Observations of a day-time mid-latitude ionospheric trough

first_imgA summer, dayside, mid-latitude trough detected by a digital ionosonde located at Halley (76°S, 27°W, L = 4.2) is described. The trough is found to be present in the F2-region only and its movements are found to conform to known trough dynamics. The F1-layer shows a greater degree of development within the trough; slant type sporadic E reflections are present underneath the trough minimum. Satellite data from the northern hemisphere show a conjugate trough, with rapid ion flow occurring within it. Possible formation processes for the trough are examined. It is unlikely that depleted nightside plasma could have contributed to the trough. The trough is formed by the effect of enhanced F2 recombination rates combined with a differing solar production term for the plasma associated with the trough minimum and equatorial edge.last_img read more

An additional record of a placental mammal (Order Astrapotheria) from the Eocene of West Antarctica

first_imgRecently, fossil land mammals have been recorded in the James Ross Island area, east of the Antarctic Peninsula, from the marine middle-late Eocene strata of Seymour Island. These include two endemic species of polydolopid marsupial: Antarctodolops dailyi Woodburne & Zinsmeister 1984, and Eurydolops seymourensis Case, Woodburne & Chaney 1988, and three partly determinate placentals identified as a tardigrade edentate, a sparnotheriodontid litoptern and a trigonostylopid astrapothere (Bond et al. 1989). The marsupials are represented by fragmentary jaw and complete dental material, the litoptern and astrapothere only by tooth fragments. All are recorded from Unit TELM 5 of the La Meseta Formation (Sadler 1988), the two ungulates at a lower level than the rest. The subject of the present note is a second tooth fragment from Seymour Island identified as an astrapothere. It is worth recording because such mammal remains are rare and it is from TELM 4, the unit below that yielding the other land mammalslast_img read more

Climatic implications of background acidity and other chemistry derived from electrical studies of the Greenland Ice Core Project ice core

first_imgHigh-resolution continuous profiles were obtained on the Greenland Ice Core Project (GRIP) ice core using two different electrical methods. After correction for temperature and density, the electrical conductivity method (ECM) technique responds only to acidity, while dielectric profiling (DEP) responds to acid, ammonium, and chloride. Detailed chemistry on a section of glacial-age ice allows us to confirm the calibration factor for chloride in DEP. Acidity dominates the DEP variability in the Holocene, Allerod/Bolling, and larger interstadials; ammonium dominates in the Younger Dry as, while chloride is the major contributor in cold periods including smaller interstadials. From the electrical signals plotted on a linear timescale we can deduce the background (nonvolcanic) acidity of the ice, varying from always acidic in the Holocene to always alkaline in the cold periods. In the interstadials, the ice is close to neutral, with most of it acidic in larger interstadials, most of it alkaline in smaller ones, and rapid alternations within interstadials. It is not clear whether neutralization of individual acidic particles occurred in the atmosphere or whether acid and alkaline particles coexisted until deposition in the snowpack. The changes in acidity observed at GRIP apply at least to all of Greenland and probably to much of North America. There would have been ecological effects and important changes in the uptake of some chemicals onto ice. If acidic sulfate particles were neutralized and removed from the atmosphere, which remains uncertain, then there are atmospheric chemistry and radiative effects that require further investigation.last_img read more

Global evolution of a substorm-associated DP2 current system observed by superDARN and magnetometers

first_imgThis paper deals with an evolution of the electric field in the dayside auroral and equatorial ionosphere during asubstorm on July 16, 1995. A southward turning of the IMF detected by WIND (171 Re) caused enhancements in the auroral electrojet intensity in the 7–10 MLT and 15.5–18.5 MLT sectors as observed by the IMAGE (74-56 cgmlat) and CANOPUS (70-58 cgmlat) magnetometer chains. SuperDARN detected an equatorward motion of the radar scattering region at speeds of several −10 degs/hour in the dayside (05–17 MLT), suggesting an increase in the flux of the open magnetic field in the polar cap. Furthermore, coherent magnetic variations are observed at subauroral to equatorial latitudes simultaneously with the auroral magnetic variations within a temporal resolution of 10 s. This suggests that the electric field increase during the growth phase is established instantaneously around the convection reversal in the 15.5–18.5 MLT sector, and furthermore penetrates instantaneously to mid and low latitudes. SuperDARN detected a continuous equatorward motion of the auroral oval during the expansion phase around the cusp, which implies a continuous magnetic merging at the day-side magnetopause during the expansion phase. A rapid decrease in the electric field is inferred from coherent auroral and equatorial magnetic field decreases during the recovery phase, which may have been caused by northward turning of the IMF. This magnetic field decrease resembles the change in magnetic field of the counter-electrojet at the dip equator in the afternoon sector.last_img read more

Opening history of Powell Basin, Antarctic Peninsula

first_imgThe opening of Powell Basin was part of the regional response to N55°W relative plate motion of South America away from Antarctica, which led to the formation of Drake Passage during the Eocene and Oligocene. Restoration of microplates around the basin using gridded magnetic anomalies from its margins illustrates the pre-break-up continuity of the Pacific Margin Anomaly magnetic high associated with a Mesozoic arc-batholith. Newly compiled magnetic anomaly data over the Powell Basin show subdued linear seafloor spreading type anomalies. These are used, together with marginal and regional geology, to constrain the opening history of the basin. Magnetic reversal modelling suggests that slow spreading in Powell Basin probably occurred between 29.7 Ma and 21.8 Ma, following rifting of Mesozoic continental crust with associated break-up volcanism. A simple, two-phase model for the rotation of the South Orkney Microcontinent away from the Antarctic Peninsula accounts for the pattern of magnetic reversals recorded in Powell Basin, and for the structure of its margins.last_img read more

Significant intra-annual variability in krill distribution and abundance at South Georgia revealed by multiple acoustic surveys during 2000/01

first_imgThree separate acoustic surveys of Antarctic krill (Euphausia superba) were conducted around South Georgia in the 2000/01 season: in October 2000 (early-season); during late December/early January 2000/01 (mid-season), and in March 2001 (late-season). The surveys were the first in a newly planned five-year series of observations designed to complement and extend an existing time series regularly maintained by the British Antarctic Survey since 1996 (and on a more ad hoc basis since the early 1980s). We hoped that conducting several surveys in one season would provide information on short-term variability that could be used to set data from more restricted once-per-season ‘snap-shot’ cruises in a broader context. The early- and late-season surveys were associated with logistic support voyages to South Georgia and were restricted to four transects within a box to the northwest of South Georgia. The dedicated mid-season survey covered that box in more detail (twice as many transects) and, in addition, examined boxes to the north, northeast and southwest of the island. Together these surveys provided temporally and spatially extensive coverage around South Georgia. Krill density in the western box in the early-season survey was very low (3.5 g m(-2)) but rose significantly (P = 0.020) by mid-season (to 34.7 g m(-2)). In a pattern that is consistent with observations from previous years, krill density in the western box in the mid-season survey was less than that in the eastern box (80.4 g m(-2)). Analysis of transect data obtained in the western box in the mid-season survey revealed no significant difference in the mean krill density derived from only those four transects surveyed early- and late-season, or from the full eight transects. Our first occupation of a survey box off the central north coast of South Georgia in mid-season revealed a krill density of 47.2 g m(-2) that was intermediate between the eastern and western areas. The size structure of the krill in the central region also reflected a mix of those to the east (generally small) and west (generally large). Krill density to the southwest of South Georgia was 32.1 g m(-2) in mid-season. By March, krill density in the western survey area had fallen significantly (P = 0.037) from the mid-season high to 7.8 g m(-2). Our multiple surveys at South Georgia have revealed major intra-annual changes in krill density at the island and have shown that the timing of the acoustic survey can affect significantly the estimate of krill density. The multiple estimates of krill density will allow reproductive performance indices for top level predators to be compared to prey availability at more appropriate time-scales than previous single ‘snap-shot’ acoustic survey data have allowed. This is a crucial step in the elucidation of response functions of dependent species to changes in krill abundance, and could be a useful contribution to ecosystem management.last_img read more

The effect of geometry on ice shelf ocean cavity ventilation: a laboratory experiment

first_imgA laboratory experiment is constructed to simulate the density-driven circulation under an idealized Antarctic ice shelf and to investigate the flux of dense and freshwater in and out of the ice shelf cavity. Our results confirm that the ice front can act as a dynamic barrier that partially inhibits fluid from entering or exiting the ice shelf cavity, away from two wall-trapped boundary currents. This barrier results in a density jump across the ice front and in the creation of a zonal current which runs parallel to the ice front. However despite the barrier imposed by the ice front, there is still a significant amount of exchange of water in and out of the cavity. This exchange takes place through two dense and fresh gravity plumes which are constrained to flow along the sides of the domain by the Coriolis force. The flux through the gravity plumes and strength of the dynamic barrier are shown to be sensitive to changes in the ice shelf geometry and changes in the buoyancy fluxes which drive the flow.last_img read more

Effects of temperature on extracellular hydrolase enzymes from soil microfungi

first_imgSoil microbes play important roles in global carbon and nutrient cycling. Soil microfungi are generally amongst the most important contributors. They produce various extracellular hydrolase enzymes that break down the complex organic molecules in the soil into simpler form. In this study, we investigated patterns of amylase and cellulase (which are responsible for breaking down starch and cellulose, respectively) relative activity (RA) on solid media at different culture temperatures in fungal strains from Arctic, Antarctic and tropical soils. Fungal isolates from all three regions were inoculated onto R2A media supplemented with starch for amylase and carboxymethylcellulose and trypan blue for cellulase screening. The isolates were then incubated at 4, 10, 15, 20, 25, 30, 35 and 40 °C and examined for activity after 5 and 10 days, for tropical and polar isolates, respectively. The data obtained indicate that the polar fungal strains exhibited similar patterns of amylase and cellulase RA. Both Arctic and Antarctic fungi showed highest RA for amylase and cellulase at 35 °C, while colony growth was maximised at 15 °C. Colony growth and RA of the polar isolates were negatively correlated suggesting that, as temperatures increase, the cells become stressed and have fewer resources available to invest in growth. Unlike polar isolates, tropical isolates did not exhibit any trend of colony growth with temperature, rather having idiosyncratic patterns in each isolate. The low enzyme production and RA levels in the tropical strains may suggest both a low ability to respond to temperature variation in their natural thermally stable tropical habitats, as well as a level of thermal stress limiting their enzyme production ability.last_img read more

Can the optimisation of pop-up agriculture in remote communities help feed the world?

first_imgThreats to global food security have generated the need for novel food production techniques to feed an ever-expanding population with ever-declining land resources. Hydroponic cultivation has been long recognised as a reliable, resilient and resource-use-efficient alternative to soil-based agricultural practices. The aspiration for highly efficient systems and even city-based vertical farms is starting to become realised using innovations such as aeroponics and LED lighting technology. However, the ultimate challenge for any crop production system is to be able to operate and help sustain human life in remote and extreme locations, including the polar regions on Earth, and in space. Here we explore past research and crop growth in such remote areas, and the scope to improve on the systems used in these areas to date. We introduce biointensive agricultural systems and 3D growing environments, intercropping in hydroponics and the production of multiple crops from single growth systems. To reflect the flexibility and adaptability of these approaches to different environments we have called this type of enclosed system ‘pop-up agriculture’. The vision here is built on sustainability, maximising yield from the smallest growing footprint, adopting the principles of a circular economy, using local resources and eliminating waste. We explore plant companions in intercropping systems to supply a diversity of plant foods. We argue that it is time to consume all edible components of plants grown, highlighting that nutritious plant parts are often wasted that could provide vitamins and antioxidants. Supporting human life via crop production in remote and isolated communities necessitates new levels of efficiency, eliminating waste, minimising environmental impacts and trying to wean away from our dependence on fossil fuels. This aligns well with tandem research emerging from economically developing countries where lower technology hydroponic approaches are being trialled reinforcing the need for ‘cross-pollination’ of ideas and research development on pop-up agriculture that will see benefits across a range of environments.last_img read more