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The mechanisms underlying the current greenhouse gas (GHG) forced decline in Mediterranean rainfall remain a matter of debate. To inform our understanding of the current and projected drying, we examined extended arid intervals in the late Quaternary, Eastern Mediterranean (EM) Levant indicated by substantial salt deposits in a Dead Sea sediment core covering the past 220 kyr. These arid events occurred during interglacials, when the Earth was at perihelion to the sun in boreal fall and during glacial–interglacial transitions, associated with icesheet melting. Climate models forced with realistic late Quaternary insolation variations show that when the Earth is closest to the Sun in boreal fall, the North Atlantic latitudinal surface temperature gradient in the winter intensifies. In response, the overlying midlatitude North Atlantic jet stream and the extratropical storm track move poleward while sea-level pressure rises in the subtropics. These changes bring about a weakening of the Mediterranean storm track and a decline in rainfall over the entire basin. During glacial–interglacial transitions, meltwater from continental icesheets forced abrupt subpolar North Atlantic cooling. This also strengthened the latitudinal surface temperature gradient, likely causing similar atmospheric response and aridity in the Mediterranean. There is a strong resemblance between this paleoclimate scenario and the climatic changes corresponding to the present and projected GHG drying of the EM. Hence, the late Quaternary palaeohydrology of the Dead Sea indicates an important North Atlantic centered response to external forcing, which leads to Mediterranean drying and is relevant in the present. 

Abstract. Spatially distant sources of neodymium (Nd) to the ocean that carry different isotopic signatures (εNd) have been shown to trace out major water masses and have thus been extensively used to study large-scale features of the ocean circulation both past and current. While the global marine Nd cycle is qualitatively well understood, a complete quantitative determination of all its components and mechanisms, such as the magnitude of its sources and the paradoxical conservative behavior of εNd, remains elusive. To make sense of the increasing collection of observational Nd and εNd data, in this model description paper we present and describe the Global Neodymium Ocean Model (GNOM) v1.0, the first inverse model of the global marine biogeochemical cycle of Nd. The GNOM is embedded in a data-constrained steady-state circulation that affords spectacular computational efficiency, which we leverage to perform systematic objective optimization, allowing us to make preliminary estimates of biogeochemical parameters. Owing to its matrix representation, the GNOM model is additionally amenable to novel diagnostics that allow us to investigate open questions about the Nd cycle with unprecedented accuracy. This model is open-source and freely accessible, is written in Julia, and its code is easily understandable and modifiable for further community developments, refinements, and experiments. 

Abstract Chemical events involving deep carbon- and water-rich fluids impact the continental lithosphere over its history. Diamonds are a by-product of such episodic fluid infiltrations, and entrapment of these fluids as microinclusions in lithospheric diamonds provide unique opportunities to investigate their nature. However, until now, direct constraints on the timing of such events have not been available. Here we report three alteration events in the southwest Kaapvaal lithosphere using U-Th-He geochronology of fluid-bearing diamonds, and constrain the upper limit of He diffusivity (toD ≈ 1.8 × 10⁻¹⁹cm²s⁻¹), thus providing a means to directly place both upper and lower age limits on these alteration episodes. The youngest, during the Cretaceous, involved highly saline fluids, indicating a relationship with late-Mesozoic kimberlite eruptions. Remnants of two preceding events, by a Paleozoic silicic fluid and a Proterozoic carbonatitic fluid, are also encapsulated in Kaapvaal diamonds and are likely coeval with major surface tectonic events (e.g. the Damara and Namaqua–Natal orogenies).