Molten rock rising beneath the Atlantic floor meets cold seawater, and scientists are about to map the hidden plumbing that carries that water through the young crust. This circulation accounts for roughly a quarter of global heat loss from the Earth’s interior, yet the actual pathways of fluid flow have remained invisible. Previous studies have measured vent fluids and mineral deposits, but these represent only a fraction of the total system. The team will deploy powerful electromagnetic transmitters near the seabed at the Lucky Strike vent field on the Mid-Atlantic Ridge, combined with a year-long network of earthquake sensors, to produce the first high-resolution 3D images of how hydrothermal fluids move from molten rock to the ocean above. If successful, the research will reveal how heat and chemicals transfer between the Earth’s interior and the oceans, and how those pathways shift over months to decades. This is fundamental science—it will not directly change a product or policy tomorrow. But understanding how hydrothermal systems deposit minerals that are critical for low-carbon technologies, and how they sustain unique deep-sea ecosystems, could inform future resource exploration and conservation decisions. Similar geophysical imaging has, in the past, transformed understanding of everything from groundwater reserves to volcanic hazards.
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At mid-ocean ridges, plates move apart and the resulting space is filled with rising hot material that melts to form new ocean crust. Interaction between this hot young crust and cold seawater results in hydrothermal circulation that is responsible for ~25% of global heat loss. This circulation influences the chemistry of the oceans and crust, feeds unique ecosystems that hold clues to the origin of life and deposits minerals that are critical to modern technology and to a low-carbon future. Scientists can study this circulation by making measurements on fluids that emerge and on the mineral deposits that they form. Drilling into young crust and instrumentation of the resulting boreholes provides further insights. But focused venting of hot fluids and the associated mineral deposits must represent a small fraction of the overall flow. The pathways of circulation remain elusive because we have lacked a way of imaging this flow, which can change significantly over time as molten rock cools and hydrothermal fluids find new pathways, particularly at mid-ocean ridges where the plate separation is slow and molten rock is only episodically present. Two geophysical techniques can image active flow: seismology, which detects and locate small earthquakes resulting from cracking of the rocks by fluids; and electromagnetic imaging techniques that detect variations in resistivity due to changes in temperature and composition of the pore fluid. Recent developments in these techniques provide opportunities for previously impossible high-resolution three-dimensional imaging of fluid pathways. The aim of our project is to determine how hydrothermal circulation transfers heat and chemicals from molten rock below a mid-ocean ridge to the ocean above, and how this circulation changes on annual to decadal timescales, by carrying out a novel geophysical experiment at the “Lucky Strike” vent field on the slow-spreading Mid-Atlantic Ridge. This site is unique because: it is the only place on a slow-spreading ridge where molten rock has been imaged and mapped with seismic techniques; it was the focus of a 3D controlled source electromagnetic (CSEM) study in 1999, yielding data that can only be analysed fully with techniques developed much more recently; and it has been the focus since 2010 of a European observatory, involving continuous observations, including of small earthquakes. At this site we will conduct a high-resolution 3D CSEM study using powerful transmitters close to the seabed. We will monitor resistivity changes over a one-year period using passive electromagnetic techniques. We will combine these observations with published information on sound speeds beneath Lucky Strike to distinguish the effects of rock composition from those of fluids. We will monitor small earthquakes for one year, using a larger set of instruments than available from the observatory, allowing us to distinguish earthquakes resulting from hydrothermal flow from those resulting from stretching of the crust. Using time-lapse electromagnetic modelling techniques currently under development, we will explore how hydrothermal flow patterns have changed since 1999 and how they change over a year. We will use the earthquake observations to determine likely locations of such changes. We will combine all of these results with data from the observatory, including measurements of the temperature and composition of fluids venting through the seafloor, to develop an integrated 3D view of the whole system from the molten rock below to the ocean above and its variation over time.
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