GLACIO-METEROLOGICAL AND ISOTROPIC STUDIES ALONG THE EGIG LINE, CENTRAL GREENLAND

The geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were dete rmined along an east-west transect through central Greenland. This stu dy is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature meas urements in 17 steam-drilled boreholes along the eastern part of the t ransect. The firn temperatures at 15 m depth range from -31.6 degrees C at Dome GRIP (3230 m a.s.l.) to -11.4 degrees C at Caecilia Nunatak (eastern ice margin at 1600 m a.s.l.) and -18 degrees C at T05 (near t he western ice margin at 1900 m a.s.l.). The temperature/altitude grad ient changes from -0.7 degrees C (100m)(-1) in the ice divide region t o -1.1 degrees C (100 m)(-1) in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG lin e is -0.7 degrees C degrees lat(-1). The average annual accumulation d ecreases significantly from the west (similar to 47 cm a(-1) water equ ivalent at T05) towards the ice divide (20-25 cm a(-1) water equivalen t from T99 to, T43). Accumulation rates are constantly low east of the ice divide (similar to 23-17 cm a(-1) water equivalent), thus dividin g central Greenland into two climatologically different regions. The a verage delta(18)O and delta D values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. p artial derivative(18)O/partial derivative T-m = 0.69 parts per thousan d C-1). Different regression lines for the western and eastern part, h owever, should be applied. Unlike the mean annual temperature, the iso topic minimum along the EGIG line lies east of the ice divide. This ge ographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Signi ficant parts of the water precipitated over the western slope are attr ibuted to cyclonic systems entering Greenland from the west. The deute rium excess shows no significant geographical trend but a uniform seas onal variation at all sites along the EGIG line, suggesting equal cont ributions from vapour-source areas of the water precipitated over cent ral Greenland.