Pollen-Based Stratigraphy of Is-Fiord Bottom Sediments, Western Spitsbergen

Abstract

A pioneering high-resolution palynological investigation was conducted on bottom sediments retrieved from Is-fiord, Western Spitsbergen, during contract work in the Marine Arctic Geological Research Expedition (MAGE, Murmansk, Russian Federation) with the “Arcticcoal” Company. Three 140–190-cm-thick gravity cores were studied for pollen and spores, with the main aim of clarifying local patterns of the down-core pollen and spore distributions to further define the stratigraphic positions of retrieved marine strata. In spite of extremely low concentrations and the predominance of reworked microfossils, marine pollen spectra are quite similar to those known from radiocarbon-dated lake sediments and peat exposures on the coasts of the neighbouring fiords of Bulle (Dorozhkina 2005), Van Mijen (Zelikson 1971), and Hornsunn (Srodon 1960), provided that far-sourced pollen of conifers and spores of ferns are eliminated from marine pollen spectra compositions. The correlation of pollen zones (PZs) that were established in fiord sediments with those established in peat and lacustrine coastal sections enabled pollen-based stratigraphy to be established for Is-fiord bottom sediments, leading to an understanding of the features of the coastal vegetation and the tracking of the phases of its evolution based on marine pollen data. The oldest pollen spectra of the studied bottom-sediment sections are provisionally dated to the late Sub-Boreal period. They characterize the lowermost soft silty pelite layer and document that grass–cereal–sedge associations and heather bogs with green and sphagnous mosses dominated the vicinity of Is-fiord by the end of the late Sub-Boreal period, whereas osiers occupied elevated habitats. Pollen spectra in the upper part of the silty pelite layer in cores 11 and 14 and the whole section of core 9 from the northeastern inner part of the fiord are distinguished by peaks of Salix sp., Betula sect. Nanae-type, and Ericales pollens, and show the lowest percentages of spores of green mosses, thus supporting the reconstruction of heath and osier expansion under climatic conditions that were no colder than modern conditions. The characteristics of pollen spectra of the 22–25-cm-thick topmost over-watered layer are very similar to those from the surface sediments of Is-fiord. Therefore, their accumulation might be dated to the Sub-Atlantic period. They are notable for a considerable increase in sedge pollen, regarded as evidence for coastal bogging, probably due to a slight humidification of the climate. Extremely low pollen concentrations possibly reflect very high accumulation rates during the time of pelitic sedimentation.