A SCOPE Gradients study with CBIOMES cross-over has provided new insights into how phytoplankton adapt to varying nutrient conditions across the North Pacific Ocean, significantly impacting global carbon storage.
Reporting by Helen Hill for CBIOMES
Published in the Proceedings of the National Academy of Sciences, the research led by researchers from Mount Allison University, Dalhousie University, MIT, and other institutions explores the relationship between phytoplankton’s macromolecular composition and the elemental ratios of carbon (C), nitrogen (N), and phosphorus (P) in ocean particulate matter.
The study presents high-resolution measurements of particulate C:N:P ratios along a transect from the subtropical to subpolar North Pacific. It reveals a decline in the C:N ratio moving northwards, primarily due to an increase in protein relative to carbohydrates and lipids. This trend is attributed to phytoplankton’s physiological acclimation to nutrient availability. Researchers found that the macromolecular composition of particulate matter, including proteins, carbohydrates, lipids, DNA, RNA, and polyphosphate, closely mirrors the observed C:N:P patterns. Protein content, in particular, showed a significant increase in the nutrient-rich subpolar regions, driving the lower C:N ratios.
The study suggests that phytoplankton adjust their macromolecular content in response to nutrient supply, with protein allocation increasing under higher nutrient conditions. This acclimation mechanism provides a biochemical basis for the large-scale patterns in ocean C:N:P ratios. The findings challenge the traditional use of a fixed Redfield Ratio (C:N:P = 106:16:1) in global carbon cycle models. Instead, the study advocates for incorporating flexible C:N:P ratios that reflect phytoplankton’s physiological responses, potentially leading to more accurate predictions of ocean carbon storage.
Understanding the variability in ocean C:N:P ratios is crucial for predicting how efficiently atmospheric carbon can be sequestered in the deep ocean. This research enhances our knowledge of marine biogeochemistry and underscores the importance of phytoplankton in regulating global carbon cycles. By linking macromolecular composition to elemental ratios, the study provides a mechanistic framework that could improve the accuracy of carbon-cycle models. Developing such tools is a central aspect of CBIOMES.
The researchers emphasize the need for further studies across different ocean regions to validate their findings and refine biogeochemical models. They also highlight the potential for using macromolecular data to better understand the role of detritus and heterotrophic organisms in shaping ocean C:N:P patterns. This study marks a significant step forward in marine science, offering new perspectives on the dynamic interactions between marine organisms and their environment. As climate change continues to impact ocean ecosystems, such insights are vital for developing effective strategies to mitigate its effects.
Paper
Justin D. Liefer, Angelicque E. White, Zoe V. Finkel, Andrew J. Irwin, Mathilde Dugenneb, Keisuke Inomura, François Ribalet, E. Virginia Armbrust, David M. Karl, Matthew H. Fyfe, Christopher M. Brown, and Michael J. Follows (2024), Latitudinal patterns in ocean C:N:P reflect phytoplankton acclimation and macromolecular composition, PNAS, doi: 10.1073/pnas.2404460121