Scientists from the University of Southampton have discovered that ancient peat bogs in the Southern Hemisphere contain traces of a major climate change that occurred about 15 thousand years ago. An international team of researchers has shown that strong shifts in southwest winds at the end of the last Ice Age stimulated the rapid development of wetland ecosystems. The work was published in the journal Nature Geoscience.
For decades, geologists could not explain why peatlands spread across the Southern Hemisphere after the end of the Ice Age, from South America and Australia to southern Africa and the sub-Antarctic islands. It turns out that changes in atmospheric circulation play an important role.
According to the study's lead author, Associate Professor Zoe Thomas, the shift of winds north about 15,000 years ago changed the mixing of waters in the Southern Ocean, the largest natural carbon sink on the planet. Because peatlands are huge carbon reserves, their rapid growth during this period represents an important restructuring of the global carbon cycle.
Peat deposits form when wetlands accumulate layers of decaying vegetation over thousands of years. Using radiocarbon dating of peat samples collected across the Southern Hemisphere, scientists have determined when the climate became wet enough for such ecosystems to thrive. It turns out that periods of active marsh formation occur in synchrony with wind shifts and changes in atmospheric carbon dioxide concentrations.
Modern observations show that the southwest wind is shifting again, but towards Antarctica – a trend associated with current global warming. Thomas warns that this could weaken the ocean's ability to sequester carbon and lead to an increase in droughts and wildfires in the southern continents.
Co-author of the study, Heidi Cadd from the University of Wollongong, noted that if the planet's largest carbon sink becomes less efficient, atmospheric carbon dioxide concentrations will increase even faster, increasing global warming.
