ICE RAFTING HISTORY FROM THE SPITSBERGEN ICE CAP OVER THE LAST 200 KYR

Three piston cores taken from the mid to upper continental slope of th e Spitsbergen margin have been used to elucidate the calving history o f the Spitsbergen ice mass for the last 200 kyr. The abundance of clas ts 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 f raction coarser than 63 mu m was also measured and compared to the cla st counts to assess the validity of this parameter as a measure of IRD content. The correlation between clast counts and the fraction >63 mu m was poor, and it was concluded that the fraction >63 mu m was a poo r measure of IRD in the Spitsbergen cores. In cores close to a major c ontinental landmass, or from an area of steep submarine relief the fra ction >63 mu m is likely to be affected by factors other than ice raft ing alone. The IRD peaks identified in this study were thought to be p roduced by the following; Advance of the Spitsbergen ice cap during pe riods of increased moisture supply during interstadial periods (mid st age 5 and stage 3); Disintegration of a large ice mass on the continen tal 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 IR D input to the Spitsbergen margin and postulated ice advances from ter restrial evidence. The IRD peaks found from the Spitsbergen margin app ear to be produced by a different mechanism from that proposed for the production of the Heinrich layers of the North Atlantic. These are th ought to be produced by the collapse of the Laurentide ice sheet once it reaches a threshold size. Correlation of Heinrich layers produced f rom a mid-latitude ice sheet with the IRD events of the Norwegian-Gree nland Sea is not possible due to their different mechanism of formatio n. In fact, there is possibly an antiphase relationship as Heinrich la yers are formed mainly during glacial periods, whereas IRD peaks in th e Greenland Sea are produced during periods of rapid ice advance when moisture supply is high (when relatively warm Atlantic waters enter th e Norwegian-Greenland Sea during interstadial periods), as well as dur ing melting events.