Volcanic Substrates Research Articles

Pattern and process of vegetation change (succession) on two northern New Zealand island volcanoes

Pattern and process of vegetation change (succession) were compared on two northern North Island volcanoes: Whakaari (White Island) and Rangitoto Island where the endemic woody tree Metrosideros excelsa is the primary colonizer of raw volcanic substrates. Quantitative data from our previous publications (see References) and the references therein illustrate sequences of vegetation succession following significant volcanic eruptions. New information on Rangitoto Island M. excelsa patch dynamics and updated vascular species statistics for Whakaari have also been included. We also draw on supporting data from M. excelsa forest on the mainland and long-inactive volcanic islands in the Bay of Plenty, to provide a context for understanding the vegetation dynamics on Whakaari and Rangitoto Island. Species facilitation, light availability, humidity, substrate and disturbance history are all key determinants of vegetation succession across these volcanic landscapes.

Chemical Modifications and Diatom Community Development on Volcanic Clayey Sediments During an Indoor Maturation Experiment

Maturation experiments of volcanic mud samples with mineral water were followed up during 120 days at constant room temperature (20ºC) to track geochemical modifications induced by the process and, eventually, the development of diatom communities. Different abiotic conditions were tested during the experiments. Mud samples were collected in Azores and Madeira Archipelagos (Portugal) and the biological inoculum was collected from the edge of a fumarole from Azores (Portugal). The assemblages of diatoms were dominated by Nitzschia species both in the inoculum and on maturated muds. Although one of the samples from São Miguel island (Azores) was dominated by Nitzschia cf. thermalis var. minor, the mud sample from Porto Santo (Madeira) allowed the development mainly of Nitzschia communis during maturation experiments. Associations between chemical composition and samples’ mineralogical signature were established by cluster analysis. Slight enrichment on Na+ and Ca2+ was detected in samples after maturation and exchangeable cations content was improved by the process. This research includes a multidisciplinary approach that contributes to the understanding of interactions between volcanic substrates and specific diatom species and geochemical modifications induced by maturation in volcanic materials.

First combined flux chamber survey of mercury and CO2 emissions from soil diffuse degassing at Solfatara of Pozzuoli crater, Campi Flegrei (Italy): Mapping and quantification of gas release

There have been limited studies to date targeting gaseous elemental mercury (GEM) flux from soil emission in enriched volcanic substrates and its relation with CO2 release and tectonic structures. In order to evaluate and understand the processes of soil–air exchanges involved at Solfatara of Pozzuoli volcano, the most active zone of Campi Flegrei caldera (Italy), an intensive field measurement survey has been achieved in September 2013 by using high-time resolution techniques. Soil–air exchange fluxes of GEM and CO2 have been measured simultaneously at 116 points, widely distributed within the crater. Quantification of gas flux has been assessed by using field accumulation chamber method in conjunction with a Lumex®-RA 915+ portable mercury vapor analyzer and a LICOR for CO2 determination, respectively. The spatial distribution of GEM and CO2 emissions correlated quite closely with the hydrothermal and geological features of the studied area. The highest GEM fluxes (from 4.04 to 5.9×10−5gm−2d−1) were encountered close to the southern part of the crater interested by an intense fumarolic activity and along the SE–SW tectonic fracture (1.26×10−6–6.91×10−5gGEMm−2d−1). Conversely, the lowest values have been detected all along the western rim of the crater, characterized by a weak gas flux and a lush vegetation on a very sealed clay soil, which likely inhibited mercury emission (range: 1.5×10−7–7.18×10−6gGEMm−2d−1). Results indicate that the GEM exchange between soil and air inside the Solfatara crater is about 2–3 orders of magnitude stronger than that in the background areas (10−8–10−7gm−2d−1). CO2 soil diffuse degassing exhibited an analogous spatial pattern to the GEM fluxes, with emission rates ranging from about 15 to ~20,000gCO2m−2d−1, from the outermost western zones to the south-eastern sector of the crater. The observed significant correlation between GEM and CO2 suggested that in volcanic system GEM volatilizes from substrate in a similar manner to the release of CO2. The quantitative estimation of the total amount of CO2 and GEM released from the Solfatara crater gave values of about 304±13 and 3.7±0.2×10−6td−1, respectively. Finally, based on our dataset and previous work, we propose that an average GEM/CO2 molar ratio of ~2×10−8 (n=9) is best representative of hydrothermal degassing. Taking into account the uncertainty in global hydrothermal CO2 emissions from sub-aerial environments (~1012Molyr−1), we infer a global volcanic GEM flux from hydrothermal environments of ~about 8.5tyr−1. Although this value has to be considered as a lower limit for the global emission of GEM from these sources, we suggest that on a local scale hydrothermal activity can be regarded as a significant source of GEM than previously recognized to the atmospheric pool.

Naturally occurring heavy radioactive elements in the geothermal microcosm of the Los Azufres (Mexico) volcanic complex

The Los Azufres geothermal complex of central Mexico is characterized by fumaroles and boiling hot-springs. The fumaroles form habitats for extremophilic mosses and ferns. Physico-chemical measurements of two relatively pristine fumarolic microcosms point to their resemblance with the paleo-environment of earth during the Ordovician and Devonian periods. These geothermal habitats were analysed for the distribution of elemental mass fractions in the rhizospheric soil (RS), the native volcanic substrate (VS) and the sediments (S), using the new high-sensitivity technique of polarized x-ray energy dispersive fluorescence spectrometry (PEDXRF) as well as instrumental neutron activation analysis (INAA) for selected elements. This work presents the results for the naturally occurring heavy radioactive elements (NOHRE) Bi, Th and U but principally the latter two. For the RS, the density was found to be the least and the total organic matter content the most. Bi was found to be negligibly present in all substrate types. The average Th and U mass fractions in the RS were higher than in the VS and about equal to their average mass fractions in the S. The VS mass fraction of Th was higher, and of U lower, than the mass fractions in the earth's crust. In fact for the fumaroles of one site, the average RS mass fractions of these elements were higher than the averaged values for S (without considering the statistical dispersion). The immobilization of the NOHRE in the RS is brought about by the bio-geochemical processes specific to these extremophiles. Its effectiveness is such that despite the small masses of these plants, it compares with, or may sometimes exceed, the immobilization of the NOHRE in the S by the abiotic and aggressive chemical action of the hot-springs. These results indicate that the fumarolic plants are able to transform the volcanic substrate to soil and to affect the NOHRE mass fractions even though these elements are not plant nutrients. Mirrored back to the paleo times when such plant types were ubiquitous, it would mean that the first plants contributed significantly to pedogenesis and the biogeochemical recycling of even the heaviest and radioactive elements. Such plants may potentially be useful for the phytostabilisation of soil moderately contaminated by the NOHRE. Furthermore where applicable, geochronology may require taking into account the influence of the early plants on the NOHRE distributions.

Diameter growth rates of tawa (Beilschmiedia tawa) across the middle North Island, New Zealand – implications for sustainable forest management

Tawa (Beilschmiedia tawa (A. Cunn.) Kirk) remains a minor but significant hardwood timber in New Zealand, currently sourced from tawa-dominant forest on freehold and Maori land where selective harvesting under sustainable management plans is permitted. Sustainable management plans require reliable tree growth estimates, which are used to calculate annual volume increment and harvest levels. The aims of this study were to model the relationship between diameter growth rate and tree size using existing data, and to determine the influences of within-stand competition, local climate and soil parent material on growth rates. A dataset was compiled on the diameter growth rates of nearly 1800 trees from a wide range of published and unpublished sources for the middle North Island. Non-linear quantile regressions were used to model average growth and growth of the fastest 25% of stems, termed rapid growth. Across the middle North Island, average growth of a 400 mm DBH (diameter at breast height) tree was 1.8 mm year−1 and rapid growth was 2.8 mm year−1. Overall, the model accounted for 12% of the total variation in growth rate. The effect of size on diameter growth rate was modest but positive. Within-stand competition reduced tawa diameter growth rates, particularly when basal area exceeded 100 m2 ha−1. Also, climate (winter minimum temperature and annual vapour pressure deficit) had little influence on growth rates and explained 10% of variation in stem growth. The fastest growth rates were on soils derived from Tertiary mudstone in inland Taranaki. Most of the existing data on growth rates of tawa are for trees growing on volcanic substrates. This means that the markedly faster growth on some sedimentary rather than volcanic substrates suggests that growth rates and volume increment may be underestimated for many sites in the middle North Island beyond the Volcanic Plateau. A growth dataset more representative of the range of substrates occupied by tawa is needed for management plans elsewhere in the North Island.

CHERTS OF THE BARBERTON GREENSTONE BELT, SOUTH AFRICA: PETROLOGY AND TRACE-ELEMENT GEOCHEMISTRY OF 3.5 TO 3.3 GA OLD SILICIFIED VOLCANICLASTIC SEDIMENTS

Research Article| December 01, 2013 CHERTS OF THE BARBERTON GREENSTONE BELT, SOUTH AFRICA: PETROLOGY AND TRACE-ELEMENT GEOCHEMISTRY OF 3.5 TO 3.3 GA OLD SILICIFIED VOLCANICLASTIC SEDIMENTS A. HOFMANN; A. HOFMANN Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa, e-mail: ahofmann@uj.ac.za Search for other works by this author on: GSW Google Scholar R. BOLHAR; R. BOLHAR Department of Geology, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa School of Earth Sciences, University of Queensland, Brisbane, Qld 4072, Australia, e-mail: rbolhar71@gmail.com Search for other works by this author on: GSW Google Scholar B. ORBERGER; B. ORBERGER ERAMET, 1 Avenue Albert Einstein, 78190 Trappes, France, Université Paris Sud XI, UMR IDES 8148, Département des Sciences de la Terre, Bât 504-509, 91405 Orsay Cedex, France, e-mail: beate.orberger@erametgroup.com Search for other works by this author on: GSW Google Scholar F. FOUCHER F. FOUCHER Centre de Biophysique Moléculaire, CNRS, Rue Charles Sadron, 45071 Orléans, France, e-mail: frederic.foucher@cnrs-orleans.fr Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2013) 116 (2): 297–322. https://doi.org/10.2113/gssajg.116.2.297 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. HOFMANN, R. BOLHAR, B. ORBERGER, F. FOUCHER; CHERTS OF THE BARBERTON GREENSTONE BELT, SOUTH AFRICA: PETROLOGY AND TRACE-ELEMENT GEOCHEMISTRY OF 3.5 TO 3.3 GA OLD SILICIFIED VOLCANICLASTIC SEDIMENTS. South African Journal of Geology 2013;; 116 (2): 297–322. doi: https://doi.org/10.2113/gssajg.116.2.297 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract A suite of green and carbonaceous black chert interbedded with submarine volcanic rocks from several stratigraphic levels of the Onverwacht Group of the Barberton greenstone belt, from the top of the ~3.48 Ga Komati Formation to the base of the ~3.26 Ga Fig Tree Group have been investigated petrologically and geochemically. Provenance analysis was undertaken using immobile trace element ratios in comparison with potential source rocks from the Barberton granitoid-greenstone terrain. Raman spectroscopy was used to better characterise carbonaceous matter in different chert varieties. Green cherts consist predominantly of silicified mafic to ultramafic volcaniclastic material. Black cherts contain volcaniclastic and/or epiclastic material of ultramafic to felsic composition, admixed with carbonaceous matter. In several cases, the clastic sediment is compositionally distinct to the volcanic substrate, suggesting that it represents volcanic material of relatively distal sources. Soon after settling out of the water column, lithification due to silicification took place. It gave rise to excellent textural preservation, but strongly modified the mineralogical and chemical composition of the seafloor sediments. Zircon, Cr-spinel and rare phosphate minerals are the only primary minerals remaining, while clastic grains have been largely replaced by a fine intergrowth of microquartz, Ti-oxide and K-bearing mica. Chemical changes are similar to those reported previously for silicification of volcanic rocks from the Barberton belt and are consistent with low-temperature hydrothermal processes common to the Palaeoarchaean seafloor environment. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Resilience against exotic species invasion in a tropical montane forest

AbstractQuestionHow do canopy disturbance and soil properties structure vascular plant community species composition and resilience to encroachment by exotic species in a tropical montane wet forest?LocationHawai'i Experimental Tropical Forest (HETF), a tropical montane wet forest, on Mauna Kea, Hawai'i Island, Hawai'i, USA.MethodsPrevious studies employing airborne LiDAR were used to define three zones across an elevation gradient from 900 to 1500 m. Within each zone, a ~1000‐m block transect was selected to cross two different volcanic substrates: one derived from surface lava and one derived from thick ash deposits. Non‐metric multidimensional scaling (NMS) scores of vegetation data were related to independently‐derived environmental NMS scores and spatial location with generalized additive models (GAM).ResultsVascular plant species composition in all elevation zones consists of three NMS axes, which are best modelled by one of three possible environmental NMS axes or by location. The first NMS axis of species composition in the lowest elevation zone (40% variance explained (VE)) is a function of location on volcanic substrates (61% deviance explained (DE)). The second lowest elevation axis (27% VE) is a function of unexplained spatial heterogeneity (31% DE). The third lowest elevation NMS axis (24% VE) is a function of the spatial mosaic of canopy disturbance (16% DE). In the middle elevation zone, species composition most strongly relates to the interaction between volcanic substrate and the condition of the soil surface for all three NMS axes (41%, 27%, 24% VE; 70%, 16%, 24% DE). The primary axis of species composition in the highest elevation zone (41% VE) corresponds with substrate and soil condition (55% DE) but the second and third axes of species composition (27% and 25% VE) relate to canopy dieback disturbance (36%, 14% DE). Counts of exotic species and 0–2 m height class native tree species respond to the type of volcanic substrate and soil surface condition in all three elevation zones. Lava‐derived substrates have a higher incidence of exotic species and less native tree regeneration; whereas ash‐derived substrates have higher numbers of native tree species regenerating and many fewer exotic species.DiscussionThe tropical montane forests on Mauna Kea reflect a native‐dominated plant community response to disturbance on both lava‐ and ash‐derived volcanic substrates, and a higher propensity for exotic species to occur on the lava‐derived substrate. Native plant communities on ash‐derived soils may have higher resilience to exotic invasion than communities on lava‐derived substrates. Our results indicate resource managers should explicitly account for variation in soils and substrate type when prioritizing, implementing and monitoring management interventions to foster native plant assemblages and control the spread of exotic and invasive species.

Contrasting radon background levels in volcanic settings: clues from 220Rn activity concentrations measured during long-term deformation experiments

To better understand the mechanisms leading to different radon background levels in volcanic settings, we have performed two long-term deformation experiments of 16 days using a real-time setup that enables us to monitor any variation of radon activity concentration during rock compression. Our measurements demonstrate that, in the case of highly porous volcanic rocks, the emanating power of the substrate changes as a function of the volcanic stress conditions. Constant magmatic pressures, such as those observed during dike intrusions and hydrothermal fluid injections, can result in pervasive pore collapse that is mirrored by a significant radon decrease until a constant emanation is achieved. Conversely, repeated cycles of stress due to, for example, volcano inflation/deflation cycles, cause a progressive radon increase a few days (but even weeks and months) before rupture. After rock failure, however, the formation of new emanation surfaces leads to a substantial increase of the radon signal. Our results suggest that surface deformation in tectonic and volcanic settings, such as inflation/deflation or constant magmatic pressures, have important repercussions on the emanating power of volcanic substrates.

Origin of the Hawaiian rainforest and its transition states in long-term primary succession

Abstract. This paper addresses the question of transition states in the Hawaiian rainforest ecosystem with emphasis on their initial developments. Born among volcanoes in the north central Pacific about 4 million years ago, the Hawaiian rainforest became assembled from spores of algae, fungi, lichens, bryophytes, ferns and from seeds of about 275 flowering plants that over the millennia evolved into ca. 1000 endemic species. Outstanding among the forest builders were the tree ferns (Cibotium spp.) and the 'ōhi'a lehua trees (Metrosideros spp.), which still dominate the Hawaiian rainforest ecosystem today. The structure of this forest is simple. The canopy in closed mature rainforests is dominated by cohorts of Metrosideros polymorpha and the undergrowth by tree fern species of Cibotium. When a new lava flow cuts through this forest, kipuka are formed, i.e., islands of remnant vegetation. On the new volcanic substrate, the assemblage of plant life forms is similar to the assemblage during the evolution of this system. In open juvenile forests, a mat-forming fern, the uluhe fern (Dicranopteris linearis), becomes established. It inhibits further regeneration of the dominant 'ōhi'a tree, thereby reinforcing the cohort structure of the canopy guild. In the later part of its life cycle, the canopy guild breaks down often in synchrony. The trigger is hypothesized to be a climatic perturbation. After the disturbance, the forest becomes reestablished in about 30–40 yr. As the volcanic surfaces age, they go from a mesotrophic to a eutrophic phase, reaching a biophilic nutrient climax by about 1–25 K yr. Thereafter, a regressive oligotrophic phase follows; the soils become exhausted of nutrients. The shield volcanoes break down. Marginally, forest habitats change into bogs and stream ecosystems. The broader 'ōhi'a rainforest redeveloping in the more dissected landscapes of the older islands loses stature, often forming large gaps that are invaded by the aluminum tolerant uluhe fern. The 'ōhi'a trees still thrive on soils rejuvenated from landslides and from Asian dust on the oldest (5 million years old) island Kaua'i but their stature and living biomass is greatly diminished.

Toponymic Data Helps to Reveal the Occurrence of Previously Unknown Populations of Wild Zamia pumila L. on Volcanic Substrates in South Central Puerto Rico

This is the first report of the occurrence of wild Zamia pumila L. Zamiaceae populations on various volcanic substrates in the piedmont area of south central Puerto Rico. Data acquisition and its field confirmation were possible after the identification of toponymic names in old and current maps, and historic documents of the island in which one of the indigenous names for the genus (marunguey [marungüey] or marungueyes) has been used for naming some localities. These preliminary data have deep implications for paleo- and neoethnobotanical research, and for population ecology of the species in Puerto Rico, because they expand the traditionally accepted range for the species on the island. Zamia has been described as one of the main food plants among pre- and post-Columbian inhabitants in two islands of the Greater Antilles, Hispaniola and Puerto Rico, where the most sophisticated pre-Columbian society of the Antilles, the Taínos, emerged. Our findings suggest that Zamia might have been more available to humans, as a food source, than previously thought.

Toponymic Data Helps to Reveal the Occurrence of Previously Unknown Populations of Wild Zamia pumila L. on Volcanic Substrates in South Central Puerto Rico

This is the first report of the occurrence of wild Zamia pumila L. Zamiaceae populations on various volcanic substrates in the piedmont area of south central Puerto Rico. Data acquisition and its field confirmation were possible after the identification of toponymic names in old and current maps, and historic documents of the island in which one of the indigenous names for the genus (marunguey [marungüey] or marungueyes) has been used for naming some localities. These preliminary data have deep implications for paleo- and neoethnobotanical research, and for population ecology of the species in Puerto Rico, because they expand the traditionally accepted range for the species on the island. Zamia has been described as one of the main food plants among pre- and post-Columbian inhabitants in two islands of the Greater Antilles, Hispaniola and Puerto Rico, where the most sophisticated pre-Columbian society of the Antilles, the Taínos, emerged. Our findings suggest that Zamia might have been more available to humans, as a food source, than previously thought.

Historical Land-Cover Classification for Conservation and Management in Hawaiian Subalpine Drylands

We used aerial photography from 1954 and airborne LiDAR and imaging spectroscopy from 2008 to infer changes in extent and location of tallstature woody vegetation in 127 km2 of subalpine dry forest on the island of Hawai'i (Pōhakuloa Training Area), and to identify 25.8 km2 of intact woody vegetation for restoration and management. Total cover of woody vegetation was 54.7 km2 in 1954 and 58.6 km2 in 2008. Approximately 28.9 km2 underwent woody vegetation change (22.7%) between 1954 and 2008. Increases in woody vegetation cover occurred in 16.4 km2, and 12.5 km2 represented reduction of woody vegetation cover (12.9% and 9.8% of the 127 km2 study area, respectively). Our findings suggest that 3.9 km2 (3.0%) experienced a net increase in woody vegetation cover between 1954 and 2008. Spatial patterns suggest that fires may be the primary driver of reductions in woody vegetation cover. Increases could be due to regeneration of dry forest trees or measurement errors associated with historical imagery. Areas remaining in woody vegetation cover over the 53-yr study interval can be targeted for restoration and management. We discuss challenges to integrating historical photography with contemporary conservation and management in Hawai'i and the Pacific and we outline additional studies that would help to improve estimates. The methods and analysis are general and could be applied to other dryland ecosystems with complex volcanic substrates in Hawai'i and the Pacific.

Runoff generation in a steep, tropical montane cloud forest catchment on permeable volcanic substrate

Most studies to date in the humid tropics have described a similar pattern of rapid translation of rainfall to runoff via overland flow and shallow subsurface stormflow. However, study sites have been few overall, and one particular system has received very little attention so far: tropical montane cloud forests (TMCF) on volcanic substrate. While TMCFs provide critical ecosystem services, our understanding of runoff generation processes in these environments is limited. Here, we present a study aimed at identifying the dominant water sources and pathways and mean residence times of soil water and streamflow for a first‐order, TMCF catchment on volcanic substrate in central eastern Mexico. During a 6‐week wetting‐up cycle in the 2009 wet season, total rainfall was 1200 mm and storm event runoff ratios increased progressively from 11 to 54%. With the increasing antecedent wetness conditions, our isotope and chemical‐based hydrograph separation analysis showed increases of pre‐event water contributions to the storm hydrograph, from 35 to 99%. Stable isotope‐based mean residence times estimates showed that soil water aged only vertically through the soil profile from 5 weeks at 30 cm depth to 6 months at 120 cm depth. A preliminary estimate of 3 years was obtained for base flow residence time. These findings all suggest that shallow lateral pathways are not the controlling processes in this tropical forest catchment; rather, the high permeability of soils and substrate lead to vertical rainfall percolation and recharge of deeper layers, and rainfall‐runoff responses appeared to be dominated by groundwater discharge from within the hillslope.

Seagrass-Meadow Sedimentary Facies In A Mixed Siliciclastic-Carbonate Temperate System In the Tyrrhenian Sea (Pontinian Islands, Western Mediterranean)

Abstract The paper presents the characteristics of surface sediments in a seagrass-dominated environment of the inner shelf of the Pontinian Islands (Tyrrhenian Shelf, Central Mediterranean). The aims of this work are to characterize the carbonate production and sedimentary processes of a representative high-latitude, temperate Posidonia oceanica–dominated area, to discuss the role of seagrass in the siliciclastic–carbonate mixing processes, which provide analogs for interpreting the occurrence and importance of these types of deposits in the rock record. The majority of sediments are poorly sorted siliciclastic skeletal sand. Based on grain type and abundance and carbonate content, these deposits include six subfacies. The different subfacies reflect environmental changes within the seagrass environment associated with variations in light penetration and hydrodynamic conditions. Additionally, the seagrass facies range from purely carbonate to mixed carbonate–siliciclastic, depending on the amount of siliciclastic input and on the capacity of seagrasses to trap allochthonous sediments while hosting carbonate-producing biota. The type of substrate and the erosion and transport processes control the siliciclastic input. In these Pontinian seagrass meadows, sedimentary facies contain abundant siliciclastic grains produced by erosion of the volcanic substrate and trapped by seagrass blades and rhizomes. This Pontinian example illustrates that in heterozoan-dominated seagrass settings, mud-producing green algae are not present or are not calcifying, and consequently, seagrass deposits are much more grainy than photozoan counterparts. Ancient heterozoan tropical seagrass deposits likely will be discriminated from their temperate or subtropical counterparts only by careful taxonomic analysis of skeletal grains.

Long‐term carbon storage through retention of dissolved aromatic acids by reactive particles in soil

AbstractSoils retain large quantities of carbon, thereby slowing its return to the atmosphere. The mechanisms governing organic carbon sequestration in soil remain poorly understood, yet are integral to understanding soil‐climate feedbacks. We evaluated the biochemistry of dissolved and solid organic carbon in potential source and sink horizons across a chronosequence of volcanic soils in Hawai'i. The soils are derived from similar basaltic parent material on gently sloping volcanic shield surfaces, support the same vegetation assemblage, and yet exhibit strong shifts in soil mineralogy and soil carbon content as a function of volcanic substrate age. Solid‐state13carbon nuclear magnetic resonance spectra indicate that the most persistent mineral‐bound carbon is comprised of partially oxidized aromatic compounds with strong chemical resemblance to dissolved organic matter derived from plant litter. A molecular mixing model indicates that protein, lipid, carbohydrate, and char content decreased whereas oxidized lignin and carboxyl/carbonyl content increased with increasing short‐range order mineral content. When solutions rich in dissolved organic matter were passed through Bw‐horizon mineral cores, aromatic compounds were preferentially sorbed with the greatest retention occurring in horizons containing the greatest amount of short‐range ordered minerals. These minerals are reactive metastable nanocrystals that are most common in volcanic soils, but exist in smaller amounts in nearly all major soil classes. Our results indicate that long‐term carbon storage in short‐range ordered minerals occurs via chemical retention with dissolved aromatic acids derived from plant litter and carried along preferential flow‐paths to deeper B horizons.

Soil properties, strontium isotopic signatures and multi‐element profiles to authenticate the origin of vegetables from small‐scale regions: illustration with early potatoes from southern Italy

We propose a method for the authentication of the origin of vegetables grown under similar weather conditions, in sites less than 10 km distance from the sea and distributed over a rather small scale area (58651 km(2)). We studied how the strontium (Sr) isotopic signature and selected elemental concentrations ([Mn], [Cu], [Zn], [Rb], [Sr] and [Cd]) in early potatoes from three neighbouring administrative regions in the south of Italy were related to the geological substrate (alluvial sediments, volcanic substrates and carbonate rocks) and to selected soil chemical properties influencing the bioavailability of elements in soils (pH, cation exchange capacity and total carbonate content). Through multiple-step multivariate statistics (PLS-DA) we could assign 26 potatoes (including two already commercialised samples) to their respective eight sites of production, corresponding to the first two types of geological substrates. The other 12 potatoes from four sites of production had similar characteristics in terms of the geological substrate (third type) and these soil properties could be grouped together. In this case, more discriminative parameters would be required to allow the differentiation between sites. The validation of our models included external prediction tests with data of potatoes harvested the year before and a study on the robustness of the uncertainties of the measurement results. Annual variations between multi-elemental and Sr isotopic fingerprints were observed in potatoes harvested from soils overlying carbonate rocks, stressing the importance of testing long term variations in authentication studies.

Interaction of Gravity Flows With a Rugged Mid-Ocean-Ridge Seafloor: An Outcrop Example from Macquarie Island

Rugged bathymetry along slow-spreading mid-ocean ridges has the potential to impinge a strong control on gravity flows derived from oceanic fault scarps. Sedimentary lithofacies from the Macquarie Island ophiolite supports this hypothesis by displaying systematic variations that correspond with volcanic substrate differences and proximity to rift-related faults. Pillow-basalt terranes are associated with tightly confined bedrock corridors that funnel gravity flows into one direction. Vertical lithofacies variations formed from high-density to low-density turbidity currents record successive fill stages of the corridor axis. During initial stages tight confinement in the axis suppressed flow dilution and fluid turbulence. With continued corridor-axis filling, more dilute gravity flows predominated and formed lateral gradations from axial coarse-grained turbidites into thinly interbedded overbank lithofacies along corridor margins. These gravity-flow lithofacies converge into very thin muddy condensed intervals along inter-corridor highs where significant bottom-current reworking occurred. Conversely, partly confined tabular-basalt-floored basins promoted lateral expansion and dilution of gravity flows throughout the duration of basin filling. Variable paleocurrent-indicator directions record multiple reflections of single gravity-flow events off basin-bounding fault barriers. Coarsening-upward trends in these partly confined basins from thinly interbedded pelagic chert and ripple-bedded sandstones up into stacked turbidites preserves the ponding of sediment-starved submarine fans. In general, these ponded basins preserve the fine-grained distal ends of a gravity-flow continuum from coarse-grained fault-proximal en masse failures and cohesionless debris flows into medial high-density turbidity flows and distal dilute turbidity flows.

Chemistry of hot springs along the Eastern Lau Spreading Center

The Eastern Lau Spreading Center (ELSC) is the southernmost part of the back-arc spreading axis in the Lau Basin, west of the Tonga trench and the active Tofua volcanic arc. Over its 397-km length it exhibits large and systematic changes in spreading rate, magmatic/tectonic processes, and proximity to the volcanic arc. In 2005, we collected 81 samples of vent water from six hydrothermal fields along the ELSC. The chemistry of these waters varies both within and between vent fields, in response to changes in substrate composition, temperature and pressure, pH, water/rock ratio, and input from magmatic gases and subducted sediment. Hot-spring temperatures range from 229° to 363 °C at the five northernmost fields, with a general decrease to the south that is reversed at the Mariner field. The southernmost field, Vai Lili, emitted water at up to 334 °C in 1989 but had a maximum venting temperature of only 121 °C in 2005, due to waning activity and admixture of bottom seawater into the subseafloor plumbing system. Chloride varies both within fields and from one field to another, from a low of 528 mmol/kg to a high of 656 mmol/kg, and may be enriched by phase separation and/or leaching of Cl from the rock. Concentrations of the soluble elements K, Rb, Cs, and B likewise increase southward as the volcanic substrate becomes more silica-rich, especially on the Valu Fa Ridge. Iodine and δ 7Li increase southward, and δ 11B decreases as B increases, apparently in response to increased input from subducted sediment as the arc is approached. Species that decrease southward as temperature falls are Si, H 2S, Li, Na/Cl, Fe, Mn, and 87Sr/ 86Sr, whereas pH, alkalinity, Ca, and Sr increase. Oxygen isotopes indicate a higher water/rock ratio in the three systems on Valu Fa Ridge, consistent with higher porosity in more felsic volcanic rocks. Vent waters at the Mariner vent field on the Valu Fa Ridge are significantly hotter, more acid and metal-rich, less saline, and richer in dissolved gases and other volatiles, including H 2S, CO 2, and F, than the other vent fields, consistent with input of magmatic gases. The large variations in geologic and geophysical parameters produced by back-arc spreading along the ELSC, which exceed those along mid-ocean ridge spreading axes, produce similar large variations in the composition of vent waters, and thus provide new insights into the processes that control the chemistry of submarine hot springs.

Mineralogical evidence for a local volcanic origin of the parent material of Bermuda Quaternary paleosols

The alternation of carbonate deposits and paleosols compose the emerged part of the Bermuda archipelago. The pedological units present a complex and diversified mineralogy. Former studies demonstrated that the paleosols are not primarily a product of the unique dissolution of the surrounding carbonates, but contain a massive input of allochthonous non-carbonate detrital material. Researchers during more than the past three decades have attributed this flux of insoluble residues (IR) to Saharan dusts. We carried out systematic field and mineralogical analyses on the Quaternary paleosols from the Bermuda archipelago. Their mineralogical assemblage predominantly includes carbonates, clay minerals (kaolinite, chlorite and chlorite/vermiculite), phosphates, and aluminium and iron oxides/hydroxides. This assemblage is strikingly close to the mineralogy of the weathered volcanic substrate of Bermuda, but noticeably different from the mineralogy of Saharan dust. Moreover, we found volcanic lithoclasts in numerous paleosol profiles all over the archipelago and in all the recorded time intervals. We thus consider the volcanic seamount underlying Bermuda as the main source of non-carbonate minerals detected in the paleosols. This hypothesis further resolves the anomalous maturity of Bermudan paleosols compared to their southern counterparts in the Bahamas and Barbados.

Phosphorus and soil development: Does the Walker and Syers model apply to semiarid ecosystems?

The Walker and Syers model of phosphorus (P) transformations during pedogenesis is widely accepted for the development of humid ecosystems, but long-term P dynamics of more arid ecosystems remain poorly understood. We tested the Walker and Syers model in semiarid piñon-juniper woodlands by measuring soil P fractions under tree canopies and in intercanopy spaces along a well-constrained, approximately 3000 ka (1 ka = 1000 years) volcanic substrate age gradient in northern Arizona, USA. The various pools of soil P behaved largely as predicted; total soil P and primary mineral P declined consistently with substrate age, labile inorganic P increased early in soil development and then declined at later stages, and organic phosphorus increased consistently across the chronosequence. Within each site, soils under tree canopies tended to have higher concentrations of labile and intermediately available P fractions compared to intercanopy soils. However, the degree of spatial heterogeneity conferred by tree islands was moderated by the stage of soil development. In contrast, tree islands had no influence on within-site distribution of more recalcitrant soil P pools, which appear to be controlled solely by the stage of pedogenesis. Coincident with declines in total P, primary mineral P, and labile inorganic P, we found that phosphatase enzyme activity increased with substrate age; a result consistent with greater ecosystem-level P demand on older, more highly weathered substrates. Our results suggest that, compared to humid climates, reduced inputs of water, energy, and acidity to semiarid ecosystems slow the rate of change in P fractions during pedogenesis, but the overall pattern remains consistent with the Walker and Syers model. Furthermore, our data imply that pedogenic change may be an important factor controlling the spatial distribution of labile P pools in semiarid ecosystems. Taken together, these data should both broaden and unify terrestrial ecosystem development theory.