The origin of sinuous rilles

This report describes the distribution and morphology of sinuous rilles and presents data on rille geometry. Examples of the relation between sinuous rilles and the regional structure are given. Leading theories for the origin of sinuous rilles are discussed and evaluated. It is concluded that the general weight of evidence is against water erosion. The ash flow theory is not excluded, but evidence in its favor is weak. The best explanations involve lava tube formation for certain sinuous rilles, and faulting for others. In some cases, a gradation between faulting and igneous activity is noted.     

Unveiling the atmospheres of giant exoplanets with an EChO-class mission

More than a thousand exoplanets have been discovered over the last decade. Perhaps more excitingly, probing their atmospheres has become possible. With current data we have glimpsed the diversity of exoplanet atmospheres that will be revealed over the coming decade. However, numerous questions concerning their chemical composition, thermal structure, and atmospheric dynamics remain to be answered. More observations of higher quality are needed. In the next years, the selection of a space-based mission dedicated to the spectroscopic characterization of exoplanets would revolutionize our understanding of the physics of planetary atmospheres. Such a mission was proposed to the ESA cosmic vision program in 2014. Our paper is therefore based on the planned capabilities of the Exoplanet Characterization Observatory (EChO), but it should equally apply to any future mission with similar characteristics. With its large spectral coverage (0.4 ? 16 μm), high spectral resolution (λ/Δλ > 300 below 5 μm and λ/Δλ > 30 above 5 μm) and 1.5m mirror, a future mission such as EChO will provide spectrally resolved transit lightcurves, secondary eclipses lightcurves, and full phase curves of numerous exoplanets with an unprecedented signal-to-noise ratio. In this paper, we review some of today’s main scientific questions about gas giant exoplanets atmospheres, for which a future mission such as EChO will bring a decisive contribution.     

Community-based production of geographic information using open source software and Web 2.0

This article presents an innovative approach to citizen-led production of Web-based geographic information where new and/or existing digital map features are linked to annotations or commentary and citizens engage in synchronous and/or asynchronous discussion. The article discusses the relationship of the approach to public participation geographic information systems (PPGISs) and the emerging challenges associated with volunteered geographic information. A custom-developed, open source software tool named MapChat is used to facilitate the citizen inputs and discussions. The information generated from applying the approach through a series of community workshops is presented and discussed in light of current issues in PPGIS and volunteered geographic information research.     

Developing coastal adaptation to climate change in the New York City infrastructure-shed: process, approach, tools, and strategies

While current rates of sea level rise and associated coastal flooding in the New York City region appear to be manageable by stakeholders responsible for communications, energy, transportation, and water infrastructure, projections for sea level rise and associated flooding in the future, especially those associated with rapid icemelt of the Greenland and West Antarctic Icesheets, may be outside the range of current capacity because extreme events might cause flooding beyond today??s planning and preparedness regimes. This paper describes the comprehensive process, approach, and tools for adaptation developed by the New York City Panel on Climate Change (NPCC) in conjunction with the region??s stakeholders who manage its critical infrastructure, much of which lies near the coast. It presents the adaptation framework and the sea-level rise and storm projections related to coastal risks developed through the stakeholder process. Climate change adaptation planning in New York City is characterized by a multi-jurisdictional stakeholder?Cscientist process, state-of-the-art scientific projections and mapping, and development of adaptation strategies based on a risk-management approach.     

Toxicities of antifouling biocide Irgarol 1051 and its major degraded product to marine primary producers

Irgarol 1051 (2-methythiol-4-tert-butylamino-6-cyclopropylamino-s-triazine) is an algaecide commonly used in antifouling paints. It undergoes photodegradation which yields M1 (2-methylthio-4-tert-butylamino-6-amino-s-triazine) as its major and most stable degradant. Elevated levels of both Irgarol and M1 have been detected in coastal waters worldwide; however, ecotoxicity effects of M1 to various marine autotrophs such as cyanobacteria are still largely unknown. This study firstly examined and compared the 96 h toxicities of Irgarol and M1 to the cyanobacterium Chroococcus minor and two marine diatom species, Skeletonema costatum and Thalassiosira pseudonana. Our results suggested that Irgarol was consistently more toxic to all of the three species than M1 (96 h EC50 values: C. minor, 7.71 microug L(-1) Irgarol vs. > 200 microg L(-1) M1; S. costatum, 0.29 microg L(-1) Irgarol vs. 11.32 microg L(-1)M1; and T. pseudonana, 0.41 microg L(-1) Irgarol vs. 16.50 microg L(-1)M1). Secondly, we conducted a meta-analysis of currently available data on toxicities of Irgarol and M1 to both freshwater and marine primary producers based on species sensitivity distributions (SSDs). Interestingly, freshwater autotrophs are more sensitive to Irgarol than their marine counterparts. For marine autotrophs, microalgae are generally more sensitive to Irgarol than macroalgae and cyanobacteria. With very limited available data on M1 (i.e. five species), M1 might be less toxic than Irgarol; nonetheless this finding warrants further confirmation with additional data on other autotrophic species.     

A survey of anthropogenic vegetation changes in West Africa during the last century — climatic implications

The extent of albedo change resulting from anthropogenic modification of the vegetation cover over the last century has been investigated in West Africa. The climatic implications of these changes are briefly discussed.West Africa spans a suite of vegetation zones ranging latitudinally northward from tropical rainforest to desert scrub, and comprises environmental problems from extremely rapid deforestation of the tropical forests in Ivory Coast or Ghana to desertification in the Sahel.Historical vegetation changes have been digitized on a 1° × 1° grid map based on a literature survey of government censuses, forestry and agricultural reports, supplemented by atlases, and other historical, economic and geographic sources.The principal processes of land cover modification during the last century include clearing of the natural vegetation for agriculture, grazing, logging, and degradation of marginal semi-arid to arid ecosystems by excessive grazing or cultivation. Forestry surveys for West Africa suggest clearance of around 56% of the forest zone; estimated losses for Ivory Coast, Ghana, and Liberia range between 64% and 70%. Estimates of total land conversion range between 88 million ha, from the digitized land use map (Figure 4) to 122.8 million ha, from extrapolation of forestry data (Section 3.1).The change in albedo corresponding to the land use modification is relatively small, using conservative estimates for desertification amounting to an increase of around 0.4% regionally over 100 yr and 0.5% since agriculture began. Thus 4/5 of the total albedo may have occurred within the last century. Additional assumptions regarding desertification and a lower albedo value for tropical forest compensate for each other and do not significantly alter the result of the initial calculation. The maximum zones of increased albedo are concentrated in the forest zone (4°–8° N) and savanna-southern sahel (10°–12°) which correspond to zones of maximum agricultural and population growth. Between 13° N and 17° N, the albedo change is small or negative due to both less intensive land utilization and replacement of scattered vegetation on exposed sandy soil by lower albedo irrigated crops.These estimates may represent a lower limit, particularly if desertification is more extensive than initially assumed. Under an extreme assumption that the entire Sahel zone between 14°–20° N has been desertified, the regional mean albedo could increase by as much as 4%. This represents an upper limit to likely historical anthropogenic disturbances of the land surface.Although historical climate records show three major droughts during the 20th century (1910–1920, 1940's, 1969–1975, possibly continuing into the 1980's; Nicholson, 1980a; Hare, 1983), and stream flow fluctuations which correlate well with precipitation (Faure and Gac, 1981;Palutikof et al., 1981), these records do not appear to indicate a regional secular decrease in precipitation as suggested by several climate models. Evidence for apparent desiccation or desert creep (= desertification) may be attributed, in large part, to adverse changes in soil and stream hydrology caused by anthropogenic disruption of the vegetation cover.     

Regional sea level changes projected by the NASA/GISS Atmosphere-Ocean Model

Sea level has been rising for the past century, and coastal residents of the Earth will want to understand and predict future sea level changes. In this study we present sea level changes from new simulations of the Goddard Institute for Space Studies (GISS) global atmosphere-ocean model from 1950 to 2099. The free surface, mass conserving ocean model leads to a straightforward calculation of these changes. Using observed levels of greenhouse gases between 1950 and 1990 and a compounded 0.5% annual increase in CO₂ after 1990, model projections show that global sea level measured from 1950 will rise by 61?mm in the year 2000, by 212?mm in 2050, and by 408?mm in 2089. By 2089, 64% of the global sea level rise will be due to thermal expansion and 36% will be due to ocean mass changes. The Arctic Ocean will show a greater than average sea level rise, while the Antarctic circumpolar region will show a smaller rise in agreement with other models. Model results are also compared with observed sea level changes during the past 40 years at 12 coastal stations around the world.     

Monitoring sea level changes

Future sea level rise arouses concern because of potentially deleterious impacts to coastal regions. These will stem not only from the loss of land through inundation and erosion, but also from increased frequency of storm floods, with a rising base level, even with no change in storm climatology, and from saltwater intrusion and greater amounts of waterlogging. Current sea level trends are important in formulating an accurate baseline for future projections. Sea level, furthermore, is an important parameter which integrates a number of oceanic and atmospheric processes. The ocean surface demonstrates considerable variability on diurnal, seasonal, and interannual time scales, induced by winds, storm waves, coastal upwelling, and geostrophic currents. Secular trends in sea level arise from changes in global mean temperature and also from crustal deformation on local to regional scales. The challenge facing researchers is how best to extract the climate signal from this noise.This paper re-examines recent estimates of sea level rise, discusses causes of variability in the sea level records, and describes methods employed to filter out some of these contaminating signals. Evidence for trends in long-term sea level records and in extreme events is investigated. Application of satellite geodesy to sea level research is briefly reviewed.     

River profiles along the Himalayan arc as indicators of active tectonics

Longitudinal profiles along sixteen major transverse Himalayan rivers add important constraints to models of active continental subduction and its evolution. These profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases. The base of the zone of increased gradients correlates with (1) the topographic front between the Lesser and High Himalayas, (2) the narrow belt of intermediate-magnitude thrust earthquakes, (3) the Main Central Thrust zone (MCT). These features define a small circle in the central portion of the Himalayan arc. These correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising High Himalayas and the Lesser Himalayas. No sharp increases in gradient are observed near the Main Boundary Thrust (MBT), except on a few rivers, such as the Jhelum or Kundar, where the MBT lies close to both the MCT and the seismic belt. Thus, it is unlikely that the MBT is a major tectonic boundary. The diversion of river courses along the MBT and around anticlines in the Sub Himalayas has probably been caused by aggradation near the rosion-deposition boundary, upstream of uplifts in the Mahabharat range and Sub Himalayas.A parallel is drawn between the Himalayas and New Guinea based on the hypothesis that continent-arc collision, of the type occurring in northern Australia, preceded continent-continent collision in the Himalayas. The present sedimentary/tectonic phase in New Guinea resembles the Subathu (Paleocene-Eocene) phase in the Himalayas. Incipient counterparts of the major Himalayan structures, including the MCT and the MBT, are recognized in New Guinea. The drainage patterns in the Himalayas and in New Guinea bear a similar relation to major structures. This suggests that (1) the tectonic evolution of the Himalayas has been rather uniform since early stages of collision, and (2) the Himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the High Himalayas.