Further evidence for oceanic excitation of polar motion

While the role of the atmosphere in driving variations in polar motion is well established, the importance of the oceans has been recognized only recently. Further evidence for the role of the oceans in the excitation of polar motion is presented. To estimate the equatorial excitation functions, χ ₁ and χ ₂ , for the ocean, we use velocity and mass fields from a constant-density ocean model, driven by observed surface wind stresses and atmospheric pressure, for the period 1993–1995; comparison with similar functions derived from a more complex density-stratified ocean model indicates the effectiveness of the simple constant-density modelling approach. Corresponding atmospheric excitation functions are computed from NCEP/NCAR re-analyses. Results indicate significant improvements in the agreement with the observed polar motion excitation when the simulated oceanic effects are added to atmospheric excitation. Correlations between the polar motion and the geophysical signals at periods of 15–150 days increase from 0.53 to 0.80 and from 0.75 to 0.88 for χ ₁ and χ ₂ , respectively. The oceanic signals are particularly important for seasonal variations in χ ₁ (correlation increases from 0.28 to 0.85 when oceanic excitation is included). A positive impact of the oceans on more rapid polar motion is also observed, up to periods as short as 5 days. The sensitivity of the results to different forcing fields and different amounts of friction in the oceans is also discussed.     

The integration of South African fisheries into the global economy: Past,present and future

The integration of the South African fisheries into the global economy has operated as a powerful constraint on post-apartheid fisheries reform. The shedding of South Africa's international pariah status and currency depreciation enhanced access to and competitiveness on global markets, sparking a demersal-led export boom, which has favoured incumbent producers. Increased exports have also allowed the post-apartheid state and nascent black capital to maximise their returns from the fisheries through cost recovery and share purchases. The protection and promotion of the fisheries’ “international competitiveness”, inter alia sought through “sustainable fishery” certification of the hake industry with the Maritime Stewardship Council (MSC), has in turn provided a cover-all for the refusal of populist redistribution demands and special treatment for black small capital.     

The at-rest earth pressure coefficient prediction using simple elasto-plastic constitutive models

The paper deals with the theoretical prediction of the at-rest earth pressure coefficient for normally consolidated soils (k_0(NC)) using simple elasto-plastic constitutive models. In the first part of the work, the k_0(NC) expressions derived from critical state soil mechanics models are critically discussed. It is shown that, adopting typical values of the models parameters, the experimental k_0(NC) values are usually over-predicted. In the second part, a possible modification of the critical state model formulation, which allows to predict lower k_0(NC) values for a fixed angle of shearing resistance, is considered. Finally, a discussion of the results and some brief conclusions are proposed.     

Delineation of saltwater intrusion zones using the time domain electromagnetic method: the Nabeul–Hammamet coastal aquifer case study (NE Tunisia)

The time domain electromagnetic method (TDEM) is applied to monitor, to delineate and to map the saltwater intrusion zones in the Mediterranean Plio‐Quaternary aquifer. Forty‐two TDEM soundings were carried out in the coastal plain of Nabeul–Hammamet region (NE Tunisia). TDEM resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater–seawater transition zone. The geoelectric sections showing the vertical configuration of seawater intrusion, with the brackish‐salty‐saturated zones, have a resistivity ranging from ~0.1 to 5 Ω?m and are detected at a depth lower than 1.5 m. The salinized zones are located at Nabeul (Sidi Moussa, Sidi El Mahrsi, Al Gasba and Mrazgua) and at Hammamet (Touristic zone of Hammamet north and south, Baraket Essahel) and reached a distance of 4 km from the coastline, indicating a severe state for the aquifer in these zones. These TDEM results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells. Moreover, in the northeastern part, the presence of a saltwater front located far from the coast and along the NW–SE major surface fault can be explained by two hypothesis: (i) this fault seems to provide a conduit for seawater to move readily towards the water wells and (ii) the clay and gypsum infiltration of marine Messinian deposits through the fault plane leads to low resistivities. Finally, it comes out from this study that TDEM survey has successfully depicted salinized zones of this coastal aquifer. Copyright © 2012 John Wiley & Sons, Ltd.     

The volcanic history of Mars: High-resolution crater-based studies of the calderas of 20 volcanoes

Determining absolute surface ages for bodies in the Solar System is, at present, only possible for Earth and Moon with radiometric dating for both bodies and biologic proxies such as fossils for Earth. Relative ages through cratering statistics are recognized as one of the most reliable proxies for relative ages, calibrated by lunar geologic mapping and Apollo program sample returns. In this work, we have utilized the Mars Reconnaissance Orbiter’s ConTeXt Camera’s images which provide the highest resolution wide-scale coverage of Mars to systematically crater-age-date the calderas of 20 of Mars’ largest volcanoes in order to constrain the length of time over which these volcanoes - and major volcanic activity on the planet, by extension - were active. This constitutes the largest uniform and comprehensive research on these features to date, eliminating unknown uncertainties by multiple researchers analyzing different volcanoes with varied data and methods. We confirm previous results that Mars has had active volcanism throughout most of its history although it varied spatially and temporally, with the latest large-scale caldera activity ending approximately 150 ma in the Tharsis region. We find a transition from explosive to effusive eruption style occurring in the Hesperian, at approximately 3.5 Ga ago, though different regions of the planet transitioned at different times. Since we were statistically complete in our crater counts to sizes as small as ∼60 m in most cases, we also used our results to study the importance of secondary cratering and its effects on crater size-frequency distributions within the small regions of volcanic calderas. We found that there is no “golden rule” for the diameters secondaries become important in crater counts of martian surfaces, with one volcano showing a classic field of secondaries ∼2 crater diameters from the center of its primary but not affecting the size-frequency distribution, and another clearly showing an influence but from no obvious primary.     

Measurements of volcanic SO2 and CO2 fluxes by combined DOAS,Multi-GAS and FTIR observations: a case study from Turrialba and Telica volcanoes

Over the past few decades, substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic SO₂ emissions. However, measurements of CO₂ emissions still present many difficulties, partly due to the lack of instruments that can directly measure CO₂ emissions and partly due to its strong atmospheric background. In order to overcome these difficulties, a commonly taken approach is to combine differential optical absorption spectroscopy (DOAS) by using NOVAC scan-DOAS instruments for continuous measurements of crateric SO₂ emissions, and electrochemical/NDIR multi-component gas analyser system (multi-GAS) instruments for measuring CO₂/SO₂ ratios of excerpts of the volcanic plume. This study aims to quantify the representativeness of excerpts of CO₂/SO₂ ratios measured by Multi-GAS as a fraction of the whole plume composition, by comparison with simultaneously measured CO₂/SO₂ ratios using cross-crater Fourier transform infrared spectroscopy (FTIR). Two study cases are presented: Telica volcano (Nicaragua), with a homogenous plume, quiescent degassing from a deep source and ambient temperature, and Turrialba volcano (Costa Rica), which has a non-homogeneous plume from three main sources with different compositions and temperatures. Our comparison shows that in our “easier case” (Telica), FTIR and Multi-GAS CO₂/SO₂ ratios agree within a factor about 3 %. In our “complicated case” (Turrialba), Multi-GAS and FTIR yield CO₂/SO₂ ratios differing by approximately 13–25 % at most. These results suggest that a fair estimation of volcanic CO₂ emissions can be provided by the combination of DOAS and Multi-GAS instruments for volcanoes with similar degassing conditions as Telica or Turrialba. Based on the results of this comparison, we report that by the time our measurements were made, Telica and Turrialba were emitting approximately 100 and 1,000 t day^?1 of CO₂, respectively.     

EChO spectra and stellar activity II. The case of dM stars

EChO is a dedicated mission to investigate exoplanetary atmospheres. When extracting the planetary signal, one has to take care of the variability of the hosting star, which introduces spectral distortion that can be mistaken as planetary signal. Magneticvariability has to be taken into account in particular for M stars. To this purpose, assuming a one spot dominant model for the stellar photosphere, we develop a mixed observational-theoretical tool to extract the spot’s parameters from the observed optical spectrum. This method relies on a robust library of spectral M templates, which we derive using the observed spectra of quiet M dwarfs in the SDSS database. Our procedure allows to correct the observed spectra for photospheric activity in most of the analyzed cases, reducing the spectral distortion down to the noise levels. Ongoing refinements of the template library and the algorithm will improve the efficiency of our algorithm.