Snow Accumulation in North Greenland over the Last Millennium - Towards an Interdisciplinary Approach in Earth System Science - page 183

rst by Ohmura and Reeh
( 1991 ). Updated maps of the accumulation rate were then presented by Ohmura
et al. ( 1999 ) and Bales et al. ( 2001 , 2009 ). More recently, maps of the accumulation
rate or estimates of the mass balance for varying periods are produced by modeling
the precipitation over Greenland using regional atmospheric circulation models
(e.g. Dethloff et al. 2002 ; Burgess et al. 2010 ; Hanna et al. 2011 ; Box et al. 2013 ).
Box et al. ( 2013 ) reconstructed the accumulation history over the last 400 years and

Accumulation rates in Greenland were compiled

find for example that the Greenland ice sheet net snow accumulation rate increased
by 12 % from the end of the Little Ice Age (1840 AD).
Due to the huge dimensions of the polar ice sheets data coverage is not at all
evenly distributed (e.g. Ohmura and Reeh 1991 ; Box et al. 2013 ). Until the
beginning of the era of deep cores in Greenland (GRIP, GISP2, NGRIP and NEEM)
at about 1990 most work focused on the central and southern parts of Greenland
(e.g. NEEM community members 2013 ). North Greenland was only covered
sparsely, mainly by the PARCA activities (e.g. Mosley-Thompson 2001 ) and the
North Greenland Traverse (NGT). The NGT started at the Summit of the Greenland
ice sheet after the GRIP ice core was completed (in summer 1993) and ended at the
NGRIP drill site about 350 km northwest of Summit in summer 1996. A total of 13
deep ice cores 70 175 m long were drilled during the NGT (see Fig. 1 ).

In this contribution within the ESSReS-framework we present an overview of the
evolution of the accumulation inNorthGreenland over the last 500 - 800 years, the rst
such overview for the data sparse North Greenland region. The accumulation histories
are derived by carefully aligning the time scale for the 13 NGT cores by volcanic
matching, and subsequently using measured density data to convert average annual
layer thickness between volcanic horizons to accumulation rate estimations.

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2 Methods

The lengths of the investigated ice cores and the coordinates of the drill sites are
given in Table 1 . An overview of their positions is given in Fig. 1 .
The drill sites of cores B21 B30 (except B22) are lying on the main ice divide

leading from the Summit to the Northwest and then splitting north of site B29 into a
branch towards the Northeast (B23 and B21). Core B22 has been drilled in the
windward side and all other cores (B16

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B20) in the lee-side of the ice divides.

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ect the impurity
content in the ice are used to date the cores. The basis of the dating is the well know
pattern of volcanic events present in DEP records (Fig. 2 ).
The accumulation rate, given here as equivalent height of a water column (mmWE/
a), is derived from the deposited snow mass per time in a core. During the

The Di Electric Pro ling (DEP)-records of the cores which re fl

eld
campaign the length and weight of each single piece of core were measured. From
these results and the known diameter of the cores an average density for each single
piece was calculated. In the AWI cold room laboratories the density of the cores was
additionally measured in millimeter resolution by absorption (Wilhelms 1996 )orX-

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