A continuous velocity field for Norway

In Norway, as in the rest of Fennoscandia, the process of Glacial Isostatic Adjustment causes ongoing crustal deformation. The vertical and horizontal movements of the Earth can be measured to a high degree of precision using GNSS. The Norwegian GNSS network has gradually been established since the early 1990s and today contains approximately 140 stations. The stations are established both for navigation purposes and for studies of geophysical processes. Only a few of these stations have been analyzed previously. We present new velocity estimates for the Norwegian GNSS network using the processing package GAMIT. We examine the relation between time-series length and precision. With approximately 3.5 years of data, we are able to reproduce the secular vertical rate with a precision of 0.5 mm/year. To establish a continuous crustal velocity field in areas where we have no GNSS receivers or the observation period is too short to obtain reliable results, either interpolation or modeling is required. We experiment with both approaches in this analysis by using (i) a statistical interpolation method called Kriging and (ii) a GIA forward model. In addition, we examine how our vertical velocity field solution is affected by the inclusion of data from repeated leveling. Results from our geophysical model give better estimates on the edge of the network, but inside the network the statistical interpolation method performs better. In general, we find that if we have less than 3.5 years of data for a GNSS station, the interpolated value is better than the velocity estimate based on a single time-series.     

The look of agricultural landscapes – How do non-crop landscape elements contribute to visual preferences in a large-scale agricultural landscape?

ABSTRACT

Efficiency in agricultural food production has long been in focus and this has affected the spatial structure of agricultural land use. One outcome has been extensive criticism based on a wide range of negative consequences, such as for biodiversity, accessibility, cultural heritage, and aesthetics. In line with the European Landscape Convention (ELC), management of people’s everyday landscapes is important. In Norway, agricultural landscapes are the ‘everyday landscape’ for a large proportion of the population. The aim of the article is to contribute to the understanding of landscape changes perceived as positive or negative by the inhabitants. The authors focused on grain-crop dominated landscapes and the impact of smaller non-crop elements on people’s landscape preferences. They administered a photo-based questionnaire using manipulated photos to assess preferences for different agricultural landscapes. Additionally, people’s perceived objectives for the agricultural sector and agriculture’s primary functions were assessed. The results documented positive perceptions of added landscape elements and that people were both aware of and agreed on the multifunctional role of agriculture. The authors conclude that if the public’s preferences are to be taken into consideration, such as during policymaking, it is important to maintain various landscape elements in the large-scale grain field landscapes of Norway.     

Quantifying sediment connectivity: Moving toward a holistic assessment through a mixed methods approach

The sediment connectivity concept is particularly suitable for tackling complex, multidisciplinary questions through systems thinking. However, it is unclear how to directly measure connectivity, and so proxy variables are often applied by indices to provide estimates. In this study, we critically evaluate a broad range of connectivity indices encompassing structural and functional connectivity as well as hillslope channel coupling. We then discuss their role in providing a more holistic estimation of connectivity within the Tahoma Creek Watershed, WA. Of the 14 km of channel below the glacier front, the upper 6 km (0–6 km) are coupled to the adjacent hillslopes. Coupled reaches correspond to regions with a high proportion of area contributing sediment and relatively high connectivity values, where all measures decrease in the downstream direction. A significant transition occurs near river kilometer 6. Here the valley bottom abruptly widens, deposition occurs, and the hillslopes become decoupled from the active channel. This transitional reach is also identified as a geomorphic hotspot based on the network structure. The lower 8 km of channel downstream of this reach are largely depositional and percent contributing area and connectivity values remain low, eventually reaching a minimum. Despite their limitations, we found each method to provide unique and useful information regarding connectivity. The effect of scale and event magnitude on connectivity is illustrated. We also found vegetation, topographic characteristics, and network structure to be important in high-gradient glacio-volcanic landscapes. The choice of an index will depend on the research objectives, data availability, and the proxy variables that best describe the variability within the defined area.     

Remembering Tore Gjelsvik (1916–2006)

Tore Gjelsvik, former director of the Norwegian Polar Institute, died at the beginning of this year. He is fondly remembered by a great many people. In this piece, Olav Orheim recalls the man and his key role in Norwegian polar activities. Orheim was head of Antarctic Research at the Norwegian Polar Institute in 1972–1993 and was the institute's director from 1993 to 2005.     

Cross-matching with interpreted warping of 3D streamer and 3D ocean-bottom-cable data at Valhall for time-lapse assessment

Legacy streamer data and newer 3D ocean‐bottom‐cable data are cross‐matched and analysed for time‐lapse analysis of geomechanical changes due to production in the Valhall Field. The issues relating to time‐lapse analysis using two such distinctly different data sets are addressed to provide an optimal cross‐matching workflow that includes 3D warping. Additionally an assessment of the differences between the imaging using single‐azimuth streamer and multi‐azimuth ocean‐bottom‐cable data is provided. The 3D warping utilized in the cross‐matching procedure is sensitive to acquisition and processing differences but is also found to provide valuable insight into the geometrical changes that occur in the subsurface due to production. As such, this work also provides a demonstration of the use of high‐resolution 3D interpreted warping to resolve the 3D heterogeneity of the compaction and subsidence. This is an important tool for Valhall, and possibly other fields, where compaction and subsidence (and monitoring thereof) are key factors in the reservoir management since the predominant observed production‐induced changes are compaction of the soft, high‐porosity chalk reservoir, due to pore‐pressure reduction, and the resultant overburden subsidence. Such reservoir compaction could have significant implications for production by changing permeabilities and production rates. Furthermore the subsidence effects could impact upon subsea installations and well‐bore stability. Geomechanical studies that have previously been used to model such subsidence and compaction are only constrained by observed surface displacements and measured reservoir pressure changes, with the geological overburden being largely neglected. The approaches suggested herein provide the potential for monitoring and assessment in three dimensions, including the probable heterogeneity and shearing, that is needed for full understanding of reservoir compaction and the resultant effects on the overburden to, for example, mitigate well‐bore failures.     

Chelation of divalent metal ions by brown algal polyphenols

High-molecular-weight, nondialyzable polyphloroglucinols from the marine brown algae Ascophyllum nodosum and Fucus vesiculosus (Phaeophyceae, Fucales) chelate the divalent metal ions Sr²⁺, Mg²⁺, Ca²⁺, Be²⁺, Mn²⁺, Cd²⁺, Co²⁺, Zn²⁺, Ni²⁺, Pb²⁺ and Cu²⁺ in weakly acidic aqueous solution. Values of the relative selectivity coefficients k have been calculated relative to Mn²⁺; the ionotropic series with the algal polyphenols are similar to those with catechol and pyrogallol. These studies may serve as a guide for the examination of metal chelation by brown algal polyphenols both in situ and after exudation into seawater.     

Progress in optical dating of guano-rich sediments associated with the Deep Skull, West Mouth of the Great Cave of Niah, Sarawak, Borneo

The West Mouth of the Great Cave of Niah is one of the major archaeological sites in Southeast Asia; the radiocarbon chronology of this site currently places the earliest presence of Homo sapiens (a Deep Skull find) in Southeast Asia at about 45 ka BP. An optical dating programme using sand-sized quartz was initiated in the West Mouth to complement the radiocarbon chronology. This paper reports on the progress in dating a key sample (sample 376r) that was taken from deposits containing the Deep Skull. A somewhat novel procedure was developed to separate and clean quartz grains from the unusual guano-rich deposits. From this, only a small quantity of quartz grains could be recovered and 36 aliquots (1 mm in diameter) were prepared, each consisting of 80 grains. This sample was dated by means of the single-aliquot regenerative-dose (SAR) method using the protocols of Murray and Wintle [2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73], and of Choi et al. [2003. Luminescence dating of well-sorted marine terrace sediments on the southeastern coast of Korea. Quaternary Science Reviews 22, 407–421]. The results showed a wide distribution of equivalent doses; this distribution is inferred to be due to bioturbation, variable bleaching at deposition, and to local variations in the dose rate within the sample site. Dose rates were measured using both field (in-situ γ-ray spectrometry, IGRS) and laboratory (inductively coupled plasma mass spectrometry/atomic emission spectrometry, ICP-MS/AES; and isotope dilution, ID) methods. There was significant disagreement between the concentrations of radioisotopes found using laboratory and field measurements, indicating sediment heterogeneity and also possible disequilibrium in the ²³⁸U decay chain. Future work in the West Mouth should therefore concentrate on taking sediment samples of at least 500–600 cm³, improving the dose rate estimates (e.g. by high-resolution γ-ray spectrometry) and investigating other luminescence signals (e.g. red thermoluminescence) as potential geochronometers.