Estimating Mass Flux From Size‐Fractionated Filtered Particles: Insights Into Controls on Sinking Velocities and Mass Fluxes in Recent U.S. GEOTRACES Cruises. Issue 4 (13th April 2022)

• Record Type: Journal Article
• Authors: Xiang, Yang; Lam, Phoebe J.; Burd, Adrian B.; Hayes, Christopher T.
• Is Part Of: Global biogeochemical cycles. Volume 36:Issue 4(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-04-13
• Subjects: sinking velocity -- total mass flux -- porosity -- Arctic Ocean -- biological pump -- GEOTRACES; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2021GB007292
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: We compile full ocean‐depth size‐fractionated (1–51 and >51 μm) particle concentration and composition of suspended particulate matter from three recent U.S. GEOTRACES cruises, and exploit detailed information of particle characteristics measured to give insights into controls on sinking velocity and mass flux. Our model integrates the concept of fractal scaling into Stokes' Law by incorporating one of two porosity‐size power law relationships that result in fractal dimensions of 1.4 and 2.1. The medians of pump‐derived total (>1 μm) mass flux in the upper 100 m of gyre stations are 285.1, 609.2, and 99.3 mg/m 2 /d in the North Atlantic, Eastern Tropical South Pacific, and Western Arctic Ocean cruises, respectively. In this data set, variations in particle concentration were generally more important than sinking velocity in controlling variations in mass flux. We examine different terms in a Stokes' Law model to explore how variations in particle and water column characteristics from these three cruises affect mass flux. The decomposition of different aspects of the Stokes' relationship sheds light on the lowest total mass flux of the three cruises in the Western Arctic, which could be explained by the Arctic having the lowest particle concentrations as well as the lowest sinking velocities due to having the smallest particle sizes and the most viscous water. This work shows the importance of both particle characteristics and size distribution for mass fluxes, and similar methods can be applied to existing and future size‐fractionated filtered particulate measurements to improve our understanding of the biological pump elsewhere. Plain Language Summary: In this study, we compile concentrations and chemical compositions of marine suspended particles from the full water column in three cruises in different ocean basins, and estimate their corresponding mass sinking velocity and flux. Estimating how fast particles sink and the magnitude of particle flux can help us better understand the cycling of elements in the ocean, including carbon. Not surprisingly, we find that places with higher particle concentrations tend to have higher particle flux. Other factors, such as the chemical composition and size of marine particles and viscosity of seawater compete for influence: some mineral phases in particles, characterized by higher densities, provide excess weight to enhance particle flux; in contrast, smaller particles tend to sink more slowly compared to larger particles. In the high‐latitude Arctic Ocean, marine particles have high concentrations of ballasting minerals; this alone, however, cannot outcompete the most viscous water, smallest particle size and concentrations, leading to much smaller mass fluxes compared to tropical oceans. Key Points: Particle concentration, composition, and size partitioning from three transect cruises are used to estimate mass flux Particle sinking velocity is estimated using a modified Stokes' law that incorporates porosity‐size power relationships The Arctic cruise has lower mass flux than the other two cruises due to high seawater viscosity, small particle sizes and low concentrations