Projected evolution of circulation types and their temperatures over Central Europe in climate models

The study deals with changes in large-scale atmospheric circulation (represented by circulation types) and associated surface air temperatures as projected in an ensemble of regional climate models (RCMs) from the ENSEMBLES project. We examine changes of circulation type frequencies and means of daily maximum and minimum temperatures within circulation types in individual seasons for two time slices of transient runs under the SRES A1B scenario (2021–2050 and 2071–2100) with respect to the control period (1961–1990). To study the influence of driving data, simulations of the driving general circulation models (GCMs) also are evaluated. We find that all models project changes of atmospheric circulation that are statistically significant for both future time slices. The models tend to project strengthening of the westerly circulation in winter and its weakening in summer. We show that increases of daily maximum and minimum temperatures in all seasons differ for individual circulation types. There are, however, only few features of the projected changes in the future circulation–temperature links that are common among the models, in particular relatively smaller warming for westerly types. Only in winter, projected changes in circulation types tend to contribute to the projected overall warming. This effect is negligible and mostly opposite in the other seasons. We also detect a strong influence of driving data on RCMs’ simulation of atmospheric circulation and temperature changes.     

The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required to balance the budget. The National Center for Atmospheric Research is supported by the National Science Foundation     

Climate Impact Response Functions: An Introduction

The concept of climate impact response function is introduced and placed into the context of integrated assessment models to analyze policy options under climate change constraints. An example of developing such response functions is presented that entails a global model of potential natural vegetation driven by a climate change pattern derived from a general circulation model. A large array of strenuous issues are introduced that will be addressed by the set of papers included in this Special Issue.     

Megabenthic diversity patterns and community structure of the Blanes submarine canyon and adjacent slope in the Northwestern Mediterranean: a human overprint?

The composition and structure of megabenthic communities in the Blanes canyon and adjacent open margin (Northwestern Mediterranean) were studied. The aim was to assess the effect of the canyon and commercial fishing intensity on the community composition and structure of benthic megafauna by (i) describing the megabenthic community composition, (ii) quantifying faunal abundance and biomass and (iii) describing community structure with MDS analyses and biodiversity indices. The results are compared between three sites (canyon head, canyon wall and open margin) located between 435 m and 700 m. Samples were collected using a commercial bottom trawl between April 2003 and March 2004. These sites are exploited by the local fishing fleet that targets the rose shrimp Aristeus antennatus . A total of 131 megabenthic species were identified from the three sites, with fishes and decapod crustaceans being the most speciose, most abundant and of higher biomass. The species richness, abundance and biomass of non-crustacean invertebrates were low. There were no significant differences in total abundance and biomass between the three sites. However, community structure analysis suggests that the open margin community is significantly different from the canyon head and canyon wall, with a lower species richness, lower diversity and lower evenness. The open margin community also reflects a higher degree of disturbance compared to the two canyon habitats. The results indicate that there is a canyon effect on the community structure of benthic megafauna, but this may be modulated by differing fishing pressure, which adds an additional factor to margin heterogeneity.     

Efficient multivariable submarine depth-control system design

An efficient solution for the multivariable submarine control design at low-depth conditions under the influence of wave disturbances is presented. The analysis and control design process is carried out under the framework of individual channel analysis and design (ICAD), which is based on the multivariable structure function (MSF). Classical frequency-domain control techniques based on Bode and Nyquist plots are used. Robustness is stated in terms of gain and phase margins. The closed-loop system includes low-order diagonal controllers facilitating its implementation, assessment, and tuning. ICAD discloses new physical insights of the submarine dynamical behaviour. Previous designs based on diagonal controllers consider the input–output channels defined by pairing the bow hydroplane angle with the depth and the stern hydroplane angle with the pitch angle. The alternative input–output pairing leads to unstable closed-loop systems. This phenomenon is associated with hydroplane reverse control. Here it is shown that MSF-based diagonal controllers can be applied effectively for both sets of channel configurations. Emphasis is placed on satisfying design specifications aiming at maintaining the depth low. The solution presented is more feasible and clearer to apply in practice than those so far reported in the literature.     

Skin toxins in coral‐associated Gobiodon species (Teleostei: Gobiidae) affect predator preference and prey survival

Predation risk is high for the many small coral reef fishes, requiring successful sheltering or other predator defence mechanisms. Coral‐dwelling gobies of the genus Gobiodon live in close association with scleractinian corals of the genus Acropora. Earlier studies indicated that the low movement frequency of adult fishes and the development of skin toxins (crinotoxicity) are predation avoidance mechanisms. Although past experiments showed that predators refuse food prepared with goby skin mucus, direct predator–prey interactions have not been studied. The present study compares the toxicity levels of two crinotoxic coral gobies – Gobiodon histrio, representative of a conspicuously coloured species, and Gobiodon sp.3 with cryptic coloration – using a standard bioassay method. The results show that toxin levels of both species differ significantly shortly after mucus release but become similar over time. Predator preferences were tested experimentally in an aquarium in which the two gobies and a juvenile damselfish Chromis viridis were exposed to the small grouper Epinephelus fasciatus. Video‐analysis revealed that although coral gobies are potential prey, E. fasciatus clearly preferred the non‐toxic control fish (C. viridis) over Gobiodon. When targeting a goby, the predator did not prefer one species over the other. Contrary to our expectations that toxic gobies are generally avoided, gobies were often captured, but they were expelled quickly, repeatedly and alive. This unusual post‐capture avoidance confirms that these gobies have a very good chance of surviving attacks in the field due to their skin toxins. Nonetheless, some gobies were consumed: the coral shelter may therefore also provide additional protection, with toxins protecting them mainly during movement between corals. In summary, chemical deterrence by crinotoxic fishes seems to be far more efficient in predation avoidance than in physical deterrence involving body squamation and/or strong fin spines.     

A New Method for Low‐Temperature Decomposition of Chromites and Dichromium Trioxide using Bromic Acid Evaluated by Chromium Isotope Measurements

In recent years, routine application of the stable isotope determination of chromium (Cr) in environmental and health protection research has led to the search for simpler chromite decomposition techniques. As the range of Cr isotope abundance ratios in nature is very narrow, conventional chromite decomposition techniques are no longer suitable, due to the relatively high risk of contamination during laboratory procedures. We have developed a protocol for the decomposition of chromites based on oxidation by bromic acid at room temperature. The procedure takes 15 d and requires two doses of bromic acid during the reaction period (day 1 and 8), due to the limited stability of the reagent. Chromium extracted by alkaline oxidative fusion and by bromic acid decomposition yielded statistically indistinguishable δ⁵³Cr values, measured by multi‐collector inductively coupled plasma‐mass spectrometry following addition of a ⁵⁰Cr‐⁵⁴Cr double‐spike.