Decoding Climate from the Caves of Angola

[MUSIC]

[Video of a cape bison standing in the rain.]

NATHALIE GOODKIN (Curator, Division of Physical Sciences): One of the challenges, in any continent,

[Storm clouds and rain roll over an African savannah.]

GOODKIN: –is predicting precipitation from the perspective–

[A woman walks through rows of dead corn, inspecting them.]

GOODKIN: –of agriculture and how do you–

[People harvest crops in the fields of South Africa.]

GOODKIN: –secure your food supply?

[GOODKIN appears on screen, speaking to the camera.]

GOODKIN: Historically on the African continent, everyone has looked to El Niño to predict where the rain might happen in any given year.

[A giant globe appears, with the camera focused on the Pacific ocean. Text appears over the ocean: “El Niño (center of action)”]

GOODKIN: But El Niño is happening in the Pacific Ocean.

[The globe rotates to the other side, until we see the African continent in the center. On the west and east sides, respectively, the Atlantic and Indian oceans are highlighted with text.]

GOODKIN: And so we’re trying to get a better understanding of how the Atlantic and the Indian Ocean play a role.

[A row of stalagmites, cave formations on the floor of the cave pointing upwards.]

NIKITA KAUSHAL (Postdoctoral Scholar, Division of Physical Sciences): Stalagmites from caves are really amazing at reconstructing droughts.

[KAUSHAL appears on screen, speaking to the camera.]

KAUSHAL: This part of the African continent that’s just south of the equator, that is a real gap for this kind of data.

[A group of people walk into a large cave entrance.]

KAUSHAL: And so I was looking for caves in the region and where they had reported that–

[Camera pans down a stalactite hanging from the ceiling of a cave nearly connecting with a stalagmite below it.]

KAUSHAL: –they had seen stalagmites. Angola on the west coast was one of them.

[More small stalactites with water dripping off of them appear. The American Museum of Natural History logo appears. A title appears over background footage of people in caves: “Decoding Climate from the Caves of Angola; Constantine S. Niarchos Expedition.”]

[Several people in hard hats and full-body suits explore the interior of a cave.]

KAUSHAL: A way to think about caves is that they’re like this little home–

[KAUSHAL appears on screen, speaking to the camera.]

KAUSHAL: –that protects things that are inside them.

[A person exploring a cave picks up animal bones.]

KAUSHAL: If you’ve had a tiger that got bones back to the cave–

[A cave filled with water appears.]

KAUSHAL: –or if you’ve had floods that brought deposits into the cave in the past,

[A cave with long dripping stalactites and stalagmites.]

KAUSHAL: –the cave is really good at preserving all of them.

[KAUSHAL appears on screen, speaking to the camera. Text appears: “Nikita Kaushal, Postdoctoral Scholar, Division of Physical Sciences”]

KAUSHAL: So in that sense, yeah, caves are fantastic locations to look for paleontological records and archaeological records and climate records.

[A wide panorama of mountains in Angola, with a blue sky above and patchy scrubland in the foreground. On top of it, the outline of the country Angola draws on the screen with text labeling it as Angola.]

GOODKIN: Right now we’re in Lubango, Angola,

[To the southwest corner of Angola, a star appears labelling Lubango & Tchivinguiro Cave.]

GOODKIN: –about an hour away from one of the more well-known caves in this region called Tchivinguiro Cave, to study–

[GOODKIN appears on screen speaking to the camera. Text appears: “Nathalie Goodkin, Curator, Division of Physical Sciences.”]

GOODKIN: –how evaporation and precipitation patterns have changed over the past tens of thousands of years.

[Scientists walk among a scrubland path.]

KAUSHAL: Tchivinguiro was one that really popped out from–

[DANIELA DE MATOS looks at a geological map.]

KAUSHAL: –archaeological reports of Daniela de Matos who’s joined us on this trip.

[Closeups of the geological map, showing the Humpata region of Angola.]

DANIELA DE MATOS (Researcher, University of Lisbon): The Tchivinguiro cave is located in southwestern Angola–

[A plateau rises above clouds into the sky.]

DE MATOS: –at about 1600 meters above mean sea level.

[DE MATOS appears on the screen, speaking to camera. Text appears: “Daniela de Matos, Researcher, University of Lisbon.”]

DE MATOS: The Tchivinguiro cave is actually located on what we call a karstic depression, so where water gathers–

[A pool of water reflects the blue sky, with cavers putting on helmets in the foreground.]

DE MATOS: –and then washes into the rock.

[Flashlights illuminate stalagmites and stalactites in Tchivinguiro cave.]

DE MATOS: Because of these conditions, there are wonderful stalactites and stalagmites.

[A scientist looks up along with the camera towards a column that extends to the ceiling in the cave.]

KAUSHAL: And you do need a cave in order to grow a stalagmite.

[An illustrated diagram shows rain falling on plant-covered soil, and water trickling down through a layer of soil and into a layer of limestone.]

GOODKIN: The water falls onto the surface of the planet and it percolates through the rock,

[Differently colored circles move from the soil and rock into the water streams.]

GOODKIN: –and it absorbs different chemicals from the minerals as it moves through the rock.

[Below the rock layer, a layered cross section of a stalactite hanging down from the roof of a cave appears. A drop of water appears at the tip of the stalactite.]

GOODKIN: And then it drips into the cave where the atmospheric conditions change.

[Many green-colored circles appear inside the drop of water and are labelled as carbon dioxide.]

KAUSHAL: The amount of carbon dioxide in the water is much more–

[Just a few green circles of carbon dioxide appear in the air around the drop of water.]

KAUSHAL: –than in the cave air. So in order to get balance,

[Some of the green carbon dioxide circle move from the drop of water into the air, so there are now equal circles in the air and in the water droplet.]

KAUSHAL: –the water loses this carbon dioxide–

[White circles appear in the water droplet to fill up the extra space from the carbon dioxide that left the water. They are labelled as calcium carbonate.]

KAUSHAL: –and you precipitate calcium carbonate again.

[Below the stalactite and the water droplet appears a stalagmite poking up from the ground. The water droplet falls and lands on the stalagmite, while another water droplet forms on the stalactite above.]

GOODKIN: As the water falls on the bedrock of the cave, it deposits–

[A new layer appears on top of the stalagmite on the floor of the cave, making it larger. This layer is labelled as calcium carbonate.]

GOODKIN: –a calcium carbonate mineral where the water lands. And that’s what we refer to as–

[The rock hanging down from the ceiling dripping the water is labelled as a stalactite, and the rock rising up from the ground that the water is dripping onto is labelled as a stalagmite.]

GOODKIN: –stalagmites or stalactites, and that depends on whether it’s–

[Footage of stalactites hanging down from the ceiling of a cave followed by footage of a stalagmite growing up from the floor of a cave.]

GOODKIN: –hanging down from the ceiling or growing up from the ground.

[KAUSHAL reappears on screen, speaking to the camera.]

KAUSHAL: And the way that I remember them was, stalactites hold tight to the roof, and stalagmites are on the floor and trying to reach the roof with all their might. [LAUGHS]

[Several scientists use a rock pick to try and break a stalagmite off of the cave floor.]

KAUSHAL: Stalagmites record a lot about the environment around them–

[Hands hold up different stalagmites, showing the base, where concentric circles of different layers can be seen.]

KAUSHAL: –all of the time that they’ve been precipitating. And stalagmites can really grow over tens of thousands of years.

[KAUSHAL reappears on screen speaking to the camera.]

KAUSHAL: So it really gives us information from, locally, did you have a drought at that time? And what was the pattern of the drought? To, a much larger scale, like,

[Scientists place an extracted stalagmite in a collection bag.]

KAUSHAL: –how were sea surface temperatures or circulation changes–

[KAUSHAL and GOODKIN review notes while in a cave, with helmets and headlamps on.]

KAUSHAL: –impacting these very local droughts?

[DE MATOS talking and looking around inside a cave, wearing a cave suit and a helmet with a headlamp.]

DE MATOS: For me as an archeologist, I’m interested in all the ways that–

[DE MATOS reappears on screen, speaking to the camera.]

DE MATOS: –the environment changes and how humans are involved in these changes.

[GOODKIN and DE MATOS stand around a geological map of Angola, along with other scientists.]

DE MATOS: This partnership added a new dimension to the work that–

[KAUSHAL speaks to another scientist, nodding.]

DE MATOS: –we’ve been doing here in the last few years.

[EVANDRA DA MATA appears on screen, speaking to camera in Portuguese. Text appears: “Evandra da Mata, Professor, University of Namibe.”]

EVANDRA DA MATA (Professor, University of Namibe) [In translation]: I’ve worked on the caves project with Daniela since 2019. I’m interested in the erosion processes in this plateau region,

[DA MATA takes a picture of a wall inside the cave.]

DA MATA [in translation]: –and how this has affected–

[DA MATA looks at stalactites hanging from the ceiling.]

DA MATA [in translation]: –the formation of the caves.

[DA MATA reappears on screen, speaking to the camera.]

DA MATA [in translation]: It’s the geological heritage of Angola, in particular.

[DE MATOS, DA MATA, and GOODKIN among others stand in front of the entrance to the cave, and head inside.]

[“Welcome to Tchivinguiro cave!””Thank you Daniela”]

[KAUSHAL reappears on screen, speaking to the camera.]

KAUSHAL: I’m always excited to go into caves because caves in particular, until you go inside,

[The scientists duck below a rocky cave ceiling to enter the cave.]

KAUSHAL: it’s so hard to know what they would be like.

DE MATOS: When we walk into the cave, you see there are–

[Close up shot of clear pools of water on the floor of the cave.]

DE MATOS: –water pools. So we actually have to–

[A first person perspective of crossing a water pool on a log. A person in an orange vest attempts to help the cameraperson across.]

DE MATOS: –pass wooden bridges to reach the interior of the cave.

[GOODKIN crawls on her hands and knees through several narrow passages in a bright orange cave suit.]

DA MATA [In translation]: In the middle it’s hard to access because it becomes narrow and it’s also damp,

[GOODKIN, KAUSHAL and DE MATOS stop to rest on their sides and sitting, in a narrow cave passage.]

DA MATA [in translation]: which makes it really hard to get through.

[DE MATOS speaks in the video: “There’s just a little bit more of a crawl, you just need to lower your body a bit more.” SCIENTIST: “That was not in your description!” [LAUGHTER]]

[DA MATA emerges from a narrow section of the cave to stand up.]

DA MATA [In translation]: But after that we reach the large chambers,

[DA MATA and other scientists climb up a steep section of the cave.]

DA MATA [in translation]: –the wider ones where we find–

[KAUSHAL stands in front of a row of stalactites hanging down.]

DA MATA [in translation]: –really beautiful stalactites and stalagmites.

[A scientist looks up at stalactites hanging down all around him, illuminated by his headlamp.]

DE MATOS: And these are some of the most beautiful karstic formations that we have here in Angola,

[KAUSHAL bends over some water to collect a water sample, with stalagmites and stalactites in the background.]

DE MATOS: –and that actually I’ve seen in tropical karst.

[Hands take notes in a notebook illuminated by a headlamp.]

GOODKIN: Today was quite an adventure. It was very clear–

[GOODKIN points to stalagmites inside the cave.]

GOODKIN: –right off the bat that there were a lot of samples,

[A scientist holds up a very large stalagmite that has broken off from the ground.]

GOODKIN: –that were going to be useful–

[GOODKIN and KAUSHAL review notes together inside the cave.]

GOODKIN: –for our research.

[Outside the cave, KAUSHAL holds up an extracted stalagmite to inspect it.]

KAUSHAL: When we get a stalagmite, we want to know what happened.

[KAUSHAL reappears on screen, speaking to the camera.]

KAUSHAL: But we really also want to know when it happened.

[KAUSHAL uses a circular saw to cut a stalagmite in half with a BUZZING sound. GOODKIN watches from nearby.]

KAUSHAL: So usually when we first get the stalagmite we cut it open,

[Hands turn over a sliced segment of stalagmite, where different layers like tree rings are clearly visible.]

KAUSHAL: and then we take a little bit of powder from the bottom,

[Hands use a metal spatula to scrape parts of the stalagmite into a test tube vial.]

KAUSHAL: –a little bit of powder from the top–

[A lab assistant uses a computer monitor to look at the section of stalagmite that he is scraping with a spatula.]

KAUSHAL: –and we send it off to a lab that can do radiometric dating. That will tell us the time period over which the stalagmite grew.

[KAUSHAL reappears on screen, speaking to the camera.]

KAUSHAL: And that’s actually one of the most exciting parts, like when you get the results back and then you can see whether the stalagmite grew a few hundred years or a few thousand years,

[Different hands pick up different stalagmites that have been sliced in half, and wrap them in foil.]

KAUSHAL: –or it grew a couple thousand years and then really stopped for 10,000 years before it started again. It gives us a better way to formulate questions.

[A still image of one of the stalagmites’ cross-sections fills the screen, with layers very visible. Text appears: “calcium carbonate” and “CaCO₃”]

KAUSHAL: The stalagmite is composed of calcium carbonate.

[The “O” in “CaCO₃” moves to the center of the screen and is surrounded by a circle. Next to it, the text “oxygen” appears. In the circle, images of rain falling appear.]

KAUSHAL: The oxygen is from the water that was raining at that time. By studying the oxygen, we get some information about how–

[Behind the “O” in the circle, images of rainclouds forming appear. Text appears beneath “oxygen”: “(water cycle)”.]

KAUSHAL: –the larger water cycle changed in the past because ultimately,

[Behind the “O”, images of waves crashing appear. The word oxygen fades away and the “O” circle moves to the left.]

KAUSHAL: –the water is coming from the ocean.

[The “C” in “CaCO₃” moves to the center of the screen and is surrounded by a circle. Next to it, the text “carbon” appears. In the circle, images of plants appear.]

KAUSHAL: The carbon is coming mainly from vegetation. So it tells you about how the vegetation on top of the cave–

[Beneath the word “carbon” text appears: “(environment)”.]

KAUSHAL: –might have changed in the past.

[The word carbon fades away and the “O” circle moves to the left. The “Ca” in “CaCO₃” moves to the center of the screen and is surrounded by a circle. Next to it, the text “calcium & other elements” appears.]

KAUSHAL: Along with calcium, you can also get these tiny bits of other elements. You can get some–

[In the circle with “Ca”, the “Ca” shrinks a bit and new text “Mg” and “Sr” appear, the chemical symbols for magnesium and strontium.]

KAUSHAL: –magnesium, you can get some strontium.

[Behind the “Ca”, “Mg” and “Sr” in the circle, images of cracked dry earth appear. Text below “calcium & other elements” appears: “(drought)”]

KAUSHAL: That’s what really tells us about the local drought. So how many years it went over, how severe it was, and that’s– that’s what we really want.

[The text “calcium & other elements” disappears and the three circles– “Ca”, “O” and “C”– spread across the screen and are connected by a dotted line.]

KAUSHAL: And then we link it up to all of the other things.

[The three circles fade and we are left with just the image of a stalagmite cut open to reveal the layers inside.]

GOODKIN: What we’re really hoping is that the stalagmites–

[A bracket stretches from one end of the stalagmite to the other. On the left, towards the tip of the stalagmite, the text “younger” appears. On the right, towards the base, the text “older” appears. Below the bracket, the text “climate systems changing”]

GOODKIN: –that we collect come from a date range when the climate system was changing.

[GOODKIN reappears on screen, speaking to the camera.]

GOODKIN: By looking at how this region changed in those time periods, we can get a much better understanding of how this region might change in the next several hundred years–

[KAUSHAL takes a water sample in the cave.]

GOODKIN: –when we are very likely to be undergoing a significant warming.  

[A scientist chips away at the base of a stalagmite with a rock hammer. GOODKIN and KAUSHAL review notes in the cave.]

DE MATOS: Our work is extremely important–

[DE MATOS reappears on screen speaking to the camera.]

DE MATOS: –not just for the academic community, but for all the community–

[A beautiful panorama view of Angolan mountains.]

DE MATOS: –in Lubango and in–

[A baobab tree with mountains in the background.]

DE MATOS: the Huíla Province.

[Aerial footage over Angola farms and salt mines in the dry season, appearing brown.]

KAUSHAL: The goal very much is to understand–

[A river gorge in Angola with beautiful striated rock on either side.]

KAUSHAL: –how rainfall will change in Angola.

[KAUSHAL reappears on screen speaking to the camera.]

KAUSHAL: You have climate models that are saying that when the temperature gets higher, this is how the rainfall is going to change. But there is no data to check against.

[KAUSHAL holds up two stalagmites.]

KAUSHAL: So the nice thing is, with stalagmites and with other natural archives like this, we can give them that data.

[Credits roll.

The Constantine S. Niarchos Expedition featured here was generously supported by the Stavros Niarchos Foundation (SNF).

Producer

Lee Bucknell

Additional Camera

Nathalie Goodkin

iStock / Abram81, Anatoly Kireev, bgfoto, Bilanol, BlackBoxGuild, claire222, Dedy Andrianto, Frederico Santa Martha, Graphicscoco, kiattisakch, LordHenriVoton, luza studios, MartinHarvey, mlharing, Paola Giannoni, Philip Thurston, simonkr, Wirestock

Images

Nikita Kaushal

iStock / Dave Primov

Music

Warner/Chappell Production Music / “Edge of Decisions” by Troy Marcus William Hewson (PRS), “Creative Pressure” by Marco Andrea Pes (PRS), “Authentic Process” by Alex Deeping (PRS), “Gliding Through” by Ben Howells (PRS)

Special Thanks

Carlos Bumba & TAC Tours

Cheryl Mayefsky

Community of Tchivinguiro Cave

Instituto Nacional do Patrimonio Cultural (INPC)

José Fernandes

Leonildo de Sousa

Lucas Goodkin

Michael Laumanns

End credits.]

[MUSIC ENDS]