Abstract
Abstract. 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.
Highlights
Model DevelopmentM available measurements have limited temporal resolution, are labor-intensive, ologically important trace elements from sunlit, productive and require ship support
Observational gaps limit our understanding of particle flux attenuation through the upper mesopelagic because available measurements have limited temporal resolution, are labor-intensive, ologically important trace elements from sunlit, productive and require ship support
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Summary
M available measurements (sediment traps and radiochemical Particles settling into the deep ocean remove carbon and bitracers) have limited temporal resolution, are labor-intensive, ologically important trace elements from sunlit, productive and require ship support. We present an inference from measurements of upper-ocean elemental balapproach for calibrating this optical proxy in units of carbon flux, discuss in detail the related, inherent physical and optiamniccersob(Eiaml reersspoinraetitoanl.T(,B1hu9er9d7e;CtMarliy.c,ho2a0se1lps0)eh.tNeaolr.n,ee19o9f 4th)easnedmdeetehpcal assumptions, and look forward toward the requirements ods resolve flux at timescales shorter than 24 h, and upperfor the quantitative application of this method in highly time- ocean sediment trap deployments are generally limited to resolved studies of particle export and flux attenuation. We describe our analysis method, which is amenable to automation and to use with large datasets, and present a new, high-resolution particle flux proxy dataset collected over several months in the Sargasso Sea, south of Hawaii, and in the subtropical North Pacific We use these data to examine variability of particle flux over short spatiotemporal scales and to illustrate the complexity of connections to overlying watercolumn processes
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