Holocene variability of the North Atlantic Irminger current on the south- and northwest shelf of Iceland

Abstract

Abstract The Irminger Current (IC) transports heat and nutrients to the Icelandic shelf and its fluctuations are strongly linked to variations in the strength of the North Atlantic surface flow from the south. By using benthic foraminiferal assemblages and their stable isotopic composition in two marine sediment cores located in the pathway of the IC on the West Iceland shelf we were able to derive bottom water temperature estimates at a ~ 100 year resolution and define the temperature difference between the core sites throughout the Holocene. These are the first transfer function bottom water temperatures presented from the Icelandic shelf based on benthic foraminiferal assemblages. Our findings demonstrate a delayed Holocene Thermal Maximum in the marine current system around Iceland compared to the Northern Hemisphere summer insolation receipts. The maximum heat transport in the IC occurred between 8 and 4 ka years, later than some previous records report. A reconstruction of the ambient seawater δ18O based on paired samples of C2 transfer function temperature estimates and oxygen isotopic composition indicates repeated freshwater input to the N-Atlantic inflow in the early Holocene impacting the current system before 8 ka. Two fundamental regime shifts are evident in the paleoceanography and foraminiferal properties during the Holocene, occurring around 8 ka towards more stable conditions and again around 4 ka towards more unstable conditions. Increasing fluctuation with similarities to the Great Salinity Anomaly in the 1970s occur after 4 ka.