ALBERT

Description: Publication date: March 2015 Source: GeoResJ, Volume 5 Author(s): A. Poortinga , J.G.S. Keijsers , S.M. Visser , M.J.P.M. Riksen , A.C.W. Baas Coastal dunes are the primary defence protecting the coastline from the destructive forces of the sea in The Netherlands. Aeolian processes are important in this context as they contribute to dune accretion and thus the safety of the coastal hinterland. In this study, we analyze horizontal and vertical variability of event scale aeolian sand transport on a wide beach on the island of Ameland, The Netherlands. Data were obtained from a meteorological station, groundwater monitoring wells and a camera installed on the beach. Fifteen aeolian transport events (two involving onshore winds, seven longshore and six offshore) were measured using a comprehensive grid of 37 customized MWAC traps. The highest sand transport rates and largest variability was found for alongshore events. Surface moisture, governed by groundwater, was found to be an important controlling parameter for aeolian transport rates and vertical flux profiles. Groundwater levels were largely dominated by beach inundation, influencing the groundwater table for a two week period. Variations in vertical flux profiles between traps were larger for wet sand transport events than dry ones. In general, sand transport rates were highest at the foreshore and lowest at the dune toe. Sand transport dynamics are dependent on local conditions such as beach dimensions, beach orientation and also meteorological and surface characteristics. Moderate (high frequency, low magnitude) events are also capable of transporting large amounts of sand. Future studies should include spatially explicit measurements of elevation and surface moisture to obtain a more complete understanding of the complex sand transport dynamics.

Description: Publication date: September–December 2014 Source: GeoResJ, Volumes 3–4 Author(s): A. Määttänen , M. Douspis Recent datasets on heterogeneous deposition mode ice nucleation have revealed a strong dependence of the contact parameter m on temperature, ranging from linear to exponential, depending on the experiments. We analyze recent datasets using a Monte Carlo Markov Chain method with the full classical nucleation theory including spherical and planar geometry. The method we use allows us to test models of the temperature dependence of the contact parameter and evaluate their performance. We estimate the applicability of different forms of contact parameter temperature dependence, including a new well-behaved suggestion. Such a function has a more physical behavior at high and low temperatures and might thus be more easily applicable in atmospheric modeling. However, because of their limited temperature range, the present datasets are unable to reveal the behavior of the contact parameter in low temperatures, and we are unable to fully validate the proposed function. We thus call for more heterogeneous nucleation experiments reaching low temperatures (〈170 K). Such datasets may be significant for studies on, for example, polar mesospheric clouds, Mars ice clouds, and perhaps exoplanet clouds. This work provides a new framework, valid even for very small ice nucleus sizes, for analyzing heterogeneous nucleation datasets.

Description: Publication date: March–June 2014 Source: GeoResJ, Volumes 1–2 Author(s): P. Nomikou , M.M. Parks , D. Papanikolaou , D.M. Pyle , T.A. Mather , S. Carey , A.B. Watts , M. Paulatto , M.L. Kalnins , I. Livanos , K. Bejelou , E. Simou , I. Perros The morphology of a volcanic edifice reflects the integrated eruptive and evolutionary history of that system, and can be used to reconstruct the time-series of prior eruptions. We present a new high-resolution merged LiDAR-bathymetry grid, which has enabled detailed mapping of both onshore and offshore historic lava flows of the Kameni islands, emplaced in the centre of the Santorini caldera since at least AD 46. We identify three new submarine lava flows: two flows, of unknown age, lie to the east of Nea Kameni and a third submarine flow, located north of Nea Kameni appears to predate the 1925–1928 lava flows but was emplaced subsequent to the 1707–1711 lava flows. Yield strength estimates derived from the morphology of the 1570/1573 lobe suggest that submarine lava strengths are approximately two times greater than those derived from the onshore flows. To our knowledge this is the first documented yield strength estimate for submarine flows. This increase in strength is likely related to cooling and thickening of the dacite lava flows as they displace sea water. Improved lava volume estimates derived from the merged LiDAR-Bathymetry grid suggest typical lava extrusion rates of ∼2–3 m 3 s −1 during four of the historic eruptions on Nea Kameni (1707–1711, 1866–1870, 1925–1928 and 1939–1941). They also reveal a linear relationship between the pre-eruption interval and the volume of extruded lava. These observations may be used to estimate the size of future dome-building eruptions at Santorini volcano, based on the time interval since the last significant eruption.

Description: Publication date: March–June 2014 Source: GeoResJ, Volumes 1–2 Author(s): Rainer Nerlich , Stuart R. Clark , Hans-Peter Bunge Most authors agree that parts of the Caribbean plate are an igneous Plateau underlain by Farallon lithosphere that was trapped in between the North and South American plates. However, the origin of the thickened crust is debated. The theory of oceanic plateaus forming as magmatic outpouring related to a plume arrival became prominent when Large Igneous Provinces could be traced back to hotspots. The present-day proximity of the Galapagos hotspot made it an obvious candidate for associating its plume head arrival with the formation of the Caribbean Plateau. However, it was shown that in a fixed or moving Indian-Atlantic hotspot reference frame, plate reconstructions predicted the Galapagos hotspot a thousand or more kilometres away from the Caribbean plate at the time of Plateau formation (∼88–94 Ma). Here, we calculate the goodness of fit for the Pacific hotspot reference frame and the recently developed Global Moving Hotspot Reference Frame. We show that both frames lead to good correlations between the paleo-positions of the Caribbean Plate and the Galapagos hotspot, when a docking time of the Caribbean plate to South America of 54.5 Ma is assumed. As this result is consistent with abundant evidence that lends support for a Galapagos hotspot origin of the rocks that form the Caribbean Plateau, proposed alternative mechanisms to explain the thickened crust of the Caribbean Plateau seem to be unnecessary. Finally, based on our model, we also derived an age distribution of the lithosphere underneath the thickened crust of the Caribbean Plateau.

Description: Publication date: Available online 3 December 2013 Source: GeoResJ Author(s): Scott King , Steve Donovan , Simon George , Lyatt Jaeglé , David Pyle , Stephan van Gasselt , Vasile Ersek

Description: Publication date: September–December 2014 Source: GeoResJ, Volumes 3–4 Author(s): Jeffrey M. Dick , Katy A. Evans , Alex I. Holman , David Leach , Kliti Grice The formation of base metal sulfide deposits requires not only a source of metals but also reduced sulfur. If incoming sulfur is present in ore fluids as sulfate, then a source of electrons is needed to drive the reduction of sulfate to sulfide. The oxidation of organic matter can release electrons that provide the reducing capacity, whether it be in low- or high-temperature settings that are conducive to biological or thermochemical sulfate reduction (BSR or TSR). The amounts of organic matter reacted and sulfide minerals formed can be estimated by mass balance calculations. In this study, an integrated mass balance expression is formulated that takes into account the sulfide mineral content and organic carbon content and H/C ratios of mineralised and non-mineralised rocks. Model calculations based on carbon, sulfur and redox budget balances suggest that the extent of oxidation of the organic matter present at the Here’s Your Chance (HYC) Pb–Zn deposit is insufficient for reduction of the required quantity of sulfate. The results imply that externally derived reducing capacity and/or reduced sulfur is required to form the metal resource. Possible sources include hydrocarbon-rich fluids from deeper parts of the sedimentary sequence or formation of sulfide and organic matter as products of BSR during sedimentation/early diagenesis. However, the observed oxidation of organic matter associated with the deposit suggests that at least some reducing capacity is locally derived. Therefore, our calculations are consistent with genetic models for HYC that have multiple sources of redox budget for sulfate reduction.

Description: Publication date: March 2015 Source: GeoResJ, Volume 5 Author(s): Willem Renema Accurate assessment of location and timing of speciation of species is needed to discriminate between macroevolutionary models explaining large scale biodiversity patterns. In this paper I evaluate fossil evidence of variation in geographical ranges through time, as well as spatio-temporal variation in morphological parameters to examine geographical aspects of speciation and range variation. Specifically I test for geographical morphological stability within time slices and for temporal modes of morphological change within lineages. Past distribution ranges of all species of the large benthic foraminifera Cycloclypeus have been documented on paleogeographic maps. From those samples with sufficiently well preserved specimens internal morphological data were measured and analysed. Within a small sample of six species in a single genus of reef associated large benthic foraminifera evidence for heterogeneity in geographic speciation modes, including vicariance, peripheral speciation, and sympatric speciation in the centre of the range has been found. Morphological evolution was found to be either homogeneous over large geographic ranges or spatially restricted. In time two gradually evolving lineages were found. Furthermore, an evolutionary transition of two species that previously was regarded as gradual, is shown to be punctuated with intermediate populations occurring restricted in both time and space. I demonstrate the marked heterogeneity of evolutionary processes and the difficulty to make assumptions regarding tempo and mode of evolution. Furthermore, I introduce the concept of geographically undersampled punctuations. This example exposes some of the pitfalls when conclusions regarding the mode and location of speciation are based on the combination of phylogeny and extant distribution alone. Graphical abstract

Description: Publication date: September–December 2014 Source: GeoResJ, Volumes 3–4 Author(s): Marina Alletti , Alain Burgisser , Bruno Scaillet , Clive Oppenheimer We present results from a series of experiments on the partitioning of chlorine between a hydrous fluid phase and a phonolitic melt that we then use to model specific aspects of volcanic degassing. Experiments were performed from 250 to 10 MPa on a phonolite from Erebus lava lake, Antarctica, at 1000 °C near the QFM solid buffer. Only one of 48 experimental samples shows coexistence of low-density vapour and high-density brine in the fluid phase while 35 samples are unambiguously in the vapour field. Large uncertainties in the H 2 O–NaCl phase diagram at the P – T considered do not allow us to assign reliable phase behaviour to the remaining samples. We select a vapour-dominated subset of our dataset to establish an empirical HCl solubility law valid at low pressures and salinities. This law is incorporated into a thermodynamical model of degassing, which we use to compute equilibrium temperatures from gas measurements made at Erebus in 2010. The quiescent lake activity features cyclic temperature variations between 1000 and 1050 °C, which is consistent with thermal convection within the shallow plumbing system. Backward tracking of representative gas compositions and temperatures shows the evolution with pressure of the molar ratio of SO 2 /HCl in the gas, a quantity that is often measured in volcanic plumes. Model outputs suggest that this ratio can vary by up to an order of magnitude when the pressure changes from atmospheric to 100 MPa, depending on degassing style (coupled vs. decoupled ascent of gas and melt).

Description: Publication date: March 2015 Source: GeoResJ, Volume 5 Author(s): Tea Mumladze , Adam M. Forte , Eric S. Cowgill , Charles C. Trexler , Nathan A. Niemi , M. Burak Yıkılmaz , Louise H. Kellogg The Greater Caucasus Mountains contain the highest peaks in Europe and define, for over 850 km along strike, the leading edge of the second-largest active collisional orogen on Earth. However, the mechanisms by which this range is being constructed remain disputed. Using a new database of earthquake records from local networks in Georgia, Russia, and Azerbaijan, together with previously published hypocenter locations, we show that the central and eastern Greater Caucasus Mountains are underlain by a northeast-dipping zone of mantle seismicity that we interpret as a subducted slab. Beneath the central Greater Caucasus (east of 45°E), the zone of seismicity extends to a depth of at least 158 km with a dip of ∼40°NE and a slab length of ∼130–280 km. In contrast, beneath the western GC (west of 45°E) there is a pronounced lack of events below ∼50 km, which we infer to reflect slab breakoff and detachment. We also observe a gap in intermediate-depth seismicity (45–75 km) at the western end of the subducted slab beneath the central Greater Caucasus, which we interpret as an eastward-propagating tear. This tear coincides with a region of minimum horizontal convergence rates between the Lesser and Greater Caucasus, as expected in a region of active slab breakoff. Active subduction beneath the eastern Greater Caucasus presents a potentially larger seismic hazard than previously recognized and may explain historical records of large magnitude (M 8) seismicity in this region. Graphical abstract

Description: Publication date: March 2015 Source: GeoResJ, Volume 5 Author(s): Ralph D. Lorenz , Brian K. Jackson Dust devils are convective vortices rendered visible by lofted dust, and may be a significant means of injecting dust into the atmosphere, on both Earth and Mars. The fraction of vortices that are dust-laden is not well-understood, however. Here we report a May/June 2013 survey on a Nevada desert playa using small stations that record pressure and solar flux with high time resolution (2 Hz): these data allow detection of vortices and an estimate of the dust opacity of the subset of vortices that geometrically occult the sun. The encounter rate of vortex pressure drops of 0.3 hPa or larger is 50–80 per 100 days, with 0.6 hPa or larger drops occurring about 3 times less often. Obscuration events associated with pressure drops occur less frequently, in part because near-misses must be in the sunward direction to cause attenuation of the solar beam and in part because some vortices are not dust-laden. 40% of vortex events had no detectable attenuation, and only 20% of events caused dimming greater than about 2% (a maximum of ∼35%), with stronger dimming tending to occur with larger pressure drops. The distribution suggests dust lifting may be dominated by a few intense devils, complicating estimation of the total flux into the atmosphere. Graphical abstract

Description: Publication date: September–December 2014 Source: GeoResJ, Volumes 3–4 Author(s): Ralph D. Lorenz , Stephen P. Scheidt Equipment for performing low-altitude aerial photography for geomorphological studies on 10–1000 m scales is described, with particular reference to study of sand dunes. An automatic digital camera is lofted by a parafoil kite: the arrangement costs around $400, collapses into a volume of ∼2 l and can be deployed in a few minutes, making it convenient for field use when wind conditions (>4 m/s) permit. Some operational considerations are discussed and we demonstrate two scientific applications – change detection to show a dune at White Sands has not advanced in an 11-month interval and the generation of a digital elevation model of Bruneau Dune.

Description: Publication date: March–June 2014 Source: GeoResJ, Volumes 1–2 Author(s): Hanna Silvennoinen , Elena Kozlovskaya , Eduard Kissling , Grigoriy Kosarev We present a new Moho map for the Early-Proterozoic northwestern part of the Fennoscandian Shield, where the POLENET/LAPNET passive seismic array was located. The map is based on previously published and re-evaluated controlled source seismic data and P-wave receiver functions as well as new estimates of the Moho depth obtained by our analysis of P-wave receiver functions at broadband stations of the POLENET/LAPNET array. We estimated individual data quality for all input data and combined them into a new Moho map using CRUST3D software. The software seeks the simplest (smoothest) Moho surface that is consistent with all seismic data within their individual uncertainty limits. The new Moho map indicates that the crustal thickness in the study region varies between 42 km and 58 km, with the greatest thickness being reached in two separate areas in the northeast and the southeast. Two areas with relatively flat and shallow Moho, with an average Moho depth of c. 44 km, are located in the eastern and south-western parts of the study area. These two areas are separated by the Moho depression, with a maximum depth of 58 km. They can be associated with the Archean core of the Karelian craton and with the part of it that was reworked during the Early Proterozoic, respectively. A region with an average Moho depth of c. 47 km can be seen in the northern part of our study area, deepening to c. 55 km in the northeastern corner.

Description: Publication date: September–December 2014 Source: GeoResJ, Volumes 3–4 Author(s): Qing Zhang , J.E. Thompson Atmospheric aerosol particles may undergo phase separation due to differences in miscibility. This alters the morphology of particles such that they are no longer well-mixed, simple spheres. As a result, scattering and absorption of sunlight in Earth’s atmosphere could be affected. In turn, this may alter direct climate forcing by aerosols. In this work we examine the impact of phase separation on aerosol optics for the bi-sphere, core–shell, and engulfed morphologies. We find bi-spherical particles often exhibit very different scattering and absorption cross-sections for a mid-visible wavelength (0.53 μm) relative to an equivalent, volume-weighted spherical case. Optical differences are largely driven by the particle shape, rather than differences in refractive index between phases. However, when averaged across a typical urban particle size distribution, the differences in light scattering largely vanish and bi-sphere and volume equivalent models generally agreed to within 10% for dielectric particles. For particles that are light absorbing, the bi-sphere and volume averaged cases often yielded dissimilar results with the volume-averaged case reflecting absorption >10% more than the phase separated particles. This was particularly true for bi-spheres in which one component particle is strongly light absorbing. Core–shell and engulfed morphologies yield volume scattering efficiencies within a few percent of volume-weighted spheres. However, modeled light absorption between the phase separated and volume averaged models frequently differ by >20% when inclusions absorb light strongly. Therefore, modeling light absorption of mixed-phase particles through the volume-mixing rule cannot be recommended.

Description: Publication date: March–June 2014 Source: GeoResJ, Volumes 1–2 Author(s): Z. Peng , N. Carrasco , P. Pernot The APSIS reactor has been designed to simulate in the laboratory with a VUV synchrotron irradiation the photochemistry occurring in planetary upper atmospheres. A N 2 – CH 4 Titan-like gas mixture has been studied, whose photochemistry in Titan’s ionospheric irradiation conditions leads to a coupled chemical network involving both radicals and ions. In the present work, an ion–neutral coupled model is developed to interpret the experimental data, taking into account the uncertainties on the kinetic parameters by Monte Carlo sampling. The model predicts species concentrations in agreement with mass spectrometry measurements of the methane consumption and product blocks intensities. Ion chemistry and in particular dissociative recombination are found to be very important through sensitivity analysis. The model is also applied to complementary environmental conditions, corresponding to Titan’s ionospheric average conditions and to another existing synchrotron setup. An innovative study of the correlations between species concentrations identifies two main competitive families, leading respectively to saturated and unsaturated species. We find that the unsaturated growth family, driven by C 2 H 2 , is dominant in Titan’s upper atmosphere, as observed by the Cassini INMS. But the saturated species are substantially more intense in the measurements of the two synchrotron experimental setups, and likely originate from catalysis by metallic walls of the reactors.