 (near the western ice margin at 1900 ma.s.l.). The temperature/altitude gradient changes from −0.7°C (100 m) −1 in the ice divide region to −1.1°C (100 m) −1 in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is −0.7°C°lat −1 . The average annual accumulation decreases significantly from the west (∼47 cm a −1 water equivalent at T05) towards the ice divide (20-25 cm a −1 water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (∼23-17 cm a −1 water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ 18 O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂ 18 O/∂T m =0.69‰°C −1 ). Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.