KM2112 SCOPE-Paragon-1 24-hour Particle Flux

The 2021 SCOPE-PARAGON research expedition was a coordinated effort to characterize particle dynamics and remineralization in the upper 500 m of the North Pacific Subtropical Gyre. Despite the importance of particles as key sites of biological activity in an otherwise dilute seawater medium, there remain major gaps in our understanding of the specific processes and organisms controlling particle transformations. The 2021 SCOPE-PARAGON cruise was directed towards understanding the processes and rates of biological particulate matter transformations (e.g., production, decomposition, sinking) as well as the ecological interactions that occur in association with suspended and sinking particles. These targeted studies of particle dynamics at Station ALOHA would leverage ongoing ecological and biogeochemical modeling efforts in SCOPE. Particle Interceptor Traps (PITs; Knauer et al., 1979) were prepared, deployed, and processed according to this protocol to quantify vertical particulate matter fluxes during the PARAGON I expedition. To isolate sinking particles and prevent flushing, a high-density brine solution was prepared by dissolving 4250 g of potassium chloride (KCl) in 50 L of Milli-Q water, which was then pre-filtered to eliminate background contamination. This filtered KCl solution was added to individual PIT tubes with a mouth opening of 0.0039 m². For each deployment twelve PITs were deployed at 150 m for a collection period of approximately 24 hours. The PITs were affixed to a PVC cross attached to a single free-floating array. Upon recovery, the density interfaces were visually identified and marked, and the overlying seawater layer was siphoned off to 5 cm above the brine interface. The remaining volumes containing the captured particulate matter were pre-screened through a 335 µm NITEX mesh, pooled into a 20 L carboy, and homogenized by gentle rolling. Finally, precise volumetric aliquots were drawn from the mixture for discrete biogeochemical analyses, including Particulate Adenosine 5-Triphosphate (PATP, 0.5 L), Particulate Phosphorus (PPO4, 0.5 L), Total Particulate Carbon and Total Particulate Nitrogen (TCTN, 2.0 L), Particulate Inorganic Carbon (PIC, 1.5 L), Particulate Silica (PSi, 0.25 L) and Chlorophyll a/ Pheophytin (Chla/Pheo, 0.15 L). Equivalent volumes of the filtered KCl solution were filtered and analyzed concurrently for blank corrections. The timestamp is in UTC.