The closest analog to modern times is no longer very close, according to a study.
A new study from an ancient period that is considered the closest natural analogue to the era of modern human carbon emissions has found that massive volcanism has sent large waves of carbon into the oceans for thousands of years, but that nature does not. is close to what humans are doing today. The study estimates that humans are now introducing the element three to eight times faster, or maybe even more. The consequences for life both in the water and on land are potentially catastrophic. The findings appear this week in the magazine Proceedings of the National Academy of Sciences.
Researchers at Columbia UniversityThe Lamont-Doherty Earth Observatory examined the conditions of the ocean 55.6 million years ago, once known as the Paleocene-Eocene Thermal Maximum (PETM). Prior to this, the planet was already considerably warmer than it is today, and the rising CO2 levels of the PETM caused temperatures to rise by another 5-8 degrees C (9 to 14 degrees F). The oceans absorbed large amounts of carbon, stimulating chemical reactions that made the waters highly acidic and killing or damaging many marine species.
Scientists have known for years about the PETM carbon wave, but until now they have been shaky about what caused it. Aside from volcanism, hypotheses have included the sudden dissolution of frozen methane (which contains carbon) from the ocean floor mud, or even a collision with a comet. The researchers were also unsure about how much carbon dioxide was in the air, and thus how much the oceans absorbed. The new study solidifies both the volcano theory and the amount of carbon that was released into the air.
The research is directly relevant to today, said lead author Laura Haynes, who did the research as a graduate student at Lamont-Doherty. “We want to understand how the earth system will now respond to rapid CO2 emissions,” he said. “The PETM is not the perfect analog, but it is the closest thing we have. Today things are moving much faster.” Haynes is now an assistant professor at Vassar College.
Until now, the marine studies of the PETM have relied on scant chemical data from the oceans and assumptions based on some degree of conjecture that researchers have inserted into the computer models.
The authors of the new study answered the questions more directly. They did this by growing tiny shelled marine organisms called foraminifera in seawater which they formulated to resemble the highly acidic conditions of the PETM. They recorded how organisms absorbed the element boron in their shells as they grew. They then compared these data with analyzes of boron from fossilized foraminifera in the Pacific and Atlantic ocean floor cores covering the PETM. This allowed them to identify carbon isotope signatures associated with specific carbon sources. This indicated that volcanoes were the main source, likely from massive eruptions centered around what is now Iceland, as the North Atlantic Ocean opened up and Northern North America and Greenland separated from Northern Europe.
The researchers say the carbon pulses, which others estimate to have lasted for at least 4,000 to 5,000 years, added up to 14.9 quadrillion tons of carbon to the oceans, a two-thirds increase from their previous content. The carbon would have come from the CO2 emitted directly from the eruptions, from the combustion of the surrounding sedimentary rocks and from some methane gushing from the depths. As the oceans absorbed carbon from the air, the waters became highly acidic and remained so for tens of thousands of years. There is evidence that this killed much of life in deep water, and possibly other marine creatures as well.
Today, human emissions are skyrocketing carbon dioxide in the atmosphere, and the oceans are absorbing much of it again. The difference is that we’re introducing it much faster than volcanoes have – within decades instead of millennia. Atmospheric levels have risen from around 280 parts per million in 1700 to around 415 today, and are on track to continue to rise rapidly. Atmospheric levels would already be much higher if the oceans weren’t absorbing so much. As they do so, the rapid acidification begins to put stress on marine life.
“If you add carbon slowly, living things can adapt. If you do it very quickly, that’s a really big deal, “said study co-author Bärbel Hönisch, a geochemist from Lamont-Doherty. He pointed out that even at the much slower pace of the PETM, marine life has seen great deaths.” The past has seen some truly dire consequences, and this does not bode well for the future, “he said.” We are overcoming the past and the consequences are likely to be very serious. “
Reference: 14 September 2020, Proceedings of the National Academy of Sciences.