Importance of biogenic opal as ballast of particulate organic carbon (POC) transport and existence of mineral ballast‐associated and residual POC in the Western Pacific Subarctic Gyre

Abstract

We determined particulate organic carbon (POC) and mineral ballast (biogenic opal: Opal, CaCO 3 , lithogenic material) fluxes and estimated mineral ballast carrying coefficients (CCs) using time‐series sediment trap (ST) data from multiple depths in the Western Pacific Subarctic Gyre (WSG). The deep sea POC flux was highly correlated with mineral ballast flux, which accounted for almost 100% of the POC flux. About 70% was associated with Opal flux, suggesting its importance to vertical POC transport in the WSG unlike previous reports documenting importance of CaCO 3 . Opal had the highest CC at all depths, but CC decreased with decreasing depth, as did the fraction of “mineral ballasts‐associated” POC (M‐POC). Conversely, the residual POC fraction (R‐POC) increased with decreasing depth, from about at most 10% at ca. 5000 m to 80% at ca. 150 m. Thus, total POC flux includes M‐POC and R‐POC, and decomposition rate are greater in R‐POC than in M‐POC.