Award: OCE-1538686

Marine phytoplankton account for about half (or 50 Pg C y-1) of global primary productivity and live for one week on average before being consumed by zooplankton. Approximately10 Pg C y-1 settles from the surface layer as sinking aggregates containing both particulate organic and inorganic carbon (POC and PIC). The carbon that reaches the deep ocean remains isolated from the atmosphere for centuries. This process, the "biological carbon pump" (BCP), is a fundamental player in the global carbon cycle. To date, most observations of the BCP are limited both spatially and seasonally due to the requirement to have attending ships or nearby islands to support such studies. The Carbon Flux Explorer (CFE), a robotic 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-cm2), while rigorously defined and highly precise, has not been calibrated in terms of particulate organic carbon (POC), nitrogen (PN), and phosphorus (PP). In this project, a novel 3D printed particle sampler using cutting edge additive manufacturing was developed and integrated with the CFE (Fig. 1). 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 1 to July 2 2017 California Current Ecosystem – Long Term Ecological Research (LTER) process study (Fig. 2). Regression slopes for VA:POC and VA:PN (units mATN-cm2:mmol; R2 in parentheses) were 10.1x103 (0.86), 10.0x104 (0.87) respectively and were not sensitive to environment or classes of particles sampled (Fig. 3). The detailed calibration study results are available online (Bourne et al. 2018, Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-294, in review). The project succeeded in its goal of calibrating the CFE and thus provides justification for wider deployments of CFEs in remote and biologically dynamic waters. Such deployments will provide badly needed observations of the biological processes that transport and redistribute carbon in the ocean. Such observations are required for improved ocean carbon cycle simulations and prediction, for understanding controls of atmospheric CO2, and for the understanding of how energy flows from surface waters through biological food webs to the deep sea. This project supported the STEM PhD dissertation research of one graduate student and research projects for three undergraduates. One note: during our month long expedition, we deployed 2 CFEs and 2 CFE-Cal robots. One CFE was violently attacked and sunk in 4000 m of water by a short-fin Mako shark on June 20th 2017 just as it was about to be recovered. This was a shock to all involved in the study. Last Modified: 07/25/2018 Submitted by: James K Bishop