Abstract
AbstractSinking particles are critical to the ocean's “biological pump,” sequestering carbon from the atmosphere. Particles' sinking speeds are a primary factor determining fluxes and subsequent ecological and climatic impacts. While size is a key determinant of particles' sinking speeds, observations suggest a variable size‐sinking relationship, affected by other particle properties, resulting in substantial spread in parameterizations of particle sinking and fluxes. We compile particle size‐sinking observations and apply hierarchical Bayesian statistical models to resolve the size‐sinking relationship while accounting for other factors. We find an overall scaling close to the general Navier‐Stokes drag equation, and differences between particle types, open ocean versus coastal/laboratory particles, and in situ versus ex situ methods. These results can help harmonize how Earth system models parameterize particle fluxes and support a weaker size‐dependence than often assumed, with implications for the flux contribution of small particles and the predicted future shrinking of marine particle populations.
Highlights
The continual flux of organic carbon from the surface to the deep ocean sequesters carbon from exchanging with the atmosphere, and maintains atmospheric CO2 and global temperature appreciably below what they would otherwise be (Sarmiento & Gruber, 2006; Sigman & Boyle, 2000; Sigman et al, 2010; Williams & Follows, 2011)
Sinking particles are critical to the ocean's “biological pump,” sequestering carbon from the atmosphere
We find an overall scaling close to the general Navier-Stokes drag equation, and differences between particle types, open ocean versus coastal/laboratory particles, and in situ versus ex situ methods. These results can help harmonize how Earth system models parameterize particle fluxes and support a weaker size-dependence than often assumed, with implications for the flux contribution of small particles and the predicted future shrinking of marine particle populations
Summary
The continual flux of organic carbon from the surface to the deep ocean sequesters carbon from exchanging with the atmosphere, and maintains atmospheric CO2 and global temperature appreciably below what they would otherwise be (Sarmiento & Gruber, 2006; Sigman & Boyle, 2000; Sigman et al, 2010; Williams & Follows, 2011). The majority of organic carbon flux occurs via the gravitationally forced sinking of marine particles created in the sunlit upper ocean from photosynthesis. As they sink, particles are decomposed (“remineralized”) which releases inorganic carbon back to solution in seawater at the depth where remineralization occurs (Herndl & Reinthaler, 2013). The balance of sinking speed and remineralization determines the depth of carbon sequestration, which in turn determines the residence time before the sequestered carbon can be released back to the atmosphere (Buesseler & Boyd, 2009; DeVries et al, 2012; DeVries & Primeau, 2011). Understanding the controls on particle sinking speeds is critical for understanding the biological pump's role in marine biogeochemistry and climate
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