BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-5517-2013 Autonomous, high-resolution observations of particle flux in the oligotrophic ocean Estapa M. L. 1 Buesseler K. 1 Boss E. https://orcid.org/0000-0002-8334-9595 2 Gerbi G. 3 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole MA, USA School of Marine Sciences, University of Maine, Orono ME, USA Departments of Physics and Geosciences, Skidmore College, Saratoga Springs NY, USA 16 08 2013 10 8 5517 5531 Copyright: © 2013 M. L. Estapa et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/5517/2013/bg-10-5517-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/5517/2013/bg-10-5517-2013.pdf

Observational gaps limit our understanding of particle flux attenuation through the upper mesopelagic because available measurements (sediment traps and radiochemical tracers) have limited temporal resolution, are labor-intensive, and require ship support. Here, we conceptually evaluate an autonomous, optical proxy-based method for high-resolution observations of particle flux. We present four continuous records of particle flux collected with autonomous profiling floats in the western Sargasso Sea and the subtropical North Pacific, as well as one shorter record of depth-resolved particle flux near the Bermuda Atlantic Time-series Study (BATS) and Oceanic Flux Program (OFP) sites. These observations illustrate strong variability in particle flux over very short (~1-day) timescales, but at longer timescales they reflect patterns of variability previously recorded during sediment trap time series. While particle flux attenuation at BATS/OFP agreed with the canonical power-law model when observations were averaged over a month, flux attenuation was highly variable on timescales of 1–3 days. Particle fluxes at different depths were decoupled from one another and from particle concentrations and chlorophyll fluorescence in the immediately overlying surface water, consistent with horizontal advection of settling particles. We finally present an approach for calibrating this optical proxy in units of carbon flux, discuss in detail the related, inherent physical and optical assumptions, and look forward toward the requirements for the quantitative application of this method in highly time-resolved studies of particle export and flux attenuation.

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