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Abstract. To understand the vertical variations in carbon fluxes inbiologically productive waters, four autonomous carbon flux explorers(CFEs), ship-lowered CTD-interfaced particle-sensitive transmissometer andscattering sensors, and surface-drogued sediment traps were deployed in afilament of offshore flowing, recently upwelled water, during the June 2017California Current Ecosystem – Long Term Ecological Research process study.The Lagrangian CFEs operating at depths from 100–500 m yielded carbon fluxand its partitioning with size from 30 µm–1 cm at three intensivestudy locations within the filament and in waters outside the filament. Sizeanalysis codes intended to enable long-term CFE operations independent ofships are described. Different particle classes (anchovy pellets, copepodpellets, and > 1000 µm aggregates) dominated the 100–150 mfluxes during successive stages of the filament evolution as it progressedoffshore. Fluxes were very high at all locations in the filament; below150 m, flux was invariant or increased with depth at the two locationscloser 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 thethree successively occupied locations within the plume, and in transitionalwaters. Interestingly, the flux profiles for all particles< 400 µm were a much closer fit to the canonical Martinprofile (b−0.86); however, most (typically > 90 %) ofthe particle flux was carried by > 1000 µm sized aggregateswhich increased with depth. Mechanisms to explain the factor of 3 fluxincrease between 150 and 500 m at the mid-plume location are investigated. 

Abstract. The magnitude and controls of particulate carbon exported from surface watersand its remineralization at depth are poorly constrained. The Carbon FluxExplorer (CFE), a Lagrangian float-deployed imaging sediment trap, has beendesigned to optically measure the hourly variations of particle flux tokilometer depths for months to seasons while relaying data in near-real timeto shore via satellite without attending ships. The main optical proxy forparticle load recorded by the CFE, volume attenuance (VA; units ofmATN&thinsp;cm²), while rigorously defined and highly precise, has not beenrobustly calibrated in terms of particulate organic carbon (POC), nitrogen(PN) and phosphorus (PP). In this study, a novel 3-D-printed particle samplerusing cutting edge additive manufacturing was developed and integrated withthe CFE. Two such modified floats (CFE-Cals) were deployed a total of15 times for 18–24&thinsp;h periods to gain calibration imagery and samples atdepths near 150&thinsp;m in four contrasting productivity environments during theJune 2017 California Current Ecosystem Long-Term Ecological Research (LTER)process study. Regression slopes for VA&thinsp;:&thinsp;POC and VA&thinsp;:&thinsp;PN (unitsmATN&thinsp;cm²:&thinsp;mmol; R², n, p value in parentheses) were1.01×10⁴ (0.86, 12, &lt;&thinsp;0.001) and 1.01×10⁵(0.86, 15, &lt;&thinsp;0.001), respectively, and were not sensitive toparticle size classes or the contrasting environments encountered. PP was notwell correlated with VA, reflecting the high lability of P relative to C andN. The volume attenuance flux (VAF) to POC flux calibration is compared toprevious estimates.