NORTH ATLANTIC OCEAN CIRCULATION DURING THE LAST GLACIAL MAXIMUM: A COMBINED MODELLING AND MAGNETIC SEDIMENT PROXY STUDY

Ocean modelling and palaeo-data studies provide evidence that the thermohaline circulation may have existed in a different configuration in the past. Here, we combine ocean model results and sediment proxy data, to investigate N. Atlantic circulation at the Last Glacial Maximum (LGM). Ocean model experiments at UEA (Norwich) indicate the existence of three possible stable ocean circulation states during the LGM. Two states have formation of intermediate/deep water in the North Atlantic (with different formation sites, rates and sinking depths); the third state has all deep water formation in the Southern Ocean. Forcing fields from these circulation states are used to provide input fields for an iceberg trajectory model, which is then used to investigate the effect of these different surface circulation patterns on iceberg drift. Magnetic measurements of deep-sea sediments have been used to identify ice-rafted detritus (IRD), allowing reconstruction of LGM iceberg trajectories. Magnetic measurements have the benefit of being relatively rapid and also non-destructive. The magnetic properties of > 130 deep-sea LGM sediment samples, from across the North Atlantic, have been measured, together with samples from potential source areas. Fuzzy c-means cluster analysis of selected, diagnostic magnetic parameters was used to characterise the sediment and identify the main controls on sedimentation. The clustering maps identify the enhanced distribution of windblown African dust, which spans the entire low latitude N. Atlantic. The magnetic properties of sediments along the eastern coast of Greenland, and in the Labrador Sea and central Atlantic, identify the distribution of magnetite-dominated IRD. The IRD in sediments east of the Gulf of St. Lawrence is characterised by the presence of haematite. Of the three modelled ocean states, the magnetic data support those with intermediate/deep water formation in the North Atlantic.