A 144-cm-long core was obtained in Lake Petit (2200 m a.s.l., Mediterranean French Alps) in order to reconstruct past interactions between humans, the environment and the climate over the last five millennia using a multidisciplinary approach involving sedimentological, geochemical and botanical analyses. We show a complex pattern of environmental transformation. From 4800 to 4200 cal. BP, podzol-type soils progressively developed under forest cover. This stable situation was interrupted by a major detrital pulse at 4200 cal. BP that we consider as a tipping point in the environmental history. At this point, pedogenetic processes drastically regressed, leading to the development of moderately weathered soils. More frequent detrital inputs are recorded since 3000 cal. BP (ad 1050) as the human impact significantly increased in the catchment area. We conclude that destabilisation of the environment was triggered by climate and exacerbated by human activities to a stage beyond resilience.

Podzol

10.1177/0959683613508158

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Sea-surface salinity variations in the Northern Caribbean Sea across the mid-Pleistocene transition

Sophie Sépulcre Laurence Vidal Kazuyo Tachikawa Frauke Rostek Édouard Bard

Abstract. This study aimed at documenting climate changes in tropical area in response to the Mid-Pleistocene Transition (MPT) by reconstructing past hydrologic variations in the Northern Caribbean Sea and its influence on the stability of the Atlantic Meridional Overturning Circulation (AMOC) during the last 940 kyr. Using core MD03-2628, we estimated past changes in sea surface salinity (SSS) using Δδ18O, the difference between the modern and the past δ18O of seawater (obtained by combining alkenone thermometer data with the δ18O of the planktonic foraminifera Globigerinoides ruber (white) and corrected for ice-sheet volume effects). Today, the lowest SSS values in the studied area are associated with the northernmost location of the Inter-Tropical Convergence Zone (ITCZ). The Δδ18O record exhibits glacial/interglacial cyclicity with higher values during all glacial periods spanning the last 940 kyr, indicating increased SSS. At a longer timescale, the Δδ18O exhibits a shift toward lower values for interglacial periods during the last 450 kyr, when compared to interglacial stages older than 650 kyr. A rise in SSS during glacial stages may be related to the southernmost location of the ITCZ, which is induced by a steeper interhemispheric temperature gradient and associated with reduced northward cross equatorial oceanic transport. Therefore, the results suggest a permanent link between the tropical salinity budget and the AMOC during the last 940 kyr. Following the MPT, lower salinities during the last five interglacial stages indicate a northernmost ITCZ location, forced by changes in the interhemispheric temperature gradient that is associated with the poleward position of Southern Oceanic Fronts that amplified the transport of heat and moisture to the North Atlantic. These processes may have contributed to amplification of the climate cycles that followed the MPT.

Intertropical Convergence Zone

Deglaciation

δ18O

10.5194/cpd-6-1229-2010

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Glacial/Interglacial hydrologic changes in the south west Pacific

EAEJA (2003)

Laurence Vidal Kazuyo Tachikawa Corinne Sonzogni Luc Beaufort Édouard Bard

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