Onset of millennial climate variability with the intensification of Northern Hemisphere glaciation

The Quaternary Period (the last 2.58 Ma) was characterized by the waxing and waning of large ice sheets in the Northern Hemisphere. Using sediment sequences from the Iberian Margin, we demonstrate that expansion of Northern Hemisphere ice sheets around 2.7 Ma was accompanied by the emergence of millennial climate variability (MCV) during glacial periods. The onset of MCV at ~2.7 Ma was heralded by isolated precursor events, followed by multiple millennial climate oscillations at ~2.5 Ma. These events coincided with deposition of ice-rafted detritus in the North Atlantic, suggesting a role for marine-terminating ice sheets. Once established, MCV became an intrinsic feature of glacial climates of the Quaternary. Our findings underscore the profound impact Northern Hemisphere glaciation had on climate variability across multiple time scales.