Month: May 2021

British Antarctic Survey, 1975–76

first_imgSix British Antarctic Survey stations were operational during the year. A new station, at Rothera Point, Adelaide Island, is being built to replace Adelaide station. Its development is providing a unique opportunity to study changes in the microbial, invertebrate, plant and birdpopulations as a result of human activities, including the inevitable atmospheric pollution and the localized influence of tracked vehicles. Several small sites have been set up to study these changes. Among the senior Survey staff to visit the bases this season were Dr R. M. Laws (Director), and Mr W. R. Piggott (Head of Atmospheric Sciences). Other visitors included Dr B.B. Roberts, Dr L. Ferraz, a Brazilian observer, and Mr D. Smith, a British artist.last_img

The occurrence of Anopaea (Bivalvia: Inoceramidae) in the Antarctic Peninsula

first_imgThe genus Anopaea represents a small but distinctive group of inoceramid bivalves that apparently remained functionally endobyssate. The somewhat unusual morphology (for an inoceramid) probably results from structural modifications tofacilitate sediment penetration at a high angle and anchorage by an antero-ventral byssus. Although never as common as thecontemporary genera Retroceramus and Inoceramus, Anopaea is now known from temperate bivalve assemblages in both the Northern and Southern Hemispheres. It persisted from the Late Jurassic (Tithonian) to the Early Cretaceous (Neocomian), and possibly even later.last_img

The terrestrial Protozoan fauna of South Georgia

first_img75 taxa of Protozoa (18 flagellates, 9 naked rhizopods, 20 testate rhizopods and 28 ciliates) were found in 14 samples of mineral materials, peats, soils and guano collected from the sub-Antarctic island of South Georgia. The results confirm the existence of distinct natural communities of protozoan species related to the different classes of habitat in the sub-Antarctic and maritime Antarctic, but suggest that species characteristic of the maritime Antarctic also occur in the sub-Antarctic and species characteristic of bryophyte peats also occur in soils with angiosperm vegetation. The diversity of the fauna of different habitats can be related to degree of soil development and successional stage of associated vegetation. Comparison of the data on the testate rhizopod fauna of South Georgia with those from other sub-Antarctic locations shows a clear trend of faunal pauperization with latitude.last_img read more

A numlerical model of blowing snow around an Antarctic building

first_imgThe accumulation of drifting snow around buildings in regions of severe climate has important implications on their design and location. This paper studies one such building, at a station run by the British Antarctic Survey and located on the Brunt Ice Shelf at the edge of the Antarctic continent. Four previous stations have bccn built in the area, the buildings of which werc designed to becomc covercd in snow and all have been crushed within a few years. The current station, Halley V, consists of three buildings which are all raised from the ice shelf by means oflegs. They were designed in such a way that the action of the wind blowing underneath the buildings would keep them clear of snow. This paper describes a model which predicts the shape and position of drift formation, and then compares the results with those observed at Halley. This modd is a first attempt to address the problem and as such the paper can be considered to be a progress report; improvements arc currently being made as part of continuing research. It is found that there is some qualitative agreement and possible reasons for a few quantitative discrepancies are discussed. Both the model and the true data show clearly that the new design is very effective in prolonging the useful life of the buildingslast_img read more

On determining the noon polar cap boundary from SuperDARN HF radar backscatter characteristics

first_imgPrevious work has shown that ionospheric HF radar backscatter in the noon sector can be used to locate the footprint of the magnetospheric cusp particle precipitation. This has enabled the radar data to be used as a proxy for the location of the polar cap boundary, and hence measure the flow of plasma across it to derive the reconnection electric field in the ionosphere. This work used only single radar data sets with a field of view limited to ∼2 h of local time. In this case study using four of the SuperDARN radars, we examine the boundary determined over 6 h of magnetic local time around the noon sector and its relationship to the convection pattern. The variation with longitude of the latitude of the radar scatter with cusp characteristics shows a bay-like feature. It is shown that this feature is shaped by the variation with longitude of the poleward flow component of the ionospheric plasma and may be understood in terms of cusp ion time-of-flight effects. Using this interpretation, we derive the time-of-flight of the cusp ions and find that it is consistent with approximately 1 keV ions injected from a subsolar reconnection site. A method for deriving a more accurate estimate of the location of the open-closed field line boundary from HF radar data is described.last_img read more

Sm–Nd mineral ages and P–T constraints on the pre-Grampian high grade metamorphism of the Slishwood Division, north-west Ireland.

first_imgGranulite-facies metamorphism affecting the Slishwood Division was extreme. Three samples yielded P–T conditions of 15.8, 14, 14.9kbar at 810, 750 and 880°C, respectively. Four Sm–Nd mineral isochrons, defined by granulite-facies basic and pelitic metamorphic assemblages, yield ages of 544 ± 52 Ma, 539 ± 11 Ma, 596 ± 68 Ma and 540 ± 50 Ma. These ages confirm that granulite- and earlier eclogite- facies metamorphism took place before the c. 470Ma Grampian Orogeny. Detailed chronological interpretation is inhibited by microscopic inclusions within, and isotope disequilibrium between, the dated minerals. It is possible that the ages record crystallisation of either the granulite or eclogite-facies assemblages. However, it is more likely that they record post-metamorphic cooling. Relict pre-granulite-facies igneous minerals from a metagabbro body possibly date its intrusion at 580 ± 36 Ma. Extreme metamorphism in the late Neoproterozoic to Early Cambrian suggests that the Slishwood Division is exotic to Laurentia.last_img read more

Refilling of the slot region between the inner and outer electron radiation belts during geomagnetic storms

first_imgEnergetic electrons (≥50 keV) are injected into the slot region (2 < L < 4) between the inner and outer radiation belts during the early recovery phase of geomagnetic storms. Enhanced convection from the plasma sheet can account for the storm-time injection at lower energies but does not explain the rapid appearance of higher-energy electrons (≥150 keV). The effectiveness of either radial diffusion (driven by enhanced ULF waves) or local acceleration (during interactions with enhanced whistler mode chorus emissions), as a potential source for refilling the slot at higher energies, is analyzed for observed conditions during the early recovery phase of the 10 October 1990 storm. We demonstrate that local acceleration, driven by observed chorus emissions, can account for the rapid enhancement in 200–700 keV electrons in the outer slot region near L = 3.3. Radial diffusion is much less effective but may partially contribute to the flux enhancement at lower L. Subsequent outward expansion of the plasmapause during the storm recovery phase effectively terminates local wave acceleration in the slot and prevents acceleration to energies higher than ∼700 keV. A statistical analysis of energetic electron flux enhancements and wave and plasma properties over the entire CRRES mission supports the concept of local wave acceleration as a dominant process for refilling the slot during the main and early recovery phase of storms. For moderate storms, the injection process naturally becomes less effective at energies ≥1 MeV, due to the longer wave acceleration times and additional precipitation loss from scattering by electromagnetic ion cyclotron waves. However, during extreme events when the plasmapause remains compressed for several days, conditions may occur to allow wave acceleration to multi-MeV energies at locations normally associated with the slot.last_img read more

The 2007 Antarctic ozone hole

first_imgThe 2007 Antarctic ozone hole is reviewed from a variety of perspectives, making use of various Australian data and analyses. The 2007 ozone hole was relatively modest, particularly in comparison to that of 2006, due in part to a disturbance to the polar vortex in early September that led to an influx of ozone-rich air. Ozone depiction was still severe however in the lower stratosphere. The long-term outlook for recovery is described, with Antarctic ozone currently forecast to return to 1980 levels around the period 2055-2080.last_img

Present weather-sensor tests for measuring drifting snow

first_imgIn Antarctica, blowing snow accounts for a major component of the surface mass balance near the coast. Measurements of precipitation and blowing snow are scarce, therefore collecting data would allow testing numerical models on mass flux over that region. A present weather station (PWS) Biral VPF730 has been set up at the coast in Cap Prud’homme station, 5km away from Dumont D’Urville (DDU), firstly to quantify precipitation. As we could expect determination of blowing snow fluxes from the PWS data, we first choose to test such a device on our experimental site, the Lac Blanc Pass. An empirical calibration was done with a SPC (Snow Particle Counter). Even if the physics of phenomenon was not well capture, the fluxes outputs are better than those from the FlowCapt. The first data from Antarctica were re-analyzed. The new calibration seems to be accurate for estimating the high blowing snow flux with an interrogation for the precipitation effects.last_img read more

Southern Hemisphere westerly wind changes during the Last Glacial Maximum: model-data comparison

first_imgThe Southern Hemisphere (SH) westerly winds are thought to be critical to global ocean circulation, productivity, and carbon storage. For example, an equatorward shift in the winds, though its affect on the Southern Ocean circulation, has been suggested as the leading cause for the reduction in atmospheric CO2 during the Last Glacial period. Despite the importance of the winds, it is currently not clear, from observations or model results, how they behave during the Last Glacial. Here, an atmospheric modelling study is performed to help determine likely changes in the SH westerly winds during the Last Glacial Maximum (LGM). Using LGM boundary conditions, the maximum in SH westerlies is strengthened by ∼+1 m s−1 and moved southward by ∼2° at the 850 hPa pressure level. Boundary layer stabilisation effects over equatorward extended LGM sea-ice can lead to a small apparent equatorward shift in the wind band at the surface. Further sensitivity analysis with individual boundary condition changes indicate that changes in sea surface temperatures are the strongest factor behind the wind change. The HadAM3 atmospheric simulations, along with published PMIP2 coupled climate model simulations, are then assessed against the newly synthesised database of moisture observations for the LGM. Although the moisture data is the most commonly cited evidence in support of a large equatorward shift in the SH winds during the LGM, none of the models that produce realistic LGM precipitation changes show such a large equatorward shift. In fact, the model which best simulates the moisture proxy data is the HadAM3 LGM simulation which shows a small poleward wind shift. While we cannot prove here that a large equatorward shift would not be able to reproduce the moisture data as well, we show that the moisture proxies do not provide an observational evidence base for it.last_img read more