Abstract
Ocean ecosystems constitute the largest habitable volume on Earth and regulate climate, support fisheries and a global Blue Economy valued at an estimated $1.5 trillion annually and provide services on which human wellbeing depends. Four decades of satellite ocean color observations have transformed understanding of phytoplankton distribution, biodiversity, and productivity, and NASA's PACE mission is now extending this record with unprecedented hyperspectral and polarimetric capabilities. Yet, passive ocean color remote sensing remains fundamentally two-dimensional – it detects only the optical signature of the uppermost, sunlit ocean; provides little or no coverage during polar night, persistent cloud cover, and low-sun conditions; and offers no independent means of validating its own retrievals. This white paper, submitted in response to the ESAS 2028 Request for Information under the Biosphere sphere, presents the science case and a phased observing strategy for achieving a four-dimensional (three spatial dimensions plus time), pole-to-pole characterization of global ocean ecosystems. The vision presented here draws heavily on Earth’s Living Ocean, the science vision report of NASA’s Ocean Biology and Biogeochemistry Program. We recommend 1) sustaining hyperspectral ocean color and polarimetric continuity, 2) adding a mature, ocean-optimized profiling lidar to resolve water column particle distributions and fill coverage gaps in polar and persistently cloudy regions, 3) expanding autonomous and suborbital in situ observing networks, and 4) investing in ecosystem models and data assimilation systems capable of ingesting these complementary data streams. Together, these elements would resolve a critical, decades-old gap in our ability to characterize, understand, and predict how global ocean ecosystems – from phytoplankton production to the fisheries and top predators they sustain – are responding to compounding natural and human-driven stressors, and whether those ecosystems are approaching thresholds beyond which their structure and function change abruptly and persistently.