Maxime Debret

One-to-one coupling of glacial climate variability in Greenland and Antarctica.

Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth’s climate dynamics. For the last glacial period, ice core studies have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard–Oeschger events in Greenland through the Atlantic meridional overturning circulation. It has been unclear, however, whether the shorter Dansgaard–Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations, and whether these events are linked by the same mechanism. Here we present a glacial climate record derived from an ice core from Dronning Maud Land, Antarctica, which represents South Atlantic climate at a resolution comparable with the Greenland ice core records. After methane synchronization with an ice core from North Greenland, the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard–Oeschger events by the bipolar seesaw6. The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North, suggesting that they all result from a similar reduction in the meridional overturning circulation.

Climate variability features of the last interglacial in the East Antarctic EPICA Dome C ice core

Whereas millennial to submillennial climate variability has been identified during the current interglacial period, past interglacial variability features remain poorly explored because of lacking data at sufficient temporal resolutions. Here we present new deuterium data from the EPICA Dome C ice core, documenting at decadal resolution temperature changes occurring over the East Antarctic plateau during the warmer-than-today last interglacial. Expanding previous evidence of instabilities during the last interglacial, multicentennial subevents are identified and labeled for the first time in a past interglacial context. A variance analysis further reveals two major climatic features. First, an increase in variability is detected prior to the glacial inception, as already observed at the end of Marine Isotopic Stage 11 in the same core. Second, the overall variance level is systematically higher during the last interglacial than during the current one, suggesting that a warmer East Antarctic climate may also be more variable.

Coupled Rock-Eval pyrolysis and spectrophotometry for lacustrine sedimentary dynamics: Application for West Central African rainforests (Kamalété and Nguène lakes, Gabon)

In recent years, Nguène Lake and Kamalété Lake (Gabon, West Central Africa) have been studied repeatedly, providing comprehensive reconstructions of environmental changes over the last millennia. Both lakes are in different geomorphological and environmental settings. They are therefore excellent sites to test new methodological approaches. Indeed, the sedimentary cores provide various facies, and the previous studies provide references for calibrating the results of new methods. In this methodological issue, the present study aims to evaluate the potential of spectrophotometric and Rock-Eval coupled analysis to describe the Holocene lake and marsh deposits from tropical moist forests. This assessment is carried out on samples taken from two well-documented reference cores. The spectrophotometric analysis provides reproducible colour measurements, which inform about the nature of the main colour-bearing constituents. Coupled with Rock-Eval pyrolysis, this technique can be used to describe lithological changes and identify the probable source of sedimentary organic matter. In the studied cases, this approach identified the facies dominated by detrital terrigenous inputs (‘iron bearing’ signature and high OI values) and those associated with a more abundant primary production (‘chlorophyll’ signature, low OI and high HI), providing a distinction between palustrine and lacustrine dynamics. However, although the facies are comparable, sedimentary dynamics and sediment sources may vary depending on geomorphological and climatic contexts.

2000 Years of Grazing History and the Making of the Cretan Mountain Landscape, Greece

Understanding the processes that led to the recent evolution of Mediterranean landscapes is a challenging question that can be addressed with paleoecological data. Located in the White Mountains of Crete, Asi Gonia peat bog constitutes an exceptional 2000-years-long sedimentary archive of environmental change. In this study, we document the making of the White Mountains landscape and assess human impact on ecosystem trajectories. The paleoenvironmental reconstruction is based on high-resolution analyses of sediment, pollen, dung fungal spores and charcoal obtained from a 6-m core collected from the bog. Multiproxy analyses and a robust chronological control have shed light on anthropogenic and natural processes that have driven ecological changes, giving rise to the present-day Mediterranean ecosystem. Our results suggest that sediment accumulation began during the transition from the Hellenistic to the Roman period, likely due to watershed management. The evolution of the peat bog as well as vegetation dynamics in the surrounding area were linked to past climate changes but were driven by human activities, among which breeding was of great importance. Charcoal analysis reveals that fire was largely used for the construction and maintenance of sylvo-agropastoral areas. Pollen data allow the identification of three main vegetation assemblages: 1) evergreen oak forest (before ca. 850 AD), 2) heather maquis (ca. 850 to 1870 AD), 3) phrygana/steppe landscape. Rapid changes between phases in vegetation development are associated with tipping-points in ecosystem dynamics resulting from anthropogenic impact. The modern ecosystem did not get established until the 20th century, and it is characterized by biodiversity loss along with a dramatic drying of the peat bog.