New Insights into Marine Snow: Physics Behind Nutrient Cycling Revealed

A recent study from researchers at Brown University and the University of North Carolina at Chapel Hill has unveiled novel insights into the physics of marine snow, a crucial component in the ocean's nutrient cycling system. Published in the Proceedings of the National Academy of Sciences on June 21, 2025, the research explores how organic particles, which descend from the ocean's surface, interact with varying fluid densities to influence their sinking rates.

Marine snow consists of organic particles, including decomposed plant and animal matter, that aggregate with dust and other materials as they sink through the ocean. This phenomenon not only creates a visually captivating scene reminiscent of a snow globe but is also vital for cycling carbon and nutrients throughout marine ecosystems.

According to Dr. Robert Hunt, a postdoctoral researcher at Brown's School of Engineering and the lead author of the study, the speed at which these particles sink is influenced by their ability to absorb salt relative to their volume. “It basically means that smaller particles can sink faster than bigger ones,” Dr. Hunt stated, a finding that contradicts traditional expectations in fluids with uniform density.

This research stems from earlier investigations into neutrally buoyant particles, which typically stop sinking at certain depths. Dr. Hunt, during these studies, observed unexpected behaviors in particle sinking, prompting the development of a new theoretical model that accounted for the porosity of the particles and their capacity to absorb salt.

Dr. Daniel Harris, an associate professor of engineering at Brown and a co-author of the study, emphasized the significance of their findings. “We ended up with a pretty simple formula where you can plug in estimates for different parameters—the size of the particles or the speed at which the liquid density changes—and get reasonable estimates of the sinking speed,” he explained. This formula offers predictive power that could benefit further research into ocean nutrient cycling and the behavior of microplastics in marine environments.

The experimental setup for this study involved creating a linearly stratified body of water, allowing researchers to manipulate fluid density. By using 3D-printed molds, the team produced particles of varying shapes and sizes made from agar, a gelatinous substance derived from seaweed. Observations captured through cameras confirmed their predictions, revealing that smaller, spherical particles tend to sink faster than larger ones, while elongated particles displayed different characteristics, sinking more effectively than spherical ones of equivalent volume.

The findings are pivotal, offering insights not only into the natural processes of carbon cycling but also potential engineering applications. Dr. Harris expressed a desire to collaborate with oceanographers and climate scientists to explore the implications of their research further. Co-authors of the study include Dr. Roberto Camassa and Dr. Richard McLaughlin from UNC Chapel Hill.

The implications of this research extend beyond marine snow and have the potential to inform strategies for carbon capture in larger bodies of water. As the effects of climate change intensify, understanding these fundamental processes becomes increasingly crucial. By refining our understanding of particle behavior in stratified fluids, researchers can contribute to more effective approaches for managing oceanic ecosystems and addressing global climate challenges.

This study is part of ongoing research efforts to better understand the complexities of ocean dynamics and nutrient cycling, which are essential for maintaining the health of marine environments and combating climate change.