A global ocean inventory of anthropogenic mercury based on water column measurements

• Published in: Nature (London) Vol. 512; no. 7512; pp. 65 - 68
• Main Authors: Lamborg, Carl H., Hammerschmidt, Chad R., Bowman, Katlin L., Swarr, Gretchen J., Munson, Kathleen M., Ohnemus, Daniel C., Lam, Phoebe J., Heimbürger, Lars-Eric, Rijkenberg, Micha J. A., Saito, Mak A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 07.08.2014; Nature Publishing Group
• Subjects: 704/172/169/827; Anthropogenic factors; Atmosphere; Carbon dioxide; Carbon Dioxide - analysis; Emissions; Environment; Environmental aspects; Environmental Monitoring - methods; Estimates; Expeditions; Food Chain; Food webs; Human Activities; Humanities and Social Sciences; letter; Mercury; Mercury - analysis; Methylmercury; multidisciplinary; Ocean, Atmosphere; Oceanography; Oceans; Oceans and Seas; Oxygen - metabolism; Properties; Ratios; Science; Sciences of the Universe; Seawater - chemistry; Surface water; Thermocline; Trace metals; Water chemistry; Water column; Water Pollutants, Chemical - analysis
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature13563

GEOTRACES sampling of deep water from the Atlantic, Pacific and Southern oceans allows an estimate of the amount (tripled in surface waters) and distribution (two-thirds increase in water less than a thousand metres deep) of anthropogenic mercury accumulating in the global ocean. Oceanic mercury pollution estimated Large amounts of the toxic trace metal mercury have been released into the environment as a result of human activities such as mining and burning of fossil fuels. Estimates of the amount of mercury that have reached the ocean as a result of such anthropogenic activities remain uncertain and are largely based on model studies. This paper presents an estimate of the total amount and spatial distribution of anthropogenic mercury in the global ocean based on oceanographic measurements of mercury and related parameters from several expeditions including data from recent GEOTRACES cruises. The findings suggest that there has been a tripling of the surface water mercury content and a ∼150% increase in the amount of mercury in the underlying thermocline water layer. Mercury is a toxic, bioaccumulating trace metal whose emissions to the environment have increased significantly as a result of anthropogenic activities such as mining and fossil fuel combustion 1 , 2 . Several recent models have estimated that these emissions have increased the oceanic mercury inventory by 36–1,313 million moles since the 1500s 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . Such predictions have remained largely untested owing to a lack of appropriate historical data and natural archives. Here we report oceanographic measurements of total dissolved mercury and related parameters from several recent expeditions to the Atlantic, Pacific, Southern and Arctic oceans. We find that deep North Atlantic waters and most intermediate waters are anomalously enriched in mercury relative to the deep waters of the South Atlantic, Southern and Pacific oceans, probably as a result of the incorporation of anthropogenic mercury. We estimate the total amount of anthropogenic mercury present in the global ocean to be 290 ± 80 million moles, with almost two-thirds residing in water shallower than a thousand metres. Our findings suggest that anthropogenic perturbations to the global mercury cycle have led to an approximately 150 per cent increase in the amount of mercury in thermocline waters and have tripled the mercury content of surface waters compared to pre-anthropogenic conditions. This information may aid our understanding of the processes and the depths at which inorganic mercury species are converted into toxic methyl mercury and subsequently bioaccumulated in marine food webs.