Research team receives NSF climate change grant

A team of researchers across the United States, including Cornell College Professor of Geology Rhawn Denniston, is embarking on a new mission to answer questions about climate change in Portugal.

The National Science Foundation (NSF) has awarded the team more than $676,000 to study stalagmites from caves in central and southern Portugal as a means of investigating how rainfall changed over decades and centuries starting 2,500 years ago.

“Droughts and floods are likely to become more extreme in a warming world, and the area near the Mediterranean Sea appears to be a hotspot for climate change,” Denniston said. “By studying past climate variability in this region, we hope to better understand what climates may look like there in the future as our planet warms.”

The team is especially focused on the impacts of a phenomenon known as the North Atlantic Oscillation (NAO). Denniston describes the NAO as an atmospheric teeter-totter, with the northern end located in Iceland and the southern end located in Portugal. The teeter-totter flips back and forth sporadically every few years or decades. When the NAO is in one position, Portugal and Spain get drier while northern Europe becomes wetter, and when the NAO flips back the other way, the opposite effect occurs. The NAO influences other parts of the climate system, as well, including where hurricanes make landfall on the East Coast of the U.S. 

“Ultimately, we hope to determine the importance of the Azores High pressure system (which is the southern node of the NAO) in controlling the hydroclimate in Portugal and the surrounding region,” said Alan Wanamaker of Iowa State University, the project’s lead researcher. “This research will yield past estimates for how quickly hydroclimate changed from wet to dry conditions and vice versa. Because the Iberian region is currently experiencing increasing aridity associated with global warming, our work will provide a hydroclimate baseline that will be used to help contextualize modern conditions, including extreme events, by looking at naturally occurring variability for the past 2,500 years.” 

The NAO has been the topic of considerable debate because of its climatic importance and because of suggestions that during medieval times, the teeter-totter became locked into one position for centuries, something that hasn’t been observed in modern history.

Each member of the research team has a distinct role in this project. The team is led by Iowa State’s Wanamaker, who, along with a Ph.D. student, will oversee the collection and analysis of the stalagmites. Denniston and five Cornell students will focus on collecting and understanding how conditions such as air temperature, humidity, and air pressure change in and above the caves. They will also study how rainfall above the cave impacts the rate and chemistry of water dripping into the cave in order to better understand the chemical signals in the stalagmites.

“When rain falls above the cave, the water soaks through the ground to get into the cave,” Denniston said. “There are different isotopes of oxygen and hydrogen in the water, and we need to know what happens to these isotopes as the water infiltrates. We will also be looking at trace elements such as magnesium and strontium in the drip water and that are leached from the bedrock. Studying drip water is important because the drip water is really where the climate signals lie; the stalagmites just preserve those chemical signals. So we are wondering what happens to the drip water if it is a really hot, dry year. Does it look different if it’s a cool, wet year? ”

The data will help the team link the chemistry of the stalagmites to the precipitation patterns that Portugal experienced over past centuries.

“The only way we know the impact of the climate is if we reconstruct the climate at really fine scales,” Denniston said. “Stalagmites are really great for this kind of work because we can date layers as young as one year old and as ancient as 500,000 years old. They can tell us all kinds of information, including about past rainfall.”

Joining Wanamaker and Denniston are geologists from the University of New Mexico and Union College, and a climate modeler from the Woods Hole Oceanographic Institution.