Geochemical analysis of the last ice age may contain clues to future climate change and preparedness strategies

Located in Northern California within a major transitional climate zone between the Pacific Northwest and Southwest United States, the Shasta Lake Caverns (LSC) stalagmites contain geochemical clues to help researchers understand how The climate changed during the end of the last ice age (14,000—37,000 years ago) and predicted what can happen amid climate changes in modern times.

A type of speleothem, stalagmites are impressive rock formations made of calcium carbonate that grow upward from cave floors. It can take thousands of years to grow; of water droplets that make the slow journey of rainwater through the earth and finally drip through fractures in the roofs of the caves to the floor. Jessica Oster, associate professor of earth and environmental sciences and paleoclimatologist, measured the geochemical properties within stalagmites, including stable oxygen and carbon isotopes in LSC to understand how climatic and environmental factors in the region changed during and after the last ice age.

The article, “Stalagmite records from various Northern California proxies reveal dynamic regional hydroclimate patterns during the last glacial cycle,” was published online in the journal Quaternary Science Reviews the 24th of June. It is available for free download until August 13.

While scientists have been working for over a century to reconstruct the climatic history of the western United States, the numerous mountain ranges and microclimates that span the region contribute to wide variations in climate change in this area. It is remarkable to have a record of LSC in Northern California due to its location on the boundary between the US Southwest and the Pacific Northwest, two parts of the western US experiencing different climates today and They have responded differently to climate change in the past.

A benefit of speleothems as recorders of climate change is that they can be dated with precision and precision by measuring isotopes of uranium and thorium trapped in the stalagmite as it grows. This powerful dating tool works up to 500,000 years before the present, much more in the past than radiocarbon dating, which peaks at 50,000 years. Oster and his collaborators came out with two stalagmites and analyzed their geochemistry. They found that the amount of rainfall in LSC varied rapidly in the past, concurrent with known climatic changes during and after the last ice age that have been observed in other paleoclimatic records across the northern hemisphere. They also discovered that there were periods of time when the weather near the LSC was more similar to the Pacific Northwest climate, and other periods when it was more similar to the Southwest, indicating that the location of the boundary between these zones may not always have been been located where we understand it to be today.

The large and rapid variations in rainfall recorded by LSC stalagmites demonstrate that the climate in Northern California is sensitive to changes occurring in other parts of the world, and that rainfall in this area may increase or decrease in response to changes. relatively small in the global climate. . In particular, Oster was able to connect the climate changes identified at LSC, a National Natural Monument located two and a half hours north of Sacramento, with those of the reference climate record for the Northern Hemisphere, the records of the Greenland ice core. It is plausible that if the climate changes in Greenland and Northern California were related back then, they could be related now (currently, the Greenland ice sheet is melting fast).

“Our findings offer us clues to the behavior of the region’s climate system and what the rain does in California in response to climate changes that may already be occurring around the world,” Oster said. “We can use this backward looking research to look forward. This is tremendously important because the semi-arid environment around Lake Shasta Caverns is sensitive to changes in rainfall and nearby Lake Shasta is the largest reservoir of water in the Any change in the rainfall around Lake Shasta has the potential to impact water resources for the entire state of California. “

As we enter unknown climate territory, large-scale models that help guide the global community often do not provide enough regional-level information on what local communities should prepare for. Having a strong paleoclimatic history provides a valuable framework for understanding how the regional climate changed in the past and what could come in the future.

The project, which started as student Izzy Weisman’s master’s thesis and benefited from the contributions of several of Oster’s undergraduate students, has opened the doors to future research, including the development of quantitative reconstructions of how the rain changed in the past, which will be of great help. use for local city and resource planners. This work is also of interest to environmental scientists who examine responses to climate change in regions with similar geological characteristics around the world.