Late Quaternary palaeoceanographic evolution in the Skagerrak, north eastern North Sea

Abstract

This thesis investigates a radiocarbon dated composite sediment core from the Skagerrak basin (GC372650) and uses foraminifera to reconstructs the late Quaternary palaeoceanographic evolution of the North. The Skagerrak is an ideal location to reconstruct oceanographic change as it is critical in controlling water exchange between the Baltic Sea and the North Sea. Foraminiferal assemblage zones effectively highlight variations in hydrological conditions throughout the core. Sediments deposited between 12,600 and 11,200 cal. BP reflect cooler, ice proximal conditions during the Younger Dryas, with water temperatures warming throughout this period. The opening of a new outlet across central Sweden from the Baltic occurred at c. 11,200 cal. BP, and existed for about 1000 years, before its gradual closure at c. 10,500 cal. BP. Increased Atlantic inflow during the early Holocene is interrupted by a cooling event at c. 9400 cal. BP, though it is unclear if this was part of a wider climatic cooling, or a strengthened North Jutland Current.

The Littorina transgression facilitated the initiation of the modern hydrological system at c. 8500 cal. BP with the opening of the English Channel; this was evidenced by a sudden bloom in Hyalinea balthica. Shortly after, around 8300 cal. BP, the opening of the Danish Straits occurred, allowing exchange between the North Sea and the Baltic Sea. Outflow from the Baltic was greatest in the subsequent 2000 years but decreased after 6000 cal. BP. At the same time, a strengthening of the South Jutland Current (SJC) and corresponding drop in water temperatures occurred. After the weakening of the SJC around 3000 years later, conditions were relatively stable with increasing Atlantic Inflow, though a distinct cooling between c. 3000 and 2200 cal. BP may correspond to 'neoglacial' cooling observed elsewhere.

Between 420 and 160 cal. BP, the return of cold water fauna indicate a drop in temperatures due to the Little Ice Age. The duration of this cold phase in GC372650 is considerably shorter than in other investigations, only showing change during the maximum of the LIA. Following this, recent oxygen depletion, evidenced by a sudden increase in Textulari earlandi, is probably a result of increased specimen abundance due to additional nutrient input. Although eutrophication cannot be ruled out as a possibility, variations in the NAO index seem to correlate well with the timing of oxygen depletion.