Ancient History in Greenland Ice

Thrun classics what's in a storing like me doing in a place like this I think we're gonna find out over the next hour why I'm so attracted to this this sort of work this and thanks for coming out today this is year two of what I call the Yale Nile initiative which is an excuse to talk about history and paleo climate altogether around not just the now River Basin but more broadly as well and I am really thrilled to be able to welcome Joe McConnell from the desert Research Institute I'm here today to kind of kick us off this year Joe is a research professor in the hydrology division of the desert Research Institute very well known to everyone in ice core science kind of broadly real pioneer and continuous flow analysis his lab is really famous for having two icp-ms a--'s which when I see these things as in a store and they're kind of magic boxes these things these are amazing machines and I think the only lab in the world that allows real data to be visualized or data to be visualized in real time which is spectacular I'm taking some of my students out there in about three weeks and we're really excited to go out there and have fun with ice core analysis hey Joe besides just basic ice core science of course the last few years she's gotten hooked on doing history and archaeology and were really grateful in the ancient history community for all kinds of reasons it's Michael Segal a postdoc in Joe's lab and Joe as an author as well in nature from three years ago on a new chronology of volcanic eruptions in Antarctic and Greenland ice that revolutionized pre-industrial history I think it's one of the most important papers in ancient history in decades I think I make all my students read it because it's fundamentally a few months ago in the Proceedings of the National Academy of Sciences this fundamentally interesting paper lead pollution recorded in Greenland ice indicates European emissions attract plagues Wars and imperial expansion during antiquity this is a phenomenally interesting paper it's lit up the world of Iron Age archeology and a particular Roman historians and it really is court of a first sort of paper that's going to generate I think years of research in Roman history and the first millennium BC world's let alone work in ice core analysis so with that as a brief introduction I will turn the floor over to dr. Joel McConnell okay can you hear me okay yeah thank you all for coming and thanks to Joe Manning for the invitation I was telling Brian Skinner a minute ago that I first set foot in on Yale campus and in this lecture hall 40 years ago this month hard to believe and it was to hear Brian give his introductory geology class so anyway who would have thought I'd be here talking about history but anyway ok so I'm going to talk about ancient the titled zinc's in history and ice I have two primary collaborators on the work that I'm going to talk about Andrew Wilson some of you historians may know him at Oxford and Andreya Stoll is a very well known atmospheric modeler in Norway at the Norwegian Institute of polar research sorry err research and then we had other co-authors a couple of people Monica and Nathan from my group Sabina Eckart from neela as well a couple more people from Oxford Elizabeth and mark Pollard and then JP Steffensen from the University of Copenhagen definitely a very much a collaborative effort funding always have to acknowledge the funding so most of the work that I do is funded by NSF some by NASA but most of my NSF Arctic and Antarctic programs I've made about 25 trips to the green to Greenland over the last 25 years and about more than 10 trips to Antarctic for these funded by these programs so the specific work most of the specific work I'm going to be talking about today was funded by the John Feld fund at Oxford and the desert Research Institute my Institute so some of you may know some of the historians may know that in the 90s people measured lead in ice in Greenland ice Rossmann at all in 97 and hung at all in 94 and they published this record this was the Rossman record so this is concentration these are isotopes on this axis and you can see that during you know a thousand BC to 1600 ad it looks like and you can see there was this increase during the the Greek and Roman period and it dropped in the isotopes and this created a lot of buzz in the history and historian world about what information you could get from ice and as a result of that well this is just another graph of the same data the same concentration points and so these guys measured 18 measurements over this 18 nineteen hundred year period and each measurement represented what they thought was two years of ice so that was the record that historians were using for these these studies of Roman economy and the Greek economy and so forth and after that so the the Andrew Wilson and mark Pollard from Oxford came to me because they knew I could measure led very accurately in ice and this is the record that we developed and this is what I'm going to be talking sort of around and about today and you can see you get a very different picture of of lead pollution in Greenland from this much much higher resolution record and so our measurements have instead of having 18 we have 21,000 measurements across the same time period and we have about twelve measurements per year during antiquity okay so it's a very different record that in gives you a much different picture but you can see that the average concentrations are pretty much an agreement there it's very much an agreement with the previous work so an outline of what I'm going to talk about because this is kind of a mixed audience of Earth scientists and historians I thought I'd kind of try to Fred thread the needle between the two I'm gonna talk about the archive of past environmental change in glacier ice just to kind of bring you up to speed with that and then I'm going to talk about continuous my record during antiquity the specific paper that Joe referred to and then some conclusions and future plans so imagine you're standing on an ice sheet there's snow falling around you it's gonna pile up around your feet and it's going to be very low-density fluffy stuff as it as time goes by it's gonna start to age and be buried and that's going to form a surface layer that's harder and more compact eventually this thing is going to squeeze down trapping air bubbles and then and then the ice and eventually at about 60 to 110 meters depending on the site you're gonna turn from a fern or old snow into ice so you're going to close the pores off the air bubbles off and then you're going to trap at that point some picture of the atmosphere at that time right and these are the the seminal records that you hear about and climate change science of carbon dioxide and carbon monoxide and methane so really fundamental cornerstones of climate change science well different than that are is that what's in the precipitation itself so that's the water isotopes and water isotopes we use as a proxy of temperature of site temperature very well known again very much a cornerstone of climate change science comparing especially water isotopes to the gas records right in addition to that you get sea spray you get aerosol so-called aerosols and by aerosols I mean very small droplets or particles that are in the air all around us they come from in the natural world things like sea spray and dust and then in the more recent period maybe the last three thousand years you get pollutants and so I'm just going to show you this quick little a little part of the simulation this is a simulation from NASA and it's a simulation of aerosols moving around the earth some of you may have seen it in this you can see down here sea salts are color coded blue desert dust is red organic and black carbon is green and then the sulfates in white and just as you're watching it you know you can see things coming off of biomass burning plumes in Africa and South America you can see dust coming off the Sahel in the Sahara and you can see pollutants and so forth and I won't read it for very long I don't think let's see this work I personally find this very mesmerizing it's kind of like watching a fire you know you can see everything kind of swirling around so you can see the as an example you can see the big sea salt storms circulating and circling Antarctica alright sweeping around there you can see sulfates coming off of the industrial parts of the North America Western Europe and and Asia you can see here's the dust dust swirls coming off of the Sahel and sweeping out over the Atlantic and fertilizing it and then watch here you see these these big biomass burning plumes coming off of these regions now some of that aerosol you're not much of it have quite a small percentage of it uh actually ends up getting swept up over the Greenland and Antarctic continents and gets deposited with the precipitation or gets dry deposited onto the snow and gets buried and that's what we measure with the ice core right so and then every once in a while just to make sure everybody's on the same page every once in a while you get a nuclear explosion which we know very well about in Nevada you get a nuclear explosion or you get a cosmic ray burst in the upper atmosphere or you get volcanic eruption that creates a sulphur to increase in sulphur in the atmosphere and those get deposited all around the earth pretty much at the same time and that gives you an I so Kron then we can then use for cross dating ice cores we can use it for confirming our dating and we can use it for synchronizing to other archives things like lake sediments or ocean sediments and things like that so yeah so then we go draw an ice core you can see we're just going to drill an ice core from the top to the bottom the ice at the top is the age of when we drilled the ice core here so whatever date we started drilling and it's just going to go down however far I think the longest ice core is about 3.4 kilometers long so they're just gonna penetrate ice down 3.4 kilometers for a couple of miles this is just a quick schematic of what a glacier and ice sheet looks like in this case an ice sheet so you can divide it into sort of two zones the accumulation zone so that's where you're in positive surface mass balance so more snow is falling out of the sky then is melting and so you got a that's where you're building up layers year after year after year you have the ablation zone where that the opposite is the case you have negative mass balance in order to keep this thing at steady state you have to transport through flow ice flow you have to transport mass from the accumulation zone into the ablation zone so you can imagine normally we would go to the accumulation zones to drill ice cores because we want layers piling up year after year we don't want we don't wanna be missing years or we don't wanna have negative mass balance I should add that these days there is quite a bit of work going on in the ablation zones and that's because you don't have to drill through hundreds or thousands of meters of snow to get to the old stuff the old stuff is exposed right at the surface so if you want big samples we typically nowadays you go to the ablation zones you can imagine it's very difficult to date this ice it's very there's a lot of flow distortion and then there's also the dating issue but there is quite a bit of work going on in that area so so I just thought I'd say a little bit about sampling the archive so that you can imagine I divide it up into three three different methods of sort of scales the deep sampling is this is a Millenial scaler multi-male neol scale work this is an example at stipple dome so these are big projects might take four to five six years they usually involve multiple institutions and often involve multiple countries the big operations cost tens of millions of dollars this is another example from the danish group the danes do a lot of drilling in greenland because of their historical connection to greenland this is the campus in 2011 at neem and so this is the geodesic dome they had built and it's pretty neat you live in this thing this is the galley you don't work in this part you just live here and recreative now put this thing on skis and so they can drag it around the ice sheet so this has been dragged to the other side of the ice sheet and it's now being used in the egret project anyway it's a really neat building and I'm amazed that they're able to drag it across the ice sheet but you can see a c-130 IUS el c-130 there a ski plane and that's for the heavy lift capacity to provide the logistics for the camp now most of the work as I said we just recreation this building most of the work actually happens in trenches and these are you know maybe 30 feet or ten meters deep that are using you snowblower to make them and then you cover them over you can see the advantages or the disadvantage is that it's cold and you feel like a troglodyte in there the advantage though is the weather can be doing anything upstairs and you have no idea what it is so you can work in any environments this is the deep drill so this drill will eventually go down 2.8 kilometers and then Phi and then intermediate sampling would be what maybe 100 to 200 meter long course and by the way the total depth is 200 meters we handle it in typically one meter sections so anyway the and I die my group has done a lot of this kind of work including the Arctic Circle Traverse where we went by snow will be across Greenland collecting ice cores and doing radar surveys might take you let's say a few days to a week or two to drill to a 100 to 200 meter core and then I've also done some work this is with the Australians at Aurora Basin in East Antarctica and you can see this is the camp there the the buildings where we work and these are all a sleeping tents everybody has their own sleeping tent to have some privacy and get away from people a little bit supplied by not by c-130 but supplied by Basler aircraft as a DCO stretched dc-3 and then this has been the drilling operation so this very small little drilling town again invented a little bit into the snow this is the old surface right here and a tent so you can work in any environment and you can see this is Christmas dinner it's not too bad life is pretty good we got wine we got pretty good shape and then if you're really good Santa Claus will show up and you can you've got to be good anyway and then there's sampling shallow sampling and my group is this was originally what we sort of specialized in and these would be maybe 30 meter cores maybe you're looking at a decade's to maybe one century long record and you can this is a technique that I developed called commuter Corning and the reason was that when we first started doing this we would get taken out by a ski plane the twin otter like this on skis we'd get dropped off of all of our camping gear plane would go away and a couple days later if we're lucky they come back and get us but at one point in time we were had the beginning of a project we got her we are on our fourth of eight sites and we got stuck for a week at a site and our generator was giving out and our stoves were giving out it was touch-and-go anyway so I came up with this idea of keeping that twenty million dollar plane and the pilots with us so they don't get to leave and they're not going to leave us out there in that situation so the key is to be home in time for dinner and then weigh if you're if you're stuck in or whatever by the weather or by broken planes or whatever you're stuck on the coast so it's much safer and it's actually cheaper because you're flying out full of ice of empty ice core boxes and camping gear and so forth you get dropped off you do your I mean you don't get dropped off you do your work and you fly back light on fuel and heavy on ice cores so it only takes one round-trip instead of two round trips those NASA loved us because of this now you can imagine you're a pilot or a co-pilot and you're sitting up there and you're it's about minus 25 minus 30 and you think well what am I going to do you can sit in the plane and watch us and get really cold or you can help us and so there's the copilot the pilot it makes a big difference especially when you get a really big strong Danish pilot who can lift our co-pilot he could lift anything so ice core analysis I just thought I'd say a little bit about ice core analysis so in the old days as in this record we were talking about earlier from Rossman these were their 18 points that they measured over this nineteen hundred year period right eighteen measurements two years each now why would they measure so little make so few measurements fundamental question right well the reason was because they were doing discrete sample analysis and from metals very very low levels of metals they were loading up a piece of ice right here into a into a lathe that's a hand lathe and they were scraping very carefully by hand they were chiseling off ice and catching it in this little bucket so they're all dressed up in their clean gear and all that sort of thing on working under a laminar bench and so forth and they're slowly scraping this off and you know progressively working their way towards the that could uncontaminated inner part of the ice you can imagine hugely time-intensive I've been told that it took some of my hyung and colleagues up to six months to make to chisel those eighteen samples it's a big deal right we have gotten around that now and that's why we have this so many more samples like this by using continuous analysis and Joe alluded to it a minute ago so continuous analysis rather than discrete and in this case we're going to use well so let's back up a little bit so here's the cylindrical core so you can imagine a cylindrical core about 10 centimeters in diameter a meter long we're gonna cut from that approximately three point three by three point three centimeter by a hundreds of one meter long 100 centimeter long stick of ice it's like this long stick and we can cut in one project we actually cut seven of those sticks from one 10 centimeter core so we can analyze the core over and over again we don't use anywhere near hold the ice on one analysis then we're gonna clean the ends very carefully as you can see here for those of you who know who Michael Siegel is he's the hand model here we're going to use this is a ceramic potato peeler you can buy from Amazon or whatever but but it's really important that we get the ends really clean and so ceramic is really the only way to go we can get it clean enough for these metals and then we're going to load that stick so there's that stick I was talking about we're gonna load it up into this melter stand here that we developed and the ice is just gonna fall by gravity down onto this heated melter plate I'll show you in a second here's the melter plate down here it's just going to fall by gravity the melter plate is very the temperatures controlled very carefully and that water is going to melt and we're going to suck it off and analyze it real time in about a million dollars worth of analytical equipment let's see [Music] so this is what the melter head looks like and so you can see that about three and a half three point three by three point three centimeters stick of ice it's on top of it these ridges that are engraved into the melter head separate the meltwater into different sections the innermost 10% is what we analyzed using those high-resolution icp-ms is that Joe mentioned for elemental measurements the next twenty percent or so we're going to pump off into different of a whole Bank of instruments that we measure things like nitrate and sulfate that's sorry nitrate and ammonium and things that are water isotopes things that are very difficult to contaminate and occur at much higher levels and then the final 70 percent the outer seventy percent we're gonna throw away is potentially contaminated so instead of chiseling day after day month after month we're going to use the melter system to clean the ice to decontaminate the ice so we're only going to use that innermost 10% well the difference is we don't have to chisel it just we just happens in real time it's fantastic yeah so let me show you let's see where are we next no so this is a schematic and I won't bore you with the details here but this is a schematic there's the melter stand in the cold room falls down onto the melter head we take that 10% inner part and send it off to this it's this kind of setup so the two icp-ms is right here we collect fractions for later on analysis if we want as an archive and then the other part we send over this direction in this particular case I'm showing that this is our gaps method we don't do the gas measurements ourselves so we used to think of those gases that were bubbling out of the water we used to think of that as a waste product and be annoyed by it because we don't want those air bubbles to go through our system but starting about three or four years ago four or five years ago now the Danes and the French and the people at Oregon State were developing methods to measure that gas in in continuous mode as well and it's all a function of technology its cavity ring down measurement systems that make it possible but so now we can get methane and Co measurements continuously as part of this whole thing so out of that little stick of ice we can get about 35 different measurements of elements and chemical species and then as well as the gases and the water isotopes all out of that little 3x3 three point three by three point three six so it's really revolutionized this our industry and that we can get so much information out of so little ice and that saves other rights for other applications for those who are interested this is sort of what we're doing at the periodic table nowadays so the ones that are in solid circles we routinely measure so we're covering a pretty good part of the periodic table the ones that are dashed like plutonium down here we only measure that under special circumstances just as a little aside to plutonium we published the paper last year moved here before on continuous measurements of plutonium and so what we're doing that for is to try to see the bomb pulses 53 to 54 to 63 period of thermonuclear testing and we need that we'd like to know that for the thermonuclear perspective but also for dating ice cores and we came up with a continuous method for that but the the height of the peak of the bomb pulse period is one part per quadrillion so that's one gram in 10 to the fifteenth grams of plutonium is extinct to make that measurement is extremely sensitive analytical equipment so so let me just show you this little video of the lab just to give you a picture worth a thousand words kind of thing the first couple of seconds is a green for some unknown reason it'll change here so this is Nathan my my PhD students working on the core and so he's just shaving it down to make sure it'll fit in the melter stand so that's you know one meter long about three and a three point three by three point three in cross-section you can imagine in the ice we can't tell what's up or down so once it's and until we analyze it and so we want to keep up so up is all those to the right and he's put that X in there to mark the top of the core so we can keep track of it it goes through the melter and now he's cleaning the ends very carefully because the ends are gonna go into the melter system they're not going to get thrown away as part of that 70% so since that's going into the analytical system we need it to be really really clean very very clean so he's done that now he's we've loaded it up into the melter stand you can see the ice poking out the top there it's falling by gravity down onto the melter head and slowly melting I should add that the melter head is made out of a ceramic a silica carbide so you can clean it with konk acid and all that we do routinely this is it sped up obviously but there's the ice falling through the melter head and there's time right there and you can see that Nathan's whipping in there he's very fast and yeah you can just see the ice and so you can imagine we get we can generate data incredibly quickly compared to the old days in fact my group is sort of swimming in data we can't the group is not big enough to publish all these data in a timely way so if you need data talk to me so anyway so then you can see the water is being pumped in the air bubbles and so forth are being pumped into different analytical systems when my students first sort of postdocs first see this they freaked out because of all that spaghetti but after you get used to it it's pretty clear how it works so you can see all that gas water mixture is getting pumped through the whole system and then we go through bubble detectors to determine the air water mixture we're seeing and that sort of thing and those of you in just seminar will see all this and get to scrape ice yourselves here soon and then in this case we're doing gases so you can see the bubbles going into that 1d bubbler and that sealed so the gas is going out the top okay so I hope I've covered that first part what the archive is how its formed some of the issues you know accumulation versus ablation zone that kind of thing how we sample that with different different scales and then our discreet versus continuous analysis so now I thought I'd talk a little about a little bit about this lead during antiquity story and it's there are some extremely important steps in all this so I'm not just going to go straight to the record so this is the paper that Joe alluded to or mentioned and it was as I said earlier it was collaboration with historians at Oxford archaeologists at Oxford our group the Norwegian Institute for air research and the University of Copenhagen and their main contributions they provided us with the ice so a very important contribution so first of all so the question we're gonna ask is why does Greenland lead well what does Greenland lead pollution tell us about ancient economies during antiquity first question who cares right well I hope this audience cares I hope I don't have to convince you but certainly ancient has an economic historians a political scientists and archeologists would like to know some quantitative information about ancient economies and what what controlled that were what drove increases and decreases in economic activity so oops sorry has environmental scientists of course we'd also like to know you know we'd like to know assess human impacts and the idea that humans were having a measurable impact on the environment 2,000 or 3,000 years ago is not something that you kind of take lightly why lead well led it turns out was that most of the silver that existed in most of the silver that was mined by the Romans and they and they wanted silver for their coinage because they were a silver based coinage most of that silver occurred as lead and Galena ores so led silver combination and pretty much sort of rule of thumb for every gram of silver they produced they produced 99 grams of lead and led with this lower boiling point was easily a lot of it was scaped and was into the atmosphere was emitted into the atmosphere and transported around the earth another nice thing about lead is has very low background levels in the natural environment the other sort the other primary sources would be dust continental dusts or just the lead occurring in dust or rock and then also bucket some volcanic eruptions have significant amount of lead in them the other thing as I mentioned we have a little bit is we have very low detection limits so when we were doing this experiment you know we can redesign we can reconfigure this depending on our what our scientific objectives are in a particular project in this case we took this low resolution icp-ms and we only is that for LED measurements actually thallium lead and bismuth was the suite and by doing that we were able to get lots and lots of measurements and end up with a detection limit on the order of about 0.01 picograms per gram so that's 10 to the minus 12 grams per gram so a very very low levels and very important for this kind of work as I mentioned I think we analyzed a total of four hundred and twenty three meters of archived North grip - ice for this project alright Joe Morgan cannot answer this question although it'd be a good test to see if he is paying attention last fall so so anybody want to hazard a guess of what the three most important words and paleo environmental work is anybody all right I won't make you do it dating dating and dating and this is a quote from Jeff stirring house I don't know whether he lifted it from someone else and this is important especially if you're going to try to do accurate you need accurate independent dating especially if you're gonna try to infer causality so you see a change in the in the ice core record or some other archive you see a change in history if you're gonna say one is somehow linked to the other implying causality boy you better make sure you're dating is completely independent because if it's not you're just tuning to get the correlation right so really really important dating is absolutely critical so I'm gonna say a little bit about that so this is a one meter section from 380 to 381 meters depth in the ice core in the North group to ice core and I've plotted a bunch of different parameters so ammonium and sea salt sodium in green non-si south calcium in purplish I guess the magenta something and then the two LED measurements from the two icp-ms is in in the blues and then I've plotted just to emphasize it I've plotted an on sea salt sulfur - sea salt sodium ratio and that's the one we could use for dating so would anybody like to hazard a guess as to how many years you see across this remember there's an annual cycle and all those chemist chemicals so right so one meter and and we've got clearly one annual cycle - annual cycle three four five right so if we date this again we're just going to start at the top and we're just going to count backwards these annual cycles we're going to count them backwards so here's 80 1980 1880 17 and so forth and you can see it's very clear the annual cycles in this section are very clear I mean there's not really a lot of debate so we dated this ice core completely not completely independently from 12 59 the eruption of Somalis in Indonesia a very distinctive marker and ice cores we measured we started there and we just counted backwards one year at a time for the whole record all the way back to about 1200 BC so 20 but whatever that is 3,300 years something like that I mean 35 anyway so that's that's how we date it and we're gonna in this case we use the midwinter non sea salt sulfur - sea salt sodium minimum that we could see in the ice right so we just arbitrarily assigned this date of January 1st every year and that's how we date the core we'd also like to be able to evaluate those chronologies in some way so the dating of the ice core referred to as a chronology we'd like to be able to date it in some independent way and the way we do that is we compare it to beryllium 10 and we can do it turns out with link to the tree ring records - the ice core records through cosmogenic nuclides and that would be 10 beryllium and ice and C 14 in wood we can do this at annual scales using these very high frequency one to two year events that were reported by Miyake originally in nature and Michael Siegel that Joe mentioned that Michael Siegel was really took this and ran with it or we can do it into Keadle time scales published by Adelphia Mishler their techniques and the advantage is that we can then look at the ice core chronology that we developed and we can try to do something we can evaluate it and try it independently and try to assess the uncertainties in the ice core dating and I'm not going to go into too much detail but we did this so this is our our age scale - the Intel tree ring age scale and what you see there gray is their their one sigma uncertainty in their dating and you can see that our are dating fits within their one there nor one sigma so from that we infer that we've got about a plus or minus two year maximum dating uncertainty in our record so to say to a historian I think it's safe to say to say to a historian or certainly to an archaeologist that you have one to two year uncertainty in your dating 2,000 years ago is a pretty nice thing and we also did that with the Rossman at all or the Huong at all dating those 18 points we evaluated their age scale and age scales has AB evolved a lot in the last 30 years as you can imagine and it turned out that they were about 30 years off so historians were using that information to infer things and not only were there hardly any samples but they were also miss dated by about 30 years in antiquity so things have been proved another question has led provenance so archaeological evidence suggests that Western Europe and China were the sort of the two possibilities for where these emissions could be coming from so the question is how do we know this is European lead and not Egyptian not Chinese lead right and the way we know that well first of all we built on rossmann Rosslyn's results so rossmann Kevin Rossmann had measured the isotopes in those 13 samples as I showed you at the beginning and then if you plot it on 208 over 207 and 206 over 207 and you plotted in this space you can see that they kind of fall along this line right here and these circles represent different sources different ore bodies in Europe and it looks like you know all these measurements are consistent with a mixing model of European lead so there's we can't say it is lead it's from Europe what we can say is it's consistent with Europe right so it could be coming from China still based on just the isotopic evidence alone so we took that idea and we kind of well first of all I mean let me say so possible emissions sites are in Western Europe in China during antiquity central Greenland up here is a long way from those lead silver mines in in antiquity down in Europe so we're looking at basically transport from down here all the way up to Greenland so long-range transport is implicit of course is even longer from China right so we can use a very much state-of-the-art atmospheric model to investigate this this is this flex part model that andreas stole and to be an aircard contributed way to do this kind of modeling basically you have a source receptor so if you're doing it in the forward direction you start with the source say the lead emissions and you have the receptors out there and you transport the lead from the source to the receptors you can run it in backward mode as well and look at the sort receptor to source relationship we need to have a very very detailed atmospheric fields to do this kind of work and of course they don't exist for antiquity so we used the 20th century reanalysis fields and assume that the meteorology was basically the same at least at the large-scale so this is the result this is the ice core sitting right here in the circle and this is where we model the emissions coming from down in here and this is these in this in backward mode so this is this receptacle source and what we found was that n group to the I square site was about 10 times more sensitive to European emissions than it is to Chinese emissions so it is possible that you're getting Chinese emissions but they would have to be extremely large to overwhelm the Greenland signal all right so you can see a China over here they're very small numbers and we're bigger numbers in here so so from that we think that we think between the isotopes Oh is one more one more slide on that we also looked at the fallout pattern as you moved away from the emissions areas that proved the the hypothesized emissions down here and we looked at peat bog records published peat bog records as she moved away from this we would expect that to drop off more or less exponentially as you move away from the source and that is indeed what we found you can see the black or the different speed sorry peat bog records and the red is our records so it looks like there's it behaves as though the source is in southern Europe we also wanted to do for the first time in ice core study I think we wanted to use the atmospheric modeling to assess how much in how much variability we would see in deposition just from the atmospheric transport alone so we use the same Flex part modeling and what you come up with is a year-to-year difference in atmospheric transport results in about a 60% coefficient of variation in the amount of lead that's deposited so even if you had a constant source in southern Europe by the time you transport in deposit in Greenland it's going to have about a 60% year-to-year variability in the deposition if you apply an 11-year median filter to it you preserve the medium filter will preserve step functions but you'll knock down a lot of that variability and again up was about a 22 percent coefficient of variation so in the paper we always used a narrow bar of plus or minus 22% when we talk about the lead record why Greenland why go to Greenland to do this you might think going to the to the Alps would make more sense helps are much closer and so forth but unlike Greenland alpine glaciers unlike Greenland ice sheet alpine glaciers are very thin and they have complex flow histories so if you get down to ancient history if you get down a thousand or two thousand years ago the layers are extremely thin I mean millimeters or sub millimeter thick layers making dating difficult independent dating difficult and I would argue impossible it also makes it because there's still little material you can't do that 10 beryllium sort of cosmogenic nuclei did sort of comparison there's just not enough material and so it makes it very difficult to quantitatively assess how good those chronologies are and then finally sites can be very heavily influenced by in europe can be very heavily influenced by small nearby emissions and this is just an example of that so this is that same flex part modeling but this time for an ice core a theoretical ice core from cold the dome on my bunk in the French Alps and you can see on the scale here we're fifty to a hundred times more sensitive to emissions right around the Alps then we would be to emissions from Spain so you can get a record but there's a pretty good chance that record is going to be a local record of emissions from a nearby mine mine down the bottom of the valley below the ice core site so there are some advantages in going far away whereas well we're in Greenland up here we're seeing sort of continental wide emissions because there of course are no emission sources anywhere near Greenland particularly at this time ok so let me just walk you through the interpretation of the record so two thing well first of all we've we've switched from total lead to lead pollution and we did that on the vertical axis and we did that by subtracting the component of dust so we measure a dust tracer and we used the crustal abundance to subtract the dust potential the potential dust component and then we used and we then we also has to mate a volcanic component not a big deal it's about 13% of the total measured lead is what we subtracted so it's not a big part of the signal we are also going to convert we also converted from constant raishin to flux so we're looking at depositional flux onto the ice by multiplying by the water accumulation the concentration times of water accumulation and then we're also going to use the Flex part modeling to convert we could convert it and we did in the paper from lead pollution in Greenland to estimate it let emissions in Europe and we can do that with the sensitivity modeling for one kilogram per second of lead emission in southern Spain the model would suggest you'd get 12.9 on average twelve point nine micrograms per meter squared of lead deposited in central Greenland so we can use the lead pollution record to reconstruct european-wide emissions granted with some estimate with some assumptions but so anyway so at 0.75 micrograms per meter squared per year of pollution in Greenland would equate to 1.8 kilotons per year of emissions and it turns out the archeological estimates were pretty darn close to this I think they were maybe within 50% of that number so gives you a nice warm and fuzzy right our record goes from in this case we're going from 1100 BC to 800 AD so for those non historians in the audience that's the Iron Age through classical and late antiquity into the early Middle Ages that includes the rise and fall of the Greek and Roman empires as well as the migration what we used to call the dark ages and I think now is called the migration period so let's just walk through it a little bit so you can see this first rise back here well what was that and we can't say this is what it was but it is at least coeval with the Phoenician expansion of trading from the eastern Mediterranean towards the western Mediterranean right you can see that the concentration goes up he initially here the bounces up and down excuse me by by coincidence this big jump happens at around the time that Alexander the Great consolidated power we didn't talk about that in the paper because we really didn't have a very good explanation for why that would have changed let emissions but anyway it rises up you could see some big drops and then right here that you see this big bite out of the record and here it rises and drops rapidly it stays down for about 80 or a hundred years and then it jumps back up here stays high and then it falls dramatically right here and eventually reaches a nadir right here so what are those what do they correspond to in history and if we compare them it turns out that this corresponds to the crisis of the Roman for a public so this is the end of the Roman Republic when everybody's fighting each other in their civil wars Marc Antony and Cleopatra here at the end and so forth and that represent a very big dip in the lead pollution record suggesting a much lower production of silver at least in a spot in the Iberian Peninsula so you had this big drop and then in the third century this other dip corresponds to the third century crisis of Imperial Rome another another period of political and still an instability and military hierarchy right so very nicely the two big bites out of the record fit very nicely with what we know about history during this period in between those two crises was the Parkes Romana and I'm not sure if that's an accepted phrase and that the history world but for us dia fights it is anyway so yeah this is the period the parker mata is a period of the ger differs from Caesar Augustus through Marcus Aurelius approximately 27 BC to AD 180 and you can see that during that period emissions were quite high and fairly stable indicating substantial growth in the Roman economy during the Imperial period you can also notice if you look carefully at it you can see that lead pollution rose about ten years after the beginning of the Puck's Romana after imperial rule and Octavian becoming Caesar Augustus and taking over it took about 10-15 years for that to rise maybe closer to ten I guess and then it also drops the lead pollution dropped quite dramatically what about 15 years before the death of Marcus Aurelius in the end of the parks Romana so the question is why when Andrew and I first saw this we were a little bit puzzled by it it turns out that it went avian took over as Caesar Augustus he didn't immediately seize control it took him about nine or ten years to establish control over the provinces and spent in Spain and Gaul and exactly pretty much exactly when it should let go shooting up and the reason that is and we think it's because of large-scale administrative changes that follow this pacification so it's all about organization all about getting us into those mines and having a mind like crazy and smelt like crazy right and it does coincide this very immediate and persistent increase in lead and then on the other side on the other side this drop on this side corresponds exactly I mean to the year always keeping in the back of your head plus or minus 1 to 2 years uncertainty of the age scale the advent of the Antonine plague one of the two that there were two great plagues in Roman antiquity one was the Antonine plague the other was the plague of Cyprian and you can see we get this big drop in 165 and andyc and the drop continues to 193 more or less and that was thought to be the smallpox killing off roughly a third of the population of the Roman Empire and then the very the nadir of our record occurs here and that exactly corresponds to the plague of Cyprian which I think historians aren't quite sure exactly what causes that but again a big die-off the other great plague of Roman antiquity it's a very nice agreement with the historical record there and then finally linking back to the economy we've plotted silver and Roman coinage so this is the amount of silver per Roman denarii coin Denarius coin and you can see that the red so this is based on hoards measurements and hoards and you can see that the the coins the fineness and the coins the silver content in the coins drops off really pretty much in parallel with our drop off and lead pollution and what we would postulate is effectively a tracer or an indicator of silver production in the Roman Empire at least from Spain especially and then it got so bad that in the after the after the plague of Cyprian the Romans abandoned silver coinage at this point because and went to a bronze and gold coin set up again you can see the agreement is very nice with our record so let me conclude by saying I hope I've convinced you that ice cores collected from glaciers and ice sheets can contribute to historical studies glaciers and one of the big advantages of glaciers is they sort of consistently and and objectively record pollution that history environmental history you know there's nobody making a decision about land we wrote this or we found the papyrus and the you know of an animal or whatever there's nothing like that it's a it's a pretty objective recorder just sitting out there recording information year after year century after century it does have its variability as I mentioned that 66 6 percent 6 my row is 60% coefficient of variation but at least it's something we can quantify and work with and evaluate continuous measurements I think I'm sure I hope I showed you that are much more efficient and especially much more cost-effective than discrete measurements distal records do have some advantages over a proximal particularly at proximal to sources potential sources atmospheric understand understanding the atmospheric transport deposition is really really important we feel and I think is the future and then dating dating and dating of course as usual and then replication between sites and we haven't replicated the Roman period yet but we have replicated a lot of other periods in the leg records and we get very nice replication for the blood record I've hope I hope I've convinced you that led closely tracked historical events during antiquity that periods of social unrest coincided mostly with downturns in pollution unrest definitely but Wars sometimes increase sometimes decreased plagues were especially especially had a major impact the Pax Romana contrary to the previous interpretations on those 18 points the PAC's Romana is seen now as a period of strong economic growth and then finally the silver in the Dinaric declined in parallel in terms of future plans obviously we would like to extend this these records in this analysis in either direction we'd like to go back from the beginning of the iron via the Iron Age back into the Bronze Age and the collapse of the Bronze Age and all that sort of thing and wait of course like to go this way we're working on this because we have these records but as I'll see tell you in a minute we don't have these records although we're working on getting them we'd also like to take the work that Jo Manning has done and this is what we were talking about yesterday and while we were eating many times we were talking about extending this this linkage between explosive volcanism climate and ancient history or historical events back and Jo and in this paper he worked on Ptolemaic Egypt we'd like to of course go back in time to the Bronze Age collapse and and the New Kingdom and so forth well you might say you might say well Joker's go do it Jose Jose just go do it but fundamental to both of these objectives is collection of and development of much longer accurately dated records of these score records right the problem in Greenland ice cores is that you went and you end up hitting them the brittle ice the over-pressured brittle ice at about 600 meters which corresponds to about a thousand bc roughly depending on the site and when you hit that brittle ice when you soon as you it's over pressured you bring it up to the surface you drill it you bring it up to the surface and if you're not extremely careful and sometimes even if you are extremely careful it explodes and that's because it's you know it's overpressure and some explode well you can imagine for our continuous analysis that makes it very difficult to measure or impossible to measure it so then you say well what about all those coastal domes are small Arctic Islands in the Arctic Ocean well the problem there is those are like like the Alpine course they tend to be relatively thin and they thin too rapidly to get any kind of independent dating so we analyzed one from noosa peninsula last year or two years ago and the annual layer thickness at 0 1 ad let's say is is on the order of a millimeter thick so very difficult to to date independent we can get a record but we can't date it independently and if you're going to do this historical work that's what you need anyway thanks and happy to take any questions and just for you historians there's the famous Andrew Wilson from Oxford helping his key came out to the lab and helped us analyze the core anyway thank you [Applause] questions comments come on you historian thank you very much that was much above my paygrade but I had a question about what what can and can't be measured would it be possible to measure ting given that given its significance in the creation of bronze and it's perhaps being able to help with problems of identifying where the tin was coming from during the Bronze Age yeah it's a good question so when the when the Oxford people first came to me they were really hoping we could get copper because of the bronze connection and it's a signal-to-noise ratio issue so there's quite a bit of copper out there in dust and seawater and so forth and so the background variability is reasonably high and the pollution signal is relatively low unlike LED you know they're not producing they're not losing that much copper we'd like to measure still silver as well but again silver has the same problem the signal-to-noise ratio just isn't there now that said Hong Hong reported measurements of copper from those 18 samples he reported measurements of copper but we measure copper but we just don't see any any signal yet now we could put more effort into maybe that's what we'll do if we're successfully getting funding to collect more more cores and and tin by the way sorry tin is in the same boat tin zinc things like that have quite a high background variability so detecting the pollution signal is harder thank you okay so arsenic again is a difficult one we would have to it turns out that arsenic has isobaric interferences in the icp-ms so we would have to dedicate one instrument just arsenic if we were going to measure arsenic we have measured antimony as a kind of an indicator you know a proxy if you will of arsenic and we don't see we see a lot of recent antimony pollution very clearly with the coal burning era you can see big increases in antimony but we don't see it in in this period again I think it's a signal noise issue and yeah maybe we'll redouble our efforts to try to get it can you simultaneously look for some climate signals I mean there are some fairly rapidly changing climate signals through this thousand year period that you described your can you look at that as well somehow sure and I guess one of the questions is so the focus of this study was specifically on the lead pollution as an indicator of the economy you could imagine linking volcanoes or linking and looking at water isotopes and things like that to see if there were as any evidence of climate drivers of some of that instability so you have you know the crisis of the Roman Republic was it just societal or was there a climate driver behind it certainly with all the things we measure with you know dust for heredity and black carbon for biomass burning water isotopes and so forth we measure a lot of things that you could use we do use as climate proxies but we haven't done that yet so actually it's one of the things we were kind of talking about everyone's being very shy thank you that was really fascinating and I'll confess up front I haven't done science in a very long time so please forgive me if this is a silly question but I'm really interested in the comments you made about the the distant sources of ice and more localized sources of ice and I'm wondering if there's any way that the more localized sources could perhaps refine the picture or contribute to the picture that you've given us here in any meaningful way and is it the question all basically revolves around are you interested in those local sources or not because the people out people for instance have been looking and using p-box to study the local sources of pollution for decades and so that's the question is sorry if you if you can see through those local sources or if you're interested in those local sources great but if you're not there's always sustained you're going to be swamped by those local sources and then there's the dating the dating question is huge right I think a lot of the Alpine cores basically then many of them offend to the point where you can't see em you can't even guess what the age is prior to about 300 400 years ago and others do have a more uniform layering but again you have no way there's the other thing I didn't mention is they tend to be dirty you know an alpine core you can throw a rock and hit a rock and hit something at the surface whereas in Greenland you know we're 500 kilometers from the nearest rock at the surface and so consequently they're much dirtier so seeing volcanoes seeing detecting volcanoes for validation of your age scale and things like that much more difficult than in the Alpine and then in the the polar ice cores which is what that might be a local sources we're gonna redo diagram you talked about that increase yeah you're talking about this increase here yeah so the historians we were milking the publications so we stopped at 800 because this is really about classical antiquity we do have records that go in fact number of records that go up to the present and that's the thing we're working on now is trying to interpret the Middle Ages the lead records in Middle Ages I think most of my historian colleague thinks this is a Charlemagne and the something like that Kings so there's just to show you you say you hadn't done science in a while for me I hadn't done history in a long time so when I first met these guys from Oxford and they took my hand and said they were classicists and I tried to act like I knew what they're talking about and as soon as I got on some time myself I looked up on the internet what the heck is a class now I know now I know but anyway that's oh yeah Charlemagne and then the other thing is so there I think we're gonna have to look at patterns of course we want to get isotopes to try to to pin it down but we're gonna have to look at patterns including the the peat bogs and I don't know if you noticed earlier but now that event was in some peat bogs and not in others and I think what that's telling us is that I don't think that Charlemagne after all I think that's men dips in in Britain I think that's led mining in in Britain but we shall see so stay tuned how useful are these measurements for understanding things in the southern hemisphere yes there's great question so of course transporting aerosol in the troposphere across the equator is virtually impossible because it either gets rained out or it doesn't circulate in the right way you can't get some stratospheric transport but probably not of these things we did we did do work in the southern hemisphere we published the paper three or four years ago looking at lead pollution over the last 400 years based on an array of ice cores and you know Brian Skinner's colleagues are responsible for this in 1888 pollution in antarctica turned on almost like a light switch it went from low levels to all of a sudden high and that was it correlates and the isotopes correlate exactly to the beginning of mining and smelting in Port Pirie in South Australia and in literally in one year you can see it all over Antarctica in one year it's amazing so the other thing that's amazing is that pollution lead pollution arrived at South Pole 22 years before almonds and the Scott so it's hard to imagine they were skiing over you know clearly polluted snow on their way there so I guess I guess Scott was trudging and I'm sitting was gliding along on his skis but locations or where the lights coming from that certain area seems so we need to rely this record being so distal again we're focused on the big picture almost not continental continental scale but certainly are largely regional emissions one of the reasons for that whole coefficient of variation analysis with the modeling the atmospheric modeling was because I had to stop Andrew from seeing a bump and saying oh that's the that's the destruction of the Roman two legions and the Teutonic forest or something I was trying to pull him back from to over interpreting the record so we certainly see spikes they whether they're just transport spikes or maybe volcanic spikes we don't know but the overall pattern is consistent with with the pollution source yeah so for instance this peak right here everybody wants to know what that is and my guess is is the volcano and I guess it's my guess is it's volcanic tuff rap [Music] yeah great question neat certainly people are looking at teeth and at bones for lead and lead in those two archives let's call them and in fact we're working on that I was telling Joelle and others at lunch that we're working on that earlier in that we're working on using our lead record to try to assess background pollution exposure so up until this time if you read books about you know some people there was actually speculation that the fall of the Roman Empire was because of the health impacts especially on IQ and things like that of the elite I don't think that would you say that's right I think that's most people wouldn't believe that was significant in the fall of Rome but but I don't know not a historian but the anyway we're interested in in the atmospheric background level so we can now with this modeling in these emissions we can assess with modeling what what the concentrations were likely to be and assess sort of what the background exposure to lead was was in the general population so epidemiological study of it but but there are measurements of people of bones of lead that are published in the literature our challenge I think is going to be finding people who are separate from say leaded pipes or drinking led Sweden wine and things like that it's going to be finding that background so this is the know the background concentration not in addition to any exposure you'd get through food or or water or whatever yeah it's really sad that in the mines I'm no those you know the things I've read suggest that the life life expectancy of a slave once he entered the mines in lead mines was six years it would have been a grisly job and a grisly death I think so [Music] well so the question is about LED using more detailed measurements of lead isotopes to make a more detailed study of LED provenance both during this time period and during well both directions right we don't certainly don't like to do it that way in that way and one of the reasons that we did we stopped to the analysis here in antiquity is because once you get over here now there are lots and lots of sources and so we really do need to have isotopes to help us tease that apart the problem so I've contacted the manufacturers of our icp-ms is and the people who have maybe you have a multi collector icp-ms in this building I don't know so maybe I should talk to somebody but anyway the I've contacted their research groups in hopes of getting them to try to make measurements at these levels at very very difficult measurements to make and basically all the manufacturers I've talked to have said we can't do it so you have to go someplace else anyway yeah we'd like we'd very much like to we'd like we'd like we have samples through this whole period you remember those fraction collectors that were built into the analytical system so we have samples going all the way through there that it's the same water that gets injected to the icp-ms so we know we can we can monitor all the count of quantum contamination thing issues so we have samples going all the way through this and we'd like to run those samples for isotopes but as I said they they say they can't measure it so even the latest and greatest can't measure it so I guess the only option is going to be we're gonna have to evaporate evaporate them to concentrate the LED and so we and that's the only way that's a lot more work than just handing somebody a bomb and running it through their multi collector icp-ms well that's a good question general you know the modern transport issues but I think you back in time the climate system apart there's are there simulations to try to return those are amended aspect are we sort of just assumed that in our case we just assumed it was stable and it's because you need such a sophisticated fields and so when we talked to what's your name Betty Otto blazer I think it is a 10-car you know the uncertainties that would be associated with trying to reconstruct fields for this time period are much greater than it we just wouldn't work so we're really kind of stuck I mean the issue for this situation was is there I mean another an alternative explanation to this would be is was there a major circulation change like a change in a mock or something like that right here right here right here and nothing else that we measure in the ice cores those 35 different things we measure none of them show anything that suggests a climate change at that point and to my knowledge there's no other evidence from trees or anything else of any significant change in circulation but it is always an issue of course it's always out there that maybe long-range transport shiftin enough to actually create an anomaly yeah so you'd be amazed though at how few eruptions actually have an independent historical date on them what's the oldest do you know what the older wealth Santorini I guess well we don't know which eruption it was we don't know what erupted right at 44 44 BC yeah we know there was a major eruption there were two and 40 we think maybe 44 46 BC but we don't know what their source was so but yeah definitely whenever there are is a date that we can compare to a radiocarbon date or historical date we tied that to the volcanic record and of course we look for tough runs you tempers a little like the is a little bit like the provenance question you can only say that it's consistent with this source but you can't really say it is that source because you could have multiple volcanoes with reasonably close to the same source last minute [Applause] [Music]

Channel: YaleUniversity

Views: 149,899

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Keywords: Yale, Ice Core science, Ancient History and silver mining, Greenland, Desert Research Institute, Yale Nile Initiative

Id: qtA_3Z1N0ho

Length: 67min 21sec (4041 seconds)

Published: Thu Sep 27 2018

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From /r/LDQ

Joe McConnell, Research Professor at the Desert Research Institute, Reno, surveys the latest research in ice core research and methods, and how results from ice core Geochemistry provides new and exciting information for ancient historians. Emphasis is placed on his recent work on lead isotopes in Greenland ice and its value for the Roman economy. This presentation was part of the Yale Nile Initiative Lecture Series