Dr. Marcel van der Meer

Marine geochemist Marcel van der Meer studies, amongst other things, the salt content, salinity, in seas and oceans in the past to better understand future climate developments. ‘Salt can help us to reconstruct ocean circulations in the past. The large global ocean circulation distributes heat across the earth. An example is the warm Gulf Stream which transports heat from the Atlantic Ocean around the equator towards Western Europe. Changes in this circulation can have a big effect on the climate and vice versa. If the ice caps melt as a result of global warming causing the uppermost water layer of the North Atlantic Ocean to become less saline, then that could slow the warm Gulf Stream. This could potentially even lead to colder conditions in Western Europe.’

Fossil algae

‘One way of studying changes in the ocean circulation and the melting ice masses in the past is to reconstruct salinity. Unfortunately, it is not possible to directly determine past salinities from ocean floor layers that are millions of years old. Therefore we need to take an indirect path.’

‘Just like the salt concentration, the concentration of deuterium in seawater depends on the balance between evaporation and precipitation and the mixing of salt and freshwater. Deuterium is a rare form of hydrogen, which is twice as heavy as normal hydrogen. And even better: that deuterium can still be measured in molecular fossils of algae, for example.’

‘From experiments with algae cultured at different salinities, we have learned that at higher salinities, algae take up more deuterium. Deuterium is therefore a good tool to learn something about the salinity at a certain location and time. Subsequently, that salinity can also tell us how the current in the ocean flowed during a certain period. After all, due to more evaporation, there is more salt in the water at the equator than around the poles.’

Modern algae

‘When you try to derive ocean currents in the past from salinity and try to “measure” that salt concentration, in its turn, from deuterium in algae, you need to have a really good understanding about how those algae incorporate that deuterium in their cell components. We therefore study various living algae and how they take up deuterium. Ultimately, that research could enable us to make better predictions about the climate of the future.’