[Paige Wise USC] There is a volcano beneath the surface of the South Pacific that most people will never see, never hear about, and never think about. But it is doing something extraordinary: it is feeding the ocean.
Between Nuku’alofa, the main island of Tonga, and the open sea, the water is extraordinarily clear; it’s the kind of blue that makes you wonder if there is anything living in it at all. The western tropical South Pacific is what oceanographers call a “low-nutrient, low-chlorophyll” region where biology is not exceptionally active and the process of photosynthesis, which draws down atmospheric carbon, is limited by the scarcity of nutrients.
2026 Wrigley Institute Graduate Fellow Paige Wise traveled to Tonga for six weeks to collecting samples in the open ocean around an underwater volcano. These samples will be analyzed for dissolved trace metals, helping researchers better understand how the volcano influences ocean chemistry and marine ecosystems. (Courtesy of Paige Wise)
However, satellites tracking phytoplankton, the microscopic algae at the base of nearly every marine food web, reveal a bloom of biological activity here, a chlorophyll patch stretching over 360,000 square kilometers, roughly the size of Japan. Something is fertilizing this water. The leading hypothesis points to a shallow underwater volcano, known as Volcano 1, sitting along the Tonga-Kermadec Arc at depths between 200 and 450 meters and producing iron-rich hydrothermal fluids.
Iron is the nutrient that limits the growth of a type of phytoplankton called diazotrophs, which create nitrate from nitrogen gas in the atmosphere. Nitrate, in turn, is the nutrient that limits the growth of most other phytoplankton across much of the open ocean. Too little of it, and phytoplankton cannot photosynthesize, draw down atmospheric carbon, and support ecosystems. The open ocean is so depleted in iron that adding a small amount can trigger massive blooms of diazotrophs, which in turn create massive blooms of phytoplankton.
Volcanic hydrothermal systems like Volcano 1 vent iron-rich fluids directly into the water column, and researchers have found that these plumes can travel vertically from depth all the way up into the sunlit surface layer where photosynthesis happens. The question I have come to Tonga to help answer is: how exactly does this happen, and how long does the iron stick around once it gets there?
A Niskin bottle used to collect hydrothermal plume waters hundreds of meters below the ocean surface. The bottle is lowered open, then snaps shut once it’s reached depth, trapping a parcel of water that is brought to the surface to be later analyzed in a lab. (Photo: Paige Wise)
To find out, my team and I spent a collective of 6 weeks between January and March of 2026 in the small island nation state of Tonga, aboard small, local fishing vessels collecting samples in the open ocean around Volcano 1. We used an instrument called a Miniature Autonomous Plume Recorder (MAPR) to hunt for the chemical fingerprint of hydrothermal activity in the water column. MAPRs measure oxidation-reduction potential, turbidity, temperature, and pressure as they descend through the water. When a MAPR passes through a hydrothermal plume, these sensors detect a dramatic change in the chemistry of the seawater: a sudden drop in oxidation-reduction potential, a spike in turbidity from particles carried by the hot fluid.
We also collected water samples at depth using Niskin bottles which are essentially large plastic tubes that snap shut on command, capturing seawater at a precise depth. Back in the lab, these samples will be analyzed for dissolved trace metals, including iron and manganese. Manganese is particularly useful as a tracer: it scavenges out of the water more slowly than iron, leaving a detectable signal farther from the vent. By tracking manganese, we can map where the plume has been.
Beyond just detecting the plume, I am trying to quantify its effect on biology. At plume-impacted stations, we ran incubation experiments collecting surface water, spiking it with different concentrations of iron or other nutrients, sealing it in bottles, and leaving it in the sun to see what grows. These stations allow us to measure how responsive the local phytoplankton community is to iron addition. Combined with the plume-tracing data, the goal is to build a picture of the pathway: vent fluid rises from depth, iron enters the photic zone, phytoplankton respond, and a bloom follows.
Wise (right) speaks with observers associated with the Tongan Ministry of Fisheries and Ministry of Lands. (Courtesy of Paige Wise)
he field season did not go according to plan (they rarely do). On our first cruise, equipment malfunctions forced us back to port. Later deployments contended with island-driven currents, rough seas, and the general chaos of doing precision science from a small boat. But woven through those challenges were some of the most rewarding experiences of my life: working alongside collaborators from the Tongan Ministry of Fisheries and Ministry of Lands, learning from the captain and crew of our fishing vessel, and being welcomed by hosts who were extraordinarily gracious in helping a team of scientists settle into Tonga.
The Tonga-Kermadec Arc is the longest subduction system on Earth, stretching over 2,500 kilometers. Along its length, dozens of volcanic systems may be contributing iron and other trace metals to the overlying ocean at levels we are only beginning to understand. If shallow hydrothermal systems like Volcano 1 are significant, persistent sources of bioavailable iron, then they are players in the ocean’s carbon cycle because phytoplankton take up carbon dioxide as they grow. Understanding this source, its magnitude, and its variability matters not just for the South Pacific, but for how we think about the ocean as a whole.
Paige Wise is supported by the USC Dornsife Wrigley Institute Graduate Fellowship
Astrobiology, Oceanography, Biodiversity,
