Seismic properties of an asthenospherized lithospheric mantle: constraints from lattice preferred orientations in peridotite from the Ronda massif

Recent developments in paleomagnetism and environmental magnetism provide new tools for the detailed correlation of climatically induced magnetic mineralogy changes in sedimentary sequences. Studies of these changes contribute to the reconstruction of climate history for the glacial¯interglacial cycles of the Late Pleistocene and to the delineation of the range of natural variability for global climate during the past hundred thousands years. Here we show that sharp coercivity minima observed in fine-grained sediments from the continental rise of the western Antarctic Peninsula correlate to the major rapid cooling events of the northern Atlantic (Heinrich layers). We interpret such an environmental magnetic signal in terms of variations in deep sea diagenetic processes of sulfide formation, which reflect changes in the input of detrital organic matter controlled by sea-ice extent. With the inherent uncertainties in age controls, the sedimentary paleoclimatic markers of the two hemispheres are almost contemporaneous, but interhemispheric time lags or leads of the order of 1¯2 kyr (such as those recently reported from the Greenland and Antarctic ice cores) are also compatible with the data.