Upper Holocene Stratigraphy and Pollen Case Study of Isfjorden, West Spitsbergen (Svalbard, Norway)

Abstract

Three bottom sediment cores (140–190 cm long) taken from Isfjorden, West Spitsbergen, were analysed for pollen and spores with the main aim of elucidating the local pattern of pollen and spore succession in order to establish age control and define the stratigraphy of marine sediments. Isfjorden bottom sediments consist of greyish-green silty pelite with gruss, detritus, and pebble inclusions. The upper 25 cm are water-saturated and nonplastic. In spite of extremely low concentrations, and the predominance of reworked pre-Quaternary microfossils, the marine pollen spectra appear quite similar to those known from radiocarbon-dated lake sediments and peat exposures on the coasts of neighbouring Billefjorden, Van Mijenfjorden, and Hornsundfjorden, provided that long-distance transported pollen of conifers, tree birches, and spores of ferns are eliminated from marine pollen spectra compositions. The correlation of pollen zones (PZ) established in fjord sediments with those known from peat and lake sections enables the pollen-based stratigraphy of Isfjorden bottom sediments to be established and further reconstruction to be made of the major stages of the late Holocene terrestrial vegetation history of West Spitsbergen. The oldest pollen records date back to about 2.8–3 ka. They characterize the lowermost silty pelite layer (intervals 180–150 cm in core 11 and 190–60 cm in core 14 from the southwestern part of the fjord). At this time, moss–cereal–sedge fens and heather bogs in the coastal areas coexisted with rocky tundra vegetation at higher elevations. A marked increase in the content of Salix sp., Betula sect. Nanae-type, and Ericales pollen is recorded in the upper part of the pelite layer in cores 11 and 14. Similar spectra dominate core 9 from the northeastern inner part of the fjord. The percentage of green moss spores is extremely low. This type of spectra is suggestive of a warmer-than-present climate in West Spitsbergen. The upper water-saturated layer of all three cores contains pollen assemblages that are very similar to those identified in the Isfjorden surface sediment samples. Therefore, they have been likely accumulated during the last 2000 years. These uppermost pollen assemblages show a sharp increase in sedge pollen. This suggests the expansion of coastal fens, which can be attributed to an increase in the amount of precipitation. Extremely low pollen concentrations in Isfjorden bottom sediments possibly reflect very high accumulation rates during the time of silty pelite layer sedimentation.