Megafauna of the German exploration licence area for seafloor massive sulphides along the Central and South East Indian Ridge (Indian Ocean)

The growing interest in mineral resources of the deep sea, such as seafloor massive sulphide deposits, has led to an increasing number of exploration licences issued by the International Seabed Authority. In the Indian Ocean, four licence areas exist, resulting in an increasing number of new hydrothermal vent fields and the discovery of new species. Most studies focus on active venting areas including their ecology, but the non-vent megafauna of the Central Indian Ridge and South East Indian Ridge remains poorly known. In the framework of the Indian Ocean Exploration project in the German license area for seafloor massive sulphides, baseline imagery and sampling surveys were conducted yearly during research expeditions from 2013 to 2018, using video sledges and Remotely Operated Vehicles. This is the first report of an imagery collection of megafauna from the southern Central Indian- and South East Indian Ridge, reporting the taxonomic richness and their distribution. A total of 218 taxa were recorded and identified, based on imagery, with additional morphological and molecular confirmed identifications of 20 taxa from 89 sampled specimens. The compiled fauna catalogue is a synthesis of megafauna occurrences aiming at a consistent morphological identification of taxa and showing their regional distribution. The imagery data were collected during multiple research cruises in different exploration clusters of the German licence area, located 500 km north of the Rodriguez Triple Junction along the Central Indian Ridge and 500 km southeast of it along the Southeast Indian Ridge.

Deep-sea mining

Mining the extensive accumulations of minerals on the seafloor of the deep ocean might provide important resources, but it also has the potential to lead to widespread environmental impacts. Some of these impacts are unknown, and some may differ for the three main resource types: polymetallic nodules, seafloor massive sulphides, and polymetallic (cobalt-rich) crusts. Here, we detail the mining processes and describe the ecosystems associated with the minerals of interest. We then explain the expected impacts of mining, and discuss their potential effects on deep-ocean ecosystems. We also highlight the missing evidence needed to underpin effective environmental management and regulation of the nascent deep-sea mining industry.

Mining the Deep: A global assessment of biodiversity and research effort at deep-sea hydrothermal vents in relation to mining of seafloor massive sulphides

When the RV Knorr set sail for the Galapagos Rift in 1977, the scientists aboard expected to find deep-sea hydrothermal vents. What they did not expect to find was life—abundant and unlike anything ever seen before. Submersible dives revealed not only deep-sea hydrothermal vents but entire ecosystem surrounding them, including the towering bright red tubeworms that would become icons of the deep sea. This discovery was so unexpected that the ship carried no biological preservatives. These first specimens were fixed in vodka from the scientists’ private reserves.Since that first discovery, deep-sea hydrothermal vents have been found throughout the oceans. As more regions are explored, newly discovered vent fields present the potential for entirely species and ecosystems. Increasingly, however, it is not scientific discovery, but the financial value of vent fields, and the ores they contain, that is driving exploration in the deep sea. Over the last five decades, a new industry has emerged to explore the potential of mining Seafloor Massive Sulphides (deep-sea hydrothermal vents that contain high concentrations of rare and precious metals). Multiple enterprises are developing mining prospects that include both active and inactive deep-sea hydrothermal vent fields. In order to understand the impacts of exploitation at deep-sea hydrothermal vents, scientists and miners must establish environmental baselines. Biodiversity is frequently used as a proxy for resilience and as a metric for assessing biological baselines but, since research effort is not distributed equally across the oceans, biodiversity estimates in the deep sea are rarely comprehensive. Studies have predominantly focused on a few key biogeographic provinces, while other regions have only been sampled sparingly. Managers, regulators, and mining companies are working from incomplete data, with inferences about the consequences, as well as mitigation and remediation practices, often drawn from studies of few vent ecosystems that are often different from those in which the impacts are expected to occur. To better assess our current understanding of deep-sea hydrothermal vent biodiversity, we undertook a quantitative survey of the last 40 years of vent research. A stark north/south divide was detected, demonstrating that while research was disproportionately focused in the Northern Hemisphere, mining prospects were overwhelmingly positioned in the Southern Hemisphere. In addition, we provided a ranked assessment of biodiversity in eight major biogeographic provinces, identified knowledge gaps in the available deep-sea hydrothermal vent exploration literature, and assessed sampling completeness to provide further guidance to regulators, managers, and contractors as they develop comprehensive environmental baseline assessments.

Au and Te Minerals in Seafloor Massive Sulphides from Semyenov-2 Hydrothermal Field, Mid-Atlantic Ridge

The Semyenov-2 hydrothermal field located at 13°31′N of the Mid-Atlantic Ridge (MAR) is associated with an oceanic core complex (OCC) and hosted by peridotites and basalts with minor amounts of gabbro and plagiogranites. Seafloor massive sulphides (SMS) are represented by chimneys with zonality, massive sulphides without zonality and sulphide breccia cemented by opal and aragonite. The mean value of Au (20.6 ppm) and Te (40 ppm) is much higher than average for the MAR SMS deposits (3.2 ppm and 8.0 ppm, respectively). Generally, these high concentrations reflect the presence of a wide diversity of Au and Te minerals associated with major mineral paragenesis: primary native gold, melonite (NiTe2) and tellurobismuthite (Bi2Te3) are related to high-temperature chalcopyrite (~350 °C); electrum (AuAg)1, hessite (Ag2Te) and altaite (PbTe) are related to medium- and low-temperature Zn-sulphide and opal assemblages (260–230 °C). Calaverite (AuTe2) and Te-rich “fahlore” Cu12(Sb,As,Te)4S13 are texturally related to the chalcopyrite-bornite-covellite. Enrichment of Au in sulphide breccia with opal and aragonite cement is driven by the re-deposition and the process of hydrothermal reworking of sulphide. The low-temperature fluid mobilizes gold from primary sulphide, along with Au and Te minerals. As a result, the secondary gold re-precipitate in cement of sulphide breccia. An additional contribution of Au enrichment is the presence of aragonite in the Cu-Zn breccia where the maximal Au content (188 ppm) is reached.