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A look into the past environment of Yellowstone Lakes
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A look into the past environment of Yellowstone Lakes

Yellowstone Caldera Chronicles, a weekly column by scientists and collaborators from the Yellowstone Volcano Observatory, is published every week. Sabrina Brown, assistant professor of environmental science at Defiance College, contributes this week’s article.

The Greater Yellowstone Ecosystem, which includes Yellowstone Lake as its core, is made up of diverse environments that are sensitive to climate change since the end of an ice age approximately 14-15 thousand years ago. Scientists took a 11.82 m (38.1 ft) sediment core from the northern lake to reconstruct the climate and environment conditions in Yellowstone Lake and the catchment area. The core contained diatoms fritules. These are diatoms which are a type of algae. They are hard and porous cell wall diatoms. Also, the sediment core contained pollen and charcoal data. This data was used to document changes and fire history.

A digital elevation map for Yellowstone National Park (left), with Yellowstone Lake’s location indicated by the blue box. Satellite image (right), of the study site, with core YL16-2C collection location shown by the orange circle Original publication in Sabrina Browns dissertation (2019).

Data from core YL16-2C provides a continuous record on the climate history in Yellowstone Lakes basin between 9,900 years ago and nearly the present. The results show that most ecosystem changes are gradual and were caused by slow changes to the seasonal cycle of solar power input. This resulted in warm and dry summer conditions at the beginning of the record (9.900-6.300 years ago), and then progressively changed to cooler, wetter conditions over time.

The record also highlighted periods when there were rapid environmental changes. These changes were most likely caused by sudden changes of climate (temperature, and/or precipitation). A series of climate fluctuations occurred between 7,800 and 6,800 years ago. There was also significant warming between 4,500 to 3,000 years ago and 1,000 to 700 years ago. This period is known as the Medieval Warm Period. These rapid climate fluctuations resulted in short-term changes to vegetation and algae. Other research in the park showed that the Medieval Warm Period saw a megadrought. Old Faithful was left dryFor almost 150 years!

The Yellowstone Lake sediment record’s early part (9,880-6,300 years ago) was characterised by an open forest, frequent fires, high summer evaporation rates, early spring snowmelt, low nutrient availability and early melting of lake ice. The record’s middle section (6,300 to 3,000 years ago) shows a cooler climate. This resulted in a denser forest establishment, larger fire episodes, and less summer evaporation. Further cooling and increased moisture in this record’s most recent section (3,000 years ago to current times) led to the creation of a closed forest with few but large fire episodes, reduced summer evaporation, high runoff into the lake, and decreased summer evaporation. The lake sediment’s climate history clearly shows how climate conditions shaped Yellowstone’s ecosystem.

Sabrina Brown collects samples from Yellowstone Lake core (YL16-2C) at the National Lacustrine Core Facility at the University of Minnesota.

The data clearly show that Yellowstone Lake and the catchment area had a climate history similar to this region of GYE. Conditions were warmer and drier in this region than they were in the recent past due to greater solar energy input. The climate became more humid and cooler throughout the record, reaching the pre-industrial conditions and low temperatures. The sediment record shows that climate had little influence on lake level. This suggests to me that Yellowstone Caldera’s inflation and deflation might be more important than the climate on Yellowstone Lake’s depth and shoreline development.

This sediment-core record is a great record of climate change over the past few centuries, but it doesn’t have the resolution needed to reconstruct more recent changes. If you are interested in learning more about Yellowstone’s recent climate history, The Greater Yellowstone Climate AssessmentThis is a great resource. The sediment core analysis can however provide insight into the future climate and how the GYE’s vegetation and environment might react to these changes. Understanding the past is a key tool to understand the future.

The data from the Yellowstone Lake Core and the combined data show that climate has significantly influenced the fragile ecosystems of Yellowstone National Park. This article provides more information about the research. for details.

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