The Phase A study of the ESA M4 mission candidate ARIEL

ARIEL, the Atmospheric Remote sensing Infrared Exoplanet Large survey, is one of the three M-class mission candidates competing for the M4 launch slot within the Cosmic Vision science programme of the European Space Agency (ESA). As such, ARIEL has been the subject of a Phase A study that involved European industry, research institutes and universities from ESA member states. This study is now completed and the M4 down-selection is expected to be concluded in November 2017. ARIEL is a concept for a dedicated mission to measure the chemical composition and structure of hundreds of exoplanet atmospheres using the technique of transit spectroscopy. ARIEL targets extend from gas giants (Jupiter or Neptune-like) to super-Earths in the very hot to warm zones of F to M-type host stars, opening up the way to large-scale, comparative planetology that would place our own Solar System in the context of other planetary systems in the Milky Way. A technical and programmatic review of the ARIEL mission was performed between February and May 2017, with the objective of assessing the readiness of the mission to progress to the Phase B1 study. No critical issues were identified and the mission was deemed technically feasible within the M4 programmatic boundary conditions. In this paper we give an overview of the final mission concept for ARIEL as of the end of the Phase A study, from scientific, technical and operational perspectives.     

Pollen sequence from the Chilean Lake District during the Llanquihue glaciation in marine Oxygen Isotope Stages 4–2

Pollen stratigraphy of a core taken from a fen at Fundo Nueva Braunau (40°17.49′S, 73°04.83′W), situated 2 km beyond the western border of Llanquihue‐age glacial drift, spans an age range from an estimated 60 000–70 000 BP to about 14 000 ¹⁴C yr BP (marine Oxygen Isotope Stages 4–2). The location at present is in the contact zone of Valdivian Evergreen Forest and Lowland Deciduous Beech Forest. Early and late in the pollen record, as indicated by assemblages of southern beech (Nothofagus dombeyi type) and grass (Gramineae), the site was located in Subantarctic Parkland. Intervening assemblages represent expansion of Valdivian–North Patagonian Evergreen Forest (> 49 355 to about 40 000 ¹⁴C yr BP) and North Patagonian Evergreen Forest–Subantarctic Parkland (approximately 40 000 to 30 000 ¹⁴C yr BP). Climate over the time span was under the storm regime of the Southern Westerlies and apparently uninterruptedly wet. When Subantarctic Parkland expanded, cold conditions with summer temperatures estimated at 8–9°C (7°C lower than present) resulted in episodes of glacier maxima. Climate moderated during the period of forest expansion, at which time glaciers were in a state of recession. Contrasting with the continuously wet climate of the Lake District for the period of record, climate in semi‐arid–arid, subtropical Chile underwent extended intervals of precipitation. Data from both the terrestrial and marine realm implicate the Southern Westerlies as the cause of intensified storm activity at lower latitudes. Copyright © 2000 John Wiley & Sons, Ltd.     

Saharan Dust Transport and High-Latitude Glacial Climatic Variability: The Alboran Sea Record

Millennial to submillennial marine oscillations that are linked with the North Atlantic's Heinrich events and Dansgaard–Oeschger cycles have been reported recently from the Alboran Sea, revealing a close ocean-atmosphere coupling in the Mediterranean region. We present a high-resolution record of lithogenic fraction variability along IMAGES Core MD 95-2043 from the Alboran Sea that we use to infer fluctuations of fluvial and eolian inputs to the core site during periods of rapid climate change, between 28,000 and 48,000 cal yr B.P. Comparison with geochemical and pollen records from the same core enables end-member compositions to be determined and to document fluctuations of fluvial and eolian inputs on millennial and faster timescales. Our data document increases in northward Saharan dust transports during periods of strengthened atmospheric circulation in high northern latitudes. From this we derive two atmospheric scenarios which are linked with the intensity of meridional atmospheric pressure gradients in the North Atlantic region.     

Granulometric selectivity in Liza ramado and potential contamination resulting from heavy metal load in feeding areas

The stomach contents of thin-lipped grey mullets Liza ramado were analysed in terms of granulometric composition and compared to the sediment of potential feeding areas in the Tagus estuary. Total organic matter (TOM) content and heavy metal content were determined in the surface sediment of three areas and eight trace elements were quantified: Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn. The three sampled areas did not differ in TOM; and the heavy metal content was below Effects Range-Low level for most elements. The mean observed concentrations were present in the following sequence: Zn > Pb > Cr > Cu ≈ Ni > Co > Cd > Hg. Stomach contents granulometric composition provided information about the feeding selectivity of the mullets. Sediment fractions with particle size between 20 and 50 μm are preferred, independently of the fishes' length. Smaller standard length (SL) fishes have a higher positive selection of fine grained sediments than those with a larger SL. Finer fractions usually have higher concentration of heavy metals, which makes younger specimens of the thin-lipped grey mullet potentially more exposed to heavy metal load in the estuary. Metal concentration was not independent from the sampling point, presenting higher values near the margins and the estuary tidal drainage system. This means that during the first period of each tidal cycle, the mullets will feed first on the most contaminated areas, as a consequence of their movement following the rising tide to feed on previously exposed areas.     

The Effect of Heavy Tamping on Structured Residual Clay Site

This paper examines the effect of heavy tamping (dynamic compaction) on highly porous structured residual clayey soil. The aim of this study is to analyse the feasibility of this technique when applied on lightly bonded residual soil sites, which are commonly found in tropical and subtropical regions. This soil has some interesting characteristics, such as high fine grain soil percentages (56% clay and 22% silt), a plastic index of 11%, high porosity (initial void ratio of 1.21), high hydraulic conductivity (about 10^?5 m/s) and a high stiffness at small strains (E?=?49.2-MPa). The research involves field [Cone Penetration Test (CPT) and the dynamic compaction] and laboratory (triaxial tests, characterization and hydraulic conductivity) investigation. According to laboratory tests, the void ratio decreased to 0.96, hydraulic conductivity decreased to 2.8?×?10^?7 m/s, the effective peak friction angle (?′) increased from 30.5° (in natural conditions) to about 35.5°, and the triaxial stiffness at small strains decreased to E?=?20-MPa due to dynamic compaction. CPT results have shown an improved depth in which CPT tip strength (q_t) increased from nearly 650-kPa to an average of 1700-kPa and CPT sleeve friction (f_s) increased from approximately 50-kPa to about 130-kPa. Horizontal displacements were observed up to about 4.0 m of depth (approximately the same depth at which CPT results showed soil improvement). It was concluded that heavy tamping reduces soil voids and substantially increases soil strength, but also breaks soil structure and decreases soil stiffness. It is thus not a suitable ground improvement solution for highly porous structured residual clayey soil.