Dr Sebastian Breitenbach
Dr Sebastian Breitenback is a German research associate at the Department of Earth Sciences at Cambridge University. His work focuses on climate change, paleoclimate systems and Earth-Ocean-Atmosphere systems, with a particular interest in clumped isotope paleothermometry and carbonates. His most recent paper created a great deal of buzz as he and his colleagues uncovered ancient Chinese cave drawings linked to climate change.
We have already about 100 years ago early people, early papers, that tried to reconstruct climate conditions.
On first interest in science
I think about my first science experience or how did I get involved with the geosciences, I think that was with my parents at the beach; I always liked picking up pebbles and searching for fossils and things. Of course, that’s not what I’m doing right now but I think that was the first touch. At school I think I had a lot of fun with science, especially geography and everything outdoors, biology, that was the best of it, and not so much the math, I have to admit, but anything that was with rocks or with sediments or with woods, mountains, that’s basically what I was interested in. It’s just lovely to be outdoors, it’s just great and you get muddy, you get dirty, and you can grab things really, not just physically but also with your mind, and you can question things, how looked a valley many thousand years ago, for example, or how did climate affect this region, why is a forest here not a savannah, these kinds of questions. My decision to get into geography and geology, that was pretty early on, from school times on I knew I would just study this subject and there was only the question do I go into geology and geography right from the start or do I go into archaeology and paleoecology and things in this direction, but at the end I’m doing both now so that’s fine.
On current research
So what do I do right now? There are quite a few different things. So my work is always kind of around speleothems, so that’s cave deposits, you know about stalagmites and stalactites, they grow in caves as carbonate deposits and the cool thing about them is first of all you have to go caving, which is already great, but then these deposits contain information about the past, they tell us, if you can read them, they tell us quite a lot about the environment at the time when they grew, so that includes climate information, that includes surface vegetation, that includes hydrology, and it’s like a library, you can read stalagmites with geophysical or geochemical methods, you can read the archives and you can read them like a book. But of course you have to learn first how to read, you have to understand the letters and you have to appreciate the library, so we don’t want to disturb the library, we don’t want to pull pages from the books because then its actually very troublesome to decipher the information, the message that’s in there. But once you can read them it’s like a poem or like a history book depending on what questions you're after and we try to extract this information and make it readable for everybody, so it’s a kind of translation thing.
So currently i work with stalagmites from very different places: from India, from China, from Russia, from Belize in Central America, from Germany, and we use stable isotopes that we can measure in the laboratory to extract information about past rainfall changes or temperature changes or how climate behaves over the last half a million years, for example. We had one important study in Siberia where we actually dated the stalagmites, which you have to do always in the first place because you want to have a time axis, otherwise you don’t know when things happened, and together with Oxford we dated quite a lot of different stalagmites from Siberia to actually reconstruct when was permafrost, so frozen ground above the cave, and when not. Interestingly, we found very clear answers, we can really pinpoint the timing when there was no water in the cave and when there was permafrost, and the change over time is related with climate changes on a global scale, so we can go back and compare it to other records, marine sediments, other stalagmites, whatever other information is there, and we can actually link it to climate change that’s ongoing. That’s important for the global climate warming discussion, of course.
In a different study we just published that you probably have read, is the Tan paper where we actually for the first time, to my knowledge, found inscriptions on cave walls which tell us by the day what happened at the time. So it was not like “Kim was here” but actually it’s much more important, it’s much more informative. We find that, for example, there’s an inscription that the local mayor was here and he took 120 or 200 people to collect water from the cave because on the surface there was a big drought and people were afraid and had trouble finding water. These things happened repeatedly over the last 500 years and with this kind of information we can pinpoint the exact relationship between the geochemical reconstruction that we do, and this is always a proxy, it’s not a real measurement in a meteorological sense, but it’s actually proxy information. And there’s always an ambiguity as to what this proxy actually means, is it temperature, is it just random noise, is it really the climate thing, and if it’s climate, how strong is that link between climate and human society. So in this case we find clear cut evidence that climate changed and it impacted the region and the people directly so we can actually see that many people died, many people became frightened and had trouble to feed themselves so they migrated to different regions or they led into rebellions, for example, so that actually corroborates our climate data that if you reconstruct very strongly, and that’s cool find.
On the history of such research
Well this research started very early on already, we have already about 100 years ago early people, early papers, that tried to reconstruct climate conditions at some point in the past using stalagmites, but really the real things set off with the onset of dating capabilities; before the advent of uranium series dating there was almost no way to know when things happened. You could open stalagmites and count layers and just assume they are annual and count back in time, but the problem is not all the layers are annual, they could also be 10 years or whatever so that’s pretty weak. In the eighties, some of the big people in this business - very good geochemists - developed the uranium series decay methods which actually work similar to the C14 radiometric dating, so we know that uranium is built into the stalagmite but that which it decays is not, so we have at the beginning when you deposit a carbonate, you do not have the thorium. With time, though, uranium decays to thorium and we can calculate what time that meets and how all of this layer is in the stalagmite. This method is now extremely widely used and it’s the means to actually pinpoint our proxies in time, we can fix this event happened then and then, and the errors get increasingly small.
So ten years ago people would be happy if they had an error of plus/minus 50 to 100 years or so. But instruments get better, methods are better and better and so now we have…sometimes, if you get lucky, there’s always a luck component of course, we can get down to plus/minus one year error, and that’s pretty amazing because now we can for the first time look at these records again and extract not just millennial scale changes, what happened over the last hundred thousand years or so, or last ten thousand years, but we can look at sub-decadal changes, what happened the last five years or the last hundred years in really, really high detail. So with this we can actually also start thinking about connections between different sub-systems of the climate, of the world climate, so we can look at the monsoon, for example, and check how are different regions in China and India and Indonesia, how are they linked on a seasonal to inter-annual scale? How does ENSO, El Nino, play a role in this, how are they linked? With errors of plus/minus 20 or 100 years it’s very hard to do such connections, but now with an error of a year or two we can actually better work on this issue. That’s quite important because, as you probably heard, there is a prediction that this winter will be a very big, maybe a record El Nino and if that happens then it could very well be that Australia will see a drought, that Indonesia would see a drought, maybe parts of China will get drier, but we are never sure, we know too little about the whole system, about how the interaction really works, to make a clear prediction and that’s what we are working on.
How old do the speleothems need to be to be useful in your predictions?
How old should a stalagmite be, that really depends on the research question you're after. So for example you could ask, what is the relationship between Antartica and Greenland and climate in the tropics on really long timescales, so from the last glacial to our current warm conditions, and then you have to look at a couple of hundred thousand years to see the links and understand these links. So we need stalagmite records that cover 300,000 years, 500,000 or so, and we do have those but we probably will not find a single stalagmite that covers 500,000 years but we will find many stalagmites in one cave, or maybe in two nearby caves, and then we can build a composite record and see the changes.
Last week there was just the summer school in Oxford where different specialists and PhD students met to discuss exactly these kinds of records that you can produce with stalagmites. You could also ask what happened in the last 2,000 years in different areas in the world, maybe in Europe or maybe in Central America, because if you for example work with, say, archaeologists and you want to understand how climate influenced the thriving or the collapse of civilisations then you need of course…you have to cover the last 100 or maybe 2,000 years or so, but you want to know it at very high resolution, spatial resolution and also temporal resolution. So we had a study that was published in 2012 in Science where we worked with archaeologists in the Maya region and we looked at great detail into the Maya collapse, the classic Maya, and you need a different record, you need a better dated record than if you look at the last 100,000 years or so. Then we had another study where we actually looked at seasonal changes in the monsoon, so this took a very tiny small 2.3cm long stalagmite from a cave in north eastern India and we milled lots and lots of small samples, every 15 micron or so, and extracted seasonal patterns and we had maybe eight to fifteen signs per year which is quite amazing, and so it really depends on what research question you want to answer what kind of stalagmite you need.
On gaps in the data
To make best use of our information on paleo climate records it’s always advisable to combine multiple archives from different places and multiple proxies. One proxy is always kind of influenced by several factors, several physical processes, so it’s good to have several that actually help you to delineate different processes. And also, one cave may be just influenced by whatever, by human or animal activity, and so it’s good to compare it with some other records from this region that should also show the same signal or similar signal. Combining these kind of archives often gives you similarities but it also gives you loads of differences and sometimes these differences are very interesting because you can look at the spatial scale and pinpoint, OK here it was drier and at the same time there it was wetter, and that’s exactly what we are after; we are quite sure that at it was not all over the place drier or wetter, you have spatial variability, and it’s difficult to reconstruct it but that’s the fun of it.
So when we look at reconnections from different places we sometimes find that our information that we add corroborates earlier finds, and sometimes not of course and then the question is why, why does it not fit, what’s different, and often it boils down to chronological uncertainties and of course every new study is probably better than the last, but that’s not always the case. Sometimes, though, earlier findings are amazingly accurate already but then people have critiqued it for whatever reason and so it’s good to have actually corroborating information and say, yes, see, we find these things here as well. Sometimes it’s also interesting to look at the regional differences as well so China, for example, is quite big so you would not expect that something that happens somewhere near Korea is also happening somewhere in Southern China, so if we find two archives from these different places we can reconstruct these differences or similarities and, for example, our Tan paper corroborates earlier finds that another stalagmite from a different region in China also already hinted at so they also said, yeah, the collapse or the change from one dynasty to another has to do with climate variability and we see the same thing. Some people look at this just theoretically and they look at historic records in the archives and then do the statistics and say, well, apparently there is a link between temperature and dynastic dynamics. But it’s good to have this on the ground data, something that we have really in hand and you can control. But of course you want to combine these different records because they tell you different stories.