Fluid flow and methane occurrences in the Disko Bugt area offshore West Greenland: indications for gas hydrates?

The present study is the first to directly address the issue of gas hydrates offshore West Greenland, where numerous occurrences of shallow hydrocarbons have been documented in the vicinity of Disko Bugt (Bay). Furthermore, decomposing gas hydrate has been implied to explain seabed features in this climate-sensitive area. The study is based on archive data and new (2011, 2012) shallow seismic and sediment core data. Archive seismic records crossing an elongated depression (20×35 km large, 575 m deep) on the inner shelf west of Disko Bugt (Bay) show a bottom simulating reflector (BSR) within faulted Mesozoic strata, consistent with the occurrence of gas hydrates. Moreover, the more recently acquired shallow seismic data reveal gas/fluid-related features in the overlying sediments, and geochemical data point to methane migration from a deeper-lying petroleum system. By contrast, hydrocarbon signatures within faulted Mesozoic strata below the strait known as the Vaigat can be inferred on archive seismics, but no BSR was visible. New seismic data provide evidence of various gas/fluid-releasing features in the overlying sediments. Flares were detected by the echo-sounder in July 2012, and cores contained ikaite and showed gas-releasing cracks and bubbles, all pointing to ongoing methane seepage in the strait. Observed seabed mounds also sustain gas seepages. For areas where crystalline bedrock is covered only by Pleistocene–Holocene deposits, methane was found only in the Egedesminde Dyb (Trough). There was a strong increase in methane concentration with depth, but no free gas. This is likely due to the formation of gas hydrate and the limited thickness of the sediment infill. Seabed depressions off Ilulissat Isfjord (Icefjord) previously inferred to express ongoing gas release from decomposing gas hydrate show no evidence of gas seepage, and are more likely a result of neo-tectonism.     

Velocity distributions of waves and currents in the combined flow

The theoretical model presented here is designed to predict waves and currents velocity profiles in the combined wave and current motion near a fixed bed. It is also valid for the pure wave motion, because the pure wave motion is only a special case of the combined flow. This model has been derived by using the equation of motion and the eddy viscosity assumptions which are somewhat different from those of former authors. Although the model is simple, the predictions are quite good compared with experimental data from Jonsson and Carlsen (1976) No. 1 and No. 2, Van Doorn (1981) V00RA, V10RA and V20RA, Van Doorn (1982) S00RAL, S10RAL and S20RAL, and Jensen (1989) Test-12 and Test-13.     

The ultramafic cumulate series,Gardiner complex,East Greenland

The ultramafic cumulate series of the ultramafic, alkaline and carbonatite bearing Gardiner complex in East Greenland is divided in: 1) Contact zone of plagio-clase-bearing alkaline rocks chilled to the surrounding gneisses and alkaline lavas; 2) a banded sequence of dunites to mt-pyroxenites; 3) a zoned dunite — cpx-dunite ring and 4) in the centre of the complex ol-pyroxenites and mt-pyroxenites.The zones and bands are superimposed with gradational contacts and are increasingly younger towards the centre of the complex. Primocrysts and intercumulus phases, which are equivalent to phenocryst phases in magmatic liquids show that these rocks accumulated from nephelinitic to nepheline-hawaiitic magmas and the contact rocks from less alkaline basanitic magma types similar to the regional alkaline magmas.The cumulates apparently formed in a magma chamber of a nephelinitic volcano, resting on the regional basalts of the Kangerdlugssuaq area.     

Signals of tree volume and temperature in a high‐resolution record of pollen accumulation rates in northern Finland

Pollen accumulation rates (PARs) provide a potential proxy for quantitative tree volume (m³ ha^?1) reconstruction with reliable absolute pollen productivity estimates (APPEs). We obtained APPEs for pine, spruce and birch at their range limits in northern Finland under two temperature periods (‘warm’ and ‘cold’) based on long‐term pollen trap and tree volume records within a 14‐km radius of each trap. APPEs (mean ± SE; × 10⁸ grains m^?3 a^?1) tend to be higher for the ‘warm’ periods (pine 123.8 ± 24.4, birch 528.0 ± 398.4, spruce 434.3 ± 113.7) compared with the ‘cold’ periods (pine 95.5 ± 37.3, birch 317.3 ± 282.6, spruce 119.6 ± 37.6), although the difference is only significant for spruce. Using an independent temperature record and the APPEs obtained, we reconstruct a low‐frequency record of pine volume changes over the last 1000 years at Palomaa mire, where a high‐resolution record of Pinus PARs is available. Five phases are distinguished in the reconstruction: moderate pine volume, AD 1080–1170; high volume, AD 1170–1340; low volume, AD 1340–1630; very low volume, AD 1630–1810; and rising pine volume, AD 1810–1950. These phases do not coincide with periods of high or low June–July–August temperatures, and thus appear to reflect regional variations in tree volume, while high‐frequency changes within each time‐period block show variations in PARs in response to temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

An application of least-squares inverse analysis in kinetic interpretations of hydrous pyrolysis experiments

A least-squares inverse method is applied to the estimation of optimum kinetic parameters with statistical error bounds from concentration data obtained in isothermal hydrous pyrolysis experiments. The inverse method requires the specification of a data-parameter relationship (e.g., classical kinetic theory), the prior covariance matrices of data and parameter errors, as well as the prior central estimates of data and parameters. The reaction scheme considered is the common case of kerogen breakdown by Gaussian-weighted independent parallel first-order reactions and bitumen cracking by a single first-order reaction. The nonlinearity of the problem is reduced by a logarithmic transformation, which suggests a parameterization in terms of logarithmic concentrations, activation energies, and logarithmic Arrhenius factors. The linearized variance analysis is valid for the case studied, and the posterior covariance matrix reveals which parameters are constrained by the data. We find that the statistical errors in the average activation energy and the associated Arrhenius factor are strongly correlated. Hence, the parameters which determine the temperature dependence of the reaction rate have not been resolved independently. Furthermore, the kinetic results are very sensitive to the presence of a distribution of activation energies in kerogen breakdown. This distribution is not constrained by the data. As a consequence, neglecting the consideration of distributions of activation energies results in activation parameter values which are much too low. This is the major reason for the commonly encountered discrepancy between kinetic parameter values obtained from hydrous pyrolysis and micropyrolysis experiments, respectively.     

Adaptive lives. Navigating the global food crisis in a changing climate

Human adaptation to climate change is gaining increasing academic as well as political attention. Understanding how and what people around the world adapt to is, however, difficult. Climate change is often, if not always, only one of a multiplicity of exposures perforating local communities. In Biidi 2, a small Sahelian village in northern Burkina Faso, climate variability have had a great influence on inhabitants’ lives since the major droughts of the early 1970s and 1980s. Tracing the intertwinement of drought, diminishing agricultural production and the need to buy food, this article explores how villagers attempt to attract development projects and negotiate with political parties in order to negate the impact of the global food crisis on their livelihoods. In doing so the article attempts to show how adaptation to climate variability is related to multiple, intersecting processes, and in this specific case is a matter of navigating changing socioeconomic factors. Using recent theory from social anthropology, adaptation is explored as a matter of social navigation. It is suggested that this theoretical approach might help nuance and elucidate how, and to what, local people around the world adapt.