Researchers use ancient DNA to reconstruct past biodiversity in the Arctic

Climate change causes fast changes in the environmental conditions in the Arctic, such as increasing temperatures, decreasing sea ice cover, a retreat of glaciers and associated changes in hydrography. The Molecular Ecology and Paleogenomics Research Group in NORCE is studying how these changes impact marine biodiversity.

Most studies on the effects of environmental changes on biodiversity have so far focused on large organisms. Our researchers are now studying smaller organisms like marine microbes or plankton to see how sensitive they are to these changes and how they will be impacted.

Sedimentary ancient DNA

Senior researcher Agnes Weiner explains that marine sediment archives are important to study how organisms responded to past changes over very long time scales (decades to thousands of years). This knowledge can then be used to get a better understanding of how the organisms may be impacted in the future. However, past biodiversity reconstructions have until recently been limited to the fossil record of only a very few lineages. Now, our scientists have a new key to past biodiversity - sedimentary ancient DNA. This is environmental DNA from any organism that has lived in the marine ecosystem at any point in time.

At some point, the DNA of organisms sinks down to the sea floor and gets preserved in the sediment. If we go out and collect sediment cores, we can extract this DNA again from the sediment layers and use it as a proxy to reconstruct past biodiversity. At the same time, we can use traditional palaeoecological proxies such as isotopes to reconstruct the past environmental conditions. And if we then bring the environmental conditions of the past and the biodiversity of the past together, we can get a good understanding of how past environmental changes have impacted past biodiversity, Weiner explains.

Core samples from the Hinlopen Strait

The group has several projects that use sedimentary ancient DNA for past climate and biodiversity studies, mainly in the polar regions, funded by the Norwegian Research Council and European Research Council. In the project “NEEDED” Weiner and colleagues Stijn De Schepper, Tristan Cordier and Margit H. Simon are developing this method for the high Arctic together with researchers from the Institute of Oceanology of the Polish Academy of Sciences (IO PAN) . They have been studying a site that is located on the northern coast of Svalbard outside of the Hinlopen Strait. This site has experienced varying influence of Atlantic versus Arctic water and associated changes in sea ice conditions over geological history.

The researchers recovered two different cores from this site, one five-meter-long gravity core that covers the last 10,000 years before present and a half meter long core covering the last thousand years.

Our first analysis shows that the climate in this region was rather stable over the last 10,000 years, with only a minor decrease in temperature and increase in sea ice. A sneak preview of the ancient DNA data suggests that the biodiversity was likely stable too, but in depth analyses still need to be done, Weiner says.

Ancient DNA reconstructions often recover a wide diversity of microalgae, but there can be also traces of soft-bodied organisms such as worms and jellyfish. The advantage of using this method is that one can also see organisms that usually don't leave a traditional fossil record, and in this way, obtain a more comprehensive picture of past marine communities.