Steven Goldstein Presents his Work on Rethinking How the Rare Earth Elements Move Through the Oceans

Steven Goldstein Presents his Work on Rethinking How the Rare Earth Elements Move Through the Oceans

Steven Goldstein, a scientist at the New Mexico Consortium and Los Alamos National Laboratory, recently gave a presentation titled, Does the Neodymium Oceanic Residence Time Paradox Really Exist? at the 2025 American Geophysical Union Meeting, held December 14-19 in New Orleans. In this presentation, he revisited a long-standing question in ocean science about the behavior of the element neodymium and other rare earth elements.

Neodymium is part of a group of rare earth elements that scientists use to trace ocean circulation and study past and present environmental change. For decades, researchers have pointed to an apparent contradiction known as the neodymium oceanic residence time paradox.  Namely, the neodymium isotopic composition of seawater differs between the ocean basins, suggesting that the element moves through the ocean relatively quickly, while estimates based on river inputs indicate it should remain in the ocean much longer.

In his presentation, Goldstein explained that this contradiction may not be real. Much of the research on neodymium and other rare earth elements in seawater relies on unfiltered or coarsely filtered samples, meaning that material described as dissolved could include tiny particles and microscopic clusters known as colloids. These particles are common in rivers and coastal waters and continue to influence neodymium and rare earth element chemistry even in the open ocean.

Because neodymium concentrations are much higher in particles than in seawater, even small amounts of particles or exchanges between particles and water can strongly affect seawater concentrations. Goldstein also noted that neodymium behaves differently from elements that are evenly mixed throughout the ocean, making the idea of a single ocean residence time less useful.

When particle interactions and different forms of neodymium are taken into account, the apparent paradox largely disappears. Goldstein’s work suggests that scientists may need to rethink some of the assumptions used to describe how neodymium and the other rare earth elements exist and move through the oceans.

This research contributes to a better understanding of ocean chemistry and highlights the complex role that particles play in shaping the movement of trace elements in the marine and other environments.