This is a story about a missing volcano
and it's sponsored by Morning Brew.
There are about 1600 active or recently active volcanoes in the world.
And in late 1808 or early 1809, we're not quite sure
one of them erupted and changed the world's climate.
You see, when volcanoes erupt, they give off a large amount
of sulfur dioxide gas, which then oxidizes in the atmosphere
and forms tiny droplets of sulfates that we call aerosols.
If the eruption is large enough,
those aerosols are injected into the stratosphere.
The middle part of the atmosphere where they can hang around.
A large eruption, whether it's high latitude or tropical,
is going to put these aerosols in the stratosphere
and that will essentially block out sunlight coming into the planet.
So that will cause, at least in the summer, a cooling effect.
This is Professor Rob Wilson at the University of St Andrews,
who studies how the Earth's climate varied in the past,
specifically using tree rings.
Imagine you look at a stump of a conifer.
It doesn't matter if it's spruce or pine. You can see the rings very clearly.
There's a light band and then there's a dark band.
So the light band is basically the spring
and early summer growth where the cells are relatively large.
But then as you get this darker band, what we call the 'Latewood',
this is the sort of the final months of growth of the tree
of that summer season, of that growing season.
The cell walls are those of those cells are much thicker,
and that's where all the density is.
But the amount of material in those cell walls
is a very direct function of the summer temperature.
And then if you then have a network of sites around the Northern Hemisphere
and essentially you just average them together, then that large scale response
to the aerosols of the eruptions will give you a nice cold anomaly.
This has happened plenty of times before, maybe once or twice a century.
For the past thousand years, we see these cooling events
in the tree records caused by large volcanic eruptions.
You know, Tambora.
So that's 1815.
And then the 1257 events and the 1453 or 1458 event
they're seen as the big ones of the last thousand years.
The eruption of 1808 or 1809, though, was different for at least two reasons.
Firstly, normally when a big eruption happens,
the whole planet cools by about the same amount everywhere.
But in this case, the temperature response was weird.
So just as an example, if you look at the spatial cooling of 1816,
it's pretty much everywhere, not quite everywhere, but it's a sort of
hemispheric cooling period there's a couple of areas where it warms.
The 1809 and the 1810 year.
Then you get some regions that cool very strongly, but some regions that warm
and you get these weird dipoles over North America is a really good example.
And actually that makes it dynamically very interesting because clearly
it probably wasn't as strong an event as maybe the 1815, as Tambora.
It was strong enough to cause substantial cooling.
But then what else is happening
in the climate system that would create this spatial complexity?
Secondly, however, in those previous huge eruptions, we've identified
which volcano was responsible either immediately or through some analysis.
The thing that makes 1808 so interesting
is that we don't know which volcano erupted and caused the cooling.
We literally have a
but we've only discussed one
line of evidence when there are in fact three lines of evidence
we can use to narrow down our potential suspects.
And using these pieces of evidence,
it’s entirely possible that this case will be cracked soon.
The second piece of evidence lies near the poles.
Every year, fresh snow falls on the ice sheets of Antarctica and Greenland.
The snowfall compacts the snow underneath.
And over time, those layers of snow get turned into layers of ice.
Similar to tree rings,
there are distinct layers representing summer and winter snowfall from each year.
And so by counting layers down from the surface, you go backwards in time.
But it's not just snow that you find in these layers.
The sulfate aerosols produced by volcanic eruptions are there too.
And so you can see in if you take that ice core down
through the ice sheet, you can measure the concentration of sulfate,
and you'll see there's a sort of background level of sulfate.
And then every time a volcanic eruption goes off, you get big peak in sulfate.
So you get essentially just the levels, 'bing' eruption, 'bing' eruptions.
So that's a great record of sort of past volcanic frequency.
This is Dr. Andrea Burke,
also at the University of St Andrews, who's a geochemist.
In her research, she looks at isotopes of sulfur.
So sulfate isotopes are awesome!
They provide this beautiful fingerprint for a lot of processes
that we want to reconstruct on volcanic eruptions.
So remember, the isotopes are variations of an element
that just have different numbers of neutrons in the nucleus.
So sulfur, for example, 95% of sulfur atoms have 16 protons
in the nucleus and 16 neutrons,
but 4% also have 16 protons
and 18 neutrons,
and less than 1% have 16 protons and 17 neutrons.
Normally, these isotopes behave slightly differently, a process called
fractionation in a way that depends on their slightly different masses.
So anytime you have a physical or biological fractionation
process on the isotopes, it follows a very predictable mass dependent line.
One of the few exceptions to this is when sulfur
compounds are exposed to UV radiation.
That UV radiation essentially imparts this very weird
signature that we call mass independent fractionation.
And that really happens in the stratosphere,
that signature that gets preserved in ice cores.
So when we look at the sulfate peak associated
with a volcano, we can measure that isotope signature.
So that's a sort of first order thing, but then we can get a bit more
because in terms of getting latitude,
what we find is that tropical eruptions
really only deposit sulfur at the poles when they've made it up
into the stratosphere because the poles are really far from the tropics.
And we can contrast that with eruptions from Iceland
or from Chukotka or Alaska.
And in those eruptions, you get a sort of normal isotope signature,
followed by the stratospheric component, if there is one.
And so that's how we can distinguish latitude as well as any sort
of rough altitude from these sulfur isotopes.
To summarize then by looking at the ratio of sulfur
isotopes in ice cores in the years following a volcanic eruption,
we can estimate an approximate latitude of the volcano that spewed
those sulfates out into the atmosphere.
In the case of 1808 or 1809,
this analysis indicates our culprit was probably near the equator.
So that really narrows things down.
But to get a definite identification, we need another piece of evidence.
In a previous case, this was provided by written records.
The huge eruption of 1257 was for a long time.
Also a mystery.
But ice core analysis indicated it was probably near the equator
in a great piece of detective work.
Researchers then found a series of writings from medieval
Indonesia called the Babad Lombok, that describes
a cataclysmic eruption of Mount Somalis sometime before the year 1300.
They suspected this was their volcano.
This suspicion was confirmed by what will be our third line of evidence,
a fingerprint.
As well as sulfates, another trace of volcanic eruptions get trapped in ice cores
tiny shards of glassy material produced in the eruption called Tephra.
These are significant
because every volcano on earth produces a very slightly different kind of Tephra.
As we see like a real big difference
between like arc volcanoes and something like an Icelandic one.
Right. So Iceland's
sitting right on your mid-Atlantic ridge, whereas with arcs, right.
We think of the arc volcanoes.
So all along the Pacific Ocean, essentially you get that subducting slab
and that slab, that ocean slab.
It's not just basalt ocean crust going down.
On top of that is sediments and seawater and core water.
So it's got a lot of different stuff going down.
So you get very different chemistries and those are quite easy
to sort of fingerprint.
We have fingerprints on the crime scene.
What we now need is a criminal database of samples of all the fingerprints
from all the volcanoes on Earth in order to identify one of them as the culprit.
But getting those samples is surprisingly challenging.
A lot of times the terrestrial record just under records, right?
So you get erosion zeroed away or it's covered by another one.
And so I think that's really where the challenge is,
is that you can get you can find different ice cores.
There's an ever growing library of characterization of tephra.
But actually imagine that that sort of curation
of this library is ’A’ very challenging thing.
And ‘B’, it's not complete because the geological record is not.
This particular volcano almost comes down to probably a bit of luck
understanding the geochemistry because, you know, there's probably tephra layers
from this volcanic event.
They can do the geochemical fingerprint, but then they need
to have the same geochemical fingerprint from a known volcano.
And if they don't have it in the database, they don't identify it.
So some poor geologist is probably hiking around Indonesia or
the Philippines or wherever the volcanoes could be, and one day
someone will stumble across it.
Sometime soon, then we may have an answer to which
volcano was behind the mystery cooling of 1809.
And if we do, then we might be a bit further along understanding
other mystery events in our past climate, such as the huge events of 536 A.D.
There's no shortage of unanswered questions in paleo climate,
but if we can just get that last piece of evidence in the scientific courtroom
any day now, a climate cold case may just be solved.
As we’ve just seen, we can't make good decisions without information to base them on.
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Thank you so much for watching the video right the way to the end.
I hope you enjoyed this one
because this was one of my favorite stories I've ever covered, not least
because of the cool isotope analysis
that Dr. Burke was talking about.
Patreons had access to a bonus video of her talking about her research
in a lot more detail.
Would love to have included it in this, but it would have made it too long.
So if you not a patreon, please do sign up.
You get access to bonus content like that.
Thank you to Professor Wilson and to Dr. Burke for helping me with this video.
Do check out their research at the links below.
If you'd like to see some more stuff from me, then here's some recommended viewing
and that just leaves me to say thank you again for watching
and I'll see you in the next one.