Description: Antarctica has traditionally been considered continental inside the coastline of ice and bedrock since Press and Dewart (1959). Sixty years later, we reconsider the conventional extent of this sixth continent. Geochemical observations show that subduction was active along the whole western coast of West Antarctica until the mid-Cretaceous after which it gradually ceased towards the tip of the Antarctic Peninsula. We propose that the entire West Antarctica formed as a back-arc basin system flanked by a volcanic arc, similar to e.g. the Japan Sea, instead of a continental rift system as conventionally interpreted. Globally, the fundamental difference between oceanic and continental lithosphere is reflected in hypsometry, largely controlled by lithosphere buoyancy. The equivalent hypsometry in West Antarctica (−580 ± 335 m on average, extending down to −1.6 km) is much deeper than in any continent, but corresponds to back-arc basins and oceans proper. This first order observation questions the conventional interpretation of West Antarctica as continental, since even continental shelves do not extend deeper than −200 m in equivalent hypsometry. We present a suite of geophysical observations that supports our geodynamic interpretation: a linear belt of seismicity sub-parallel to the volcanic arc along the Pacific margin of West Antarctica; a pattern of free air gravity anomalies typical of subduction systems; and extremely thin crystalline crust typical of back-arc basins. We calculate residual mantle gravity anomalies and demonstrate that they require the presence of (1) a thick sedimentary sequence of up to ca. 50% of the total crustal thickness or (2) extremely low density mantle below the deep basins of West Antarctica and, possibly, the Wilkes Basin in East Antarctica. Case (2) requires the presence of anomalously hot mantle below the entire West Antarctica with a size much larger than around continental rifts. We propose, by analogy with back-arc basins in the Western Pacific, the existence of rotated back-arc basins caused by differential slab roll-back during subduction of the Phoenix plate under the West Antarctica margin. Our finding reduces the continental lithosphere in Antarctica to 2/3 of its traditional area. It has significant implications for global models of lithosphere-mantle dynamics and models of the ice sheet evolution.

Description: Highlights • Temporally close-spaced double eruption within a couple of hundreds of years. • Magmas are variably tapped from zoned magma chambers during eruptions due to changing magma discharge rates and/or vent migration. • Eruptions started with a series of fallouts featuring stable eruption columns followed by fluctuating and partially collapsing eruption columns. • Eruptive volumes sum up to a total of 25.6 km3 and 40.5 km3 tephra volume, eruption column heights have been between 20–33 km. • Potential hazards from similar sized eruptions around Coatepeque Caldera are indicated even in the distal regions around San Salvador. Abstract The Coatepeque volcanic complex in El Salvador produced at least four Plinian eruptions within the last 80 kyr. The eruption of the 72 ka old Arce Tephra formed the Coatepeque Caldera and was one of the most powerful explosive eruptions in El Salvador. Hitherto it was thought that the Arce tephra had been emplaced only by one, mostly Plinian, eruptive event that ended with the deposition of a thick ignimbrite. However, our stratigraphic, geochemical, and zircon data reveal a temporally closely- spaced double eruption separated by a gap of only a couple of hundred years, and we therefore distinguish Lower and Upper Arce Tephras. Both eruptions produced in the beginning a series of fallout units generated from fluctuating eruption columns and turning wind directions. The final phase of the Upper Arce eruption produced surge deposits by several eruption column collapses before the terminal phase of catastrophic ignimbrite eruption and caldera collapse. Mapping of the individual tephra units including the occurrences of distal marine and lacustrine ash layers in the Pacific Ocean, the Guatemalan lowlands and the Caribbean Sea, result in 25.6 km3 tephra volume, areal distribution of 4 × 105 km2 and eruption column heights between 20–33 km for the Lower Arce eruption, and 40.5 km3 tephra volume, including 10 km3 for the ignimbrite, distributed across 6 × 105 km2 and eruption column heights of 23–28 km for the Upper Arce eruption. These values and the detailed eruptive sequence emphasize the great hazard potential of possible future highly explosive eruptions at Coatepeque Caldera, especially for this kind of double eruption.

Description: The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO2) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO2 thresholds in biological and cryosphere evolution.

Description: Snow is an important driver of ecosystem processes in cold biomes. Snow accumulation determines ground temperature, light conditions and moisture availability during winter. It also affects the growing season’s start and end, and plant access to moisture and nutrients. Here, we review the current knowledge of the snow cover’s role for vegetation, plant-animal interactions, permafrost conditions, microbial processes and biogeochemical cycling. We also compare studies of natural snow gradients with snow manipulation studies, altering snow depth and duration, to assess time scale difference of these approaches. The number of studies on snow in tundra ecosystems has increased considerably in recent years, yet we still lack a comprehensive overview of how altered snow conditions will affect these ecosystems. In specific, we found a mismatch in the timing of snowmelt when comparing studies of natural snow gradients with snow manipulations. We found that snowmelt timing achieved by manipulative studies (average 7.9 days advance, 5.5 days delay) were substantially lower than those observed over spatial gradients (mean range of 56 days) or due to interannual variation (mean range of 32 days). Differences between snow study approaches need to be accounted for when projecting snow dynamics and their impact on ecosystems in future climates.

Description: The Yedoma region is unique in the permafrost region of the Northern Hemisphere and is characterized by a particularly high ground ice content in the sediment. These frozen deposits store a large amount of carbon and thus have the potential to influence the global climate. Especially the upper layers are susceptible to thaw processes, as they are exposed to increasingly rising mean annual air temperatures. The Northeastern Siberian Yedoma domain is of particular interest in this study. The morphology of ground ice is highly variable and the exact abundance and distribution is still unknown in large parts of Siberia. For an accurate overview of the distribution of intrasedimentary ground ice content, data from 26 sites in Northeastern Siberia were examined. The data were taken from data repositories (e.g., PANGAEA), expedition reports, scientific papers etc. and has been synthesized in a template in Excel. Of relevance was the absolute ice content (wt%) at different depths. Five depth classes were investigated: depth class 1: 0-0.99m; depth class 2: 1-1.99m; depth class 3: 2-2.99m; depth class 4: 3-24.99m; depth class 5: 25-65m. Using the mean absolute ice content for each depth class, ArcGIS was used to create a map for the distribution of ice content. R was applied to represent the ground ice content distribution at the different depths. Furthermore, the focus was on other parameters such as stratigraphy, total organic carbon content and landscape types, which were also examined with respect to the absolute ice content. The ice content is distributed very heterogeneously in Northeastern Siberia, averaging between 30 and 60 wt% over all depths. In large parts of the study area, the ice content in the upper three meters is with 40 to 65 wt% much higher than in the deeper sediment layers. In the depths of 3-65m, the ice content ranges from 20 to 50 wt%. Investigations of the age classes showed that the mean absolute ice content in thermokarst deposits (MIS 1) is with 48.60 wt% higher than in older sedimentary units. The TOC content also decreases significantly with depth. The Yedoma sediment composition and depositional regimes are highly variable. Even on a small scale, large differences in ice content could be observed. With the given data basis, no concrete statements about the vertical and horizontal ice content could be made for the whole study area. The model created in this study can be applied to model the absolute ground ice content based on the TOC content. Assessing the nature and content of ground ice in the upper layers in Northeastern Siberia is fundamental to environmental assessment and important for quantifying carbon fluxes and understanding permafrost response to climate change.

Description: L’articolo richiama l’attenzione sulla distribuzione di genere nel settore dell’alta formazione in Italia e all’estero per le scienze della terra e offre un'analisi della situazione delle ricercatrici nell’INGV e in altri enti pubblici di ricerca quali CNR, OGS, ISPRA studiandone i pattern per rilevare differenze e similitudini.

Description: Published

Description: 87-94

Description: OS: Terza missione