Biogeochemical processes accounting for the natural mercury variations in the Southern Ocean diatom ooze sediments

• Main Authors: Zaferani, Sara, Biester, Harald
• Format: Text
• Language: English
• Published: 2020
• Subjects: East Antarctica; Southern Ocean; Antarc*; Antarctica
• Online Access: https://doi.org/10.5194/os-2019-132; https://www.ocean-sci-discuss.net/os-2019-132/

Understanding the marine biogeochemical cycle of mercury is crucial as consumption of mercury enriched marine fish is the most important pathway of mercury uptake by humans. However, due to the lack of long term marine records, the role of the oceans in the global mercury cycle is poorly understood and we do not have well documented data of natural mercury accumulations during changing environmental conditions, e.g. sea surface conditions in the ocean. To understand influence of different sea surface conditions (climate induced changes in ice coverage and biological production) on natural mercury accumulation, we used a continuous ~ 170 m Holocene biogenic sedimentary record from Adélie Basin, East Antarctica, which mainly consists of silica based skeletons of diatoms. We performed Principal Component Analysis and regression analysis on element concentrations and corresponding residual of element concentrations, respectively to investigate the link between sediment mercury accumulation, terrestrial inputs, and productivity. Preindustrial mercury accumulation in the remote pristine marine Antarctica showed extremely high accumulation rates (median: 556 µg m −2 yr −1 ) that displayed periodic-like variations. Our analysis shows that the variations in total mercury concentrations and accumulation rates are associated with biological production and related scavenging of available water phase mercury by rapidly sinking algae or algae derived organic matter after intense algae blooms. High accumulation rates of other studied elements further revealed that in regions of high primary productivity, settling of biogenic materials removes many other elements from ocean surface (through scavenging or biological uptake). In conclusion, the link between mercury cycling and primary production will need to be considered in future studies of the marine mercury cycle under future primary production enhancement through climatic, temperature, and nutrient availability changes.