Articles | Volume 12, issue 9
Research article
07 Sep 2016
Research article |  | 07 Sep 2016

Mode transitions in Northern Hemisphere glaciation: co-evolution of millennial and orbital variability in Quaternary climate

David A. Hodell and James E. T. Channell

Abstract. We present a 3.2 Myr record of stable isotopes and physical properties at IODP Site U1308 (reoccupation of DSDP Site 609) located within the ice-rafted detritus (IRD) belt of the North Atlantic. We compare the isotope and lithological proxies at Site U1308 with other North Atlantic records (e.g., sites 982, 607/U1313, and U1304) to reconstruct the history of orbital and millennial-scale climate variability during the Quaternary. The Site U1308 record documents a progressive increase in the intensity of Northern Hemisphere glacial–interglacial cycles during the late Pliocene and Quaternary, with mode transitions at  ∼  2.7, 1.5, 0.9, and 0.65 Ma. These transitions mark times of change in the growth and stability of Northern Hemisphere ice sheets. They also coincide with increases in vertical carbon isotope gradients between the intermediate and deep ocean, suggesting changes in deep carbon storage and atmospheric CO2. Orbital and millennial climate variability co-evolved during the Quaternary such that the trend towards larger and thicker ice sheets was accompanied by changes in the style, frequency, and intensity of millennial-scale variability. This co-evolution may be important for explaining the observed patterns of Quaternary climate change.

Short summary
For the past 2.7 million years the Earth's climate has switched more than 50 times between a cold glacial and warm interglacial state. We found the trend towards larger ice sheets over the past 2.7 million years was accompanied by changes in the style, frequency, and intensity of shorter-term (millennial) variability. We suggest the interaction between millennial climate change and longer-term variations in the Earth's orbit may be important for explaining the patterns of Quaternary climate.