California boasts hundreds of caves, many of them hidden in the Sierra Nevada foothills. These caves hold much more than beautiful icicle-like stalactites and stalagmites. Trapped inside the stalagmites are tiny droplets of fossilized precipitation from climates long ago. In “Nature Tells Its Story Part 2” of Unfold, UC Davis researchers discuss how these water droplets provide a “climate archive” that may help us predict future shifts in rain, snow and drought. 

In this episode: 

Isabel Montañez, distinguished professor, UC Davis Department of Earth and Planetary Sciences

Barbara Wortham, doctoral student, UC Davis Department of Earth and Planetary Sciences

Audio transcriptions may contain errors.

Amy Quinton Kat, what is this? 

Kat Kerlin It's down on the corner by Creedence Clearwater Revival. 

Amy Quinton OK, but it sounds a little different than that. 

Kat Kerlin Well, the sound you're hearing is water dripping in a cave onto a glass plate where scientists are letting calcite grow. They're monitoring the drip rate while also singing. 

Amy Quinton Because what else are you going to do in a cave but monitor water while singing? You're going to have to tell me a little bit more than that. 

Kat Kerlin Well, we've been exploring how nature tells its story. 

Amy Quinton Right. In last week's episode, we talked about how a fish's eyeballs can tell us about their life history, where it's been and what it's eaten. 

Kat Kerlin Yeah. And apparently ancient water from caves can tell us a lot, too. I learned from UC Davis doctoral student Barbara Wortham that caves are like a giant sponge that can soak up rain from 20,000 years ago and store it in rock. 

Amy Quinton So it's like ancient water. 

Kat Kerlin Exactly. The water actually fossilizes. They call it fossilized drip water. 

Barbara Wortham Caves actually collect all of those raindrops that fall on top of them. And they record all of that history that is coming with the raindrop through time. And so that is what I'm actively trying to uncover, is all of that history that comes with the water and the isotopes in the water.

Kat Kerlin That history can tell us about not only Earth's past climate, but maybe even its future one. In this episode of Unfold, it’s 'Nature Tells Its Story, Part Two. Caves and Really Old Water.' 

Amy Quinton Coming to you from UC Davis, this is Unfold, a podcast that breaks down complicated problems and unfolds curiosity-driven research. I'm Amy Quinton. 

Kat Kerlin And I'm Kat Kerlin. Have you ever been inside a cave, Amy? 

Amy Quinton I have, but I'm totally claustrophobic, so I didn't stay very long. 

Kat Kerlin Oh, that's a shame. There are hundreds of caves here in California. We've got lava caves, chimney caves, big caverns that look like underground cathedrals. There's some really cool ones at Sequoia and Kings Canyon National Park. 

Barbara Wortham My favorite cave in California is Lilburn Cave, which is in the southern Sierra Nevada. It's the biggest mapped cave in California and it is made out of marble, which is striped rocks. And so you walk through it and there's these beautiful formations that have been made by, you know, millions of years of water running over them. They're smooth and they undulate and they look like water themselves and they're all striped. So they just have this beautiful effect in the cave. 

Photo or gray and white striped marbled rock from inside a cave
Marble banding inside Lilburn Cave. Marble is originally sourced from the ocean. As the ocean rocks got slammed onto the continent it metamorphosed into striped marble. (Greg Roemer-Baer)

Amy Quinton That is really so cool. That sounds so amazing. Like when do we get to go? 

Kat Kerlin I know it sounds fabulous, Barbara mostly studies caves in the Sierra Nevada mountain range and those caves are full of stalagmites and stalactites. 

Amy Quinton Those are the pointy things that look like rock icicles that hang from the top of the cave or shoot up from the bottom. I forget which is which. 

Kat Kerlin Yeah, I get it confused, too. Stalagmites grow up and stalactites hang down like icicles. A way to remember it is the one with a 'C' stalactite is for ceiling and stalagmite with a ‘G’ is for ground. 

Amy Quinton Of course you have to know how to spell it. 

Kat Kerlin I suppose that's true, 

Amy Quinton But thanks for that. 

Kat Kerlin Any time. That water is rich in the mineral calcite. So when water drips off the stalactite, it hardens and slowly builds a stalagmite on the floor. Each drop trapped in that rock is like a little time capsule. It's kind of like when scientists take samples of sediment cores from the ocean floor or cores from ice in the Arctic. Well, Barbara takes samples from stalagmites. 

Researchers look at water dripping off a stalagmite inside a cave.
Then UC Davis Ph.D. candidate Barbara Wortham and Cave Research Foundation West member David Angel monitored the drip-rate at Glacier Pool. (Greg Roemer-Baer)

Amy Quinton So stalagmites are a little like tree rings, like you can figure out how old they are because their layers grow year by year, kind of like we discussed with the fish eyeballs in last week's episode. 

Kat Kerlin Oh, that's so funny. You link that. So that's one reason climate scientists started looking at caves in the first place. But now it goes way beyond growth rings. Scientists like Barbara can analyze the chemical signatures of stalagmites to really get climate information from them. But first she has to get to the caves, which is not always easy. Barbara sent us some video of this. It shows Barbara tromping through the Sierra Nevada forests in winter with her snowshoes and trekking polls in order to get to these remote caves. She has to carefully cross icy streams. 

Amy Quinton In snowshoes, that sounds really dangerous. 

Kat Kerlin Well, she says once she arrives in a cave, it's pure joy and discovery. 

Barbara Wortham Caves are these really crazy things. They're so variable and unique and independent. You could walk into a cave and it's like you're walking into a ballroom. They're huge. They echo. You have so much space around you that the light on your head that you need to use in order to see doesn't even reach the wall like it runs out. The light source runs out before you get to the wall. 

Amy Quinton That's cool, but also fairly scary. 

Kat Kerlin Why are you afraid of the dark? Now, pay attention. 

Barbara Wortham But you can also be in caves where you're crawling through a tiny tube that's as wide as your shoulders and you're pushing your bag in front of you or you you've got it tied to your foot so that you can pull it behind you with the samples that you're trying to take. They're a very variable environment to work in, which is cool and you do need to understand all of that difference in environment in order to do what I do. 

Amy Quinton So what exactly does she do in there? 

Kat Kerlin Well, she's taking a lot of measurements like temperature and how the air moves. 

Barbara Wortham Some of these caves breathe literally daily. They recirculate all of their air through a process that we call cave ventilation. So how often does that happen? Is that going to impact all of these records that we tried to create from the cave deposits? 

Kat Kerlin And she's collecting drip water. She's looking for that fossilized water to squeeze out of those stalagmites. 

Amy Quinton Ex-squeeze me? Did you say squeeze? 

Kat Kerlin Indeed I did. This part kind of astounds me. Apparently, when water moves through a cave, it brings with it calcium carbonate. When those calcium carbonate crystals grow together, they can trap rainwater between the crystals. 

Barbara Wortham And so you can imagine that if you have a bunch of Legos and you're putting your Legos together, you can't exactly push them all the way together. There's a tiny, minuscule amount of space between them. And in that miniscule amount of space, tiny amounts of that rainwater gets trapped. And so we are trying to get that water out between the Legos of calcium carbonate. 

Amy Quinton OK, but wait, rocks aren't exactly sponges. 

Kat Kerlin Which is why I asked her how she does this. 

Barbara Wortham And the way we do that is quite fun for me because I get to be in a lab where I basically spin something that squeezes the rock. It literally squeezes the rock to super high pressures. And I spin it and spin and spin it until no more water gets squeezed out of the rock and measure all of the water that has come out of it. 

Kat Kerlin And that's important because really this is all about water and not just ancient water. You may have noticed that things are exceptionally dry in California? 

Amy Quinton Yeah, we're in the second drought I've been in since I moved here in 2012. 

Kat Kerlin Some wonder if that drought ever really even ended or if we're in some megadrought. But by looking at the past, Barbara is hoping that this ancient water’s secrets will help us manage our water resources going forward, especially with a changing climate. 

Barbara Wortham Twenty-thousand-year-old water is really interesting because CO2 has changed quite a bit. And so what I'm trying to do is really understand how this variability in CO2, which causes variability in temperature, how does that impact our water resources and precipitation in the Sierra Nevada? And you can get all of that from 20,000-year-old water because it was falling in a different CO2 and temperature landscape than what we have now. And so that's really what I'm trying to get at, is this climate change signal and how it impacts our water resources in the Sierras. 

Five UC Davis researchers inside marble rock formations of cave
Members of Cave Research Foundation West and Barbara Wortham stand in a part of Lilburn Cave. Striped marble forms through thousands of years of Redwood Creek slowly dissolving the rock. (Greg Roemer-Baer)

Kat Kerlin Notice, she says, our water resources. She's talking super, hyper local water information. Global climate models are really important, but they're not very granular. What Barbara's collecting through this water is climate information about exactly where we live. We can compare the two to get a bigger, more precise picture of what the climate was like here under similar CO2 conditions in the past. 

Amy Quinton So if they collected drip water in a cave in Kentucky or Texas, for example, then they could also get that local climate information. 

Kat Kerlin That's right. 

Amy Quinton People have been studying caves for a long time, but this research is fairly new, right? 

Kat Kerlin Right. Barbara calls fossilized drip water the new frontier. She's one of the first to try it in the US. When she's done, she and her colleagues will have created the first record of fossilized drip water that exists in the state, possibly even in North America. 

Isabel Montañez It is exciting that you would even preserve these fluids in something this old. 

Kat Kerlin That's Isabelle Montañez, a UC Davis professor in the Department of Earth and Planetary Sciences and Barbara's advisor. 

Isabel Montañez It's kind of like DNA in, you know, being found in stuff that's millions of years old. We have samples that we could be exploring - this will happen in the future - that go back to 70,000 years. 

Kat Kerlin Isabel's been working for years on key questions that she says caves can help answer. 

Isabel Montañez No one had been asking the question: do we have records of past rainfall and past seasonality? When did we have droughts? And I knew that the caves scattered throughout the foothills of the Sierra Nevada and as well as caves elsewhere, there are some along the coast, I knew that these were unexplored and that they had the potential to be an archive or what I like to call crystallized climate. 

Amy Quinton Crystallized climate Kat. I like that. 

Kat Kerlin Alliteration. It's a beautiful thing. That phrase also conveys a sense of wonder and curiosity, doesn't it? I mean, a lot of scientists, including Isabel, talk about that being at the root of their work. 

Isabel Montañez The reason I do what I do, I mean, I think the reason I wanted to be who this sort of career back when I was in the eighth grade is comes down to the forensic science. I mean, it's always about being a detective in the science, you know, in the scientific realm. And so every new approach we can try to develop, if it's successful is, you know, just the coolest thing. It is all about trying to find the new and the unexplored. 

Amy Quinton So what have they found that's new? 

Kat Kerlin They took those ancient fluids and looked at their noble gas concentrations, which no one had done before. Apparently, noble gases are hypersensitive to temperature changes. They found that the central Sierra Nevada was exactly five degrees Celsius colder 18,000 years ago than it is today. 

Isabel Montañez That means that we are looking at about five degrees of temperature between when ice sheets were spanned out into Montana and Wyoming and Oregon and Washington versus today. And I think that's really insightful, right, in that if five degrees from ice sheets down in in Oregon and covering Montana and Idaho and we're looking at potentially four degrees total change in our future. I mean, it's really eye opening, right? 

Amy Quinton That is eye opening and a bit scary. So what does this mean for California? Did she say anything about that? 

Kat Kerlin She did. Isabel told me that for us in the Southwest, it's looking like periods of drought fluctuating with these rain dumps called atmospheric rivers. But she has some caveats because our planet has never actually experienced what we're doing to it now. 

Isabel Montañez These switches in the past from our normal rainfall patterns to drought conditions, no doubt happened, turned over in a decade or so and then may have lasted for centuries. But those changes are still far longer term and happen much more slowly than what we know we are doing now and what we are seeing has changed now. So whatever we discover may be analogous to what we might predict in the future, but we should anticipate they could be faster in terms of change and performance perhaps even amplified. 

Kat Kerlin So consider that a warning. The Earth's sensitivity to CO2 may be higher than we realized and we may be underestimating the changes ahead. 

Amy Quinton Geez, Kat, way to end this on a happy note. 

Kat Kerlin Right? I'm sorry. Perhaps you'd prefer I stick to just talking about caves. 

Amy Quinton No, this is important. So what is the next step for these researchers? 

Kat Kerlin Their next step is analyzing this water to learn about something very top of mind for we westerners, wildfire. 

Isabel Montañez We've done some exploratory work. We know that they contain organic molecules that came from the soil and they washed down with the rain as it went through the soil. And what some preliminary work we've done says that those molecules can actually tell us about past wildfires. So that's our next area. We're going to try to develop a couple of different approaches using those molecules. So, yeah, there's probably a whole treasure trove in those in that water that we haven't yet explored. 

Amy Quinton Ancient fire, Kat. Nature's story continues to unfold. 

Kat Kerlin Oh, you said it. And you can hear more Unfold episodes at Thanks for listening. 

Amy Quinton Unfold as a production of UC Davis. It's produced by Cody Drabble. Original music for Unfold comes from Damien Verrett and Curtis Jerome Haynes. Hey, if you like this podcast, check out UC Davis's other podcast, The Backdrop. It's a monthly interview program featuring conversations with UC Davis scholars and researchers working in the social sciences, humanities, arts and culture. Hosted by public radio veteran Soterios Johnson. The conversations feature new work and expertise on a trending topic in the news. Subscribe wherever you get your podcasts. 

Related Stories: