“Exploring the Quaternary mercury cycle”
Alice Paine – University of Oxford (UK)
Speaker Nomination Form: https://paleopercs.com/nominate-speakers/
Weekly Feedback Form:
https://forms.gle/KP2zJojeqgfQnimd8
For more, visit our website: https://paleopercs.com/
okay I think most people have joined so happy afternoon happy Tuesday afternoon everyone welcome to n p par seminar um and I’m very happy to announce that this week’s speaker is Alis Spain from the University of Oxford in the UK and she will be talking about exploring the cordary Mercury cycle so for the people that don’t know it I will quickly explain in the format of today’s seminar so first we’ll start with a quick welcome and announcements I’m doing that right now then we’ll have the talk which is around 30 minutes followed by a moderated Q&A that will be around 10 minutes um and please don’t forget to send your questions to VI in the chat to the questions at failure B’s host who will answer all your questions um I would like to stress that today we don’t have a tea talk um tea time talk um but if you have any further questions for Alis she has told us that she’s very happy to answer you via email or socials which will be linked in the chat shortly so a bit more housekeeping B your pars values of participation of all folks interested in valo sciences and please remember to abide by our code of conduct during today’s seminar you should have signed this prior to um signing up for p Parks if you somehow haven’t read this then please go to our website and still read through it um if you would like to so you can ask questions by chatting to the questions at the Paleo Park host um if you would like to ask a question yourself you you can also use the raise hand function and we will um ask you to ask a question also if you have any technical issues you can ask them to the questions at P BG’s host so um one more thing we also have close captures buil into zoom and you can use the CC button to either show them or hide them whatever you prefer and finally we are always happy to um hear about other outstanding El career scientists so we’ be very happy if you can nominate another one um that will can be done in the link here this will also be dropped in the chat and we’re also very happy to hear about any feedback that you have for us um either demographic like who is watching the seminars or if you have any um criticism or tips for us we would also love to hear that and this link will also be dropped in the chat window so now that’s out the way I would like to tell you a bit more about today’s speaker Alice pay so Alice did her bachelors in physical geog at University of leits in the UK she then moved on to do her Masters at the University of Durham currently she is in the very final stages of her PhD at University of Oxford and then um in September she’s moving on to a postto at University of baso to work on the Metra or Mitra project so without further Ado I would like to um hand the screen share over to Ellis and you can start with your presentation thank you Ellis thank you so much for that introduction thank thank you also for the invitation to come speak today it’s um I make no uh I’ll openly say that paleo perks has been a an organization that I’ve had great respect for for a long time and so to actually be here giving a talk is uh is really cool and so and a nice way to close out the PHD as well to to talk about the what I’ve been essentially selling my life to for the past four years um I wanted to start with this slide and this quote um because change really is the theme that is wov throughout um this talk that I’m going to give today and the research that ultimately this talk is about um it’s a story of change it’s a story of how the Earth system has evolved over the past million years or so um and what we can do to understand different parts of how this change has happened because we know change doesn’t happen in isolation change is not a single entity it can um manifest in different ways um and the ways that um sort the modes of change we’re going to be focusing on in particular is how the Mercury Cycles changed um and so this is the title of talk and also of my thesis that I’m submitting next week so um as Nina said very much in the closing stages um and this talk will really be a summary of what I’ve been doing for the past four years so we’re going to sort of talk through um the different records I’ve been looking at to explore this cycle the cycle of mercury which is the element um and look at how the S of key themes and key lessons that we can take from this with change being the theme of understanding ultimately how this cycle has changed throughout the past million years also and how we can disentangle these changes uh using Lake settlement records in particular and you’ll see I’ve included a gorgeous photo of a lake um here this is Lake presus this is one of the Three Lakes that I’ll be uh referring to today um you can already see you know the landscape is um peppered with snow there’s mountains um there’s undulating topography and all these things will as you’ll see will become significant to uh and pertinent to the uh discussion as we move through the top so before I start I just want to uh clarify on the terminology I’m using because I appreciate uh there’s in paleo climate there’s lots of different terms and I’m sure a lot of you are familiar with them already but just in case anyone isn’t I thought it’d be good to kind of touch base and make sure everyone is clear so theary as I refer to it here refers to the Past 2.5 million years of Earth history it’s divided into two epochs so we’ve got the P scene which is about 2.5 million years ago to roughly 11.7 th000 years ago um at which point then the hallene starts which is of course the epoch that we are in today subject to uh to debate whether we are still in the hallene or whether we’ve moved to anine but that’s someone else’s uh area of expertise so I’m going to skirt around that and uh we’re not going to be concerned about that so as it relates to today we’re going to talk about the P scene and the holos scene and those will be two the two epochs that we’re referring to specifically um and so what was changing on the earth during theery of the past two million years well as you can see a lot was changing on Earth um this is an artist’s impression of what the Earth may have looked like during the last glacial maximum so roughly about 26,000 years ago but it can be taken rough as a sort rough analog for glaciations because we know the Earth was repeatedly glaciated throughout theery and so you had the advance of uh High latitude ice sheets that also grew in volume during this time um and this happened with a very in a very cyclic nature so you had the waxing and waning of ice sheets um corresponding to the glacials so high ice volume inter glacials low ice volume and with these oscillations you had uh changes in dust export so you had very um High atmospheric dust concentrations during glacials um thinning of vegetation and recession of uh ecosystems during glacials lowering sea levels um and continental glaciers also becoming a lot larger and um advancing and subsequently the opposite happened during interg glacial so you had very Lush uh vegetation and ecosystems uh reductions in dust reductions in ice sheet volume and extent uh and rising sea levels so you’ve got this very distinct um oscill oscillations between the two different states of the earth system if you like and you may be thinking well that’s all well and good but why are these changes important to Mercury the element you know that that’s what the talk today is about why why are these changes actually important and why do we care we care because the biog chemical cycles of the Earth are intrinsically coupled to these climate States as I mentioned at the start changes don’t happen in isolation changes happen as part of interwoven interconnected uh feedbacks and loops and systems um and the climate system is uh certainly one of those um or at least exhibits that kind of behavior and so changes in the climate system and changes in the surface environment of the earth also elicit changes in the biogeochemical cycles too and when I’m talking about biogeochemical cycles I’m talking about the movement of different elements between the atmosphere the solid the solid earth and then the biosphere or the terrestrial Earth if you like so that’s uh like forests um oceans um they obviously can of course be distinguished further into different spheres um but as as we’re as keep things nice and simple we’ll just think atmosphere surface um environment and then solid earth so sort of subterrain um regions and so given that the biogeochemical cycles are coupled to The Climate system uh Mercury is particularly an interest and a particularly interesting element to look at um when we’re thinking about how climate is affecting biog chemical cycling because it’s an extremely Rare Element but also it’s an extremely toxic element when it’s in the surface environment um because it can interact with different uh components and different substances in this realm um which makes it very uh toxic to uh living creatures and it can bioaccumulate very readily too and so it can um really Mount the concentrations can really Mount up in different what we call sinks on the Earth’s surface and that’s not good news we don’t want that and so understanding how this element moves and what causes this element to move in between different compartments of the earth system and different sinks is really really important for us to know and then the problem is of course we are only limited in how much we can actually um how far into the past we can look directly uh because human beings uh have not been here for very long and we’ve got a very limited window of direct observation however it’s crucial that we understand how Mercury oscillates during the glacial inter glacial Cycles too um because these are ultimately analoges for the kind of climate changes that we may expect to see in the future so very very abrupt changes that affect all compartments of the earth system and so given that we can’t directly observe these given the time scales they occur on we need to look further into the past and see how mercury has changed in the past and on this slide I include just some of the key uncertainties that we have in relation to this cycle on these kinds of time scales so for example example we don’t know fully exactly how sedimentary records um or at least terrestrial records accumulate and retain Mercury on these time scales and so um I should probably State as well sedimentary archives are going to be what I’m mainly focusing on in this talk um there are ice core records of mercury and these are being developed continuously um and sort of growing in number however sedimentary records uh we’re going to focus on for now and exactly how these archives retain Mercury and accumulate mercur the processes the mechanisms are still very much uh very there’s lots of gaps in our understanding and so we need to that’s a really key area for our Focus um if the process that may drive cycling of mercury between the environmental compartments actually changes between environments so between for example polar tropical midle latitude sites are these any different do the process change or are there are some kind of um consistent processes that are Universal wherever you go on Earth um ultimately how the mer Cycles evolved on these time scales no there’s not many studies that have looked at this in real depth um especially in this quaternary time domain we’ve got lots of modern studies we’ve got an increasing number of studies in deep time so talking like qucious Jurassic periods of time but in this quaternary period there’s not as many and so there’s a lot for us to learn in this area and ultimately the last point is the the key why behind what you know us doing this we need to know how sensitive the global Mercury cycle is to climate change on different scales because with that knowledge we can then think about the future and think about how sensitive the Mercury cycle might be to change um as we continue to morph and change our our earth’s climate and you know at unprecedented rates so it’s really important we understand how that could affect Mercury and what impacts that could have on ecosystems and society and so as alluded to at the start change being the key theme we need to define the different uh scales of change that I’m going to be talking about today and as I alluded to just then you’ve got local scale changes happening on annual scales and these are within direct observation so we can measure these directly however in this piece of research in this talk we’re looking mainly at the regional and Global scales of change and these are the changes that happen maybe over hundreds thousands of years that exceed direct observation and so this is where we need to put our um our forensic glasses on this is where we need to put our time travel glasses on and start to look back in time and figure out how we can look back in time and use the geological and Sentry record to look at Mercury further back in time and so number two is highlighted because that’s where we’re going to start with the first chapter of this story um and with this first chapter we’re going to focus in on the last glacial period so the last 100,000 years of Earth history um and history of mercury cycling and to do that we’re going to look at the lakes of Lake and Lake Presa these are two Lakes located in the Balkans actually slap bang next to each other as you can see via the uh the photo on the left there um they’re both tectonic Lakes so they are both formed by tectonic activity um in the Balkan region um and both of the core sections that we we analyzed here correspond to the most recent 100,000 years of Earth history um and so the key question that we wanted to uh EXP La by looking at these two lakes in tandem is do they record similar changes in Mercury cycling and so our hypothesis was these Lakes are slap B next to each other they’re both tanic Lakes they’re both in the same kind of environment we would expect the Mercury records to be similar or fairly similar in terms of the signals they they uh they retain but as is the case in science that wasn’t the case and our hypothesis was proved to be not correct um so as you can see here by the two Mercury profiles that I pasted here Lake ID at the top and lake presper at the bottom the spikes that we see in Mercury are occurring at different times the Maxima in Mercury are happening at different times um and the plots essentially look very very different if you saw these two plots you would not think that they were two Lakes located next to each other in exactly the same place and bear in mind as well these two Lakes will have experienced exactly the same climate changes um so the the during the last glacial cycle we had you know the progressive growth of the ice sheets we had um the change corresponding change in temperature ice extent all these kinds of things these two Lakes would have experienced exactly the same thing and so the fact that their Mercury records are so different actually suggest to us that it’s not just global scale climate changes that are affecting the Mercury composition of these L cements there’s something else that must be going on and so thinking about the first the first difference between the two aside from the visual fact that they look very different one of the key differences between these two Lakes is the fact that mercury appears to be hosted by different uh compounds and so just for a bit of background following deposition into a lake uh Mercury can be buried into the sediment um in relation to the availability of what we call a host phase and this host phase effect of the a like a shuttle so Mercury will attach to this host face and then be pulled down and sequestered into the sediment by this space and this may be organic carbon this may be detrital or clastic minerals so like like cicc particles that you get from the catchment that come in washed in by Rivers rainfall that sort of thing um it’s important to note here that only a small amount of the variations in Mercury so the changes in Mercury only a small amount of this can be explained by the availability of these host phases um so what that essentially means is that mercury is doing its own thing a lot of the time like the signals we see are not Reliant just on more organic carbon or more detal materials being pulled down sediment Mercury is doing its own thing but there is a slight bit of covariance there um and the small bits of covariant we do see they are different between the two lakes and so Lake presper you see a positive positive albeit weak correlation with organic matter like orid you see a positive correlation with the trial minerals instead so you’ve already got these this key difference between the two legs you know that some certain aspects of the Mercury signals are being pulled down by host phasers not all of it only a small amount is but the Mercury that is being sequestered by these host phasers are different between the two Lakes so already key difference there but including the bubble on the right hand side there a key take home messages given how weak these correlations are changes in Mercury Supply to appears to be the most dominant control on the signals so it’s not just the availability of organic carbon and tral minerals like like I said Mercury is very much doing its own thing um and it’s the amount of mercury actually present in the laks that that we suspect is causing the signals to appear the way we do um and so that leads me on to the second difference which is uh how the different Mercury records respond to glaciation and so in like OCD we see the signal in Mercury Peak between 35 um and 12,000 years ago so that’s corresponding roughly to the height of glaciation so sort of peak you know soil erosion the trial mineral influx due to glacial action due to wind driven erosion recession of vegetation all these glacial proces making a very harsh very abrasive environment where you’ve got a lot of sediment coming into the lake and we think Mercury to uh whereas Lake presper the largest signal and you’ll see that is a it’s a really prominent signal here and it really stands out um amongst you know the signals prior to it um we think that’s actually to do with deglaciation so after the peak glacial conditions experienced in the catchment you had this massive influx of mercury related to The Melting of glaciers uh potentially if like parts of like Presa were frozen over if Mercury accumulated above the ice once the ice had melted it would mean again a lot more Mercury going into Lake uh the a per a broke throwing a permafrost in the catchment too um so all these things driving a huge and overwhelming amount of mercury into this Lake during deglaciation instead um and the third difference with these two Lakes is the hallene signals too and so it’s kind of pretty self-explanatory this slide so Lake OCD you see decreasing Mercury As you move through the hallene um like press instead you see a net increase in Mercury and actually the a lot of the increase in Mercury occurs in conjunction with increase in BIO productivity too suggesting that maybe that has something to do with the Mercury signals potentially due to the action of algae and these other sort of autotrophic uh organisms in the water column helping to further pull Mercury out the water column and sequester it down FS too um and so again different processes whereas in Lake o ID during that same period of bioproductivity in Lake presper we see nothing really happening in fact with decrease in Mercury so further attesting to the differences between these two leges and so that kind of leads us to the concluding question we had was why do the two Lakes despite being so close together why have they recorded such different signals and we suspect it’s to do with this the differences in the Basin size and bimmetry um in a nutshell lake preser is incredibly shallow um especially relative to its surface area which is actually fairly comparable to orid whereas ID is incredibly deep it’s incredibly deep system and what you have there essentially is differences in the sensitivity of these Lakes to the influx of different elements and so for example if you were to deposit a given quantity of mercury into Lake presper the the lower volume means that that would have be substantially more poignant and profound than the same given quantity of mercury deposit in a large in a more voluminous Lake like like orid um and the differences in Beth themetry also mean that these Lakes have different sensitivity to climate changes too and so if you had an influx of mercury coming from melting per frosting glaciers accessing Lake OCD the higher volume would mean it would have much less of an effect than if it went into Lake Presa which is incredibly shallow and is therefore a lot more sensitive to changes in sedimentation and climate and evaporation and precipitation and all these different factors um and so ultimately the conclusion of this part of our work was that different that it’s really like specific features um that appear on these time scales especially to dictate how Mercury is preserved in the sedimentary record and the kinds of processes that these signals um capture and so there is a paper associated with this uh with this work there’s a QR code on the screen there but also you’ll be able to find uh on my research gate and on my website as well links to the paper um where you can have a read more about these records and what they can tell us about Mercury so chapter two of this uh of this journey we’re looking at Lake buum so going slightly further south to warmer climates more tropical climates um lake basum is a Crater Lake it Formed roughly a million years ago following a meteorite impact um and as a result this is a lake that unlike presar arid where you had Rivers flowing into it and you had groundwaters all these kinds of things lake basun is completely isolated from from the regional hydrological Network because it is a you know essentially just a hole in the ground where where the meteorite hit and it’s the only natural lake in Ghana and so it’s almost like a perfect little petri dish for environmental change it just anything anything can go in but it has no way of getting out other than Water by evaporation and so what we can do is we can we can use the sensitivity of this Lake to hydr climate with because given this nature it’s very the water level and the lake itself is very sensitive to changes in precipitation evaporation so hydr climate and we can ask well has hydroclimate affected Mercury so and we can really uh test whether hydroclimate is a driving factor in Mercury cycling in this Lake and similar to PR Berard 2 this um this sequence corresponds roughly to the past 100, years or so and from what we what we um found with the Mercury data is there two potential drivers are very ility in mercury in like with on these kind of time scales number one changes in Mercury Supply and number two the availability of organic matter so this host phase that I was talking to talking about sorry before um First Chain change in Mercury Supply so similar to presper andorid uh Mercury Supply appears to be really important in terms of the Mercury signals that this uh Lake preserves um and what we find is that we find that higher mercur concentrations actually correspond to higher lake levels um um and on a broader scale if we zoom out a little bit this also corresponds to wet conditions across North Africa and the Mediterranean so it looks like or at least the question we can ask is does more rainfall act as an incre a way to increase the Mercury Supply is there Mercury being rained out of the atmosphere into Lake B and so therefore when you have more rainfall would you expect there to be more mercury in the lake and given the fact that the lake level of L we is sensitive to hydroclimate in that you have higher lake levels during wetter periods and particularly during for example the hallene where you had certain periods where the lake actually overflowed the top of the rim because it was so wet and so our hypothesis or at least our theory is that uh rainfall is constituting the main source or driver of Mer changes in Mercury Supply to this like but then you also have that effect in conjunction with the availability of organic matter um because a deeper Lake means a lake that’s more productive but it also means more a more stratified or layered water column which essentially causes the bottom Waters and sediments to be um incredibly oxygen depleted which is really really good for burial of organic carbon and actually we find that there is a positive correlation between Mercury uh and organic carbon in the system albe it not the strongest correlation of course like like pres anded it’s still still fairly weak um but what we do find actually is by given that this correlation does exist and that is positive it seems that the it or it could be at least suggested that the effect of organic matter availability is having some effect on Mercury too and therefore during wetter periods you’ve got more organic matter being buried and more organic matter shuttling mercury into the sediments um as a as a broad mechanism and like coupled effect between more rainfall causing more Mercury to actually ENT the lake and then more organic matter uh driving that uh transmission from the water column into the sediments and so this is just a h schematic uh diagram that essentially summarizes what we’ve just talked about then um so the key points being that mercury fluxes appear to increase during humid periods um and um deep and essentially this could be due to several factors including uh direct precipitation and Al damaging so the draw down by biotic uh cre so creatures and organisms um and enhanced organic matter burial in the sediments um there we go um here’s a QR this is a QR code uh for the presentation that I gave at inqua last year in Rome um the manuscript is currently in review for this paper so hopefully it should be out for you fairly soon um but until then if you are interested to see more of the figures have another look and see and Ponder of this some more like I said there’s a QR code there so if you scan that the slides that I presented at the uh conference will be will be there for you to uh to look at at your leisure and finally the final part of what I’m um of this kind of story uh Journey if you like uh is going back to Lake ID and I know we’re not meant to have favorites but this lake is is my favorite so I I’m not ashamed of that all um and this in particular is absolutely fascinating So This Record goes back uh 1.3 million years um it’s one of the longest terrestrial uh sedimentary records that we have uh currently for the cery um and given the length of this record we could ask a really unique and rare question so how has the Mercury cycle or how has this Lake retained Mercury across multiple glacial and spacial Cycles so the past past sort of chapters that I was referring to we were just looking at the last glacial Cycles the most recent glaciation with this record we can look at multiple glacial cycles and so look at whether Mercury is systematically changing between them if those signals were consistent and whether or if there are differences what could be driving these differences and how ultimately predictable is a Mercury cycle between glacial and glacial uh climate conditions so to start off with we found that uh the deposition of carbonates in this Lake was affecting the mer concentrations quite significantly um I won’t go into too much detail with this because it could be its own talk in itself but essentially what we had to do is first we had to correct for the carbonate and so what that meant is we had to uh subtract the amount of um Al at least calculate the amount of mercury that we would have in the lake if it wasn’t being diluted by the deposition of this carbonate which in Lake oid is predominantly ingenic calite um and so once we calculated this we could then start to think really about what the Mercury was doing um throughout throughout time so this statement again Mercury Supply appears to be the most one of the most important things uh as it relates to Mercury signals in this Lake um however one thing that is important to note with this as well is that it doesn’t seem to be doing uh or at least in Lake Arrid there doesn’t seem to be a very consistent signal of GL inter gracial variability throughout so we have up to a certain point we have um or rather I’m getting ahead of myself actually I’ve just realized got my head of myself so the point of this the point of this slide and ultimately the uh the main take-home message is that when we’re looking thinking about the host phases it’s only quartz or the detrital fraction that really correlates a positively with Mercury um when we think about uh organic carbon that was actually a negative correlation and so that’s suggesting that um in fact Merc the higher the organic carbon is the lower the Mercury is which if you recall is quite different to like some for example um but this um this relationship between mercur and the detrital phase again it’s fairly weak it’s not a really conclusive relationship and in particular following carbonate the carbonate correction so if you didn’t correct for the carbonate you’ve got a really strong correlation between the amount of mercury in the sediments and the amount of quarts and sediments however when you correct with the carbonate this relationship becomes a lot weaker which just to us actually it’s not solely the availability of the trial fraction that’s driving draw down of mercury inance like there are other things going on too and I’ve included this there the results for spam and rank rolling window analysis in this slide just to illustrate the point there as well it’s not just about a weak correlation between Mercury and the triple fraction actually this relationship is also changing a lot during time it’s not just a state AR relationship all the way through and so already we can see this length of this record is affording some really interesting insights into how Mercury is interacting with different sedentary components and ultimately that it is interacting in different ways over different time periods and so if we know that mercury Supply so the one of the main fe uh mainly important features is uh control by uh the size and stability of different what we call Source reservoirs so where Mercury is being stored in the catchman the size and stability of these will dictate how much mercury is actually getting into the lake um how readily Mercury is removed from these reservoirs and transported into a lake um and how effective this transport is from the catchment to the lake itself um and so given this is uh these are the key factors driving change of mercury Supply what are the key factors about Lake o ID that we that would predispose this Lake to having uh such uh pronounced because you’ll see in the blue box there we typically considered over the length of the record on average we have higher Mercury during glacials so during glacial periods why could that be and what could be driving an increase in Mercury during glacials well it’s an open Basin which means that you’ve got inputs from Rivers precipitation uh groundwater through a cast system um so you’ve got Mercury that could be coming from lots of different angles um it’s techologically active and so you’ve got uh lot ground movements you got differences um in sedimentation as a result of these high sensitivity to vegetation and so you’ve got the vegetation that is essentially uh waxing and waning in relation to glacial and glacial climate variability and so you’ve got really profound changes in the catchment and that also relates to the uh High the changes in sedimentation in particular High uh detrital matter fluxes um which is enhanced during glacials by the recession of vegetation uh soil degradation and the you know the thinning of of soils too you’ve not got a very productive ecosystem When there’s less rain it’s drier and it’s colder and so with all these things in mind we can say okay these are the these are some of the factors and special things about Lake Arrid that could uh facilitate enhanced Mercury Supply during glacials as a general rule but and it’s a big but this isn’t consistent throughout this glacial rise in Mercury is not consistent throughout the record and so what you’re seeing here is the result of a spectral analysis when we ran it on the Mercury data and if you can see before um 780,000 years ago the dominant frequency or at least the dominant uh cycle that we see in Mercury with the increase decrease is about 43 to 45,000 years which is broadly equivalent to the obliquity uh orbital um periodicity and so that’s suggesting to us that the dominantly Mercury is varying calling to glacial into glacials but after 780,000 years ago we have there’s a weak 97,000 year component which sugesting that part of it may be related to orbital forcing still because that’s um that’s related to the um eccentricity uh mode of climate change but then you’ve also got it’s a lot less clear and you’ve not got the dominant signals most likely related to noise um so these large 564 and 270,000 year Cycles appear to be more noisy and so this increase in noise and reduction cyclicity following 780,000 years ago essentially suggests to us that something has happened something has changed in the system in that time of course the mid placing transition is a one huge candidate for this uh this change and not only is the midli in transition documented in European propy records but it’s also documented in Lake ID too so you’ve got um changes in the pollen counts changes in sedimentation changes in the datom preserved in this Lake um all these changes that that are ultimately signaling major alterations in terrestrial biomass Continental ice accumulation and sedimentation and all of these we know to be critical to the terrestrial Mercury cycle and so all of them could have interl sort of interacted with each other to elicit this increase in the irregularity or increase in heterogeneity that we see in the Mercury after 780,000 years gone and so there are two implications of this binding or this this shift in Mercury uh Mercury cycling after the mid Pine transition is and these are not only could change in like chemistry depth morphology catchment structure all dictate the extent to which uh global scale climate changes affect how Mercury is cycled in these systems but also that these major climate transitions these major and abrupt and really distinct climate transitions could have effects on Mercury that Cascade and that have feedback driven effects that propagate long after the uh the transition has happened itself you know for example we see the transition round about here in Mercury and you see all of a sudden a net increase here and actually a shift in the Baseline Mercury to a higher level and so this is sugesting to us that the effects of this transition did they weren’t shortlived they lasted a long long time and so with that in mind it’s really important for us to consider how or at least recognize that these kind of very abrupt climate transitions have the capacity to impact the Mercury cycle in this way and the effects you know aren’t going to go away as fast as maybe the transition occurred so they’re not going to scale Mally in time as well and so ultimately what can we learn from these likes what lessons and key take her messages um first of all the Mercury enrichments are produced by um in Lake terrestrial Lakes are produced by elevated Mercury Supply or inputs rather than solely the availability of a host phase like organic carbon or the organic matter and the trial fraction um climate variability on local Regional and Global scales could all influence terrial Mercury cycle and also be detected in sediments too um however the lake itself and the characteristics of the lake itself constitute a really important control on these Mercury signals too and how these the Mercury cycles of these systems respond to climate um such that you’re unlikely to find Two Lakes that have identical stratagraph signals you know they’re going to be factors related to each of them that influence the signals that they produce and how Mercury is preserved in these records and so of course lots of new questions to ask and you know these are just some of the questions that uh I hope will be answered in the future and they’re questions that I’ll I’m taking away from my PhD and hopefully with a chance to investigate further as we uh as we go forward into the future um but I think they’re really exciting ones too I think they’re questions that are certainly answerable and I think they they will only become more clear with the increasing development of Lake sediment records like this and long Mercury records with the same kind of resolution you know where you can start to look at 100, year uh variability in the speed at which changes in Mercury occur related to different sedimentary uh changes and different uh environmental changes too you know changes in the catch but vegetation all these kinds of things and also looking at other major climate transitions of the praries so you know the strengthening of the Walker circulation in the tropics um theary glaciation as a whole you know could these major transitions have imp fact the Mercury cycle too or if not what factors could be driving that you know so lots still left to do um but equally exciting and so I can want to conclude today by just acknowledging some of the the members of the incredible team that have had the real privilege of working with throughout this past four years and on this work and you know it feels quite kind of an understatement to put them just on a slide to say thank you but these people really have made a huge impact on me and my work and I would not be doing what I’m doing now going onto the post do and I would not have the same love for science that I do now if it was not for the opportunity to work with these people and learn from them and interact with them and so yeah they they deserve a shout out here and I think they are ABS they’re a fantastic team and I’m very very very lucky um and so with that thank you so much for coming to listen this afternoon I hope you found it useful and um I will happily take any questions I’d love to hear any of your thoughts or ideas or anything like that so yeah thank you so much for your attention thank you so much for that great talk Alis it was really interesting um just a quick reminder if you have any questions for Alis please send them to the questions that paleo par host and then we will read them out loud so in the meantime we already have some questions and as I said I will post them in the chat as well as read them out just reminder you can send your questions um anonymously or with your name attached whatever you prefer have have a nice we already have one question I would just leave it here from person Hab it settle I hope it pronounce this correctly um great talk have you ever thought about mapping mercury in surface elements of one system or compare two two cores from one system that’s a great question it’s actually something that is a project that’s ongoing as we speak um in classic PhD fashion I’ve got data sets that I haven’t got in my thesis but that are uh still that still need analyzing and so we actually have a second call from Lake ID um we have what it’s called the Pani core it was taken in the same drilling campaign as deep core that I was talking about just then and it’s taken slightly to the East and even though it’s taken near the shores and so it’s not it’s not got the same uh resolution or at least the same uh continuous nature as the Deep record we’re running Mercury analyses on that to we’ve got to about 600 700,000 years back now um and so with the main goal of um like you so rightly pointed out there comparing the two and seeing whether with you know with the hypothesis given that they’re literally in the same base we’d expect them to be very very similar and so if they’re not that’ll give us something really interesting to to have a look at um although I can’t give you any teases on what we’re going to find just yet though because I need to uh I need to align the age model on them um I minut I’ve got lots of data that actually that need sorting out so um but no it’s a work in progress and it’s certainly a really interesting question and equally for other Lakes too you know ID is a great example of a lake where you’ve got lots of cores available um but I think the more d diverse environments that we can do these kinds of studies on um ultimately the better in the long term thank you I think that was a very clear answer um we have another question from Mike saski um he’s asking if the abundance of mercury is related to the source and if vulcanism is a source and did you look at the vulcanism record over this time oh such a such a good question um and actually one that’s kind of ironic because my this project did not start off as exploring theary Mercury cycle it started off as sniffing out volcanic fingerprints using mercury in theary sediment records however we found in the first six months that actually you could not detect uh volcanic eruptions with Mercury spikes in these sediments uh at all and so my PhD went up in smoke uh and so we had to P make a small pivot um but really the the the underlying uh theory behind that was um if you look at the Deep time sediments that I alluded to you’ve got evidence that mercury enrichments are preserving episodes of larous Province volcanisms these milliony year episodes of huge um volcanic activity and so the hypothesis was well could we detect single volcanic eruptions in higher resolution Lake sediment records um and so we went in with the assumption that maybe we could see these Mercury spikes corresponding to volcanic eruptions and we explored this both in terms of Ash layers so ocar uh and pra both have volcanic ash layers in them um and there was no Mercury perturbations that were measurable prior to intra or after these lash layers which was surprising and equally when you look at the uh NE volcanism over you know you look at the net frequency of volcanic eruptions relative to the Mercury perturbations you just can’t disentangle that from catchment based processes you know you couldn’t say so for example in like preser you have the big spike the sort of bigger peaks in Mercury um in the hallene um was itle yeah so you see an increas in uh Mercury concentration here during the hallene and you also at the same time see an increase in the number of volcanic eruptions in our volcanic record however it’s likely that this it’s not due to an increase in volcanism it actually probably to do with an increase just in the number of options that are deserved and known in the record you know and so when you go further back in time with volcanic records you have the issue of Spar recording and so it looks like there are fewer volcanic records are further back you go or eruptions when actually there’s just more eruptions that have been lost from the record that we don’t know happened and so trying to disentangle those is really a broader Global Trends is really difficult and so if you don’t have then Mercury enrichments corresponding to the ash layers that that s adds a final nail in the coffin to think well we’re probably not going to see anything and even if maybe they there was a perturbation to the Mercury cycle by a volcanic eruption um it’s likely because eruptions are typically less than a year in duration it maybe they perturb the Mercury cycle for a very short period of time shorter than the window of resolution that we can get in sediments of this age you know that even like presper with a resolution was about 50 years um that it it may be that that’s just too large a window to capture any Vol any volcanic induced perations to the Mercury cycle so a lot of facts conspired against it I think but ultimately um it looks like uh Lake s records on these time scales um don’t appear to capture any enrichments for volcanism that can be disentangled and and conclusively isolated away from catchment based processes and other environmental [Music] phenomena thanks a lot very clear explanation was actually wondering that myself as someone who mainly knows Mercury as a lip organism indicator okay so torson and Mike I say thank you very much for the answer um we have another question from Krick sersan he asks how important is the biological accumulation of heavy metals so in this case mercury in animals of higher trophic level and by effect also population populations of such animals in affecting the global Mercury cycle this is this is a great question I’m going to there’s only a limited amount that I can I guess speak to because this is very much focused on the sort of contemporary Mercury cycling um and I’ve got you know there are people who are far more versed to speak on this than than I am um but yeah it’s for sure important and it kind of speaks to the point that we were that I was referring to a bit ago um related to the different res reservoirs and terrestrial environments in which Mercury is stored and so when we’re thinking about how Mercury is moved around the environment you’ve got these different places where it can be stored and eventually mobilized and deposited um in and sequestered into geological um materials so sediment JS that sort of thing um if you’ve got more the problem in the modern day that we have is that um or rather should I say in geological time when humans weren’t mucking up the environment pretty much you had this Natural Balance of mercury being emitted from the uh solid earth by volcanoes by geothermal activity and these kinds of things and it would be cycled through the atmosphere through the terrestrial realm and it would be a very balanced cycle the problem we have today is that we are emitting or bringing Mercury from the solid earth into the atmosphere and environment at a much faster rate and so the balance is completely off and so it means that you’ve got this much higher susceptibility of Bio accumulation in um terrestrial um floor and FAA and especially there’s studies as well that come out that say that you know higher temperatures and um these kinds of climate changes actually favor processes like methylation of mercury so that’s where you have the conversion of mercury um to these bioaccumulating toxic forms from interactions with different environmental um materials if you like and so not only do we have more Mercury actually around in The Trestle environment we also have more um susceptibility to it being um bio sort methylated and bio accumulating the surfice environment and so to your question yeah I imagine that the or organic um plants animals are constituting an even more um important sink or reservoir for mercury in the modern day and age to their detriment as well because of course bio accumulation of mercury is you know as we we tragically with the mimata disaster mercury poisoning is not nice at all and this is a particular worry for the Arctic where you’ve got you know a lot that what we call um things like the cold condensation effect where you’ve got more Mercury being transported to the poles and being deposited in these um High latitude regions and so there’s a big concern about arctic fish and animals and people um take bearing the brunt of a lot of this uh Mercury contamination but I will also say that there’s very there’s a sparity of Records actually and studies in the tropics looking at Mercury cycling in the tropics and how rainfall because we saw with B rainfall may actually be really really important um for bringing mercury into the Sur environment too and if you have more rainfall and more flooding in these kind of tropical regions maybe that could have more an effect on M too so it’s the answer the my answer ultimately is probably and I’m I suspect it strongly is a case that you know living beings are becoming more um susceptible to bio accumulation in Mercury but exactly how and the Dynamics of that is still very much uh still a lot to learn in that respect thank you I think that was a very concise answer um I have another question that is somewhat related I think um so the question is do anthropogenic factors influence theer Mery signal and are there chances of the signal contamination due to Temporary Mercury accumulation in the sediments yes so so ultimately yes human human beings anthropogenic activity is one of is the most significant perturbator of the Mercury cycle in the modern day and age and actually anthropogenic activity is the main reason why we’re really struggling to uh study the Mercury cycle without looking further back in time and why looking back in time is so so important now because you have because of androgenic activity you’ve got you know sediment records oceans are just so swamped and contaminated with Mercury that it’s hard to actually disentangle and understand what which of those which signals are natural and which are anthropogenic and you know it becomes a very muddy very complex thing and so that’s why that’s why we’re now seeking to look further back in time where you’ve not got humans McKing everything off essentially um and where you can start to isolate different factors and then because once you have that information you can then think well relative to human activity how important were natural process and look at the two compared to each other and think well how if if you superimpose human activity on top of these environmental processes what kind of effect could you expect would they cancel each other out would they amplify each other would they you know one one reduce the other um so that’s that that’s a a key question at the minute but absolutely absolutely mercur Mercury cycling is uh at the mercy of anthropogenic activity at the minute and um I don’t think that’s going to aate for uh anytime soon because uh human beings don’t seem to be slowing down with the industrial activity and it’s I should stay say as well that it’s human activities um when I say that it’s mainly things like um industrial pollution so burning of fossil fuels um artisanal gold mining so mining practices tend to be bad deforestation as well by liberation of Mercury from sort of vegetation sinks um they’re kind of the key um part the processes driving Mercury uh cycle changes but of course there are lots of different factors too so um they’re just the kind of main the main ones when you think of dirty human activities and industrial pollution it tends to be that kind of stuff thank you again for that answer um do you have time for a few more questions of course yeah okay great because we still have Fu so candan has another question and he asked although Mercury radio isotopes are stable how important is fractionation and are certain radio isotopes more readily available for sequestration as compared to other Mercury Isotopes this is a fantastic question and one I don’t feel like I I can answer um because we’ve been we’ve been focusing um mainly on just meas measurement of mercury concentrations and accumulation rates Mercury Isotopes is a field that I am very lot less familiar in it’s not something Isotopes aren’t something that we measured in this study in particular um what I do know is that mercury Isotopes can be very good in terms of distinguishing different sources of mercury um in the environment and you can start to get a real handle on Where the mercury is coming from um in relation to you know the ice toes and how they changed I know that the ice core Community have really drawn upon this quite well um in measurement of the Mercury ice topes in ice which can quite given how Mercury is quite a complex element um it makes measuring it in ice by the means that we were doing um so by combustion me methods um whereas the the the the instrument that we use essentially is like it like paralyzes the Mercury so you burn it at about thousand degrees um and measure the Mercury up obviously with ice you can’t do that um and so I the ice the ice like the ice call Community have been uh really drawing upon this Mercury Isotopes and I think a paper came out in nature last year year um that was looking at the last glacial uh maximum um using mercury ice toes in ice calls from the Arctic or I think it might be Greenland actually um so yeah it’s it’s something on the rise but I I’m afraid I don’t I can’t fully answer that question perhaps the the detail that it deserves um just because ice toes weren’t something that we were we were looking at specifically here um if you’d like to drop me an email I can certain we can certainly have a chat about it over that because I can and I can send you um or at least direct you to the literature that uh is really good there are some great reviews out there for mercury ice tubs um that are well worth a read if you this is something that interests you um but yeah I’m sorry I can’t give more details on that thank you that’s more than fair I think um if you have some more time we have another question from S saan I think for this um it’s better if you read the question and go back to the correct plot so it’s what exactly changed the 800 Kil time period in the Mercury qz plot for 50 kilo years I think you that caused the shift from consistent positive Peaks to negative values so is it this one or is it this one Sandra if you could quickly type in the chat um oh okay I can the previous slide he says yeah this one yeah great question uh so this so this is this is an interesting one because in short we don’t entirely know um because there are lots of interacting factors this this change um in the relationship between Mercury and the trial fraction does correspond to that window in which the midp scene transition was occurring um and so you’ve got the the the essentially the intensification of the glacial and spal Cycles um I kind of skirted over it because I was aware that I was going uh going a bit close to my time um but essentially during the mid pene transition you had this shift from uh 40 the sort of 40,000 year periodicity of the glacial andal Cycles um which is illustrate which I Illustrated in this uh figure here you had these more frequent glacial inter glacial Cycles here and during the midf scene transition something changed what what exactly changed we still don’t know that’s still a topic of you know immense Fascination to the P Community as I’m sure a lot of you will know um and we changed to these 100 killie uh glacial Cycles so the glacial Cycles not only became longer lasting but that also meant they became more intense and had a much more profound effect on the environment and so one possibility is that with this intensification of the glacial Cycles you also had intensification of processes that would drive increased Mercury Supply to this Lake by uh and also corresponding the trifle minerals too so increased erosion um decreas in the stability of the of the vegetation in the catchman soil degradation and so this it’s possible this represents the intensification of those processes that were perhaps influential prior to the uh mid P transition but also um a lot more severe afterwards one thing as well that I didn’t didn’t mention in as much detail is the fact that Lake Arrid has also been progressively getting wider deeper throughout its history and at this point here at sort of round about between 600 800,000 years ago the lake underwent a pretty uh major shift in uh it became substantially deeper and wider and it became more analogous to the Basin that we see today and so whether that widening or deepening has anything to do with it too maybe a change in sedimentation um that could that’s also a plausible mechanism however I say mechanism the mechanism by which a base in wiing or deepening could impact Mercury cycling is a little bit ambiguous a little bit nebulous it’s not 100% clear um what would actually cause that or whether you know the mercur and what would drive a Mercury cycle to shift simply due to a change in sedimentation related to a basin um so there’s lots of hypotheses that could explain this um but it’s uh ultimately I think the main take home message that we at least focus on here is something the Mercury cycle was not the same after 780,000 years or so as it was before and so you’ve got this this change in this fundamental change that happened round about this between the 800 600,000 year period and that lasted but up until the present day and so that’s the the main I guess take home message of this of this plot for now um but we’re you know we’re finding trying to think of ways to continue exploring this idea and this uh the change the reasons for this change essentially um and what why why it happened because I think it’s fascinating I think it look it looks really intriguing the fact that you have this this really profound change and so really disentangling and drilling down on the mechanisms by which has happened um I think it’ll be a really cool thing to do in the future and something I think that’ll become a lot more um will be facilitated by development of similarly long records you know so can we get other Lake sediment records crossing the midp scene transition where we measure the Mercury and see if a similar shift occurs because then we can start to think what could it be something to do with lake ocit or is it something that was happening on a global scale that affected all lakes and the environmental changes that happen on a global scale was it that instead like what to what extent were these two things interacting and how important were they equally um I hope that answers your question Okay and like like I mentioned um more than happy to continue chatting about this over um email because I think it’s fascinating I could talk about this all day so yeah I hope that’s all right yeah thank you there was a great question also classic says thank you for answering his questions um yeah I think since we are at the top of the hour um I would like to close the question session um again as Alis already said you can contact her at a later Point via email um so Ellis I want to thank you again massive thanks for your great talk and your great to the questions um so before everyone leaves um I would like to share my screen again for some final announcements as usual so once again thank you for joining us um once again we would really appreciate it if you can fill out the weekly feedback form so um we can keep learning um as um sorry as promised previously here are also Ellis’s socials in the chat and her email so if you can reach out with questions um you’re free to do so um and then I want to invite you all to next week’s semar on the second of July normal time 15 UTC this will be given by Janette poo who is going to talk about comers from North Central Florida so F paleontology from California State University in the US