A review of millennial-scale climate variability over the past 1.5-million year from marine sediment cores in the North Atlantic

Monday, 15 December 2014: 8:00 AM
David A Hodell, University of Cambridge, Cambridge, United Kingdom
Our view of millennial-scale climate variability is shaped by the last glacial cycle when frequent, large and abrupt temperature changes occurred over Greenland and the North Atlantic, including “Dansgaard-Oeschger” and “Heinrich events”. The leading cause to explain these events is freshwater forcing from ice-sheets that affected sea ice extent, heat transport, and Atlantic Meridional Overturing Circulation. Several long records now exist that extend the history of millennial climate variability back to ~1.5 Ma. These records document how suborbital variability evolved as boundary conditions changed throughout the Pleistocene, including the Middle Pleistocene Transition (MPT) when the climate system transitioned from smaller ice volume fluctuations dominated by 41-kyr cycles before 1250 ka to larger ice sheets with quasi 100-kyr cycles after 650 ka.

Examination of these records lead to the following observations:

  • Millennial-scale variability was a persistent feature of glacial climates for the past 1.5 Ma.
  • Suborbital climate variability was enhanced during glacial periods (“noisy glacials”) and suppressed during full interglacial periods (“quiet intergalcials”)
  • The occurrence of strong millennial variability appears to be related to an ice-sheet size/volume threshold (McManus et al., 1999), presumably triggered when ice sheets grow large enough to reach the coast and interact with the ocean.
  • No two glacial cycles were alike with respect to either the magnitude or pacing of millennial climate variability.
  • The most significant change in ice rafted detritus (IRD) that occurred across the MPT was the appearance of Heinrich events, whose widespread occurrence was limited to the last ~650 ka (since MIS 16)
  • The growth of very large ice sheets in the latest Pleistocene introduced a new type of dynamic behavior of the Laurentide Ice Sheet marked by Heinrich layers.
  • IRD and benthic δ13C were tightly coupled during glacials periods for the last 1.5 Ma, supporting a persistent link between fresh-water forcing and deep-water circulation
  • Suborbital variability provides an important source of “noise” in the climate system that may play a role in noise-assisted transitions, such as glacial terminations and perhaps even the MPT itself.