Fate of dissolved black carbon in the deep Pacific Ocean

Black carbon (BC), a byproduct of biomass and fossil fuel combustion, may impact the climate because it can be stored on Earth's surface for centuries to millennia. Dissolved BC (DBC) occurs ubiquitously in the ocean. However, the DBC cycle in the ocean has not been well constrained. Here, we show the basin-scale distribution of DBC in the Pacific Ocean and find that the DBC concentrations in the deep Pacific Ocean decrease along with deep-ocean meridional circulation. The DBC concentration is negatively correlated with apparent oxygen utilization, a proxy of the integrated flux of sinking particles, in the deep Pacific Ocean, implying that DBC is removed from the deep ocean to abyssal sediments through sorption onto sinking particles. The burial flux of BC to abyssal sediments is estimated to be 0.040-0.085 PgC yr^-1, corresponding to 1.5-3.3% of the anthropogenic CO₂ uptake by the ocean.