Dataset: Measurements of sinking particle types from deployed Particle Interceptor Trap System (PITS) at the Bermuda Atlantic Time-series Study (BATS) site from Jul 2021 to Mar 2023

Samples for the Bermuda Atlantic Time-series Study (BATS) were collected during monthly cruises in July 2022 (AE2214), November 2022 (AE2224), and March 2023 (AE2306) for seasonal comparison. Particle Interceptor Traps (PITs) were deployed at depths of 150 m, 200 m, and 300 m.

Sinking particles were collected using triplicate polycarbonate gel cups per depth, each containing 100 mL of 12% Tissue Tek polyacrylamide gel to preserve particle structure (Durkin et al., 2015; Ebersbach & Trull, 2008). Gel cups were housed in 70 mm diameter PIT tubes overlaid with dense seawater collected below the halocline (~1000 m), which was filtered (0.2 µm capsule filter, Pall Corp.) and fixed with 2% formalin (final concentration).

Triplicate PIT tubes fitted with acid-cleaned polycarbonate membrane filters (0.8 µm pore size) and filled with poisoned seawater brine (50 g NaCl L⁻¹, 0.7% formalin) were deployed alongside gel cups to measure bulk particulate organic carbon (POC) flux. Membrane filters were processed using standard BATS protocols for C/N analysis (Knap et al., 1997).

After recovery, seawater above the dense brine layer was siphoned off, and remaining seawater was drained. Excess seawater on gel cup surfaces was removed before storage at -80°C. Gel cups were transported on dry ice from Bermuda Institute of Ocean Sciences (BIOS) to Arizona State University for image analysis.

Gel cup surfaces were imaged with a Zeiss Discovery.V12 Stereo Microscope equipped with a 3.2 MP color camera. A Python-based image analysis pipeline was used to segment particles and quantify sinking particle types and size distributions. For each gel cup, 20 images were captured at two gel depths. Microscope optics and camera settings calibrated for magnification and color balance before imaging; calibration files available upon request.

Particles were categorized as fecal aggregates (dense, dark), phytodetrital aggregates (fluffy, amorphous), crustacean fecal pellets, euphausiid fecal pellets, or debris (fragments <60 µm). Non-sinking particles (animal tissue, molts, swimmers) were excluded.

Particle areas (µm²) were measured using the Particle Image Analysis tool, then converted to biovolumes (µm³) using shape-specific formulas: spherical for fecal and phytodetrital aggregates, combined spherical/cylindrical for crustacean fecal pellets, and cylindrical for euphausiid pellets. Debris particles were treated as spherical. Biovolumes were converted to carbon content (mg C per particle) using published conversion factors from multiple ocean regions (Alldredge & Gotschalk, 1990; Silver & Bruland, 1981; Durkin et al., 2021).