Ice rafting history from the Spitsbergen ice cap over the last 200 kyr

Abstract

Three piston cores taken from the mid to upper continental slope of the Spitsbergen margin have been used to elucidate the calving history of the Spitsbergen ice mass for the last 200 kyr. The abundance of clasts larger than 2 mm was used as a measure of ice rafted detritus (IRD) in the cores, these clasts were counted from X-ray photographs. The fraction coarser than 63 μm was also measured and compared to the clast counts to assess the validity of this parameter as a measure of IRD content. The correlation between clast counts and the fraction >63 μm was poor, and it was concluded that the fraction >63 μm was a poor measure of IRD in the Spitsbergen cores. In cores close to a major continental landmass, or from an area of steep submarine relief the fraction >63 μm is likely to be affected by factors other than ice rafting alone. The IRD peaks identified in this study were thought to be produced by the following; Advance of the Spitsbergen ice cap during periods of increased moisture supply during interstadial periods (mid stage 5 and stage 3); Disintegration of a large ice mass on the continental shelf during deglaciations (stages 6/5e, 5b/5a and 2/1 boundaries); Summer melting of a large ice mass during glacial periods (stage 6). A good correlation was found between interpreted ice advances from IRD input to the Spitsbergen margin and postulated ice advances from terrestrial evidence. The IRD peaks found from the Spitsbergen margin appear to be produced by a different mechanism from that proposed for the production of the Heinrich layers of the North Atlantic. These are thought to be produced by the collapse of the Laurentide ice sheet once it reaches a threshold size. Correlation of Heinrich layers produced from a mid-latitude ice sheet with the IRD events of the Norwegian-Greenland Sea is not possible due to their different mechanism of formation. In fact, there is possibly an antiphase relationship as Heinrich layers are formed mainly during glacial periods, whereas IRD peaks in the Greenland Sea are produced during periods of rapid ice advance when moisture supply is high (when relatively warm Atlantic waters enter the Norwegian-Greenland Sea during interstadial periods), as well as during melting events.