Vertical fluxes of polycyclic aromatic hydrocarbons in the northern Gulf of Mexico

• First study to quantify the concentrations and vertical fluxes of particulate PAHs in the northern GOM.
• Vertical flux is an important mechanism of particle bound PAHs transport to deeper ocean in this region.
• Dissolved PAHs were three orders of magnitude lower than those reported during DWH oil spill.

Polycyclic aromatic hydrocarbon (PAH) concentrations in dissolved, suspended and sinking phases were measured in the northern Gulf of Mexico during 2012 and 2013 to estimate rate of loss of particulate PAHs from the water column via sinking fluxes. The concentrations of suspended particulate ΣPAH43 varied between 0.29–0.72 ng/L in 2012 and 0.17–1.31 ng/L in 2013 while dissolved ΣPAH43 varied between 31.2–51.2 ng/L and 24.2–58.0 ng/L in 2012 and 2013, respectively. The concentrations of dissolved PAHs were found to be orders of magnitude lower than the values reported during DWH oil spill. Sediment trap-based vertical sinking fluxes of particulate ΣPAH43 varied between 2.21–7.78 μg m− 2 day− 1 in 2012 and 1.95–2.53 μg m− 2 day− 1 in 2013. The vertical fluxes are found to be an important loss term for particle bound PAHs in this region with 3.1–6.7% of total particulate PAH inventory in the euphotic zone being lost daily via this pathway. The reported variability in the sinking rates of particle bound PAHs from the upper ocean can impact the residence time of PAHs in the upper ocean.