Marine particles host a crucial microbial process with global implications

In a groundbreaking discovery, researchers from the Leibniz Centre for Marine Tropical Research (ZMT) in Bremen, Germany, along with collaborators from the Center for Ocean Life at DTU Aqua and researchers in the USA, have demonstrated that microbial fixation of nitrogen can occur on marine snow particles. This study, published in Nature Communications, offers the first explanation of how marine-snow-associated N2 fixation takes place.

The two-year research project suggests that this process is crucial for global marine nitrogen cycling, plankton growth, and productivity. The study, led by Lasse Riemann, Professor at the Department of Biology, University of Copenhagen, shows that a marine particle can become densely colonized by bacteria, leading to low oxygen concentrations on the particle, which allows for the anaerobic process of N2 fixation.

The growth of bacteria on marine snow particles causes extensive respiration, a process that has puzzled scientists for years. However, this study provides a comprehensive understanding of the role these particles play in the cycling of many nutrients in the ocean.

Subhendu Chakraborty, a postdoc at the Department of Biology, University of Copenhagen, is the first author of the study. The researchers modeled rates of N2 fixation, which were found to be comparable to actual rates measured in marine waters. Lasse Riemann expresses confidence in the model used in the study, stating that it accurately represents the complex interactions between marine microbes and particles.

Marine snow, consisting of debris from diverse organisms in the water column, is typically collected using bottles attached to a rosette. The depth distribution of N2 fixation in the marine water column is dependent on the size, density, and sinking speed of the marine snow particles.

The researchers are hopeful that their study will inspire future work on microbial life on marine particles. They believe that understanding the role of marine snow in nitrogen fixation could lead to a better understanding of the global marine nitrogen cycle and its impact on climate change.

The study can be accessed using the DOI 10.1038/s41467-021-23875-6. This research marks a significant step forward in our understanding of the ocean's nutrient cycles and could have far-reaching implications for future research in marine biology and climate science.