Pyrogenic PAHs Have\nDifferent Biogeochemical Fates\nin the Eastern Indian Ocean

Understanding the fate of polycyclic aromatic hydrocarbons\n(PAHs)\nin the deep ocean is crucial for elucidating the biogeochemical cycle\nof organic carbon under anthropogenic influences. In this study, surface\nsediments were collected from the deep sea of the Eastern Indian Ocean\n(water depth: 2161–4545 m) and analyzed for 29 semivolatile\norganic compounds (SVOCs), including parent PAHs and their alkylated\nderivatives, as well as source biomarkers. The target SVOCs (∑<sub>29</sub>SVOCs: 23.0–183 ng/g, ∑<sub>16</sub>PAHs: 11.3–93.3\nng/g) were mainly from pyrogenic sources, namely coal combustion,\ntraffic emissions, and wood burning. The contributions from wood burning\nand coal combustion exhibited distinct trends with increasing total\norganic carbon contents, suggesting different dominant biogeochemical\nbehaviors. Major fractions of PAHs from wood burning can be biodegraded\nor photodegraded, leading to a depletion-dominated fate in the water\ncolumn. Conversely, PAHs from coal combustion showed an accumulation-dominated\nfate via their sedimentation due to their persistence and hydrophobicity.\nThis study highlights the distinct biogeochemical fates of PAHs from\nbiomass or fossil fuel combustion in deep oceans and has implications\nfor the marine cycle of refractory organic carbon under anthropogenic\nimpacts.