Upwelling Enhances Mercury Particle Scavenging in the California Current System

Area of Science:

• Marine Biogeochemistry
• Trace Metal Oceanography
• Coastal Ecosystem Dynamics

Background:

• Coastal upwelling delivers essential nutrients for primary production but also introduces toxic mercury (Hg).
• Elevated mercury levels in the ocean raise concerns about bioaccumulation of monomethylmercury (MMHg), impacting human and environmental health.

Purpose of the Study:

• To investigate the influence of upwelling on mercury cycling in the California Current System (CCS).
• To analyze the roles of particle scavenging and sea-air exchange in mercury's fate during upwelling events.

Main Methods:

• Collection and analysis of suspended and sinking particle samples from upwelled and non-upwelled water parcels.
• Modeling of mercury inventories and fluxes in the upper ocean under varying upwelling conditions.

Main Results:

• Higher total particulate mercury and sinking flux were observed in the upwelling region compared to offshore areas.
• Model simulations quantified that upwelling enhances mercury sinking fluxes by 41% driven by increased primary production.

Conclusions:

• Upwelling significantly increases the sinking flux of mercury from the ocean's mixed layer.
• Enhanced mercury export via sinking particles is crucial for understanding mercury's delivery to the deep ocean and potential MMHg formation.