Vasiliki Margari

Interglacials of the last 800,000 years

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, 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.

The new chronology of the Ceprano calvarium (Italy)

IntroductionThe fossil human calvarium known as Ceprano (Latium, Italy) iscommonly dated to 800e900 ka, on the basis of geological andstratigraphical inferences (Ascenzi et al., 1996, 2000). This chro-nology appeared somehow consistent with the “archaic”morphology of the calvarium and its peculiar combination offeatures, which gave rise to a controversial taxonomic identity(Ascenzietal.,1996,2000;Clarke,2000;Manzietal.,2001;Mallegniet al., 2003; Bruner and Manzi, 2005, 2007). A re-evaluation of thislate Early Pleistocene chronology has been advanced by Muttoniet al. (2009) on the basis of paleomagnetic data. This hypothesis istested here, based on the combined evaluation of the multidisci-plinary evidence collected during recent systematic excavations.The specimen was discovered on 13 March 1994 within a claylevel partly destroyed by bulldozers working for a new road ina locality known as Campogrande (Fig. 1), about 3 km SW ofCeprano and 100 km SE of Rome, in Central Italy (for review andreferences see Manzi, 2004). The sediment containing the cranialfragments yielded more than 50 fragments. However, the craniumremainedincompletebecauseneitherportionsof thefacenorteethwere retrieved.The geological history of the Campogrande area was initiallyreferred to two main stratigraphic complexes (Ascenzi et al., 1996,2000; Ascenzi and Segre, 1997a,b): 1) upper fluvio-colluvialdeposits, with variable occurrence of volcanoclastic products (lateEarly to Middle Pleistocene); 2) lower lacustrine deposits, withoutvolcanoclastic products (roughly predating 1.0 Ma). The layercontaining the human calvarium was considered to belong to thelower portion of the upper stratigraphic complex. Its chronologywas inferred as more ancient than the Acheulean site of FontanaRanuccio, near Anagni (458 5.7 ka; Segre and Ascenzi, 1984),possiblyolderthan700ka,adatecorrespondingtothebeginningofthe volcanic activity in the region (Fornaseri, 1985).Given the presence in the Ceprano basin of various LowerPaleolithic assemblages, the archaic features of the calvarium andits hypothetical chronological position were considered in associ-ation with Mode 1, or Oldowan, techno-complexes (Biddittu,1984;Ascenzietal.,1996,2000).Mode1Paleolithicintheareacomefromvarious localities, including Arce, Castro de’ Volsci, Fontana Liri(Biddittu, 1972, 1974), as well as from the Campogrande area itself(see SOM-1), whose assemblages are characterized by flint orlimestone pebble-tools (mostly choppers, chopping-tools andpercussion tools), by debitage with hammerstone flakes, and byrelatively frequent cores, with a low degree of exploitation, mostoften unifacial, and high frequencyof cortical striking platforms. Asfor Mode 2 or Acheulean assemblages, new recent data (excava-tions 2001e2006; see below) have made it possible to bettercharacterize the material from Campogrande. These materials arenot numerically rich, but they yield evidence of each production

Land-ocean changes on orbital and millennial time scales and the penultimate glaciation

Past glacials can be thought of as natural experiments in which variations in boundary conditions influenced the character of climate change. However, beyond the last glacial, an integrated view of orbital- and millennial-scale changes and their relation to the record of glaciation has been lacking. Here, we present a detailed record of variations in the land-ocean system from the Portuguese margin during the penultimate glacial and place it within the framework of ice-volume changes, with particular reference to European ice-sheet dynamics. The interaction of orbital- and millennial-scale variability divides the glacial into an early part with warmer and wetter overall conditions and prominent climate oscillations, a transitional mid-part, and a late part with more subdued changes as the system entered a maximum glacial state. The most extreme event occurred in the mid-part and was associated with melting of the extensive European ice sheet and maximum discharge from the Fleuve Manche river. This led to disruption of the meridional overturning circulation, but not a major activation of the bipolar seesaw. In addition to stadial duration, magnitude of freshwater forcing, and background climate, the evidence also points to the influence of the location of freshwater discharges on the extent of interhemispheric heat transport.

Enhanced climate instability in the North Atlantic and southern Europe during the Last Interglacial

Considerable ambiguity remains over the extent and nature of millennial/centennial-scale climate instability during the Last Interglacial (LIG). Here we analyse marine and terrestrial proxies from a deep-sea sediment sequence on the Portuguese Margin and combine results with an intensively dated Italian speleothem record and climate-model experiments. The strongest expression of climate variability occurred during the transitions into and out of the LIG. Our records also document a series of multi-centennial intra-interglacial arid events in southern Europe, coherent with cold water-mass expansions in the North Atlantic. The spatial and temporal fingerprints of these changes indicate a reorganization of ocean surface circulation, consistent with low-intensity disruptions of the Atlantic meridional overturning circulation (AMOC). The amplitude of this LIG variability is greater than that observed in Holocene records. Episodic Greenland ice melt and runoff as a result of excess warmth may have contributed to AMOC weakening and increased climate instability throughout the LIG.It is important to establish a baseline for natural climate variability under relatively warm conditions. Here we show that the Last Interglacial in the North Atlantic and southern Europe was characterized by enhanced climate instability relative to the pre-industrial Holocene.