Forward modelling of seismic response from North Sea Chalk

Seismic inversion has become a standard tool for porosity prediction in chalk exploration and field development. AVO (amplitude versus offset) processing for fluid prediction is, however, still not widely applied in chalk. Forward modelling may help to assess the value of acquiring these data, as well as support subsequent interpretation. This paper presents a forward modelling tool to simulate seismic response resulting from changes in degree of compaction and fluid contents in profiles. Modelling is carried out with software developed by Norsk Hydro A/S (the Compound Model Builder), where the Geological Survey of Denmark and Greenland has supplied special capabilities to model North Sea Chalk. The forward modelling is illustrated with a seismic line straddling the Dan and Halfdan chalk fields (Fig. 1). Hydrocarbons are found in the uppermost Danian and Maastrichtian chalk where porosity may exceed 30%. Production takes place from wells centred on an anticline in the Dan Field, and although structural closure is lacking for the Halfdan Field, a surprising laterally continuous oil column is found between the two fields (e.g. Jacobsen et al. 1999; Albrechtsen et al. 2001). The modelling target is the effect on seismic data of such oil occurrences. The rather subtle impact on rock properties requires very realistic and detailed modelling. Fortunately, the pelagic deep-water origin of the chalk makes it very uniform laterally, such that compaction effects and fluid changes handled by the modelling tool account for lateral seismic changes, whereas well data support vertical changes

The Development of Fisheries in Greenland, with Focus on Paamiut/Frederikshåb and Sisimiut/Holsteinsborg

Situated along a mountainous coastline between cold seas and continental ice, Greenland’s human populations face severe environmental constraints. Both individual and cultural survival have always depended upon flexible use of the available resources and, when these fail, relocation. The 20th century saw great transitions, notably from Danish colonial to Greenlandic Home Rule government; an almost fivefold increase in population (from 12,000 to 56,000); and from a seal-hunting subsistence economy to commercial fisheries in a new global marketplace. But throughout these transitions, the economy remained tied to renewable resources, and therefore could not transcend the underlying environmental constraints. Greenland’s 20th century history demonstrates anew the adaptive necessities of flexible resource use and relocation, in this tough and highly variable environment. At the beginning of the 20th century, most Greenlanders lived by subsistence hunting and fishing. Seals were their staple resource. Seal populations were falling, however, due to overhunting throughout the northern Atlantic. Warming seas and retreating ice margins around southwest Greenland made the remaining seals less accessible to hunters there as well. At the same time the settlement populations, and their material needs, were increasing. The traditional seal-hunting livelihood thus grew untenable, and alternatives were urgently needed. Commercial fisheries—particularly for Atlantic cod (Gadus morhua), which began to appear abundantly with warming waters off southwest Greenland during the 1920s—provided just such an alternative (Mattox 1973). Investment in commercial cod fishing, initially under the direction of Danish planners (especially following recommendations of the Greenland Commission of 1948, published in 1950) and after 1979 Greenland’s own Home Rule government, built up Greenland’s capacity to capture and market this resource as the basis for a new modern economy. Unfortunately, as with seals before them, cod populations fell under the combined pressure of over-exploitation and environmental change. By the early 1990s cod were gone, while other marine resources, especially shrimp, had become the export pillar of Greenland’s economy. This repeated pattern of synergistic interaction between resource consumption and environmental variation, visible not just in the 20th century but in some earlier episodes as well (Amarosi et al. 1997), makes Greenland particularly interesting as a case study showing the human dimensions of climatic change. A striking feature of the cod-to-shrimp transition, well documented because it occurred so recently, has been its locally uneven effects. The overall value of the present shrimp fishery is comparable to the previous cod fishery, but it does not always benefit the same people or places. Some former cod-fishing communities have lost their economic foundation, while others, well-positioned for shrimping, have gained (Hamilton, Lyster and Otterstad 2000). The west Greenland municipalities of Paamiut and Sisimiut could be viewed as a loser and a winner, respectively, during the cod-to-shrimp transition. Even these relatively straightforward examples, however, well illustrate the complexity with which modern social systems mediate the impacts of environmental change. This repeated pattern of synergistic interaction between resource consumption and environmental variation, visible not just in the 20th century but in some earlier episodes as well (Amarosi et al. 1997), makes Greenland particularly interesting as a case study showing the human dimensions of climatic change. A striking feature of the cod-to-shrimp transition, well documented because it occurred so recently, has been its locally uneven effects. The overall value of the present shrimp fishery is comparable to the previous cod fishery, but it does not always benefit the same people or places. Some former cod-fishing communities have lost their economic foundation, while others, well-positioned for shrimping, have gained (Hamilton, Lyster and Otterstad 2000). The west Greenland municipalities of Paamiut and Sisimiut could be viewed as a loser and a winner, respectively, during the cod-to-shrimp transition. Even these relatively straightforward examples, however, well illustrate the complexity with which modern social systems mediate the impacts of environmental change

Human population growth offsets climate-driven increase in woody vegetation in sub-Saharan Africa

The rapidly growing human population in sub-Saharan Africa generates increasing demand for agricultural land and forest products, which presumably leads to deforestation. Conversely, a greening of African drylands has been reported, but this has been difficult to associate with changes in woody vegetation. There is thus an incomplete understanding of how woody vegetation responds to socio-economic and environmental change. Here we used a passive microwave Earth observation data set to document two different trends in land area with woody cover for 1992-2011: 36% of the land area (6,870,000 km2) had an increase in woody cover largely in drylands, and 11% had a decrease (2,150,000 km2), mostly in humid zones. Increases in woody cover were associated with low population growth, and were driven by increases in CO2 in the humid zones and by increases in precipitation in drylands, whereas decreases in woody cover were associated with high population growth. The spatially distinct pattern of these opposing trends reflects, first, the natural response of vegetation to precipitation and atmospheric CO2, and second, deforestation in humid areas, minor in size but important for ecosystem services, such as biodiversity and carbon stocks. This nuanced picture of changes in woody cover challenges widely held views of a general and ongoing reduction of the woody vegetation in Africa

The impact of a physician-staffed helicopter on outcome in patients admitted to a stroke unit: a prospective observational study

Patient characteristics, patients admitted to the stroke unit and diagnosed with stroke. GEMS: ground emergency medical services; HEMS: helicopter emergency medical services; IQR: interquartile range; AMI: acute myocardial infarction. Co-morbidity was defined as having at least one of the following conditions: diabetes, atrial fibrillation, hypertension, previous myocardial infarction, previous stroke. (DOCX 20 kb