Understanding Today's Online GIS User Through the Lens of a WorldMap Survey

WorldMap is an open source online mapping application which aims to lower barriers for scholars who wish to visualize, analyze, organize, present, and publish mapped information. In late 2013, 290 respondents among the 8,000 registered users participated in an online survey in which they described their activities, purposes, experiences, and preferences regarding the system. Participants also described their professional background, GIS skill level, age, gender, and country of work. This study analyzes the results of the survey, by summarizing the responses to each question independently and by examining the relationships and dependencies of these answers across the different questions to try to better understand why users responded the way they did. The study is based on the user‐centered design (UCD) approach. We aim to use the survey results to improve our understanding of user demographics and needs. Findings from this study will be used to guide WorldMap improvements, and we hope the findings will also shed light on the broader requirements of online GIS users.     

Environmental impacts of dredging on seagrasses: a review

Main potential impacts on seagrasses from dredging and sand mining include physical removal and/or burial of vegetation and effects of increased turbidity and sedimentation. For seagrasses, the critical threshold for turbidity and sedimentation, as well as the duration that seagrasses can survive periods of high turbidity or excessive sedimentation vary greatly among species. Larger, slow-growing climax species with substantial carbohydrate reserves show greater resilience to such events than smaller opportunistic species, but the latter display much faster post-dredging recovery when water quality conditions return to their original state. A review of 45 case studies worldwide, accounting for a total loss of 21,023 ha of seagrass vegetation due to dredging, is indicative of the scale of the impact of dredging on seagrasses. In recent years, tighter control in the form of strict regulations, proper enforcement and monitoring, and mitigating measures together with proper impact assessment and development of new environmental dredging techniques help to prevent or minimize adverse impacts on seagrasses. Costs of such measures are difficult to estimate, but seem negligible in comparison with costs of seagrass restoration programmes, which are typically small-scale in approach and often have limited success. Copying of dredging criteria used in one geographic area to a dredging operation in another may in some cases lead to exaggerated limitations resulting in unnecessary costs and delays in dredging operations, or in other cases could prove damaging to seagrass ecosystems. Meaningful criteria to limit the extent and turbidity of dredging plumes and their effects will always require site-specific evaluations and should take into account the natural variability of local background turbidity.     

Post-Marquette discharge from Glacial Lake Agassiz into the Superior basin

Glacial Lake Agassiz, the largest of the North American glacial lakes, discharged through several different outlets during its history, although the timing and location of discharge remain controversial. However, one discharge event is well established based on extensive onshore observations: drainage through the Nipigon Lake area into the Superior basin about 10,700 years ago, following retreat of ice of the Marquette advance from the basin. High-resolution, single-channel seismic-reflection data collected with a small airgun were acquired to test the hypothesis that the Post-Marquette drainage event left diagnostic stratigraphic and geomorphic signatures beneath Lake Superior. The unique bathymetry of northwestern Lake Superior, where water depth plunges off Nipigon and Black Bays, makes this location ideal for the characterization of the post-Marquette depositional and erosional features. According to our hypothesis, the initial, sudden discharge of high-velocity water would have eroded channels through the bays. The steep and sudden drop-off into the Superior basin would have caused the flow to slow and drop much of the sediment it was carrying. Our results confirm the existence of both erosional features and depositional sediment packages related to Lake Agassiz discharge at this time. The erosional features include deeply incised bedrock channels in the bays. The depositional features comprise subaqueous fans that are thickest in the deep water areas adjacent to the outlets and thin lakeward and laterally away from the channels. The seismic character of the basal units of the fans, proximal to the channels, is chaotic and only very weakly stratified, suggesting that these deposits represent coarse sediment laid down during the initial, high-energy stages of the flood. These sediments are overlain by a stratified package which is interpreted as the fine grained sediment associated with the later, low-energy stages of the flood. The combination of channels and subaqueous fans is inferred to be diagnostic of high-energy Lake Agassiz discharge into the Superior basin, and they serve as analogs for hypothesized discharge at other times.     

Negative ion chemistry in Titan's upper atmosphere

The Electron Spectrometer (ELS), one of the sensors making up the Cassini Plasma Spectrometer (CAPS) revealed the existence of numerous negative ions in Titan's upper atmosphere. The observations at closest approach (∼1000 km) show evidence for negatively charged ions up to ∼10,000 amu/q, as well as two distinct peaks at 22±4 and 44±8 amu/q, and maybe a third one at 82±14 amu/q. We present the first ionospheric model of Titan including negative ion chemistry. We find that dissociative electron attachment to neutral molecules (mostly HCN) initiates the formation of negative ions. The negative charge is then transferred to more acidic molecules such as HC₃N, HC₅N or C₄H₂. Loss occurs through associative detachment with radicals (H and CH₃). We attribute the three low mass peaks observed by ELS to CN⁻, C₃N⁻/C₄H⁻ and C₅N⁻. These species are the first intermediates in the formation of the even larger negative ions observed by ELS, which are most likely the precursors to the aerosols observed at lower altitudes.     

Quaternary glaciation in the Nubra and Shyok valley confluence, northernmost Ladakh, India

Three glacial stages (Deshkit 1, Deshkit 2 and Dishkit 3 glacial stages) are identified in the Nubra and Shyok valleys in northernmost Ladakh, northwest India, on the basis of geomorphic field mapping, remote sensing, and ¹⁰Be terrestrial cosmogenic nuclide surface exposure dating. The glacial stages date to ∼ 45 ka (Deshkit 1 glacial stage), ∼ 81 ka (Deshkit 2 glacial stage) and ∼ 144 ka (Deshkit 3 glacial stage). A mean equilibrium line altitude depression of ∼ 290 m for the Deshkit 1 glacial stage was calculated using the area accumulation ratio, toe-to-headwall ratio, area-altitude, and area-altitude balance ratio methods. Comparison of glaciation in the Nubra and Shyok valleys with glaciations in the adjacent Central Karakoram of northern Pakistan and northern side of the Ladakh Range of northern India indicates that glaciation was synchronous on Milankovitch timescales across the region during MIS-6, but differed greatly in extent, with more extensive glaciation in the Karakoram than the morphostratigraphically equivalent glaciation on the northern slopes of the Ladakh Range. This highlights the strong contrast in the extent of glaciation across ranges in the Himalaya-Tibetan orogen, necessitating caution when correlating glacial successions within and between mountain ranges.     

Negative ions in the Enceladus plume

During Cassini’s Enceladus encounter on 12th March 2008, the Cassini Electron Spectrometer, part of the CAPS instrument, detected fluxes of negative ions in the plumes from Enceladus. It is thought that these ions include negatively charged water group cluster ions associated with the plume and forming part of the ‘plume ionosphere’. In this paper we present our observations, argue that these are negative ions, and present preliminary mass identifications. We also suggest mechanisms for production and loss of the ions as constrained by the observations. Due to their short lifetime, we suggest that the ions are produced in or near the water vapour plume, or from the extended source of ice grains in the plume. We suggest that Enceladus now joins the Earth, Comet Halley and Titan as locations in the Solar System where negative ions have been directly observed although the ions observed in each case have distinctly different characteristics.     

Multiscalarity of the Nutrient–Chlorophyll Relationship in Coastal Phytoplankton

The relationship between nitrogen (N) and phytoplankton chlorophyll a (Chl) establishes a basis for understanding eutrophication in coastal marine ecosystems. A substantial literature exists on cross-ecosystem analysis of this relationship, but there is little information on cross-scale patterns. A collection of observational records in Bedford Basin (Canada) was used to construct the N–Chl relationship at four time scales: intra-day, intra-annual, interannual, and interdecadal. Additionally, a dataset of contingent observations from 16 biogeochemical ocean provinces was used to construct the N–Chl relationship at large spatial scale. In Bedford Basin, N statistically predicts Chl at time scales that are short (intra-day, intra-annual) and long (interdecadal) but not intermediate (interannual). There is an apparent stoichiometric regularity in the dependence of Chl on N that crosses time scales. Further, an apparent similitude exists between the local pattern at long time scale and the global pattern at large space scale.     

Little ice age alluvial fan development in Langedalen, western Norway

This paper reports a preliminary investigation of the sedimentary succession in two alluvial fans in western Norway. Sedimentological information is supplemented by palaeoecological data from pollen analysis and the age of the sequence is constrained by six radiocarbon age estimates on woody fragments and peat. These data suggest that significant accumulation of fan sediments took place after AD 1637–1685. Before this, the fluvial landscape and the adjacent slopes may have been more stable with the development of Betula , Salix and Alnus woodland on the valley floor and sides. Although there is no indication of gradual climatic deterioration in the vegetation record from these sites, the radiocarbon chronology suggests that enhanced fan development was coincident with the climatic change associated with the 'Little Ice Age'. This was probably a response to glacier expansion and increased discharge and sediment supply to the alluvial fans from outlets of the Jostedalsbreen ice cap on the southern side of Langedalen. Initial response to climate change in this setting was therefore enhanced geomorphic activity and instability of the valley-side slopes.     

Radar observations of auroral zone flows during a multiple-onset substorm

We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every \sim12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are \sim1 h MLT wide (\sim600 km), and initially expand poleward to a width of \sim300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50–100 m s⁻¹ or less during the first few minutes, before surging equatorward at 0.5-1.0 km s⁻¹ during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed \sim100 mho, before decaying over a few minutes. This value compares with Hall conductivities of \sim20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.     

KRb ratios in Precambrian granulite terranes

Concentrations of potassium and rubidium are reported for 62 Precambrian shield whole-rock samples belonging to the pyroxene granulite facies of world-wide distribution. Compared with the Main Trend established by Shaw (1968) for igneous and quasi-igneous rocks of the upper crust, the high-grade metamorphic granulites exhibit a similar correlation but with a measurable depletion in Rb for a given K content. The Metamorphic Trend may be described by the equations: log₁₀ (ppm Rb) = 1.136 log₁₀ (per cent K) + 1.495 or ppm Rb = 31.28 (per cent K)^1.136. The square of the product moment correlation coefficient shows that 80 per cent of the variation in Rb is associated with variation in K.All suites studied have initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios less than 0.707. This low value argues against repeated extraction of Rb and K through time on a regional scale. Rather, the major depletion in these lithophile elements occurred in the early stages of crustal evolution.