A Glacial Sedimentary System in Northwest Spitzbergen
The record of climate change in Signedalen and Krossfjorden, northwest Spitsbergen, since the Late Weichselian glacial maximum, has been constructed using an integrated analysis of lacustrine, terrestrial and marine sediments. Thirty-four piston cores were taken from two series of linked lakes in Signedalen, fed by three small cirque glaciers. Six further cores were taken from the fjord inlet, Signehamna, into which meltwater from the linked glacier-fed lakes and a further two glaciers drain. Signehamna drains into Lilliehookfjorden, which with Mollerfjorden, combines to form Krossfjorden, from which 16 .cores were made available. Cores were analysed for moisture content, loss-on-ignition, bulk density, grain size, magnetic susceptibility, infra-red stimulated luminescence, by X-radiography and by radioisotopic dating methods, 210Pb and 14C. Bathymetric maps were constructed following echo sounding survey of the lakes. Seventy-two water samples from the linked lakes were used to assess contemporary environmental conditions, and to aid interpretation of sedimentary structures within core sediments. Results of lichenometric survey of moraine ridges and pro-talus deposits in and around Signedalen were analysed using discriminant analysis, and compared with Werner's (1988) lichen growth curve in order to establish a chronology of moraine stabilisation. Seismic records of Krossfjorden have revealed evidence of glacier advance at least as far as the sill separating Krossfjorden from the outer parts of the fjord and shelf associated with the Late Weichselian glacial maximum (Sexton et al., in press). Overlying the basal unit of a possible till , or sediments associated with rapid glacier retreat, is a blanket of homogeneous sediment formed by ice-distal deposition during the Holocene. There is no evidence of Younger Dryas glacier expansion preserved in the marine sediments, or in terrestrial moraines. Denudation rates calculated from lacustrine sediment accumulation infer the presence of smaller glaciers in Signedalen during the Younger Dryas than at present. The early to mid Holocene appears to have been characterised by relatively warm conditions, with much reduced glacier presence in Signedalen. Evidence of Neoglacial cooling, between approximately 3,000 yr BP and 1,500 yr BP, is found in lichenometric recorckof talus deposits, although precise dating of the inception, and duration of this cooling is problematic. No moraine sediments are recorded from this period. The Little Ice Age maximum, dated by licheno~etry to AD 1890, was the most extensive glacier advance to have affected the cirque glaciers of Signedalen and the tidewater glaciers of Krossfjorden, and is associated with the highest denudation rates recorded in the lacustrine sediments. It also appears to have been responsible for the formation of rock glaciers within the protalus deposits of Signedalen. Since this date, a general retreat of glaciers has been interrupted periodically by still-stands or slight readvances when climatic conditions deteriorated.
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