The existence and break-up of the Antarctic land bridge as indicated by both amphi-Pacific distributions and tectonics

Amphi-Pacific disjunct distributions between South America and Australasia are correlated with the breakup and changing palaeo-climate of Gondwana. For a long period, with a temperate climate, Antarctica formed a land bridge between Australia and South America, allowing species to disperse/vicariate between both continents. Dated phylogenies in the literature, showing sister-clades with a distribution disjunction between South America and Australia, were used for the correlation. The initiation of the Antarctic Circumpolar Current, and a change to a colder Antarctic climate is associated with the opening of the Drake Passage between South America and Antarctica at c. 30 Ma, and the final separation of Australia and Antarctica along the South Tasman Rise at c. 45 Ma. The distribution data highlighted the existence of a southern disjunct distribution pattern, which may be the result of continental vicariance/dispersal. This is strongly indicative of a connection between Antarctica, South America and Australia; which later provided a dispersal pathway and facilitated vicariance after break up. The taxa that likely dispersed/vicariated via Antarctica included all species with a more (sub)tropical climate preference. Twelve distributions, younger than 30 Ma, are interpreted as the result of long distance dispersal between South America and Australia; these taxa are suited to a temperate climate. The climatic signal shown by all taxa is possibly a consequence of the Australian plate\u27s asynchronous rifting over tens of millions of years in combination with climate changes. These events may have provided opportunities for tropical and sub-tropical species to disperse and speciate earlier than what we observe for the more temperate taxa

Lakes beneath the ice sheet: The occurrence, analysis, and future exploration of Lake Vostok and other Antarctic subglacial lakes

Airborne geophysics has been used to identify more than 100 lakes beneath the ice sheets of Antarctica. The largest, Lake Vostok, is more than 250 km in length and 1 km deep. Subglacial lakes occur because the ice base is kept warm by geothermal heating, and generated meltwater collects in topographic hollows. For lake water to be in equilibrium with the ice sheet, its roof must slope ten times more than the ice sheet surface. This slope causes differential temperatures and melting/freezing rates across the lake ceiling, which excites water circulation. The exploration of subglacial lakes has two goals: to find and understand the life that may inhabit these unique environments and to measure the climate records that occur in sediments on lake floors. The technological developments required for in situ measurements mean, however, that direct studies of subglacial lakes may take several years to happen

IODP Expeditions 309 and 312 drill an intact section of upper oceanic basement into gabbros

The Integrated Ocean Drilling Program's (IODP) Expeditions 309 and 312 successfully completed the first sampling of an intact section of upper oceanic crust, through lavas and the sheeted dikes into the uppermost gabbros. Hole 1256D, which was initiated on the Ocean Drilling Program's (ODP) Leg 206, now penetrates to >1500 mbsf and >1250 m sub-basement. The first gabbroic rocks were encountered at 1407 mbsf. Below this, the hole penetrates 3c100 m into a complex zone of fractionated gabbros intruded into contact metamorphosed dikes

Identifying deformation mechanisms in molecular dynamics simulations of laser shocked matter

In this paper we demonstrate a new post-processing technique that allows straightforward identification of deformation mechanisms in molecular dynamics simulations. We utilise reciprocal space methods by calculating a per-atom structure factor (PASF) to visualise changes in volume, orientation and structure, thus allowing unambiguous discrimination between key deformation/relaxation mechanisms such as uniaxial strain, twinning and structural phase transformations. The full 3-D PASF is reduced to a 2-D representation by taking only those points which lie on the surface of an ellipsoid passing through the nearest reciprocal lattice points. Projecting this 2-D representation onto the set of spherical harmonics allows for a numerical characterisation of the system state that easily captures various plastic deformation mechanisms that have been historically difficult to identify. The technique is used to successfully classify high temperature twinning rotations in shock compressed tantalum and to identify the α to ω phase transition in group-IV hcp metals

Robust estimation in time series

The main purpose of this work is to study empirically by means of simulations, the robustness of a set of proposals to estimate the parameters in the MA(1) time series model. The non-normal populations are mixtures of normal distributions, defined by g(x) = pN(0, k) + (1 − p)N(0, 1), where the proportion of contamination most frequently used is p = 0.10 and k is the variance of the distribution used in the contamination; α is taken to be 0.90, which is close to the region of non-invertibility. Key results are that the estimation procedures used in the study provide good results in terms of biases in the estimation of the parameters, and that the biases are not changed when contaminated errors (mixtures) are considered. The estimation of the variance of the contaminated errors is also studied through simulations.Fil: Mentz, Raúl Pedro. Universidad Nacional de Tucumán. Facultad de Ciencias Económicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Martinez, Carlos Ismael. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Tucumán. Facultad de Ciencias Económicas; Argentin