Beneath Iceland, an enormous blob of hot rock slowly rises from deep within the mantle, delivering magma to one of the most volcanically active places on Earth.
But the influence of the Iceland Plume goes far beyond volcanic activity. Over millions of years, the plume has pulsed rhythmically, causing the seabed to rise and fall, possibly diverting the flow of deep ocean currents that help regulate heat and ultimately stabilize the global climate.
In a new study, Cambridge earth scientists studied volcanic rocks drilled from the seabed 600 kilometres south of Iceland to reconstruct the plume’s dynamic history, finding that its evolution has been more complex than previously thought.
Taking the plume’s pulse
The basalt rocks analysed in the study were amongst nearly 6,600 metres of rock and sediment drilled beneath the seabed near the Reykjanes Ridge by International Ocean Discovery Program (IODP) Expedition 395.
The expedition, involving Cambridge Earth Sciences’ Nicky White, targeted a series of chevron-patterned ridges and troughs that represent features etched onto the seabed as the underlying mantle plume fluctuated in temperature.
Another borehole was drilled from an area of older rocks unaffected by these surface ridges. It was these rock samples that Callum Pearman, PhD student at Cambridge Earth Sciences, used for his new study.
Pearman and fellow-PhD student Chia-Yu Tien analysed chemical clues within the rocks, comparing their fingerprint with other seafloor basalts from around the world, including locations distant from mantle plumes.
Top: a core section containing dark basalt glass, below: one of the basalt rock samples viewed under the microscope. Credit: Callum Pearman.
Their data supports a body of evidence to show that the plume’s imprint on the seabed diminished around 38 million years ago, before slowly becoming re-established toward the present day.
“These results highlight a more dynamic history of plume–ridge interaction than is often assumed,” said Pearman. “If the plume’s influence did collapse, which we think it did, it could have had major implications for ocean circulation in the North Atlantic.”
While some scientists have proposed that the Iceland plume fluctuated in size and influence through time, others have argued that it remained relatively stable.
“Our data strongly suggest that the plume’s influence underwent periods of collapse and resurgence. The magnitude of the geochemical variability we observed through time was unexpected,” said Pearman
Previously, evidence for the plume’s collapse had been limited to geophysical evidence, such as the presence or absence of ridges and fracture zones on the seabed.
Mantle plumes are thought to be at their most productive early in their history. When the North Atlantic Ocean first opened, the Iceland plume fuelled volcanism over a huge area, forming ancient volcanic provinces; remnants of which are still seen in the Giant’s Causeway, Northern Ireland, Fingal’s cave, Scotland, and parts of Greenland.
Pearman explained that when rifting begins, magma may surge to the surface as new ocean crust forms. As the rift matures, the plume head cools and runs through its reserves so that its influence fades and magma production becomes more focused along the developing spreading centre. He says this is a possible explanation for the observed reduction in plume influence around 38 million years ago.
“Because of this unique rock record, we can chemically test models of plume-evolution, adding another piece to the jigsaw puzzle in our understanding of this enigmatic mantle upwelling.”
Reference: Pearman, C., Tien, C.Y., White, N., Maclennan, J., Murton, B., Gibson, S., Day, J., Parnell-Turner, R. and IODP Expedition 395 Scientists, 2026. Collapse and resurgence of the Iceland mantle plume. Nature Communications.
Feature image: IODP 395 scientists (including Nicky White on right) examining rock cores drilled during the expedition.