Mechanisms of abrupt climate change of the last glacial period

Abstract

More than a decade ago, ice core records from Greenland revealed that the last glacial period was characterized by abrupt climate changes that recurred on millennial time scales. Since their discovery, there has been a large effort to determine whether these climate events were a global phenomenon or were just confined to the North Atlantic region and also to reveal the mechanisms that were responsible for them. In this paper, we review the available paleoclimate observations of abrupt change during the last glacial period in order to place constraints on possible mechanisms. Three different mechanisms are then reviewed: ocean thermohaline circulation, sea ice feedbacks, and tropical processes. Each mechanism is tested for its ability to explain the key features of the observations, particularly with regard to the abruptness, millennial recurrence, and geographical extent of the observed changes. It is found that each of these mechanisms has explanatory strengths and weaknesses, and key areas in which progress could be made in improving the understanding of their long‐term behavior, both from observational and modeling approaches, are suggested. Finally, it is proposed that a complete understanding of the mechanisms of abrupt change requires inclusion of processes at both low and high latitudes, as well as the potential for feedbacks between them. Some suggestions for experimental approaches to test for such feedbacks with coupled climate models are given.

North Atlantic forcing of tropical Indian Ocean climate

“…The effect of AMOC slowing on tropical climate can be studied with freshwater hosing experiments using coupled atmosphere-ocean general circulation models. Such numerical experiments consistently show a southward displacement of the ITCZ over the Atlantic Ocean in response to North Atlantic cooling induced by a perturbation of the AMOC 1, 19,20 . However, these experiments provide ambiguous results for the tropical Indo-Pacific region, with the response and sensitivity of the region to North Atlantic freshwater perturbations being strongly model dependent 20 .…”

“…3a). This cooling quickly propagates zonally throughout the Northern Hemisphere through atmospheric advection by the westerly winds and mixing 19 . The tropical mean circulation responds to the Northern Hemisphere cooling (and Southern Hemisphere warming) by generating anomalous energy transport from the southern hemisphere to the Northern Hemisphere.…”

The first estimation of Fleuve Manche palaeoriver discharge during the last deglaciation: Evidence for Fennoscandian ice sheet meltwater flow in the English Channel ca 20–18 ka ago

“…Rahmstorf, 1995), and some abrupt decreases of the THC and climate cooling during the last glacial period have been directly linked to increased freshwater flux into the North Atlantic (e.g. Broecker et al, 1989;Clark et al, 2001;Clement and Peterson, 2008). Considering the above estimates, the Fleuve Manche freshwater discharge ranges from ca 0.01 to 0.4 Sv over the 18.3-17.5 ka interval, i.e.…”

“…Considering the above estimates, the Fleuve Manche freshwater discharge ranges from ca 0.01 to 0.4 Sv over the 18.3-17.5 ka interval, i.e. a meltwater release important and sufficiently sustained to reduce significantly the THC strength according to many simulations (see Clement and Peterson (2008) for a thorough review). Modelling experiments could assist in the evaluation of the impact of the Fleuve Manche discharge at ca 18 ka on the concomitant THC strength reduction.…”

Systematic study of the impact of fresh water fluxes on the glacial carbon cycle

“…These changes, called abrupt events (Clement and Peterson, 2008), are characterized by an abrupt warming followed by a cooling in the Northern Hemisphere. In the Southern Hemisphere, Antarctica starts to warm as soon as temperatures drop in Greenland, then Antarctica cools down when Greenland rapidly warms (EPICA community members, 2006;Ahn and Brook, 2008;Barker et al, 2009).…”