High-resolution marine flux measurements, in situ respiration rate determinations, and meta-omic surveys of sinking particulate matter in the ocean’s three primary oxygen deficient zones

A key challenge to understanding carbon cycling in the ocean is determining the flux of particulate organic matter out of the surface ocean and quantitating the respiration and utilization of this dynamic pool. To address this challenge, we have developed a free-drifting, unpoisoned particle trapping and incubation platform which collects sinking marine particles and allows for in situ experimentation. Across the project’s history, five generations of trap-incubators have been deployed in multiple locations including the world’s three largest open ocean oxygen deficient zones; the eastern tropical North Pacific, the eastern tropical South Pacific, and the Arabian Sea. Flux measurements and metabolic rates are integrated with multi-omic sequencing, trace metal measurements, and modeling, to better understand how organic matter is produced, degraded, and cycled. Across the ETNP, ETSP and Arabian Sea, a range of POM attenuation curves deviant from a traditional Martin curve are observed. Notably, in the ETNP, a secondary peak is observed in the flux curve, showing the importance of Prochlorococcus, which were identified in trapped particles through genomic and proteomic sequencing (Fuchsman et al, 2019). Identified peptides included high confidence matches to proteins from taxa unanticipated to be in the relatively uncharacterized sinking particulate matter, including many from the fungus Dikarya, enriching our understanding of particle colonization over time and space (Duffy et al., submitted). Also in the ETNP, trap-incubator systems collected particulate matter and performed O₂ and pH-monitored in situ incubations of particle-concentrated and control seawater chambers with injected isotope-labeled substrates. Incubation experiments with ¹⁵NO₂ and ¹⁵NH₄ reveal rates of N₂ production due to sinking particles to be in the range of 1.4 – 4.8 nM N₂ day^-1 at an offshore station.