Trans-neptunian objects

Summary. The trans-neptunian objects (TNOs) constitute a new class of solar system object that was discovered only recently to exist beyond the orbit of Neptune. About 400 trans-neptunian objects have been detected over the past nine years and more than ten new objects are being discovered every month. All of the TNOs known to date fit into three dynamical classes: the classical, the resonant and the scattered objects. The total mass of the TNOs currently orbiting the Sun is estimated from the observed luminosity distribution to be of the order of 10–20% of the Earth's mass. However, theoretical investigations of the formation and evolution of the trans-neptunian belt into its currently observed shape suggest that it was much more massive in the past. The physical characterisation of TNOs starts to reveal some of the basic properties of these objects, such as size, shape and rotation and provides a first glance into the diversity of their surfaces. TNOs cover a very diverse range of colours, possibly reflecting different surface compositions. First evidence for the presence of water ice was found in a spectrum of one TNO while others do not show the characteristic absorption bands. The TNOs are now regarded as the likely source of some short-period comets. Owing to giant-planet and collisional perturbations, some TNOs may evolve into Centaurs, i.e. objects orbiting the Sun in the region between Jupiter and Neptune, which are further perturbed to become Jupiter-family short-period comets. Together with smaller debris generated by collisional shattering, the TNOs might represent a belt that has evolved from a more massive circumstellar disc into its present structure. Received 15 May 2001 / Published online 5 October 2001     

Tide circulation patterns in a coastal lagoon under sea-level rise

This study evaluates the patterns and effects of relative sea-level rise on the tidal circulation of the basin of the Ria Formosa coastal lagoon using a process-based model that is solved on an unstructured mesh. To predict the changes in the lagoon tidal circulation in the year 2100, the model is forced by tides and a static sea level. The bathymetry and the basin geometry are updated in response to sea-level rise for three morphological response scenarios: no bed updating, barrier island rollover, and basin infilling. Model results indicate that sea-level rise (SLR) will change the baseline current velocity patterns inside the lagoon over the ~100-year study period, due to a strong reduction in the area of the intertidal basin. The basin infilling scenario is associated with the most important adjustments of the tidal circulation (i.e., increases in the flood velocities and delays in the ebb tide), together with an increase in the cumulative discharges of the tidal inlets. Under sea-level rise and in the basin infilling scenario, the salt marshes and tidal flats experience increases in the tidal range and current asymmetry. Basin infilling changes the sediment flushing capacity of the lagoon, leading to the attenuation of the flood dominance in the main inlet and the strengthening of the flood dominance in the two secondary inlets. The predictions resulting from these scenarios provide very useful information on the long-term evolution of similar coastal lagoons that experience varying degrees of SLR. This study highlights the need for research focusing on the quantification of the physical and socio-economic impacts of SLR on lagoon systems, thus enabling the development of effective adaptation strategies.     

Integrated Electrical Resistivity Tomography and Ground Penetrating Radar Measurements Applied to Tomb Detection

The integrated use of electrical resistivity tomography (ERT) and ground penetrating radar (GPR) measurements, and in particular the joint analysis of 2D and 3D data, can represent a valid solution for target identification at complex archaeological sites. A good example, in this respect, is given by the case study of a Phoenician–Punic necropolis in the archaeological site of Nora, in southern Sardinia (Italy), where GPR and ERT measurements were collected before site excavation. In this specific case, the mix of soil and air in the buried chambers, as well as the orientation and the complex spatial distribution of these structures into the sandstone bedrock, generated a number of anomalies difficult to interpret only using 2D results. Only the integration of all GPR and ERT data in a 3D view, and the comparison with archaeological evidence after the excavation, allowed a solid interpretation of geophysical anomalies visible in the 2D sections. Overall, this case study demonstrates the efficiency of the combined use of GPR and ERT acquisitions and shows how, in general, only the joint analysis of 2D data and in a 3D view can help the interpretation of the real distribution of the buried archaeological remains at similar archaeological complex sites.     

Observed heating effects of conjugate photoelectrons

A gridded spherical electrostatic analyzer aboard Injun 5 has been used to measure fluxes of thermal and hyperthermal electrons at subauroral latitudes in the midnight sector of the northern ionosphere between altitudes of 2500 and 850 km. Due to the offset between the geomagnetic and geographic poles hyperthermal fluxes, consisting of energetic photoelectrons that have escaped from the sunlit southern hemisphere are observed along orbits over the Atlantic Ocean and North America but not over Asia. The ambient electron temperatures (T_e) near 2500 km have their highest values at trough latitudes for all longitudes. At altitudes near 1000 km elevated electron temperatures in the trough were not a consistent feature of the data. Equatorward of the trough, in the longitude sector to which conjugate photoelectrons have access, T_e ～ 4000 K at 2500 km and ～ 3000 K at 1000 km. For regions with the conjugate point in darkness T_e ? 2300 K over the 1000–2500 km altitude range. The effective thermal characteristics of conjugate photoelectrons are studied as functions of altitude and latitude. The observations indicate that (1) at trough latitudes elevated electron temperatures in the topside ionosphere are mostly produced by sources other than conjugate photoelectrons, and (2) at subtrough latitudes, in the Alantic Ocean-North American longitude sector, conjugate photoelectrons contribute significantly to the heating of topside electrons. Much of the conjugate photoelectron energy is deposited at altitudes >2500 km then conducted along magnetic field lines into the ionosphere.     

Assessing the effects of post‐pine beetle forest litter on snow albedo

The effect of forest litter on snow surface albedo has been subject to limited study, mainly in the hardwood‐dominated forests of the northeastern United States. Given the recent pine beetle infestation in Western North America and associated increases in litter production, this study examines the effects of forest litter on snow surface albedo in the coniferous forests of south‐central British Columbia. Measured changes in canopy transmittance provide an indication of canopy loss or total litterfall over the winter of 2007–2008. Relationships between percent litter cover, an index of albedo, snow depth, and snow ablation during the 2008 melt season are compared between a mature, young, and clearcut coniferous stand. Results indicate a strong feedback effect between canopy loss and subsequent enhanced shortwave transmittance, and litter accumulation on the snow surface from that canopy loss. However, this relationship is confounded by other variables concurrently affecting albedo. While results suggest that a relatively small percent litter cover can have a significant effect on albedo and ablation, further research is underway to extract the litter signal from that of other factors affecting albedo, particularly snow depth. Copyright © 2010 John Wiley & Sons, Ltd.     

Tributyltin and polycyclic aromatic hydrocarbon levels in Mobile Bay, Alabama: a review

A review of the levels of polycyclic aromatic hydrocarbons (PAH) and tributyltin (TBT) in sediments from Mobile Bay, Alabama, shows that overall levels of PAH decrease from the upper bay (RI) to the lower bay (RIV). Analysis of PAH ratios indicate that pyrogenic sources such as fossil fuel combustion are dominant. There are so few data on TBT in sediments that spatial trends cannot be identified.Levels of PAHs in oyster tissues decrease from the upper bay (RI) to the lower bay (RIII). Although there is no significant temporal trend for PAH levels in bivalves for the US; in the bay, levels in Region II (RII) have decreased significantly and are currently below the national median. There is no trend in Region III (RIII), where levels remain below RII and the national median. RI and RIV had too few data for trend analysis.Mean levels of TBT in oyster tissues decrease from the upper bay (RI) to the lower bay (RIII). Temporal trend analysis indicates a significant decreasing trend for TBT in the US but no significant trend was detected for RII and RIII in Mobile Bay. TBT levels in RII are consistently higher than levels in the US and RIII, which are similar. Data from RI are too limited for analysis and there are no data for RIV.     

Extinction versus backscatter relationships for lidar applications at 351 nm: maritime and desert aerosol simulations and comparison with observations

Functional relationships linking at λ₀=351 nm aerosol extinction α_λ0^aer and backscatter coefficient β_λ0^aer of maritime and desert type aerosols are determined to allow for inversion of the single-wavelength lidar signals. Such relationships are derived as mean behavior of 20,000 extinction versus backscatter computations, performed for aerosol size distributions and compositions whose describing parameters are randomly chosen within the naturally observed variability. For desert-type aerosols, the effect of the particle non-sphericity is considered and it is shown that the extinction to backscatter ratio of non-spherical dust particles can be up to 60% larger than the values obtained for spherical particles. Aerosol extinction and backscatter coefficient profiles obtained inverting the single-wavelength lidar signal with the modeled relationships are then compared to the same profiles measured by a combined elastic-Raman lidar operating at 351 nm. Analytical back trajectories and satellite images are used to characterize advection patterns during lidar measurements and to properly choose the modeled functional relationship. A good accordance between the two techniques is found for advection patterns over the lidar site typical of maritime and dust conditions. Maximum differences between the model-based α_λ0^aer and β_λ0^aer vertical profiles and the corresponding ones measured by the combined elastic-Raman lidar technique are of 30% and 40% in maritime and desert dust conditions, respectively. The comparison of elastic-Raman lidar measurements and model-based results also reveals that particle non-sphericity must be taken into account when mineral dust-type aerosols are directly advected over the measurement site.     

On the devil's tracks: unexpected news from the Foresta ichnosite (Roccamonfina volcano,central Italy)

The Foresta ichnosite is well known for preserving some of the oldest human fossil footprints recorded in Europe so far. This research aims to: i) describe new footprints that are larger than those already reported, some of which form a new trackway that moves in the opposite direction to all the others; ii) announce the discovery of some stone tools also in the surroundings of the Foresta ichnosite. The new results increase the total number of human fossil footprints to at least 81, specify the direction and the number of footprints of Trackway C, and identify three new directions of walking at the site. More compelling and complete estimates of the dimensional range of all ichnological evidence enables us, furthermore, to estimate the number of trackmakers walking on the trampled surface as a minimum of five, one of them likely being an adult male. The general shape of all the recorded footprints suggests that the Foresta trackmakers share some similarities with those at Sima de los Huesos, and belong to the same taxonomical group as the Ceprano skull. All the new evidence enables us to better understand the presence of hominin populations in the Roccamonfina volcano area during the Middle Pleistocene. © 2020 John Wiley & Sons, Ltd.     

Analysis of occurrence patterns and biological factors of cetaceans based on long‐term and fine‐scale data from platforms of opportunity: Madeira Island as a case study

Management and conservation issues are addressed through the identification of areas of particular importance, which requires the acquisition of baseline information on species distribution and dynamics. These types of data are particularly difficult to obtain at high resolution for large marine vertebrates like cetaceans, given that dedicated surveys are complex and logistically expensive. This study uses daily presence–absence sighting data of cetaceans collected year‐round from whale‐watching boats to support the theory that fine‐scale data obtained from platforms of opportunity can provide valuable information on species occurrence and group dynamics. Data from 7,551 (daily) sightings comprising 22 species were collected from 3,527 surveyed days over 11 years (mean of 321 days per year, SD = 17) in the pelagic environment of Madeira Island. Cetaceans were observed on 92% of the surveyed days, and a mean of 15.4 (SD = 1.5), 8.2 (SD = 2.0) and 2.1 (SD = 1.2) species were recorded per year, month, and day, respectively. There were significant differences in the number of species per month (p < .001), with the highest diversity recorded in June. At least nine species, comprising 96% of all sightings, were found to use the Madeiran waters on a regular basis, such as the Atlantic spotted dolphin (Stenella frontalis), the short‐beaked common dolphin (Delphinus delphis), the bottlenose dolphin (Tursiops truncatus), and others featured in the Red List of the International Union for Conservation of Nature as Endangered, Vulnerable, and Data Deficient. In addition, 10 species were found to use the Madeiran waters for travelling, feeding, resting, socializing and calving, which suggests that the southern and southeastern waters of Madeira Island constitute an area of interest for cetaceans. This study characterizes the cetaceans’ community structure (occurrence, aggregation sizes, behaviours, proportion of calves, and inter‐specific relationships) of a poorly studied region, providing important information for managers. Finally, the advantages and limitations of using fine‐scale data from a type of platform of opportunity that is increasing along coastlines globally are discussed.