The geology of Antarctica: a review

first_imgGeological field work in Antarctica and the off-lying islands during the past two decades has contributed materially to the establishment of the stratigraphical succession in both East and West Antarctica. The tectonic evolution of Antarctica is discussed in relation to the known stratigraphical and structural data for the continent, and the rôle of Antarctica in several reconstructions of the former supercontinent of Gondwanaland critically examined. In this context, various aspects of the palaeogeography, palaeoclimatology, geochronology and stratigraphy of Antarctica is reviewed.last_img

A new sedimentological interpretation for part of the Santa Marta Formation, James Ross Island

first_imgThe regional geology and lithostratigraphy of the Late Cretaceous strata of north-east James Ross Island have been described by a number of authors (e.g. Olivero et al. 1986, Pirrie 1989). The aim of this short note is to describe a sequence of strata currently assigned to the Santa Marta Formation, and to reinterpret the processes and environments of deposition of this sequence.last_img

Doppler shift pulsations on whistler mode signals from a VLF transmitter

first_imgWhistler mode signals from the NAA transmitter (24 kHz) received at Faraday, Antarctica are processed to obtain the Doppler shift at a much higher time resolution than has previously been possible. This has allowed the observation of pulsations of about 13 mHz frequency which are believed to be associated with hydromagnetic waves in the magnetosphere. The pulsations are observed separately on signals with a number of discrete group delay features that can be interpreted as individual whistler ducts. Using the measured pulsation phase over the array of ducts the phase velocity and wave normal direction of the hydromagnetic wave in the equatorial plane are estimated. The direction of propagation is consistent with a source on the dayside magnetopause. The association between whistler mode Doppler shifts and hydromagnetic waves has been reported before but not, as far as we are aware, using an experimental technique that allows measurements on individual ducts in order to determine the direction of propagation of the hydromagnetic wave.last_img read more

Global relationships amongst black-browed and grey-headed albatrosses: analysis of population structure using mitochondrial DNA and microsatellites

first_imgThe population structure of black-browed (Thalassarche melanophris and T. impavida) and grey-headed (T. chrysostoma) albatrosses was examined using both mitochondrial DNA (mtDNA) and microsatellite analyses. mtDNA sequences from 73 black-browed and 50 grey-headed albatrosses were obtained from five island groups in the Southern Ocean. High levels of sequence divergence were found in both taxa (0.55–7.20% in black-browed albatrosses and 2.10–3.90% in grey-headed albatrosses). Black-browed albatrosses form three distinct groups: Falklands, Diego Ramirez/South Georgia/Kerguelen, and Campbell Island (T. impavida). T. melanophris from Campbell Island contain birds from each of the three groups, indicating high levels of mixture and hybridization. In contrast, grey-headed albatrosses form one globally panmictic population. Microsatellite analyses on a larger number of samples using seven highly variable markers found similar population structure to the mtDNA analyses in both black-browed and grey-headed albatrosses. Differences in population structure between these two very similar and closely related species could be the result of differences in foraging and dispersal patterns. Breeding black-browed albatrosses forage mainly over continental shelves and migrate to similar areas when not breeding. Grey-headed albatrosses forage mainly at frontal systems, travelling widely across oceanic habitats outside the breeding season. Genetic analyses support the current classification of T. impavida as being distinct from T. melanophris, but would also suggest splitting T. melanophris into two groups: Falkland Islands, and Diego Ramirez/South Georgia/Kerguelen.last_img read more

Fracture of Antarctic shelf ice

first_imgWe have investigated the fracture of Antarctic shelf ice core using two fracture mechanics test methods: the chevron-notched short-rod specimen loaded in tension and the chevron-notched round-bar specimen loaded in three-point bending. These tests have been used to measure the fracture initiation toughness, Kinit, at which crack growth starts, on samples taken through the entire thickness of the Ronne Ice Shelf, from low-density firn through consolidated meteoric ice to basal marine ice. The fracture data are presented together with depth profiles of relevant physical and mechanical properties derived from the test specimens: temperature, density, elastic modulus, and grain size. It is found that the trend in measured fracture toughness closely reflects changes in ice density and elastic modulus. We augment the experimental study by presenting a fracture mechanics analysis of ice shelf surface and basal crevassing which directly incorporates our measurements. For the examined ice shelf profiles, basal crevasses are found to be inherently unstable unless an external restraining force is imposed, which has important implications for overall ice shelf stability. On the other hand, surface crevassing is shown to be innately stable at depth. Our fracture mechanics model is used to predict local ice shelf back stresses in the vicinity of basal crevassing and is validated directly against field observations of crevasse penetration on the Ronne Ice Shelf.last_img read more

Investigating radiation belt losses though numerical modelling of precipitating fluxes

first_imgIt has been suggested that whistler-induced electron precipitation (WEP) may be the most significant inner radiation belt loss process for some electron energy ranges. One area of uncertainty lies in identifying a typical estimate of the precipitating fluxes from the examples given in the literature to date. Here we aim to solve this difficulty through modelling satellite and ground-based observations of onset and decay of the precipitation and its effects in the ionosphere by examining WEP-produced Trimpi perturbations in subionospheric VLF transmissions. In this study we find that typical Trimpi are well described by the effects of WEP spectra derived from the AE-5 inner radiation belt model for typical precipitating energy fluxes. This confirms the validity of the radiation belt lifetimes determined in previous studies using these flux parameters. We find that the large variation in observed Trimpi perturbation size occurring over time scales of minutes to hours is primarily due to differing precipitation flux levels rather than changing WEP spectra. Finally, we show that high-time resolution measurements during the onset of Trimpi perturbations should provide a useful signature for discriminating WEP Trimpi from non-WEP Trimpi, due to the pulsed nature of the WEP arrival.last_img read more

Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

first_imgWe use the Shreve hydraulic potential equation as a simplified approach to investigate potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets. We validate the method by demonstrating its ability to recall the locations of >60% of the known subglacial lakes beneath the Antarctic Ice Sheet. This is despite uncertainty in the ice-sheet bed elevation and our simplified modelling approach. However, we predict many more lakes than are observed. Hence we suggest that thousands of subglacial lakes remain to be found. Applying our technique to the Greenland Ice Sheet, where very few subglacial lakes have so far been observed, recalls 1607 potential lake locations, covering 1.2% of the bed. Our results will therefore provide suitable targets for geophysical surveys aimed at identifying lakes beneath Greenland. We also apply the technique to modelled past ice-sheet configurations and find that during deglaciation both ice sheets likely had more subglacial lakes at their beds. These lakes, inherited from past ice-sheet configurations, would not form under current surface conditions, but are able to persist, suggesting a retreating ice-sheet will have many more subglacial lakes than advancing ones. We also investigate subglacial drainage pathways of the present-day and former Greenland and Antarctic ice sheets. Key sectors of the ice sheets, such as the Siple Coast (Antarctica) and NE Greenland Ice Stream system, are suggested to have been susceptible to subglacial drainage switching. We discuss how our results impact our understanding of meltwater drainage, basal lubrication and ice-stream formation.last_img read more

Assimilation of sea surface temperature, sea ice concentration and sea ice drift in a model of the Southern Ocean

first_imgCurrent ocean models have relatively large errors and biases in the Southern Ocean. The aim of this study is to provide a reanalysis from 1985 to 2006 assimilating sea surface temperature, sea ice concentration and sea ice drift. In the following it is also shown how surface winds in the Southern Ocean can be improved using sea ice drift estimated from infrared radiometers. Such satellite observations are available since the late seventies and have the potential to improve the wind forcing before more direct measurements of winds over the ocean are available using scatterometry in the late nineties. The model results are compared to the assimilated data and to independent measurements (the World Ocean Database 2009 and the mean dynamic topography based on observations). The overall improvement of the assimilation is quantified, in particular the impact of the assimilation on the representation of the polar front is discussed. Finally a method to identify model errors in the Antarctic sea ice area is proposed based on Model Output Statistics techniques using a series of potential predictors. This approach provides new directions for model improvements.last_img read more

Modeling of the Influence of Sea Ice Cycle and Langmuir Circulation on the Upper Ocean Mixed Layer Depth and Freshwater Distribution at the West Antarctic Peninsula.

first_imgThe Southern Ocean is chronically undersampled due to its remoteness, harsh environment, and sea ice cover. Ocean circulation models yield significant insight into key processes and to some extent obviate the dearth of data; however, they often underestimate surface mixed layer depth (MLD), with consequences for surface water-column temperature, salinity, and nutrient concentration. In this study, a coupled circulation and sea ice model was implemented for the region adjacent to the West Antarctic Peninsula, a climatically sensitive region which has exhibited decadal trends towards higher ocean temperature, shorter sea ice season, and increasing glacial freshwater input, overlain by strong interannual variability. Hindcast simulations were conducted with different air-ice drag coefficients and Langmuir circulation parameterizations to determine the impact of these factors on MLD. Including Langmuir circulation deepened the surface mixed layer, with the deepening being more pronounced in the shelf and slope regions. Optimal selection of an air-ice drag coefficient also increased modeled MLD by similar amounts and had a larger impact in improving the reliability of the simulated MLD interannual variability. This study highlights the importance of sea ice volume and redistribution to correctly reproduce the physics of the underlying ocean, and the potential of appropriately parameterizing Langmuir circulation to help correct for biases towards shallow MLD in the Southern Ocean. The model also reproduces observed freshwater patterns in the West Antarctic Peninsula during late summer and suggests that areas of intense summertime sea ice melt can still show net annual freezing due to high sea ice formation during the winter.last_img read more

WCC alters schedule rules in hopes of more NCAA bids

first_img Tags: Basketball/WCC March 26, 2018 /Sports News – Local WCC alters schedule rules in hopes of more NCAA bids Associated Press Written by FacebookTwitterLinkedInEmailSAN BRUNO, Calif. (AP) — The West Coast Conference is altering its scheduling with the hope of getting better treatment in terms of seeding and at-large bids for the NCAA Tournament.The WCC Presidents’ Council announced Monday that the 10-team league will go to a 16-game schedule next season instead of an 18-game double round-robin. Also starting in 2019-20, all WCC schools will be required to play a multi-team event each season, play more home games that road games, and play no more than two non-Division I opponents. The league also must approve all “guarantee” games when a WCC school is paid to play on the road by an opponent.The changes come just weeks after Gonzaga only got a No. 4 seed in the NCAA Tournament despite finishing the season ranked eighth in the nation and No. 25 Saint Mary’s was denied an at-large bid for the fourth time in 10 years despite winning 25 games.The league also is changing the format of the men’s and women’s tournaments. The seventh through 10th seeds will play in the opening round with the two winners meeting the fifth and sixth in the second round. The winners of those games will play the third and fourth seeds in the third round. The top two seeds will get byes straight to the semifinals.last_img read more