Architecture of the deep critical zone in the Río Icacos watershed (Luquillo Critical Zone Observatory,Puerto Rico) inferred from drilling and ground penetrating radar (GPR)

In the critical zone, surficial bedrock interactions result in the formation of a mantle of chemically‐ and physically‐altered material defined here as regolith. In the watershed of the Río Icacos, an upland river draining the Luquillo Mountains in tropical Puerto Rico, we explored the influence of lithology (quartz diorite versus hornfels‐facies volcaniclastic rock) on weathering. Regolith profiles were studied by drilling boreholes and imaging the subsurface using ground penetrating radar (GPR). Overall, the regolith structure is not laterally continuous but rather is punctuated by zones of deep fractures that host in situ weathering, corestones, and colluvial material. GPR images of these vertical zones show reflectors at 15–20 m depth. Thus, the architecture of the critical zone in the upper Luquillo Mountains is highly dependent on lithology and its influence on fracture development. At the highest elevations where hornfels overlies quartz diorite, positive feedbacks occur when the water table drops so that oxidative weathering of biotite in the more felsic rock creates microfractures and allows deeper infiltration of meteoric waters. Such exposure results in some of the fastest weathering rocks in the world and may contribute to formation of the knickpoint in the Río Icacos watershed. This work represents the first study combining GPR and drilling to look at the structure of the deep critical zone and demonstrates: (1) the importance of combining direct methods (such as drilling) with indirect methods (such as GPR) to understand the architecture of the critical zone in tropical systems; (2) the interplay of the surficial stress regime, lithology and climate in dictating the architecture of weathering. Copyright © 2016 John Wiley & Sons, Ltd.     

Radiocarbon deficiencies of US Gulf Coast lakes compromise paleo-hurricane records

Radiocarbon assays of sediments from Lake Shelby, US Gulf Coast, exhibit substantial ¹⁴C deficiencies of 9.3% and 4.7% for the limnic sapropel and associated fresh-water clams Rangia cuneata, respectively. Measured radiocarbon dates from the sapropel and clams require corrections of 785 ± 80 and 365 ± 90 ¹⁴C yr (1σ), respectively, in order to achieve consistency with the radiocarbon time scale. Lake sediments of the US Gulf Coast serve as unique repositories of pre-historic hurricane strikes. Previously unrecognized radiocarbon deficiencies likely render compromised chronologies of the paleo-hurricane records, and erroneous estimates of return period and landfall probability that are derived from the storm chronologies. The recalculated severe hurricane chronologies suggest that the annual landfall probabilities of the last millennium on the US Gulf Coast are equal to, or higher than, the preceding three millennia.     

Exploring how alternative mapping approaches influence fireshed assessment and human community exposure to wildfire

Attaining fire-adapted human communities has become a key focus of collaborative planning on landscapes across the western United States and elsewhere. The coupling of fire simulation with GIS has expanded the analytical base to support such planning efforts, particularly through the “fireshed” concept that identifies areas where wildfires could ignite and reach a human community. Previous research has identified mismatches in scale between localized community wildfire planning and the broader fireshed considering patterns of wildfire activity across landscapes. Here we expand upon this work by investigating the degree to which alternative geospatial characterizations of human communities could influence assessment of community exposure and characterization of the fireshed. We use three methods of mapping human communities (point, raster, and polygon) and develop three fireshed metrics (size, number of fires reaching houses, and number of houses exposed), and apply this analytical framework on a 2.3 million ha case study landscape encompassing the Sierra National Forest in California, USA. We simulated fire occurrence and growth using FSim for 10,000 iterations (fire seasons) at 180-m resolution. The simulation resulted in 3.9 large fires per million ha per year, with a mean size of 3432 ha. Results exhibit similarities and differences in how exposure is quantified, specifically indicating that polygons representing recognized community boundaries led to the lowest exposure levels. These results highlight how choice of the mapping approach could lead to misestimating the scope of the problem or targeting mitigation efforts in the wrong areas, and underscore the importance of clarity and spatial fidelity in geospatial data representing communities at risk.     

Mapping distortion of detectors in UVIT onboard AstroSat observatory

Ultraviolet Imaging Telescope (UVIT) is one of the payloads onboard AstroSat, India’s first multi-wavelength Astronomy mission. UVIT is primarily designed to make high resolution images in wide field, in three wavelength channels simultaneously: FUV (130–180 nm), NUV (200–300 nm) and VIS (320–550 nm). The intensified imagers used in UVIT suffer from distortions, and a correction is necessary for these to achieve good astrometry. In this article we describe the methodology and calculations used to estimate the distortions in ground calibrations.     

Sedimentary environments of the east-central Bering Sea continental shelf

A factor analysis of 180 bottom sediment samples from the east-central Bering Sea continental shelf identifies five factors that account for 95% of the variation in the 17 whole ø size classes that were used as variables. Factor I represents coarse sediments that have been bypassed in areas of active water circulation. Factors II and III represent fine and very fine sands that have been hydraulically sorted, reworked, and mixed. Factor IV represents coarse to medium silt that has been segregated from areas of relatively high energy. Factor V represents both the production of sediments finer than medium silt and deposition within the lowest-energy environment in this area.Modern and palimpsest sediments are areally prevalent over this section of the shelf. Relict sediments occur in only a few small areas. The dispersal of sediments is affected by surface and tidal currents as well as wave action. Ice rafting is not an important geological agent. Data from the eastcentral Bering Sea shelf indicate that sediments on subarctic continental shelves are not necessarily characterized by an abundance of rocky sediments or gravel.     

Marine ecosystem management: Fish abundance and size under exploitation

This study is targeted on policy makers and environmental scientists to illustrate the typical historical scale of depletion of our fish stocks, and what current and emerging legislation might mean for fisheries management and the metrics of fish stocks. The population demography of the Bristol Channel sole is described since 1820. Their decline in abundance, and change in length compositions, are modelled. By 2000, the mature stock had been depleted to less than 5% of its original size, and larger sole were rarely caught. The implications of maximum sustainable yield targets, and of good environmental status, are examined.     

The stratigraphic and geographic distribution of giant craters and remobilised sediment mounds on the mid Norway margin,and their relation to long term fluid flow

Large craters associated with mounds of remobilised sediment have been recently mapped on the mid Norway margin in the Møre Basin. These craters and mounds may be linked to the long term migration of fluids upwards from the lower levels of the Møre Basin which exploit hydrothermal vent complexes emplaced in the late Paleocene and early Eocene. All of the craters are located on a regionally correlative seismic surface that is correlated with the basal shear plane of Slide W, a slide located at the base of the Plio-Pleistocene Naust Formation. The Craters are positioned in the western area of the Møre Basin at the foot of the continental slope on the crests and flanks of Miocene domes, where Oligocene biosiliceous ooze subcrops on the basal shear surface of Slide W. Not all of the craters are filled by Slide W. Mounds are emplaced above those craters which are filled by Slide W on the top surface of Slide W. Stratal relationships show that the mounds were emplaced on the paleo-seabed. We present and discuss two models that illustrate processes that may have been involved in the formation of craters and remobilisation of sediments. In one model, an eruption of fluid from beneath remobilises ooze into ooze mounds in a single event triggering slope failure, whereas in the other model the emplacement of Slide W and later slides loads low density ooze causing it to undergo liquefaction, a process which may have been facilitated by the trapping of continuous long term fluid migrating from beneath, causing the ooze to remobilise into ooze mounds in two or more events.     

Does canopy wetness matter? Evapotranspiration from a subtropical montane cloud forest in Taiwan

Evapotranspiration (ET) and canopy wetness were measured over a 2‐year intensive field campaign at the Chi‐Lan Mountain cloud forest site in Taiwan. Eddy covariance and sap flow methods were applied to measure ET and tree sap flow of the endemic yellow cypress (Chamaecyparis obtusa var. formosana). ET was 553 mm yr^?1 over the study period with an annual rainfall and fog deposition of 4893 and 288 mm yr^–1, respectively. The duration of canopy wetness exceeded actual fog or rain events (mostly in the afternoon), and the intercepted water was evaporated later in the following dry morning. The cumulative wet duration accounted for 52% of time over the study period, which was longer than the duration of rainfall and fog altogether (41%). As it adapted to the extremely moist environment, the yellow cypress behaved in a wet‐enhanced/dry‐reduced water use strategy and was sensitive to short periods of dry atmosphere with high evaporation potential. During dry days, the sap flow rate rose quickly after dawn and led to conservative water use through midday and the afternoon. During periodically wet days, the canopy was mostly wetted in the morning, and the interception evaporation contributed largely to the morning ET. The initiation of morning sap flow was postponed 1–3 h, and the sap flow rate tended to peak later at midday. The midday canopy conductance was higher in the periodically wet days (10.6 mm s^–1) as compared with 7.6 mm s^?1 in the dry days. Consequently, the dry‐reduced water use strategy led to much lower annual ET with respect to the available energy (~46%) and high precipitation input (~11%). The moist‐adapted ecohydrology we report reveals the vulnerability of montane cloud forests to prolonged fog‐free periods. More research is urgently needed to better understand the resilience of these ecosystems and formulate adaptive management plans. Copyright © 2012 John Wiley & Sons, Ltd.