Scientists from the University of California Riverside revealed the consequences of the warming that occurred in ancient times on the global circulation of ocean waters, which expressed in the weakening of sea currents. The results of the study were published in the journal Proceedings of the National Academy of Sciences (PNAS).
The oceanic overturning circulation system is called the “global conveyor belt” because it redistributes heat across the planet, making large regions of Earth at high latitudes habitable. This includes currents that move warm seawater from the equator to the poles, and changes in these are associated with dramatic changes in climate.
Researchers analyzed tiny foraminiferal fossils recovered from ancient deep-sea sediments to reconstruct how the ocean "pipeline" responded to warming about 50 million years ago. At that time, Earth's climate was similar to the conditions predicted for the end of this century. The ocean depths were 12 degrees Celsius warmer, and during hyperthermic events, when there were peaks in atmospheric CO2, water temperatures rose by an additional three degrees.
Foraminifera incorporate chemical elements from the oceans into their shells. Oxygen isotopes in calcium carbonate indicate the temperature of the water and the amount of ice, while carbon isotopes can determine how long the water has been isolated from the ocean's surface. Water that was recently at the surface is enriched with carbon-13, which is reflected in the chemistry of the shells. Water that has been at depth for a long time contains more carbon-12.
During the Eocene, the atmosphere contained about 1,000 parts per million of carbon dioxide, which contributed to the high temperatures of that era. Today's atmosphere contains about 425 parts per million, but emissions of 37 billion tons of CO2 per year could lead to early Eocene-like conditions.
The authors conclude that the Eocene hyperthermal events coincided with a repeated weakening of the global overturning circulation. This result is consistent with previous research suggesting that current climate change is weakening the Atlantic overturning circulation, which is warming North America and Europe.
Source: lenta.ru