Carbon export and fate beneath a dynamic upwelled filament off the California coast

Abstract

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.

Bridging the gaps between particulate backscattering measurements and modeled particulate organic carbon in the ocean

“…The exclusion of PISCES mesozooplankton (ZOO2) from the comparison increases model-observation mismatch, with BGC-Argo LPOC exceeding PISCES estimates around 2-fold, although the high correlation remains (r = 0.76, p< 10 −10 ). Imaging devices mounted on BGC-Argo floats may provide a more accurate quantification of LPOC, allowing for the separation of detrital LPOC (Trudnowska et al, 2021) from mesozooplankton and micronekton (Haëntjens et al, 2020) and the separa-tion and quantification of particle classes contributing to flux across the complete particle spectrum (Bourne et al, 2021).…”

Iron Limitation and Biogeochemical Effects in Southern California Current Coastal Upwelling Filaments

“…Bourne et al. (2021) found these pellets in Cycle MBF‐Up were full of diatom frustules and fragments. We found that ∼9% of the bSi inventory at Cycle MBF‐Up is exported to 150 m, whereas ∼24% is exported at Cycle MBF‐AF.…”

“…The same is true for bSi, except for at Cycle MBF-Up in the ∼100 and 150 m traps, which is likely a result of the production of anchovy fecal pellets (Figure 11). Bourne et al (2021) found these pellets in Cycle MBF-Up were full of diatom frustules and fragments. We found that ∼9% of the bSi inven tory at Cycle MBF-Up is exported to 150 m, whereas ∼24% is exported at Cycle MBF-AF.…”

A new, global optical sediment trap calibration

“…It is also useful to define a second variant of atn for the situation where the illuminating light source is uncollimated and the detector has a wide acceptance angle. This is the case if atn is measured using a camera (Bishop et al 2016; Bourne et al 2019, 2021). Here, we adopt the name which is analogous to the downward, diffuse attenuation coefficient K d ( K d ( z ) = −d/dz ln( E d ( z )), where E d ( z ) is the depth‐resolved plane irradiance; Mobley 2022).…”

“…Occasionally, profiling floats equipped with beam transmissometers (Bishop et al 2004; Bishop and Wood 2009; Estapa et al 2013, 2017, 2019 b ) or upward‐looking cameras (Bishop et al 2016; Bourne et al 2019, 2021) are used as optical sediment traps (OSTs), providing proxy measurements that are specific to gravitational POC flux and can be used under steady‐state conditions. In the OST method, sinking particles are intercepted by the sensor itself (the upward‐facing optical window of a vertically mounted transmissometer or camera) and the rate of change in the measured light attenuance provides the proxy for flux.…”