Traces of water heated to 300 degrees have been found near the “Lost City”

To find out where this water comes from, scientists drilled a borehole nearly 1.3 kilometres deep near the ‘Lost City’. The chemical composition of the samples extracted from it showed that some of the water had been trapped amongst hot rocks for a long time and had been heated to at least 300 °C.

It is important to note that the researchers did not discover a boiling lake beneath the surface, nor did they measure such a temperature directly. At the time the samples were taken, the water was considerably cooler. Its past was revealed by the chemical ‘fingerprint’ left behind after contact with the hot rocks.

Details

The ‘Lost City’ hydrothermal field is situated on the Atlantis underwater mountain range near the Mid-Atlantic Ridge. Light-coloured carbonate towers rise from the seabed there, formed by minerals that precipitate out of the water.

Unlike plants on the Earth’s surface, the local microorganisms do not need sunlight. They utilise hydrogen, methane and other substances produced when water interacts with the rocks.

Until now, scientists did not know how deep this system extends or exactly where the water acquires its unusual chemical composition.

In 2023, members of the international IODP 399 expedition drilled borehole U1601C approximately 800 metres from the ‘Lost City’. The drill reached a depth of 1,268 metres below the seabed and passed mainly through peridotite — a rock typically found in the upper part of the Earth’s mantle.

After drilling was completed, the researchers extracted water from various levels of the borehole. The upper samples consisted mainly of seawater and fresh water used during the drilling operations. However, with increasing depth, the proportion of natural water seeping from fractures in the rock increased. In some samples, it reached approximately 80 per cent.

This water contained almost no magnesium, but was found to be rich in calcium, lithium, rubidium, caesium and strontium. Such a combination of elements arises when water interacts with hot rocks over a long period: some substances remain within the minerals, whilst others dissolve into the fluid.

Calculations showed that chemical equilibrium between the water and the rocks could have been established at a temperature of at least 300 °C. The liquid then rose up through the fractures and mixed with cooler water.

Its composition turned out to be close to that which scientists had previously hypothesised for the deep-seated source of the ‘Lost City’. This is the first direct evidence that water which has passed through very hot rocks is indeed circulating beneath the Atlantis massif.

However, the study does not yet prove the existence of a direct channel between the drilled well and the White Towers. Scientists are therefore cautious in suggesting that the water discovered may be part of a single hydrothermal system.

Where does the energy for life come from?

Seawater seeps into cracks in the ocean floor and sinks to great depths. There, it is heated and reacts with the rocks of the Earth’s mantle.

During these reactions, both the water and the rock itself are transformed. In particular, hydrogen may be produced, which then rises closer to the surface and becomes a source of energy for microorganisms.

This process can be compared to a hidden system of pipes. The water sinks down, passes through hot rock, changes its composition and returns to the seabed. Along with it, substances that sustain life in complete darkness are carried upwards.

However, it was not possible to reliably measure the hydrogen content in the new samples. The water was collected several days after drilling, without using airtight containers, so the dissolved gases may have escaped.

Why this is important

The research helps us understand how life can exist without solar energy. The ‘Lost City’ ecosystem depends not on photosynthesis, but on chemical processes within the seabed.

The data obtained are also important for studying the circulation of water and chemical elements between the ocean and the Earth’s deep layers. They show that seawater is capable of penetrating more than a kilometre into oceanic rock, heating up there and returning to the surface.

Similar conditions may exist beyond Earth. Oceans are likely hidden beneath the icy surfaces of Jupiter’s moon Europa and Saturn’s moon Enceladus. If water there interacts with a rocky seabed, sources of chemical energy may also arise within it.

This does not mean that life necessarily exists on these moons. However, *The Lost City* illustrates what a habitable environment for microorganisms might look like in an ocean where sunlight never penetrates.

Background

‘The Lost City’ was discovered in 2000. Its light-coloured towers stand in stark contrast to the dark ‘black cigars’ – other deep-sea vents associated with volcanic activity.

The water emerging from the ‘Lost City’s’ towers is relatively cool, but is highly alkaline and contains large amounts of hydrogen and methane. Some of the towers reach the height of a multi-storey building.

Scientists regard such vents as a possible model for the conditions in which early life on Earth might have originated. The new study does not test this hypothesis directly, but it helps to understand where such systems obtain their water and chemical energy.

The study has significant limitations. The samples were mixed with the water used during drilling, and it is not yet possible to determine the exact contribution of different rock types. The scientists plan to return to the well once it has stabilised and obtain cleaner samples using sealed samplers.

Source

The study by K. Jeffrey White and his colleagues, “Borehole Waters From Hole U1601C (Atlantis Massif) Provide Constraints for a Deep-Sourced Formation Water That (Could) Feed the Lost City Hydrothermal Field” was published in the journal Geochemistry, Geophysics, Geosystems in 2026.