Late Weichselian local ice dome configuration and chronology in Northwestern Svalbard: Early thinning, late retreat

摘要

The chronology and configuration of the Svalbard Barents Sea Ice Sheet (SBSIS) during the Late Weichselian (LW) are based on few and geographically scattered data. Thus, the timing and configuration of the SBSIS has been a subject of extensive debate. We present provenance data of erratic boulders and cosmogenic ~(10)Be ages of bedrock and boulders from Northwest Spitsbergen (NWS), Svalbard to determine the thickness, configuration and chronology during the LW. We sampled bedrock and boulders of mountain summits and summit slopes, along with erratic boulders from coastal locations around NWS. We suggest that a local ice dome over central NWS during LW drained radially in all directions. Provenance data from erratic boulders from northern coastal lowland Reinsdyrflya suggest northeastward ice flow through Liefdefjorden. ~(10)Be ages of high-elevation erratic boulders in central NWS (687-836m above sea level) ranging from 18.3±1.3ka to 21.7±1.4ka, indicate that the centreof a local ice dome was at least 300m thicker than at present. ~(10)Be ages of all high-elevation erratics (>400m above sea level, central and coastal locations) indicate the onset of ice dome thinning at 25-20ka. ~(10)Be ages from erratic boulders on Reinsdyrflya ranging from 11.1±0.8ka to 21.4±1.7ka, indicate an ice cover over the entire Reinsdyrflya during LW and a complete deglaciation prior to the Holocene, but apparently later than the thinning in the mountains. Lack of moraine deposits, but the preservation of beach terraces, suggest that the ice covering this peninsula possibly was cold-based and that Reinsdyrflya was part of an inter ice-stream area covered by slow-flowing ice, as opposed to the adjacent fjord, which possibly was filled by a fast-flowing ice stream. Despite the early thinning of the ice sheet (25-20ka) we find a later timing of deglaciation of the fjords and the distal lowlands. Several bedrock samples (~(10)Be) from vertical transects in the central mountains of NWS pre-date the LW, and suggest either ice free or pervasive cold-based ice conditions. Our reconstruction is aligned with the previously suggested hypothesis that a complex multi-dome ice-sheet-configuration occupied Svalbard and the Barents Sea during LW, with numerous drainage basins feeding fast ice streams, separated by slow flowing, possibly cold-based, inter ice-stream areas.