Ancient ocean circulation slowdown points to future climate risks

A study from the University of California, Riverside shows that Extreme heat in Earth’s past has reduced the exchange of surface and deep ocean waters.. This system, often described as “global pipeline“, redistributes heat throughout the world, making large areas of the planet suitable for life.

Changes in global ocean circulation in the past and their implications for the future

Research published in Proceedings of the National Academy of SciencesPNAS, used fossilized shells from ancient deep-sea sediments to demonstrate how the conveyor belt worked some 50 million years ago. The climate of this period resembles the conditions expected at the end of this century. unless significant reductions in carbon dioxide emissions are achieved.

Oceans regulate Earth’s climate moving warm water from the equator to the poles, balancing temperatures. Without this circulation, the tropics would be much hotter and the poles much colder, leading to dramatic climate changes. Oceans also remove carbon dioxide anthropogenic atmosphere. Oceans are far away largest carbon reserve on the Earth’s surface at present, he said Sandra Kirtland TurnerVice President of the UCR Department of Planetary and Earth Sciences and first author of the study.

Present tense The oceans contain nearly 40 trillion tons of carbon, more than 40 times the amount of carbon in the atmosphere.. Oceans also absorb about a quarter of man-made CO emissions.₂Kirtland Turner said.

If ocean circulation slows, ocean carbon uptake may also decrease, increasing the amount of CO2.₂ which remains in the atmosphere.

Hyperthermic phenomena

The research team studied the era early Eocenebetween 49 and 53 million years ago, when The earth was much warmer. During hyperthermia, CO peaks₂ and temperatures, the ocean depth warmed by up to 12°C, with an additional warming of 3°C. Although the exact reason hyperthermic phenomenaand they occurred long before the existence of man, These hyperthermal events are the best proxy for future climate change.Kirtland Turner said.

Researchers reconstructed deep ocean circulation models During these hyperthermal events, they analyzed small fossil shells of foraminifera, microorganisms found in the oceans. How creatures build their shellsinclude elements from the oceans, and we can measure differences in the chemistry of these shells to extensively reconstruct information about ancient ocean temperatures and circulation patterns.Kirtland Turner said.

Layers of calcium carbonate and its oxygen isotopes indicate the water temperature and ice level at that time.

Carbon isotopes in shells reveal the age of the water, reflecting how long it has been isolated from the surface. This method helps to restore the patterns of movement of deep ocean waters.

Foraminiferal shells reflect nearby photosynthetic activity, indicating the recent presence of surface water. Photosynthesis only occurs at the surface of the ocean, so water that has recently been at the surface has a rich signal. carbon-13 it reflects off the shells as the water sinks into the ocean depths, Kirtland Turner said. In contrast, water that has been isolated from the surface for a long time has accumulated relatively more carbon-12 as the remains of photosynthetic organisms sink and decompose. Therefore, older water contains relatively more carbon-12 compared to “younger” water.

Research results

The team used climate models to simulate the ancient ocean’s response to warming, confirming the results by analyzing foraminifera shells. During the Eocene CO₂ atmospheric concentration was approximately 1000 parts per million (ppm).what contributed high temperatures.

Today the atmosphere contains about 425 ppm.. human emissions flows almost 37 billion tons of CO₂ year could have led to conditions similar to those of the early Eocene. by the end of this century.

Kirtland Turner highlights need to reduce emissions. It’s not an all-or-nothing situation, he said. Every small incremental change matters when it comes to carbon emissions. Even a small reduction in CO emissions₂ they correlate with lower impacts, fewer human casualties, and fewer changes to the natural world.

Link

Sandra Kirtland Turner et al. Sensitivity of ocean circulation to warming during the early Eocene greenhouse period. PNAS 2024. https://doi.org/10.1073/pnas.2311980121.