Science Advances: Glaciers Decrease Oxygen Levels Over 800,000 Years
Photo: Yuzhen Yan
Scientists at Rice University in the United States have discovered an unknown mechanism for decreasing oxygen levels in the Earth's atmosphere, which has been in effect for 800 thousand years, starting in the late Pleistocene. This is reported in an article published in the journal Science Advances.
One of the main physical and chemical processes that consume atmospheric oxygen is the weathering of sedimentary rocks. Another reason could be the oxidation of organic carbon, held under glaciers for millions of years, but exposed when the ice melted. Researchers analyzed ice cores containing ancient air bubbles and showed that the oxygen content in the Earth's atmosphere has dropped by about 0.2 percent over the past 800,000 years.
Oxygen levels began to drop after the duration of glaciers on Earth doubled about a million years ago. These glaciations date back to the current ice age, which began about 2.7 million years ago. During the ice ages, the ice caps increased, covering up to a third of the planet's area, and then retreated to the poles again. As the duration of glacial cycles has more than doubled, the magnitude of sea level fluctuations has also increased.
As the sea level drops as the glaciers advance, the land area that can be weathered increases. However, the contribution of this process, scientists have estimated only a quarter of the observed drop in oxygen concentration. Conversely, oxygen consumption caused by glacial erosion of carbon-containing rocks may explain the observed decline.
