High production of methylmercury in the anoxic waters of the Black Sea

As part of the GEOTRACES MedBlack cruise, the research vessel Pelagia occupied 12 full-depth stations in the Black Sea along an East-West transect between July 13th and 25th, 2013. In the permanently anoxic waters of the Black Sea, a high fraction (up to 57%) of total mercury (HgT) was found to be methylmercury (MeHg). These levels are comparable to oxic open-ocean subsurface maxima. Using a 1D numerical model, the authors demonstrated that MeHg inputs from rivers, the Mediterranean Sea and sediments are negligible and that MeHg is produced in situ in the anoxic waters. The authors also reported an increasing trend of HgT and MeHg concentrations in the anoxic waters. The numerical modeling suggests that more drastic reductions of Hg emissions are required to reach decreasing Hg and MeHg levels in the Black Sea.

18 RosatiFigure: Concentrations of Hg species in the water column (OL = oxic layer, SOL = suboxic layer, AOL = anoxic layer) and sediments of the Black Sea. a) observed methylmercury (MeHg) distribution across the sampling stations of the GEOTRACES cruise; b) profile of dissolved Hg (HgD) observed (circles = layer means, bars = standard deviations) and modeled (triangles = model mean, coloured area = range of modeled concentrations) in the water; c) concentrations of total Hg (HgT) observed and modeled in the sediments. Click here to view the figure larger.


Rosati, G., Heimbürger, L. E., Melaku Canu, D., Lagane, C., Laffont, L., Rijkenberg, M. J. A., Gerringa, L. J. A., Solidoro, C., Gencarelli, C. N., Hedgecock, I. M., De Baar, H. J. W., Sonke, J. E. (2018). Mercury in the Black Sea: new insights from measurements and numerical modeling. Global Biogeochemical Cycles. http://doi.org/10.1002/2017GB005700

Latest highlights

Science Highlights

Thorium-Protactinium fate across the tropical Atlantic Ocean: what reveals the water column-sediment coupling

Twenty seawater profiles and twenty core-top 231-protactinium and 230-thorium analyses were realised by Ng and colleagues along five depth transects across the northern tropical Atlantic open ocean.


Science Highlights

Constraining Oceanic Copper Cycling through Artificial Intelligence and Ocean Circulation Inverse Model

Using available observations of dissolved copper, artificial neural networks, and an ocean circulation inverse model, authors calculated a global estimate of the 3-dimensional distribution and cycling of dissolved copper in the ocean


Science Highlights

Particulate rare earth elements distributions, processes and characterisation of nepheloids in the North Atlantic

Lagarde et al. realised the first basin scale section of particulate rare earth elements concentrations across the North Atlantic Ocean.


Science Highlights

Isopycnal mixing controls protactinium and thorium distributions in the Pacific Southern Ocean

Pavia and co-workers determined the physical and chemical speciation as well as the vertical distribution of Protactinium-231 and Thorium-230 at 12 stations across the Southern Pacific Antarctic Circumpolar Current…