Rapid strengthening of westerlies accompanied intensification of Northern Hemisphere glaciation

The trigger, pace, and nature of the intensification of Northern Hemisphere Glaciation (iNHG) are uncertain, but can be probed by study of ODP Site 1208 North Pacific marine sediments. Herein, we present magnetic proxy data that indicate a 4-fold increase of dust between similar to 2.73 and similar to 2.72 Ma, with subsequent increases at the start of glacials thereafter, indicating a strengthening of the mid-latitude westerlies. Moreover, a permanent shift in dust composition after 2.72 Ma is observed, consistent with drier conditions in the source region and/or the incorporation of material which could not have been transported via the weaker Pliocene winds. The sudden increase in our dust proxy data, a coeval rapid rise in dust recorded by proxy dust data in the North Atlantic (Site U1313), and the Site 1208 shift in dust composition, suggest that the iNHG represents a permanent crossing of a climate threshold toward global cooling and ice sheet growth, ultimately driven by lower atmospheric CO2.

Automated summary

By studying marine sediments from ODP Site 1208 in the North Pacific, we found that there was a 4-fold increase in dust between approximately 2.73 and 2.72 million years ago, followed by subsequent increases during the start of glacials. This indicates a strengthening of the mid-latitude westerlies. We also observed a permanent shift in dust composition after 2.72 million years ago, suggesting drier conditions in the source region and/or the inclusion of material that could not have been transported by weaker winds during the Pliocene. The sudden increase in our dust proxy data, along with similar increases recorded in the North Atlantic and the shift in dust composition, suggests that the intensification of Northern Hemisphere Glaciation represents a permanent crossing of a climate threshold towards global cooling and ice sheet growth, driven by lower atmospheric CO2.