Reconstruction of glaciation over the past 6 Myr from ice-borne deposits in the Norwegian Sea

Abstract

IT is well known that a significant intensification of Northern Hemisphere glaciation occurred ∼2.5 Myr ago, in contrast to the much earlier onset (∼35 Myr) of glaciation in Antarctica1–3. Much less is known about the behaviour of the climate before 2.5 Myr, and it has remained unclear when sizeable glaciers first started to develop in the Northern Hemisphere. Here we deduce the history of high-northern-latitude glaciation over the past 6 Myr from records of ice-borne deposits in deep-sea sediments of the Norwegian Sea. We find that glaciers large enough to reach sea level were present in the Norwegian Sea area as early as 5.5 Myr, three million years before the intensification of glaciation at 2.5 Myr. Fluctuations in ice volume can be deduced from the oxygen isotope record, but this provides only a global average, which may not reflect the history of ice-sheet growth in specific regions. From a comparison of the oxygen isotope records with the record of ice-rafted material, we derive an estimate of the relative contributions of Southern and Northern Hemisphere glaciation to global variations in ice volume.