Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period

Climate of the Past Discussions 02/2010; 6(1). DOI: 10.5194/cpd-6-135-2010
Source: DOAJ


Since its discovery in Greenland ice cores, the millennial scale climatic variability of the last glacial period has been increasingly documented at all latitudes with studies focusing mainly on Marine Isotopic Stage 3 (MIS 3; 28–60 thousand of years before present, hereafter ka) and characterized by short Dansgaard-Oeschger (DO) events. Recent and new results obtained on the EPICA and NorthGRIP ice cores now precisely describe the rapid variations of Antarctic and Greenland temperature during MIS 5 (73.5–123 ka), a time period corresponding to relatively high sea level. The results display a succession of long DO events enabling us to highlight a sub-millennial scale climatic variability depicted by i) short-lived and abrupt warming events preceding some Greenland InterStadial (GIS) (precursor-type events) and ii) abrupt warming events at the end of some GIS (rebound-type events). The occurrence of these secondary events is suggested to be driven by the Northern Hemisphere summertime insolation at 65° N together with the internal forcing of ice sheets. Thanks to a recent NorthGRIP-EPICA Dronning Maud Land (EDML) common timescale over MIS 5, the bipolar sequence of climatic events can be established at millennial to sub-millennial timescale. This provides evidence that a linear relationship is not satisfactory in explaining the link between Antarctic warming amplitudes and the duration of their concurrent Greenland Stadial (GS) for the entire glacial period. The conceptual model for a thermal bipolar seesaw permits a reconstruction of the Antarctic response to the northern millennial and sub-millennial scale variability over MIS 5. However, we show that when ice sheets are extensive, Antarctica does not necessarily warm during the whole GS as the thermal bipolar seesaw model would predict.

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    • "Similar criteria are used by Alley et al (2001) and Ditlevsen et al (2005). 2 Here, we are not mentioning about possible triggers of DO events, which may act in much faster time scales, such as weather forcing (Monahan et al, 2008), solar variability (Goosse et al, 2002; Braun et al, 2008), or tidal forcing (Keeling and Whorf, 2000). 3 In particular, Capron et al (2010) suggest a link between NHS insolation which can affect temperature, seasonality, hydrological cycle, and ice sheet growth in the high latitudes. On the other hand, possible effects of the change in the latitudinal gradient of annual mean insolation (i.e., obliquity forcing) are emphasized by Masson-Delmotte et al (2005), Olsen et al (2005) as well as Friedrich et al (2010). "
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    ABSTRACT: Dansgaard-Oeschger (DO) events are abrupt millennial-scale climate changes mainly detected in the North Atlantic region during the last glacial cycle. The frequency of the DO events varied in time, supposedly because of changes in background climate conditions. Here, we investigate the influences of external forcings on DO events with statistical modelling. We assume two types of generic stochastic dynamical systems models (double-well potential-type and oscillator-type), forced by the northern hemisphere summer insolation change and/or the global ice volume change. The models are calibrated by maximizing their likelihood and compared using the Bayesian Information Criterion (BIC). Among the models, the stochastic oscillator model forced by both insolation and ice volume changes is favored by the NGRIP calcium ion data. The BIC scores provide positive evidence for the ice volume forcing in the presence of the insolation forcing but weak evidence for the insolation forcing in the presence of the ice volume forcing. Consistently with their BIC scores, stochastic oscillator models with at least ice volume forcing reproduce well the frequency changes of warming transitions in the last glacial period across Marine Isotope Stages (MISs) 2, 3, and 4. Finally, using the selected model, we simulate the average number of warming transitions in the past four glacial periods, and compare the result with an Iberian margin sea-surface temperature (SST) record (Martrat et al., Science, vol.317, p.502, 2007). The simulation result supports the previous observation that abrupt millennial-scale climate changes in the penultimate glacial (MIS 6) are less frequent than in the last glacial (MISs 2, 3, and 4). On the other hand, it suggests that the number of abrupt millennial-scale climate changes in older glacial periods (MISs 6, 8, and 10) might be larger than inferred from the SST record.
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    ABSTRACT: Since the early 1960s, the ice core community has produced a wealth of scientific results from a still relatively limited number of deep drilling sites in Greenland and Antarctica with the longest record extending back to the last interglacial in Greenland and covering eight glacial–interglacial cycles in Antarctica. Although measurements performed on the first ice cores, Camp Century and Byrd, largely focused on the isotopic composition of the ice as an indicator of climate change, the number of studied parameters has steadily increased encompassing numerous measurements performed on the entrapped air bubbles, on various impurities as well as on the ice itself. The climatic information provided by these various paleodata time is extremely rich. The relationships between forcing factors and climate, about the importance of carbon cycle feedbacks, about the occurrence of abrupt climate variability, and about the interplay between polar climate, ice sheet dynamics, and sea-level variations are examples that are highly relevant to future climate change. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website
    No preview · Article · Sep 2010
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    ABSTRACT: We compare the present and last interglacial periods as recorded in Antarctic water stable isotope records now available at various temporal resolutions from six East Antarctic ice cores: Vostok, Taylor Dome, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML), Dome Fuji and the recent TALDICE ice core from Talos Dome. We first review the different modern site characteristics in terms of ice flow, meteorological conditions, precipitation intermittency and moisture origin, as depicted by meteorological data, atmospheric reanalyses and Lagrangian moisture source diagnostics. These different factors can indeed alter the relationships between temperature and water stable isotopes. Using five records with sufficient resolution on the EDC3 age scale, common features are quantified through principal component analyses. Consistent with instrumental records and atmospheric model results, the ice core data depict rather coherent and homogenous patterns in East Antarctica during the last two interglacials. Across the East Antarctic plateau, regional differences, with respect to the common East Antarctic signal, appear to have similar patterns during the current and last interglacials. We identify two abrupt shifts in isotopic records during glacial inception at TALDICE and EDML, likely caused by regional sea ice expansion. These regional differences are discussed in terms of moisture origin and in terms of past changes in local elevation histories which are compared to ice sheet model results. Our results suggest that, for coastal sites, elevation changes may contribute significantly to inter-site differences. These elevation changes may be underestimated by current ice sheet models.
    Full-text · Article · Oct 2010 · Climate of the Past Discussions
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