Comparison of the quantitative determination of soil organic carbon in coastal wetlands containing reduced forms of Fe and S

The performance of the Walkley–Black wet oxidation chemical method for soil organic carbon (SOC) determination in coastal wetland soils (mangroves, coastal lagoons, and hypersaline tidal flats) was evaluated in the state of Ceará along the semiarid coast of Brazil, assessing pyrite oxidation and its effects on soil C stock (SCS) quantification. SOC determined by the chemical oxidation method (C_WB) was compared to that assessed by means of a standard elemental analyzer (C_EA) for surficial samples (<30 cm depth) from the three wetland settings. The pyrite fraction was quantified in various steps of the chemical oxidation method, evaluating the effects of pyrite oxidation. Regardless of the method used, and consistent with site-specific physicochemical conditions, higher pyrite and SOC contents were recorded in the mangroves, whereas lower values were found in the other settings. C_WB values were higher than C_EA values. Significant differences in SCS calculations based on C_WB and C_EA were recorded for the coastal lagoons and hypersaline tidal flats. Nevertheless, the C_WB and C_EA values were strongly correlated, indicating that the wet oxidation chemical method can be used in such settings. In contrast, the absence of correlation for the mangroves provides evidence of the inadequacy of this method for these soils. Air drying and oxidation decrease the pyrite content, with larger effects rooted in oxidation. Thus, the wet oxidation chemical method is not recommended for mangrove soils, but seems appropriate for SOC/SCS quantification in hypersaline tidal flat and coastal lagoon soils characterized by lower pyrite contents.     

Multi‐kilometre long pathway of geofluids migration: Clues concerning an ophiolite serpentinization setting possibly responsible for the inferred abiotic provenance of methane in thermal water outflows of the South‐West Carpathians (Romania)

Methane occurrences displaying signatures of a possible abiotic origin had previously been reported in the South‐West Carpathians (Romania). Such an accumulation, at Tisovi?a, was intercepted by a well drilled in an ophiolitic rocks massif, whereas in two other localities—situated tens of kilometres faraway—the concerned methane is released via thermal groundwater outflows that are apparently not associated with any ultramafic products. By using groundwater ionic compositions, corroborated with previously published isotopic (¹³C‐CH₄, ²H‐CH₄, ³He/⁴He) and molecular gas analyses, we assessed in more detail the conjectured abiotic provenance of methane, and quantitatively investigated the hypothesis of a progressive mixing between two, abiotic and thermogenic, methane end‐members. The corresponding geofluids behaviour was modelled by hypothesizing a “concealed” ophiolite serpentinization setting (largely similar to that at Tisovi?a), whose abiotic methane production was “diverted” towards remote discharges at ground surface, via a ~20‐km‐long flowpath supposedly generated by recently operating extensional tectonics.     

Multiscale Variability of Twenty-Two Coastal Phytoplankton Time Series: a Global Scale Comparison

We provide an introduction and a foreword to the Special Issue “Phytoplankton Time Series in Estuaries and Coastal Ecosystems”. This issue includes long-term investigations (10–40 years) of 22 coastal ecosystems and a comparative analysis of chlorophyll a from 84 time series. The results and conclusions provided by these studies help to illuminate the disparities and similarities in long-term phytoplankton dynamics among a wide range of coastal systems and provide insight into the major driving factors responsible for short- and long-term trends in phytoplankton communities.     

The composition of garnet in garnet-rich rocks in the southern Proterozoic Curnamona Province, Australia: an indicator of the premetamorphic physicochemical conditions of formation

Garnet-rich rocks occur throughout the Proterozoic southern Curnamona Province, Australia, where they are, in places, spatially related to Broken Hill-type Pb-Zn-Ag deposits. Fine-scale bedding in these rocks, their conformable relationship with enclosing metasedimentary rocks, and their enrichment in Mn and Fe suggest that they are metamorphosed chemical precipitates. They formed on the floor of a 1.69?Ga continental rift basin from hydrothermal fluids mixed with seawater and detritus. Garnet in garnet-quartz and garnet-amphibole rocks is generally light rare earth element (LREE) depleted, and has flat heavy REE (HREE) enriched chondrite-normalized REE patterns, and negative Eu anomalies (Eu/Eu*?<?1). Garnet in garnet-rich rocks from the giant Broken Hill deposit has similar REE patterns and either positive (Eu/Eu*?>?1) or negative Eu anomalies. Manganese- and Mn-Ca-rich, Fe-poor garnets in garnetite, garnet-hedenbergite, and garnet-cummingtonite rocks at Broken Hill have Eu/Eu*?>?1, whereas garnet in Mn-poor, Fe-rich quartz garnetite and quartz-garnet-gahnite rocks from Broken Hill, and quartz garnetite from other locations have Eu/Eu*?<?1. The REE patterns of garnet and its host rock and interelement correlations among REEs and major element contents in garnet and its host rock indicate that the Eu anomaly in garnet reflects that of its host rock and is related to the major element composition of garnet and its host rock. The value of Eu/Eu* in garnet is related to its Mn, Fe, and Ca content and that of its host rock, and the distribution of REEs among garnet and accessory phases (e.g., feldspar). Positive Eu anomalies reflect high amounts of Eu that was preferentially incorporated into Mn- and Mn-Ca-rich oxides and carbonates in the protolith. In contrast, Eu/Eu*?<?1 indicates the preferential discrimination against Eu by Fe-rich, Mn-poor precursor minerals. Precursors to Mn-rich garnets at Broken Hill formed by precipitation from cooler and more oxidized hydrothermal fluids compared to those that formed precursors to Mn-poor, Fe-rich garnet at Broken Hill and the other locations. Garnet from the Broken Hill deposit is enriched in Zn (> 400?ppm), Cr (> 140?ppm), and Eu (up to 6?ppm and positive Eu anomalies), and depleted in Co, Ti, and Y compared to garnet in garnet-rich rocks from other localities. These values, as well as MnO contents ?>?15 wt. % and Eu/Eu*?>?1 are only found at the Broken Hill deposit and are good indicators of the presence of Broken Hill-type mineralization.     

New constraints on the Messinian sealevel drawdown from 3D seismic data of the Ebro Margin,western Mediterranean

We present new 3D seismic and well data from the Ebro Margin, NW Mediterranean Sea, to shed new light on the processes that formed the Messinian Erosion Surfaces (MES) of the Valencia Trough (Mediterranean Sea). We combine these data with backstripping techniques to provide a minimum estimate of the Messinian sea level fall in the EBRO Margin, as well as coupled isostasy and river incision and transport modeling to offer new constraints on the evolution of the adjacent subaerial Ebro Basin. Four major seismic units are identified on the Cenozoic Ebro Margin, based on the seismic data, including two major prograding megasequences that are separated by a major unconfirmity: the MES. The 3D seismic data provide an unprecedented view of the MES and display characteristic features of subaerial incision, including a drainage network with tributaries of at least five different orders, terraces and meandering rivers. The Messinian landscape presents a characteristic stepped‐like profile that allows the margin to be subdivided in three different regions roughly parallel to the coastline. No major tectonic control exists on the boundaries between these regions. The boundary between the two most distal regions marks the location of a relatively stable base level, and this is used in backstripping analysis to estimate the magnitude of sea level drop associated with the Messinian Salinity Crisis on the Ebro Margin. The MES on the Ebro Margin is dominated by a major fluvial system, that we identify here as the Messinian Ebro River. The 3D seismic data, onshore geology and modeling results indicate that the Ebro River drained the Ebro Basin well in advance of the Messinian.     

Evidence that Synchrotron Emission from Nonthermal Electrons Produces the Increasing Submillimeter Spectral Component in Solar Flares

We investigate the origin of the increasing spectra observed at submillimeter wavelengths detected in the flare on 2 November 2003 starting at 17:17 UT. This flare, classified as an X8.3 and 2B event, was simultaneously detected by RHESSI and the Solar Submillimeter Telescope (SST) at 212 and 405 GHz. Comparison of the time profiles at various wavelengths shows that the submillimeter emission resembles that of the high-energy X rays observed by RHESSI whereas the microwaves observed by the Owens Valley Solar Array (OVSA) resemble that of ∼50 keV X rays. Moreover, the centroid position of the submillimeter radiation is seen to originate within the same flaring loops of the ultraviolet and X-ray sources. Nevertheless, the submillimeter spectra are distinct from the usual microwave spectra, appearing to be a distinct spectral component with peak frequency in the THz range. Three possibilities to explain this increasing radio spectra are discussed: (1) gyrosynchrotron radiation from accelerated electrons, (2) bremsstrahlung from thermal electrons, and (3) gyrosynchrotron emission from the positrons produced by pion or radioactive decay after nuclear interactions. The latter possibility is ruled out on the grounds that to explain the submillimeter observations requires 3000 to 2×10⁵ more positrons than what is inferred from X-ray and γ-ray observations. It is possible to model the emission as thermal; however, such sources would produce too much flux in the ultraviolet and soft X-ray wavelengths. Nevertheless we are able to explain both spectral components at microwave and submillimeter wavelengths by gyrosynchrotron emission from the same population of accelerated electrons that emit hard X rays and γ rays. We find that the same 5×10³⁵ electrons inferred from RHESSI observations are responsible for the compact submillimeter source (0.5 arcsec in radius) in a region of 4500 G low in the atmosphere, and for the traditional microwave spectral component by a more extended source (50 arcsec) in a 480 G magnetic field located higher up in the loops. The extreme values in magnetic field and source size required to account for the submillimeter emission can be relaxed if anisotropy and transport of the electrons are taken into account.     

Coupling the terrestrial hydrology model with biogeochemistry to the integrated LAND surface model: Amazon Basin applications

ABSTRACT

We coupled the hydrologic routing and flood dynamics model Terrestrial Hydrology Model with Biogeochemistry (THMB) to the Integrated LAND Surface Model (INLAND) and compared simulations of the discharge and flood extent area against gauge station and satellite-based information in the Amazon Basin. The coupled model represents well the seasonality of the flooding and discharge, but underestimates both of them. This can be related to an already discussed underestimate of the precipitation in the east of the Andes Mountains. A photosynthesis limitation on the flooded area was also included, showing changes in plant productivity and reduction in vegetation carbon stocks. Despite its limitations, the model proves to be a valuable tool for studies of the hydrological cycle and flood dynamics response to climate change projections, allowing it to be used to represent the feedbacks between continental surface water cycle and vegetation.     

Holocene small mammals hunted by owls and humans in southern Brazil: taphonomic evidence and biological significance

Understanding resource utilization and economic diversification amongst Holocene hunter‐gatherers in southern Brazil requires in‐depth taphonomic analysis of faunal assemblages. Three Early to Late Holocene archaeological sites (Garivaldino, Pilger and Sangão) in Rio Grande do Sul State, southern Brazil, revealed large assemblages of small mammal (?1 kg) remains, composed mainly of rodents. To appreciate depositional processes of fauna in relation to human consumption, taphonomic attributes and processes were evaluated. The results indicated that the remains accumulated through different antemortem taphonomic pathways, apparently linked to the size and natural history of the species represented. The small‐ and medium‐sized (<150 g) cricetid rodents (e.g. Pseudoryzomys simplex and Sooretamys angouya) were represented by a low proportion of teeth with lightly digestive corrosion suggesting that they were derived from the predatory activity of owls, possibly Tyto alba. In contrast, large‐sized cricetids (>150 g; Kunsia tomentosus, Gyldenstolpia sp. and Holochilus sp.), and several caviomorph rodents with aggregated spatial distributions (Echimyidae (?Dicolpomys fossor, Phyllomys sp., ?Clyomys riograndensis and ?Euryzygomatomys mordax), Caviidae (Cavia sp.) and Ctenomyidae (Ctenomys sp.)) showed evidence of thermoalteration patterns and cut marks on bones, suggesting human exploitation. A postmortem depositional environment was deduced from dendritic and branched patterns of rootlet etching, apparent mostly at Garivaldino and Pilger. Polished areas and holes on bone surfaces, and impregnation of manganese showed moderate (Sangão) or low (Garivaldino and Pilger) incidence, pointing to water transport under moderate (Pilger) and low (Garivaldino and Sangão) energy over short distances. The results obtained here provide the first clear evidence of early human exploitation of small mammals in southern Brazil, suggesting a diversification of economies. In addition, as several of the recorded rodents are today regionally or biologically extinct, a preliminary discussion about the potential impact of humans on this process is provided.     

Magnetochronology of synorogenic Miocene foreland sediments in the Fars arc of the Zagros Folded Belt (SW Iran)

The timing of deformation in the northern Zagros Folded Belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences. The foreland basin infill in the northern part of the Fars arc is composed of supratidal sabkha deposits (Razak Fm), medium‐grained deltaic deposits (Agha Jari Fm) and coarse conglomerates of nearshore fan delta deposits at the base (Bakhtyari Fm, Bk1) and continental alluvial deposits at the top of the section (Bakhtyari Fm, Bk2). A magnetostratigraphic study was carried out in a composite section spanning about 1300 m on the northern flank of the Chahar–Makan syncline. Magnetostratigraphic correlation of the Razak Fm with chron C6n yields an age of 19.7 Ma at the base of the composite section. The transition to Agha Jari Fm is correlated with chron C5Cn, yielding an age of 16.6 Ma. The transition to the conglomerates of the Bakhtyari Fm (Bk1) correlates with the chron C5AD at approximately 14.8 Ma, which is considerably older than previously thought. The base of the Bakhtyari Fm growth strata, and thus the beginning of the deformation in northern Fars, is dated at 14–15 Ma. The topmost preserved Bakhtyari Fm (Bk1) is folded and unconformably overlain by Bakhtyari Fm (Bk2) conglomerates. This indicates that tectonic deformation in northern Zagros was already underway in the Middle Miocene.     

Lichenometric dating using Rhizocarpon subgenus Rhizocarpon in the Patagonian Andes, Argentina

This study represents the first attempt to develop and apply lichenometric dating curves of Rhizocarpon subgenus Rhizocarpon for dating glacier fluctuations in the Patagonian Andes. Six glaciers were studied along the Patagonian Andes. Surfaces of known ages (historical evidences and tree-ring analyses) were used as control sites to develop indirect lichenometric dating curves. Dating curves developed for the studied glaciers show the same general logarithmic form, indicating that growth rate of subgenus Rhizocarpon decreases over time. The strong west–east precipitation gradient across the Andean Cordillera introduces statistically significant differences in the growth curves, with faster growth rates in the moist west sites than the drier eastern sites. Latitudinal difference among the studied glaciers does not appear to be a major factor regulating lichen growth rates. Therefore, we developed two lichenometric curves for dating glacier fluctuations in wetter and drier sites in the Patagonian Andes during the past 450 yrs. Application of the developed curves to moraine dating allowed us to complement glacial chronologies previously obtained by tree-ring analyses. A first chronosequence for moraine formation in the Torrecillas Glacier (42°S) is presented. Our findings confirm the utility of lichenometry to date deglaciated surfaces in the Patagonian Andes.