Researchers led by a Tulane University oceanographer have uncovered a method to gauge ocean oxygen levels and their relationship with atmospheric carbon dioxide during the last ice age, over 11,000 years ago. Published in Science Advances, the study sheds light on the oceans’ influence on past glacial melting cycles and enhances predictions regarding how ocean carbon cycles will react to global warming.
As ice ages shift to warmer climates, oceans regulate atmospheric CO2 by releasing the stored greenhouse gas from deep within the ocean. The study establishes a compelling connection between global ocean oxygen levels and atmospheric CO2, spanning from the last ice age to the present day. It highlights the potential for increased carbon release from the deep sea as the climate warms.
Lead researcher Yi Wang, an assistant professor of Earth and Environmental Sciences at Tulane University School of Science and Engineering, emphasizes the significance of the Southern Ocean in governing the global ocean oxygen reservoir and carbon storage. The findings are expected to impact our understanding of how the ocean, particularly the Southern Ocean, will dynamically influence future atmospheric CO2 levels.
Collaborating with scientists from the Woods Hole Oceanographic Institution, a renowned independent nonprofit organization dedicated to ocean research, exploration, and education, Wang’s team analyzed seafloor sediments from the Arabian Sea. By examining isotopes of thallium in the sediments, which indicate past oxygen levels, the researchers reconstructed average global ocean oxygen levels from thousands of years ago.
Wang explains that the study breaks new ground by examining metal isotopes on glacial-interglacial transitions, allowing them to essentially recreate the past. The thallium isotope ratios demonstrated an overall decline in global ocean oxygen during the last ice age compared to the current interglacial period. The research highlighted a millennium-long global ocean deoxygenation during abrupt warming in the Northern Hemisphere, with the ocean gaining more oxygen during abrupt cooling from the last ice age to the present. The observed changes were attributed to Southern Ocean processes.
Sune Nielsen, co-author of the research and associate scientist at WHOI, emphasized the significance of the study as the first to present an average depiction of how global ocean oxygen content evolved during Earth’s transition from the last glacial period to the warmer climate of the past 10,000 years. The data underscore the critical role of the Southern Ocean in modulating atmospheric CO2, particularly concerning anthropogenic climate change impacts on high-latitude regions.
