Late Pleistocene-Holocene history of Svalbard ice caps and glaciers – integrating marine, terrestrial and lacustrine archives
The Arctic regions are affected by the modern climate change to a greater extent than the global average. This effect is called the Arctic amplification and is reflected in air temperatures rising with double rate and increased precipitation compared to the global average. The climate of Svalbard is strongly related to variations in the atmospheric and oceanic circulation patterns, and the archipelago is, therefore, ideal location to study the climate sensitivity of the Arctic. This dissertation presents research on the Late Pleistocene and Holocene glacial history of Svalbard. Marine, lacustrine and terrestrial archives are assessed in a confined geographical area in northern Wijdefjorden, northern Spitsbergen, and the regional timing of the deglaciation, Holocene Thermal Maximum, Holocene Glacial Minimum as well as the onset of the Neoglacial are identified (Papers I-III). The research focus is on Wijdefjorden, Femmilsjøen and the NW part of the Åsgardfonna ice cap. The results are placed in a regional context and compared to studies across Svalbard. A review of the Holocene glacial history of Svalbard is presented in Paper IV, where all Holocene chronological data from Svalbard are re-calibrated or calculated and gathered in one database. The landforms in the fjord (Paper I) and the lowermost acoustic and sedimentary facies (Papers I-II) are interpreted to be indicative of grounded, warm-based ice occupied the fjord during the Last Glacial. By contrast, Paper III speculates that parts of the terrestrial terrain are similar to forelands of cold-based glaciers in Antarctica, which may have been covered by cold-based and little erosive glacier ice during the Last Glacial. Among the findings are that northern Svalbard deglaciated early. Wijdefjorden is inferred to deglaciate at least prior to 12.4 ± 0.3 cal. ka BP and potentially prior to 14.5 ± 0.3 cal. ka BP. Femmilsjøen deglaciated potentially prior to 16.1 ± 0.3 cal. ka BP. Deglaciation occurred in a stepwise manner and was characterised by fluctuating water temperatures and sea ice cover. Overarching, the Svalbard fjords deglaciated rapidly during the first half of the Early Holocene, however the overall retreat was punctuated by dynamic ice-advances of smaller tributary glaciers. Femmilsjøen was isolated from the marine environment c. 11.4 cal. ka BP. The regional Holocene glacial minimum coincided with the Holocene thermal maximum (between 10.1 ± 0.4 and 3.2 ± 0.2 cal. ka BP), during which time the ice cap Åsgardfonna was small or close to absent. Collectively in Svalbard, the Holocene glacial minimum most likely occurred between 8.0 and 6.0 cal. ka BP. Thus, the Holocene thermal maximum and Holocene glacial minimum in northern Wijdefjorden seems extended compared to the rest of Svalbard. In the fjord, seawater temperatures show a gentle decrease and the sea-ice proxy a gentle increase from c. 6.0 cal. ka BP, but values do not accelerate until c. 0.5 cal. ka BP. In Svalbard, Neoglacial glacier advances occurred generally from 4.0 to 0.5 cal. ka BP and with the Little Ice Age representing the last cold-spell of the Neoglacial. In Femmilsjøen, glacial influence recommenced from 3.2 ± 0.2 cal. ka BP, and glaciers in the catchment reached sizes no smaller than their current extent within c. 1.0 ka. The Holocene climate and glacial variability of Svalbard are strongly coupled to atmospheric and oceanic forcings.