Iron (Fe) is a common element found in hot fluids coming out of the seafloor at places like mid-ocean ridges. Scientists used to think that most of this iron stayed close to these hydrothermal vents and didn't travel far in the ocean. However, new evidence suggests that some of this iron can actually travel long distances in the ocean and even reach the top layer where sunlight reaches, which is important for the growth of microscopic plants called phytoplankton. In our research, we wanted to figure out how fast this iron moves away from a major undersea mountain range called the southern East Pacific Rise. To do this, we used naturally occuring radioactive materials called radium isotopes, which are also found in the hydrothermal fluids but don't react like iron does. We used underwater robots and measurements taken from instruments towed behind ships to locate two types of hydrothermal discharges - high and low temperature - then, we measured the levels of both iron and radium isotopes. We found that the hot water coming out of the seafloor had slightly more radium isotopes than the normal seawater, but the cold water had a lot more of a specific radium isotope called 223-Ra. This is similar to what another study found near Hawaii, where they thought this specific radium isotope came from a process involving seawater circulating through rocks. Our data used these measurements of radium isotopes and iron to figure out how fast the fluids are moving and how long the iron stays near the southern East Pacific Rise. This will help us improve our computer models that predict how important this hydrothermal iron is for the growth of phytoplankton and in turn their abiliyt to remove carbon dioxide from the surface of the ocean. Last Modified: 09/26/2023 Submitted by: Matthew A Charette