Abstract. The magnitude and controls of particulate carbon exported from surface waters and its remineralization at depth are poorly constrained. 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 for particle load recorded by the CFE, volume attenuance (VA; units of mATN cm2), 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 3-D-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 h periods to gain calibration imagery and samples at depths near 150 m 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 cm2: mmol; R2, n, p value in parentheses) were 1.01×104 (0.86, 12, < 0.001) and 1.01×105 (0.86, 15, < 0.001), respectively, and were not sensitive to particle size classes or the contrasting environments encountered. PP was not well correlated with VA, reflecting the high lability of P relative to C and N. The volume attenuance flux (VAF) to POC flux calibration is compared to previous estimates.

Concentrations of Cd and P were determined in particle samples collected using the multiple unit large volume in situ filtration system (MULVFS) from 50 profiles at 34 different locations throughout the Atlantic, Pacific, and Southern Oceans since 1991. Consistent methodology has been used. This data set of Cd:P in size fractionated particles gives insight into the processes that lead to differences in regional Cd:P particle values as well as how the formation and remineralization of these particles lead to dissolved deep water ratios that increase from the North Atlantic to the North Pacific. With large spatial and temporal variation, this data set allows us to study the effects of an El Niño, upwelling, large‐scale in situ Fe fertilization, low‐oxygen conditions, and seasonal variation on the Cd:P in particles. Overall, Cd:P tends to be higher (~1–2 mmol/mol) in particles gathered in biologically dynamic waters and is much lower (typically ~0.1 mmol/mol) in oligotrophic regions. Using multiple linear regression analysis, we investigate how euphotic zone parameters important to photosynthesis including nitrate, phosphate, silicate, temperature, and euphotic zone depth affect the Cd:P ratio in particles. Using the results of the analysis, we create global seasonal maps of predicted particulate Cd:P distributions. We find that three factors—local dissolved nitrate, silicate concentrations, and euphotic zone depth—can predict 59% of the variation in particulate Cd:P. We verified our projections using in situ filtration samples collected during GEOTRACES expeditions GA03 (North Atlantic) and GP16 (South Pacific).

Abstract. To understand the vertical variations in carbon fluxes in biologically productive waters, four autonomous carbon flux explorers (CFEs), ship-lowered CTD-interfaced particle-sensitive transmissometer and scattering sensors, and surface-drogued sediment traps were deployed in a filament of offshore flowing, recently upwelled water, during the June 2017 California Current Ecosystem – Long Term Ecological Research process study. The Lagrangian CFEs operating at depths from 100–500 m yielded carbon flux and its partitioning with size from 30 µm–1 cm at three intensive study locations within the filament and in waters outside the filament. Size analysis codes intended to enable long-term CFE operations independent of ships are described. Different particle classes (anchovy pellets, copepod pellets, and > 1000 µm aggregates) dominated the 100–150 m fluxes during successive stages of the filament evolution as it progressed offshore. Fluxes were very high at all locations in the filament; below 150 m, flux was invariant or increased with depth at the two locations closer to the coast. Martin curve b factors (± denotes 95 % confidence intervals) for total particulate carbon flux were +0.37 ± 0.59, +0.85 ± 0.31, −0.24 ± 0.68, and −0.45 ± 0.70 at the three successively occupied locations within the plume, and in transitional waters. Interestingly, the flux profiles for all particles < 400 µm were a much closer fit to the canonical Martin profile (b−0.86); however, most (typically > 90 %) of the particle flux was carried by > 1000 µm sized aggregates which increased with depth. Mechanisms to explain the factor of 3 flux increase between 150 and 500 m at the mid-plume location are investigated.