Diversity of Growth Rates Maximizes Phytoplankton Productivity in an Eddying Ocean. Issue 3 (1st February 2022)

• Record Type: Journal Article
• Authors: Freilich, Mara A.; Flierl, Glenn; Mahadevan, Amala
• Is Part Of: Geophysical research letters. Volume 49:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-02-01
• Subjects: vertical velocity -- nutrient supply -- phytoplankton growth -- diversity -- new production; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL096180
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: In the subtropical gyres, phytoplankton rely on eddies for transporting nutrients from depth to the euphotic zone. But, what controls the rate of nutrient supply for new production? We show that vertical nutrient flux both depends on the vertical motion within the eddying flow and varies nonlinearly with the phytoplankton growth rate. Flux is maximized when the growth rate matches the inverse of the decorrelation timescale for vertical motion. Using a three‐dimensional ocean model and a linear nutrient uptake model, we find that phytoplankton productivity is maximized for a growth rate of 1/3 day −1, which corresponds to the timescale of submesoscale dynamics. Variability in the frequency of vertical motion across different physical features of the flow favors phytoplankton production with different growth rates. Such a growth‐transport feedback can generate diversity in the phytoplankton community structure at submesoscales and higher net productivity in the presence of community diversity. Plain Language Summary: The productivity of phytoplankton is the result of a two‐way coupling between the rate of phytoplankton growth and nutrient supply by physical mechanisms. A three‐dimensional model of an oceanic eddy flow field maximizes its nutrient flux to the sunlit surface layer when the average phytoplankton growth rate is approximately 1/3 day −1, which is consistent with observations. Different features of the flow field experience variable frequencies in the up/down motion and favor different phytoplankton growth rates to maximize new production, providing a way to generate diversity in the community composition of phytoplankton. Since changing the grid resolution of ocean models alters the vertical velocities, the biological growth rates also ought to be altered to represent the appropriate physical‐biological coupling. Key Points: Nutrient flux depends nonlinearly on the rate of biological nutrient uptake with a maximum at a particular rate In a subtropical eddy field, the nutrient uptake rate that maximizes nutrient flux corresponds to the frequency of submesoscale dynamics Variability in vertical velocity characteristics on water mass trajectories could favor phytoplankton with a diversity of growth rates