North Atlantic Oscillation sensitivity to the El Niño/Southern Oscillation polarity in a large-ensemble simulation

A large ensemble modeling experiment with the Melbourne University General Circulation Model is presented. Thirty 17-year-long independent simulations were performed. All integrations were forced by the same observed sea surface temperatures, obtained from the Atmospheric Model Intercomparison Project II. The simulations were analyzed to assess the sensitivity of the North Atlantic Oscillation (NAO) to the El Niño/Southern Oscillation (ENSO) polarity. The results show signals of the ENSO phases both in the mean strength of the NAO as well as in its internal variability. During the cold ENSO phase, the probability density function of the NAO index presents a small but positive mean value, whereas it is negative during the warm ENSO phase. Also, the NAO variability associated with each ENSO phase shows a different behavior: during the warm phase the probability density function of the NAO index presents a larger variance and suggests a bimodality, whereas no bimodality is suggested in the cold phase.     

High-Frequency Hydroacoustic Monitoring in an Underground Iron Mine

The monitoring of the stability of old mines constitutes an important research objective for our institution, BRGM. The study reported here shows the contribution of high-frequency (>30 kHz) acoustic emissions to the detection of the damage within a rock mass, during an experiment within a pilot site of an old flooded iron mine. The experiment consisted of recording all the hydroacoustic events in a broad frequency band (between 30 Hz and 180 kHz), during 18 months. The monitoring network has been calibrated by a triggered block fall that made it possible to highlight a relationship between the occurrence of high-frequency/low-frequency hydroacoustic emissions and rock falls. The events recorded have been associated with the micro-failure of the rock mass near the roof, prior to the detachment of the blocks. This monitoring showed important high-frequency hydroacoustic activity, which may be associated with mechanical instabilities generated by the evolution of water pressure during the experiment. In conclusion, the high-frequency hydroacoustic activity appears to be a good indicator of instability and, therefore, this new technique constitutes a promising tool for monitoring abandoned underground cavities.     

Ophiolite emplacement by strike-slip tectonics between the Pontide Zone and the Sakarya Zone in northwestern Anatolia, Turkey

Northwestern Anatolia contains three main tectonic units: (a) the Pontide Zone in the north which consists mainly of the Gstanbul-Zonguldak Unit in the west and the BallLda<-Küre Unit in the east; (b) the Sakarya Zone (or Continent) in the south, which is juxtaposed against the Pontide Zone due to the closure of Paleo-Tethys prior to Late Jurassic time; and (c) the Armutlu-OvacLk Zone which appears to represent a tectonic mixture of both zones. These three major tectonic zones are presently bounded by the two branches of the North Anatolian Transform Fault. The two tectonic contacts follow older tectonic lineaments (the Western Pontide Fault) which formed during the development of the Armutlu-OvacLk Zone. Since the earliest Cretaceous, an overall extensional regime dominated the region. A transpressional tectonic regime of Coniacian/Santonian to Campanian age caused the welding of the Gstanbul-Zonguldak Unit to the Sakarya Zone by an oblique collision. In the Late Campanian, a transtensional tectonic regime developed, forming a new basin within the amalgamated tectonic mosaic. The different tectonic regimes in the region were caused by activity of the Western Pontide Fault. Most of the ophiolites within the Armutlu-OvacLk Zone belong to the Paleo-Tethyan and/or pre-Ordovician ophiolitic core of the Gstanbul-Zonguldak Unit. The Late Cretaceous ophiolites in the eastern parts of the Armutlu-OvacLk Zone were transported from Neo-Tethyan ophiolites farther east by left-lateral strike-slip faults along the Western Pontide Fault. There is insufficient evidence to indicate the presence of an ocean (Intra-Pontide Ocean) between the Gstanbul-Zonguldak Unit and the Sakarya Zone during Late Cretaceous time.     

Spatiotemporal changes in cadmium contamination in the Seine estuary (France)

Cadmium (Cd) is among the major contaminants in the Seine estuary. In the biota, the RNO (Réseau National d’Observation, the French Mussel-Watch) has shown that Cd concentrations in mussels living at the mouth of the estuary are related to changes in inputs to this area of phosphogypsum, a calcium sulphate that is a by-product of the phosphoric acid naturally enriched with Cd. In the water column, Cd concentrations at several key estuary sites show a very marked trend toward decreased contamination in the particles as well as in the dissolved phase. The behavior of Cd in the estuary has been studied between 1991 and 1998 in the framework of the scientific program Seine-Aval. This program has highlighted punctual Cd inputs in the estuarine water column. The partition of Cd between the dissolved and the particulate phase, previously described in various estuaries, is characterized by an intense phenomenon of solubilization in the mixing zone freshwater-seawater, but the colloidal Cd fraction remains low along the whole salinity gradient, about 5% to 10% of the apparent dissolved fraction. Although the decrease of inputs induced a fall of Cd concentrations in the water column, laboratory experiments show that the estuarine particles are far from being exhausted in Cd. Despite continuous efforts to reduce the urban and industrial inputs into the estuarine and coastal waters, the Seine estuary still remains very contaminated by Cd.     

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.     

The volcano of Capelinhos (Azores), the solar activity and the earth-tide

Bulletin of Volcanology - Correlations on the eruptive behaviour of the volcano of Capelinhos (Fayal island) in 1957–58, with (a) solar activity, and (b) earth-tide amplitudes, by way of a...     

The submarine volcano of Capelinhos and the tectonics of the Azores

Bulletin of Volcanology - In another paper of the author, a picture of the tectonics of the Azores was presented. The morphological analysis showed evidence of a folded and faulted structure and...