No abstract

Antarctic ice preserves an ~800 kyr record of dust activity in the Southern Hemisphere. Major efforts have been dedicated to elucidate the origin of this material in order to gain greater insight into the atmospheric dust cycle. On the basis of Pb isotopes in Antarctic dust samples and potential sources, this contribution demonstrates for the first time that Patagonia is the main contributor of dust to Antarctica during interglacial periods as well as glacials, although the potential importance of Tierra del Fuego remains unclear because of its geochemical similarities to Patagonia. An important new finding is that the Puna‐Altiplano sector of the continent is a second important dust source to eastern Antarctica during both glacials and interglacials, being more prominent during interglacials. The data indicate South America is the primary dust source to Antarctica during both glacials and interglacials.

This study provides a detailed description of the sources, transport, dispersion, and deposition of two major dust events originating from the high‐altitude subtropical Puna‐Altiplano Plateau (15–26°S; 65–69°W) in South America. A long and severe drought provided the right conditions for the onset of both events in July 2009 and 2010. Dust was transported SE and deposited over the Pampas region and was observed to continue to the Atlantic Ocean. Dust monitoring stations located downwind recorded both events, and samples were characterized through chemical and textural analysis. Through a combination of meteorological data and satellite observations (CALIPSO and MODIS detectors), we estimate the emission flux for the 2010 event. This estimate was used to constrain the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) transport model and simulate the dust event. Both satellite imagery and model results agree in the location and extension of the dust cloud. CALIPSO detected dust between ~6000 and ~8500 m a.s.l., which remained at this height during most of its trajectory. The dust cloud mixed with a strong convective system in the region, and the associated precipitation brought down significant amounts of dust to the ground. Dust particle size analysis for both events indicates that near the sources dust samples show median modes of 12.4–14.1 µm, similar to modes observed 1300 km away. Chemical composition of sediments from potential dust sources shows distinct signatures within the Puna‐Altiplano Plateau, the Puna sector being clearly different from the Altiplano area. In addition, both sources are markedly different from the Patagonian chemical fingerprint. These results have important implications to improve the interpretation of paleo‐environmental archives preserved on the Argentine loess, Antarctic ice cores, and Southern Ocean marine sediments.

As the most abundant cation in archaeal, bacterial, and eukaryotic cells, potassium (K+) is an essential element for life. While much is known about the machinery of transcellular and paracellular K transport–channels, pumps, co-transporters, and tight-junction proteins—many quantitative aspects of K homeostasis in biological systems remain poorly constrained. Here we present measurements of the stable isotope ratios of potassium (41K/39K) in three biological systems (algae, fish, and mammals). When considered in the context of our current understanding of plausible mechanisms of K isotope fractionation and K+ transport in these biological systems, our results provide evidence that the fractionation of K isotopes depends on transport pathway and transmembrane transport machinery. Specifically, we find that passive transport of K+ down its electrochemical potential through channels and pores in tight-junctions at favors 39K, a result which we attribute to a kinetic isotope effect associated with dehydration and/or size selectivity at the channel/pore entrance. In contrast, we find that transport of K+ against its electrochemical gradient via pumps and co-transporters is associated with less/no isotopic fractionation, a result that we attribute to small equilibrium isotope effects that are expressed in pumps/co-transporters due to their slower turnover rate and the relatively long residence time of K+ in the ion pocket. These results indicate that stable K isotopes may be able to provide quantitative constraints on transporter-specific K+ fluxes (e.g., the fraction of K efflux from a tissue by channels vs. co-transporters) and how these fluxes change in different physiological states. In addition, precise determination of K isotope effects associated with K+ transport via channels, pumps, and co-transporters may provide unique constraints on the mechanisms of K transport that could be tested with steered molecular dynamic simulations.

Atmospheric dust is an integral component of the Earth system with major implications for the climate, biosphere and public health. In this context, identifying and quantifying the provenance and the processes generating the various types of dust found in the atmosphere is paramount. Isotopic signatures of Pb, Nd, Sr, Zn, Cu and Fe are commonly used as sensitive geochemical tracers. However, their combined use is limited by the lack of (a) a dedicated chromatographic protocol to separate the six elements of interest for low-mass samples and (b) specific reference materials for dust. Indeed, our work shows that USGS rock reference materials BHVO-2, AGV-2 and G-2 are not applicable as substitute reference materials for dust. We characterised the isotopic signatures of these six elements in dust reference materials ATD and BCR-723, representatives of natural and urban environments, respectively. To achieve this, we developed a specific procedure for dust, applicable in the 4-25 mg mass range, to separate the six elements using a multi-column ion-exchange chromatographic method and MC-ICP-MS measurements.

Mineral dust is a natural tracer of atmospheric composition and climate variability. Yet, there is still much to be known about the Southern Hemisphere dust cycle during the last Pleistocene. Major efforts have attempted to solve the ‘puzzle’ of the origin of the potential source areas that contribute dust to the Southern Ocean and East Antarctica (EA). Here we present a comprehensive geochemical characterization of an important potential source area, which role as a dust supplier to different environments of the SH has significantly been underestimated, that is, the Southern Africa (SAF) region. On the basis of Sr-Nd-Pb isotope ratios and rare earth element concentrations analyzed in sediments collected along the major dust-producing areas in the Namibian coast (Kuiseb, Omaruru and Huab riverbeds and the Namibian sand sea region), this study demonstrates for the first time that SAF emerges as the second most important dust source to EA during interglacial times.

Mineral dust is a natural tracer of atmospheric composition and climate variability. Yet, there is still much to be known about the Southern Hemisphere dust cycle. Major efforts have attempted to solve the puzzle of the origin of the potential source areas contributing dust to the Southern Ocean and East Antarctica. Here we present a comprehensive geochemical characterization of a source area, whose role as a dust supplier to high latitude environments has significantly been underestimated. Sediments collected within the major dust-producing areas along the Namibian coast in Southern Africa (Kuiseb, Omaruru and Huab river catchments and the Namib Sand Sea region), were analyzed for radiogenic isotope ratios and rare earth element concentrations. We find that during warm periods, the Southern African dust signature can be found in archives of the Southern Hemisphere, especially in the Atlantic sector of the Southern Ocean and peripheral areas of the East Antarctic plateau.

Hepatitis E virus (HEV) is an RNA virus responsible for over 20 million infections annually. HEV’s open reading frame (ORF)1 polyprotein is essential for genome replication, though it is unknown how the different subdomains function within a structural context. Our data show that ORF1 operates as a multifunctional protein, which is not subject to proteolytic processing. Supporting this model, scanning mutagenesis performed on the putative papain-like cysteine protease (pPCP) domain revealed six cysteines essential for viral replication. Our data are consistent with their role in divalent metal ion coordination, which governs local and interdomain interactions that are critical for the overall structure of ORF1; furthermore, the ‘pPCP’ domain can only rescue viral genome replication in trans when expressed in the context of the full-length ORF1 protein but not as an individual subdomain. Taken together, our work provides a comprehensive model of the structure and function of HEV ORF1.