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14 mars 2017
Interglacials of the last 800,000 years

Fig. 1. Definition of interglacials based on sea level. (top) δ18O of benthic foraminifera in the LR04 stack [Lisiecki and Raymo, 2005]; (bottom) probability maximum Red Sea relative sea level [Rohling et al., 2009] (orange line); and deconvolved δ18O of seawater [Elderfield et al., 2012] (grey line). Marine Isotopic substages of interglacial status are indicated (as well as interstadials MIS 5a and 5c). Note that there is some confusion in the literature about the lettering of substages in MIS 9 and 15. Here we use the substage numbering recommended in a recent paper [Railsback et al., 2015], such that the oldest substages in MIS 9 and 15 are 9e and 15e. Dashed lines mark values discussed in the text that might be used in the definition of interglacials

Interglacials, including the present (Holocene) period, are warm, low land ice extent (high sea level), end-members of glacial cycles. Based on a sea level definition, we identify eleven interglacials in the last 800,000 years. Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (last interglacial) and 11c (~400 ka ago) were globally strong (warm), while MIS 13a (~500 ka ago) was cool at many locations. A step change in strength of interglacials at 450 ka is apparent only in atmospheric CO2 and in Antarctic and deep ocean temperature. The onset of an interglacial (glacial termination) seems to require a reducing precession parameter (increasing Northern Hemisphere summer insolation), but this condition alone is insufficient. Terminations involve rapid nonlinear reactions of ice volume, CO2, and temperature to external astronomical forcing. The precise timing of events may be modulated by millennial-scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere. The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes. Interglacials have been typically 1030 ka long. The combination of minimal reduction in northern summer insolation over the next few orbital cycles, owing to low eccentricity, and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future.

 

Authors : A. Berger, A. Landais, … V. Masson-Delmotte et al.

Ref. : Reviews of Geophysics, Vol. 54 Reviews of Geophysics, Vol. 54

 

Maj : 30/03/2017 (109)

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