Calculating Quaternary glacial erosion rates in northeast Scotland

Northeast Scotland is an area exhibiting selective erosion by Quaternary ice sheets. In this area both glacial and preglacial landforms exist in close proximity. The depths of erosion which this modification represents are calculated on the assumption of various depths of preglacial weathering. A depth of erosion of between 34 and 62 m per unit area is indicated. Calculated rates of erosion are 0.021 mm a^-1 for the entire 2.3 m.y. of the Quaternary, and between 0.1 and 0.5 mm a^-1 on the assumption that glacial conditions existed in this area for 500,000 years and 100,000 years, respectively. These figures are compared to the offshore sedimentary record in the adjacent west-central North Sea. The volume of sediment deposited offshore is equivalent to a depth of erosion of 195 m per unit area, yielding an average erosion rate of 0.085 mm a^-1 over the entire Quaternary. Rates of erosion were low in the preglacial Pliocene (0.049 mm a^-1) and early Quaternary (0.063 mm a^-1). The expansion of ice sheets across the area in the middle Quaternary was associated with a sharp increase in the rates of erosion (> 0.13 mm a^-1) but the last (late Devensian) ice sheet in the area was less erosive (< 0.095 mm a^-1). The estimated rates of erosion represented by the offshore sedimentary record therefore exceed the estimated rates of glacial erosion from the onshore geomorphological reconstruction.