Correlations between pelagic distribution of Common and Brünnich's Guillemots and their prey in the Barents Sea

Correlations between guillemots (including Common Guillemots Uria aalge and Brünnich's Guillemots U. lomvia) and their prey (divided into five prey categories, capelin Mallotus villosus , herring Clupea harengus , polar cod Boreogadus saida , plankton, and a mixture of other prey species) at two depths (10-100 m and 100-200m) were estimated along an extended transect of 3,060 nautical miles (5,667 km) in the Barents Sea in April/May 1986. Spatial concordance was highest during daylight hours when the largest number of birds were seen on water (presumably feeding birds). Capelin was the single prey category which was most often associated with birds but no single prey category could alone explain the distribution of birds. Although only a small fraction of guillemots could be identified to species, there was some evidence that capelin were of greater importance to Common than to Brünnich's Guillemots. Overall correlation between birds and total prey density was statistically significant at the smallest scale of 5 nautical miles (n.m.). The removal of herring from the calculations increased the strength of the correlation. The depth at which prey was located had little effect on the distribution of birds. The correlation between birds and prey was scale dependent, and reached a maximum at 90 n.m., although there seemed to be some upper threshold in the coefficient at c. 40 n.m. Numerical concordance (including only 5 n.m. periods where both prey and birds were present) was significant at the 5 n.m. scale but was higher for high density than for low density prey patches. The results are discussed in relation to the few similar studies in other oceans and in relation to the severe reduction of important prey species in the Barents Sea.     

Profitability of fossil-fuel production under different instruments in international climate policies

This article discusses how different climate policy instruments such as CO₂ taxes and renewable energy subsidies affect the profitability of fossil-fuel production, given that a fixed global climate target shall be achieved in the long term. Within an intertemporal framework, the model analyses show that CO₂ taxes reduce the short-term profitability to a greater extent than technology subsidies, since the competition from CO₂-free energy sources does not become particularly noticeable until decades later. Due to, for example, the discounting of future revenues, most fossil-fuel producers prefer subsidies to their competitors rather than CO₂ taxes. However, this conclusion does not apply to all producers. Oil producers outside OPEC lose the most on the subsidizing of CO₂-free energy, while CO₂ taxes only slightly reduce their profits. This is connected to OPEC's role in the oil market, as the cartel chooses to reduce its extraction significantly in the tax scenario. The results seem to be consistent with the observed behaviour of important players in the climate negotiations.     

Late Holocene glacier variations and climate at Jan Mayen

Jan Mayen is a small (373 km²) remote island in the Norwegian Sea. One third of it is covered by glaciers, all located on the Beerenberg volcano. There have been at least two Holocene periods of glacier expansion at Jan Mayen. The first may have taken place around 2500 B.P. Some glaciers had their maximum extent during the second period, around 1850 A.D. They have subsequently shown an oscillating retreat, with marked expansion around 1910, and with a minimum extent around 1950. Many glaciers advanced again around 1960. The advance of Sørbreen probably culminated around 1965. The climate appears to have been more arctic-continental than today during these two periods of glacier advances, caused by expanded pack ice cover in the East Greenland current and strong influence from the Greenland-Arctic high pressure area. The interplay between the high pressure area and the low pressure tracks in the North Atlantic Ocean determines the climate over the north-western part of the Atlantic, and this results in parallel climate and glacier variations within this region. We conclude, contrary to previous reports, that the advances of the glaciers around 1960 were caused by reduced summer temperatures and ablation, and not by increased precipitation.     

Duration of ship-following by Kittiwakes Rissa tridactyla in the Barents Sea

Ship-following Kittiwakes Rissa tridactyla were caught and dye-marked with picric acid on three occasions from a ship trawling in the Barents Sea in August 1986. The ship trawled regularly every 20-30 nautical miles and most of the trawl contents were fed to the birds accompanying the ship. Kittiwakes followed the ship for an average of 480-591 min. Between trawl-stations the birds rested on lifeboats and on the rail of the ship, and resting birds showed aggressive behaviour towards neighbours and intruders. The mean departure rate ranged from 4.2 to 5.1% per hour, and the turnover rate was 32 hours. It is obvious that the Kittiwakes behaved opportunistically and had adapted to exploit the waste from the commercial fisheries in the area.     

ON THE CONSTRUCTION OF THE 3D BAND-LIMITED EXTRAPOLATION OPERATOR IN THE SPACE-FREQUENCY DOMAIN1

Based on an expansion of the band-limited 3D extrapolation operator in terms of orthogonal Chebyshev polynomials, a closed form expression of the space-frequency response is presented. A key step is an evaluation of the (inverse) 2D Fourier transform of circularly symmetric functions, which is related to the (zero-order) Hankel transform. Hankel transforms of individual members of the orthogonal set of polynomials are available from tables and summation of series; hence, the real and the imaginary parts of the space-frequency response can be found in terms of cylindrical and spherical Bessel functions, respectively. The procedure permits an efficient and accurate evaluation of the space-frequency response.