The effect of a northward shift in the southern hemisphere westerlies on the global ocean

We examine the effect of a northward shift in the position of the southern hemisphere subpolar westerly winds (SWWs) on the vertical and horizontal distribution of temperature and salinity in the world ocean. A northward shift of the SWWs causes a latitudinal contraction of the subpolar gyres in the southern hemisphere (SH). In the Indian and Pacific, this leads to subsurface warming in the subtropical thermocline. As the southern margins of the gyres move into latitudes characterised by warmer surface air temperature (SAT), the layers at mid-depth below 400 m depth become ventilated by warmer water. We characterize the approximation of the ventilated thermocline in our coarse resolution model using a set of passive tracer experiments, and illustrate how the northward shift in the SWWs causes an equatorward shift in the latitude of origin of water ventilating layers deeper than 400 m in the Indian and Pacific, leaving the total surface ventilation of the upper 1200 m unchanged. In contrast, the latitudinal constraint on the Antarctic Circumpolar Current posed by the Drake Passage causes a cooling and freshening throughout the Atlantic thermocline; here, subsurface thermocline water originates from higher latitudes under the wind shift. On longer timescales Atlantic cooling and freshening is reinforced by a reduction in North Atlantic Deep Water (NADW) formation and surface salinification of the Indian and Pacific Oceans. In effect, the latitude of zero wind stress curl in the SWWs regulates the relative importance of the “cold water route” via the Drake Passage and the “warm water route” associated with thermocline water exchange via the Indian Ocean. Thus, a more northward location of the SWWs corresponds with a reduced salinity contrast between the Indian/ Pacific Oceans and the Atlantic. This results in reduced NADW formation. Also, a more northward location of the SWWs facilitates the injection of cool fresh Antarctic Intermediate Water into the South Atlantic subtropical gyre. Beyond these changes, on a millennial timescale, the deep ocean warms throughout the water column in response to the wind shift. Global salinity stratification also becomes less stable, as more saline water remains at the surface and accumulates in the Indian and Pacific thermocline. The freshening of the deep ocean reflects a reduced stirring of the global ocean due to reduced net circulation arising from a misalignment between the westerlies and the topographically constrained ACC. Our results lend support to the idea that a more equatorward location of the SWW maximum during glacial climates contributed to cooler and fresher conditions in the Atlantic, inhibiting NADW.     

Startle response of captive North Sea fish species to underwater tones between 0.1 and 64 kHz

World-wide, underwater background noise levels are increasing due to anthropogenic activities. Little is known about the effects of anthropogenic noise on marine fish, and information is needed to predict any negative effects. Behavioural startle response thresholds were determined for eight marine fish species, held in a large tank, to tones of 0.1-64 kHz. Response threshold levels varied per frequency within and between species. For sea bass, the 50% reaction threshold occurred for signals of 0.1-0.7 kHz, for thicklip mullet 0.4-0.7 kHz, for pout 0.1-0.25 kHz, for horse mackerel 0.1-2 kHz and for Atlantic herring 4 kHz. For cod, pollack and eel, no 50% reaction thresholds were reached. Reaction threshold levels increased from approximately 100 dB (re 1 microPa, rms) at 0.1 kHz to approximately 160 dB at 0.7 kHz. The 50% reaction thresholds did not run parallel to the hearing curves. This shows that fish species react very differently to sound, and that generalisations about the effects of sound on fish should be made with care. As well as on the spectrum and level of anthropogenic sounds, the reactions of fish probably depend on the context (e.g. location, temperature, physiological state, age, body size, and school size).     

A kinematic study of the integral shaped filament:what roles do filaments play in forming young stellar clusters?

Young protoclusters(embedded stellar clusters) are responsible for the vast majority of star formation currently occurring in the Galaxy. Recent observations suggest a scenario in which filamentary structures in the interstellar medium represent the first step towards precluster clumps and eventually star formation. Whether filaments continuously fuel the star formation process when the cluster accretes material is still an open question. In this paper, we present a case study of the famous ‘integral shaped filament'(ISF) in the Orion A molecular cloud and we seek to study the kinematics which is truly originated from the ISF. We firstly define the central ridge of the ISF with NH_3,~(12) CO,~(13) CO and N_2H~+. Undulations are present in all the ridges. Moreover, a large scale offset is apparent in the ridges as derived by different tracers, which may be explained by the slingshot mechanism proposed by Stutz Gould. We fit the velocity field of the ISF and find the derived velocity gradient is about 0.7 km s~(-1) pc~(-1) which may come from an overall contraction. We propose a method to check the accretion flow along the ISF by using the velocity deviations of different molecular tracers, which is better than the common method of using the velocity distribution of one tracer alone. Using the velocity deviations, we also find that OMC-1 to 5 are located close to the local extrema of the fluctuations, which may demonstrate that gas flows toward each clump along the ISF.     

Is there more to eels than slime? An introduction to papers presented at the ICES Theme Session in September 2006

The following 15 papers in this issue of the ICES Journal ofMarine Science are based on presentations given at a Theme Session—"Isthere more to Eels than Slime?"—at the ICES Annual ScienceConference held in Maastricht, the Netherlands, during September2006. International involvement in research on the Europeaneel (Anguilla anguilla) started in 1968, when a draft synopsisof eel biology, fisheries, and aquaculture was prepared at theEuropean Inland Fisheries Advisory Commission (EIFAC) sessionin Rome. By 1975, an ICES Eel Working Group had been set up(WGEEL), and it met in Copenhagen to document information oneel populations and fisheries and, for the first time, to notedeclining trends in catches. These were the subjects of a jointEIFAC/ICES symposium in Helsinki in 1976, where mitigation byrestocking was first proposed,     

Environmental issues in urban groundwater systems: a multidisciplinary study of the Paranhos and Salgueiros spring waters,Porto (NW Portugal)

This study presents the results of a multidisciplinary approach, using hydrogeochemical, isotopic and ecotoxicological analyses, performed to assess the nature and suitability for use of Paranhos and Salgueiros spring waters (Porto city, NW Portugal). Based on the surface activities located along the course of the springs, 23 water samples were collected. All the samples were analysed for major element concentrations. The isotopic techniques employed included δ²H, δ¹⁸O and ³H. Standard acute bioassays with Daphnia magna were also performed. The hydrogeochemical analyses showed a nitrate and sulphate-enriched composition for these groundwaters, resulting mainly from urban drainage and sewer leakage. In the ecotoxicological analyses, no significant mortality was observed in any of the tests performed. The results obtained in this study suggest that Porto urban groundwater could be suitable for irrigation uses.     

Exploring pathways for sustainable water management in river deltas in a changing environment

Exploring adaptation pathways into an uncertain future can support decisionmaking in achieving sustainable water management in a changing environment. Our objective is to develop and test a method to identify such pathways by including dynamics from natural variability and the interaction between the water system and society. Present planning studies on long-term water management often use a few plausible futures for one or two projection years, ignoring the dynamic aspect of adaptation through the interaction between the water system and society. Our approach is to explore pathways using multiple realisations of transient scenarios with an Integrated Assessment Meta Model (IAMM). This paper presents the first application of the method using a hypothetical case study. The case study shows how to explore and evaluate adaptation pathways. With the pathways it is possible to identify opportunities, threats, timing and sequence of policy options, which can be used by policymakers to develop water management roadmaps into the future. By including the dynamics between the water system and society, the influence of uncertainties in both systems becomes clearer. The results show, among others, that climate variability rather than climate change appears to be important for taking decisions in water management.     

Characterising meridional overturning bistability using a minimal set of state variables

A close approximation of key state variables and salt fluxes for both the North Atlantic Deep Water (NADW) “on” and “off” states in a General Circulation Model (GCM) is constructed, yielding a natural stability condition. Here, stability is linked to the effect of feedbacks on infinitesimal salinity anomalies on the average Atlantic salinity. The stability condition simply states that the total advective salt feedback must be negative in each steady state, ensuring stability by damping the growth of infinitesimal salinity perturbations. However, a decomposition of the salt feedback into three components shows that only the interaction between the mean salinity and infinitesimal perturbations of the meridional flow have the potential to render a state unstable, holding the key to state transitions. In contrast, the interaction between the mean meridional flow and infinitesimal salinity perturbations yields a negative (stabilising) component feedback. Similarly, the gyre salt flux also stabilises the overturning states. Furthermore, the nodes limiting the “on” and “off” state regimes in the GCM can be accurately computed based on linear fits of basic state variables and the gyre salt flux. It is shown that the NADW “on” state closest to collapse must be contained within a neighbourhood of fresh water exporting states. Finally, the role of temperature in the bistability structure is elucidated.     

Escherichia coli strains harvested from springs in Kampala,Uganda: cell characterization and transport in saturated porous media

We hypothesized that the transport of Escherichia coli strains harvested from springs could be characterized by a similar set of cell characteristics and transport parameters. The hypothesis was tested by sampling springs throughout the Lubigi catchment in Kampala, Uganda. Chemo‐physical parameters in addition to total coliform concentrations were determined. Furthermore, E. coli strains were harvested, and cell properties determined. Column experiments in saturated quartz columns of 7 cm height were conducted to determine transport parameters of selected E. coli strains. Using a two‐site non‐equilibrium sorption model, transport was modelled by fitting breakthrough data in HYDRUS 1D. Results indicated faecal contamination of the springs with high concentrations of total coliforms, chloride and nitrate. Furthermore, the maximum relative E. coli concentrations (C/C₀)_max in the column experiments were high. Compared with our previous work on E. coli strains, collected from a pasture and from zoo animals, attachment was low. Modelling revealed that both equilibrium and kinetic sorption were not important under conditions employed in the experiments. These observations are explained by the way in which the strains were harvested: from termination points of flow lines (springs). Such strains may possess characteristics that might have influenced their transport in the subsurface leading to their low attachment efficiency and possibly contributing to the lack of influence of equilibrium and kinetic sorption characteristics. There was no significant correlation between cell properties and transport parameters. Furthermore, 58% of the tested strains were of the O21:H7 serotype, and all definable serotypes identified were associated with diseases. We speculate that this serotype may possess characteristics that allow preferential transport through the aquifers of the area. We demonstrated that bacteria harvested from termination points of flow lines compared with those obtained from pollution sources, which have not undergone transport yet, present a good option for the assessment of bacteria transport characteristics in aquifers. Copyright © 2013 John Wiley & Sons, Ltd.     

Sun–Earth L_{1} and L_{2} to Moon transfers exploiting natural dynamics

This paper examines the design of transfers from the Sun–Earth libration orbits, at the \(L_{1}\) and \(L_{2}\) points, towards the Moon using natural dynamics in order to assess the feasibility of future disposal or lifetime extension operations. With an eye to the probably small quantity of propellant left when its operational life has ended, the spacecraft leaves the libration point orbit on an unstable invariant manifold to bring itself closer to the Earth and Moon. The total trajectory is modeled in the coupled circular restricted three-body problem, and some preliminary study of the use of solar radiation pressure is also provided. The concept of survivability and event maps is introduced to obtain suitable conditions that can be targeted such that the spacecraft impacts, or is weakly captured by, the Moon. Weak capture at the Moon is studied by method of these maps. Some results for planar Lyapunov orbits at \(L_{1}\) and \(L_{2}\) are given, as well as some results for the operational orbit of SOHO.