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Dissipation of tidal energy by Antarctic ice shelves

first_imgFLEXING of ice shelves may dissipate enough tidal energy to have a significant effect on the Moon’s retreat from the Earth. It is generally agreed that tidal friction slows the rotation of the Earth and decelerates the Moon in its orbit1. The total energy dissipated can be calculated from observations of the Moon’s motion and agrees closely with estimates of the gravitational work done by the Sun and Moon on the ocean tidal bulge2. Therefore dissipation of tidal energy is considered to occur mainly in the ocean with small upper limits being set on energy losses in the Earth’s mantle and core. Because the amount of tidal dissipation in shallow seas3 and internal tides4 is uncertain it is of interest to search for additional dissipative mechanisms. In this note the possibility of tidal bending of ice shelves is examined.last_img read more

Age of the Glen Dessary Syenite, Inverness-shire: diachronous Palaeozoic metamorphism Across the Great Glen

first_imgApparently igneous zircons from the Glen Dessary syenite complex give concordant U-Pb ages averaging 456 ± 5 Ma which is taken to date crystallization. The complex was deformed and metamorphosed to amphibolite facies subsequent to emplacement so that this age is a maximum for these orogenic events in the western Moine Series. Other age data indicate that amphibolite facies conditions associated with pegmatite emplacement continued until ca. 430 Ma contrasting with the north-east Highlands where tectonism and metamorphism was completed by 460 Ma ago. The disparity between hornblende and mica K-Ar ages suggests that cooling from 500 to 300°C took about 20 Ma. Higher blocking temperatures are indicated for U-Pb in monazite and sphene than for U-Pb in apatite.last_img

Attachment and growth of antarctic soil cyanobacteria and algae on natural and artificial substrata

first_imgThe attachment to artificial substrata (carborundum paper) of cyanobacteria and algae isolated from Antarctic fellfield soils was investigated using a simulated flow apparatus. Generally, the rugosity of the substratum was less important than the morphology and extent of mucilage production of the microflora in determining attachment success. However, the smoothest grades of substratum did increase the retention of the fine filaments of the cyanobacterium Pseudanabaena and decrease the retention of the large filaments of the chlorophyte Zygnema. Filaments of the motile cyanobacterium Phormidium and cells of the motile diatom Pinnularia showed good retention on all grades of paper, with that of Phormidium being the highest of all taxa at 90–100%. The coccoid chlorophyte Planktosphaerella was poorly retained on all grades of substratum. Growth rates of the same organisms on fellfield soils were little affected by soil rugosity, although the largest soil particles (1–2 mm) did cause a decrease in the growth rate of Phormidium and increase in that of Planktosphaerella. These results indicate the importance of the cyanobacterial-algal flora, and especially the motile component, in the stabilization of fellfield soils.last_img read more

Subglacial Lake Ellsworth: a candidate for in situ exploration in West Antarctica

first_imgRadio-echo sounding reveals a 10 km-long lake beneath similar to3.4 km of ice near the Ellsworth Mountains in West Antarctica, 20 km from the ice divide. Subglacial Lake Ellsworth is located within a distinct topographic hollow, which is similar to1.5 km deeper than the surrounding bed. Judging by bed slopes flanking the lake, the water depth is at least 10s of metres. Calculations of basal temperature reveal the ice base to be warm both now and during full glacial periods. As the environments of subglacial lakes are broadly similar, life may be expected in Lake Ellsworth as in any other. Given this, its physical characteristics, and the fact that the West Antarctic Ice Sheet has been accessed on several occasions, Lake Ellsworth is an excellent candidate for in situ examination.last_img

Early Carboniferous (Late Tournaisian–Early Viséan) ostracods from the Ballagan Formation, central Scotland, UK

first_imgThe Ballagan Formation (Late Tournaisian–Early Viséan) of central Scotland yields an ostracod fauna of 14 species in ten genera, namely Beyrichiopsis, Cavellina, Glyptolichvinella, Glyptopleura, Knoxiella, Paraparchites, Sansabella, Shemonaella, Silenites and Sulcella. The ostracods, in combination with palynomorphs, are important biostratigraphical indices for correlating the rock sequences, where other means of correlation, especially goniatites, conodonts, foraminifera, brachiopods or corals are absent. Stratigraphical distribution of the ostracods, calibrated with well-established palynomorph biozones, identifies three informally defined intervals: a sub-CM palynomorph Biozone interval with poor ostracod assemblages including Shemonaella scotoburdigalensis; a succeeding interval within the CM palynomorph Biozone where Cavellina coela, Cavellina incurvescens, Sansabella amplectans and the new species Knoxiella monarchella and Paraparchites discus first appear; and, an upper interval, in the upper CM Biozone, marked by the appearance of Sulcella affiliata. At least locally in central Scotland, S. affiliata permits a level of resolution equivalent to a sub-zonal upper division of the CM Biozone. The fauna, flora, sedimentology and stable isotope composition (δ13C and δ18O) of carbonate minerals in the Ballagan Formation suggest the ostracods inhabited brackish, hypersaline and ephemeral aquatic ecologies in a coastal floodplain setting.last_img read more

Measurements from ground and balloons during APE-GAIA – A polar ozone library

first_imgMany long-term monitoring sites in Antarctic regions, which deploy ground-based stratospheric remote sensors and fly radiosondes or ozonesondes on balloons, supported the Airborne Polar Experiment in September and October 1999. Support consisted of supplying data to the campaign in real time, and in some cases by increasing the frequency of measurements during the campaign. The results will strengthen scientific conclusions from the airborne measurements. But results from these sites are allowing important scientific studies of new aspects of the ozone hole in their own right, because like the aircraft and its campaign, many sites traverse the vortex edge and are close to the largest source of lee waves, or measure infrequently observed trace gases such as HNO3. Examples of such studies are the behaviour and value of NO2 in midwinter, ozone filamentation with no apparent horizontal advection, the frequency and amplitude of gravity waves over the Antarctic Peninsula, mixing in the lowest stratosphere in Antarctic spring, the mechanism and frequency of HNO3 enhancement above the ozone peak in midwinter, and trends in UV dose in southern South America.last_img read more

Estimating migratory connectivity of gray catbirds (Dumetella Carolinensis) using geolocator and mark-recapture data

first_imgUnderstanding the connectivity between breeding and nonbreeding populations of migratory birds is fundamental to our knowledge of biological phenomena such as population dynamics and dispersal. Moreover, our ability to quantify migratory connectivity has inevitable consequences for both conservation and management of species that utilize distinct geographic locations. Technology is rapidly advancing our ability to track birds throughout the annual cycle and to collect data on the degree of connectivity among breeding and nonbreeding populations. We combined two direct methods, mark recapture (n = 17) and geolocation (n = 6), to estimate the migratory connectivity of breeding and nonbreeding populations of Gray Catbirds (Dumetella carolinensis). Data from geolocators show that birds breeding in the Mid-Atlantic overwinter in both Cuba and southern Florida. Mark recapture data supported our geolocator results but also provided a broader spatial perspective by documenting that Mid-Atlantic and Midwestern populations occupy distinct geographic localities during the nonbreeding period. This research underscores the importance of geolocators, as well as other tools, to advance our understanding of migratory connectivity. Finally, our results highlight the potential value of U.S. Geological Survey (USGS) Bird Banding Laboratory mark recapture data, which are often underutilized in ornithological research.last_img read more

Geological constraints on glacio-isostatic adjustment models of relative sea-level change during deglaciation of Prince Gustav Channel, Antarctic Peninsula

first_imgThe recent disintegration of Antarctic Peninsula ice shelves, and the associated accelerated discharge and retreat of continental glaciers, has highlighted the necessity of quantifying the current rate of Antarctic ice mass loss and the regional contributions to future sea-level rise. Observations of present day ice mass change need to be corrected for ongoing glacial isostatic adjustment, a process which must be constrained by geological data. However, there are relatively little geological data on the geometry, volume and melt history of the Antarctic Peninsula Ice Sheet (APIS) after Termination 1, and during the Holocene so the glacial isostatic correction remains poorly constrained. To address this we provide field constraints on the timing and rate of APIS deglaciation, and changes in relative sea-level (RSL) for the north-eastern Antarctic Peninsula based on geomorphological evidence of former marine limits, and radiocarbon-dated marine-freshwater transitions from a series of isolation basins at different altitudes on Beak Island. Relative sea-level fell from a maximum of c. 15 m above present at c. 8000 cal yr BP, at a rate of 3.91 mm yr−1 declining to c. 2.11 mm yr−1 between c. 6900–2900 cal yr BP, 1.63 mm yr−1 between c. 2900–1800 cal yr BP, and finally to 0.29 mm yr−1 during the last c. 1800 years. The new Beak Island RSL curve improves the spatial coverage of RSL data in the Antarctic. It is in broad agreement with some glacio-isostatic adjustment models applied to this location, and with work undertaken elsewhere on the Antarctic Peninsula. These geological and RSL constraints from Beak Island imply significant thinning of the north-eastern APIS by the early Holocene. Further, they provide key data for the glacial isostatic correction required by satellite-derived gravity measurements of contemporary ice mass loss, which can be used to better assess the future contribution of the APIS to rising sea-levels.last_img read more

Factors influencing the stable carbon isotopic composition of suspended and sinking organic matter in the coastal Antarctic sea ice environment

first_imgA high resolution time-series analysis of stable carbon isotopic signatures in particulate organic carbon (delta C-13(POC)) and associated biogeochemical parameters in sea ice and surface waters provides an insight into the factors affecting delta C-13(POC) in the coastal western Antarctic Peninsula sea ice environment. The study covers two austral summer seasons in Ryder Bay, northern Marguerite Bay between 2004 and 2006. A shift in diatom species composition during the 2005/06 summer bloom to near-complete biomass dominance of Proboscia inermis is strongly correlated with a large ~10 parts per thousand negative isotopic shift in delta C-13(POC) that cannot be explained by a concurrent change in concentration or isotopic signature of CO2. We hypothesise that the delta C-13(POC) shift may be driven by the contrasting biochemical mechanisms and utilisation of carbon-concentrating mechanisms (CCMs) in different diatom species. Specifically, very low delta C-13(POC) in P. inermis may be caused by the lack of a CCM, whilst some diatom species abundant at times of higher delta C-13(POC) may employ CCMs. These short-lived yet pronounced negative delta C-13(POC) excursions drive a 4 parts per thousand decrease in the seasonal average delta C-13(POC) signal, which is transferred to sediment traps and core-top sediments and consequently has the potential for preservation in the sedimentary record. This 4 parts per thousand difference between seasons of contrasting sea ice conditions and upper water column stratification matches the full amplitude of glacial-interglacial Southern Ocean delta C-13(POC) variability and, as such, we invoke phytoplankton species changes as a potentially important factor influencing sedimentary delta C-13(POC). We also find significantly higher delta C-13(POC) in sea ice than surface waters, consistent with autotrophic carbon fixation in a semi-closed environment and possible contributions from post-production degradation, biological utilisation of HCO3- and production of exopolymeric substances. This study demonstrates the importance of surface water diatom speciation effects and isotopically heavy sea ice-derived material for delta C-13(POC) in Antarctic coastal environments and underlying sediments, with consequences for the utility of diatom-based delta C-13(POC) in the sedimentary record.last_img read more

Abrupt changes in high-latitude nutrient supply to the Atlantic during the last glacial cycle

first_imgThe supply of nutrients to the low-latitude thermocline is largely controlled by intermediate-depth waters formed at the surface in the high southern latitudes. Silicic acid is an essentialmacronutrient for diatoms, which are responsible for a signifi cant portion of marinecarbon export production. Changes in ocean circulation, such as those observed during thelast deglaciation, would infl uence the nutrient composition of the thermocline and, therefore,the relative abundance of diatoms in the low latitudes. Here we present the fi rst recordof the silicic acid content of the Atlantic over the last glacial cycle. Our results show thatat intermediate depths of the South Atlantic, the silicic acid concentration was the same atthe Last Glacial Maximum (LGM) as it is today, overprinted by high silicic acid pulses thatcoincided with abrupt changes in ocean and atmospheric circulation during Heinrich Stadialsand the Younger Dryas. We suggest these pulses were caused by changes in intermediatewater formation resulting from shifts in the subpolar hydrological cycle, with fundamentalimplications for the nutrient supply to the Atlantic.last_img read more