Research sheds new light on the role of sea ice in controlling atmospheric carbon levels

A new study has highlighted the crucial role that sea ice in the Southern Ocean played in controlling atmospheric carbon dioxide levels during times of past climate change, and could provide a critical resource for developing future models of change. climate.

For the study, an international team of researchers, led by Keele University and including experts from the University of Exeter, showed that seasonal growth and the destruction of sea ice in a warming world increases the amount of marine life present in the sea ​​around Antarctica, which lowers carbon from the atmosphere and stores it in the deep ocean.

Having captured half of all the human-related carbon that has entered the ocean to date, the Southern Ocean around Antarctica is crucial in regulating the levels of carbon dioxide resulting from human activity, so that understanding the processes that determine its effectiveness as a carbon sink over time is crucial. to reduce uncertainty in future climate change models.

To better understand this process, the researchers studied data related to a period when atmospheric CO_two The levels changed rapidly.

This occurred after the Last Ice Age, approximately 18,000 years ago, when the world made a natural transition to the warm interglacial world in which we live today.

During this period, CO_two It rapidly increased from around 190 parts per million (ppm) to 280 ppm over about 7,000 years, but one particular period stands out; a period of 1,900 years where CO_two stabilized levels at an almost constant level of 240 ppm.

The cause of this plateau, which occurred about 14,600 years ago, is unknown, but understanding what happened during this period could be crucial in improving projections of climate change.

Professor John Love, from the Exeter Biosciences department and co-author of the study, said: “My research group and I are very excited to be part of this important research. We developed new techniques in cell biology to find, collect and analyze the rare. and Very small particles and cells that had been frozen in ice for millennia.

“Like flies in amber, these tiny fragments provide a unique window into past events, allowing our colleagues in Earth, Atmosphere, and Ocean science to develop a better understanding of climate change at the time. and now”.

Lead author Professor Chris Fogwill, director of Keele University Institute for Sustainable Futures, said: “The cause of this long plateau in global atmospheric CO_two levels may be critical to understanding the potential of the Southern Ocean to moderate atmospheric CO_two“

To resolve this question, the researchers traveled to the Patriot Hills blue ice area of ​​Antarctica to develop new evidence records for marine life captured in the ice cores, with the support of Antarctic Logistics and Expeditions (ALE).

Blue ice areas are the perfect laboratory for Antarctic scientists because of their unique topography. Created by fierce high-density catabatic winds, the top layer of snow is effectively eroded, exposing the ice underneath. As a result, ice flows to the surface, providing access to the old ice below.

Professor Chris Turney, a visiting fellow at the Keele Institute for Liberal Arts and Sciences at UNSW Sydney, said: “Instead of drilling miles into the ice, we can simply cross an area of ​​blue ice and travel back in time.

“This provides an opportunity to sample large amounts of ice to study past environmental changes in detail. Organic biomarkers and DNA from the Southern Ocean are introduced to Antarctica and preserved in ice, providing a unique record in a region where we have few scientific observations. “

Using this approach, the team discovered that there was a marked increase in the number and diversity of marine organisms present in the 1,900-year period when CO_two stagnant, an observation that had never been recorded before.

This provides the first recorded evidence of increased biological productivity and suggests that processes in the high latitude of the Southern Ocean may have caused CO_two plateau. However, the driver of this marked change remained unknown, and the researchers used climate models to better understand the changes in the Southern Ocean to understand the potential cause.

This model revealed that the plateau period coincided with the largest seasonal changes in sea ice during a pronounced cold phase in the Southern Ocean known as the Antarctic Cold Reversal. During this period, sea ice grew widely throughout the Southern Ocean, but as the world warmed rapidly, sea ice was rapidly destroyed each year during the summer.

The researchers will now use these findings to underpin the development of future models of climate change. The inclusion of sea ice processes that control carbon climate feedbacks into a new generation of models will be crucial in reducing uncertainties around climate projections and will help society adapt to future warming.

The study is published in Nature Geoscience.