A Saturnian gas ring and the recycling of Titan's atmosphere

Atoms which escape Titan's atmosphere are unlikely to possess escape velocity from Saturn, and can orbit the planet until lost by ionization or collision with Titan. It is predicted that a toroidal ring of between ～1 and ～10³ atoms or molecules cm^?3 exists around Saturn at a distance of about 10 times the radius of the visible rings. This torus may be detectable from Earth-orbit and detection of nondetection of it may provide some information about the presence or absence of a Saturnian magnetic field, and the exospheric temperature and atmospheric escape rate of Titan. It is estimated that, if Titan has a large exosphere, ～97% or more of the escaping atoms can be recaptured by Titan, thereby decreasing the effective net atmospheric loss rate by up to two orders of magnitude. With such a reduction in atmospheric loss rates, it becomes more plausible to suggest that satellites previously thought too small to retain an atmosphere may have one. It is suggested that Saturn be examined by Lyman-α and other observations to search for the gaseous torus of Titan. If successful, these could then be extended to other satellites.The effect of a hypothetical Saturnian magnetosphere on the atmosphere of Titan is investigated. It is shown that, if Saturn has a magnetic field comparable to Jupiter's (～10 G at the planetary surface), the magnetospheric plasma can supply Titan with hydrogen at a rate comparable to the loss rates in some of the models of Trafton (1972) and Sagan (1973). A major part of the Saturnian ionospheric escape flux (～ 10²⁷ photoelectrons sec^?1) could perhaps be captured by Titan. At the upper limit, this rate of hydrogen input to the satellite could total ～0.1 atm pressure over the lifetime of the solar system, an amount comparable to estimates of the present atmospheric pressure of Titan.     

Comparing threshold definition techniques for rainfall‐induced landslides: A national assessment using radar rainfall

Translational landslides and debris flows are often initiated during intense or prolonged rainfall. Empirical thresholds aim to classify the rain conditions that are commonly associated with landslide occurrence and therefore improve understating of these hazards and predictive ability. Objective techniques that are used to determine these thresholds are likely to be affected by the length of the rain record used, yet this is not routinely considered. Moreover, remotely sensed spatially continuous rainfall observations are under‐exploited. This study compares and evaluates the effect of rain record length on two objective threshold selection techniques in a national assessment of Scotland using weather radar data. Thresholds selected by ‘threat score’ are sensitive to rain record length whereas, in a first application to landslides, ‘optimal point’ (OP) thresholds prove relatively consistent. OP thresholds increase landslide detection and may therefore be applicable in early‐warning systems. Thresholds combining 1‐ and 12‐day antecedence variables best distinguish landslide initiation conditions and indicate that Scottish landslides may be initiated by lower rain accumulation and intensities than previously thought. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Interpretation of epikarstic cave drip water recession curves: a case study from Velika Pasica Cave,central Slovenia

ABSTRACT

Recession curves are widely used in hydrological studies and projects, such as in rivers, streams or springs. However, no cave drip water has been analysed with recession curves. In this paper, four cave drips were monitored in the Velika Pasica Cave, in order to discover the water flow and storage properties of the epikarst. Various methods were applied in the recession analysis, combining the hydrological characteristics of the four drips: for the slow water in the epikarst, the matching strip method was the identified as the appropriate model for the drip water recession analysis. According to the recession coefficient k, the water flow in the epikarst was divided into fast flow, intermediate flow and slow flow. The volume of water retained in the reservoir (the epikarst storage) could be presented as a function of its specific recession coefficient.

EDITOR D.Koutsoyiannis; ASSOCIATE EDITOR X. Chen     

The timing and nature of recession of outlet glaciers of Hielo Patagónico Norte, Chile, from their Neoglacial IV (Little Ice Age) maximum positions

The dates of recession of eleven outlet glaciers of the Hielo Patagónico Norte (Northern Patagonian Icefield) from their recent maximum positions have been inferred from dendrochronology, lichenometry, radiocarbon dating and historical sources. We have refined the dating for part of the Little Ice Age period in this area placing a glacial advance to between AD 1650 and 1766 with the latter date favoured as conformable with historical records and an uncalibrated radiocarbon determination. Glacier recession from maximal positions began in the early 1860s–1870s. Recession was largely synchronous on the western and eastern sides of the Icefield. This synchronicity suggests that climate forcing over-rides second-order controls on glacier behaviour such as the nature of the terminal environment (e.g. calving/non-calving) or differences in glacier drainage basin area. We argue that this icefield-wide glacier recession represents a response to post-Little Ice Age warming, and provides further evidence for the global extent and near synchronous termination of the Little Ice Age.     

Age verification,growth and life history of rubyfish Plagiogeneion rubiginosum

Age verification of rubyfish (Plagiogeneion rubiginosum) was sought using the bomb radiocarbon chronometer procedure. Stable isotopes were investigated for life history characteristics. Radiocarbon (¹⁴C) and stable isotope (δ¹⁸O and δ¹³C) levels were measured in micro-samples from five otoliths that had been aged using a zone count method. All the core ¹⁴C measurements were ‘pre-bomb’ indicating ages of at least 45 years, and the ¹⁴C measurements across the otolith sections suggested that the zone-count ageing method described herein is not biased. Maximum estimated age was 100 years. There was no significant between-sex difference in the von Bertalanffy growth curves. The δ¹⁸O values indicated that rubyfish are near-surface as juveniles, and move deeper with age. Adults appear to reside in 600–1000 m; this is deeper than most trawl-capture data suggest, but not implausible, and has stock assessment implications. The δ¹³C values reflect fish metabolic rates, trophic feeding levels and oceanographic conditions. The stable isotopes record the environmental life history of each fish, and have value in distinguishing stocks and/or indicating vertical and latitudinal migratory patterns.     

Interpreting the Ca isotope record of marine biogenic carbonates

An 18 million year record of the Ca isotopic composition (δ^44/42Ca) of planktonic foraminiferans from ODP site 925, in the Atlantic, on the Ceara Rise, provides the opportunity for critical analysis of Ca isotope-based reconstructions of the Ca cycle. δ^44/42Ca in this record averages +0.37 ± 0.05 (1σ SD) and ranges from +0.21‰ to +0.52‰. The record is a good match to previously published Neogene Ca isotope records based on foraminiferans, but is not similar to the record based on bulk carbonates, which has values that are as much as 0.25‰ lower. Bulk carbonate and planktonic foraminiferans from core tops differ slightly in their δ^44/42Ca (i.e., by 0.06 ± 0.06‰ (n = 5)), while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger, leaving open the question of the cause of the difference. Modeling the global Ca cycle from downcore variations in δ^44/42Ca by assuming fixed values for the isotopic composition of weathering inputs (δ^44/42Ca_w) and for isotope fractionation associated with the production of carbonate sediments (Δ_sed) results in unrealistically large variations in the total mass of Ca²⁺ in the oceans over the Neogene. Alternatively, variations of ±0.05‰ in the Ca isotope composition of weathering inputs or in the extent of fractionation of Ca isotopes during calcareous sediment formation could entirely account for variations in the Ca isotopic composition of marine carbonates. Ca isotope fractionation during continental weathering, such as has been recently observed, could easily result in variations in δ^44/42Ca_w of a few tenths of permil. Likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in Δ_sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean. Until better constraints on variations in δ^44/42Ca_w and Δ_sed have been established, modeling the Ca²⁺ content of seawater from Ca isotope curves should be approached cautiously.     

Entanglement of New Zealand fur seals in man-made debris at Kaikoura, New Zealand

New Zealand fur seals in the Kaikoura region breed near a town with expanding tourist and fishing industries and commonly come ashore entangled in nets and plastic debris. However, the rate at which entanglement occurs was previously unknown. A decade of Department of Conservation seal callout data was analysed to determine the level of entanglement in the region and the most common debris type. Monitoring of adult female fur seals released from entanglement provided information on the potential for serious wounds to heal and survivorship of released individuals. Entanglement rates of pinnipeds in Kaikoura are some of the highest reported world-wide (average range: 0.6-2.8%) with green trawl net (42%), and plastic strapping tape (31%) together contributing the most to debris types. Nearly half of the reported entangled seals are successfully released (43%) and post-release monitoring shows that with appropriate intervention the chance of an individual surviving even with a significant entanglement wound is high. Our study demonstrates that while entanglement in the region is high, a successful intervention protocol may help reduce the potential for entanglement-related mortality in the region.