On the use of IPCC-class models to assess the impact of climate on Living Marine Resources

The study of climate impacts on Living Marine Resources (LMRs) has increased rapidly in recent years with the availability of climate model simulations contributed to the assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Collaboration between climate and LMR scientists and shared understanding of critical challenges for such applications are essential for developing robust projections of climate impacts on LMRs. This paper assesses present approaches for generating projections of climate impacts on LMRs using IPCC-class climate models, recommends practices that should be followed for these applications, and identifies priority developments that could improve current projections. Understanding of the climate system and its representation within climate models has progressed to a point where many climate model outputs can now be used effectively to make LMR projections. However, uncertainty in climate model projections (particularly biases and inter-model spread at regional to local scales), coarse climate model resolution, and the uncertainty and potential complexity of the mechanisms underlying the response of LMRs to climate limit the robustness and precision of LMR projections. A variety of techniques including the analysis of multi-model ensembles, bias corrections, and statistical and dynamical downscaling can ameliorate some limitations, though the assumptions underlying these approaches and the sensitivity of results to their application must be assessed for each application. Developments in LMR science that could improve current projections of climate impacts on LMRs include improved understanding of the multi-scale mechanisms that link climate and LMRs and better representations of these mechanisms within more holistic LMR models. These developments require a strong baseline of field and laboratory observations including long time series and measurements over the broad range of spatial and temporal scales over which LMRs and climate interact. Priority developments for IPCC-class climate models include improved model accuracy (particularly at regional and local scales), inter-annual to decadal-scale predictions, and the continued development of earth system models capable of simulating the evolution of both the physical climate system and biosphere. Efforts to address these issues should occur in parallel and be informed by the continued application of existing climate and LMR models.     

Frostquakes in New England

Frostquakes are generated by tensional fracturing of the ground due to relatively rapid freezing. They are often accompanied by explosive noise and may reach Intensity V effects, yet they are only felt in neighborhoods and are not recorded on seismic networks. Frostquakes may crack macadam, concrete slabs, shallow soil pipe and some foundation materials along the line of the fracture. They occur in the early hours of the morning in mid-winter during major cold snaps. The ones investigated occurred in glacial sand and silt and none were found on till or bedrock. The recognition of frostquakes is important in correcting the records for fault-caused earthquakes. Frostquakes in the historic record complicate the difficulty of predicting large earthquakes from small ones.     

Peierls dislocation modelling in perovskite (CaTiO<Subscript>3</Subscript>): comparison with tausonite (SrTiO<Subscript>3</Subscript>) and MgSiO<Subscript>3</Subscript> perovskite

We present here a numerical modelling study of dislocations in perovskite CaTiO₃. The dislocation core structures and properties are calculated through the Peierls–Nabarro model using the generalized stacking fault (GSF) results as a starting model. The GSF are determined from first-principles calculations using the VASP code. The dislocation properties such as collinear, planar core spreading and Peierls stresses are determined for the following slip systems: [100](010), [100](001), [010](100), [010](001), [001](100), [001](010), and All dislocations exhibit lattice friction, but glide appears to be easier for [100](010) and [010](100). [001](010) and [001](100) exhibit collinear dissociation. Comparing Peierls stresses among tausonite (SrTiO₃), perovskite (CaTiO₃) and MgSiO₃ perovskite demonstrates the strong influence of orthorhombic distortions on lattice friction. However, and despite some quantitative differences, CaTiO₃ appears to be a satisfactory analogue material for MgSiO₃ perovskite as far as dislocation glide is concerned.     

Shallow-water longshore drift-fed submarine fan deposition (Moisie River Delta, Eastern Canada)

Submarine canyons and associated submarine fans are in some cases located at the end of a littoral cell where they act as conduits for the transfer of eroded terrigenous sediments to the marine environment. Such fans are generally found in deep-water settings at >500 m water depth. Offshore the Moisie River Delta (NW Gulf of St. Lawrence, Eastern Canada), high-resolution multibeam bathymetry and seismic data led to the discovery of an unusually shallow submarine fan (≤60 m) located at the end of a littoral cell. Sediment is transported westward on the shallow coastal shelf, as demonstrated by the downcurrent displacement of oblique nearshore sandbars where the shelf narrows to less than 1 km. The steep slope near the end of the littoral cell is incised by a channel that feeds a submarine fan composed of smaller channels and depositional lobes. According to existing Holocene evolution models for the region, the fan formed within the last 5,000 years. Its evolution is largely due to the transport of sediment by longshore drift. Multibeam echosounder and seismic data also reveal that the gravity-driven accretion of the submarine fan is characterized mainly by two processes, i.e., frequent small-scale, downslope migration of sandwaves on the slope, and more episodic slumping/turbidity-current activity in the deeper part of the fan. This study documents that, besides their common deep-water location, smaller-scale submarine fans can occur also in very shallow water, implying that they could be more frequent than previously thought both in modern environments and in the rock record.     

Biogeochemical control on the temporal variability of trace element concentrations in the Oubangui river (Central African Republic)

Dissolved Ba, Cd, Co, Mn, Mo, Ni, Rb, Sb, Sr, U and V were measured in the Oubangui river (Central African Republic) during a complete flood period. The dissolved concentrations vary by factors ranging from 1.4 to 8.2 as a function of river discharge: Sr, Ba, Rb and Mo concentrations decrease with rising stage; Ni, U, Sb, Cd, V and Mn concentrations increase with rising stage. These distributions are explained by a mixing of quick flow, mostly surface runoff with delayed flow, mostly groundwater. The dual origin of stream waters is demonstrated by the major element ratios, which are close to a silicate end-member during the high-flow period and trend towards a carbonate end-member during the low-flow period. Moreover, geological heterogeneities in the Oubangui basin may play a role in the variation of concentrations observed at the basin outlet. The previously indicated presence of a subsurface carbonate sequence in the lower part of the basin is confirmed. Cd, V, Mn and Co show peak concentrations during decreasing stage. We suggest that biological processes such as release from phytoplanktonic material and dissolution of oxides or carbonate phases may explain this maximum.     

Bio‐geomorphic effects on tidal channel evolution: impact of vegetation establishment and tidal prism change

The long‐term (10–100 years) evolution of tidal channels is generally considered to interact with the bio‐geomorphic evolution of the surrounding intertidal platform. Here we studied how the geometric properties of tidal channels (channel drainage density and channel width) change as (1) vegetation establishes on an initially bare intertidal platform and (2) sediment accretion on the intertidal platform leads to a reduction in the tidal prism (i.e. water volume that during a tidal cycle floods to and drains back from the intertidal platform). Based on a time series of aerial photographs and digital elevation models, we derived the channel geometric properties at different time steps during the evolution from an initially low‐elevated bare tidal flat towards a high‐elevated vegetated marsh. We found that vegetation establishment causes a marked increase in channel drainage density. This is explained as the friction exerted by patches of pioneer vegetation concentrates the flow in between the vegetation patches and promotes there the erosion of channels. Once vegetation has established, continued sediment accretion and tidal prism reduction do not result in significant further changes in channel drainage density and in channel widths. We hypothesize that this is explained by a partitioning of the tidal flow between concentrated channel flow, as long as the vegetation is not submerged, and more homogeneous sheet flow as the vegetation is deeply submerged. Hence, a reduction of the tidal prism due to sediment accretion on the intertidal platform, reduces especially the volume of sheet flow (which does not affect channel geometry), while the concentrated channel flow (i.e. the landscape forming volume of water) is not much affected by the tidal prism reduction. Copyright © 2012 John Wiley & Sons, Ltd.     

Late orogenic extension in the Bohemian Massif: petrostructural evidence in the Hlinsko region

Abstract

The tectonic contact between low-grade metase-dimentary series and high-grade rocks in the Hlinsko region (Bohemian Massif) is commonly interpreted as a thrust of the Barrandian sediments over the upper Moldanubian nappe.

The sediments occur in an E-facing synform that contains a tonalitic laccolith on its eastern boundary with the Moldanubian, and is truncated by a granodiorite pluton to the west. The synform represents a late deformational folding event related to the granodiorite intrusion. NW-oriented normal shear in the tonalite is indicated by S-C microstructures. Kinematic criteria associated with the major foliation and lineation development in the metasediments also indicate a north-westward, normal shear. In addition, Moldanubian gneiss display late shear bands due to north-westward, normal shear. Consequently, the presumed thrust is a low-angle, normal shear zone.

Low-pressure type metamorphism (3 < P < 4 x 10² MPa) coeval with the major deformational phase in pelites of the Hlinsko synform is attributed to both the tonalite aureole and the extensive HT metamorphism (under P > 6 x 10² MPa) that has affected the underlying Moldanubian.

The possibly polyphase normal fault is consistent with the meta-morphic pressure jump between the metasediments and the Moldanubian.

We suggest that the tonalite intruded syntectonically within the normal ductile shear zone active during waning stages of the Variscan orogeny.     

L'aération naturelle et artificielle des lacs

Conclusion Par ce qui précède, on se rend compte que chaque lac constitue un cas particulier qui doit être étudié pour lui-même et que l'aération artificielle d'un lac de grandes dimensions est susceptible d'être réalisée. A notre époque les lacs prennent de plus en plus d'importance comme réservoirs pouvant servir à l'alimentation en eau potable. Pour remplir ce r?le il est indispensable que la qualité de l'eau soit satisfaisante afin d'éviter des traitements co?teux. On peut dire que l'aération artificielle, malgré le co?t initial des installations et la consommation annuelle d'énergie électrique, est le procédé le plus économique pour améliorer l'eau d'un lac eutrophe. Actuellement la consommation de l'eau augmente partout et dépasse parfois dans certaines agglomérations 1000l/habitant/par jour. Dans ces conditions les frais d'exploitation d'une station d'aération conjuguée avec un service important de distribution d'eau ne grèvent le prix de revient du mètre cube que d'un supplément minime. Il est évident que l'emploi de l'aération artificielle pour assainir un lac ne dispense pas de combattre les causes originelles de la pollution des eaux. C'est un procédé auxiliaire précieux qui peut aider un lac à rétablir son équilibre biologique compromis par les conséquences de l'eutrophie. Cet article résume les idées exposées par l'auteur à l'occasion d'un colloque organisé à Zurich le 22 février 1957 par le Prof.Jaag, président de la Commission hydrobiologique de la Société helvétique des sciences naturelles.     

Tidal Marsh Restoration Design Affects Feedbacks Between Inundation and Elevation Change

Tidal marsh (re)creation on formerly embanked land is increasingly executed along estuaries and coasts in Europe and the USA, either by restoring complete or by reduced tidal exchange. Ecosystem functioning and services are largely affected by the hydro-geomorphologic development of these areas. For natural marshes, the latter is known to be steered by feedbacks between tidal inundation and sediment accretion, allowing marshes to reach and maintain an equilibrium elevation relative to the mean sea level. However, for marsh restoration sites, these feedbacks may be disturbed depending on the restoration design. This was investigated by comparing the inundation-elevation change feedbacks in a natural versus restoration site with reduced tidal exchange in the Scheldt estuary (Belgium). This study analyzes long-term (9 years) datasets on elevation change and tidal inundation properties to disentangle the different mechanisms behind this elevation-inundation feedback. Moreover, subsequent changes in sediment properties that may affect this feedback were explored. In the restoration area with reduced tidal exchange, we found a different elevation-inundation feedback than on natural marshes, which is a positive feedback on initially high sites (i.e., sediment accretion leads to increasing inundation, hence causing accelerating sediment accretion rates) and a gradual silting up of the whole area. Furthermore, there is evidence for the presence of a relict consolidated sediment layer. Consequently, shallow subsidence is less likely to occur. Although short-term ecological development of the tidal marsh was not impeded, long-term habitat development may be affected by the differences in hydro-geomorphological interactions. An increase of inundation frequency on the initially high sites may cause inhibition of habitat succession or even reversed succession. Over time, the climax state of the restoration area may be different compared to natural marshes. Moreover, sediment-related ecosystem services, such as nutrient and carbon burial, may be positively influenced because of continuing sedimentation, although flood water storage potential will decrease with increasing elevation. Depending on the restoration goals, ecosystem trajectories and delivery of ecosystem services can be controlled by adaptive management of the tidal volume entering the restoration area.