Geochemistry of groundwater in front of a warm‐based glacier in Southeast Greenland

Groundwater in front of warm‐based glaciers is likely to become a more integrated part of the future proglacial hydrological system at high latitudes due to global warming. Here, we present the first monitoring results of shallow groundwater chemistry and geochemical fingerprinting of glacier meltwater in front of a warm‐based glacier in Southeast Greenland (Mittivakkat Gletscher, 65° 41′ N, 37° 48′ W). The groundwater temperature, electrical conductivity and pressure head were monitored from August 2009 to August 2011, and water samples were collected in 2009 and analyzed for major ions and water isotopes (δD, δ¹⁸O). The 2 yrs of monitoring revealed that major outbursts of glacier water during the ablation season flushed the proglacial aquifer and determined the groundwater quality for the next 2–8 weeks until stable chemical conditions were reached again. Water isotope composition shows that isotopic fractionation occurs in both groundwater and glacier meltwater, but fractionation due to evaporation from near‐surface soil moisture prior to infiltration has the most significant effect. This study shows that groundwater in Low Arctic Greenland is likely to possess a combined geochemical and isotopic composition, which is distinguishable from other water sources in the proglacial environment. However, the shallow groundwater composition at a given time is highly dependent on major outbursts of glacier water in the previous months.     

Sensitivity Kernels for Time-Distance Inversion

Inversion of local-area helioseismic time-distance data has so far only been done in the ray approximation (Kosovichev, 1996). Since this is a high-frequency approximation its applicability can be questioned for the solar case. Bogdan (1997) showed that for a simple solar model the localized wave packets do follow, but are not confined to, the ray path. We use an approximation based on the first Fresnel zone that has been developed in geophysics by Snieder and Lomax (1996) to go beyond the ray approximation in the inversions. We have calculated sensitivity kernels using both approximations. To test them we use a finite-difference forward modeling of the whole wave field in an acoustic medium reminiscent of the Sun. We use the finite-difference modeling to calculate sensitivity kernels for the full wave field and compare this with the other kernels. The results show that the Fresnel-zone-based kernels are in good agreement with the sensitivity obtained from the modeling. Thus these new kernels represent a significant step forward in the inversion of time-distance data.     

Painting the floor with a hammer: Technical fixes in fisheries management

Fisheries management benefits from the contribution of several academic disciplines, each with their own perspectives, concerns and solutions. In this essay we argue that the contribution of biology, economics, sociology and other relevant disciplines to fisheries would be improved if they originated from broader, more integrated analytical perspectives that are attuned to the empirical realities of fisheries management. Today, disciplinary boundaries narrow the perspectives of fisheries management, creating tunnel vision and standardized technical fixes to complex and diverse management problems. Having worked separately and together for a number of years in fisheries research and consultancy in many parts of the world we, as a group of biologists, economists and sociologists, feel that the time to rid ourselves from disciplinary dogmatism is long overdue. We claim that improvements in fisheries management will be realized not through the promotion of technical fixes but instead by embracing and responding to the complexity of the management problem.     

Local ecological knowledge and practical fisheries management in the tropics: A policy brief

This policy brief is a summary product of seven case studies examining the integration of local ecological knowledge in fisheries management. Each case began with a series of in-depth interviews with local fishers, after which their answers were examined using both social and biological approaches to assess the possibility of using the information as the basis of simple, valid and locally acceptable indictors for fisheries management. We found that allocation and knowledge issues are closely interlinked and must be addressed in concert, and that the negotiation of shared understandings between multiple sources of knowledge must be a continuous process within an adaptive framework rather than a question of identifying a fixed set of indicators.     

Holocene sedimentary and environmental development of Aarhus Bay,Denmark – a multi-proxy study

Holocene sedimentation patterns and environmental development in Aarhus Bay, Denmark, were reconstructed based on proxy analyses of two sediment cores (M1 and M5). Together, the two cores offer an opportunity to examine the history of the area during the past c. 10 000 years. The investigation consisted of acoustic mapping and multi-proxy analyses of the sediment cores including macrofossils, sediment physical properties, sediment accumulation rates, grain size, and X-ray fluorescence elemental counts. Radiocarbon dating of the two sediment successions revealed that they cover the periods c. 10 000–3700 cal. a BP (M1) and c. 4400 cal. a BP to the present (M5). The data from the M1 site indicate the presence of a near-shore lake environment between c. 10 000 and 9000 cal. a BP. The first intrusion of marine water into the area is dated to c. 9000 cal. a BP. In the following c. 1300 years, brackish-water conditions prevailed in the area characterized by a mixture of taxa from marine, limnic and terrestrial habitats, reflecting a shallow estuarine environment. Around 7700 cal. a BP full marine conditions were established, accompanied by a marked increase in sedimentation rates. The changes to full marine conditions and higher sedimentation rates are probably due to a significant sea-level rise leading to flooding of former land areas and intensified erosion. A subsequent distinct decrease in sedimentation rates around 6350 cal. a BP is presumably linked to a previously documented sea-level drop about this time. Continuous sedimentation ceased around 3700 cal. a BP in the central part of the bay, most probably due to a major sea-level lowering involving widespread erosion. In the eastern and deeper part of the bay, sedimentation continued until today. Fully marine conditions prevailed there for at least the last 4400 years.     

Tracer Tests and Image Analysis of Biological Clogging in a Two-Dimensional Sandbox Experiment

A two-dimensional flow experiment on biological clogging was carried out by biostimulating a sandbox packed with sand inoculated with bacteria. Biostimulation consisted of continuously injecting nutrients (acetate and nitrate). Clogging was visualized by frequently carrying out colored tracer experiments using Brilliant Blue. The tracer experiments were recorded with a digital camera and converted to concentration maps using an image-analysis method that revealed in detail the complex spreading pattern surrounding clogged areas. Clogging resulted in a finger-like spreading of the tracer around the main clogged area. Fingers were asymmetric and their dominant direction changed over time. Although the flow field was complex around the main clogged area, the effect on the bulk hydraulic conductivity at the scale of the sandbox was very small.