Seafloor evidence for pre-shield volcanism above the Tristan da Cunha mantle plume

Tristan da Cunha is assumed to be the youngest subaerial expression of the Walvis Ridge hot spot. Based on new hydroacoustic data, we propose that the most recent hot spot volcanic activity occurs west of the island. We surveyed relatively young intraplate volcanic fields and scattered, probably monogenetic, submarine volcanoes with multibeam echosounders and sub-bottom profilers. Structural and zonal GIS analysis of bathymetric and backscatter results, based on habitat mapping algorithms to discriminate seafloor features, revealed numerous previously-unknown volcanic structures. South of Tristan da Cunha, we discovered two large seamounts. One of them, Isolde Seamount, is most likely the source of a 2004 submarine eruption known from a pumice stranding event and seismological analysis. An oceanic core complex, identified at the intersection of the Tristan da Cunha Transform and Fracture Zone System with the Mid-Atlantic Ridge, might indicate reduced magma supply and, therefore, weak plume-ridge interaction at present times.

Description of a New Species of Pelagic Eelpout Melanostigma thalassium sp. nova (Zoarcidae) from Walvis Ridge (Southeastern Atlantic) and Identification Key for Species of the Genus from the Atlantic Ocean

A new species Melanostigma thalassium sp. n. is described from the underwater Walvis Ridge (Southeast Atlantic Ocean). This species differs from the other species of the genus Melanostigma in an original combination of characters based on the structure of the head’s lateral line system (interruption in supratemporal commissure with the loss of medial segments and the absence of pores in the temporal canal) and a nontransparent dark body. In addition, it is different in a range of the count characters in the axial skeleton and fins. A key for identifying the Atlantic species of the genus is provided.