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Antarctic studies of the coupled ionosphere-magnetosphere system

first_imgThe southern polar region offers many significant advantages over its northern counterpart for studies of the interactions of the solar wind, magnetosphere, ionosphere and thermosphere. These mainly arise from the much wider separation of the geographic and geomagnetic poles in the south compared with the north. These displacements lead to hemispheric asymmetries and to considerable longitudinal structure in the high-latitude ionosphere and magnetosphere, which is particularly striking in the south. Examples of these effects are given. In addition, observations of geospace from Antarctica have made a valuable contribution per se. Suitable illustrations are provided from invariant latitude ca. 45° to the invariant pole. Possible areas for future research, and the experimental methods that are likely to be used to overcome the logistical difficulties, are discussed.last_img read more

Trophic relations of the cephalopod Martialia hyadesi (Teuthoidea: Ommastrephidae) at the Antarctic Polar Front, Scotia Sea

first_imgSamples of the squid Martialia hyadesi were collected aboard two Japanese squid-jigging vessels carrying out commercial fishing trials at the Antarctic Polar Frontal Zone, north Scotia Sea, in February 1989. The dissected stomachs of 61 specimens were classified according to fullness and the contents were examined visually. Identifiable food items included fish sagittal otoliths, crustacean eyes, the lappets on euphausiid first antennule segments and cephalopod sucker rings. The most frequent items in the squid’s diet were the myctophid fishes Krefftichthys anderssoni and Electrona carlsbergi, the euphausiid Euphausia superba and a hyperiid amphipod, probably Themisto gaudichaudi. A small proportion of the sample had been feeding cannibalistically. Total lengths of the fish prey were estimated from sagittal otolith size using published relationships. All fish were relatively small; 7 to 35% of squid mantle-length. However, it is possible that some heads of larger fish are discarded by the squid and so are not represented by otoliths in the stomach contents. Over the size range of squid in the sample there was no relationship between size of fish prey and size of squid. Similarly, when the squid sample was divided into groups according to prey categories: crustaceans, crustaceans+fish, fish, cephalopod, there was no evidence that dietary preference was related to squid size. The prevalence of copepod-feeding myctophids in the diet of this squid, which is itself a major prey item of some higher predators in the Scotia Sea, suggests that a previously unrecognised food chain: copepod-myctophid-M. hyadesi-higher predator, may be an important component of the Antarctic oceanic ecosystem.last_img read more

Erosional history of the Transantarctic Mountains deduced from sand grain detrital modes in CRP-2/2A, Victoria Land Basin, Antarctica

first_imgDynamic provenance variations are deduced from sand-grain detrital modes in samples obtained from the CRP-2/2A drillcore. Below an important unconformity at 307metres below sea floor (mbsf), sand grains in most of the sequence were dominantly derived from Beacon sandstone and Ferrar dolerite sources, although alternating with subordinate thicknesses of strata derived from a predominantly granitoid source (Granite Harbour IntrusiveComplex; GHIC). Above the 307 mbsf unconformity, the reverse situation occurs, with most sediments dominantly sourced in the GHIC. Contributions from other sources (e.g. Jurassic Kirkpatrick basalt lavas and Proterozoic metamorphic basement) are also persistent but minor.An input of fresh volcanic detritus commenced at 307 mbsf and is ubiquitous in all the younger sediments. At least three (probably four) episodes of volcanism are identified, each lasting 1-2 M.yr in duration. The initial influx at 307 mbsf corresponds to the initiation of the McMurdo Volcanic Group (MVG) at c. 25 Ma and is much younger than estimates made previously by other workers for the oldest MVG volcanic activity in the McMurdo Sound region (Eocene?). Simultaneous major changes in the proportion of clast lithologies in CRP-2/2A suggest that the 307 mbsf unconformity is the most important petrological break within the cored sequence. It is speculated thatthe petrological contrasts across the unconformity are genetically associated with important climatic changes and/or rapid uplift episode(s) in the Transantarctic Mountains.last_img read more

Maritime Antarctic climate change: signals from terrestrial biology

first_imgThe simplicity of maritime Antarctic terrestrial ecosystems, combined with rapid changes in several environmental variables, creates a natural laboratory probably unparalleled worldwide in which to study biological consequences of climate change. The Antarctic Peninsula and Scotia Arc provide a gradient from oceanic cool temperate to frigid continental desert conditions, giving a natural model of climate change predictions. Biota are limited by the twin environmental factors of low temperature and lack of water, while also facing changes in the timing of UV-B maxima, associated with the spring ozone hole. Biological changes consistent with predictions from climate amelioration are visible in the form of expansions in range and local population numbers amongst elements of the flora. Field manipulations demonstrate (i) potential for massive species and community responses to climate amelioration, (ii) the importance of existing soil propagule banks, and (iii) biochemical responses to changing radiation environments. Antarctic species possess considerable resistance/resilience and response flexibility to a range of environmental stresses. Wide environmental variability in Antarctic terrestrial habitats also means that predicted levels of change often fall well within the range already experienced. Thus, climate amelioration may generate positive responses from resident biota, at least while they remain protected through isolation from colonization by more effective competitors. Responses are likely to be subtle and multifactorial in origin, arising from changes in resource allocation and energy economics. The integration of subtle responses may lead to greater consequential impacts in communities and ecosystems.last_img read more

Adult Antarctic krill feeding at abyssal depths

first_imgAntarctic krill (Euphausia superba) is a large euphausiid, widely distributed within the Southern Ocean [1], and a key species in the Antarctic food web [2]. The Discovery Investigations in the early 20(th) century, coupled with subsequent work with both nets and echosounders, indicated that the bulk of the population of postlarval krill is typically confined to the top 150 m of the water column [1, 3, 4]. Here, we report for the first time the existence of significant numbers of Antarctic krill feeding actively at abyssal depths in the Southern Ocean. Biological observations from the deep-water remotely operated vehicle Isis in the austral summer of 2006/07 have revealed the presence of adult krill (Euphausia superba Dana), including gravid females, at unprecedented depths in Marguerite Bay, western Antarctic Peninsula. Adult krill were found close to the seabed at all depths but were absent from fjords close inshore. At all locations where krill were detected they were seen to be actively feeding, and at many locations there were exuviae (cast molts). These observations revise significantly our understanding of the depth distribution and ecology of Antarctic krill, a central organism in the Southern Ocean ecosystem.last_img read more

Impact of ice-shelf basal melting on inland ice-sheet thickness: a model study

first_imgIce flow from the ice sheets to the ocean contains the maximum potential contributing to future eustatic sea-level rise. In Antarctica most mass fluxes occur via the extended ice-shelf regions covering more than half the Antarctic coastline. The most extended ice shelves are the Filchner–Ronne and Ross Ice Shelves, which contribute �30% to the total mass loss caused by basal melting. Basal meltrates here show small to moderate average amplitudes of <0.5ma–1. By comparison, the smaller but most vulnerable ice shelves in the Amundsen and Bellinghausen Seas show much higher melt rates (up to 30ma–1), but overall basal mass loss is comparably small due to the small size of the ice shelves. The pivotal question for both characteristic ice-shelf regions, however, is the impact of ocean melting, and, coevally, change in ice-shelf thickness, on the flow dynamics of the hinterland ice masses. In theory, iceshelfback-pressure acts to stabilize the ice sheet, and thus the ice volume stored above sea level.We use the three-dimensional (3-D) thermomechanical ice-flow model RIMBAY to investigate the ice flow in a regularly shaped model domain, including ice-sheet, ice-shelf and open-ocean regions. By using melting scenarios for perturbation studies, we find a hysteresis-like behaviour. The experiments show that the system regains its initial state when perturbations are switched off. Average basal melt rates of up to 2ma–1 as well as spatially variable melting calculated by our 3-D ocean model ROMBAX act as basalboundary conditions in time-dependent model studies. Changes in ice volume and grounding-line position are monitored after 1000 years of modelling and reveal mass losses of up to 40 Gt a–1.last_img read more

The effects and correction of the geometric factor for the POES/MEPED electron flux instrument using a multisatellite comparison

first_imgMeasurements from the Polar-Orbiting Environmental Satellite (POES) Medium Energy Proton and Electron Detector (MEPED) instrument are widely used in studies into radiation belt dynamics and atmospheric coupling. However, this instrument has been shown to have a complex energy-dependent response to incident particle fluxes, with the additional possibility of low-energy protons contaminating the electron fluxes. We test the recent Monte Carlo theoretical simulation of the instrument by comparing the responses against observations from an independent experimental data set. Our study examines the reported geometric factors for the MEPED electron flux instrument against the high-energy resolution Instrument for Detecting Particles (IDPs) on the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions satellite when they are located at similar locations and times, thereby viewing the same quasi-trapped population of electrons. We find that the new Monte Carlo-produced geometric factors accurately describe the response of the POES MEPED instrument. We go on to develop a set of equations such that integral electron fluxes of a higher accuracy are obtained from the existing MEPED observations. These new MEPED integral fluxes correlated very well with those from the IDP instrument (>99.9% confidence level). As part of this study we have also tested a commonly used algorithm for removing proton contamination from MEPED instrument observations. We show that the algorithm is effective, providing confirmation that previous work using this correction method is valid.last_img read more

Energy flow in growth and production

first_imgGrowth involves two flows of energy: the chemical energy in the monomers used to construct the macromolecules that comprise tissue (proteins, nucleic acids, lipid membranes), and the metabolic energy used to build those macromolecules. The metabolic costs of synthesising the macromolecules necessary to build tissue are well defined, and we have a robust estimate of the overall cost of growth for an individual ectotherm. At the population level the cost of production appears to be much greater for endotherms than ectotherms, the reasons for which are not fully understood. These uncertainties are important to resolve if we wish to accurately model the flow of energy through populations or ecosystems because simply scaling up from individual energetics may produce misleading results.last_img read more

Phased response of the subpolar Southern Ocean to changes in circumpolar winds

first_imgThe response of the subpolar Southern Ocean (sSO) to wind forcing is assessed using satellite radar altimetry. sSO sea level exhibits a phased, zonally coherent, bi‐modal adjustment to circumpolar wind changes, involving comparable seasonal and interannual variations. The adjustment is effected via a quasi‐instantaneous exchange of mass between the Antarctic continental shelf and the sSO to the north, and a 2‐month‐delayed transfer of mass between the wider Southern Ocean and the subtropics. Both adjustment modes are consistent with an Ekman‐mediated response to variations in surface stress. Only the fast mode projects significantly onto the surface geostrophic flow of the sSO, thus the regional circulation varies in phase with the leading edge of sSO sea level variability. The surface forcing of changes in the sSO system is partly associated with variations of surface winds linked to the Southern Annular Mode, and is modulated by sea ice cover near Antarctica.last_img read more

From warm to cold waters: new insights into the habitat and trophic ecology of Southern Ocean squids throughout their life cycle.

first_imgCephalopods play a major role in marine ecosystems, yet very little is known about the dynamics of their habitat use and trophic ecology across the stages of their life cycle, particularly in the Southern Ocean. Here, we used stable isotope analyses of δ13C (a proxy for foraging habitat) and δ15N (a proxy for trophic position) to investigate the habitat use and trophic ecology of 10 squid species, collected from the diet of Antipodean (Diomedea antipodensis antipodensis) and Gibson’s (D. a. gibsoni) albatrosses breeding at Antipodes and Adams Island (South Pacific), respectively. We analyzed isotopes in 2 sections of squid lower beaks, representing 2 stages of the life cycle: the tip of the rostrum (juvenile stage) and the wing (adult stage). Higher δ13C values in early life stages (-20.8 ± 1.7‰) than in adult life stages (-21.6 ± 1.9‰) suggest that Southern Ocean squids tend to move southwards as they grow, with oceanic fronts being an important habitat for these species. Our results also suggest that adults may move southwards with climate change, possibly impacting top predators living on northern islands. Overall, δ15N values revealed an increase in trophic position from early (6.7 ± 2.7‰) to adult life stages (9.0 ± 2.5‰) in all species. Nevertheless, significant differences between δ15N values of the 10 species, in both beak sections, suggest different feeding strategies between species and life stages.last_img read more