Lanthanoid behaviour in an acidic landscape

Lanthanoids were studied in a boreal landscape where an abundance of acid sulfate soils and Histosols provide a unique opportunity to increase the understanding of how these metals behave in acidic soils and waters and interact with soil and aqueous organic matter. In the acid sulfate soils lanthanoids are mobile as reflected in high to very high concentrations in soil water and runoff (typically a few mg l⁻¹ but up to 12 mg l⁻¹) and abundant release by several relatively weak extractants (ammonium acetate EDTA, sodium pyrophosphate, hydroxylamine hydrochloride) applied on bulk soil. Normalisation with the lanthanoid pool in the underlying parent materials (sulphide-bearing sediments deposited in brackish-water) and soil water showed that the extensive release/retention in the acidic soil was accompanied by large, and variable, fractionation trends across the lanthanoid series. In low-order streams draining these soils, the lanthanoid concentrations were high and, as indicated by frontal ultrafiltration and geochemical modelling, largely dissolved (<1 kDa) in the form of the species LnSO₄⁺ and Ln³⁺. In other moderately acidic stream waters (pH 4.3-4.6), organic complexation was predicted to be important in the <1 kDa fraction (especially for the heavy lanthanoids) and strongly dominating in the colloidal phase (1 kDa-0.45 μm). Along the main stem of a stream in focus (catchment area of 223 km²), lanthanoid concentrations increased downstream, in particular during high flows, caused by a downstream increase in the proportion of acid sulfate soils which are extensively flushed during wet periods. The geochemical models applied to the colloidal Ln-organic phase were not successful in predicting the measured fractionation patterns.     

Late Holocene high precipitation events recorded in lake sediments and catchment geomorphology,Lake Vuoksjávrátje,NW Sweden

In this paper, we show the potential of combining multi‐proxy analysis of lake sediments with catchment geomorphology to better understand palaeoenvironmental changes. Previous studies have suggested that alpine lakes in N Sweden may be highly sensitive to variations in catchment erosion and precipitation, and that this sensitivity may influence ecologically based reconstructions of past temperature changes. We analysed lake sediments covering the last 5100 years from the alpine Lake Vuoksjávrátje in NW Sweden in order to identify different erosional regimes in the lake catchment, sediment sources and lake sedimentary processes, which ultimately affect the palaeoecological record. The measured proxies include elemental geochemistry from XRF core scanning, grain size, sediment accumulation rates, fraction of terrestrial organic carbon and geomorphological mapping, supported by previously published chironomid and total organic carbon data. From the integrated results we identified time intervals when increased intensity of precipitation altered sedimentation and lake catchment erosional processes. The most prominent event occurred c. 2900 cal. a BP and is interpreted to be the result of excessive precipitation, possibly related to the climatic shift towards cooler and wetter conditions referred to as the 2.8 ka event.     

The origin of skarn beds, Ryllshyttan Zn�CPb�CAg + magnetite deposit, Bergslagen, Sweden

Thin- to medium-bedded, stratiform calc-silicate deposits (banded skarns) are a peculiar, but important, component of the supracrustal successions in the Palaeoproterozoic Bergslagen mining district of central Sweden. They are referred to as ??skarn-banded leptites?? in the literature and are common in areas and at stratigraphic levels that contain iron oxide and base metal sulphide deposits. The stratigraphic hanging wall of the stratabound Ryllshyttan Zn?CPb?CAg + magnetite deposit at Garpenberg, contains approximately 100?C150?m of interbedded aluminous skarn beds and rhyolitic ash-siltstones. The skarn beds are mineralogically variable and dominantly composed of grandite, spessartine, epidote, actinolite, quartz, clinopyroxene, and locally magnetite. Integrated field-mapping, and whole-rock lithogeochemical, microscopic and mineral chemical analyses suggest that the stratiform skarn beds are the products of at least two discrete hydrothermal events and subsequent metamorphism. The first event comprised accumulation in a quiescent subaqueous environment, below wave base, of calcareous and ferruginous sediments rich in Fe, Mn, Ca, and Mg. These chemical sediments were deposited concurrently with rhyolitic ash-silt sedimentation, thus forming a (now metamorphosed) laminated calcareous Fe formation with both a detrital rhyolitic component and rhyolitic siltstone interbeds. Positive Eu-anomalies and negative Ce-anomalies for normalized rare earth element analyses of skarn beds suggest that the iron may have been derived from exhalation of hot and reduced hydrothermal fluids, which upon mixing with more oxidized seawater, precipitated Fe oxides and/or carbonates that settled from suspension to the seafloor. The size of the positive Eu-anomalies of the chemical sediments are modified by the content of rhyolitic volcaniclastic material, which has a negative Eu anomaly, such that positive Eu-anomalies are only observed in skarn beds that possess a minor volcaniclastic component. Subsequently, the calcareous Fe formations were subjected to post-depositional alteration by hydrothermal fluids, locally yielding more manganoan and magnesian assemblages. The Mn-alteration is manifested by lateral gradations from epidote-grandite-clinopyroxene±magnetite rocks into significantly more Mn-rich quartz-spessartine rocks and massive andradite rocks over distances of less than 10?cm within individual skarn beds. Magnesian alteration is manifested by the development of discordant zones of pargasite para-amphibolites and formation of stratiform pargasite rocks texturally similar to the interlaminated grandite-epidote-ferroan diopside rocks. The latter increase in abundance towards the Ryllshyttan deposit and are associated with pre-metamorphic/pre-tectonic K?CMg?CFe±Si alteration (now biotite-phlogopite-garnet-cordierite-pargasite rocks) that is related to base metal mineralization. The zone of Mn- and Mg-altered skarn beds extends beyond the zone of pervasive K?CMg?CFe±Si alteration around Ryllshyttan. This suggests that the skarn bed progenitors, or their sedimentary contacts against rhyolitic ash-siltstones, acted as conduits to outflowing hydrothermal fluids. The chemical and mineralogical imprint, imposed on affected beds by alteration, may serve as indicators of proximity to intense K?CMg?CFe±Si alteration envelopes around other base metal sulphide deposits in Bergslagen. The last recorded event comprised syn-tectonic veining of competent massive andradite skarn beds. The veins contain quartz-albite-epidote-ferroan diopside-actinolite assemblages.     

Simulating the Carbon Cycling of Northern Peatlands Using a Land Surface Scheme Coupled to a Wetland Carbon Model (CLASS3W-MWM)

Northern peatlands store approximately one-third of the terrestrial soil carbon (C), although they cover only 3% of the global land mass. Northern peatlands can be subdivided into bogs and fens based on their hydrology and biogeochemistry. Peatland hydrology and biogeochemistry are tightly coupled to climate and, therefore, may be very sensitive to climate variability and change. To address the fate of the large peatland soil C storage under a future changed climate, a peatland C model, the McGill Wetland Model (MWM), was coupled to a land surface climate model (the wetland version of the Canadian Land Surface Scheme, CLASS3W), referred as CLASS3W-MWM. We evaluated the CLASS3W-MWM for a bog (Mer Bleue, located at 45.41°N, 75.48°W, in eastern Canada) and a poor fen (Degerö Stormyr, located at 64°11′N, 19°33′E, in northern Sweden).

CLASS3W-MWM captured the magnitude and direction of the present day C cycling very well for both bogs and fens. Moreover, the seasonal and interannual variability were reproduced reasonably well. Root mean square errors (RMSE) were <0.65 and the degree of agreements (d*) were >0.8 for the components of net ecosystem production (NEP) for both the Mer Bleue bog and the Degerö Stormyr fen. The performance of the coupled model for both bog and fen is similar to that of the stand-alone MWM driven by observed weather rather than simulated surface and soil climate. This modelling study suggests that northern peatlands are hydrologically and thermally conservative ecosystems. It was also shown that C cycling for bogs and fens was more sensitive to changes in air temperature than precipitation. Changes in temperature within the Intergovernmental Panel on Climate Change (IPCC) projected range switch the peatlands from a present-day C sink to a source, but projected changes in precipitation still maintain the peatlands as a C sink, although to a somewhat lesser degree. Increase in atmospheric CO₂ concentration enhances C sequestration for both bogs and fens. Our sensitivity analysis suggests that northern peatlands respond to changes in temperature, precipitation and doubled CO₂ concentration in a highly non-linear way. The sensitivity of C cycling in northern peatlands with respect to changes in air temperature, precipitation and the concentration of atmospheric CO₂ together is not a simple addition or subtraction of the sensitivity of the individual changes. Therefore, the sensitivity of a combination of changes in temperature, precipitation and doubled CO₂ concentration is very different from the sensitivity of peatlands to each environmental variable on their own. Our sensitivity analysis suggests that fens have a narrower tolerance to climate changes than bogs.

RÉSUMÉ [Traduit par la rédaction] Les tourbières du Nord renferment approximativement le tiers du carbone se trouvant dans le sol terrestre, même si elles ne couvrent que 3% des terres du globe. On peut subdiviser les tourbières du Nord en tourbières hautes et en tourbières basses selon leur hydrologie et leur biogéochimie. L'hydrologie et la biogéochimie des tourbières sont intimement liées au climat et peuvent donc être très sensibles à la variabilité et au changement climatique. Pour étudier comment évoluera le stockage du carbone dans les grands terrains tourbeux sous un climat futur modifié, nous avons couplé un modèle de carbone de tourbière, le McGill Wetland Model (MWM), à un modèle climatique de surface terrestre (la version terres humides du CLASS3W canadien), c'est-à-dire le CLASS3W–MWM. Nous avons évalué le CLASS3W–MWM pour une tourbière haute (Mer Bleue, situé à 45,41°N, 75,48°O, dans l'est du Canada) et pour une tourbière basse ombrotrophe (Degerö Stormyr, situé à 64°11′N, 19°33′E, dans le nord de la Suède).

Le CLASS3W–MWM a très bien capturé la grandeur et la direction du recyclage actuel du carbone, tant pour les tourbières hautes que pour les tourbières basses. De plus, la variabilité saisonnière et interannuelle a été raisonnablement bien reproduire. Les écarts-types étaient <0,65 et les degrés de concordance (d*) étaient >0,8 pour les composantes de la production nette de l’écosystème tant pour la tourbière haute Mer Bleue que pour la tourbière basse Degerö Stormyr. La performance du modèle couplé pour la tourbière haute et la tourbière basse est semblable à celle du MWM autonome piloté par des conditions observées plutôt que par un climat simulé de la surface et du sol. Cette étude par modèle suggère que les tourbières du Nord sont des écosystèmes hydrologiquement et thermiquement conservatifs. Il a aussi été démontré que le recyclage du carbone pour les tourbières hautes et basses était plus sensible aux changements dans la température de l'air que dans les précipitations. Des changements de température de l'ordre de ceux projetés par le Groupe d'experts intergouvernemental sur l’évolution du climat (GIEC) font que les actuels puits de carbone que constituent les tourbières se transforment en sources, mais les changements projetés dans les précipitations maintiennent encore les tourbières comme des puits de carbone, quoique dans une moindre mesure. L'accroissement de la concentration du CO₂ atmosphérique améliore la séquestration du carbone à la fois pour les tourbières hautes et les tourbières basses. Notre analyse de sensibilité suggère que les tourbières du Nord réagissent aux changements dans la température et les précipitations et à une concentration doublée de CO₂ d'une façon fort peu linéaire. La sensibilité du recyclage du carbone dans les tourbières du Nord par rapport aux changements dans la température de l'air, les précipitations et la concentration du CO₂ atmosphérique ensemble n'est pas une simple addition ou soustraction de la sensibilité aux changements individuels. Par conséquent, la sensibilité à une combinaison de changements dans la température et les précipitations et à une concentration doublée de CO₂ est très différente de la sensibilité des tourbières à chaque variable environnementale prise seule. Notre analyse de sensibilité suggère que les tourbières basses ont une plus faible tolérance aux changements climatiques que les tourbières hautes.     

Theory and Experiment on an Elastically Moored Cylindrical Buoy

In this paper, we compare simulated forces and accelerations for a moored floating buoy with full-scale experimental results in real ocean waves. The buoy is moored with a wire connected by springs to a concrete foundation situated at the seafloor. This study aims to develop a computer model using potential theory with a linearized free-surface boundary condition to describe the motion of such a system. The intention is to use the model for future study of wave-energy absorption and design of converters. Another objective is to see how complex a model is required to get accurate results. The method used is computationally fast and makes it possible to couple linear buoy wave interaction with nonlinear generator models, so that different loads and latching can be studied. A computationally fast method is required to model farms of wave-energy converters     

Landslide databases in the Geological Surveys of Europe

Landslides are one of the most widespread geohazards in Europe, producing significant social and economic impacts. Rapid population growth in urban areas throughout many countries in Europe and extreme climatic scenarios can considerably increase landslide risk in the near future. Variability exists between European countries in both the statutory treatment of landslide risk and the use of official assessment guidelines. This suggests that a European Landslides Directive that provides a common legal framework for dealing with landslides is necessary. With this long-term goal in mind, this work analyzes the landslide databases from the Geological Surveys of Europe focusing on their interoperability and completeness. The same landslide classification could be used for the 849,543 landslide records from the Geological Surveys, from which 36% are slides, 10% are falls, 20% are flows, 11% are complex slides, and 24% either remain unclassified or correspond to another typology. Most of them are mapped with the same symbol at a scale of 1:25,000 or greater, providing the necessary information to elaborate European-scale susceptibility maps for each landslide type. A landslide density map was produced for the available records from the Geological Surveys (LANDEN map) showing, for the first time, 210,544 km² landslide-prone areas and 23,681 administrative areas where the Geological Surveys from Europe have recorded landslides. The comparison of this map with the European landslide susceptibility map (ELSUS 1000 v1) is successful for most of the territory (69.7%) showing certain variability between countries. This comparison also permitted the identification of 0.98 Mkm² (28.9%) of landslide-susceptible areas without records from the Geological Surveys, which have been used to evaluate the landslide database completeness. The estimated completeness of the landslide databases (LDBs) from the Geological Surveys is 17%, varying between 1 and 55%. This variability is due to the different landslide strategies adopted by each country. In some of them, landslide mapping is systematic; others only record damaging landslides, whereas in others, landslide maps are only available for certain regions or local areas. Moreover, in most of the countries, LDBs from the Geological Surveys co-exist with others owned by a variety of public institutions producing LDBs at variable scales and formats. Hence, a greater coordination effort should be made by all the institutions working in landslide mapping to increase data integration and harmonization.     

Retreat pattern of the Cordilleran Ice Sheet in central British Columbia at the end of the last glaciation reconstructed from glacial meltwater landforms

The Cordilleran Ice Sheet (CIS) covered much of the mountainous northwestern part of North America at least several times during the Pleistocene. The pattern and timing of its growth and decay are, however, poorly understood. Here, we present a reconstruction of the pattern of ice‐sheet retreat in central British Columbia at the end of the last glaciation based on a palaeoglaciological interpretation of ice‐marginal meltwater channels, eskers and deltas mapped from satellite imagery and digital elevation models. A consistent spatial pattern of high‐elevation (1600–2400 m a.s.l.), ice‐marginal meltwater channels is evident across central British Columbia. These landforms indicate the presence of ice domes over the Skeena Mountains and the central Coast Mountains early during deglaciation. Ice sourced in the Coast Mountains remained dominant over the southern and east‐central parts of the Interior Plateau during deglaciation. Our reconstruction shows a successive westward retreat of the ice margin from the western foot of the Rocky Mountains, accompanied by the formation and rapid evolution of a glacial lake in the upper Fraser River basin. The final stage of deglaciation is characterized by the frontal retreat of ice lobes through the valleys of the Skeena and Omineca Mountains and by the formation of large esker systems in the most prominent topographic lows of the Interior Plateau. We conclude that the CIS underwent a large‐scale reconfiguration early during deglaciation and was subsequently diminished by thinning and complex frontal retreat towards the Coast Mountains.     

Alterations in seawater pH and CO2 affect calcification and photosynthesis in the tropical coralline alga, Hydrolithon sp. (Rhodophyta)

Calcification in the marine environment is the basis for the accretion of carbonate in structures such as coral reefs, algal ridges and carbonate sands. Among the organisms responsible for such calcification are the Corallinaceae (Rhodophyta), recognised as major contributors to the process world-wide. Hydrolithon sp. is a coralline alga that often forms rhodoliths in the Western Indian Ocean. In Zanzibar, it is commonly found in shallow lagoons, where it often grows within seagrass beds and/or surrounded by green algae such as Ulva sp. Since seagrasses in Zanzibar have recently been shown to raise the pH of the surrounding seawater during the day, and since calcification rates are sensitive to pH, which changes the saturation state of calcium carbonate, we measured the effects of pH on photosynthetic and calcification rates of this alga. It was found that pH had significant effects on both calcification and photosynthesis. While increased pH enhanced calcification rates both in the light and in the dark at pH >8.6, photosynthetic rates decreased. On the other hand, an increase in dissolved CO₂ concentration to 26 μmol kg⁻¹ (by bubbling with air containing 0.9 mbar CO₂) caused a decrease in seawater pH which resulted in 20% less calcification after 5 days of exposure, while enhancing photosynthetic rates by 13%. The ecological implications of these findings is that photosynthetically driven changes in water chemistry by surrounding plants can affect calcification rates of coralline algae, as may future ocean acidification resulting from elevated atmospheric CO₂.