Interglacials of the last 800,000 years

Past Interglacials Working Group Of Pages

doi:10.1002/2015rg000482

Abstract

AbstractInterglacials, 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, a result that is robust to alternative definitions. 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. A variety of temporal trends is observed, such that maxima in the main records are observed either early or late in different interglacials. The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes. Interglacials have been typically 10–30 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.

Highlights

Interglacials of the Last 800 kaEarth’s climate of the last 800 ka (1 ka = 1000 years) is the latest stage in a slow cooling that has been in progress for the last ~50 Ma (1 Ma = 1 million years) [Zachos et al, 2008]
Large-Scale Measures (Ice Volume, Deep Ocean Temperature, and CO2) We start by considering some measures (Figure 9) that have a wide significance as an indicator, forcing and/or feedback at global scale: benthic oxygen isotopes, deepwater temperature, seawater oxygen isotope content, and atmospheric CO2
Marine Isotope Stages (MIS) 5e is an exceptionally warm interglacial in records from regions that are not represented in our compilation because they do not meet our criteria: for example, MIS 5e has the warmest sea surface temperature (SST) of any interglacial of the last 600 ka [Martrat et al, 2007; Rodrigues et al, 2011] in records from the Portuguese Margin on the east of the North Atlantic, while MIS 11c, 5e, and 9e stand out as considerably warmer than other interglacials [Caley et al, 2011] in a record from the east coast of South Africa (MD96-2048, Indian Ocean) that lacks resolution for a quantitative analysis

Summary

Introduction

The last 800 ka time period benefits from the enormous progress over recent decades in collecting and analyzing a wide range of continuous climate records from terrestrial sites, marine sediment cores, and the oldest Antarctic ice cores. It is approximately the most recent interval associated with the orientation of the Earth’s magnetic field in the “normal” polarity with the inclination vector pointing north [Shackleton et al, 1990], providing a useful sedimentary demarcation in settings where magnetic reversals are preserved. It has become possible in recent years to run Earth models of intermediate complexity (EMICs) through several glacial cycles, and full Earth system models (ESMs) for a significant range of boundary conditions, including those appropriate for some of the recent interglacials

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