12,000 years ago, Yellowstone’s dry summers began leaving a charcoal trail in its lakes. 6,000 years later, researchers found the same climate pattern linked to lower lake levels and reduced hydrothermal activity

Long before modern climate records existed, Yellowstone’s lakes were preserving evidence of changes in climate, wildfire activity, and hydrothermal systems.

A new study led by Montana State University researchers examined sediment from small lakes in Yellowstone’s Lower Geyser Basin. The records show that summers were warmer and drier than today between 12,000 and 6,000 years ago, as per a report. During that period, more charcoal accumulated in the lake sediments, while diatom records indicated lower lake levels.

Published in Proceedings of the National Academy of Sciences, the study provides a long-term view of how Yellowstone’s environment responded to changing climate conditions.

Lake sediments reveal Yellowstone’s past

The researchers collected sediment cores from several small lakes in the Lower Geyser Basin, Yellowstone’s largest geyser system. Because the lakes have no streams flowing into or out of them, material can accumulate in layers over time. Scientists can examine those layers to reconstruct changes in the surrounding environment.

Pollen reveals past vegetation, while charcoal records wildfire activity. Arsenic and cesium concentrations, along with diatom composition, provide information about hydrothermal activity, lake chemistry and water depth, as per a Phys.org report.

Radiocarbon dating and evidence from known natural events, including past volcanic eruptions, can help establish the age of the sediment layers.

Warmer, drier summers brought more fire

The sediment records showed that summers in the geyser basin were warmer and drier than today between 12,000 and 6,000 years ago.

The climate-model results matched evidence preserved in the lakebeds. Greater amounts of charcoal pointed to increased wildfire activity, while diatom records showed that lake levels were lower.

Researchers identified these relationships by comparing the sediment evidence with high-resolution paleoclimate model results for Yellowstone, as per the Phys.org report.

Lodgepole pine forests changed little

The vegetation responded differently to past climate shifts. After the glaciers covering the region retreated, a grassy steppe developed on the rhyolite volcanic soils. Lodgepole pine forests became established between 12,800 and 11,000 years ago.

Pollen records indicate that the composition of those forests changed little despite later climate changes.

Cathy Whitlock, an MSU Regents Professor emerita of Earth sciences and the study’s lead researcher, said that, "The persistence of lodgepole pine for thousands of years is explained by the infertile soils on the rhyolite volcanic plateau and lodgepole's adaptation to fire. It's been very hard for anything else to get established in that area given limited nutrients and well-drained substrates," as quoted by Phys.org.

The researchers suggest lodgepole pine will continue to dominate the plateau’s vegetation as the climate warms.

Wet periods supported stronger hydrothermal activity

The lake records also revealed a relationship between moisture and Yellowstone’s hydrothermal systems. Hydrothermal activity was stronger during wetter periods and weaker during dry periods.

The findings suggest that future warming could bring increased wildfire activity along with reduced hydrothermal activity in Yellowstone.

Michael Poland, research geophysicist and scientist-in-charge of the USGS Yellowstone Volcano Observatory, pointed out that such changes are unlikely to become noticeable over a human lifetime, as per the Phys.org report.

However, the study could help researchers understand possible changes in the timing, force, and frequency of geyser activity in Yellowstone’s hydrothermal areas.

The 1988 fires helped researchers read the record

The study builds on research Whitlock and her colleagues began after Yellowstone’s 1988 fires.

They studied charcoal deposited in lakes to determine how far particles traveled during fires, how quickly they were buried, and how those deposits could be used to reconstruct fire histories.

The charcoal-analysis techniques developed through that work are now used in fire-history studies on every continent.

That research also helped scientists better understand how charcoal is deposited and preserved in lake sediments, supporting the reconstruction of Yellowstone’s long-term fire history.

Together, the sediment evidence shows how Yellowstone’s climate, wildfire activity and hydrothermal systems have changed over thousands of years.

The ancient record points to more fire and lower lake levels during warmer, drier conditions, while wetter periods were associated with stronger hydrothermal activity. These findings give researchers a longer perspective on Yellowstone’s past and offer clues about how its environment could respond as the climate warms.