Forty-three soils (130 horizons), sampled by the geo-pedological mission organized by the State University of Gent (Belgium) in 1962 on Isla Santa Cruz (Galápagos Islands), were analysed in order to ...determine their degree of chemical evolution. Several weathering indices (Weathering Index of Parker – WIP –, Chemical Index of Alteration – CIA –, Chemical Index of Weathering – CIW –, Plagioclase Index of Alteration – PIA – and Silica–Titania Index – STI –) and multivariate statistical analysis (principal components analysis), based on chemical composition, were used. With the only exception of the STI, the indices were highly correlated (r>0.85). The highest WIP and STI values (20.9±8.2 and 70.2±2.2 respectively) were found for soils developed on basalt flows near the coast. Slightly lower values (WIP 16.8+5.1 and STI 61±3.4) were shown by brown soils developed from basaltic flows at elevations between 140 and 225ma.s.l. While the lowest values (WIP 9±5 and STI 47±6.8), representing the more weathered materials, were found for soils located at the highest elevations (>400ma.s.l.) and mostly developed on pyroclastic materials (tuff and tephra).
As the chemical composition of the geological material (basalt and tephra) is highly homogeneous, the degree of weathering is likely to depend on climatic conditions controlled by altitude and orientation. On the windward slopes of the island a gradient of increasing weathering is observed from the arid conditions predominant at the coast to elevations of 400–500ma.s.l., where much more humid conditions prevail. Principal component analysis on elemental composition also supported the interpretation that the degree of weathering (first component) and soil horizonation (second component) are both related to climatic conditions. Both, the variation of the chemical indices and the principal components of the geochemical composition are related to the bioclimatic zones: soils with the lowest degree of weathering are located in the arid coastal zone; slightly higher intensity was found for soils located in the transition and Scalesia zones; while the most weathered soils appear in the brown zone. Compared to other volcanic soils studied in the literature, soils from Isla Santa Cruz are in the upper range of chemical weathering intensity, only comparable to soils from Azores Islands and Canary Islands (Tenerife and La Gomera) developed on basalts, under oceanic conditions.
•We studied 43 soils developed on volcanic material in Isla Santa Cruz (Galápagos, Ecuador)•Several chemical indices are applied to determine the weathering intensity•Weathering seems to be influenced by climate conditions controlled by altitude and orientation•Soil elemental composition is also related to weathering and horizonation•This research is an addition to the limited scientific knowledge of soils of the Galápagos Islands
To investigate the initial phases of magmatism at the leading edge of the upwelling mantle plume, we mapped, photographed, and collected samples from two long, deep‐water lava flows located at the ...western base of the Galápagos Platform using the remotely operated vehicle Hercules. Lavas were recovered from four areas on the seafloor west of Fernandina volcano, including the western flow fronts of two deep‐water flows, heavily sedimented terrain between the two flows, and the eastern, shallower end of one flow. The sediment cover and morphologies are distinct between the western flow fronts and the eastern region based on seafloor imagery, suggesting that the long lava flows are not a single eruptive unit. Major and trace element concentrations reveal both tholeiitic and alkalic compositions and support the interpretation that multiple eruptive units comprise the deep‐water flows. Alkalic lavas have higher La/SmN ratios (2.05–2.12) and total alkali contents (5.18–5.40) compared to tholeiitic lavas, which have La/SmN ratios ranging from 1.64 to 1.68 and total alkali contents ranging from 3.07 to 4.08 wt%. Radiogenic isotope ratios are relatively homogeneous, suggesting a similar mantle source. We use petrologic models to assess three alternative mechanisms for the formation of the alkalic magmas: (1) high‐pressure crystallization of clinopyroxene, (2) mixing of high silica and mafic magmas, and (3) variable extents of melting of the same mantle source. Our modeling indicates that the alkalic samples form from lower extents of melting compared to the tholeiitic lavas and suggests that the deep‐water alkalic lavas are analogous to the initial, preshield building phase observed south of Hawaii and at the base of Loihi Seamount.
Key Points
Deep‐water lava flows at the base of the Galápagos Platform are composed of multiple eruptions, including alkalic and tholeiitic lavas
Tholeiitic lavas are formed by higher extents of melting and likely pass through the lower portion of the Fernandina magma chamber
Alkalic magmas are formed by lower extents of melting at the leading edge of the plume and may be analogous to lavas erupted at Loihi Seamount
The taxonomy of giant Galapagos tortoises (Chelonoidis spp.) is currently based primarily on morphological characters and island of origin. Over the last decade, compelling genetic evidence has ...accumulated for multiple independent evolutionary lineages, spurring the need for taxonomic revision. On the island of Santa Cruz there is currently a single named species, C. porteri. Recent genetic and morphological studies have shown that, within this taxon, there are two evolutionarily and spatially distinct lineages on the western and eastern sectors of the island, known as the Reserva and Cerro Fatal populations, respectively. Analyses of DNA from natural populations and museum specimens, including the type specimen for C. porteri, confirm the genetic distinctiveness of these two lineages and support elevation of the Cerro Fatal tortoises to the rank of species. In this paper, we identify DNA characters that define this new species, and infer evolutionary relationships relative to other species of Galapagos tortoises.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Marine debris pollution poses a significant global threat to biodiversity, with plastics being the primary debris type found in oceans due to their low-cost production and high demand worldwide. ...Microplastics (MPs, <5 mm in size) are highly bioavailable to a wide range of marine taxa, including marine mammals, through direct and indirect ingestion routes (i.e., trophic transfer). Recently, MP pollution has been detected on the Galapagos Marine Reserve, so in this study we developed a baseline framework for MP pollution in the Galapagos sea lion (GSL, Zalophus wollebaeki) through scat-based analysis. We collected 180 GSL scat samples from the southeast region following strict quality assurance/quality control protocols to detect, quantify and characterize physical-chemical properties of MPs through visual observations and μFT-IR spectroscopy. We recovered 81 MPs of varying sizes and colors in 37 % of samples (n = 66/180), consisting mostly of fibers (69 %, x¯ = 0.31 ± 0.57 particles scat−1). The number of particles per gram of sample wet weight ranged from 0.02 to 0.22 (x¯ = 0.04 ± 0.05 particles scat wet g−1). El Malecón and Punta Pitt rookeries at San Cristobal Island had the highest number of MPs (x¯ = 0.67 ± 0.51 and 0.43 ± 0.41 particles scat−1, respectively), and blue-colored particles were the most common in all samples. We identified eleven polymers in 46 particles, consisting mostly of polypropylene-polyethylene copolymer, polypropylene, cellulose, polyethylene, and polyvinyl chloride. The textile, fishing, and packaging industries are likely significant sources of microfibers into this insular ecosystem. Our results suggest that the GSL is exposed to MPs due to anthropogenic contamination that is subsequently transferred through trophic processes. These findings provide an important baseline framework and insights for future research on MP pollution in the region, as well as for management actions that will contribute to the long-term conservation of the GSL.
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•Microplastics were detected in 37 % of the samples from Galapagos sea lion scats.•Fiber-shaped and blue-colored microplastics were predominant in scat samples.•San Cristobal Island rookeries showed the highest microplastic abundance.•Most microplastics were composed of polypropylene-polyethylene copolymer.•Further research to understand MP bioaccumulation routes in top predators is prompted.
We report on new volcanic gas composition results acquired in October 2017 at Minas de Azufre, a persistent fumarolic field topping the resurgent Sierra Negra caldera, in the Galápagos archipelago. ...Our results indicate that the Minas de Azufre fumaroles are moderately hydrous (52–64 mol.% H2O) and rich in CO2 (35–46 mol.%), with total sulfur (ST) being 21–35 times less abundant than CO2. SO2, the most abundant S species, is released at an average rate of 19 ± 9 tons/day. Using a volatile saturation model that provides the composition of magmatic gases at equilibrium with western Galápagos basaltic melt (48 wt. % SiO2) in the 400–0.1 MPa pressure range, we infer that Minas de Azufre fumarolic emissions consist of a mixture of (a) magma‐derived gases coexisting with a melt at ∼50–60 MPa and (b) shallow meteoric water. We thus propose that the fumaroles are supplied by outgassing of magma stored in a ∼2 km deep sill‐like reservoir underneath the caldera floor, and that the trapdoor fault system at the western margin of the resurgent caldera block acts as a preferential pathway for magmatic gas ascent and surface discharge. Our results thus suggest that, in contrast to the majority of the volcano‐hosted hydrothermal systems worldwide, Minas de Azufre releases a relatively pristine magmatic gas.
Plain Language Summary
Magmatic gas released by intraplate, hot‐spot related volcanism can offer insight into the abundance and distribution of volatiles in the Earth's upper mantle. Unfortunately however, the available data set for hot spot magmatic gases is sparse and incomplete, due to relatively infrequent eruptions and the remote location of many hot‐spot volcanoes. Here, we present novel information for the gas chemistry and emission rate at the Minas de Azufre fumarolic field, the most active persistent gas manifestation on Sierra Negra volcano, in the western part of the Galápagos hotspot. We interpret our gas observations in tandem with results of a volatile saturation model that calculates the equilibrium composition of magmatic gases coexisting with basaltic melt under P‐T conditions relevant to Galápagos volcanism. From this comparison, we conclude that the Minas de Azufre fumarolic emissions are fed by degassing of basaltic magma stored in a ∼2 km deep sill underneath the Sierra Negra caldera floor, and that the trapdoor fault system at the western margin of the resurgent caldera block acts as a preferential pathway for magmatic gas leakage and surface discharge. Our results are relevant to a better understanding of Sierra Negra volcano and contribute to extending the volcanic gas catalog for hot‐spot volcanism.
Key Points
The composition and mass flux of volcanic gases from Minas de Azufre, in the Sierra Negra Caldera (Galápagos), are determined
Fluids are interpreted as prevalently derived from a shallow (∼2 km deep) magmatic sill underneath the caldera floor
Trapdoor faults at the resurgent caldera block's margin favor magmatic gas leakage and surface discharge
We present the first-generation global tomographic model constructed based on adjoint tomography, an iterative full-waveform inversion technique. Synthetic seismograms were calculated using ...GPU-accelerated spectral-element simulations of global seismic wave propagation, accommodating effects due to 3-D anelastic crust & mantle structure, topography & bathymetry, the ocean load, ellipticity, rotation, and self-gravitation. Fréchet derivatives were calculated in 3-D anelastic models based on an adjoint-state method. The simulations were performed on the Cray XK7 named ‘Titan’, a computer with 18 688 GPU accelerators housed at Oak Ridge National Laboratory. The transversely isotropic global model is the result of 15 tomographic iterations, which systematically reduced differences between observed and simulated three-component seismograms. Our starting model combined 3-D mantle model S362ANI with 3-D crustal model Crust2.0. We simultaneously inverted for structure in the crust and mantle, thereby eliminating the need for widely used ‘crustal corrections’. We used data from 253 earthquakes in the magnitude range 5.8 ≤ M
w ≤ 7.0. We started inversions by combining ∼30 s body-wave data with ∼60 s surface-wave data. The shortest period of the surface waves was gradually decreased, and in the last three iterations we combined ∼17 s body waves with ∼45 s surface waves. We started using 180 min long seismograms after the 12th iteration and assimilated minor- and major-arc body and surface waves. The 15th iteration model features enhancements of well-known slabs, an enhanced image of the Samoa/Tahiti plume, as well as various other plumes and hotspots, such as Caroline, Galapagos, Yellowstone and Erebus. Furthermore, we see clear improvements in slab resolution along the Hellenic and Japan Arcs, as well as subduction along the East of Scotia Plate, which does not exist in the starting model. Point-spread function tests demonstrate that we are approaching the resolution of continental-scale studies in some areas, for example, underneath Yellowstone. This is a consequence of our multiscale smoothing strategy in which we define our smoothing operator as a function of the approximate Hessian kernel, thereby smoothing gradients less wherever we have good ray coverage, such as underneath North America.
Galápagos plume-related lavas in the accreted terranes of the Caribbean and along the west coast of Costa Rica and Panama provide evidence on the evolution of the Galápagos mantle plume, specifically ...its mantle temperature, size and composition of heterogeneities, and dynamics. Here we provide new 40Ar/39Ar ages, major and trace element data, Sr–Nd–Pb isotopic compositions, and high-precision olivine analyses for samples from the Quepos terrane (Costa Rica) to closely examine the transitional phase of the Galápagos Plume from Large Igneous Province (LIP) to ocean island basalt (OIB) forming stages. The new ages indicate that the record of Quepos volcanism began at 70 Ma and persisted for 10 Ma. Petrological evidence suggests that the maximum mantle potential temperature (Tp) of the plume changed from ∼1650° to ∼1550 °C between 90–70 Ma. This change correlates with a dominant pyroxenite component in the Galapagos source as indicated by high Ni and Fe/Mn and low Ca olivines relative to those that crystallized in normal peridotite derived melts. The decrease in Tp also correlates with an increase in high-field strength element enrichments, e.g., Nb/Nb⁎, of the erupted lavas. Radiogenic isotope ratios (Nd–Pb) suggest that the Quepos terrane samples have intermediate (Central Domain) radiogenic signatures. The Galápagos plume at 70 Ma represents elevated pyroxenite melt productivity relative to peridotite in a cooling lithologically heterogeneous mantle.
•The Quepos terrane, Costa Rica records the LIP–OIB transition in the Galapagos plume.•The mantle potential temperature of the plume changed from ∼1650 to ∼1550 °C between 90–70 Ma.•A dominant pyroxenite component is observed for the first time at ∼70 Ma in the Quepos terrane.•The presence of a dense pyroxenite component may explain the observed Tp decrease.•Nb/Nb⁎ enrichments and radiogenic Pb ratios support the presence of a recycled pyroxenite source.
Summary
Plate motions relative to the hotspots over the past 4 to 7 Myr are investigated with a goal of determining the shortest time interval over which reliable volcanic propagation rates and ...segment trends can be estimated. The rate and trend uncertainties are objectively determined from the dispersion of volcano age and of volcano location and are used to test the mutual consistency of the trends and rates. Ten hotspot data sets are constructed from overlapping time intervals with various durations and starting times. Our preferred hotspot data set, HS3, consists of two volcanic propagation rates and eleven segment trends from four plates. It averages plate motion over the past ≈5.8 Myr, which is almost twice the length of time (3.2 Myr) over which the NUVEL‐1A global set of relative plate angular velocities is estimated. HS3‐NUVEL1A, our preferred set of angular velocities of 15 plates relative to the hotspots, was constructed from the HS3 data set while constraining the relative plate angular velocities to consistency with NUVEL‐1A. No hotspots are in significant relative motion, but the 95 per cent confidence limit on motion is typically ±20 to ±40 km Myr−1 and ranges up to ±145 km Myr−1. The uncertainties of the new angular velocities of plates relative to the hotspots are smaller than those of previously published HS2‐NUVEL1 (Gripp & Gordon 1990), while being averaged over a shorter and much more uniform time interval. Nine of the fourteen HS2‐NUVEL1 angular velocities lie outside the 95 per cent confidence region of the corresponding HS3‐NUVEL1A angular velocity, while all fourteen of the HS3‐NUVEL1A angular velocities lie inside the 95 per cent confidence region of the corresponding HS2‐NUVEL1 angular velocity. The HS2‐NUVEL1 Pacific Plate angular velocity lies inside the 95 per cent confidence region of the HS3‐NUVEL1A Pacific Plate angular velocity, but the 0 to 3 Ma Pacific Plate angular velocity of Wessel & Kroenke (1997) lies far outside the confidence region. We show that the change in trend of the Hawaiian hotspot over the past 2 to 3 Myr has no counterpart on other chains and therefore provides no basis for inferring a change in Pacific Plate motion relative to global hotspots. The current angular velocity of the Pacific Plate can be shown to differ from the average over the past 47 Myr in rate but not in orientation, with the current rotation being about 50 per cent faster (1.06 ± 0.10 deg Myr−1) than the average (0.70 deg Myr−1) since the 47‐Myr‐old bend in the Hawaiian–Emperor chain.
Floreana, the smallest and least inhabited island in the Galapagos, is considered both a “hell” and a “paradise”; a remote and isolated place and, at the same time, a context that today has more ...comforts and privileges than the Mainland. Extensive ethnography developed over a decade, which analyses the practices, discourses and tactics of the islanders and other social actors, shows how Floreana residents live with high levels of transformation, resemanticise, and creatively blend elements of continuity and innovation. The historical and anthropological analysis of anthropisation on this island reveals a process characterised by dynamism, paradox, and ambivalence, resulting in unique tactics of empowerment by a heterogeneous population that has, nonetheless, generated a strong local identity. The study describes a complex microislandness, in which isolation and hyper-connectivity are compatible, and where State wages, environmental protectionism, tourism, the Internet, and other global features do not impede but rather favour the concept of fleeing to and living ‘at World’s End’ in an experience that resituates the local within the global.
Three fundamental foraging patterns in air-breathing marine vertebrates have been described: epipelagic, mesopelagic and benthic. Many sea lion species with access to extensive continental shelves ...have been described as benthic foragers. Coincidently these species are considered threatened. The Galapagos sea lion Zalophus wollebaeki, a top predator in the Galapagos Islands, is also considered threatened in this ecosystem. Sea lions at the central part of the archipelago have access to a vast continental shelf. For this reason we hypothesized that sea lions within this region would dive benthically. In addition, effective protection and conservation of this species requires knowledge of their foraging patterns and habitat utilization. We investigated the diving behaviour and habitat utilization of female Z. wollebaeki of a centrally located colony situated inside the highest density area of the population using time-depth recorders and satellite telemetry. Three distinct foraging patterns were found and described (shallow, deep and bottom divers), and individuals utilizing each pattern foraged in different locations. Epipelagic, mesopelagic and benthic dives were exhibited in the sea lions' diving behaviour, but these dive types were not exclusively associated with a foraging pattern. Between foraging trips females hauled out more frequently on other islands than they did on their breeding colony. The finding of 3 distinct foraging patterns that differ spatially has direct implications for management, particularly with regard to fisheries interactions. Marine protected areas can be implemented in the regions described as Z. wollebaeki foraging areas. Z. wollebaeki's wide foraging range coupled with their use of multiple haul-out sites should be considered in future studies when determining foraging trip lengths and habitat utilization since presence/absence from the colony does not reflect foraging trip length.
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