Introduction to Khovanov Homologies. I. Unreduced Jones superpolynomial

An elementary introduction to Khovanov construction of superpolynomials. Despite its technical complexity, this method remains the only source of a definition of superpolynomials from the first principles and therefore is important for development and testing of alternative approaches. In this first part of the review series we concentrate on the most transparent and unambiguous part of the story: the unreduced Jones superpolynomials in the fundamental representation and consider the 2-strand braids as the main example. Already for the 5_1 knot the unreduced superpolynomial contains more items than the ordinary Jones.Comment: 33 page

Distribution and structure of macrobenthic fauna in the eastern Laptev Sea in relation to environmental factors

The Laptev Sea still ranks among the less known regions of the world’s ocean. Here, we describe the distribution and composition of macrobenthic communities of the eastern shelf and identify key environmental control factors. Samples were collected from dredge catches carried out at 11 stations at depths between 17 and 44 m in August/September 1993 during the TRANSDRIFT I cruise of the Russian R/V “Ivan Kireev.” A total of 265 species were identified from the samples, mostly crustaceans (94). Species numbers per station ranged from 30 to 104. Macrobenthic community distribution clearly showed a depth zonation, consisting of a “Shallow” zone (30 m) with bivalves P. arctica and Nuculoma bellotii as well as brittle stars Ophiocten sericeum and Ophiura sarsi being most abundant. According to a correlation analysis between faunal and environmental data a combination of duration of ice cover and water depth, respectively, showed the highest affinity to macrobenthic distribution. We conclude that the food input to the benthos, which is largely related to ice-cover regime, and the stress due to the pronounced seasonal salinity variability, which is primarily related to water depth, are prime determinants of macrobenthic community distribution and major causes of the prominent depth zonation in the Laptev Sea. Within the depth zones, sediment composition seems to be most significant in controlling the patterns in the distribution of the benthic fauna

Recent research on Arctic benthos: common notions need to be revised

Increased public awareness of the global significance of polar regions and opening of the Russian Arctic to foreign researchers have led to a pronounced intensification of benthic research in Arctic seas. The wealth of information gathered in these efforts has markedly enhanced our knowledge on the Arctic benthos. While some scientific concepts have been corroborated by the novel findings (e.g., low endemism and high faunistic affinity to northern Atlantic assemblages), other common notions need to be revised, particularly with regard to the often-cited differences between Arctic seas and the Southern Ocean. It has been demonstrated that benthos assemblages vary broadly in diversity between Arctic regions and that, hence, the idea of a consistently poor Arctic benthos—being in stark contrast to the rich Antarctic bottom fauna—is an undue overgeneralization. In terms of biogeographic diversity, both Arctic and Antarctic waters seem to be characterized by intermediate species richness. Levels of disturbance—a major ecological agent known to heavily affect benthic diversity and community structure—have been assumed to be relatively high in the Arctic but exceptionally low in the Southern Ocean. The discovery of the great role of iceberg scouring in Antarctic shelf ecosystems, which has largely been overlooked in the past, calls for a reconsideration of this notion. The novel data clearly demonstrate that there are marked differences in geographical and environmental setting, impact of fluvial run-off, pelagic production regime, strength of pelago–benthic coupling and, hence, food supply to the benthos among the various Arctic seas, impeding the large-scale generalization of local and regional findings. Field evidence points to the great significance of meso-scale features in hydrography and ice cover (marginal ice zones, polynyas, and gyres) as ‘hot spots’ of tight pelago–benthic coupling and, hence, high benthic biomass. In contrast, the importance of terrigenic organic matter discharged to the Arctic seas through fluvial run-off as an additional food source for the benthos is still under debate. Studies on the partitioning of energy flow through benthic communities strongly suggest that megafauna has to be adequately considered in overall benthic energy budgets and models of carbon cycling, particularly in Arctic shelf systems dominated by abundant echinoderm populations. Much progress has been made in the scientific exploration of the deep ice-covered Arctic Ocean. There is now evidence that it is one order of magnitude more productive than previously thought. Therefore, the significance of shelf–basin interactions, i.e., the importance of excess organic carbon exported from productive shelves to the deep ocean, is still debated and, hence, a major topic of on-going research. Another high-priority theme of current/future projects are the ecological consequences of the rapid warming in the Arctic. Higher water temperatures, increased fluvial run-off and reduced ice cover will give rise to severe ecosystem changes, propagating through all trophic levels. It is hypothesized that there would be a shift in the relative importance of marine biota in the overall carbon and energy flux, ultimately resulting in a switch from a ‘sea-ice algae–benthos’ to a ‘phytoplankton–zooplankton’ dominance