For many years scientists thought that groundwater — which hides in underground aquifers and slowly makes it way out to sea — wasn’t adding much to ocean chemistry.
After all, groundwater only makes up a small percentage of the global freshwater flowing into the sea. But a new study in the journal Nature Communications finds that there’s a lot more chemicals flowing through groundwater into the ocean than previously thought. That new data should help researchers make better models of Earth’s past and future climate.
“Groundwater is one of those things that people haven't paid a ton of attention to, but that’s changing,” says Boston University ecologist Wally Fulweiler, who was not involved with the new paper. In recent decades, she says, scientists have realized that groundwater "informs different things like climate models, and how much nutrients are available to produce phytoplankton, which form the base of food webs.”
The new research focused on five elements found in groundwater that are particularly important for climate modeling: lithium, magnesium, calcium, strontium, and barium. Paleo-oceanographers — scientists who study the ancient ocean — measure levels of these elements (and others) in deep sea sediments to reconstruct certain aspects of Earth's history. For instance, they can look at how intense the breakdown of Earth's crust has been over time, or how much carbon has been stored in the ocean. Until now, though, a piece of the data has been missing — the groundwater piece.
“I consider myself a geochemical Santa Claus. This is a number that so many modelers have wanted,” says lead study author Kimberley Mayfield, with a laugh. She says the research, part of her doctoral thesis at the University of California, Santa Cruz, took years of chemical analysis and lots of begging groundwater samples off strangers and colleagues. “This was a global effort by a lot of people who all wanted this question answered,” she says.
The additional data should lead to better models of Earth’s past climate, says Matthew Charette, a senior scientist at Woods Hole Oceanographic Institution and co-author on the paper.
“Certainly they'll be more accurate, because this is something that really hasn't been accounted for,” says Charette, who contributed groundwater for the study from his massive library of hundreds of samples. He says improving models of the past should help us better understand the current changes in Earth’s climate. Mayfield agrees.
“We want to improve climate models for reasons that I believe are obvious at this point,” says Mayfield. “If you ground truth a model and you know it does a very good job of understanding and predicting climates in the past, you know that it's going to do a good job with climates in the future.”