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The climate of the middle Weichselian Glaciation, Marine Oxygen Isotope Stage 3 (OIS-3), a relatively mild period compared to the glacial maxima of OIS-4 and OIS-2, consisted of long warm interstades punctuated by brief cold excursions that grew colder and more frequent with time. The OIS-4 ice sheet is generally thought to have persisted throughout OIS-3, but evidence from dated OIS-3 interstadial deposits suggests that it was swiftly reduced to small remnants which only briefly expanded and retreated. Only 30,000 years ago the deteriorating climate initiated a sustained ice advance leading toward the final glacial maximum of OIS-2. Dynamic ice-sheet models support the existence of a prolonged ice-free interval during OIS-3 induced, perhaps, by low precipitation due to extensive sea-ice cover offshore.

Two paleomagnetic excursions, the Skjong correlated with the Laschamp (about 41,000 GISP2 yr B.P.) and the Valderhaug correlated with the Mono Lake (about 34,000 GISP2 yr B.P.), have been identified in stratigraphic superposition in laminated clay deposited in ice-dammed lakes in three large caves in western Norway. During both periods the margin of the Scandinavian Ice Sheet advanced and reached the continental shelf beyond the outermost coastline. The mild, 4000-yr-long Ålesund interstade, when the coast and probably much of the hinterland were ice-free, separated the two glacial advances. The two paleomagnetic excursions have also been indirectly identified as increased fluxes of 36 Cl and 10 Be in the GRIP ice core, Greenland. This article presents a correlation between ice-margin fluctuations of the Scandinavian Ice Sheet and the stratigraphy of GRIP/GISP cores, using the paleomagnetic excursions and the 36 Cl and 10 Be peaks and thus circumventing the application of different dates or time scales. Some of the fluctuations of the Scandinavian Ice Sheet were of the "Allerød/Younger Dryas type" in the sense that its margin retreated during mild interstades on Greenland and readvanced during cold stades. However, some fluctuations were apparently not in phase with the Greenland climate.

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