Inference of mantle viscosity from GRACE and relative sea level data

Gravity Recovery And Climate Experiment (GRACE) satellite observations of secular changes in gravity near Hudson Bay, and geological measurements of relative sea level (RSL) changes over the last 10 000 yr in the same region, are used in a Monte Carlo inversion to infer-mantle viscosity structure. The GRACE secular change in gravity shows a significant positive anomaly over a broad region (>3000 km) near Hudson Bay with a maximum of ∼2.5 μGal yr⁻¹ slightly west of Hudson Bay. The pattern of this anomaly is remarkably consistent with that predicted for postglacial rebound using the ICE-5G deglaciation history, strongly suggesting a postglacial rebound origin for the gravity change. We find that the GRACE and RSL data are insensitive to mantle viscosity below 1800 km depth, a conclusion similar to that from previous studies that used only RSL data. For a mantle with homogeneous viscosity, the GRACE and RSL data require a viscosity between  1.4 × 10²¹  and  2.3 × 10²¹  Pa s. An inversion for two mantle viscosity layers separated at a depth of 670 km, shows an ensemble of viscosity structures compatible with the data. While the lowest misfit occurs for upper- and lower-mantle viscosities of  5.3 × 10²⁰  and  2.3 × 10²¹  Pa s, respectively, a weaker upper mantle may be compensated by a stronger lower mantle, such that there exist other models that also provide a reasonable fit to the data. We find that the GRACE and RSL data used in this study cannot resolve more than two layers in the upper 1800 km of the mantle.     

Empirical assessment of adaptation to climate change impacts of mountain households: development and application of an Adaptation Capability Index

The present study proposes an index to assess the potential for adaptation to climate change for households in the mountainous regions. The index provides a realistic approach to recognize social and natural factors which contribute to successful adaptation and addresses several household functions, such as social networking, livelihood strategy, adjustment strategies, resource availability and accessibility. The proposed Adaptation Capability Index (ACI) is analytically defined, mathematically formulated and field tested on mountainous households in urban and semi-urban regions of the Uttarakhand Himalaya in India. To gather data on the topic relevant to the ACI, a household scale questionnaire was developed and administered to 120 heads of households through face-to-face interviews. The results highlight higher adaptive capability of urban households and low adaptation capacity of rural households due to poor farm productivity, low accessibility and availability of resources and technological input. Future programs and policies must include and implement regulations to remedy attributive factors responsible for higher adaptation. This paper may be applicable to other mountainous regions and may provide insights for effective adaptation strategies to climate change.     

On the swimming strategies to escape a rip current: a mathematical approach

Rip currents represent significant hazards to swimmers all around the world. The danger arises when a misinformed swimmer uses an inadequate strategy to escape the rip, such as fighting the current directly. This can lead to fatigue, panic, and in some cases drowning. There exists a range of strategies put forward by experts (both lifeguards and scientists) to escape rip currents. However, these recommendations are based on a limited number of scientific studies and there is still much discrepancy surrounding the best strategy to escape a rip. Thus, here we present a simple, physics-based theoretical model aimed at assessing different escape strategies in terms of their associated ‘energetic cost’ (in work and power) for any given rip current and swimmer’s proficiency level. Many combinations of swimmers and rips are considered, including both idealised and a realistic rip current. Our quantitative results back the common knowledge that swimming against the rip (which is strongly discouraged by lifeguards) is almost universally the worst possible strategy, especially when compared against strategies favoured by experts, such as floating with the current before attempting to swim back to the shore. For a realistic rip, our results suggest that swimming directly against the rip can require several times more power from the swimmer than other strategies advised by lifeguards, thus lending further scientific support to experts’ recommendations. This study may help promote education around the dangers posed by rip currents and how best to address them.

     

The effect of orbital eccentricities on the shape of the hill-type analytical stability surfaces in the general three-body problem

Hill-type stability surfaces are computed for the general hierarchical three-body problem for non-zero eccentricities of the initial osculating orbits. Significant differences are found between them and the one obtained for initial zero eccentricities. Application is made to the triple subgroups of the Solar System; in particular it is found that no analytical guarantee of Hill-type stability can be given to any of the satellites against solar perturbations.     

Distribution, habitat use and ecology of deepwater Anemones (Actiniaria) in the Gulf of Mexico

The distribution of deepwater Actiniaria is poorly known. Rarely are these organisms identified to family, as this requires both well-preserved specimens and taxonomic expertise. Ecological information is similarly lacking. From the results of a comprehensive surveying program in the deep Gulf of Mexico, we report the occurrence of nine species of Actiniaria. For the most abundant four of these, we plot distributions and discuss habitat use, morphological variation, and feeding strategies. Actiniaria in the Gulf appear to have broad, basin-wide distributions with little depth preference. Faunal biomass is highest in the NE Gulf within submarine canyons or at the base of slope escarpments. Attachment mode is mostly opportunistic on various types of hard substrata, including trash. Sediment-dwelling forms are very abundant at an organically rich site within a large submarine canyon.