An environmental magnetic study of a marine sediment core from Disko Bugt, West Greenland : implications for ocean current variability

Abstract: An 11 m long marine sediment core was collected during a June-July 2007 scientific cruise with the German research vessel R/V Maria Sibylla Merian to the area of Disko Bugt, western Greenland. The core, designated 343340-6-1, was examined using environmental magnetic methods and X-ray fluorescence. The study contributes to a larger project designed to map the variability in sediment source and transport during the Holocene and relate these to ocean circulation, the behaviour of Greenland glaciers and climate change. Measurements of magnetic susceptibility and artificially applied magnetic remanences were performed on contiguous discrete samples from the whole length of the core. Complementary element analyses were done using X-ray fluorescence to detect shifts in major element content, which could be linked to changes in the magnetic record. The focus of the magnetic mineral identification was to distinguish between sections of elevated haematite and magnetite levels, as the relation between these two minerals is what primarily can be expected to cause any major shift in magnetic properties. An age-model was constructed for the core by means of correlation with another radiocarbon dated core from the same area, which indicates relatively ice-free conditions since approximately 8.5 kyr BP. The major mineral magnetic units comprise a relatively haematite-enriched section approximately covering the interval 1000-700 cm, followed by an area dominated by magnetite at ca. 700-400 cm. These two features comprise the main part of the core, from the bottom until around 350 cm depth, corresponding to an age of around 7.9 kyr BP. The uppermost part was not easy to interpret because the overall magnetic material content is diluted by organic content, which suggests that marine productivity increased after 7.9 kyr BP. It is argued that an increasing haematite component implies a stronger West Greenland Current (WGC). Parts that are instead dominated by magnetite, without signs of any significant amount of haematite, are thought to indicate a weaker WGC as the sediments would be influenced mainly by local, basaltic sources. These ocean current fluctuations may be connected to climate variations during the Holocene, but an improved age-model is needed to allow comparisons with other climate records.