Palynological and sedimentological data from the Isfjorden core HH16-1205-GC

Palynological and sedimentological analyses were performed on the sediment core HH16-1205-GC retrieved from the central Isfjorden, West Spitsbergen in order to retrace the climate of the last 7000 years. The record revealed an overall cooling trend with an important climate shift between 4.4 and 3.8 cal. ka BP, and millennial-scale oscillations. Over the last 7000 years, sea-surface reconstruction from dinocyst assemblages indicates a decrease in summer sea-surface temperature, from 2.5 to 1.5 °C, and primary productivity, from 750 to 650 gC m-² a-1. Predominant sediment supply from the inner part of the fjord, ice rafting, dense sea-ice cover, strongly stratified water masses, and high primary productivity is observed in the sedimentological and palynological data between 6.8 and 5.8 cal. ka BP. The interval from 4.4 to 3.8 cal. ka BP is marked by a layer of coarser material followed by a significant decrease in the grain size mode, as well as changes in geochemical properties. large-amplitude fluctuations is observed in our geochemical data after 2.0 cal. ka BP, while an increase of the dinocysts Impagidinium pallidum and Spiniferites elongatus from 2.0 to 1.2 cal. ka BP suggests enhanced Atlantic Water inflow. The sea surface conditions reconstructions and XRF ratios also reveal large-amplitude millennial fluctuations. Wavelet analysis and cross-wavelet analysis performed on multiple variables confirm a strong cyclic signal with a periodicity of 1200 to 1500 years.