A key theory that attributes Earth's climate evolution to the degradation of Himalayan rocks could not explain the slowdown in the last 15 million years, according to a Rutgers-led study.
The study in the journal Nature Geoscience could shed more light on the causes of long-term climate change. The focus is on the long-term slowdown that occurred before the recent global warming associated with humanity's greenhouse gas emissions.
"The results of our study raise more questions than they answer," said lead author Yair Rosenthal. a distinguished professor in the Department of Marine and Coastal Sciences at the School of Environmental and Biological Sciences at Rutgers University-New Brunswick. "If the cooling is not due to increased weathering of the Himalayan rocks, what processes were overlooked?"
For decades, the leading hypothesis has been that the collision of the Indian and Asian continents and the lifting of the Himalayan rock caused fresh rock fire. The earth's surface makes them more vulnerable to the effects of the weather, which capture and store carbon dioxide, an important greenhouse gas. This hypothesis, however, remains unconfirmed.
Lead author Weimin Si, a former Rutgers Ph.D. student at Brown University, and Rosenthal question the hypothesis and studied calcium carbonate-rich deep-sea sediments.
Over millions of years, weathering has taken place. Carbon dioxide and rivers taken up by rocks transport it as dissolved inorganic carbon into the ocean, which is used by algae to build up their calcium carbonate shells. When algae die, their skeletons fall to the bottom of the sea and bury, binding carbon from the atmosphere into deep-sea sediments.
As the weather increases, the accumulation of calcium carbonate in the deep sea should increase. After exploring dozens of deep-sea sediment cores as part of an international ocean drilling program, Si found that the calcium carbonate in the shells decreased significantly within 15 million years, suggesting that the weathering of the rock may not be suitable for long-term cooling responsible for.
In the meantime, scientists also surprisingly discovered that algae, known as coccolithophores, that are adapted to carbon dioxide degradation, reduce their calcium carbonate production over a period of 15 million years. This reduction was apparently not taken into account in previous studies.
Many scientists believe that acidification of the ocean by high levels of carbon dioxide will reduce calcium carbonate in algae, especially in the near future. However, the data suggest that the opposite occurred in the 15 million years before the current global warming.
Rosenthal's lab is now trying to answer these questions by studying the evolution of calcium and other elements in the ocean.
A study shows a sharp increase in carbon dioxide uptake in the oceans along the West Antarctic Peninsula
Reduced continental weathering and calcification of the oceans in connection with the late decline of atmospheric CO2 by Neogene, Nature Geoscience (2019). DOI: 10.1038 / s41561-019-0450-3, https://nature.com/articles/s41561-019-0450-3
Is the theory about the Earth's climate wrong in the last 15 million years? (2019, September 23)
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