“What we observed thanks to this method was that there was stability with regard to the diversity of cyanobacteria obtained during almost all the period, even though we noticed that there was a rupture 2,000 years ago. These changes were visible in the studies of diatoms and pigments, but were not reflected by our organisms. We also noticed that in the recent layers (over the last 70 years), there was an apparent increase in the diversity of cyanobacteria. And we know that cyanobacteria proliferate more when the temperature increases, when there is a greater exposure to the sun and there are more nutrients available, notably due to melting ice. We can therefore assume that these variations are partly determined by climate changes, and that a proliferation of cyanobacteria could be the consequence of global warming which would imply that this region of the Antarctic is also currently warming up”, explains the biologist. It should be noted that a possible important bias has not yet been ruled out.

The interest of a multi-methodology

Still at the test stage, the use of the DNA fossil as a paleolimnological tool is attractive and shows encouraging results. Certainly, other studies have been effective: the analysis of fossils of diatoms, for example, or the analysis of pigments in the sediment. 

But diatoms are not present in all ecosystems. These organisms remain a tool of choice but they are only a key to open several doors to the past. As for pigments, some deteriorate quicker than others. An observation can quickly be seen to be biased by such a particularity.

Each observation technique presents a series of limits and possible biases, which underlines the necessity to develop the use of new markers. “Observing the past is like looking at an image with distorting or different-colored glasses. By wearing blue then red then yellow glasses we will have a more reliable reconstruction of reality. In the case of this study, it was interesting to compare what other researchers were able to observe with our own findings and to note correlating events or events which reveal a bias in one of the methods, in order to further refine the research”, explains the researcher.