During the last ice age, the Southwestern U.S. was soaked by storms, while the Pacific Northwest remained dry. As global temperatures increased and ice sheets retreated, the climate patterns in both regions shifted. Recent research published in Science Advances sheds light on how groundwater levels reacted differently in these areas during this transition.

In the study, it was found that despite increased rainfall, the water table depth in the Pacific Northwest remained relatively stable, while the Southwest experienced significant groundwater loss. This discrepancy indicates that Southwestern aquifers, crucial for millions of people, could be more susceptible to future climate changes.

Alan Seltzer, the lead author of the study and an associate scientist at Woods Hole Oceanographic Institution (WHOI), mentioned that climate models predict a drier Southwestern U.S. and a wetter Pacific Northwest by the end of the century.

The research team, including seven WHOI-affiliated scientists, reconstructed groundwater level records from the Last Glacial Termination, a period of significant environmental shifts between 20,000 and 11,000 years ago. By analyzing fossil groundwater from 17 wells in Washington and Idaho dating back 20,000 years, they were able to develop a better understanding of how groundwater reacts to long-term climate changes.

Groundwater is a vital source of freshwater for the planet, supplying up to half of the water used for various purposes. With climate change putting millions of wells at risk of drying up, it is crucial to comprehend how groundwater behaves over extended periods.

The team used a unique method developed by Seltzer, involving isotopes of xenon and krypton, to calculate past water table depths. Their analysis revealed that the Pacific Northwest's groundwater levels remained stable despite increased precipitation, contrasting sharply with Southern California's water table decline during deglaciation.

Comparing the ancient groundwater data with Earth system model simulations, the researchers found close agreement, indicating the model's ability to capture key groundwater dynamics. This study highlights the vulnerability of Southwestern aquifers and the importance of integrating paleoclimate data with modern models for improved water resource planning globally.

Another study led by Seltzer's lab in collaboration with the University of Manchester focused on geological insights from ancient groundwater in the Pacific Northwest. Published in Nature Geoscience, the study analyzed groundwater from 17 wells in the Palouse Basin Aquifer, revealing insights into geological and chemical processes deep within the Earth.