The depths of the ocean are among the final frontiers of scientific exploration. Scientists have visually studied less than 0.001% of the seafloor, but oceanography is essential to understanding the climate, ecosystems, and processes deep in the Earth, including earthquakes and the resulting tsunamis.

Now, emerging technologies, including advanced drilling technologies, seismic sensors, and methods for turning deep-sea cables into a giant seismic monitoring network, are poised to solve these mysteries.

Nature has looked at how some of these tools work and the geoscience questions they could help answer.

Mapping the mantle

Plate tectonics is driven by convection, or the churning of the mantle, the layer of mostly solid rock beneath the Earth’s crust that makes up more than 80% of the planet’s volume. But the inner geological workings of the mantle remain largely a mystery.

Researchers have begun to map the convection process by measuring how different rock densities affect the propagation of seismic waves, using ocean bottom seismometers (OBS) that can run on batteries for a year or more.

OBS studies have helped show that the movement of rocks in the mantle is “like a lava lamp,” says Ana Ferreira, a seismologist at University College London (UCL). “Imagine a saucepan with boiling syrup, but different types of syrup of different densities,” he says. Particularly hot ‘plumes’ (solid mantle rock that is hotter than the surrounding mantle) create chains of mid-ocean volcanoes, such as those in Iceland or the Hawaiian archipelago.

Pioneering research in the 1990s focused on the Pacific Ocean, but now scientists are expanding their studies to the rest of the oceans. One such project, called UPFLOW, is currently analyzing data from the OBS that Ferreira and his collaborators deployed in the Atlantic around the Azores, the Canary Islands, and Madeira.

In a separate project, the team demonstrated how tools from the ocean floor could help scientists during a crisis. An earthquake storm shook the volcanic island of São Jorge in the Azores in March 2022, sparking fears of an upcoming eruption. Ferreira and his collaborators rushed to install six OBS around the island and mapped magma activity beneath the volcano.

In the end there was no eruption. “The magma reached within a kilometer of the surface. Then it stopped,” says UCL seismologist Stephen Hicks, co-author of the study.¹.

Drilling deep into the mantle

Ultimately, scientists would like to understand the depths of the Earth: a big challenge is to drill into the lower limit of the crust (called the Mohorovičić discontinuity) and take the first pristine samples of the underlying mantle.

Researchers have high hopes that a new oceanographic research vessel, the one from China Meng Xiangwhich in Mandarin means “dream”, launched at the end of 2024, was able for the first time to collect samples directly from the mantle. Meng Xiang It is equipped to drill up to 11,000 meters below the sea surface, deeper than any scientific vessel to date.

Peter Bijl, a paleoceanographer at Utrecht University in the Netherlands, was invited to visit the ship during a workshop in Guangzhou, China, in late 2024 and was impressed by the variety of laboratories and facilities on board. “It had everything one could need on a boat, and more,” says Bijl.

Tsunami detection with hydrophones

Tsunamis can start at one end of the ocean and end up causing widespread destruction at the other. Usama Kadri, an applied mathematician at Cardiff University in the United Kingdom, and his collaborators have developed an ocean-based technique to predict if and where a tsunami will cause destruction, up to several hours before its waves hit land.

Their method is based on hydrophones, or underwater microphones, which can detect low-frequency sounds that occur at the point of origin of a tsunami. Kadri and his collaborators created a mathematical model that uses hydrophone data to simulate how tsunami waves propagate around the world.². “The advantage of the software is that it can perform global calculations in less than 30 seconds,” says Kadri.

Crucially, underwater sounds travel three times faster than the tsunami itself, so they can reach hydrophones hours before the tsunami. This could give local authorities precious time to evacuate local people from low-lying coastal areas.