Fating Carbon in the South Pacific Ocean: Metabolic and Allometric Scaling Approaches to Understanding Variation in Marine Primary Productivity across Physical Regimes

Abstract: The subtropical, tropical, and equatorial Pacific Ocean encompass environments from the world's most productive fisheries to the largest and most nutrient-scarce contiguous habitats on Earth. Marine microorganisms are the unifying foundation of ecosystems across this entire spectrum of chemical and physical contexts. Yet marine microbial communities exhibit a vast diversity in traits such as size, growth rate, minimum nutrient requirements, and metabolic capabilities. Scaling up this trait diversity over the entire ecosystem leads to emergent differences in marine microbial biogeochemical functions including carbon dioxide uptake/oxygen production (primary production), carbon dioxide release/oxygen utilization (respiration), and carbon sequestration to the deep ocean (export). This talk will review observational/experimental methods and preliminary data from a field campaign sampling the North Pacific Subtropical Gyre, Equatorial Pacific, and the South Pacific Subtropics conducted in 2024. We combine kilometers-scale physical surveys of water column properties such as temperature and oxygen saturation; nearly 2000 observations of surface seawater microbial community size structure and functional composition; and daily, degree-resolution isotope incorporation experiments to model the relationships between oceanographic environmental conditions, ecosystem-scale allometrics, and biogeochemical rates associated with the ocean carbon cycle. Localized, high intensity time series sampling at unique coordinates associated with major ocean currents were demonstrated to have differences in community size structure and metabolic rates, leading to differences in the total amounts and quality of carbon exported to the deep ocean. We will also discuss a previously overlooked aspect of scaling in marine microbial ecosystem functioning - partitioning between viral and grazing mortality. Understanding the complex interplay between allometric scaling and temperature scaling in marine microbial communities will be crucial to simulating and diagnosing the fate of carbon entering Earth's largest ocean basins