Environmental change and atmospheric contamination on Svalbard: sediment chronology

Sediment cores collected from eight lakes along the western coast of Svalbard as part of a project investigating atmospheric pollution and environmental change in Arctic regions were dated radiometrically using natural ((210) Pb) and artificial ((137) Cs and Am-241) fallout radionuclides. At four sites the sedimentation rates were relatively uniform, and in consequence the Pb-210 dates were relatively unambiguous. At the remaining sites there were irregularities in the Pb-210 activity versus depth profiles, indicating significant variations in the net sediment accumulation rate during the past 120 years. At these sites, there were significant differences between Pb-210 dates calculated using the two standard simple dating models, constant rate of supply (CRS) and constant initial concentration (CIC). In most cases, stratigraphic dates based on the Cs-137 and Am-241 records supported use of the CRS model, though at one site (Ossian Sarsfjellet) the CIC model appeared more appropriate. The irregularities in the Pb-210 records were mainly caused by episodes of accelerated sedimentation due, for example, to inwash or slump events, though at some sites there appears to have been a systematic increase in sediment accumulation rates in recent decades. Sediment accumulation rates were generally lower at the northern sites, and higher at the more southerly locations. Mean sediment accumulation rates varied by an order of magnitude, ranging from 0.002 to 0.050 g cm(-2) y(-1) (0.02-0.10 cm y(-1)). (210) Pb fluxes measured from the core inventories were mostly in the range 34-80 Bq m(-2) y(-1) typical of Arctic sites. Much higher values, recorded at two sites (Birgervatnet and Daltjorna), may be due to significant inputs from the catchments during spring thaw.