Is There Hope for Accurate Carbon Flux Estimates Based on UVP Images?

The ocean's capacity to take up and store carbon via the Biological Carbon Pump (BCP) is a key uncertainty in our understanding of the global C cycle and its response to anthropogenic perturbations. The gravitational component of the BCP is the largest one, with sinking particles as the vehicles of the C to deep waters in the Particulate Organic Carbon (POC) form. The use of underwater cameras to study the particle properties has impacted the field of oceanography within the last decades, with Underwater Vision Profiler (UVP) type cameras one of the most widely used optical system, especially the 5th model (UVP5) and, most recently, the 6th one (UVP61). UVPs allow for the remote collection of large data sets on particle abundances and their size distributions and enable much higher space and temporal resolutions than traditional methods. The goal is, therefore, the global use of UVPs to develop a budget of C flux with Argo floats (equipped with UVP6s). Nevertheless, the quantitative translation of these immense datasets into biogeochemical properties remains a challenge and a systematic method to reliably calibrate particle images against C fluxes has not been established.

Here, we confront the Guidi et al. (2008)2 approach using coincident sediment trap and thorium-234 C flux, and aggregate size distribution observations with UVP5 (three UVP5 mounted on CTDs) from the two EXPORTS field campaigns: i) the North Pacific campaign (Ocean Station Papa, 50°N, 145°W) in later summer 2018, and ii) the North Atlantic campaign (Porcupine Abyssal Plain Site, 49°N, 16.5°W) in May 2021. We find the optimally tuned model explains slightly less than 50% of the variance with the matchups over the entire EXPORTS data set made with the measured sinking POC fluxes. We suggest next steps to reliably assess C export by using UVP images.

1Picheral, M. et al. (2022) 'The Underwater Vision Profiler 6: an imaging sensor of particle size spectra and plankton, for autonomous and cabled platforms', Limnology and Oceanography: Methods, 20(2), pp. 115-129. doi: 10.1002/lom3.10475.

2Guidi et al. (2008) 'Relationship between particle size distribution and flux in the mesopelagic zone', Deep-Sea Research Part I, 55(10), pp. 1364-1374. doi: 10.1016/j.dsr.2008.05.014.