Bromine soil/sediment enrichment in tidal salt marshes as a potential indicator of climate changes driven by solar activity: New insights from W coast Portuguese estuaries

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  • ... Several studies have reported the ubiquitous natural bromination of substrates such as fresh plant material, decayed litter and soil and sediment organic matter (SOM) (e.g., Leri et al., 2010;Leri and Myneni, 2012;Leri and Ravel, 2015;Joe-Wong et al., 2019), with the incorporation of Br into stable (recalcitrant) SOM components implying the longterm sequestration of both carbon and Br (e.g., Biester et al., 2004;Zaccone et al., 2008;Martínez-Cortizas et al., 2016). Within this framework, a strong direct Br-SOM relationship was found in surface and cored sediments from Portuguese salt marshes, at the SW Iberian Atlantic coast, where it was used to reconstruct past climates in connection with external (solar and volcanic) forcing (Moreno et al., 2015(Moreno et al., , 2017. Those results allowed suggesting a conceptual model for Br cycling in such settings, considering the responses to the main (abiotic and biotic) drivers (Moreno et al., 2017). ...
    ... Within this framework, a strong direct Br-SOM relationship was found in surface and cored sediments from Portuguese salt marshes, at the SW Iberian Atlantic coast, where it was used to reconstruct past climates in connection with external (solar and volcanic) forcing (Moreno et al., 2015(Moreno et al., , 2017. Those results allowed suggesting a conceptual model for Br cycling in such settings, considering the responses to the main (abiotic and biotic) drivers (Moreno et al., 2017). That model forecasted meaningful changes in Br biogeodynamics at several spatiotemporal scales under a warmer and wetter climate scenario, in which Sun's activity is a key cause of uncertainty. ...
    ... Nine surface and peat interstitial water samples were collected in the CG and LC peatlands, following Moreno et al. (2015Moreno et al. ( , 2017 for the salt marsh settings. Immediately after collection, samples were refrigerated and returned to the laboratory, where pH and conductivity values were measured. ...
    Article
    Bromine (Br) cycling in natural wetlands is highly complex, including abiotic/biotic processes and multiphase inorganic/organic Br-species. Wetland ecosystems receive Br primarily from the ocean, functioning as either sinks or sources of Br, with the overall imbalance largely decided by the prevailing climate. Aiming to trace the present-day transport of oceanogenic Br (i.e., derived from salt-water spray-droplets) and its uptake and storage in brackish and freshwater wetlands, we surveyed waters, autochthonous plants, and soils/sediments from coastal marshes and mountain peatlands in the westernmost fringe of northern Portugal. The calculated enrichment factors of bromide (Br⁻) relative to chloride in rainfall (EFsea = 16.8–75.3), rivers (EFsea = 1.3–13.9) and wetland waters, superficial (EFsea = 5.8–13.1) and interstitial (EFsea = 2.1–8.9), increased towards the inland highlands. We hypothesized that these values derived mostly from a known Br autocatalytic (heterogeneous) chemical cycle, starting at the seawater-aqueous interface and progressing in altitude. Br-bearing air masses are carried far from the Atlantic Ocean by moist westerlies, with Br⁻ rainout from the atmosphere supplying the neighbouring mountain peatlands. Average [Br] in sampled wetland soils/sediments (111–253 mg/kg) agreed with values from other coastal regions, and they were directly correlated with organic matter, varying irrespective the [Br⁻] of interstitial waters (129 μg/L–79 mg/L). According to the computed bioconcentration factors, the aqueous component was the major source of Br for all plant species investigated (BFplant/water = 2.1–508.0), as described elsewhere. However, Br contents in plants (14–173 mg/kg) evidenced interspecific differences, also suggesting a divergence from the acknowledged halophytic-glycophytic “model”. As plants are recognized producers of Br volatile molecules (e.g., methyl bromide, CH3Br), we interpreted translocation factors less than one in vascular species as explanatory of phytovolatilization rather than restriction of Br⁻ upward movement in plants. Further investigation is needed since considerable intrinsic plant variations in CH3Br emissions are mentioned in the literature.
  • ... Specimens of Juncus maritimus were collected at low tide, in both marshes' sites. Specimens were colected in at least four sub-samples along two cross-shore transects (PR and NSR_L; Moreno et al., 2017), considered representative of the low and high marsh environments. Also, two composite samples (each comprising four sub-samples) of Polytrichum commune (Chã Grande) and Sphagnum denticulatum (Lameiro das Cebolas), the most abundant bryophytic species at each site, were obtained in mires. ...
    ... Quality control included the use of blanks and reference materials, with errors  5%. The methodology used for interstitial waters is fully described in Moreno et al. (2015Moreno et al. ( , 2017. Bromide was measured by ion chromatography (IC) in samples filtered through 0.45 μm cellulose ester membrane filters, with a detection limit of 0.01 mg/L, and errors lesser than 5% for all determinations. ...
    ... But taking into account only the results from the high marsh zone, Br contents increase to 445 mg/kg in Pedras Ruivas and 133 mg/kg in N. Sra. do Rosário (Moreno et al., 2017). The lower [Br] in the soils/sediments of the later can be related to both lower OM and lower silt+clay, as previously reported (e.g., Martínez-Cortizas et al., 2016). ...
    Conference Paper
    Full-text available
    As plantas de zonas húmidas (wetlands) naturais, como os sapais e turfeiras atlânticas, desempenham um papel-chave no ciclo biogeoquímico global do bromo (Br), com reconhecidas implicações na destruição do ozono estratosférico. Com este estudo, preliminar, pretende-se avaliar o potencial de fixação do Br por espécies nativas e de ampla representação em sapais – Juncus maritimus – e turfeiras – Polytrichum commune e Sphagnum denticulatum – do NW de Portugal. O objetivo é caracterizar os inputs de Br via plantas para os solos/sedimentos das respectivas wetlandszonas húmidas, onde este elemento se encontra forte e positivamente correlacionado com a componente orgânica dos mesmos. Os resultados mostram que as 3 espécies analisadas contribuem para a fixação de Br, absorvendo-o e acumulando-o em concentrações variáveis. Tal ocorre preferencialmente a partir da água (como brometo) e não do substrato, onde, de acordo com os indicadores usados, o Br se encontra em formas não facilmente biodisponíveis. É ainda plausível que a baixa translocação em J. maritimus exprima sobretudo um processo de fitovolatilização, envolvendo a formação e(e emissão para a atmosfera) de brometo de metilo. Palavras-chave: Bromo, halófitas, briófitas, bromação, fitovolatilização
  • ... The tidal range varies between 2 m, during neap waters, and almost 4 m in spring waters, with the astronomical tide levels often enhanced by storm surges (e.g., Taborda and Dias, 1991;Araújo et al., 2011). Since both study sites have been thoroughly described in earlier papers (e.g., Moreno et al., 2017a) here we only provide a brief characterization (see Table 1). ...
    ... Fig. 1). Full methodological details are given in Fatela et al. (2014) and Moreno et al. (2014Moreno et al. ( , 2017a. The shorter core (FWCBrAR) was sampled every 0.5 cm with the aim of improving the sampling resolution of the top 28.5 cm of the FWCBr1.4 ...
    ... The upper section of the core was dated via 210 Pb measured by alpha spectroscopy, 137 Cs, and total Pb and down-core by two radiocarbon 14 C samples (69-70 cm, 90-91 cm depth) by accelerator mass spectrometry (AMS). The full chronological framework is provided in Moreno et al. (2014) for the FCPw1 core and Moreno et al. (2017a) for the FWCBr core. The chronology is reported in years of Anno Domini (years AD). ...
    Article
    A paleoclimatic reconstruction for the west coast of Portugal spanning the last six centuries is presented. This is based on the foraminiferal records of two dated sediment cores retrieved from the high marsh settings of Casa Branca (southwest coast, Mira estuary) and Caminha (northwest coast, Minho estuary), and supported by geochemical-sedimentological data. Casa Branca results, shown here for the first time, are compared with published data from Caminha, aiming to offer a more comprehensive overview of the environmental evolution of the west Iberian margin. Both marshes were originally formed in the AD 1300s during the transition of the Medieval Climatic Anomaly to the Little Ice Age, highlighting a major episode of increased sediment supply to the lower estuaries linked to climate-driven changes in continental runoff. Afterwards, the two marshes evolved under different climatic regimes, as reflected by their foraminiferal assemblages. These are more saline in Casa Branca (southwest), with Jadammina macrescens and Trochammina inflata as dominant species, than in Caminha (northwest), where Haplophragmoides spp. dominates. We suggest that a long-term trend of a net gain in evapotranspiration at Casa Branca inducing a higher marsh salinity baseline may explain this microfaunal contrast. Trochammina inflata seems to be a good indicator of drier periods in the studied area, connected to key events of aeolian large-dust input to the southwest coast of Portugal. The influence of the most important climate drivers was assessed, namely external (solar) and internal (North Atlantic Oscillation – NAO) forcings. Spectral and wavelet transform coherence analyses were used to detect solar footprints on foraminiferal and climate-related time series. A main significant quasi-periodicity was identified within the range of the secular Gleissberg cycle of solar activity modulating the annual NAO and regional spring-summer (simulated) temperatures after c. AD 1700. This stronger solar-climate coupling may be related to the known upward secular trend in the total solar irradiance after the Maunder Minimum. Keywords: southwest Europe; marsh hydrological balance; dust events; Little Ice Age; Gleissberg cycle. The link below provides free access to the article before February 06, 2019. No sign up, registration or fees are required. Share Link: https://authors.elsevier.com/c/1YFFq~1MBVZmT
  • ... content and quality (i.e. degree of decomposition) in sediments and peat(Biester et al. 2006; Bindler 2006;Martinez-Cortizas et al. 2007;Moreno et al. 2017), indicates that PC4 may represent the balance between the inorganic and organic matter fractions at the Laphroaig bog (although debromination can also occur in the more anoxic peat layers). As Br is controlled by mineral matter dilution and does not group with any of the storm indicators, it is not considered here as an indicator of sea salt spray inputs, and thereby storminess, as suggested in other studies(Orme et al. 2015; Stewart et al. 2017). ...
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    Severe winter windstorms have become an increasingly common occurrence over recent decades in northwestern Europe. Although there exists considerable uncertainty, storminess is projected to increase in the future. On centennial to millennial time scales in particular, the mechanisms forcing storminess remain unsettled. We contribute to available palaeostorm records by reconstructing changes over the last 6670 years using a coastal peat sequence retrieved from the ombrotrophic Laphroaig bog on Islay, southwestern Scotland. We use a combination of ash content, grain size and elemental chemistry to identify periods of greater storminess, which are dated to 6605, 6290–6225, 5315–5085, 4505, 3900–3635, 3310–3130, 2920–2380, 2275–2190, 2005–1860, 1305–1090, 805–435 and 275 cal. a BP. Storm signals in the first half of the record up to ~3000 cal. a BP are mainly apparent in the grain‐size changes. Samples from this time period also have a different elemental signature than those later in the record. We speculate that this is due to receding sea levels and the consequent establishment of a new sand source in the form of dunes, which are still present today. The most significant events and strongest winds are found during the Iron Ages Cold Epoch (2645 cal. a BP), the transition into, and in the middle of, the Roman Ages Warm Period (2235 and 1965 cal. a BP) and early in the Little Ice Age (545 cal. a BP). The Laphroaig record generally agrees with regionally relevant peat palaeostorm records from Wales and the Outer Hebrides, although the relative importance of the different storm periods is not the same. In general, stormier periods are coeval with cold periods in the region as evidenced by parallels with increased ice‐rafted debris in the North Atlantic, highlighting that sea‐ice conditions could impact future storminess and storm track position.
  • ... A comparison of several studies has shown that the wide variation of bromine contents in soils can be traced back to two main factors of influence. First, bromine concentration in soil mainly depends on the soil moisture content, and second, the bromine content of soil is positively correlated with the content of soil organic matter (Flury and Papritz 1993;Neal et al. 2007;Moreno et al. 2017). Since soil properties can influence related bioaccumulation and toxicity of bromine, it is important to determine soil parameters along with bromine concentrations in soils. ...
    Article
    Pollution from bromine and some of its related compounds is currently unregulated in soil from Russia and other countries,and tools for sound assessment of environmental impacts of bromine contamination are largely missing. Hence, assessingpotential implications for humans and ecosystems of bromine soil contamination is urgently needed, which requires the combi-nation of measured soil concentrations from environmental studies and quantified potential toxicity impacts. To address this need,we used data from an experimental study assessing bromine in soils (384 samples) of Tomsk oblast, Russia, starting frommeasured concentrations obtained by Instrumental Neutron Activation Analysis in an earlier study. From these data, we calcu-lated the bromine mass in soils and used these as starting point to characterize related cumulative impacts on human health andecosystems in the Tomsk region, using a global scientific consensus model for screening-level comparative toxicity character-ization of chemical emissions. Results show that the combination of sampling methodology with toxicity characterizationtechniques presents a new approach to be used in environmental studies aimed at environmental assessment and analysis of aterritory. Our results indicate that it is important to account for substance-specific chemical reaction pathways and transferprocesses, as well as to consider region-specific environmental characteristics. Our approach will help complement environmen-tal assessment results with environmental sustainability elements, to consider potential tradeoffs in impacts, related to soilpollution, in support of improved emission and pollution reduction strategies.
  • ... From the characterization of the factor loadings, the main contributors can be identified. These elements indicate a strong influence of geogenic origin (Destefan and Holanda, 2011;Moreno et al., 2017;Noce et al., 1997), although it is difficult to differentiate its origin due to the processes of transport and resuspension of the soil. The elements Ba, Na and Zn strengthen even more this origin due to their elemental concentrations, averaging 165 ng m -3 , 328 ng m -3 and 128 ng m -3 , respectively. ...
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    Particulate matter is the mixture of solid and liquid particles. It may at times cause adverse effects to human health, in the climate, ecosystem and materials. The objective of this study was to identify the sources emitting particulate matter that contributes to environmental pollution at two sites in Belo Horizonte city. The metropolitan region of Belo Horizonte is characterized by numerous mining activities and other industries, high population and, consequently, a high number of vehicles. There are therefore several sources emitting pollutants into the atmosphere. Airborne particulate matter was collected in air filters during approximately one year using a high-volume sampler in strategic points. The concentration of particulate matter results showed that, in general, the values were 40% higher than the values recommended by legislation. During the summer rainy season, no sample exceeded the recommended limits at both sampling sites. The elemental composition was determined through neutron activation analysis and these values were considered variables in the multivariate statistical analysis for the identification of the main sources of particle emission and their contributions. The results confirmed a significant influence of the soil and motor vehicles in the degradation of the region’s air quality.
  • ... Our new higher-resolution marsh foraminiferal record from Caminha indicates low-salinity foraminiferal assemblages (FAZ III; Fig. 4A, C, D) throughout AD 1654-1725 (similar to the WP1 time frame), in which T. salsa/irregularis dominates (87-52%; mean 66%). This supports an increase in wetness in the studied area during the WP1 period, concomitant with higher contents of bromine and organic matter (OM) in the marsh's soils/sediments, both representative of rainy/colder conditions (Moreno et al. 2015(Moreno et al. , 2017b. Geochemical data from this marsh also revealed a maximum of terrestrial OM contribution at this time (de la Rosa et al. 2012), moreover supporting increased continental runoff, and thus rainfall. ...
    Article
    This work presents two novel climate-related time series for the northwest of Portugal. The first is an A.D. 1626–1820 triennial-resolved wine production series, based on the Benedictine accounts from six monasteries of the Entre-Douro-e-Minho (EDM) region. The second, an A.D. 1654–2010 benthic foraminiferal record from the Caminha salt marsh, located in the lower estuary of the Minho River. The series were analysed together for the common period to outline how both palaeoclimate proxies respond to the most likely natural environmental drivers of temporal variability, solar forcing included. Singular spectral analysis revealed a common significant multi-decadal periodicity agreeing with recognized long-term changes in solar activity, i.e., the Lower Gleissberg cycle (50–80-years). The application of wavelet analysis allowed to detect high coherence at this time scale (centred at c. 64-years) between marsh foraminifera and both total solar irradiance and the North Atlantic Oscillation index. This relationship persists throughout the c. A.D. 1730–1875 period. The continuous wavelet transform results for wine production were inconclusive. Since the time span analysed is recognized as one of high socio-economic and political distress, the main human-driven impacts on wine production, particularly in the two periods of greatly reduced solar activity — the Maunder and Dalton Minima — are reviewed in the light of the available historical records. In addition to a documented climate-related agricultural crisis in Portugal, damage and losses to wine production may have been triggered by several local and international conflicts in which the country was involved. But to what extent the two influences contributed to the WP variations observed in the EDM region during both periods remains an open question.
  • ... Eighteen sediment samples were selected from cores taken at CM, KM, SP, and UPC (KM results were reported originally in Leorri et al., 2014). Representative cores with excellent and near-complete sedimentological recovery were selected based on research at each site (e.g., Kemp et al., 2017;Kirwan et al., 2012;Leorri et al., 2014;Moreno et al., 2017). Samples at each site location were selected with the objective of collecting the longest possible continuous marsh record, samples were evenly distributed when the chronology was well known (KM and SP) or in pairs to identify potential age reversals when the chronology was previously unknown (CM and UPC). ...
    Article
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    find the full paper at https://authors.elsevier.com/a/1Wo16B8ccgX~R The age and ability of salt marshes to accumulate and sequester carbon is often assessed using the carbon isotopic signatures (Δ14C and δ13C) of sedimentary organic matter. However, transfers of allochthonous refractory carbon (CRF) from the watershed to marshes would not represent new C sequestration. To better understand how refractory carbon (CRF) inputs affect assessments of marsh age and C sequestration, Δ 14C and δ13C of both total organic carbon (TOC), CRF, and non-CRF organic matter fractions were measured in salt marshes from four contrasting systems on the North Atlantic coast. To our knowledge, no salt marsh sediment study has considered refractory or allochthonous carbon in carbon budget calculations or the impact on chronologies. Stable and radiogenic isotope data suggest that while TOC was dominated by autochthonous plant inputs, CRF was dominated by locally recycled or allochthonous C, the delivery of which was controlled by the size and slope of each watershed. Steep-gradient rivers analyzed delivered Δ14C-depleted CRF to their estuarine marshes, while the site located in the low-gradient river was associated with larger CRF content. Finally, the marsh isolated from riverine input contained the least fraction of TOC as CRF. Laterally transported CRF caused only a small offset in Δ14C in relation to TOC in low-gradient systems (average Δ14C offset was -44.4 and -24.2 ‰ at each location). However, the presence of allochthonous Δ14C-depleted CRF in sediments of steep-gradient rivers led to large overestimates of the time of organic matter deposition (i.e. apparent age was older than the ’true‘ time of deposition) (Δ14C offset ranged from -170.6 to -528.9 ‰). Further, reliance on TOC or loss on ignition analyses to calculate C sequestration by marshes might produce overestimates of at least as much as 10 to 20% since neither account for the lateral transport of allochthonous carbon.
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    Atmospheric mercury depletion events (AMDEs) outside the polar region – driven by high levels of gaseous Br and BrO (i.e., BrO<sub>x</sub>) – were observed recently in the warm Dead Sea boundary layer. The efficient oxidation of gaseous elemental mercury (GEM) under temperate conditions by BrO<sub>x</sub> was unexpected considering that the thermal back dissociation reaction of HgBr is about 2.5 orders of magnitude higher under Dead Sea temperatures compared to polar temperatures, and hence was expected to significantly slow down GEM oxidation under warm temperatures. The goal of this modelling study was to improve understanding of the interaction of reactive bromine and mercury during Dead Sea AMDEs using numerical simulations based on a comprehensive measurement campaign in summer 2009. Our analysis is focused on daytime AMDE when chemical processes dominate concentration changes. Best agreements between simulations and observations were achieved using rate constants for k <sub>Hg+Br</sub> and k <sub>Hg+BrO</sub> of 2.7 × 10<sup>−13</sup> cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup> and 1.5 × 10<sup>−13</sup> cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup>, respectively. Our model also predicted that a rate constant k <sub>Hg+BrO</sub> of 5.0 × 10<sup>−14</sup> cm<sup>3</sup> molecule<sup>−1</sup> s<sup>−1</sup> may be considered as a minimum, which is higher than most reported values. These rate constants suggest that BrO could be a more efficient oxidant than Br in the troposphere as long as [Br]/[BrO] ratios are smaller than ~0.2 to 0.5. Under Dead Sea conditions, these kinetics demonstrate a high efficiency and central role of BrO<sub>x</sub> for AMDEs, with relative contributions to GEM depletion of more than ~90%. Unexpectedly, BrO was found to be the dominant oxidant with relative contributions above 80%. The strong contribution of BrO could explain why the efficiency of GEM oxidation at the Dead Sea does not critically depend on Br and, therefore, is comparable to that in cold polar regions. In order to confirm the suggested kinetics, additional studies, particularly for temperature-dependence of rate constants, are required.
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    Environmental perturbations in wetlands affect the integrated plant-microbial-soil system, causing biogeochemical responses that can manifest at local to global scales. The objective of this study was to determine how saltwater intrusion affects carbon mineralization and greenhouse gas production in coastal wetlands. Working with tidal freshwater marsh soils that had experienced roughly 3.5 yr of in situ saltwater additions, we quantified changes in soil properties, measured extracellular enzyme activity associated with organic matter breakdown, and determined potential rates of anaerobic carbon dioxide (CO2) and methane (CH4) production. Soils from the field plots treated with brackish water had lower carbon content and higher C : N ratios than soils from freshwater plots, indicating that saltwater intrusion reduced carbon availability and increased organic matter recalcitrance. This was reflected in reduced activities of enzymes associated with the hydrolysis of cellulose and the oxidation of lignin, leading to reduced rates of soil CO2 and CH4 production. The effects of long-term saltwater additions contrasted with the effects of short-term exposure to brackish water during three-day laboratory incubations, which increased rates of CO2 production but lowered rates of CH4 production. Collectively, our data suggest that the long-term effect of saltwater intrusion on soil CO2 production is indirect, mediated through the effects of elevated salinity on the quantity and quality of autochthonous organic matter inputs to the soil. In contrast, salinity, organic matter content, and enzyme activities directly influence CH4 production. Our analyses demonstrate that saltwater intrusion into tidal freshwater marshes affects the entire process of carbon mineralization, from the availability of organic carbon through its terminal metabolism to CO2 and/or CH4, and illustrate that long-term shifts in biogeochemical functioning are not necessarily consistent with short-term disturbance-type responses.
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    Volcanic emissions present a source of reactive halogens to the troposphere, through rapid plume chemistry that converts the emitted HBr to more reactive forms such as BrO. The nature of this process is poorly quantified, yet is of interest in order to understand volcanic impacts on the troposphere, and infer volcanic activity from volcanic gas measurements (i.e. BrO / SO2 ratios). Recent observations from Etna report an initial increase and subsequent plateau or decline in BrO / SO2 ratios with distance downwind. We present daytime PlumeChem model simulations that reproduce and explain the reported trend in BrO / SO2 at Etna including the initial rise and subsequent plateau. Suites of model simulations also investigate the influences of volcanic aerosol loading, bromine emission, and plume–air mixing rate on the downwind plume chemistry. Emitted volcanic HBr is converted into reactive bromine by autocatalytic bromine chemistry cycles whose onset is accelerated by the model high-temperature initialisation. These rapid chemistry cycles also impact the reactive bromine speciation through inter-conversion of Br, Br2, BrO, BrONO2, BrCl, HOBr. We predict a new evolution of Br speciation in the plume. BrO, Br2, Br and HBr are the main plume species near downwind whilst BrO and HOBr are present further downwind (where BrONO2 and BrCl also make up a minor fraction). BrNO2 is predicted to be only a relatively minor plume component. The initial rise in BrO / SO2 occurs as ozone is entrained into the plume whose reaction with Br promotes net formation of BrO. Aerosol has a modest impact on BrO / SO2 near-downwind (< ~6 km, ~10 min) at the relatively high loadings considered. The subsequent decline in BrO / SO2 occurs as entrainment of oxidants HO2 and NO2 promotes net formation of HOBr and BrONO2, whilst the plume dispersion dilutes volcanic aerosol so slows the heterogeneous loss rates of these species. A higher volcanic aerosol loading enhances BrO / SO2 in the (> 6 km) downwind plume. Simulations assuming low/medium and high Etna bromine emissions scenarios show that the bromine emission has a greater influence on BrO / SO2 further downwind and a modest impact near downwind, and show either complete or partial conversion of HBr into reactive bromine, respectively, yielding BrO contents that reach up to ~50 or ~20% of total bromine (over a timescale of a few 10 s of minutes). Plume–air mixing non-linearly impacts the downwind BrO / SO2, as shown by simulations with varying plume dispersion, wind speed and volcanic emission flux. Greater volcanic emission flux leads to lower BrO / SO2 ratios near downwind, but also delays the subsequent decline in BrO / SO2, and thus yields higher BrO / SO2 ratios further downwind. We highlight the important role of plume chemistry models for the interpretation of observed changes in BrO / SO2 during/prior to volcanic eruptions, as well as for quantifying volcanic plume impacts on atmospheric chemistry. Simulated plume impacts include ozone, HOx and NOx depletion, the latter converted into HNO3. Partial recovery of ozone occurs with distance downwind, although cumulative ozone loss is ongoing over the 3 h simulations.
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    Here we present a study of the 11 yr sunspot cycle's imprint on the Northern Hemisphere atmospheric circulation, using three recently developed gridded upper-air data sets that extend back to the early twentieth century. We find a robust response of the tropospheric late-wintertime circulation to the sunspot cycle, independent from the data set. This response is particularly significant over Europe, although results show that it is not directly related to a North Atlantic Oscillation (NAO) modulation; instead, it reveals a significant connection to the more meridional Eurasian pattern (EU). The magnitude of mean seasonal temperature changes over the European land areas locally exceeds 1 K in the lower troposphere over a sunspot cycle. We also analyse surface data to address the question whether the solar signal over Europe is temporally stable for a longer 250 yr period. The results increase our confidence in the existence of an influence of the 11 yr cycle on the European climate, but the signal is much weaker in the first half of the period compared to the second half. The last solar minimum (2005 to 2010), which was not included in our analysis, shows anomalies that are consistent with our statistical results for earlier solar minima.
  • Article
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    Tidal marshes are sedimentary environments that are among the most productive ecosystems on earth. As a consequence tidal marshes, and vegetated coastal ecosystems in general, have the potential to reduce atmospheric greenhouse gas concentrations as they efficiently sequester soil organic carbon (SOC). In the past decades, most research has focused on salt marshes, leaving carbon dynamics in brackish- and freshwater marshes largely understudied and neglecting the diversity among tidal marshes. Moreover, most existing studies underestimate total organic carbon (OC) stocks due to shallow soil sampling, which also influences reported patterns in OC storage along estuaries. We find that SOC stocks vary significantly along the salinity gradient of a temperate estuary (Scheldt estuary, Belgium and The Netherlands), from 46 kg OC m−2 in freshwater marshes to 10 kg OC m−2 in saltmarshes. In all tidal marsh sediments the OC concentration has a constant value from a certain depth below the surface downward. However, this concentration decreases with increasing salinity, indicating that the amount of stabile SOC decreases from the upper estuary towards the coast. Although net primary production of macrophytes differs along the estuary, our data suggest that these differences in OC storage are caused mainly by variations in suspended sediment concentration and stable particulate OC (POC) content in the water along the estuary. The fraction of suspended sediments and POC that is transported downstream the maximum turbidity zone is very limited, contributing to smaller amounts of long term OC sequestration in brackish- and saltmarsh sediments. In addition, high rates of sediment deposition on freshwater tidal marshes in the maximum turbidity zone promote efficient burial of OC in these marsh sediments.
  • Article
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    A seasonal study of temperature and salinity of estuarine and sediment interstitial water of tidal marshes was undertaken along three estuaries of W Portuguese coast (Minho, Tejo and Mira). The climatic N-S transition from wet Atlantic to Mediterranean features appear clearly imprinted in the distribution of tidal marsh assemblages, like foraminifera and ostracoda, mainly reflecting the water salinity gradient control. The Minho low estuary tidal marsh tends to be flooded by estuarine water ranging from 0.5‰ to 32‰ in each tide cycle, even during dry seasons. However, the marsh hydrological balance sustains a more stable environment where the salinity of interstitial water measurements yielded 8‰ to 16‰. In contrast the Tejo and Mira salt marsh flooding waters record a narrow range between 33‰ and 36‰, in spring, and between 29‰ and 36‰ in autumn. The climatic control of evaporation/ precipitation balance produces an enhanced salinity of marsh interstitial water, that can reach hypersaline conditions, with maximum records of 53‰ in Tejo and 48‰ in Mira lower estuaries. These environmental differences along the W Portuguese coast are recorded by the tidal marsh assemblages, namely foraminifera and ostracoda. In the low salinity Caminha salt marsh, living foraminifera are essentially composed by the agglutinated species Haplophragmoides manilaensis, Miliammina fusca, Pseudothurammina limnetis, Psammosphaera sp. and Trochamminita salsa. The modern ostracoda assemblage includes Leptochytere baltica, Leptochytere psammophila, Leptocythere sp. A and Tuberoloxoconcha sp.1. In the Tejo and Mira salt marsh Ammonia beccarii, Ammonia tepida, Haynesina germanica, Jadammina macrescens, Trochammina inflata, are the dominant foraminifera and Loxoconcha malcomsoni, Terrestricythere cf. elisabethae, Tuberoloxoconcha cf. atlantica and Xestoleberis labiata prevail as well as many other more marine ostracoda species, such as Basslerites teres and Leptocythere fabaeformis. This study highlights that the knowledge of driven ecological parameters of modern assemblages (usually preserved in fossil record), is fundamental to support reliable paleoclimatic and palaeoenvironmental reconstructions.
  • Article
    As a consequence of undercutting processes, the upper tidal flat wetland margins are retreating at rates of 0.8-10.5 cm/yr. Where tidal pans on the upper surface are breached, the scarp becomes dissected quickly and the horizontal retreat of the scarp reaches 45.5 cm/yr. The maximum measured retreat of 76.7 cm/yr is caused by anthropogenic activity. In places, progradation of the saltmarsh edge is observed, reaching 1 m/yr. On the lower mudflat, silty sediments and shell hash accumulate near its inland margin, close to the scarp of the high marsh, whereas sand flats and sand levees accumulate along the margins of the estuarine channels. However, in several places present-day thin deposits of sand overlay the inner margin of the low tidal mudflat as well as some portions of the high marsh surface. These sandy accumulations and the general retreat of the marsh scarp are related to the local sea-level rise. -from Author
  • Article
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    Ambrym volcano (Vanuatu, Southwest Pacific) is one of the largest sources of continuous volcanic emissions worldwide. As well as releasing SO2 that is oxidized to sulfate, volcanic plumes in the troposphere are shown to undergo reactive halogen chemistry whose atmospheric impacts have been little explored to date. Here, two-way nested simulations were performed with the regional scale model CCATT-BRAMS to test our understanding of the volcano plume chemical processing and to assess the impact of Ambrym on atmospheric chemistry at local and regional scales. We focus on an episode of extreme passive degassing that occurred in early 2005 and for which airborne DOAS measurements of SO2 and BrO columns, in the near downwind plume, have been reported. The model was developed to include reactive halogen chemistry and a volcanic emission source specific to this extreme degassing event. SO2 simulated columns show very good quantitative agreement with the DOAS observations as well as with OMI data, suggesting that the plume direction as well as its dilution are well represented. Simulations are presented with and without a high-temperature initialization that includes radicals formed by high temperature partial oxidation of magmatic gases by ambient air. When included high-temperature chemistry initialization, the model is able to capture the observed BrO/SO2 trend with distance from the vent in the near downwind plume. However, the maximum of BrO columns enhancement is still underestimated by a factor 3. The model identifies total in-plume depletion of ozone (15 ppbv) as a limiting factor to the partitioning of reactive bromine into BrO, of particular importance in this very strong plume at low background ozone conditions. Impacts of Ambrym in the Southwest Pacific region were also evaluated. As the plume disperses regionally, reactive halogen chemistry continues on sulfate aerosols produced by SO2 oxidation and promotes BrCl formation. Ozone depletion is weaker than at local scale but still between 10 to 40 %, in an extensive region few thousands of kilometres from Ambrym. The model also predicts transport of bromine to upper troposphere and stratosphere associated with convection events. In the upper troposphere, HBr is re-formed from Br and HO2. The model confirms the potential for volcanic emissions to influence the oxidizing power of the atmosphere: methane lifetime (calculated with respect to OH and Cl) is overall increased in the model due to the volcanic emissions. Reactive halogen chemistry is responsible for about 62 % of the methane lifetime increase with respect to OH, with depletion of OH by SO2 oxidation responsible for the remainder (38 %). Cl radicals produced in the plume counteract 41 % of the methane lifetime lengthening due to OH depletion. The reactive halogen chemistry in the plume is also responsible for an increase of 36 % of the SO2 lifetime with respect to oxidation by OH. This study confirms the strong influence of Ambrym emissions during the extreme degassing event of early 2005 on the composition of the atmosphere at the local and regional scales. It also stresses the importance of considering reactive halogen chemistry when assessing the impact of volcanic emissions on climate.
  • Article
    Recent investigations showed that bromine is incorporated to soil organic matter (SOM), its content increasing with humification. But few research was done on its long-term accumulation and the role played by pedogenetic processes, as those involved in organic matter stabilization. We investigated bromine content and distribution in four deep, acidic, organic-rich, Holocene soils from an oceanic area of Western Europe. Bromine concentrations (93-778μgg-1) in the silt+clay (<50μm) fraction were on average 3-times higher than those (17-250μgg-1) in the fine earth (<2mm), the former containing almost all bromine (90±5%). Inventories were between 148 and 314gm-2, indicating a rather large variability in a small area, and total estimated retention was low (6-16%). The degree of SOM bromination, expressed as the Br/C molar ratio, varied between 0.03 and 1.20mmol Br/mol C. The ratio was highly correlated (n=23, r2 0.88, p<0.01) with the age of the SOM for the last ~12ka. Partial least squares modeling indicates that bromine concentration depends on the amount of organic matter stabilized as aluminium-OM associations, and to a lesser extent on soil acidity (pH) and iron-OM associations. Thus, at scales of thousands of years, bromine accumulation in acidic soils is linked to the pool of metal-clay-stabilized organic matter.
  • Article
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    RESUMO: Foram analisados os dados de oito estações maregráficas (Viana do Castelo, Leixões, Aveiro, Cascais, Lisboa, Tróia, Sines e Lagos) durante o período em que ocorreram, na costa portuguesa, dois temporais generalizados: em Fevereiro/Março de 1978 e em Dezembro de 1981. Durante estes temporais os valores máximos da sobreelevação do nível do mar (i.e. diferença entre a maré observada e maré astronómica prevista) variaram, respectivamente, entre 0;4 e 0,9m e 0,4 e 1,2 m. Os níveis máximos de maré atingiram valores que variaram entre 3,8 e 4,3m para o temporal de 1978 e 3,6 e 4,Om para o temporal de 1981/82, excedendo a maré máxima prevista em 0,4 a 0,7m. O estudo dos registos da pressão e do vento permitiu explicar grande da sobreelevação observada em termos das condições metereológicas locais. ABSTRACT: During the storms of February/March 1978 and December 1981, data from eight tide gauge stations, on the portuguese coast, (Viana do Castelo, Leixões, Aveiro, Cascais, Lisbóa, Tróia, Sines and Lagos) were analised. During these storms the maximum surge ranged in amplitude from 0.4 to 0.9m and from 0.4 to 1 .2m, respectively. The observed maximum water leveIs ranged from 3.8 to 4.3m for the 1978 storm, and from 3.6 to 4.0m, for the 1981 storm. This leveIs exceed the predicted tidal maxima by between 0.4 and 0.7m. The comparision of surge leveIs with the barometric pressure and the wind speed sugest that the surge leveIs are mostly related with the local metereological conditions. INTRODUÇÃO O termo sobreelevação do nível do mar ou "storm surge" refere-se à subida temporária do nível do mar resultante da existência de condições metereológicas anómalas, nomeadamente de variações no campo da pressão atmosférica e/ou da acção de ventos fortes e prolongados. Esta sobreelevação é geralmente definida por meio da diferença entre o nível observado e a altura da maré astronómica prevista. O estudo deste fenómeno em Portugal revela-se de uma importância indiscutível, pois que é de grande relevância numa mais correcta avaliação e interpretação dos processos costeiros e da dinâmica sedimentar da plataforma em geral, desempenhando possivelmente um papel decisivo nas trocas sedimentares entre os depósitos litorais e os depósitos mais profundos, por um lado, e entre os depósitos submersos e emersos, por outro. Quando atinge grande amplitude (da ordem métrica), a sobreelevação do nível do mar é integrável na classe dos acontecimentos catastróficos * Contribuição DISEPLA n° A24 (Projecto PROCOST-JNICT 714/90 e DISEPLA-JNICT 692/90)
  • Article
    Biogeochemical transformations of plant-derived soil organic matter (SOM) involve complex abiotic and microbially mediated reactions. One such reaction is halogenation, which occurs naturally in the soil environment and has been associated with enzymatic activity of decomposer organisms. Building on a recent finding that naturally produced organobromine is ubiquitous in SOM, we hypothesized that inorganic bromide could be subject to abiotic oxidations resulting in bromination of SOM. Through lab-based degradation treatments of plant material and soil humus, we have shown that abiotic bromination of particulate organic matter occurs in the presence of a range of inorganic oxidants, including hydrogen peroxide and assorted forms of ferric iron, producing both aliphatic and aromatic forms of organobromine. Bromination of oak and pine litter is limited primarily by bromide concentration. Fresh plant material is more susceptible to bromination than decayed litter and soil humus, due to a labile pool of mainly aliphatic compounds that break down during early stages of SOM formation. As the first evidence of abiotic bromination of particulate SOM, this study identifies a mechanistic source of the natural organobromine in humic substances and the soil organic horizon. Formation of organobromine through oxidative treatments of plant material also provides insights into the relative stability of aromatic and aliphatic components of SOM.
  • Article
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    Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth's regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern resembling the North Atlantic Oscillation (NAO), with a lag of a few years due to ocean-atmosphere interactions. The solar/NAO relationship is, however, highly misrepresented in climate model simulations with realistic observed forcings. In addition, its detection is particularly complicated since NAO quasi-decadal fluctuations can be intrinsically generated by the coupled ocean-atmosphere system. Here we compare two multi-decadal ocean-atmosphere chemistry-climate simulations with and without solar forcing variability. While the experiment including solar variability simulates a 1-2-year lagged solar/NAO relationship, comparison of both experiments suggests that the 11-year solar cycle synchronizes quasi-decadal NAO variability intrinsic to the model. The synchronization is consistent with the downward propagation of the solar signal from the stratosphere to the surface.
  • Article
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    An absolute-dated stalagmite from Kaite Cave (Ojo Guaren ̃ a Karst Complex, N Spain) provides a nearly continuous, high-resolution record of a proxy of regional precipitation patterns through the 4.9–0.9 ka BP interval. This record is based on the Mg/Ca ratio of the calcite and its variation through the stalagmite stratigraphy, which is interpreted to be primarily driven by changes in precipi- tation amount. The calibration of the proxy is supported by the present-day monitoring carried out in the cave for the last 10 years, which reveals a robust inverse relationship between the inter-annual/inter-decadal variability of rain- fall and the Mg concentration of dripwaters and precipi- tating speleothems. The record of paleoprecipitation, based on 2400 Mg/Ca measurements, shows strong variability at inter-annual to inter-decadal scales, and more subtle but significant changes at secular to millennial scales. This long-term paleohydrological evolution outlines five suc- cessive intervals with consistent trends, which are bounded by abrupt shifts in the regional precipitation. These shifts took place at 4.65, 4.2, 2.6, and 1.3 ka BP. Significantly, the intervals of maximum precipitation of the whole record (around 4.9–4.65, 2.6–2.45, and 1.3–1.1 ka BP) can be related with episodes of minimum solar activity and cor- related with cold climatic events elsewhere.
  • Article
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    Mounting evidence from proxy records suggests that variations in solar activity have played a significant role in triggering past climate changes. However, the mechanisms for sun-climate links remain a topic of debate. Here we present a high-resolution summer sea-surface temperature (SST) record covering the past 9300 yr from a site located at the present-day boundary between polar and Atlantic surface-water masses. The record is age constrained via the identification of 15 independently dated tephra markers from terrestrial archives, circumventing marine reservoir age variability problems. Our results indicate a close link between solar activity and SSTs in the northern North Atlantic during the past 4000 yr; they suggest that the climate system in this area is more susceptible to the influence of solar variations during cool periods with less vigorous ocean circulation. Furthermore, the high-resolution SST record indicates that climate in the North Atlantic regions follows solar activity variations on multidecadal to centennial time scales.
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    Very short-lived (VSL) bromocarbons are produced at a prodigious rate by ocean biology and these source compounds (SGVSL), together with their inorganic degradation products (PGVSL), are lofted by vigorous convection to the tropical tropopause layer (TTL). Using a state-of-the-art photochemical mechanism within a global model, we calculate annual average stratospheric injection of total bromine due to VSL sources to be 5 pptv (parts per trillion by volume), with ~ 3 pptv entering the stratosphere as PGVSL and ~ 2 pptv as SGVSL. The geographic distribution and partitioning of VSL bromine within the TTL, and its consequent stratospheric injection, is highly dependent on the oceanic flux, the strength of convection and the occurrence of heterogeneous recycling reactions. Our calculations indicate atomic Br should be the dominant inorganic species in large regions of the TTL during daytime, due to the low ozone and cold conditions of this region. We propose the existence of a "tropical ring of atomic bromine" located approximately between 15 and 19 km and between 30° N and 30° S. Daytime Br / BrO ratios of up to ~ 4 are predicted within this inhomogeneous ring in regions of highly convective transport, such as the tropical Western Pacific. Therefore, we suggest that experimental programs designed to quantify the bromine budget of the TTL and the stratospheric injection of VSL biogenic bromocarbons should include a strategy for the measurement of atomic Br during daytime as well as HOBr and BrCl during nighttime.
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    Coastal salt marshes are natural sources of methyl chloride (CH3Cl) and methyl bromide (CH3Br) to the atmosphere, but measured emission rates vary widely by geography. Here we report large methyl halide fluxes from subtropical salt marshes of south Texas. Sites with the halophytic plant, Batis maritima, emitted methyl halides at rates that are orders of magnitude greater than sites containing other vascular plants or macroalgae. B. maritima emissions were generally highest at midday; however, diurnal variability was more pronounced for CH3Br than CH3Cl, and surprisingly high nighttime CH3Cl fluxes were observed in July. Seasonal and intra-site variability were large, even taking into account biomass differences. Overall, these subtropical salt marsh sites show much higher emission rates than temperate salt marshes at similar times of the year, supporting the contention that low-latitude salt marshes are significant sources of CH3Cl and CH3Br.
  • Article
    Soil organic carbon (SOC) plays an important role in soil productivity and the global carbon cycle. However, little is known about the regional distribution of SOC across the entire Loess Plateau region of China. We investigated 382 sampling sites across the region (620 000?km2) and collected 764 soil samples from the topsoil (0?20?cm) and subsoil (20?40?cm). Standard statistics were used to identify the regional SOC content and the relationships with 11 selected environmental variables. Concentrations of SOC varied within a wide range throughout the region from 0.38 to 54.03?g?kg?1, with mean values of 10.34 and 6.78?g?kg?1 for the topsoil and subsoil, respectively. Coefficient of variation values showed moderate variation for SOC in both soil layers. Significant correlations were detected between SOC and these environmental variables, notably with soil total nitrogen (TN), soil pH, and clay content. Multiple linear regression analysis indicated that TN, clay content, soil pH, elevation, and temperature had greatest effects on regional SOC variability among all the selected soil and site variables. Geostatistical analysis showed that the maximum autocorrelation ranges were 384 and 393?km for SOC in the topsoil and subsoil, respectively. Nugget-to-sill ratios were 0.52 and 0.50, which also indicated moderate spatial dependence. Maps of SOC distribution produced by the geostatistical method showed that the overall spatial pattern was characterised by an area of low SOC content surrounded by bands with higher values, which generally increased towards the region?s boundaries. The distribution pattern corresponded to that of the major regional landforms, which also influenced land use, whereby the sandy Ordos Plateau is surrounded by relatively fertile plains and valleys, where the human population density is highest, and the regional boundary is mountainous. The spatial data of SOC could be useful as an important initial state in regional SOC modelling and possibly be used in calibration and prediction processes in the remote sensing method to estimate SOC content for large-scale areas.
  • Article
    Although bromine (Br) is considered conservative in seawater, it exhibits a well established correlation with organic carbon in marine sediments. This carbon–bromine association was recently attributed to covalent bonding, with organobromine in sinking particulates providing a putative link between sedimentary organobromine and organic matter cycling in surface waters. We hypothesized that phytoplankton detritus, a major precursor of sedimentary organic matter, would be susceptible to bromination through oxidative attack. Through a series of model experiments, we demonstrate incorporation of Br into algal particulate detritus through peroxidative and photochemical mechanisms. Peroxidative bromination was enhanced by addition of exogenous bromoperoxidase, but the enzyme was not required for the reaction. Fenton-like reaction conditions also promoted bromination, especially under solar irradiation, implicating radical mechanisms in the euphotic zone as another abiotic source of brominated particulates. These reactions produced aliphatic and aromatic forms of organobromine, suggesting that lipid- and protein-rich components of algal membranes provide suitable substrates for bromination. Biogenic organobromines in certain genera of phytoplankton also appeared in both aliphatic and aromatic forms. Experimental evidence and samples from oceanic midwater sediment traps imply that the aromatic fraction is more stable than the aliphatic. These experiments establish Br as a versatile oxidant in the transformation of planktonic organic matter through both enzymatic and abiotic mechanisms. Organobromine may serve as a marker of oxidative breakdown of marine organic detritus, with the metastable component providing a short-lived indicator of early-stage oxidation. By altering the stability of aliphatic and aromatic moieties, bromination may affect the availability of organic matter to organisms, with consequences for the preservation and degradation of marine organic carbon.
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    In this study we report fluxes of chloromethane (CH3Cl), bromomethane (CH3Br), iodomethane (CH3I), and bromoform (CHBr3) from two sampling campaigns (summer and spring) in the seagrass dominated subtropical lagoon Ria Formosa, Portugal. Dynamic flux chamber measurements were performed when seagrass patches were either air-exposed or submerged. Overall, we observed highly variable fluxes from the seagrass meadows and attributed them to diurnal cycles, tidal effects, and the variety of possible sources and sinks in the seagrass meadows. The highest emissions with up to 130 nmol m−2 h−1 for CH3Br were observed during tidal changes, from air exposure to submergence and conversely. Furthermore, during the spring campaign, the emissions of halocarbons were significantly elevated during tidal inundation as compared to air exposure. Accompanying water sampling performed during both campaigns revealed elevated concentrations of CH3Cl and CH3Br, indicating productive sources within the lagoon. Stable carbon isotopes of halocarbons from the air and water phase along with source signatures were used to allocate the distinctive sources and sinks in the lagoon. Results suggest that CH3Cl was rather originating from seagrass meadows and water column than from salt marshes. Aqueous and atmospheric CH3Br was substantially enriched in 13C in comparison to source signatures for seagrass meadows and salt marshes. This suggests a significant contribution from the water phase on the atmospheric CH3Br in the lagoon. A rough global upscaling yields annual productions from seagrass meadows of 2.3–4.5 Gg yr−1, 0.5–1.0 Gg yr−1, 0.6–1.2 Gg yr−1, and 1.9–3.7 Gg yr−1 for CH3Cl, CH3Br, CH3I, and CHBr3 respectively. This suggests a minor contribution from seagrass meadows to the global production of CH3Cl and CH3Br with about 0.1 and 0.7%, respectively. In comparison to the known marine sources for CH3I and CHBr3, seagrass meadows are rather small sources.
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    The concentrations of metals (Cd, Cr, Cu, Fe, Ni, Pb and Zn) in sediments and the soft tissues of Corbicula fluminea from the Minho estuary (Northwest Iberian Peninsula) were determined to assess the spatial variation of metal bioavailability and to classify the ecological quality of the estuary. Metal concentrations in sediments showed significant spatial variation ( p < 0.0003) and ranged in concentration (dry weight basis) from 0.025-0.36 mg Cd/kg, 7-16 mg Cr/kg, 2.7-24.6 mg Cu/kg, 7.3-45 mg Ni/kg, 4.1-15 mg Pb/kg and 37.3-110 mg Zn/kg. According to the Norwegian Pollution Control Authority metal concentration guidelines for sediments, this first ecological quality classification of the Minho estuary is "Class I/II-Background/Good." Metal concentrations in the soft tissues of C. fluminea also showed significant spatial variation ( p < 0.0001) and ranged in concentration (dry weight basis) from 1.1-2.5 mg Cd/kg, 1.0-1.8 mg Cr/kg, 34-71 mg Cu/kg, 5.8-11 mg Ni/kg, 0.45-1.3 mg Pb/kg and 136-161 mg Zn/kg. The high Cu concentrations bioaccumulated by C. fluminea in the Minho estuary suggest that the estuary should be classified as "Class II/III-Moderately/Remarkably Polluted." Thus, the primary contributions of this work are that C. fluminea proved to be a good and adequate biomonitor of metal contamination in the Minho estuary and that it could be used to assess the ecological quality of estuarine ecosystems worldwide.
  • Article
    A high-resolution study of a marsh sedimentary sequence from the Minho estuary provides a new palaeoenvironmental reconstruction from NW Iberian based on geological proxies supported by historical and instrumental climatic records. A low salinity tidal flat, dominated by Trochamminita salsa, Haplophragmoides spp. and Cribrostomoides spp., prevailed from AD 140-1360 (Roman Warm Period, Dark Ages, Medieval Climatic Anomaly). This sheltered environment was affected by high hydrodynamic episodes, marked by the increase in silt/clay ratio, decrease of organic matter, and poor and weakly preserved foraminiferal assemblages, suggesting enhanced river runoff. The establishment of low marsh began at AD 1380. This low salinity environment, marked by colder and wet conditions, persisted from AD 1410–1770 (Little Ice Age), when foraminiferal density increased significantly. Haplophragmoides manilaensis and Trochamminita salsa marks the transition from low to high marsh AD 1730. Since AD 1780 the abundances of salt marsh species (Jadammina macrescens, Trochammina inflata) increased accompanied by a decrease in foraminiferal density, reflecting climate instability, when droughts alternate with severe floods. SW Europe marsh foraminifera respond to the hydrological balance, controlled by climatic variability modes (e.g. NAO) and solar activity, thus contributing to the understanding of NE Atlantic climate dynamics.
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    The Earth's climate system is driven by a complex interplay of internal chaotic dynamics and natural and anthropogenic external forcing. Recent instrumental data have shown a remarkable degree of asynchronicity between Northern Hemisphere and Southern Hemisphere temperature fluctuations, thereby questioning the relative importance of internal versus external drivers of past as well as future climate variability. However, large-scale temperature reconstructions for the past millennium have focused on the Northern Hemisphere, limiting empirical assessments of inter-hemispheric variability on multi-decadal to centennial timescales. Here, we introduce a new millennial ensemble reconstruction of annually resolved temperature variations for the Southern Hemisphere based on an unprecedented network of terrestrial and oceanic palaeoclimate proxy records. In conjunction with an independent Northern Hemisphere temperature reconstruction ensemble, this record reveals an extended cold period (1594-1677) in both hemispheres but no globally coherent warm phase during the pre-industrial (1000-1850) era. The current (post-1974) warm phase is the only period of the past millennium where both hemispheres are likely to have experienced contemporaneous warm extremes. Our analysis of inter-hemispheric temperature variability in an ensemble of climate model simulations for the past millennium suggests that models tend to overemphasize Northern Hemisphere-Southern Hemisphere synchronicity by underestimating the role of internal ocean-atmosphere dynamics, particularly in the ocean-dominated Southern Hemisphere. Our results imply that climate system predictability on decadal to century timescales may be lower than expected based on assessments of external climate forcing and Northern Hemisphere temperature variations alone.
  • Article
    present a new method for inferring the relative location (low- versus high-southern latitude), and therefore the potential climatic impact, of past eruptions based on the particle size distribution (PSD) of micrometer-sized ash measured continuously in the West Antarctic Ice Sheet (WAIS) Divide ice core. We find that particles from a high-southern latitude eruption (Buckle Island, Antarctica (1839 Common Era, C.E.)) have a PSD with mode diameter ≥5 µm coarser than the background dust (mode 5.1 µm), while ash particles originating from stratospheric tropical eruptions, including Tambora (1815 C.E.), Kuwae (1458 C.E.), and Unknown (1258 C.E.), have PSDs with mode diameters ~0.6-1.5 µm finer than the background. In addition, volcanic ash particles from global-scale eruptions are deposited ~3-6 months earlier and over a shorter time interval than sulfate aerosols. We hypothesize that this phasing is driven by differences in atmospheric processing and aerosol/particle transport and deposition.
  • Article
    rings are an important proxy for understanding the timing and environmental consequences of volcanic eruptions as they are precisely dated at annual resolution and, particularly in tree line regions of the world, sensitive to cold extremes that can result from climatically significant volcanic episodes. Volcanic signals have been detected in ring widths and by the presence of frost-damaged rings, yet are often most clearly and quantitatively represented within maximum latewood density series. Ring width and density reconstructions provide quantitative information for inferring the variability and sensitivity of the Earth's climate system on local to hemispheric scales. After a century of dendrochronological science, there is no evidence, as recently theorized, that volcanic or other adverse events cause such severely cold conditions near latitudinal tree line that rings might be missing in all trees at a given site in a volcanic year ("stand-wide" missing rings), resulting in misdating of the chronology. Rather, there is a clear indication of precise dating and development of rings in at least some trees at any given site, even under adverse cold conditions, based on both actual tree ring observations and modeling analyses. The muted evidence for volcanic cooling in large-scale temperature reconstructions based at least partly on ring widths reflects several factors that are completely unrelated to any misdating. These include biological persistence of such records, as well as varying spatial patterns of response of the climate system to volcanic events, such that regional cooling, particularly for ring widths rather than density, can be masked in the large-scale reconstruction average.
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    Recent decades have witnessed marked losses of coastal wetlands worldwide, but consistent data on salt marsh area are not available. The main goal of this study was to provide information on two Portuguese estuarine habitats (Mondego and Mira) over a period of four to six decades, and to assess how anthropogenic activities have altered the salt marsh ecosystem. Chronological sequences of aerial photographs covering a period of 54 years (1947-98) and 38 years (1958-95) for the Mondego and Mira estuaries, respectively, were considered for this study. Long-term changes in the Mondego estuary revealed a clear decline in the salt marsh area during the past six decades due to urban and industrial expansion. In contrast, the Mira estuary salt marshes remained almost unchanged since 1958. This ecosystem is relatively undisturbed by andthropogenic activities, and marsh variation seems to follow natural dynamics rather than being vulnerable to anthropogenic pressure. The sustainable management of salt marshes must be a priority concern to ensure the long-term viability of their ecological, economic and social capital.