Combined climatic and geological forcings on the spatio-temporal variability of piezometric levels in the chalk aquifer of Upper Normandy (France) at pluridecennal scale

The temporal variability of water-level fluctuations in the chalk aquifer of Upper Normandy, France is constrained by natural climate fluctuations and is closely linked to the regional geological patterns. The chalk plateaus are covered with 5–50 m thick semi-permeable surficial formations; the thickness of the underlying chalk aquifer varies from 50 to 300 m. The relationship among climate oscillations, piezometric levels, and geologic structure were investigated by correlation, Fourier spectral, and continuous wavelet analyses of selected piezometric time-series data. Analysis focused on two piezometers located on the uplifted side of a major fault and two piezometers on the downthrown side. After generalization to other piezometers in the region, it was deduced that, in the downthrown compartments, a substantial aquifer and surficial formations thickness would imply a strong attenuation of annual variability, while multi-year variability is clearly expressed. Conversely, in the uplifted compartments, a thin layer of surficial formations and small thickness of the chalk authorizes strong variations on the annual mode with respect to the contribution of long-term climatic oscillations (multi-year variability). The results then demonstrated—and proposed a spatial determination of—the differential influence of geological patterns on the filtering of climate-induced oscillations in piezometric variability.     

Tidal mixing in the Indonesian Seas and its effect on the tropical climate system

The sensitivity of the tropical climate to tidal mixing in the Indonesian Archipelago (IA) is investigated using a coupled general circulation model. It is shown that the introduction of tidal mixing considerably improves water masses properties in the IA, generating fresh and cold anomalies in the thermocline and salty and cold anomalies at the surface. The subsurface fresh anomalies are advected in the Indian Ocean thermocline and ultimately surface to freshen the western part of the basin whereas surface salty anomalies are advected in the Leuwin current to salt waters along the Australian coast. The ~0.5°C surface cooling in the IA reduces by 20% the overlying deep convection. This improves both the amount and structure of the rainfall and weakens the wind convergence over the IA, relaxes the equatorial Pacific trade winds and strengthens the winds along Java coast. These wind changes causes the thermocline to be deeper in the eastern equatorial Pacific and shallower in the eastern Indian Ocean. The El Nino Southern Oscillation (ENSO) amplitude is therefore slightly reduced while the Indian Ocean Dipole/Zonal Mode (IODZM) variability increases. IODZM precursors, related to ENSO events the preceding winter in this model, are also shown to be more efficient in promoting an IODZM thanks to an enhanced wind/thermocline coupling. Changes in the coupled system in response tidal mixing are as large as those found when closing the Indonesian Throughflow, emphasizing the key role of IA on the Indo-Pacific climate.     

Gulf Stream evolution through the Straits of Florida: the role of eddies and upwelling near Cuba

Ocean Dynamics - The meandering of the Gulf Stream through the Straits of Florida is associated with eddy activity to the north (along the Florida Keys) and the south (along the Cuban coast). This...     

What role for climate negotiations on technology transfer?

Little progress has been made in climate negotiations on technology since 1992. Yet the diffusion of climate change mitigation technologies to developing countries (non-Annex I) has increased dramatically over the last twenty years. The shift has mostly concerned emerging economies, which are now reasonably well connected to international technology flows. This is good news, as the bulk of emissions increases are expected to take place in these countries in the near future. In contrast, the least developed countries still appear to be excluded from international technology flows, mostly because of their negligible participation in the recent economic globalization. This article focuses on the policy implications of the contribution of climate negotiations to international technology diffusion.

Policy relevance

The discrepancy between the small amount of progress made in climate negotiations on technology since 1992 and the steady increase in the international diffusion of climate mitigation technologies leads to the perhaps controversial view that the diffusion of climate mitigation technologies does not need strong international coordination over technology issues under the UNFCCC. However, climate negotiations can play a key role in stimulating the demand for low-carbon technologies by setting ambitious emission reductions targets and policies.     

The role of boundary conditions in numerical models of subduction zone dynamics

Numerical studies of subduction zone dynamics on a regional scale usually use a limited spatial extent for their models and therefore need to define boundary conditions on all model edges. These boundary conditions imply a choice for the mechanical and thermal state of the surrounding regions which may influence the evolution of the model system. We investigate the role of the surface and lateral boundary conditions for simple mechanical subduction models using a standard finite element method. We find that subduction is only possible if the slab can decouple from the surface. This decoupling can be achieved by a true free surface, a free-slip surface with a weak crust for the subducting plate, or a free-slip surface with a layer of low viscosity, low density material (‘sticky air’) between the model surface and the crust. Models of slab dynamics that employ a free-slip surface reproduce trench migration, slab sinking velocities and slab geometry of models with a free surface, as long as they use either a weak crust, which can be viscous, viscoelastic and/or brittle, or a ‘sticky air’ layer. The vertical topography will however not be reproduced for free-slip models without a ‘sticky air’ layer. For ocean–ocean convergent models we find that the application of inflow boundary conditions at the edges of the subducting or overriding lithosphere controls trench motion and the geometry of the subducting slab. Inflow on the overriding side causes trench retreat and a slab resting on the lower mantle, whereas inflow restricted to the subducting side can cause trench advance and a slab which folds on the lower mantle.     

Distribution and reactivity of oxyanions (Sb, As, V, Mo) in the surface freshwater reaches of the Gironde Estuary (France)

The present work reports on the temporal variations of Sb, As, V and Mo concentrations in the surface freshwater reaches of the Gironde Estuary (SW France). Dissolved (<0.2 and <0.02 μm) and particulate Sb, As, V and Mo concentrations were measured in samples collected with high temporal resolution (every 30 min) during two consecutive tides at a fixed station located upstream of the city of Bordeaux and the maximum turbidity zone (MTZ). In addition, measurements of suspended particulate matter concentration, physico-chemical parameters, Cl⁻ concentration, water depth, current velocity and particulate Th concentration were performed either at the same time resolution or continuously. The data obtained suggested that variations in particulate As, V and Mo concentrations were most probably related to tidal cycling near the sampling site of fine grained particles from the MTZ located downstream. Significant differences in the behavior of the dissolved target oxyanions, mostly present in the <0.02 μm fraction, occurred. The behavior of Sb was conservative. Variations of the dissolved As and V concentrations showed similar cycling trends, strongly related to tidal cycles. These As and V cycles were interpreted as a mixing between upstream freshwater and downstream water enriched in dissolved As and V by desorption from the MTZ particles. The observed trend in the variation of the dissolved Mo was more complex than that of As and Sb and attributed to the mixing of the water bodies mentioned above coupled to a point source input of dissolved Mo from an intra-estuarine source. The contribution of this suspected Mo source to the dissolved Mo concentrations measured at the sampling site was estimated from the ratio of dissolved Mo to dissolved As concentrations. The additional dissolved Mo signal, coupled to the monitored ebb and flood length and associated current velocities, suggested an anthropogenic input which may derive from industrial activity near the city of Bordeaux. Extrapolating these results to the annual scale suggested that this dissolved Mo may be equivalent to 45-90% of the annual dissolved Mo flux into the Garonne Branch, highlighting the importance to further investigate the origin and behavior of Mo in the fluvial estuary near Bordeaux.     

A primitive dark inclusion with radiation‐damaged silicates in the Ningqiang carbonaceous chondrite

Abstract— A petrologic and TEM study of a remarkable dark inclusion (DI) in the Ningqiang CV3 chondrite reveals that it is a mixture of highly primitive solar nebula materials. The DI contains two lithologies. The first, lithology A, contains micron‐sized olivine and pyroxene grains rimmed by amorphous materials with compositions similar to the underlying crystalline grains. The second, lithology B, appears to preserve the mineralogy of lithology A before formation of the amorphous rims. Overall, the Ningqiang DI appears to record the following processes: 1) formation (condensation and Fe‐enrichment) of olivine crystals in the nebula with compositions of Fo_42–62; 2) irradiation, resulting in amorphitization of the olivine and pyroxene to varying degrees; 3) partial annealing, resulting in formation of fairly large, euhedral olivine and pyroxene grains with remnant amorphous sharply‐bounded rims; 4) in some cases, prolonged annealing, resulting in the formation of microcrystalline olivine or pyroxene rims. The latter annealing would have been a natural consequence of irradiation near the critical temperature for olivine; and 5) mixture of the above materials (lithology A) with nebular condensate high‐Ca pyroxene and olivine, which escaped nebular processing, to become lithology B. We suggest that the amorphous rims in lithology A formed in an energetic solar event such as a bi‐polar outflow or FU‐orionis flare.     

NWA 1152 and Sahara 00182: New primitive carbonaceous chondrites with affinities to the CR and CV groups

Abstract— We have investigated the mineralogy, petrography, bulk chemistry, and light element isotope composition of the ungrouped chondrites North West Africa (NWA) 1152 and Sahara 00182. NWA 1152 contains predominantly type 1 porphyritic olivine (PO) and porphyritic olivinepyroxene (POP) chondrules. Chondrule silicates are magnesium‐rich (Fo_{98.8 ± 1.2}, n = 36; Fs_{2.3 ± 2.1} Wo_{1.2 ± 0.3}, n = 23). Matrix comprises ?40 vol% of the sample and is composed of a micron sized silicate groundmass with larger silicate, sulfide, magnetite, and Fe‐Ni metal (Ni ?50 wt%) grains. Phyllosilicates were not observed in the matrix. Refractory inclusions are rare (0.3 vol%) and are spinel pyroxene aggregates or amoeboid olivine aggregates; melilite is absent from the refractory inclusions. Sahara 00182 contains predominantly type 1 PO chondrules, POP chondrules are less common. Most chondrules contain blebs of, and are often rimmed with, Fe‐Ni metal and sulfide. Chondrule phenocrysts are magnesium‐rich (Fo_{92.2 ± 0.6}, n = 129; Fs_{4.4 ± 1.8} Wo_{1.3 ± 1.1}, n = 16). Matrix comprises ?30 vol% of the meteorite and is predominantly sub‐micron silicates, with rare larger silicate gains. Matrix Fe‐Ni metal (mean Ni = 5.8 wt%) and sulfide grains are up to mm scale. No phyllosilicates were observed in the matrix. Refractory inclusions are rare (1.1 vol%) and melilite is absent. The oxygen isotope composition of NWA 1152 falls within the range of the CV chondrites with δ¹⁷O = ?3.43%0 δ¹⁸O = 0.70%0 and is similar to Sahara 00182, δ¹⁷O = ?3.89%0, δ¹⁸O = ?0.19%0 (Grossman and Zipfel 2001). Based on mineralogical and petrographic characteristics, we suggest NWA 1152 and Sahara 00182 show many similarities with the CR chondrites, however, oxygen isotopes suggest affinity with the CVs. Thus, neither sample can be assigned to any of the currently known carbonaceous chondrite groups based on traditionally recognized characteristics. Both samples demonstrate the complexity of inter‐ and intra‐group relationships of the carbonaceous chondrites. Whatever their classification, N WA 1152 and Sahara 00182 represent a source of relatively pristine solar system material.     

The role of the West Florida Shelf topography on the Loop Current system variability

Ocean Dynamics - The evolution of the Loop Current (LC) system under the interaction with the complex topography of the Gulf of Mexico (GoM) is examined. Focusing on the eastern GoM, we study the...