Abstract
Abstract. We present new annual sedimentological proxies and sub-annual element scanner data from the Lago Grande di Monticchio (MON) sediment record for the sequence 76–112 thousand years before present (ka). They are combined with the previously published decadal to centennial resolved pollen assemblage in order to provide a comprehensive reconstruction of six major abrupt stadial spells (MON 1–6) in the central Mediterranean during the early phase of the last glaciation. These climatic oscillations are defined by intervals of thicker varves and high Ti-counts and coincide with episodes of forest depletion interpreted as Mediterranean stadial conditions (cold winter/dry summer). Our chronology, labelled as MON-2014, has been updated for the study interval by tephrochronology and repeated and more precise varve counts and is independent from ice-core and speleothem chronologies. The high-resolution Monticchio data then have been compared in detail with the Greenland ice-core δ18O record (NorthGRIP) and the northern Alps speleothem δ18Ocalcite data (NALPS). Based on visual inspection of major changes in the proxy data, MON 2–6 are suggested to correlate with Greenland stadials (GS) 25–20. MON 1 (Woillard event), the first and shortest cooling spell in the Mediterranean after a long phase of stable interglacial conditions, has no counterpart in the Greenland ice core, but coincides with the lowest isotope values at the end of the gradual decrease in δ18Oice in NorthGRIP during the second half of the Greenland interstadial (GI) 25. MON 3 is the least pronounced cold spell and shows gradual transitions, whereas its NorthGRIP counterpart GS 24 is characterized by sharp changes in the isotope records. MON 2 and MON 4 are the longest and most pronounced oscillations in the MON sediments in good agreement with their counterparts identified in the ice and spelethem records. The length of MON 4 (correlating with GS 22) supports the duration of stadial proposed by the NALPS timescales and suggests ca. 500 year longer duration than calculated by the ice-core chronologies GICC05modelext and AICC2012. Absolute dating of the cold spells provided by the MON-2014 chronology shows good agreement among the MON-2014, the GICC05modelext and the NALPS timescales for the period between 112 and 100 ka. In contrast, the MON-2014 varve chronology dates the oscillations MON 4 to MON 6 (92–76 ka) as ca. 3500 years older than the most likely corresponding stadials GS 22 to GS 20 by the other chronologies.
Highlights
The initial build-up of the Northern Hemisphere (NH) ice sheets spanned from 122 to ca. 70 thousand years before present; the ice sheet expansion was interrupted by millennial-scale recurrent phases of ice retreat (Mangerud et al, 1998)
The high-resolution measurements provide 1–15 data points per varve depending on the annual sedimentation rate. 1354 marker layers were used to transfer the μ-X-ray fluorescence (XRF) data on timescale using the varve counting-based age–depth model performed for the sedimentary record
The counting was from top to bottom, i.e. from young to old, and the whole chronology was established in two phases of counting: (1) from the present day back to 102 ka (MON-99), the chronology was developed on the composite profile B/D and core J (Allen et al, 1999); and (2) extended on the composite profile M/O for the interval 102 to 133 ka and a revision of the interval between 19.3 and 36.8 ka (MON-07; Brauer et al, 2007)
Summary
The initial build-up of the Northern Hemisphere (NH) ice sheets (early glaciation) spanned from 122 to ca. 70 thousand years before present (hereafter ka); the ice sheet expansion was interrupted by millennial-scale recurrent phases of ice retreat (Mangerud et al, 1998). In the NorthGRIP δ18Oice record, these periods of waxing and waning of ice sheets are mirrored by abrupt climate changes between relatively warm and humid (higher δ18Oice values) interstadials (GI 20–25) and cold and dry (lower δ18Oice) stadials (GS 26–20) (NorthGRIP project members, 2004). The existence of these GIs and GSs responds to the millennialscale climate variability known as Dansgaard–Oeschger oscillation (D–O) that characterized the whole Last Glacial. In the central Mediterranean, these oscillations are reflected in the pollen record of Lago Grande di Monticchio, in southern Italy, between 111 and 80 ka (Allen et al, 1999; Brauer et al, 2007) and in the isotope record of the Corchia Cave spleothem, in central Italy (Drysdale et al, 2007)
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