High-paleolatitude Late Cretaceous paleotemperatures: New data from James Ross Island, Antarctica

first_imgOxygen-isotope analysis of well-preserved macrofossils from the Santonian-Campanian of James Ross Island and the Maastrichtian of Vega Island, Antarctica, indicates that cool high-paleolatitude temperatures prevailed during the Late Cretaceous and suggests that cooling occurred between the Santonian-Campanian and the Maastrichtian. Although more than 50% of the material showed diagenetic alteration, 52 unaltered aragonite and calcite samples were analyzed. Mean δ18O and calculated paleotemperature values were -0.23‰ and 13.6 °C, respectively, for the Santonian-Campanian, and 0.66‰ and 11.7 °C, respectively, for the Maastrichtian. In conjunction with recent Late Cretaceous paleoclimatic data from high northern paleolatitudes, these data indicate the presence of cool polar regions with broad climatic zonation during the Late Cretaceous. This may have partly controlled faunal distributions.last_img read more

Arc evolution: a magnetic perspective from the Antarctic Peninsula

first_imgThe Antarctic Peninsula is a Mesozoic–Cenozoic magmatic arc built on Palaeozoic and younger basement. It was formed by processes related to the subduction of Pacific ocean floor at its western margin, although subduction has now ceased along most of its length. The peninsula features all the tectonic components commonly associated with a developing arc system: basement, accretionary complex, magmatic arc, arc-related basins, intra-arc extension and post-subduction volcanism. Seventeen thousand kilometres of high resolution aeromagnetic data have recently been collected in a transect across part of the arc, covering an area 290 by 230 km and incorporating examples of most of the above tectonic components. The new map reveals distinct magnetic signatures, which can now be related to each of these components in a way that was not possible with reconnaissance data sets. A characteristic magnetic anomaly pattern for each component is described and comparisons drawn with magnetic studies of other arc regions.last_img read more

Seasonal and annual growth rates in the Antarctic fish Notothenia coriiceps Richardson

first_imgGrowth in Antarctic fishes is assumed to be seasonal but quantitative data are scarce. Growth rates in juvenile Notothenia coriiceps, a typical Antarctic fish, were measured using mark–recapture techniques and found to be greater when periods of liberty included summer and early autumn months and least when liberty was restricted to winter months. Weight specific growth rates ranged from −0.08–0.26% body weight day−1. Year class analysis and cohort analysis were attempted on serial samples of the population but proved ineffective methods for detecting seasonal growth in these slow growing fishes. A tentative description of the seasonal growth profile is proposed. Seasonality in growth indicates that some form of growth limitation is active; competing hypotheses of temperature and resource limitation are discussed. Annual growth rates in three year classes showed an inverse relationship with age. Parameters of the Pütter-von Bertalanffy growth equation were estimated. Comparison with other studies show the growth characteristics of N. coriiceps differ with geographical location but have not changed substantially at Signy Island over the past 25 years.last_img read more

A simple model of the convective internal boundary layer and its application to surface heat flux estimates within polynyas

first_imgA simple model of the convective (thermal) internal boundary layer has been developed for climatological studies of air-sea-ice interaction, where in situ observations are scarce and first-order estimates of surface heat fluxes are required. It is a mixed-layer slab model, based on a steady-state solution of the conservation of potential temperature equation, assuming a balance between advection and turbulent heat-flux convergence. Both the potential temperature and the surface heat flux are allowed to vary with fetch, so the subsequent boundary-layer modification alters the fluxconvergence and thus the boundary-layer growth rate. For simplicity, microphysical and radiative processes are neglected. The model is validated using several case studies. For a clear-sky cold-air outbreak over a coastal polynya the observed boundary-layer heights, mixed-layer potential temperatures and surface heat fluxes are all well reproduced. In other cases, where clouds are present, the model still captures most of the observed boundary-layer modification, although there are increasing discrepancies with fetch, due to the neglected microphysical and radiative processes. The application of the model to climatological studies of air-sea interaction within coastal polynyas is discussed.last_img read more

A method to study bacterioplankton community structure in Antarctic lakes

first_imgA method to study bacterioplankton community structure in Antarctic freshwater lake samples is described. Small samples (between 300 and 1000 ml) taken in remote field locations were used for crude DNA extraction, followed by PCR amplification of 16S rRNA gene fragments using group-specific primers. The amplification products of the PCR reaction were then separated using denaturing gradient gel electrophoresis to produce a profile of the bacterioplankton community. Whilst the technique is only semi-quantitative, it readily differentiated communities from lakes of different trophic status and from vertical profiles within different lake types. The method offers a sensitive tool for screening and monitoring Antarctic freshwater environments as a precursor and adjunct to more detailed studies.last_img read more

Subglacial bed properties from normal-incidence seismic reflection data

first_imgRecent applications of the normal-incidence seismic reflection technique to studying subglacial conditions are summarized. Some of the important aspects of the technique are discussed, including critical acquisition parameters and particular strengths and weaknesses. The main reason for deploying this technique, rather than other seismic methods, is that data acquisition is simpler and requires fewer resources. Current limitations of the technique include the inability to determine subglacial seismic velocities, uncertainty in the attenuation coefficient for ice, and assumptions of source repeatability. The reflection coefficient at the ice-bed interface is calculated from the energy reduction between primary and multiple reflections. From this, the acoustic impedance of the bed is derived and used to interpret the bed material. Beneath fast-flowing ice, dilatant, deforming sediment has been distinguished from a lodged sediment bed, using porosity as a proxy for sediment dilation. Subglacial water and permafrost have also been interpreted. Data from a number of locations can be used to develop a model of the basal conditions of a complete glacier. Results from sites on ice streams in West Antarctica show how the ice encounters a greater or lesser restraint to flow, from different basal conditions. Application to a glacier in the Arctic, suggests its most recent surge terminated when water escaped through discontinuous permafrost beneath the ice. Further glaciological questions that could be addressed using the technique are proposed.last_img read more

Comparative morphology of Southern Ocean Euphausia species: ecological significance of sexual dimorphic features

first_imgSpecies of the genus Euphausia dominate the euphausiid biomass of the Southern Ocean, the three largest being Euphausia superba, E. triacantha and E. crystallorophias. We measured a number of morphological features to identify differences between, and within, these species to obtain ecological insights. Interspecifically, the greatest difference was carapace size, with that of E. superba being by far the largest and most variable. This likely reflects its prolific spawning capacity compared with other euphausiid species. E. triacantha exhibited an extended sixth abdominal segment that could facilitate greater levels of thrust in the tail flip escape response. The pleopods, which provide propulsion in forward swimming, were more than 50% larger in E. superba, indicating a greater capacity for directional movement at high velocities. E. crystallorophias had eyes that were almost double the size of those in E. superba and E. triacantha, which may help retain visual resolution within its under-ice habitat. Intraspecifically, we found the above morphological features differed little between sexes and developmental stages in E. crystallorophias and E. triacantha, but differed significantly in E. superba. Compared to females and juveniles, male E. superba had significantly larger eyes and pleopods, whilst the carapace in males became shorter as a proportion of body length during growth. These features indicate a greater capacity for searching and swimming in males, which, we hypothesise, increases their ability to locate and fertilise females. This morphological specialisation in male E. superba is indicative of comparatively greater inter-male competition resulting from its tendency to form large, dense swarms.last_img read more

On constraining projections of future climate using observations and simulations from multiple climate models

first_imgNumerical climate models are used to project future climate change due to both anthropogenic and natural causes. Differences between projections from different climate models are a major source of uncertainty about future climate. Emergent relationships shared by multiple climate models have the potential to constrain our uncertainty when combined with historical observations. We combine projections from 13 climate models with observational data to quantify the impact of emergent relationships on projections of future warming in the Arctic at the end of the 21st century. We propose a hierarchical Bayesian framework based on a coexchangeable representation of the relationship between climate models and the Earth system. We show how emergent constraints fit into the coexchangeable representation, and extend it to account for internal variability simulated by the models and natural variability in the Earth system. Our analysis shows that projected warming in some regions of the Arctic may be more than 2 (Formula presented.) C lower and our uncertainty reduced by up to 30% when constrained by historical observations. A detailed theoretical comparison with existing multi-model projection frameworks is also provided. In particular, we show that projections may be biased if we do not account for internal variability in climate model predictions. Supplementary materials for this article, including a standardized description of the materials available for reproducing the work, are available as an online supplement.last_img read more

Bees rally falls short

first_img Written by FacebookTwitterLinkedInEmail(Albuquerque, NM)  —  The Bees ninth-inning rally fell short as they fell to the Isotopes 12-11 in Albuquerque.Trailing by four entering the ninth Salt Lake City rallied for three runs.  David Fletcher and Chris Carter homered in defeat.Parker Birdwell surrendered eight runs on 11 hits over four-and-a-third with Ralston Cash taking the loss in relief.The Bees won three-of-four in the set. April 17, 2018 /Sports News – Local Bees rally falls short Robert Lovell Tags: Baseball/PCL/Salt Lake Beeslast_img

Soccer team fakes the death of a former player; dodges game

first_img Written by November 29, 2018 /Sports News – National Soccer team fakes the death of a former player; dodges game FacebookTwitterLinkedInEmailiStock/Thinkstock(NEW YORK) — Representatives for an Irish soccer team have apologized after faking the death of one of its former players.Public broadcaster RTE reported that a representative of the team, Ballybrack FC, falsely told the Leinster Senior Football League that Fernando LaFuente — who was until recently on the squad — had perished in a “traffic accident” last week. The league subsequently postponed Ballybrack’s game on Saturday — and even held a moment of silence for LaFuente, who, it should be said, is very much alive.LaFuente, who now works for a software company, told RTE, “I was home yesterday after my work finished. I was playing some video games. … [My colleagues] started sending me all these news articles and mass media. And that’s how I found out I was dead.”Ballybrack apologized on Facebook, calling the announcement, “a gross error of judgement…made by a person who has been experiencing severe personal difficulties unbeknownst to any other members of the club.”The team added, “the person in question has been relieved of all footballing duties.”Copyright © 2018, ABC Radio. All rights reserved.center_img Beau Lundlast_img read more