Recent population trends of sooty and light-mantled albatrosses breeding on Marion Island

Sub-Antarctic Marion Island is one of the few islands where both species of Phoebetria albatrosses breed sympatrically. The last published assessment of their population trends, which reported counts up to 2008, concluded that the numbers of breeding pairs of sooty albatross P. fusca (Endangered) were decreasing, whereas numbers of light-mantled albatross P. palpebrata (Near Threatened) were increasing. Extending the counts to 2014 reversed these trends, with numbers of sooty albatrosses increasing from 2006 to 2014, and numbers of light-mantled albatrosses decreasing from 2007 to 2014. Confidence in island-wide counts is low due to the cryptic nature of the albatrosses on their largely inaccessible cliff-side nest sites, as well as counts for sooty albatrosses taking place late in the incubation period when 10?20% of nests have already failed. Given the greater conservation concern for the sooty albatross, we recommend that dedicated annual counts be conducted during the early incubation period, and be repeated shortly after the chicks hatch (late December), mid-way through the nestling period (late February) and prior to fledging (late April), to give a better idea of breeding success. Count zones also should be revised to facilitate more accurate counts, ensuring more reliable estimates of sooty albatross population trends at Marion Island.     

Contribution to the background rate of a satellite X-ray detector by spallation products in a caesium iodide crystal

The energy spectra observed in a CsI crystal in the 20 keV-2 MeV range, due to the decay of radioactive isotopes produced in the crystal by bombardment with 155 MeV protons, are presented as a function of time after irradiation.It is shown that the large number of decay products produced by spallation can account for these spectra and that these spectra are in quantitative agreement with the predictions of a semi-empirical formula due to Rudstam, which gives the numbers of different isotopes produced. This formula is used to predict the spallation that would occur in such a crystal on board a satellite due to cosmic rays and passages through the South Atlantic Anomaly. Inspection shows that the spallation produced in the latter case is well approximated by that at 155 MeV. Hence the experimental results are used to explain previously observed background rates and to predict the background rates that would occur in the U.K.5 X-ray telescope of Imperial College. Using the Rudstam formula an estimate of cosmic ray induced background is also made.The relative importance of activity resulting from neutron interactions (atmospheric albedo and spacecraft secondaries) is considered.It is suggested that the Rudstam formula provides a general method of predicting induced radio-activity in satellite materials and that observed breaks in the diffuse cosmic X-ray spectrum could be due to inadequate allowance for this source of background.     

The shape of the diffuse cosmic X-ray spectrum

Recent work by Dyer and Morfill has shown that satellite measurements of the diffuse cosmic X-ray spectrum made with crystal scintillators may include errors due to radioactive spallation products formed in the detector by inner belt and cosmic ray protons.

An estimate is made of the magnitude of this source of background for the various experimental situations and it is shown that apparent features at 40 keV and 1 MeV are likely to be due to radioactive decays in the instruments. A review is made of experiments covering the range 1 keV-100 MeV in order to ascertain whether a single exponent spectrum is capable of fitting the experimental results. The astrophysical implications of such a spectrum are briefly considered.

Suggestions are made for the location and correction for background of future experiments.

     

Dialogue, metaphors of dialogue and understandings of geography

Increasingly, human and physical geographers alike describe their research practices as involving dialogue of some kind. However, the widespread popularity of the term belies some very different understandings of its meaning and methodological implications. In this paper we reflect on these different conceptions of 'dialogical' geography as a way, first, of illustrating the broad range of understandings of research methodology now current in the discipline and, second, of identifying their implications for three long–standing controversies in the discipline: relativism and the truth of geographical knowledge, the associated dualisms between subject/object, nature/society, and realism/constructionism, and the potential for unity between human and physical geography. We argue that, while dialogue is a potentially fruitful way of understanding and practising geography, that the defence of it, like the attacks on it, is often misconceived.     

The attenuation of tidal and subtidal oscillations in the Patos Lagoon estuary

The single, long and narrow channel that usually connects choked coastal lagoons to the ocean can serve as a natural hydraulic low-pass filter that reduces or eliminates tidal and subtidal effects inside the lagoon. This study proposes an alternative method of estimating the attenuation of the tidal and subtidal oscillations throughout the Patos Lagoon estuary. The attenuation is estimated for conditions of contrasting river runoff and weather (summer and winter). A high-pass/low-pass filter (fast fourier transformation technique – FFT) is applied to time series of sea-surface elevation (SSE) measured at the mouth of the Patos Lagoon. The resulting high-frequency (tidal) and low-frequency (subtidal) signals are used in independent simulations to force the TELEMAC-2D model. Attenuation of the tidal and subtidal signals throughout the estuary is estimated by applying cross-spectral analysis between the model-generated SSE time series at different locations throughout the estuary and the filtered SSE time series measured at the mouth. Results from the proposed method suggest that: (1) the low-frequency (subtidal) oscillations are less attenuated and propagate further than the high-frequency (tidal) oscillations in the Patos Lagoon estuary; (2) the filtering capability of the Patos Lagoon estuary is expected to follow a seasonal pattern, although further investigations on an interannual time scale are recommended in order to confirm this hypothesis; (3) the influence of the oceanic boundary processes on the SSE dynamics of the lagoon is restricted to the lower estuary. Further inland, the local forcing generated by the wind and freshwater input is likely to be the main forcing effect controlling the dynamics of the system. The proposed method proved to be an efficient and alternative way of estimating the attenuation of energy in the tidal and subtidal bands throughout the access channel of a choked coastal lagoon located in an area of reduced tidal influence.Responsible Editor: Iris Grabemann     

Spatial and temporal variations in temperate forest soil carbon dioxide during the non-growing season

In the Whitehall Forest of Georgia during the 1985-86 non-growing season soil CO₂ varied with soil depth, varied spatially at constant depth, and varied temporally with changing environmental conditions. Variations with depth in the upper 1.4 m of the soil were of greater magnitude than temporal variations and spatial differences at 30 cm depth were of lesser magnitude. Mean soil CO₂ in evergreen forest was higher (0.207 per cent) than in deciduous and mixed forest (0.157 per cent). There were no trends in soil CO₂ along hillslopes or with changes in soil texture, bulk density, moisture content, or temperature. Soil CO₂ did increase near trees possibly due to increased root densities and/or more numerous pockets of microbial activity. For CO₂ at 30 cm depth, two variables–the mean daily temperature range in the month before measurement and actual evapotranspiration in the week before measurement (AET7)–explained 76 per cent of the variation in mean soil CO₂. At the profile site, where soil CO₂ was measured at five depths, 66 per cent of the variability in CO₂ was explained by soil depth, AET7, and the average daily temperature range in the two months before measurement.