The Levantine Basin - crustal structure and origin

The origin of the Levantine Basin in the Southeastern Mediterranean Sea is related to the opening of the Neo-Tethys. The nature of its crust has been debated for decades. Therefore, we conducted a geophysical experiment in the Levantine Basin. We recorded two refraction seismic lines with 19 and 20 ocean bottom hydrophones, respectively, and developed velocity models. Additional seismic reflection data yield structural information about the upper layers in the first few kilometers. The crystalline basement in the Levantine Basin consists of two layers with a P-wave velocity of 6.06.4 km/s in the upper and 6.56.9 km/s in the lower crust. Towards the center of the basin, the Moho depth decreases from 27 to 22 km. Local variations of the velocity gradient can be attributed to previously postulated shear zones like the Pelusium Line, the DamiettaLatakia Line and the BaltimHecateus Line. Both layers of the crystalline crust are continuous and no indication for a transition from continental to oceanic crust is observed. These results are confirmed by gravity data. Comparison with other seismic refraction studies in prolongation of our profiles under Israel and Jordan and in the Mediterranean Sea near Greece and Sardinia reveal similarities between the crust in the Levantine Basin and thinned continental crust, which is found in that region. The presence of thinned continental crust under the Levantine Basin is therefore suggested. A β-factor of 2.33 is estimated. Based on these findings, we conclude that sea-floor spreading in the Eastern Mediterranean Sea only occurred north of the Eratosthenes Seamount, and the oceanic crust was later subducted at the Cyprus Arc

Activation of mGluR5 Induces Rapid and Long-Lasting Protein Kinase D Phosphorylation in Hippocampal Neurons

Metabotropic glutamate receptors (mGluRs), including mGluR5, play a central role in regulating the strength and plasticity of synaptic connections in the brain. However, the signaling pathways that connect mGluRs to their downstream effectors are not yet fully understood. Here, we report that stimulation of mGluR5 in hippocampal cultures and slices results in phosphorylation of protein kinase D (PKD) at the autophosphorylation site Ser-916. This phosphorylation event occurs within 30 s of stimulation, persists for at least 24 h, and is dependent on activation of phospholipase C and protein kinase C. Our data suggest that activation of PKD may represent a novel signaling pathway linking mGluR5 to its downstream targets. These findings have important implications for the study of the molecular mechanisms underlying mGluR-dependent synaptic plasticity.Howard Hughes Medical InstituteFRAXA Research FoundationNational Institute of Mental Health (U.S.)Eunice Kennedy Shriver National Institute of Child Health and Human Development (U.S.

Temporal variability of gas seeps offshore New Zealand: multi-frequency geoacoustic imaging of the Wairarapa area, Hikurangi margin

Cold seeps on Opouawe Bank, situated in around 1000 m water depth on the Hikurangi Margin offshore North Island. New Zealand, were investigated using multibeam bathymetry, 75 and 410 kHz sidescan sonar imagery, and 2–8 kHz Chirp sediment echosounder data. Towed video camera observations allowed ground-truthing the various geoacoustic data. At least eleven different seep locations displaying a range of seep activity were identified in the study area. The study area consists of an elongated, northward-widening ridge that is part of the accretionary Hikurangi Margin and is well separated from direct terrigenous input by margin channels surrounding the ridge. The geoacoustic signature of individual cold-seep sites ranged from smooth areas with slightly elevated backscatter intensity resulting from high gas content or the presence of near-surface gas hydrates, to rough areas with widespread patches of carbonates at the seafloor. Five cold seeps also show indications for active gas emissions in the form of acoustic plumes in the water column. Repeated sidescan sonar imagery of the plumes indicates they are highly variable in intensity and direction in the water column, probably reflecting the control of gas emission by tides and currents. Although gas emission appears strongly focused in the Wairarapa area, the actual extents of the cold seep structures are much wider in the subsurface as is shown by sediment echosounder profiles, where large gas fronts were observed

Gas hydrate and P-Wave Velocity Distribution in the Yaquina Basin at the Peruvian margin

The lower boundary of the methane hydrate stability zone in continental margin sedi-mentsis often marked by a strong, phase reversed reflection subparallel to the seafloor,called the bottom simulating reflector (BSR). High resolution multichannel seismic(MCS) data from the Yaquina Basin offshore Peru at 8 deg S show a BSR that is vary-inglaterally in amplitude as well as in continuity. The amplitudes of the reflectionsabove the BSR also vary with the appearance of the BSR. Where the BSR is strong,the reflections above it are weaker compared to areas where the BSR is weak. Andalthough the strong part of the BSR is underlain immediately by strong reflections,reflections several hundred meters beneath the BSR appear weaker than those wherethe BSR is weak. This variation indicates significant heterogeneity in the distribu-tionof gas and gas hydrate in this area. Chemoherms observed at the Yaquina Basinsea floor indicate the presence of free gas in the sediments up to the seafloor. Thepresence of gas and gas hydrate within the sediment sequence significantly influencesthe P-wave velocity in the affected layers. Therefore a detailed analysis of velocityvariations enables to understand the apparently different conditions for the formationof gas hydrate along the BSR and the migration paths of the free gas. Ocean bot-tomseismometer (OBS) data from profiles coincident with the MCS data can providesuch detailed velocity depth information. Velocity analysis from OBS data included2D-ray tracing and 1D-interval-velocity analysis by means of DIX-inversion. In orderto find a trade-off between vertical resolution and minimization of errors caused bythe sensitivity of the DIX formula to velocity variations in thin layers, the data haveundergone a Kirchhoff wave-equation datuming and adjacent coherence filtering wasapplied to the data to eliminate the one sided travel path through the water columnof the OBS-observations. The derived velocity structure confirms the interpretation ofthe reflection pattern in terms of gas and gas hydrate distribution