The MEDESS-GIB drifters database

On September 9th 2014, an intensive drifter deployment was carried out in the Strait of Gibraltar. In the frame of the EU MED Program MEDESS-4MS, the MEDESS-GIB experiment consisted of the deployment of 35 satellite tracked drifters, mostly of CODE-type, equipped with temperature sensor sampling at a rate of 30 minutes. Drifters were distributed along and on both sides of the Strait of Gibraltar. The MEDESS-GIB deployment plan was designed as to ensure quasi-synoptic spatial coverage. To this end, 4 boats covering an area of about 680 NM2 in 6 hours were coordinated. As far as authors know, this experiment is the most important exercise in the area in terms of number of drifters released. Collected satellite-tracked data along drifter trajectories have been quality controlled and processed to build the here presented MEDESS-GIB data set.

Geochemical and isotopic composition of basalts from the axial Mid-Atlantic Ridge, South Atlantic

One of the essential problems of oceanic tectonics is estimation of the influence of plumes of the deep hot mantle on processes in the axial spreading zone. Areas of two giant (St. Helena and Tristan da Cunha) plumes in the Mid-Atlantic Ridge (MAR) rift zone (South Atlantic) are characterized by the effusion of basalts that differ from typical depleted riftogenic tholeiites by anomalously high contents of lithophile components and specific isotopic compositions. Moreover, the rift valley floor with basalt effusion is significantly uplifted above the adjacent sectors of the rift. The formation of the St. Helena Seamount located 400 km east of the MAR axis is related to magmatism that is active to this day. St. Helena Island is a member of the structural ensemble of large volcanic seamounts (Bonaparte, Bagration, and Kutuzov). Like St. Helena Island, each seamount incorporates a series of smaller rises of different morphologies and dimensions. Thus, a system of subparallel series of NE-trending (~45°) rises extend from the seamount ensemble to the African continent. According to the plate tectonics concept, the seamount series represent hotspots related to a deep mantle plume that can be projected onto the present-day St. Helena Island area (St. Helena plume). At the same time, the inferred topographic map based on satellite altimetry data shows that the seamount series also extend along the opposite southwestern direction (~225°) toward the axial MAR and even intersect the latter structure. This fact cannot be explained by the hotspot hypothesis, which suggests stationary positions of plumes relative to the mobile oceanic plate. In the course of Cruise 10 of the R/V Akademik Ioffe (2002), detailed geological and geophysical investigations were carried out at the junction of one structural series with the MAR rift zone located near the Martin Vaz Fracture Zone (Martin Vaz test area, 19°-20° S). The present communication is devoted to the study of lithology, geochemistry, and isotopy of basalts dredged at the test area.