64PE373 - Diary 2
18/07/2013 09:27
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Lars in the cleancontainer, sampling |
"Mercury rising" in the Black Sea "Mercury" is not only the name of a Greek God or a planet in our solar system. Mercury is also a naturally occurring element that is toxic to humans and wildlife. It is the only heavy metal that is present as a gas in the atmosphere where it stays on average for about one year. Volcanoes are well-known natural sources of mercury to the atmosphere. Yet since the industrial revolution humans emit three times more mercury than all volcanoes together. What goes up must come down and sooner or later the emitted mercury joins the oceans and continents via rain and snowfall. In aquatic ecosystems deposited mercury gets transformed by naturally occurring bacteria into toxic methylmercury. Methylmercury gets taken up by plankton, shrimp, mussels, small fish, big fish etc. Each time a predator eats its prey it accumulates all of its methylmercury. Top predators at the end of the food chain, humans included (!), therefore ingest large amounts of methylmercury. We humans are exposed to methylmercury when we eat fish. Eating two to three fish meals per week is recommended because fish is a good source of proteins and non-saturated fatty acids. But eating too much fish may cause neurotoxic effects, especially in babies and infants. |
Scientists have only begun recently to understand where methylmercury in the fish we eat comes from. Long-thought to be produced in coastal marine sediments, it is now thought that methylmercury is produced in the open ocean water column. That brings us to what exactly we do on this cruise: we try to understand the marine mercury dynamics in the Black Sea. At what depth is methylmercury formed and by whom? How much mercury deposits to sediments and how does it get there? Like a carpenter, a scientist has a toolbox containing different methods and tools to study nature. We are trying to develop a new tool called ?isotope fingerprinting?. Mercury has seven different isotopes that differ only by their mass. After sampling here on the cruise, we will analyze the mercury in the air, water and sediments of the Black Sea in our home lab at the University of Toulouse in France. We will analyze their mercury isotope fingerprints, in the hope that these will provide answers to our questions. It is the first time that anyone attempts to do this in the ocean, where mercury concentrations are extremely low: about 1 picomol of mercury per liter of sea water. This amounts to one billionth of a gram of mercury per liter of sea water. So we have been very excited to work with the NIOZ ultra-clean CTD water sampler on this cruise.
The "Mercury duo": Jeroen Sonke en Lars-Eric Heimburger