In-Situ Study Methods Used in the Discovery of Sites of Modern Hydrothermal Ore Formation on the Mid-Atlantic Ridge

Abstract

This paper presents in situ methods used in the search for areas of modern hydrothermal activity, as well as the results of their long-term use during cruises within the Russian exploration area of the Mid-Atlantic Ridge (MAR). In this study, the following methods were used: CTD-sounding, methane sounding, teleprofiling and measurements with Eh, pS, pNa, pH and EF sensors. During profiling by towed complexes (RIFT, MAK-1M), various geophysical and geochemical anomalies near high-temperature, low-temperature and inactive fields were detected. Geophysical anomalies are more distinct when profiling near the bottom, and geochemical anomalies are located at a distance from the bottom (~150–200 m). Direct signs of high-temperature discharging (black smoker′s smoke, hydrothermal buildings) and indirect signs of low-temperature discharging (lithified carbonate sediments and accumulations of endemic hydrothermal fauna) were detected during teleprofiling. We have described 6 types of complex geophysical anomalies determined by CTD-sounding that allow the detection of plumes at different stages of formation and from different sources. The use of a methane sensor during sounding makes it more likely to identify a low-temperature discharge. Methane has a highly variable nature of distribution—over distances from the first hundreds of meters to tens of kilometers and a seabed height of ~50–500 m. The use of these methods together makes it more possible to detect low- and high-temperature hydrothermal discharges within mid-oceanic ridges (MOR).