Iceland and the North Atlantic: A review

Iceland is a special volcanic island in an anomalous ocean basin. A review of the unusual features shows that among others topography and gravity are broadly positive, spreading has been and still is complex, seismicity is slightly diffuse and the chemistry of the basalts is different from that at normal ridges. In summary we observe a tendency of lithospheric dispersal and spreading in the North Atlantic and its surroundings. These observations together with what is known about Icelandic crust, heat flow, tectonic history, etc., point to a hot mantle upwelling beneath Iceland. The shape of the upwelling currents is not known. Although at present much speculation is possible, the authors prefers to think of a broad rising region uplifting the lithospheric plates such that they tend to slide away from Iceland more forcefully than is the case from normal spreading ridges.     

Polymerization of silicate and aluminate tetrahedra in glasses,melts, and aqueous solutions—I. Electronic structure of H6Si2O7, H6AlSiO71−, and H6Al2O72−

As part of a study of the effect of geologically common network modifiers on polymerization in silicate melts, glasses, and silica-rich aqueous solutions, we have studied the energies, electronic structures, and inferred chemical properties of ^IVT-O-^IVT linkages in the tetrahedral dimers H₆,Si₂O₇, H₆AlSiO₇^1?, and H₆Al₂O₇^2? using semi-empirical molecular orbital theory (CNDO/2). Our results indicate that the electron donating character of the bridging oxygen, O(br), linking two tetrahedra increases with increasing T-O(br) bond length but decreases with decreasing T-O(br)-T angles and increasing O-T-O(br) angles. This increase or decrease of the donor character of O(br) coincides with an increase or decrease of the affinity of O(br) for hard acceptors. The calculated electronic structure for the H₆Si₂O₇ molecule is compared with the observed X-ray emission, absorption, and photoelectron spectra of quartz and vitreous silica; the reasonable match between calculated and observed oxygen Kα emission spectra of vitreous silica supports our assertion that non-bonded O(br) electron density energetically at the top of the valence band controls the chemical reactivity of ^IVT-O-^IVT linkages in polymerized tetrahedral environments.     

Gulf of Alaska Atmosphere-Ocean Variability Over Recent Centuries Inferred from Coastal Tree-Ring Records

Eight tree-ring chronologies from coastal sites along the Gulf of Alaska (GOA) are used to develop a 227-year (1762–1988) reconstruction of spring/summer (March–September) coastal land temperatures for the region. This reconstruction explains 35% of the variance in the instrumental temperature data. The tree-ring records and reconstruction reflect the documented 1976 transition from cold to warm conditions in the North Pacific and are consistent with regional temperature compilations. Three of the eight ring-width series, from elevational timberline sites where trees are particularly stressed by temperature, extend back to A.D. 1600 and are used to identify additional occurrences of such transitions. The first principal component (PC) scores of these three longer records are positively correlated with spring (March–May) land and sea surface temperatures for the GOA region and are used to reconstruct land surface temperatures. Decadal-scale fluctuations in the reconstructions show agreement with decade-long changes in the intensity of the Aleutian Low pressure cell over the past century, suggesting that the tree-ring data may provide an index of past circulation changes for the northeast Pacific. Blackman-Tukey spectral analyses of both reconstructions indicate significant power at 7–11 years, with additional peaks at 3 years for the spring/summer reconstruction and 19 years for the longer spring temperature series. The modes of variation at about 3 and 7 years may correspond to those associated with the El Niño-Southern Oscillation bandwidth, whereas the 19-year term may relate to a proposed 20-year cycle of North Pacific circulation. The spring temperature series shows generally increased growth over the past century, coinciding with warmer spring temperatures in south coastal Alaska over this interval. Comparison with the entire spring series suggests that the recent warming exceeds temperature levels of prior centuries, extending back to A.D. 1600.     

The spatial context of manpower policy: Implications of current Canadian policy on regional development and planning

Macro government policies are often considered outside the context of their spatial impact. Following recent discussions of the problem, this paper is concerned with a critical review of Canadian Manpower policy in the context of national efficiency, regional equity and their interaction. Thus Manpower policy is analysed with respect to its implications concerning regional development as well as implicit regional policy. It is contended that many of the problems of Manpower policy in the spatial context can be traced back to the implicit theoretical background of Manpower policy; Human Capital theory. A radical critique of Human Capital theory is presented and a brief discussion of the ‘functional’ relationship between regional inequality and national macro-planning is also noted. In general the paper concludes that Manpower and regional policies in Canada tend to be contradictory although more research is needed to analyse the spatial impact of macro-policy which may overwhelm spatial policy and significantly influence the future of the spatial economy.     

Generation of homologous porphyrins under simulated geochemical conditions

Crude oils generally contain at least one symmetrical homologous series of porphyrins, which is usually centered at m/e 476 (DPEP) or m/e 478 (etioporphyrin). Simulated geochemical conditions in the present study resulted in decarboxylations and alkylations which ultimately led to the synthesis of homologous porphyrins from a single porphyrin. In several series of closed tube experiments, mesoporphyrin IX dimethylester (MPDME) was mixed with a variety of constituents including benzene, acetic acid, propionic acid, water and clay; the experiments were performed at temperatures between 135°C and 400°C at time intervals up to 80 days. Dealkylation, alkylation, hydrolysis, decarboxylation and metallation products were observed. An unsymmetrical homologous series of porphyrins was produced from MPDME. The dominant mass was m/e 478 (corresponding to a double deoarboxylation). Dealkylation products in multiples of 14 amu below the m/e 478 peak comprised the other members of the series. Cu-MPDME also produced homologous porphyrins. These, however, exhibited symmetry about the dominant members, similar to the symmetry found for the porphyrins of most petroleums and oil shales.     

Glacier fluctuations in the southern Peruvian Andes during the late‐glacial period,constrained with cosmogenic 3He

The occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes. Accurate constraint of both the timing and magnitude of events, such as the Younger Dryas and Antarctic Cold Reversal, is vital in order to test different hypotheses for the causes and propagation of abrupt climate change. However, in contrast to higher‐latitude regions, well‐dated records from the Tropics are rare and the structure of late‐glacial tropical climate remains uncertain. As a step toward addressing this problem, we present an in situ cosmogenic ³He surface exposure chronology from Nevado Coropuna, southern Peru, documenting a significant fluctuation of the ice margin during the late‐glacial period. Ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the Last Glacial Maximum terminus range from 11.9 to 13.9 ka and give an arithmetic mean age of 12.8 ± 0.7 ka (1σ). These data constitute direct evidence for a readvance, or prolonged stillstand, of glaciers in the arid Andes of southwestern Peru. Copyright © 2011 John Wiley & Sons, Ltd.     

Application of nonlinear optimization technique to back analyses of deep excavation

This study presents a nonlinear optimization technique (NOT) for conducting the back analyses of geotechnical engineering problems based on the field observations. Additional auxiliary techniques are incorporated to enhance the convergence and stability of the NOT. The developed NOT and additional auxiliary techniques are incorporated into a finite element code and then applied to the back analysis of excavation-induced wall deflection. A number of hypothetical excavation cases with various scenarios of stratigraphy and two quality excavation case histories are used to validate the developed NOT, in which the dominant soil parameters are treated as target parameters. Results show that the wall deflections of all hypothetical and actual excavation cases at each stage can be accurately and efficiently back-figured. The developed NOT has a potential to be an useful tool for preventing the building damage through accurately and efficiently predicting the excavation-induced deformations at subsequent stages.     

Analysis of Cassini/CIRS limb spectra of Titan acquired during the nominal mission II: Aerosol extinction profiles in the 600–1420 cm spectral range

We have analyzed the continuum emission of limb spectra acquired by the Cassini/CIRS infrared spectrometer in order to derive information on haze extinction in the 3–0.02 mbar range (∼150–350 km). We focused on the 600–1420 cm⁻¹ spectral range and studied nine different limb observations acquired during the Cassini nominal mission at 55°S, 20°S, 5°N, 30°N, 40°N, 45°N, 55°N, 70°N and 80°N. By means of an inversion algorithm solving the radiative transfer equation, we derived the vertical profiles of haze extinction coefficients from 17 spectral ranges of 20-cm⁻¹ wide at each of the nine latitudes. At a given latitude, all extinction vertical profiles retrieved from various spectral intervals between 600 and 1120 cm⁻¹ display similar vertical slopes implying similar spectral characteristics of the material at all altitudes. We calculated a mean vertical extinction profile for each latitude and derived the ratio of the haze scale height (H_haze) to the pressure scale height (H_gas) as a function of altitude. We inferred H_haze/H_gas values varying from 0.8 to 2.4. The aerosol scale height varies with altitude and also with latitude. Overall, the haze extinction does not show strong latitudinal variations but, at 1 mbar, an increase by a factor of 1.5 is observed at the north pole compared to high southern latitudes. The vertical optical depths at 0.5 and 1.7 mbar increase from 55°S to 5°N, remain constant between 5°N and 30°N and display little variation at higher latitudes, except the presence of a slight local maximum at 45°N. The spectral dependence of the haze vertical optical depth is uniform with latitude and displays three main spectral features centered at 630 cm⁻¹, 745 cm⁻¹ and 1390 cm⁻¹, the latter showing a wide tail extending down to ∼1000 cm⁻¹. From 600 to 750 cm⁻¹, the optical depth increases by a factor of 3 in contrast with the absorbance of laboratory tholins, which is generally constant. We derived the mass mixing ratio profiles of haze at the nine latitudes. Below the 0.4-mbar level all mass mixing ratio profiles increase with height. Above this pressure level, the profiles at 40°N, 45°N, 55°N, at the edge of the polar vortex, display a decrease-with-height whereas the other profiles increase. The global increase with height of the haze mass mixing ratio suggest a source at high altitudes and a sink at low altitudes. An enrichment of haze is observed at 0.1 mbar around the equator, which could be due to a more efficient photochemistry because of the strongest insolation there or an accumulation of haze due to a balance between sedimentation and upward vertical drag.