North American ice sheet dynamics controlled by obliquity (41 ka) during the early Pleistocene

During the Pleistocene, large continental ice sheets episodically apperead in the Northern Hemisphere, covering large parts of Europe and North America. Besides the results based on benthic oxygen isotope records, which predominantly represent variations in global ice volume, little is know about the timing of and astronomical control on the advances and retreats of the continental ice sheets in the Northern Hemisphere during the late Pliocene and early Pleistocene (3-2 million years (Ma) ago). Here we therefore present the first orbitally-resolved records of terrestrial higher plant leaf wax input to the North Atlantic covering the last 3.5 Ma, based on the accumulation of long-chain nalkanes and n-alkanl-1-ols at IODP Site U1313 [1]. These lipids are a major component of dust, even in remote ocean areas, and have a predominantly aeolian origin in distal marine sediments. Our results demonstrate that around 2.7 Ma, coinciding with the intensification of the Northern Hemisphere glaciation (NHG), the aeolian input of terrestrial material to the North Atlantic increased drastically. Since then, during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials. We argue that the increased aeolian input at Site U1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in North America and the associated strengthening of glaciogenic dust sources. The records thus reflect the timing of the advances and retreats of the North American ice sheets. Evolutional spectral analyses of the n-alkane records were therefore used to determine the dominant astronomical forcing in North American ice sheet advances over the last 3.5 Ma. These results demonstrate that during the early Pleistocene North American ice sheet dynamics responded predominantly to variations in obliquity (41 ka), which argues against previous suggestions of precession-related variations in Northern Hemisphere ice sheets during the early Pleistocene [2].