Chlorine isotopes constrain a major drawdown of the Mediterranean Sea during the Messinian Salinity Crisis

Hydrological restriction from the Atlantic Ocean transformed the Mediterranean Sea into a giant saline basin during the Messinian Salinity Crisis (5.97–5.33 million years ago). It is still unclear if the deposition of nearly one million km3 of evaporite salts during this event was triggered by a major (≥1 km) evaporative drawdown, or if it took place in a brine-filled Mediterranean connected to the Atlantic. Here we present evidence for a two-phase accumulation of the Mediterranean salt layer based on the chlorine stable isotope composition of halite. During the first phase, lasting approximately 35 kyr, halite deposition occurred only in the eastern Mediterranean, triggered by the restriction of Mediterranean outflow to the Atlantic, in an otherwise brine-filled Mediterranean basin. During the second phase, halite accumulation occurred across the entire Mediterranean, driven by a rapid (1 km-deep brine

Freshening of the Mediterranean Salt Giant: controversies and certainties around the terminal (Upper Gypsum and Lago-Mare) phases of the Messinian Salinity Crisis

The late Miocene evolution of the Mediterranean Basin is characterized by major changes in connectivity, climate and tectonic activity resulting in unprecedented environmental and ecological disruptions. During the Messinian Salinity Crisis (MSC, 5.97-5.33 Ma) this culminated in most scenarios first in the precipitation of gypsum around the Mediterranean margins (Stage 1, 5.97-5.60 Ma) and subsequently > 2 km of halite on the basin floor, which formed the so-called Mediterranean Salt Giant (Stage 2, 5.60-5.55 Ma). The final MSC Stage 3, however, was characterized by a "low-salinity crisis", when a second calcium-sulfate unit (Upper Gypsum; substage 3.1, 5.55-5.42 Ma) showing (bio)geochemical evidence of substantial brine dilution and brackish biota-bearing terrigenous sediments (substage 3.2 or Lago-Mare phase, 5.42-5.33 Ma) deposited in a Mediterranean that received relatively large amounts of riverine and Paratethys-derived low-salinity waters. The transition from hypersaline evaporitic (halite) to brackish facies implies a major change in the Mediterranean’s hydrological regime. However, even after nearly 50 years of research, causes and modalities are poorly understood and the original scientific debate between a largely isolated and (partly) desiccated Mediterranean or a fully connected and filled basin is still vibrant. Here we present a comprehensive overview that brings together (chrono)stratigraphic, sedimentological, paleontological, geochemical and seismic data from all over the Mediterranean. We summarize the paleoenvironmental, paleohydrological and paleoconnectivity scenarios that arose from this cross-disciplinary dataset and we discuss arguments in favour of and against each scenario

Two-photon excitation STED microscopy.

We report sub-diffraction resolution in two-photon excitation (TPE) fluorescence microscopy achieved by merging this technique with stimulated-emission depletion (STED). We demonstrate an easy-to-implement and promising laser combination based on a short-pulse laser source for two-photon excitation and a continuous-wave (CW) laser source for resolution enhancement. Images of fluorescent nanoparticles and the immunostained transcription regulator NF kappa B in mammalian cell nuclei exhibit resolutions of <50 nm and similar to 70 nm in the focal plane, respectively, corresponding to a 4-5.4-fold improvement over the diffraction barrier

STED with wavelengths closer to the emission maximum.

In stimulated emission depletion (STED) nanoscopy the wavelength of the STED beam is usually tuned towards the red tail of the emission maximum of the fluorophore. Shifting the STED wavelength closer to the emission peak, i.e. towards the blue region, favorably increases the stimulated emission cross-section. However, this blue-shifting also increases the probability to excite fluorophores that have remained in their ground state, compromising the image contrast. Here we present a method to exploit the higher STED efficiency of blue-shifted STED beams while maintaining the contrast in the image. The method is exemplified by imaging immunolabeled features in mammalian cells with an up to 3-fold increased STED efficiency compared to that encountered in standard STED nanoscopy implementations

STED with wavelengths closer to the emission maximum.

In stimulated emission depletion (STED) nanoscopy the wavelength of the STED beam is usually tuned towards the red tail of the emission maximum of the fluorophore. Shifting the STED wavelength closer to the emission peak, i.e. towards the blue region, favorably increases the stimulated emission cross-section. However, this blue-shifting also increases the probability to excite fluorophores that have remained in their ground state, compromising the image contrast. Here we present a method to exploit the higher STED efficiency of blue-shifted STED beams while maintaining the contrast in the image. The method is exemplified by imaging immunolabeled features in mammalian cells with an up to 3-fold increased STED efficiency compared to that encountered in standard STED nanoscopy implementations

Two and Three-dimensional near-field microscopy using scattering probes

International audienc

Two and Three-dimensional near-field microscopy using scattering probes

International audienc