Latitudinal patterns in ocean C:N:P reflect phytoplankton acclimation and macromolecular composition.

Area of Science:

• Marine biogeochemistry
• Oceanic carbon cycle
• Plankton ecology

Background:

• Particulate organic matter's elemental ratios (C:N:P) deviate from the Redfield Ratio in the ocean.
• Latitudinal patterns in oceanic C:N:P exist, but their drivers are unclear.
• Understanding these patterns is crucial for global carbon storage and deep ocean transport.

Purpose of the Study:

• Investigate the drivers of latitudinal C:N:P patterns in North Pacific surface waters.
• Determine the role of macromolecular composition in explaining observed C:N:P variations.
• Elucidate the contributions of physiological and community structure changes to these patterns.

Main Methods:

• Collected high-resolution data on particulate C:N:P, macromolecular composition, environmental conditions, and plankton community structure.
• Analyzed data along a transect across the North Pacific Transition Zone.
• Compared field data with culture experiments and an allocation-based model.

Main Results:

• Particulate macromolecular composition directly explains observed C:N:P patterns.
• Decreasing particulate C:N from subtropical to subpolar regions correlates with increased protein relative to carbohydrates and lipids.
• Variations in C:P and N:P relate to shifts in protein versus nucleic acids and polyphosphate.

Conclusions:

• Physiological acclimation of phytoplankton to changing nutrient supply is the most likely cause of latitudinal C:N trends.
• Macromolecular composition provides a mechanistic and biochemical basis for large-scale C:N:P variations.
• This study offers insights into the biogeochemical cycling of carbon, nitrogen, and phosphorus in the ocean.