Deep ocean sediments serve as a crucial mercury (Hg) sink in the global Hg cycle. Phytoplankton plays an important role in sequestering Hg from the atmosphere and the subsequent deposition of Hg into the sediment. However, the impact of primary productivity on Hg accumulation in the deep ocean remains poorly understood. Here we investigated the effects of marine organic carbon (OC) (representing the primary productivity) on Hg contents (especially the atmospheric source Hg) and isotope composition over the past several millennia in sediment cores from the Northwestern Pacific Ocean (NWPO). Significant correlations were observed between the Hg contents, δ²⁰²Hg, and marine OC, indicating that primary production controls Hg accumulation in the NWPO. Sea surface temperature (SST) was found to significantly affect the TOC, and Hg contents in three of five investigated cores, suggesting that temperature-driven increase in primary productivity can enhance the accumulation of atmospheric depositional Hg into the sediments. However, other factors (e.g., nutrients, light) controlling primary productivity can weaken the effects of temperature on productivity. Our findings reveal that rising SST has the potential to promote Hg accumulation in deep sea sediments via enhancing primary productivity and diminish the amount of Hg in the water column, thereby reducing its toxic effects on the marine organisms.

Mercury accumulation, Northwestern Pacific Ocean, primary productivity, Total organic carbon, Sea surface temperature