Geoscience Reference
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Fig. 2 Dating example. Volcanic marker horizons (blue bars) in the DEP record (here core B20
on water equivalent depth scale) provide ice core ages
ray imaging (Freitag et al. 2013 ). To account for the increase of density in the top
100mof the ice sheet fromabout 300 kg/m 3 for the uppermost
rn layers to the density
of ice (920 kg/m 3 ) an exponential function was
fit to the obtained density pro
les.
3 Results
The mean accumulation rates at the 12 drill sites are presented in Table 2 . They do
not exceed 200 mmWE/a and show a west-east as well as a south-north trend
(Fig. 3 ). The accumulation rates decrease northward from between 150 and
200 mm/a just north of the summit to less than 100 mm/a between 78 ° N and 79 ° N,
and they are strongly in
uenced by the ice sheet topography (Fig. 3 ). The highest
accumulation rates (180 and 176 mmWE/a) are found at the B27 and B26 drill sites
on the ice divide. The cores with the lowest accumulation rates are B19 and B20
(94 and 98 mmWE/a) with the largest distance to the ice divides in the far northeast.
This pattern in the accumulation results probably from a combination of factors.
Besides temperature and humidity of the air the shape of the coastline, the
topography and the inclination of the slopes west of the inland ice plateau play
some role for the clouds moving on to the inland ice (Benson 1962 ). The moisture-
fl
Table 2 Mean accumulation rates for North Greenland at the NGT drill sites
B16
B17
B18
B19
B20
B21
mm/a
141
114
103
94
98
109
Period
1993
1993
1993
934
1993
934
1994
1994
-
-
-
-
-
-
1640
1479
1179
1514
B22
B23
B26
B27
B29
B30
mm/a
145
121
176
180
149
166
Period
1994
1994
1995
1995
1995
1995
-
-
-
-
-
-
1479
1179
1601
1783
1479
1259
Given are mean values over the period from present (1993
1995) back to the time of the deepest
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