Heat loss from the Earth's interior via hydrothermal systems located along sub-marine volcanic systems is a fundamental process affecting the Earth: hydrothermal systems extract approximately one third of the global yearly heat lost through mid-ocean ridges, and are a primary means of chemical exchange between the solid Earth and the oceans, supporting vast sub-marine ecosystems. This process is particularly poorly understood for hydrothermal systems at slow- and ultra-slow spreading ridges, where venting occurs in a variety of host-rock types and tectonic settings. In particular, the Rainbow hydrothermal field (RHF) is a methane-, hydrogen- and iron-rich system located on an ultramafic massif within a tectonized non-transform discontinuity (NTD) of the Mid-Atlantic Ridge, where current models predict that long-term magma supply should be very low. Yet Rainbow vents high-temperature fluids at high flow rates, which is difficult to explain without a magmatic heat source. This conundrum stands in the way of our ability to develop general models for the roles of magmatic heat input and tectonic faulting on controlling ridge thermal structure and hydrothermal circulation, particularly for hydrothermal systems located in regions dominated by ultramafic lithologies, which are common at slow and ultra-slow MORs.

We carried out a multi-disciplinary field study composed of sonar mapping, gravity data collection, magnetic field data collection, seismic tomography data collection, MCS seismic data collection, and passive earthquake recordings. The MARINER (Mid-Atlantic Ridge INtegrated Experiments at Rainbow) seismic and geophysical mapping experiment was designed to examine the relationship between tectonic rifting, heat/melt supply, and oceanic core complex formation at a non-transform offset of the Mid-Atlantic Ridge, 36°14’N, the site of the ultramafic-hosted Rainbow hydrothermal system. 

Through this study, we mapped both the seafloor and the sub-seafloor environment and found large rotated blocks of crustal material, displaced by faulting, we mapped crustal thickness, and the thickness of the shallow volcanic layer produced by sub-marine volcanism, we imaged thin lenses of magma that intruded into a large block of uplifted mantle material, and are now thought to be the source of the high-temperature hydrothermal venting, and we imaged what appear to be fluid pathways for the hydrothermal system. This work will re-define some mid-ocean ridges processes, helping to re-write textbooks on this topic.

Findings made through ocean exploration are fundamental to reducing unknowns in deep-ocean areas and the solid earth beneath, and provide high-value environmental knowledge needed to address both current and emerging science and management needs. Better understanding of seafloor hydrothermal systems and heat flow provides intelligence on thermal, biological, and chemical exchange between the solid earth and the oceans and atmosphere, important exchanges that impact ocean chemistry and biological habitats. Through ocean exploration, we establish the baseline information needed to better understand environmental change, filling gaps in the unknown, to deliver reliable science that informs future decision making processes surrounding the issues we confront every day on this dynamic planet.  Information from ocean exploration unlocks the mysteries of deep-sea hydrothermal fields and the ecosystems that thrive within them. Through better understanding of these ecosystems and their habitats, there is a potential for discoveries of new medical drugs, food, energy resources, and other products. Information from deep-ocean exploration can also help predict plate tectonic processes, including earthquakes.