Biominerals and the vertical flux of particulate organic carbon from the surface ocean

Particulate inorganic carbon (PIC; calcium carbonate) is thought to be a significant source of light scattering in the sea. It also provides ballast for particulate matter, driving the ocean's biological carbon pump. During three trans-Atlantic cruises, we measured particle optical properties plus concentrations of the three major components of sinking aggregates [particulate organic carbon (POC), PIC and biogenic silica (BSi)]. PIC contributed 15-23% of particle backscattering in oligotrophic subtropical gyres and temperate waters. Light scattering properties allowed quantification of the surface PIC: POC ratio. The ratio of the two ballast minerals (PIC: BSi) was significantly, inversely, correlated to POC concentration, allowing robust modeling of the density of sinking aggregates. Results showed greater PIC: POC ratios and sinking rates in oligotrophic regions due to greater relative abundance of PIC. Citation: Balch, W.M., B.C. Bowler, D.T. Drapeau, A.J. Poulton, and P.M. Holligan (2010), Biominerals and the vertical flux of particulate organic carbon from the surface ocean, Geophys. Res. Lett., 37, L22605, doi:10.1029/2010GL044640.