Dataset: Carbon Flux Explorer CCE_LTER P1706 - Particulate Carbon Flux
Deployment: RR1710

To understand the vertical variations of carbon fluxes in biologically productive waters, four autonomous Carbon Flux Explorers (CFEs) and ship-lowered CTD-interfaced particle-sensitive transmissometer and scattering sensors 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 intense study locations within the filament and at a location outside the filament.

The Carbon Flux Explorer (CFE) dives below the surface make particle flux observations at target depths as it drifts with currents. The Optical Sedimentation Recorder (OSR) wakes once the CFE has reached the target depth. On first wake-up of a given CFE dive, the sample stage is flushed with water and images of the particle-free stage are obtained. Particles settle through a 1-cm opening hexagonal celled light baffle into a high-aspect ratio funnel assembly before landing on a 2.54 cm diameter glass sample stage. At 25-minute intervals, particles are imaged at 13 µm pixel resolution in three lighting modes: dark field, transmitted and transmitted-cross polarized.

Sampling procedures described in Bourne et al., 2019 and Bishop et al., 2016.

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 for total particulate carbon flux were +0.1, +0.87, -0.27, and -0.39 at the three successively occupied locations within the plume, and in transitional waters, respectively. Particle transfer efficiencies between 100 to 500 m were far greater within both filament and California Current waters than calculated using a classic Martin ‘b’ factor of -0.86. Interestingly, the flux profiles for all particles <400 µm were a much closer fit to Martin; however, most (typically >90%) of particle flux was carried by >1000 µm sized aggregates. Mechanisms to explain a factor of three flux increase between 150 and 500 m at the mid plume location are investigated.