The loss of Arctic sea ice is the most obvious sign of global warming for us. Scientists are using models and calculations to try to predict how fast the sea ice will retreat and when the Arctic will be considered ice-free. To do this, they also take a look into the past to be able to reconstruct the history of sea ice in other ages. Now an international research team has made an exciting discovery: a previously unnoticed molecule from an unknown group of ice algae could help reconstruct the history of sea ice and look into its future.
“We’ve shown that this molecule is a strong proxy for sea ice concentration,”Karen Wang, PhD student, Brown University
The research team, led by Professor Yongsong Huang of the Department of Earth, Environmental and Planetary Sciences at Brown University in Rhode Island, may have created a new and improved way to reconstruct sea ice cover in Earth’s past with their discovery. This would now require measuring the amounts of an organic molecule in sediment samples from a region of the Arctic Ocean. The higher the amount, the greater the sea ice cover at that location at that time. “We’ve shown that this molecule is a strong proxy for sea ice concentration,” explains the paper’s lead author, Karen Wang of Brown University in Rhode Island. “Looking at the concentration of this molecule in sediments of different ages could allow us to reconstruct sea ice concentration through time.”
“Nobody knew where it came from, or whether it was useful for anything.”Professor Yonghong Huang, Dept. Earth, Environment & Planetary Science, Brown University
The molecule with the unspectacular name tetra-unsaturated alkenone (C37:4) was identified as a product of previously unknown ice algae. Admittedly, it had been known before in samples used for sea ice reconstruction. But it was always considered a confounding factor because they actually wanted to study other, related alkenones for temperature differences. “hat was mostly what the C37:4 alkenone was known for — throwing off the temperature ratios,” explains Yongsong Huang, a professor at Brown University and project leader. “Nobody knew where it came from, or whether it was useful for anything.” So the scientists first had to find out where the molecule came from. In the process, they discovered a previously undescribed group of algae that occur under sea ice. Only then did the team investigate whether the molecule could be used as a proxy to sea ice concentrations in other ages. Here, the advantage of the molecule over other methods and indicators became apparent. This is because the molecule is more robustly conserved than fragile diatoms, for example. This allows larger periods of time to be studied, the authors write in their paper. This appeared in the current issue of the journal Nature Communications.
There are still many unanswered questions about the algae and especially about this alkenone. On the one hand, the researchers now want to find out more about the algae group and how and why they produce this alkenone in the first place. Another topic is the possibility of determining the quantity of sea ice concentrations at specific locations. In their paper, the authors write that the molecule has the “potential for quantitative sea ice reconstruction based on calibration of surface sediments.” This would allow researchers to determine not only the locations where sea ice was found in past times, but also the amount of sea ice at that time. From this, in turn, better data can be incorporated into modelling for the future of sea ice. And as things stand at present, this looks anything but bright.
Dr Michael Wenger, PolarJournal
Link to the study: Wang, K.J., Huang, Y., Majaneva, M. et al. Group 2i Isochrysidales produce characteristic alkenones reflecting sea ice distribution. Nat Commun 12, 15 (2021). https://doi.org/10.1038/s41467-020-20187-z
More on the subject: