Effects of coastal orientation and depth on the distribution of subtidal benthic assemblages

A better understanding of biological systems can only be gained if we understand what processes are important and how they operate to determine the distribution of organisms. Coastal orientation and depth can influence environmental conditions, including the degree of water motion and availability of light, which in turn may influence the horizontal and vertical patterns of organism distribution. Here, we used a mixed‐model design to examine the effects of coastal orientation and depth on the structure of benthic assemblages by comparing the abundance and distribution of macroalgae and invertebrates in shallow and deep waters on the opposing coasts of São Miguel. Generally, coastal orientation had little influence on the distribution of most taxa. In contrast, significant differences were generally associated with depth, although patterns were spatially variable at the scale of locations. This study suggests that depth, and processes operating at the scale of location, but not at the scale of the coast, have an important influence on these assemblages, and that failure to recognise such a scale of variability may hamper our ability to better understand the processes that structure these communities.     

Spectral classification of water masses under the influence of the Amazon River plume

The large amount of dissolved and particulate material discharged by the Amazon River into the Equatorial Atlantic Ocean cause distinct spectral response of its waters as compared to the nearby ocean waters. This paper shows the application of K-means clustering algorithm for classifying water masses in the region under the Amazon River plume influence according to their spectral behavior. Salinity and temperature data from 67 oceanographic stations were related to Sea-viewing Wide Field-of-view Sensor (SeaWiFS) remote sensing reflectances values and the following bio-optical products:(i) chlorophyll-a concentration, (ii) water attenuation coefficient and (iii) absorption coefficient for dissolved and detrital material. Four different water masses were identified such as:(1) oceanic water, (2) intermediate oceanic water, (3) intermediate river plume water and (4) Amazon River plume water. The spectral behavior of these water masses allowed concluding that the main active optical component of the waters in the region is the colored dissolved organic matter originated mostly from the Amazon River.     

Reconstruction of Late-Quaternary sea- and lake-level changes in a tectonically active marginal basin using seismic stratigraphy: The Gulf of Cariaco,NE Venezuela

The Gulf of Cariaco is a marginal basin located between the Cariaco Basin and the Paria Gulf, offshore NE Venezuela, along a system of active right-lateral strike-slip faults. It is connected to the Caribbean Sea via a shallow 58-m-deep sill implying that the gulf was disconnected from the global ocean during eustatic lowstands. A dense grid of high-resolution reflection seismic profiles has been used to determine the overall tectonic structure of the gulf and to establish the seismic stratigraphy of its sedimentary infill. Six unconformity-bounded seismic–stratigraphic units were identified in the upper ~ 200 m of the sedimentary infill. Detailed seismic–stratigraphic and seismic-facies analysis allowed defining a series of sedimentary features that can be used as indicators of past sea or lake level in the Gulf of Cariaco: i) delta offlap breaks, ii) evaporites, and iii) erosional unconformities. Using accurate measurements of these various indicators at several locations in the gulf and a simple total subsidence model, a relative sea/lake-level history encompassing the last 130 kyr could be reconstructed. In periods of connection with the open ocean, reconstructed relative sea level correlates well with eustatic sea level. In times of disconnection, distinct lake-level fluctuations occurred, which sometimes resulted in total dessication of the gulf. Lake-level fluctuations appear to correlate with major Heinrich Events, stadials and interstadials. MIS 4, the LGM and the Younger Dryas were thus identified in the Gulf of Cariaco sedimentary record. The last reconnection to the Caribbean Sea occurred during MWP1b (around 11.5 kyr). The very good fit of the Cariaco sea/lake-level curve with the eustatic sea-level curves (both in terms of amplitude and of timing) underscores potential for future paleoclimate research of the sedimentary record contained in this marginal basin, despite its active tectonic setting.     

Tunnel stability analysis during construction using a neuro‐fuzzy system

This paper presents an alternative strategy to evaluate the stability of tunnels during the design and construction stages based on a hybrid system, composed by neural, neuro‐fuzzy and analytical solutions. A prototype of this system is designed using a database formed by 261 cases, 45 real and the rest synthetic. This system is capable of reproducing the displacements induced at the periphery of the tunnel before and after support installation. The stability of the excavation process is evaluated using a criterion that considers dimensionless parameters based on the shear strength of the media, the induced deformation level in the ground, the plastic radii and the advance of excavation without support. The efficiency and validity of the prototype is verified with two examples of actual tunnels, one included in the database used to train the system and the other not included. The results of both examples show a better approximation than other commonly used techniques. Copyright © 2005 John Wiley & Sons, Ltd.     

Multi-hazard model for developing countries

Disaster risk assessment related to natural events has generally been carried out separately by specialists in each area of earth sciences, which has two negative consequences: Firstly, results of investigations are presented in different formats, mainly maps, which differ significantly from each other in aspects such as scale, symbols and units; secondly, it is common for an area or territory to contain several hazards that can potentially interact with each other, generating cascade effects or synergies. While some authors have proposed a multi-hazard analysis framework based on the use of probabilities, the quality and quantity of data required for this approach are rarely available in developing countries. Qualitative methods, on the other hand, have traditionally been limited to overlapping maps, without considering possible spatial interactions. Given the importance of integrated assessment of natural hazards for land use planning and risk management, this article proposes a heuristic multi-hazard model appropriate for developing countries, based on a standardization of classifications and a spatial interaction matrix between hazards. The model can be adjusted to be applied at different scales and in different territories; to demonstrate its versatility, it is applied to the municipality of Poás, Costa Rica, a territory with multiple natural hazards.

     

Microphysical and chemical characteristics of cloud droplet residuals and interstitial particles in continental stratocumulus clouds

During June and July 2003 the Sources and Origins of Atmospheric Cloud Droplets experiment (SOACED) was carried out on a mountain-top site in central Sweden. The main objective of the experiment was to characterise the microphysical and chemical properties of cloud droplet residuals and interstitial aerosol particles in continental clouds and to understand the processes controlling cloud properties at this location.Interstitial and residual aerosol size distributions, cloud liquid water content and species- and size-resolved aerosol mass concentrations are the main variables employed to address questions pertaining to the cloud droplet number concentration and scavenging efficiency during a stratocumulus cloud event observed on July 28, 2003. In this cloud event, about 56% of the aerosol mass was associated with organic species, whilst SO₄ accounted for 23% and NH₄ for 14%. NO₃ and Cl made up about 7% of the total mass.The partitioning of the aerosol particles between cloud droplets and interstitial air has been studied in terms of their microphysical properties. The scavenging efficiency, defined as the fraction of particles activated into cloud elements compared to the total amount of particles, was investigated as a function of size. The scavenging efficiency curves displayed different shapes during the cloud event, from an S-shaped curve, with low scavenging efficiency in the Aitken mode and larger scavenging efficiency in the accumulation mode, to more unusual shapes where Aitken-mode particles were either solely activated or activated in addition to accumulation-mode particles.This study suggests that alterations of the aerosol chemical composition occurred during the measurement period, changing the hygroscopic nature of the CCN and decreasing their activation diameter. It is also hypothesized that entrainment of drier air aloft may have introduced inhomogeneities in the supersaturation field and modified the S-shaped scavenging curves.     

Changes in snowmelt runoff timing in the contiguous United States

Changes in timing of snowmelt-fed streamflow have great importance for water supply, flood management, and ecological processes, as well as being a common indicator of climate change. In this study, snowmelt runoff timing change in the contiguous United States between 1957 and 2016 was investigated by analysing data from 97 streamflow gages. The annual snowmelt runoff timing shift was identified using ‘Center Time (CT)’ and ‘Spring Pulse Onset (SPO)’ methods, jointly with the monthly fractional streamflow (MFS) analysis, conducted between January and June. Since snowmelt-derived streamflow timing change is mainly induced by regional meteorological factors, such as air temperature and precipitation, their trends and relationship with CT were also examined. Shifts toward earlier snowmelt runoff timing were found by both methods, CT (8.3 days on average) and SPO (8.5 days on average). Although the results of the CT change are stronger than the SPO change, both outcomes are mostly correlated, particularly in the central and northwestern parts of the country. MFS trends support the outcomes of CT and SPO. In January, February, and especially March, a higher number of the stations indicated increasing trends in MFS. In April, May, and June, their number decreased and the number of gages with diminishing trends rose sharply. The timing difference is highly related to temperature change. Annual average temperature and temperature in the melting period increase considerably. The annual average temperature is significantly negatively correlated with CT in the vast majority of the regions. Although precipitation is not as effective as the temperature, its trends have impacts on snowmelt runoff timing change depending on the region and elevation. These results demonstrate the importance of the impacts of snowmelt runoff timing changes due to global warming on the regional and large-scale hydrology in the contiguous United States.     

Enabling collaborative GeoVisual analytics: Systems,techniques, and research challenges

Collaboration across disciplines is recognized as one of the great challenges for research in visual analysis of geographic information (GeoVisual Analytics, GVA). Considering the increasing availability of geodata and the complexity of analytical problems, the need to advance the support for collaborative work is becoming more pressing and prominent. This article contributes to this objective by reviewing the state‐of‐the‐art of the support for collaborative work in GVA systems and by identifying research challenges and proposing strategies to address them. We conducted a systematic review, resulting in the identification of 13 collaborative systems, 6 distinct collaborative techniques, and 3 research challenges. We conclude that GVA is moving toward more effective support of multidisciplinary and cross‐domain collaborative analysis. However, to materialize this potential, research is needed to improve the support for hybrid collaborative scenarios, cross‐device collaboration, and support for time‐critical and long‐term analysis.     

Geology and tectonics of the Boa Vista Basin (Paraíba, northeastern Brazil) and geochemistry of associated Cenozoic tholeiitic magmatism

The Boa Vista Basin (BVB) is located approximately 60 km southwest of Campina Grande, Paraíba, northeastern Brazil. It has a half-graben geometry controlled by dip-slip normal faults striking NE–SW. From the base to the top, the BVB is composed of (1) a lower volcanic unit of altered basalts and basaltic andesites overlying Precambrian basement rocks, (2) an intermediate unit of bentonitic shales that pass upward to medium- to coarse-grained sandstones and conglomerates and downward to sandstones and siltstones, and (3) an upper volcanic unit of massive to vesiculated basaltic flows grading to pillowed or autobrecciated basalts. These basalts show porphyritic (olivine and augite microphenocrysts), glomeroporphyritic, intersetal, pilotaxitic, and variolitic textures. They are medium-K, Fe-rich tholeiites with SiO₂ of 50.2–53.3 wt%, magnesium number of 50.54–60.21 wt%, total alkali of 2.15–3.92 wt%, and TiO₂ of 1.8–1.9 wt% and are related by low-pressure fractionation of olivine, plagioclase, magnetite, ilmenite, and apatite. They are LREE-enriched (La_N/Yb_N=8.54–44.14) with no significant europium anomaly. Trace element modeling suggests a garnet-bearing metasomatised lherzolite as their source. The geological context and geochemistry of the basalts suggest a close connection between reactivated deep-rooted Precambrian shear zones, which channeled mantle-derived Tertiary tholeiitic magmas, and continental rifting in northeastern Brazil.