Indian Ocean Hydrothermal Systems: Seafloor Hydrothermal Activities, Physical and Chemical Characteristics of Hydrothermal Fluids, and Vent-Associated Biological Communities

Abstract

In the nearly 40 years since the discovery of the deep-sea hydrothermal vent site at the Galápagos spreading center, more than 300 sites of high-temperature hydrothermal venting have been discovered and investigated around the world. Surprisingly, however, most of these sites are located in the Pacific and Atlantic Oceans, whereas only five hydrothermal vent sites have been discovered in the Indian Ocean. During the TAIGA project, we conducted four research cruises to investigate four of the five Indian Ocean hydrothermal vent sites (two of which were newly discovered during one of the TAIGA cruises) located along the Central Indian Ridge (CIR). The results of geological and geochemical analyses demonstrate wide variation in fluid chemistry, reflecting the diverse geological background of the CIR hydrothermal vent fields. Although the CIR is an intermediate-spreading ridge, the geological and geochemical features of the Kairei hydrothermal field appear to be similar to ultramafic rock-hosted hydrothermal fields found along the slow-spreading Mid-Atlantic Ridge (MAR). By contrast, the Dodo hydrothermal field shares similarities with the hydrothermal vent sites found along the fast-spreading East Pacific Rise. The Solitaire and Edmond hydrothermal fields are characterized by high pH and Cl levels, respectively, although the geological background underlying the unusual chemistry of their hydrothermal fluids is still uncertain. Additionally, extensive microbiological analyses of the Kairei hydrothermal vent site revealed that its microbial communities are affected by the chemical characteristics of the hydrothermal vent fluids. Macrofaunal analyses also revealed new faunal data for the Indian Ocean hydrothermal vents, including novel genera and families that are potentially indigenous to the Indian Ocean hydrothermal systems. In particular, the discovery and characterization of a new morphotype of "scaly-foot" gastropod raises the question of the mechanism and physiological role of iron sulfide mineralization. The results of our investigations extended knowledge of the Indian Ocean hydrothermal systems including geochemical variations of hydrothermal fluids, their relationships to the geological

Characterization of Geochemistry in Hydrothermal Sediments From the Newly Discovered Onnuri Vent Field in the Middle Region of the Central Indian Ridge

“…Interestingly, the preliminary observation and plume chemistry suggest that the OVF may be a low-temperature hydrothermal vent, probably supported by the exothermic serpentinization process (Kim et al, 2020). This venting system is thus quite different from the well-known basaltic-hosted venting systems of high-temperature and metal-rich black smoker, driven by magmatic activity in the CIR (e.g., Dodo and Edmond sites, Tivey, 2007;Nakamura and Takai, 2015). However, solid evidence for the serpentinization reaction (e.g., heat source) and the fluid temperature of the OVF is still lacking.…”

“…Systematic deep-sea exploration recently uncovered four new active hydrothermal vent fields in the middle region of the Central Indian Ridge (CIR) between 8 and 14 • S, where ridge morphology and tectonic structure (e.g., detachment faults and ocean core complexes, OCCs) control increased plume incidence at ridge flank and rift wall locations (Kim et al, 2020). These hydrothermal vent fields, located more than 800 km north of previously known vent fields (i.e., the Dodo and Solitaire fields, Nakamura and Takai, 2015) are characterized by particle-poor, diffuse venting with abundant vent fauna and sulfide deposition. Notably, these new hydrothermal vents show diverse venting styles and plume compositions, attributed to distinctive hydrothermal fluid formation conditions and transport pathways in the slow-to ultraslow-rate spreading ridge setting (Son et al, 2014;Kim et al, 2020).…”

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

“…Hydrothermal vents in the Indian Ocean are among the least studied vent ecosystems (Nakamura and Takai, 2015). This biogeographic province encompasses the entire ocean, however there is evidence that many populations are shared with the southwest Pacific, thereby representing a single larger province (Bachraty et al, 2009;Hashimoto et al, 2001;Moalic et al, 2012) The Longqi vent field (also known as Dragon Horn or SWIR Area A) is a complex of 7 hydrothermal vent chimneys towards the south edge of the Southwest Indian Ridge.…”

Microbial Community Structure and Functional Potential of Deep-Sea Sediments on Low Activity Hydrothermal Area in the Central Indian Ridge

“…The discovery of deep hydrothermal vent fields in the 1970s (Francheteau et al, 1979) has attracted great attention to scientists with over 700 vent fields discovered and investigated along mid-ocean ridges, volcanic arcs, and tectonic settings (Dick, 2019;Beaulieu and Szafrański, 2020). However, until recently, majority of the hydrothermal system discoveries and investigation have exclusively focused on the Pacific and Atlantic Oceans (Nakamura and Takai, 2015), thus, the Indian Ocean hydrothermal systems remain understudied. To date a limited number of hydrothermal fields have been identified in the Indian Ocean including the MESO Mineral Zone (Halbach et al, 1998), Kairei (Gamo et al, 2001), Edmond (Van Dover et al, 2001), Solitaire, Dodo (Nakamura et al, 2012), and Onnuri fields (Kim et al, 2020) in the Central Indian Ridge (CIR), Daxi and Wocan fields in the Carlsberg Ridge (Wang et al, 2017(Wang et al, , 2020, Mount Jourdanne (Münch et al, 2001), Yuhuang-1 (Liao et al, 2018), Longqi (Tao et al, 2012), Duanqiao (Yang et al, 2017), and Tiancheng (Zhou et al, 2018) in the South West Indian Ridge (SWIR), and Pelagia vent field (Han et al, 2018) in the South East Indian Ridge (SEIR).…”