Journal Article

Spatial and Temporal Interplay Between Oceanic Circulation and Biological Production in Shaping Carbon Export Off the California Coast

Stukel, M. R., Messié, M., Huffard, C. L., Ruhl, H. A.

2025

Overview

A major challenge in understanding the oceanic carbon cycle is estimating the sinking flux of organic carbon exiting the sunlit surface ocean, termed carbon export. Existing algorithms derive carbon export from satellite ocean color, but neglect spatiotemporal offsets created by the temporal lag between production and export, and by horizontal advection. Here, we show that a Lagrangian “growth‐advection” (GA) satellite‐derived product, where plankton succession and export are mapped onto surface oceanic circulation following coastal upwelling, succeeds in representing in situ export off the California coast. In situ export is best represented by a combination of GA export (proportional to modeled zooplankton) and export derived from ocean color (related to local phytoplankton). Both products also correlate with a long‐term time series of abyssal carbon flux. These results provide insights on export spatiotemporal patterns and a path toward improving satellite‐derived carbon export in the California Current and beyond. Plain Language Summary Climate on Earth is strongly tied to the carbon cycle, which regulates atmospheric CO2 concentration. A key component of the oceanic carbon cycle is the downward flux of organic carbon outside of the surface sunlit layer, termed carbon export, which can ultimately sink to the bottom of the ocean and be sequestered for hundreds of years. Direct measurements of carbon export are scarce, so that models and satellite data are needed to understand large‐scale patterns. Because organic carbon originates from phytoplankton fixing CO2 in the ocean surface via photosynthesis, satellite‐derived algorithms have been developed by relying primarily on phytoplankton ocean color data. However, such models display poor accuracy. One reason is that they neglect the time elapsed between photosynthesis and carbon export, which can result in a spatial offset of hundreds of kilometers. Our study explicitly considers these offsets and shows that export can also be well represented from space without ocean color, using a plankton model and satellite‐derived oceanic currents. These results provide new insights on what controls carbon export, how to represent it from space, and its spatiotemporal patterns in a productive oceanic region. Key Points Coastal upwelling, advection, and plankton dynamics explain variability in surface carbon export by sinking particles A Lagrangian growth‐advection satellite model performs as well as export derived from ocean color both for surface and abyssal carbon fluxes Satellite‐derived export products need to consider offsets between production and export, and the role of zooplankton and advection

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Abyssal zone / Advection / Algorithms / Biological production / California Current / Carbon / Carbon cycle / Carbon dioxide / Carbon dioxide concentration / carbon export / Coastal circulation / Coastal upwelling / Fluctuations / Horizontal advection / modeling / Ocean circulation / Ocean color / Ocean colour / Ocean surface / oceanic advection / Oceans / Offsets / Organic carbon / Photosynthesis / Phytoplankton / Plankton / remote sensing / Satellite data / Satellites / Upwelling / upwelling systems / Zooplankton