The study, published in the Proceedings of the National Academy of Sciences, utilized fossilized shells from ancient deep-sea sediments to demonstrate how the conveyor belt functioned around 50 million years ago. This period's climate resembles conditions predicted by the end of this century if significant carbon emission reductions are not made.
Oceans regulate Earth's climate by 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 abrupt climate changes. Oceans also remove anthropogenic carbon dioxide from the atmosphere. The oceans are by far the largest standing pool of carbon on Earth's surface today, said Sandra Kirtland Turner, vice-chair of UCR's Department of Earth and Planetary Sciences and first author of the study.
Today, the oceans contain nearly 40,000 billion tons of carbon - more than 40 times the amount of carbon in the atmosphere. Oceans also take up about a quarter of anthropogenic CO2 emissions, Kirtland Turner said. If ocean circulation slows, absorption of carbon into the ocean may also slow, amplifying the amount of CO2 that stays in the atmosphere.
The research team studied the early Eocene epoch, about 49 to 53 million years ago, when Earth was much warmer. During hyperthermals, spikes in CO2 and temperature, the deep ocean was up to 12 degrees Celsius warmer, with additional warming of 3 degrees Celsius. Though the exact cause of the hyperthermal events is debated, and they occurred long before the existence of humans, these hyperthermals are the best analogs we have for future climate change, Kirtland Turner said.
Researchers reconstructed deep ocean circulation patterns during these hyperthermals by analyzing tiny fossil shells from foraminifera, microorganisms found in oceans. As the creatures are building their shells, they incorporate elements from the oceans, and we can measure the differences in the chemistry of these shells to broadly reconstruct information about ancient ocean temperatures and circulation patterns, Kirtland Turner said.
Calcium carbonate shells and their oxygen isotopes indicate water temperatures and ice levels at the time. Carbon isotopes in the shells show the age of the water, reflecting how long it has been isolated from the surface. This method helps reconstruct deep ocean water movement patterns.
Foraminifera shells reflect nearby photosynthetic activity, indicating surface water's recent presence. Photosynthesis occurs in the surface ocean only, so water that has recently been at the surface has a carbon-13 rich signal that is reflected in the shells when that water sinks to the deep ocean, Kirtland Turner said. Conversely, water that has been isolated from the surface for a long time has built up relatively more carbon-12 as the remains of photosynthetic organisms sink and decay. So, older water has relatively more carbon-12 compared to 'young' water.
The team used climate models to simulate the ancient ocean's response to warming, validating results with foraminifera shell analysis. During the Eocene, atmospheric CO2 was about 1,000 parts per million (ppm), contributing to high temperatures. Today, the atmosphere holds about 425 ppm. Current human emissions of nearly 37 billion tons of CO2 annually could lead to similar conditions to the Early Eocene by the end of this century.
Kirtland Turner emphasizes the need to reduce emissions. It's not an all-or-nothing situation, she said. Every incremental bit of change is important when it comes to carbon emissions. Even small reductions of CO2 correlate to less impacts, less loss of life, and less change to the natural world.
Research Report:Sensitivity of ocean circulation to warming during the Early Eocene greenhouse
Related Links
University of California - Riverside
Explore The Early Earth at TerraDaily.com
| Subscribe Free To Our Daily Newsletters |
| Subscribe Free To Our Daily Newsletters |
