Cathy Whitlock, MSU Earth Sciences professor, explains that lake beds in Yellowstone National Park hold a detailed history of climate change going back to the last ice age when Crevice Lake and Blacktail Lakes, two of her study sites, were formed.
YELLOWSTONE SECRETS BURIED IN ANCIENT MUD
by Jean Arthur
Cathy Whitlock studies climate change one centimeter at a time. The MSU paleoecologist and her
students examine the past 20,000 years of the West’s environmental history since the last ice age. They scrutinize sediments in core samples taken from the bottom of lakes. One centimeter of lake mud equals about 10 years, Whitlock said of her study sites in Yellowstone National Park. “In these cores, we are looking at pollen grains, charcoal particles and maybe a few insect legs and wings that landed in the lake and sank to the bottom each year,” said Whitlock, who joined MSU’s Department of Earth Sciences last year after 14 years at the University of Oregon. “Over time, the accumulation of these materials becomes a record of how forests have developed and changed, when fires and insect outbreaks have occurred, and how the ecosystem has responded to climate changes.”
Like paleoecologists around the globe, Whitlock reconstructs the past to understand the present and the future. Findings show that Yellowstone has experienced dramatic changes in its environment in the past, and it is still changing. Projected future climate conditions because of increased greenhouse gases exceed anything the park has seen in the last 1,000 years. Whitlock said that researchers have to go back at least 6,000 years to see comparable conditions like those projected in the coming century, and even those ancient examples aren’t perfect analogues. “One difference is that current and future climate changes are occurring at a much faster rate than in the past, and we are unclear whether ecosystems can keep pace with changes of such magnitude,” she said.
Her Crevice Lake study site, a four-mile hike from the Grand Loop Road between Mammoth and Tower Junction in Yellowstone’s Northern Range, offers a unique glimpse of the past 12,000 years. Since the spring-fed lake is round and somewhat protected from wind, the lake sediments are not stirred, receive no oxygen and host no organisms at its 100-foot depth.
Whitlock discovered the laminated sediments in Crevice Lake in 1992 and collected cores in 2001. The lighter brown summer layers and darker winter layers, she says, delineate the years as clearly as tree rings detail the annual growth of trees. And like tree-ring records, the laminations at Crevice Lake preserve a record of yearly ecological changes related to variations in temperature and moisture. “We see that 10,000 years ago, the climate was warmer, drier than now,” said Christy Brile, a doctoral candidate from the University of Oregon’s geology program who works in Whitlock’s paleoecology lab. “But today, we have solar radiation and different variables that contribute to global warming. The studies do give us an idea of how resilient plant communities are to change.”
Whitlock noted that the ecosystem is continually evolving. “We are also finding that large fires, similar to those of 1988, affected many sites about 200 and 300 years ago, but fire frequency has been steadily decreasing over the last several millennia,” Whitlock said. “During warmer drier periods, like that from 11,000 to 7,000 years ago, many watersheds experienced fires every few decades. The fire activity in Yellowstone is and has been closely tied to summer drought; when droughts were more severe, fires were more frequent. The long-time perspective teaches us that present-day conditions are short-lived and shouldn’t be viewed as normal.”
A very visible example of climate change, Whitlock said, is the dry and cracking lakebed among the ponds at Blacktail Lake of Yellowstone, another Northern Range study site. Like other lakes in the park, this lake shrunk considerably in the last decade as a result of drought. Now its parched bone bed is of great interest to the paleoecologist because shifts in water level are another measure of climate change that can be detected in sediment cores. “Whitlock’s research has implications for other research around Yellowstone,” said Roy Renkin, Yellowstone biologist. “She indicated that she is finding pine beetle insect fragments in sediment cores which shows a history that supersedes human presence in the park.”
Renkin notes that tree-boring bugs have infested 50,000 acres of Yellowstone forests. The four species of bark beetles and one budworm created seas of red, dead trees in what may be the largest insect outbreak recorded in Yellowstone.
“Through Whitlock’s research, we hope to identify periods of high levels of insect activity and find out if the outbreaks occur three times a century or six to seven times,” Renkin said. “We know of mountain pine beetle outbreaks in the 1930s and late 1960s and 70s in the same areas. We have a 100-year record. Whitlock’s research goes back centuries.”
Whitlock’s research is funded by the USGS, the National Science Foundation and the National Park Service. In addition to her work in the western U.S., she is also studying fire and climate history from similar settings in Argentina and Chile. Researchers travel to MSU from all over the world to receive training in the charcoal analysis methods that she helped develop.
Aside from her research, Whitlock teaches an “inquiry” course for non-science majors as part of MSU’s Core 2.0 curriculum for undergraduates. The class, Yellowstone: A Scientific Laboratory, takes 30 students to the park for field studies then back to campus for classroom discussions and lab work.
“We need to understand the ecosystem’s response to climate change to discover what will likely happen in the future,” Whitlock said. -