Ancient Arctic water cycles are red flags to future global warming

Ancient plant life recovered in recent Arctic Ocean sampling cores shows that at the time of the last major global warming, humidity, precipitation levels and salinity of the ocean water altered drastically, along with the elevated temperatures and levels of greenhouse gases, according to a report in the August 10 issue of Nature.

The Arctic Ocean drilling expedition in 2004 allowed scientists to directly measure samples of biological and geological material from the beginning of the Palaeocene/Eocene thermal maximum (PETM), a period of rapid, extreme global warming about 55 million years ago. It has given researchers a direct resource of measurable information on global warming — from a time when the overall global temperature was higher and more uniform from the subtropics to the arctic.

“Analysis of carbon and hydrogen isotopes in the recovered fossil plants told us a lot about the way water is transported in the atmosphere and its effect on the climate,” said Mark Pagani, professor of geology and geophysics at Yale and principal author of the study. “The isotope traces we measured indicated that a large-scale alteration in the water cycle occurred and that future alterations may leave us poorly equipped to predict our water supply.”

“Without being hysteric, it is important to realize that the impact of global warming is not just about searing hot summers — it is about water as a resource. It is about when and where it rains and how much we have to drink,” said Pagani. “This is a red flag”

Pagani and his collaborators show that water and atmospheric water vapor are a major indicator of the “greenhouse” changes. Rather than just looking at changes in ocean water — that can be influenced by many factors — the researchers measured carbon and hydrogen isotopes in the fossil plants and reconstructed the pattern of precipitation and characteristics of the ancient arctic water.

“We are all familiar with what happens when atmospheric fronts from the tropics meet cool northern fronts — there is a “rainout” — water leaves the atmosphere,” said Pagani. “When that happens, the water vapor isotope level becomes more negative. We were able to measure that as traces in the plant fossils.”

“In the PETM, because there were no sharp warm and cold fronts meeting to triggering rainfall, massive amounts of water got transferred from the tropics and sub-tropics to the arctic,” said Pagani. “That drastically increased humidity and precipitation in the arctic. In turn, it led to increased river runoff that lowered the ocean salinity, changing its oxygen capacity and the plant life in the region. It also probably left the middle latitudes a lot dryer.”

Co author Matthew Huber, an assistant professor of earth and atmospheric sciences at Purdue University’s College of Science compared data from the research expedition with complex climate-model simulations to study and predict the effects of greenhouse gases. Their measurements confirm that the carbon dioxide level increase in the PETM was at least twice as large as those previously proposed.

“We now have a pretty good correlation between records of past warmth and higher carbon dioxide concentrations,” Huber said. “What it tells you is that it’s not too difficult to push the climate system to a warm state. If you work out the numbers, it’s almost identical to what we are expected to do over the next few hundred years.”

Co-authors of the work were Nikolai Pedentchouk at Yale; Appy Sluijs, Henk Brinkhuis and Gerald Dickens at Utrecht University; Stefan Schouten and Jaap Sinninghe Damste at the Royal Netherlands Institute for Sea Research, and “the Expedition 302 Scientists.”

The expedition was an operation of the Integrated Ocean Drilling Program (IODP), an international marine research program primarily funded by the National Science Foundation, and Japan’s Ministry of Education, Culture, Sports, Science and Technology. The Arctic Coring Expedition was led by the European Consortium on Ocean Research Drilling (ECORD), an IODP contributing member that represents 17 nations. ECORD is responsible for managing all IODP mission-specific operations, i.e. scientific expeditions conducted in unusual or demanding environments in which specific platform requirements must be used to meet specific science objectives. In all, 21 countries participate in IODP

From Yale University

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