Guillaume Soulet

Abrupt drainage cycles of the Fennoscandian Ice Sheet

Continental ice sheets are a key component of the Earth’s climate system, but their internal dynamics need to be further studied. Since the last deglaciation, the northern Eurasian Fennoscandian Ice Sheet (FIS) has been connected to the Black Sea (BS) watershed, making this basin a suitable location to investigate former ice-sheet dynamics. Here, from a core retrieved in the BS, we combine the use of neodymium isotopes, high-resolution elemental analysis, and biomarkers to trace changes in sediment provenance and river runoff. We reveal cyclic releases of meltwater originating from Lake Disna, a proglacial lake linked to the FIS during Heinrich Stadial 1. Regional interactions within the climate–lake–FIS system, linked to changes in the availability of subglacial water, led to abrupt drainage cycles of the FIS into the BS watershed. This phenomenon raised the BS water level by ∼100 m until the sill of the Bosphorus Strait was reached, flooding the vast northwestern BS shelf and deeply affecting the hydrology and circulation of the BS and, probably, of the Marmara and Aegean Seas.

A note on reporting of reservoir 14C disequilibria and age offsets

Reservoir age offsets are widely used to correct marine and speleothem radiocarbon age measurements for various calibration purposes. They also serve as a powerful tracer for carbon cycle dynamics. However, a clear terminology regarding reservoir age offsets is lacking, sometimes leading to miscalculations. This note seeks to provide consistent conventions for reporting reservoir 14C disequilibria useful to a broad range of environmental sciences. This contribution introduces the F14R and δ14R metrics to express the relative 14C disequilibrium between two contemporaneous reservoirs and the R metric as the associated reservoir age offset.

Assessing the blank carbon contribution, isotope mass balance, and kinetic isotope fractionation of the Ramped Pyrolysis/Oxidation instrument at NOSAMS

We estimate the blank carbon mass over the course of a typical Ramped PyrOx (RPO) analysis (150–1000°C; 5°C×min –1 ) to be (3.7±0.6) μg C with an Fm value of 0.555±0.042 and a δ 13 C value of (–29.0±0.1) ‰ VPDB. Additionally, we provide equations for RPO Fm and δ 13 C blank corrections, including associated error propagation. By comparing RPO mass-weighted mean and independently measured bulk δ 13 C values for a compilation of environmental samples and standard reference materials (SRMs), we observe a small yet consistent 13 C depletion within the RPO instrument (mean–bulk: μ=–0.8‰; ±1σ=0.9‰; n =66). In contrast, because they are fractionation-corrected by definition, mass-weighted mean Fm values accurately match bulk measurements (mean–bulk: μ=0.005; ±1σ=0.014; n =36). Lastly, we show there exists no significant intra-sample δ 13 C variability across carbonate SRM peaks, indicating minimal mass-dependent kinetic isotope fractionation during RPO analysis. These data are best explained by a difference in activation energy between 13 C- and 12 C-containing compounds ( 13–12 ∆E ) of 0.3–1.8 J×mol –1 , indicating that blank and mass-balance corrected RPO δ 13 C values accurately retain carbon source isotope signals to within 1–2‰.

Les sédiments de la mer Noire

Il y a environ 21 000 ans, la geographie de l’Europe etait bien differente de celle d’aujourd’hui. Une veritable montagne de glace, la calotte fennoscandienne, recouvrait toute l’Europe du Nord depuis les iles britanniques jusqu’a la Siberie. Le niveau des oceans etait alors plus bas de 120 metres. Un fleuve geant, le fleuve Manche, coulait sur une plaine entre la France et l’Angleterre. En Europe centrale, la mer Noire n’etait pas connectee a la mer Mediterranee et formait un grand lac dont ...