The Greenland Ice Sheet’s transformations
LLNL researchers and their collaborators are studying the Greenland Ice Sheet—the largest ice mass in the Northern Hemisphere—to better understand its history, including time periods when part or all of Greenland was ice free. Because the ice sheet is land-based and its melting adds water to the oceans, this research not only provides insight into the ice sheet’s history, but also the increased risk of sea-level rise in a warmer future.
These research findings offer evidence that there was no ice sheet in that location at some point during the last 2 million years, indicating that the center of the Greenland Ice Sheet melted away, and the island was warm enough to support a tundra ecosystem with plants and insects. In addition, during an earlier collaborative research project, the team used a different isotope clock to study the bedrock under the sediment, and findings showed that the most recent ice-free period was no more than 1 million years ago.
LLNL scientists and their collaborators have been studying the Greenland Ice sheet for more than ten years, using multiple techniques and analyzing various ice cores. Learn more about the techniques the research team uses to study the Greenland Ice Sheet, and how one ice core was originally drilled at a secret Army base in the 1960s.
Key collaborators: University of Vermont and Columbia University
Contact:
Lake sediments preserve rich environmental histories
LLNL scientists apply a variety of radiocarbon techniques as they study California’s eastern Sierra Nevada, where towering mountains hold remnants of glaciers, and snowpack feeds streams and rivers that provide water to lakes, as well as to canals, pipelines, and reservoirs that supply water to California’s cities and farms.
One example of this research involves a long-term collaboration between CAMS scientists and a research group at the University of Kentucky, focusing on the history of Mono Lake and two nearby subalpine lakes, June and Convict Lakes. Like many other small lakes in the Sierra Nevada, June Lane and Convict Lake were formed in canyons scoured by glaciers, whereas Mono Lake is much older, formed by tectonic movements.
When glaciers in the Sierra retreated 17,000 years ago, new land was exposed and gradually covered by grasses, shrubs, and trees. Pollen from these plants and trees is preserved in the lake sediments. In addition, temperature and precipitation changes lowered lake levels and changed the water chemistry, and thus the habitat for tiny crustaceans and other aquatic life, whose shells are also preserved in the sediments.
The research teams collect sediments from these lakes in cores, which contain fossil pollen, shells, and other items. They date the samples at CAMS, and analyze the fossils to reconstruct past changes in the lakes’ surroundings. Findings illuminate environmental changes that occurred since the last glacial period.
The analysis of sediments that accumulated in June Lake over recent millennia also indicate changes in the lake level, chemistry, and aquatic life. In addition, aquatic algae that form silica-based shells record conditions during regional droughts, which are characterized by stratification, where there is less mixing between water at various depths. This analysis of the aquatic algae shows that as conditions have become much drier, the June Lake aquatic ecosystem has become less productive.
Key collaborator: University of Kentucky
Contact:
Fossilized human footprints at White Sands National Park
White Sands National Park in New Mexico is the site of an ancient lake bed, where fossilized footprints of mammoths, giant sloths, and other extinct megafauna have been found—alongside human footprints. Researchers from the National Park Service and US Geological Survey who study the footprints determined that during periods when conditions were much wetter, the lake was an important resource for humans and a variety of large animals. However, they wanted to understand when the wetter ecosystem existed and help map the migration of humans to the Western Hemisphere and across the continent.
The researchers needed to test the accuracy of their initial radiocarbon dating results, measured on potentially problematic aquatic seeds. They reached out to CAMS scientists and asked them to apply radiocarbon dating to pollen preserved in the same layers as the footprints and seeds.
CAMS scientist Tom Brown pioneered pollen dating in his doctoral work in the late 1980s. Recently, CAMS scientists advanced this dating technique for use in a variety of paleoenvironmental studies, in collaboration with the director of the Flow Cytometry Core Facility at Indiana University. Researchers can use the CAMS accelerator system to measure small samples with high precision and accuracy, and they were able to determine that the pollen was the same age as the seeds, confirming that the footprints are at least 21,000 years old, thousands of years older than anyone expected.
Key collaborators: U.S. Geological Survey and Indiana University
Contact:
