Carbon‐based ocean productivity and phytoplankton physiology from space

TLDR

Ocean biogeochemical and ecosystem processes are linked by net primary production, which depends on phytoplankton biomass and physiology, yet estimating these terms from space has remained elusive. We present new satellite ocean‑color observations of phytoplankton carbon and chlorophyll biomass and demonstrate that derived Chl:C ratios track expected physiological responses to light, nutrients, and temperature. Global estimates of phytoplankton growth rates and carbon‑based NPP are produced for the first time, revealing higher values in tropical oceans, stronger seasonality at mid‑ and high latitudes, and distinct bloom dynamics, indicating that integrating phytological and remote‑sensing concepts could transform ocean carbon cycling models.

Abstract

Ocean biogeochemical and ecosystem processes are linked by net primary production (NPP) in the ocean's surface layer, where inorganic carbon is fixed by photosynthetic processes. Determinations of NPP are necessarily a function of phytoplankton biomass and its physiological status, but the estimation of these two terms from space has remained an elusive target. Here we present new satellite ocean color observations of phytoplankton carbon (C) and chlorophyll (Chl) biomass and show that derived Chl:C ratios closely follow anticipated physiological dependencies on light, nutrients, and temperature. With this new information, global estimates of phytoplankton growth rates (μ) and carbon‐based NPP are made for the first time. Compared to an earlier chlorophyll‐based approach, our carbon‐based values are considerably higher in tropical oceans, show greater seasonality at middle and high latitudes, and illustrate important differences in the formation and demise of regional algal blooms. This fusion of emerging concepts from the phycological and remote sensing disciplines has the potential to fundamentally change how we model and observe carbon cycling in the global oceans.