Preface The expedition ARK XIX/3 with the German icebreaking RV ...

Results
The grain size distribution of the bulk sediments is generally silty to clayey terrigenous
mud with varying sand, gravel and bloc content (C. 3, Matthiessen et al.). For
hydrodynamic reasons the gravel (2 - 63 mm) and bloc fraction (>63 mm) cannot be
transported by bottom currents together with the silt and clay fractions. The gravel
material is therefore interpreted as IRD from dropstones melted out at the base of ice
floats or icebergs that may have been resedimented by debris flows.
The uppermost sediments of the GKGs consist of brownish bioturbated hemipelagic
mud (see Matthiessen et al., C. 3) and hence the content of gravel grains in the
surface sediments is generally low. In most GKGs it is absent and only 1 % of the area
is covered by gravel at the stations PS64/438, 441 and 442. Epibenthic organisms like
holothurians document that no surface sediments have been lost during lift up of the
gear.
The size of the studied gravel- (N = 1058) and bloc-sized clasts (N = 3) ranges
between 2 and 330 mm with a mean of 12 mm (averaged from the intermediate
diameters). Marginally-rounded clasts are more frequent with 40 % than well-rounded
(32 %) and unrounded clasts (28 %). 11 % of the clasts were broken after the
rounding, probably by sub- or englacial deformation processes. 7 % of the clasts,
mainly well- or marginally-rounded fine sandstones and siltstones (10 % of the well- or
marginally-rounded clasts) were scratched during collisions with rock debris at the
base of the glacier.
The sphericity is on average 0.42 for all analysed clasts and 0.46 for well-rounded
clasts, with a range of 0.1 to 0.9. Well-rounded clasts are not a typical appearance for
glacial debris and demand for an explanation. The well rounding requires a fluvial or
coastal environment with frequent resedimentation. One possibility is that the rounding
of these components already existed before the glacial transport of the material. Then
there should be at least some clasts embedded into the “mother rock” that
disintegrated by physical weathering or during deformation below the glacial ice.
However, only one well-rounded vein-quartz clast of 4 cm diameter could be found
that was part of a sericite shist. Due to the shistosity and the lack of siliceous cement
small clasts of these shists can be broken easily by hand. But there must be other
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