Carbon Flux Explorer Optical Assessment of C, N and P Fluxes

Abstract. The magnitude and controls of particulate carbon exported from surface waters and its remineralization at depth are poorly known. The Carbon Flux Explorer (CFE), a Lagrangian float-deployed imaging sediment trap, has been designed to optically measure the hourly variations of particle flux to kilometer depths for months to seasons while relaying data in near-real time to shore via satellite without attending ships. The main optical proxy of particle load recorded by the CFE, volume-attenuance (VA; units of mATN-cm 2 ), while rigorously defined and highly precise, has not been robustly calibrated in terms of particulate organic carbon (POC), nitrogen (PN), and phosphorus (PP). In this study, a novel 3D printed particle sampler using cutting edge additive manufacturing was developed and integrated with the CFE. Two such modified floats (CFE-Cals) were deployed a total of 15 times for 18-24-hour periods to gain calibration imagery and samples at depths near 150 meters in four contrasting productivity environments during the June 2017 California Current Ecosystem – Long Term Ecological Research (LTER) process study. Regression slopes for VA : POC and VA : PN (units mATN-cm 2 : mmol; R 2 in parentheses) were 10.07 × 10 3 (0.86), 10.05 × 10 4 (0.87) respectively and was not sensitive to environment or classes of particles sampled. PP was not strongly correlated with VA.