Only a small percentage of the global seafloor has been investigated, leaving the deep ocean as one of the last frontiers to be explored and sampled. Mid-ocean ridges (MOR) systems extend about 60,000 kilometers around the globe, are where 70% of the volcanism on Earth occurs, and are dynamic and active tectonic regions.
A recent Nature Review paper, Früh-Green, et al. 2022, written by a multi-disciplinary team of experts summarizes what is known about MORs, their importance in regulating seawater chemistry and global chemical fluxes, and the diverse ecosystems that they support in the absence of light and under extreme conditions. The authors describe the tectonic, magmatic, and hydrothermal processes that govern how they form and change and describe some of the biogeochemical cycles at varying spreading rates.
“The first hydrothermal vent was discovered in 1977, which was followed by myriad discoveries about these amazing deep-sea environments over the next 45 years,” said OOI’s Regional Cabled Array Principal Investigator, Deborah Kelley at the University of Washington and an author of the paper. “Yet, much remains to be understood about these environments, which play a key role in regulating seawater chemistry and global chemical fluxes. Key unknowns include the evolution of the novel microbial communities that they host and the diversity of viruses. This paper summarizes some of the key discoveries that researchers have made and questions that remain to be answered.”
Among the paper’s key findings are:
- Spreading rates control variations in heat sources, magma input, and tectonic processes along MORs, providing multi-faceted habitats for life.
- Seawater circulation and hydrothermal alteration regulate seawater chemistry and change the composition and physical properties of the lithosphere (crust and upper mantle).
- Roughly 50-60% percent of global MORs are spreading at slow to ultraslow rates resulting in the exposure of lower crustal and upper mantle rocks. This spreading is creating asymmetric ridge segments that support different structures, hydrothermal processes, and vent fluid chemistry.
- Serpentinization decreases density and seismic velocities of mantle rocks, weakening the oceanic lithosphere along faults. Serpentinization also produces hydrogen and organic molecules that provide energy for microbial life.
- Unlike serpentinizing systems, basalt-hosted systems support a vast, hot and diverse microbial biosphere. Advanced technologies are allowing better characterization of the genetic makeup and metabolism of microbes and the role of viruses in shaping biodiversity.
- Hydrothermal processes govern global chemical fluxes of magnesium, iron, manganese, and other volatiles and provide nutrients to the deep ocean. Microbial interactions and oxidation of organic compounds within hydrothermal plumes produce organic carbon.
[media-caption path="/wp-content/uploads/2022/11/Screen-Shot-2022-11-29-at-10.54.32-AM.png" link="#"]Global distribution of hydrothermal vents on the seafloor. Map of the global ridge system with distribution of known sites of hydrothermal venting and sites inferred to be present from water-column studies. Hydrothermal vents occur at MORs (65% of known sites), back-arc spreading centers (22%), submarine arc volcanoes (12%) and interplate hot spot volcanoes (1%). Data from the InterRidge Vents Database. Map adapted with permission from the Center for Environmental Visualization, University of Washington.[/media-caption]
“Ocean observatories like OOI’s Regional Cabled Array and Ocean Networks Canada , are providing researchers unprecedented real-time views into these highly dynamic regions that help form the face of our planet,” added Kelley. “RCA has allowed researchers to measure and monitor activity at the magmatically robust Axial Seamount, on the Juan de Fuca MOR for example, providing insights into when it might next erupt. Such underwater observatories will only continue to advance our knowledge as we expand capabilities to observe, monitor, and sample seafloor environments and the overlying water column in real time with more sophisticated sensors and advanced underwater vehicles and robotic technologies.”
Früh-Green, G.L., Kelley, D.S., Lilley, M.D. et al. Diversity of magmatism, hydrothermal processes and microbial interactions at mid-ocean ridges. Nat Rev Earth Environ (2022). https://doi.org/10.1038/s43017-022-00364-y