Pyrogenic carbon, a byproduct of biomass and fossil fuel combustion, is an important component in global carbon cycle because it can be stored on Earth’s surface for centuries to millennia. The dissolvable condensed aromatic fraction of pyrogenic carbon occurs ubiquitously in aquatic environments on Earth’s surface and is called dissolved black carbon (DBC). DBC is known to occur ubiquitously in the ocean, but the DBC cycle and budget in the ocean have not been well constrained due to the paucity of observations on basin-scale distributions. Deep hydrothermal vents are suggested to be apossible source of thermogenic DBC, but little is known about the distribution of hydrothermal DBC in the deep ocean. Here, we show the basin-scale distributions of DBC along two transects in the eastern Pacific Ocean. The concentration and condensation degree of deep ocean DBC at the sites close to the East Pacific Rise were higher than those at the other sites, suggesting that highly condensed DBC was derived from hydrothermal systems and transported over long distances. The hydrothermal DBC concentration was quantified as a deviation from the linear relationship between the DBC concentration and apparent oxygen utilization previously observed in the central and western Pacific Ocean. The deviation was linearly correlated with excess ³He, a tracer of hydrothermal input, confirming the hydrothermal origin of the DBC. 

Primary Presenter: Youhei Yamashita, Hokkaido Univeristy (yamashiy@ees.hokudai.ac.jp)

Authors:

Youhei Yamashita,   ()

Yutaro Mori,   ()

Hiroshi Ogawa,   ()