Leaf wax also predates climate records from Antarctic ice core, which goes back only about a million years and requires a climate that could support ice. One study used leaf wax at a glance the climate of Spain was warmer about 15 to 17 million years ago. Another person looks at Humidity history of Southwest Africa over the past 3.5 million years.
Bhattacharya started using them while working as a postdoctoral fellow at Tierney’s lab. Five years ago, she and Ran Feng, a co-author, came up with the idea to study the Pliocene while riding a bus during a conference for young researchers.
Their analysis begins with marine sediments collected decades ago by research vessels Joides resolution, roaming the drilled cores of the ocean from a depth of 6 miles below the surface. The samples used for the study were taken off the coast of California: one off the Baja peninsula from a depth of more than 2,600 meters and one from the East Cortes Basin at a depth of 1,700 meters. In the Pliocene, leaf wax will be transported westward by wind to become part of this marine sediment.
Bhattacharya says the team took a cube of each core, freeze-dried them, and ran them through “a famous espresso machine,” says Bhattacharya, using solvents under pressure at high temperatures. altitude for wax extraction. They then measured the hydrogen and carbon isotope composition with a gas chromatographic-isotope ratio mass spectrometer, which separates the waxes according to their molecular weights.
“The hydrogen used to make wax comes from rainwater that plants use to grow. You can think of isotopes like a fingerprint,” Tierney said. “These isotopes really track what kind of rain you have, which is pretty cool. They can also track winter precipitation versus summer precipitation. So it’s pretty strong.”
For the second part of the study, the climate modeler Ran Feng, a professor in the University of Connecticut’s Department of Geosciences, ran simulations to determine how sea temperature affected the stronger monsoons of the mid-Pliocene. Feng found that when sea temperatures – in an area stretching from Alaska to the coast of Baja, California – were higher than in the generally warmer tropical waters off Central America, they created conditions for monsoons. stronger in the Southwest. Locally warmer air acts like a heat pump, sucking in relatively cooler tropical air and warming it, pulling in moisture. “So it creates this loop,” she said. “That’s why this can bring moisture into parts of Southwest North America.”
This is type sea heat wave has occurred off the coast of California in recent years and will become more common as temperatures rise, triggering more intense monsoon storms.
Monsoon will help solve the drought when the Southwest is dry. But they will be stronger, producing several inches of rain for short periods of time and causing more frequent flooding. “The Arizona monsoon accounts for about 60 percent of our rainfall for the year,” says Tierney. “It is an important source of water in the desert. In certain hydrological systems, it recharges groundwater. But the flip side of that is that these monsoon storms can be so intense and fast that a lot of water can end up flowing into river basins and out of the landscape. So it doesn’t always recharge the groundwater.”
Those storms also threaten the built environment, and as the climate changes, design standards for infrastructure such as roads, bridges, dams and stormwater systems fail to keep up. The National Oceanic and Atmospheric Association’s Atlas 14 reports for the US Southwest rely solely on historical rainfall, not future changes, for its projections. of the agency study abroad in the southwest was released in 2004 and last revised in 2011.
There is another worrying link between more intense monsoons and disasters: Forest fires. Greater rainfall increases fuel intake by encouraging plant growth, says Bhattacharya. Subsequent droughts set the stage for larger fires.
“We think the stronger monsoon season will create unforeseen hazards from fires and floods,” she added, noting that more research will be needed to focus on the picture. . “We are planning to go further and study this in the Pliocene to see how fire and flooding respond to a warmer climate.”
