GRIP Dielectric Profiling (DEP) Data

REFERENCES:

Wolff, E.W., J.C. Moore, H.B. Clausen, and C.U. Hammer. 1997. Climatic
implications of background acidity and other chemistry derived from
electrical studies of the Greenland Ice Core Project ice core. Journal of
Geophysical Research 102:26325-26332.

Clausen, H.B., C.U. Hammer, J. Christensen, C.S. Hvidberg, D. Dahl-Jensen,
M.R. Legrand, and J.P. Steffensen. 1995. 1250 years of global volcanism as
revealed by central Greenland ice cores. Ice Core Studies of Global
Biogeochemical cycles, annecy, France, R. Delmas (ed.). NATO Advanced
Sciences Institutes Series 1, 30:175-194.

Wolff, E.W., J.C. Moore, H.B. Clausen, C.U. Hammer, J. Kipfstuhl, and K.
Fuhrer. 1995. Long-term changes in the acid and salt concentrations of the
Greenland Ice Core Project ice core from electrical stratigraphy. Journal
of Geophysical Research 100:16249-16263.

Moore, J.C., E.W. Wolff, H.B. Clausen, C.U. Hammer, M.R. Legrand, and K.
Fuhrer. 1994. Electrical response of the Summit-Greenland ice core to
ammonium, sulphuric acid, and hydrochloric acid. Geophysical Research
Letters 21:565-568.

GRIP Members. 1993. Climate instability during the last interglacial period
recorded in the GRIP ice core. Nature 364:203-207.

Taylor, K.C., C.U. Hammer, R.B. Alley, H.B. Clausen, D. Dahl-Jensen, A.J.
Gow, N.S. Gundestrup, J. Kipfstuhl, J.C. Moore, and E.D. Waddington. 1993.
Electrical conductivity measurements from the GISP2 and GRIP Greenland ice
cores. Nature 366:549-552.

Moore, J.C., R. Mulvaney, and J.G. Paren. 1989. Dielectric stratigraphy of
ice: a new technique for determining total ionic concentrations in polar
ice cores. Geophysical Research Letters 16:1177-1180.

Moore, J.C., and J.G. Paren. 1987. A new technique for dielectric logging
of Antarctic ice cores. Journal de Physique 48:C1/155-C1/160.

DATA DESCRIPTION:

The files dep1.dat, dep2.dat, etc. contain DEP (dielectric profiling) data
from the GRIP ice core drilled at Summit, Greenland at 2 cm resolution.
The data are in two columns, depth (m) and sigma infinity
(microsiemens/m).  Sigma infinity is the high-frequency limit of the
conductivity, corrected to -15 degrees C.  The data start at 138 metres
below the surface, and continue to the bottom of the core, including
several metres of silty basal ice. 

The file gripdep.dat contains averages over a 55 cm interval (the depth
given is the mid-point of the interval).  There are a few missing
datapoints.  The data have all the corrections described in Wolff et al., 
(1995), except that large peaks from volcanic eruptions have not been
removed from this dataset (although they are generally not seen clearly in
these 55 cm averages).  Note that the level changes between 730 and 930 m
are believed to be spurious (Wolff, et al., 1995) due to poor temperature 
correction. 

Sigma infinity has a pure ice background of 9 microsiemens/m, and responds
to the chemistry of the ice. The only components known to cause an
increased sigma infinity are acidity, ammonium and chloride (Wolff et 
al., 1995; Moore, et al., 1994). A calibration is given in Wolff et al., 
(1995). During warm periods, the DEP is mainly a record of acidity, while 
during cold (glacial) periods it is responding mainly to ammonium and/or 
chloride.