The small-sized benthic biota of the Håkon Mosby Mud Volcano (SW Barents Sea slope)

R/V POLARSTERN expedition ARK XVIII/1 in summer 2002 provided the opportunity to carry out a sampling programme to assess the activity, biomass and composition of the small-sized benthic biota (size range: bacteria to meiofauna) around the active mud-oozing and methane-seeping Håkon Mosby Mud Volcano (HMMV) on the SW Barents Sea slope, Northern North-Atlantic. A total of 11 stations, covering different areas (e.g., bacterial mat sites, and pogonophoran fields) within the crater, and sites outside the caldera were sampled using a multiple corer. Subsamples were analyzed for various biogenic compounds to estimate the flux of organic matter to the seafloor (sediment-bound chloroplastic pigments indicating phytodetritus), activities (bacterial exo-enzymatic turnover rates) and the total biomass [from bulk parameters, like phospholipid (PL) concentrations in the sediments] of the smallest sediment-inhabiting organisms (range: bacteria to meiofauna). Direct investigations of bacterial numbers and biomasses as well as on meiofauna densities and composition completed our investigations at HMMV. As expected for a comparable small deep-sea area with only minor disparity in water depth between sampling sites, our investigations revealed generally no significant differences in organic matter input from phytodetritus sedimentation between sampling sites inside and outside HMMV. Bacterial exo-enzymatic activities as well as total microbial biomass (TMB) and meiofauna densities, however, exhibited generally higher values at HMMV, compared to sites outside the mud volcano. Enhanced benthic life at HMMV is based on chemosynthetic processes, making the mud volcano a “chemosynthetic oasis” in an otherwise oligotrophic deep-sea environment. As we did not find any indication for bacterial symbioses in the meiofauna, comparably rich meiofaunal assemblages at HMMV are presumably indirectly related to a general enhanced biological production.     

Braess' paradox in a generalised traffic network

Braess' paradox illustrates situations when adding a new link to a transport network might lead to an equilibrium state in which travel times of users will increase. The classical network configuration introduced by Braess in 1968 to demonstrate the paradox is of fundamental significance because Valiant and Roughgarden showed in 2006 that ‘the “global” behaviour of an equilibrium flow in a large random network is similar to that in Braess' original four‐node example’. Braess' paradox has been studied mainly in the context of the classical problem introduced by Braess and his colleagues, assuming a certain type of symmetry in networks. Specifically, two pairs of links in those networks are assumed to have the same volume‐delay functions. The occurrence of Braess' paradox for this specific case of network symmetry was investigated by Pas and Principio in 1997. Such a symmetry is not common in real‐life networks because the parameters of volume‐delay functions are associated with roads physical and functional characteristics, which typically differ from one link to another. This research provides an extension of previous studies on Braess' paradox by considering arbitrary volume‐delay functions, that is, symmetry properties are not assumed for any of the network's links and the occurrence of Braess' paradox is studied for a general configuration. Copyright © 2014 John Wiley & Sons, Ltd.