A new digital 3D atlas shows how heavy metals and trace elements are distributed in the sea - at an unprecedented level of detail. Scientists from the Institute of Chemistry and Biology of the Marine Environment (ICBM) are also involved in the international research project.
The ocean has a long memory: a new digital 3D atlas reveals this at first glance. At a depth of around 500 to 2,000 metres, a red flag runs across the Atlantic Ocean, signalling the presence of a large part of the ocean: A large proportion of the lead that poured out of the tailpipes of our cars before the introduction of unleaded petrol in North America and Europe is probably floating down here. "Geotraces" is the name of the international project in which scientists from 30 Institutes and ten countries have created the 3D atlas. This also includes scientists from the Institute of Chemistry and Biology of the Marine Environment (ICBM) at the University of Oldenburg.
However, lead is just one of many trace substances whose distribution in the world's oceans is being visualised in this level of detail for the first time. Scientists are currently working on the project as part of a global effort to track down and visualise the sources, sinks and distribution pathways of iron, cadmium, lead etc. in the sea. The new 3D atlas shows the first interim results for the Atlantic, the Arctic and the Indian Ocean.
"Overall, we are talking about very low concentrations of around one part lead per thousand billion parts water," says Prof. Dr Reiner Schlitzer from the Alfred Wegner Institute Helmholtz Centre for Polar and Marine Research in Bremerhaven, currently spokesperson for Geotraces, explaining why the lead concentrations measured in the Atlantic do not pose a direct threat to the environment. However, the low detection levels also illustrate the enormous analytical effort required for such a project, which can only be realised in a large research network.
"There are only a few highly specialised laboratories in the world that can reliably measure individual trace substances in such low concentrations," says Schlitzer. However, not only very sophisticated, but also very many analyses are required to create such an atlas of the world's oceans. So far, more than twenty-five thousand water samples of different depths from around eight hundred measuring stations have been analysed for over 200 substances. It took 15 ship expeditions to collect the data that has been analysed so far. More will follow. In Germany, in addition to the Alfred Wegener Institute and the Institute for Chemistry and Biology of the Marine Environment at the University of Oldenburg, the GEOMAR Helmholtz Centre for Ocean Research Kiel, the Max Planck Institute for Chemistry in Mainz and the Max Planck Institute for Marine Microbiology are also involved in the project.
The Marine Isotope Geochemistry research group at the ICBM is going one step further - and has been measuring not only the concentrations of specific trace elements in seawater, but also their isotopic composition as part of the Geotraces programme for two years. From this, the scientists can gain important additional information: on the sources and transport routes of trace elements in the sea and on the cycles in which the elements are integrated in the ocean.
The example of "iron" also shows the scientific treasure that the researchers have brought from the depths of the ocean to the screen and made visible in memorable visualisations. Iron is often a deficiency element in the ocean. Dust inputs from land have so far been regarded as the dominant source of this important micronutrient for algae, which is therefore of great importance in the marine ecosystem. However, a look at the digital atlas shows: A lot of iron is also released into the ocean in the vicinity of seamounts on the Mid-Atlantic Ridge or on the continental shelf of West Africa. The relatively high cadmium concentrations, on the other hand, which run in a conspicuous band along the South American Atlantic coast, do not indicate increased environmental pollution from neighbouring countries. Here, the heavy metal reflects the dispersion patterns of various ocean currents.
The aim of the new electronic atlas, which has recently been made available to everyone on the internet, is to make such correlations recognisable for all the world's oceans at a glance. And that's not all: "Regular comparisons will enable us to easily recognise how climate change or human emissions are changing the distribution of nutrients, pollutants and other trace substances in the ocean," summarises Schlitzer - provided, of course, that hundreds of fellow researchers around the world continue to feed the new atlas with data.