S2S15- Land-to-ocean sediment routing along the Chile margin (Anne Bernhardt, 10/9/20)

okay uh good morning good afternoon and uh good evening and once again welcome you to this world a large river under the auto system source to sink webinar series so today is Friday we invite professor anne bernhardt from a free university of berlin we will talk about south america the chile market so before i introduce anna so i’d like to see next week next wednesday you know our old friend uh steve Kuehl from virginia institute of marine science he will talk about the sediment and the carbon delivery and the preservation of the amazon ganges brahmaputra and Ayeyarwady and Thanlwin rivers. so please mark your calendar and also friday next friday um rebecca caldwell from Chevron um energy technology company she will talk about the global delta dataset and also the predicted delta formation on marine coastline i think both talk uh will be also very interesting please do come back so anna as you can see um originally she graduated also from the free university of berlin and then get a phd in 2011. uh i guess she spent five or six years in san francisco stanford university the phd over there and after that it back to germany has a couple posdoc to postdoc and then become professor 2017 2016 in the free university of berlin over there so Anne involved the research in south america america both atlantic side and the pacific side so today she will talk about the active modding of the chilE margin and so uh pretty sedimentary so anna uh now it’s your turn please share your screen yes i will are you okay seeing my screen paul very good okay go ahead well thank you very much paul for um this introduction and also for putting together this um bi-weekly seminar that you know we already said so in the chat before that really helps us going through these crazy times and um where many of us actually work in isolation for quite a bit however well i will take you today to the chile margin and we will talk to lead to ocean sediment roading in this this area and especially are we talking about testing the effects of climatic and geomorphic boundary conditions here and i would like to acknowledge my co-authors which are wolfgang schwangert and manfred stryker from the university of potsdam where i did my post-doc and dear cabin and my mother who work at the marum research center in bremen in january who’s at the nearest in the netherlands and here we go so we’ve been seeing several talks that talk about very big river system about global sediment export from those rivers into the oceans and we and actually next week steve cool will talk about the giants again including the amazon basin in here and so you can see that the right side on the east side of the south american continent is drained by this really big systems that discharge a lot of sediment into the ocean that’s the amazon sediment plume here um just a couple of weeks ago and you can see you can see that massive amount of sediment that’s washed into the atlantic here but today i would actually like to invite you to look at the little guys here over along the indian margin on the western side of the continent that discharge sediment into the pacific ocean and you can see here a couple of um well bigger chilean rivers in central chile this is the maula river and this is the infamous biobio river one of the largest river systems here in chile and they also discharged quite a significant amount of sediment into the pacific ocean here in this particular image during flooding stage in july 2006 and if we look at the global scale this is the compilation of milli men and fans with we

have seen this already in many talks including paul’s introduction talk a couple of weeks ago and this shows the annual sediment discharge from rivers into the coastal ocean and we can see that the andean side here of western south america does discharge about 530 million tons per year and that is quite significant and it’s even by a factor four times more than the southern part of the eastern side the site can do so this is not insignificant even though these are little however they drain very steep catchments and can actually free a bunch of sediment here so this talk will be structured as followed we i will introduce the chilean margin to you as and i will explain why we use it as a natural laboratory or what i even mean with this then we will talk about fluvial sediment supply and offshore deposition i mostly work in marine sediments so my perspective is a little bit more focused on the zinc part of the sediment ordering system but nevertheless we will talk about short and long term fluvial sediment supply and how this behaves along this margin we will talk about long-term sediment deposition in the trench and about holocene turbatite systems and how much sediment those receive along this particular area we’ll then focus on sediment export and the changing climate and geomorphic conditions as i promised earlier and then i will quickly talk about the questions that still remain open here in this area and how we are trying to address this in ongoing and future work and if you get lost along the way there’s a sidebar here on the um on the right hand side so and you know it will pop up where we are actually in the talk so if you’re lost you can get back on track here okay zooming in to cheetah this this the longest and skinniest country probably there is and first by looking at the simple real color landsat image you can see that its vegetation is quite sparse here in the north and then it gets progressively greener towards the south you can also see that this is a subduction system you know that anyways but this is the seduction trench here offshore and you can also sort of guess that this is getting deeper um towards the north and this is because there’s actually a small amount of sediment fill towards the north and we will look at this in a bit more detail so let’s zoom into this particular area of central cheetah that’s where most of my work is actually based and look at the climatic situation here and on this part i plotted the present day precipitation pattern in here where hot colors are low precipitation and cold colors are high precipitation and you can see as we go down here towards the south precipitation increases um as we go down south so it’s quite dry up here and it becomes progressively wetter or more humid down here and if you look at a couple of pictures just to get an image of how that landscape looks like this is a semi-arid region the santa garcia national national reserve um close to the city of la serena this is a semi-arid climate zone and you can see some patchy vegetation here smaller scrubs and lots of bare ground where steady sediment might be relatively or readily available for erosion moving down south a little bit in the area of our pariso into the la campana national park you’ll see that vegetation is more abundant there’s some palm trees in here the vegetation cover down here in the valley is actually quite dense on the hill slopes there’s still some bare ground um that is not covered by vegetation and then we if we go even further down south here that’s the that’s the mouth of the wheel of the riobio view and we can see that here the landscape is actually covered by quite dense forest so that climatic gradient of course because there is more precipitation towards the south has a clear impact on the vegetation pattern here good so we use the chile margin as a natural laboratory on the spatial scale and what i mean by that is that we can use this pronounced climate gradient to analyze the effect

of changing climatic zones on sediment export to the ocean so we are defining a couple of study sites along this particular gradient to see how sediment export works along this climate coding this is well data this is the modeled suspended sediment yield per square kilometer in the catchment and this is not real data this is an outcome of the bogart model that has been introduced actually just wednesday by um albert kettner and earlier by ajaya switzky in the same seminar and so what they do is they model the um the suspended sediment outflux from the um from rivers and they actually the model is quite well calibrated so we can sort of trust these values quite confidently and as you can see the um sediment yield of the from the bogart model is sadly increasing here towards the south and then it really shows a bunch of scatter it seems to peak maybe down here but there’s not necessarily a clear padding in here and this fluvial sediment yield is pre-human so we don’t not looking at human effects here but um and it averages about you know several decades if we look at longer term sediment yield and this these values are derived from cosmogenic nuclide measurements of 10 billion that quantify erosion rates and using these erosion weights we can calculate the sediment yield for each basin and this is a compiled data set mostly of data from karate 2013 and actually follow-up papers as well and they sampled the outland of catchments just at the foothill of the andes because they were interested in the origin pattern in the high endis themselves and then we added a few data points along the mouth of the major river systems as we are more interested in what comes actually out of the mouth of the river and gets discharged into the ocean and what you can see here is that there’s an increase in in sediment yield towards these latitudes and then you know given the spice data but it seems to decrease towards the south so if we plot this up in in a simpler plot the open diamonds are the values the short-term values from the bovad model and they show a bunch of square but it seems to peak they seem to peak here at 34 degrees south and then they sort of go back down if you want but there’s a bunch of scatter if we look at the longer term sediment yields that integrate over several millennia we can see that these peak at 35 34 degrees about and then they actually do go back down so the annual or the decadal and the millennial scale sediment yields do not simply increase with increasing humidity just because it’s it’s raining more it doesn’t mean that there’s more sediment coming out of those river mouth but they peak in this mediterranean climate zone around 34 degrees south and there are several working hypotheses that have been put forward that could explain or partly explain this pattern karate at all interprets this as the um well they also show that the origin palace increases non-linearly linearly with mean slope and they interpret this as a transient response to uplift patterns so as the andes are uplifting and it’s raining more in the south erosion can actually shallow the slopes relatively efficiently and now the slopes down here in the mountainous areas are actually quite low so now erosion rates have actually decreased whereas here in the mediterranean climate zones the slopes have not adjusted yet and erosion rates are still quite high there’s also recent paper by jessica schtucker she focuses a little bit more to to the north but also includes some of these data and she should suggest a bidirectional response of erosion to the influence of vegetation so what they are showing is that they are competing interaction between precipitation and vegetation on the origin in each setting and depending on who wins vegetation as a stabilizer or precipitation as an eroding asian agent this might drive the pattern so there’s several you know interesting working hypotheses out there that are tested in further research

now if we look at a third proxy of sediment flux over the very long term we actually do see a different pattern so what this plot shows is the sediment volume that’s deposited in the subduction trench out here so this is work of david ferger in 2013 and he looked at a bunch of seismic reflection profiles that crossed the trench and he calculated this the volume of sediment that’s trapped in the trench and so this integrates about one over about one million years as the oldest sediments in the trench are sort of dated there’s actually no no dueling in here but they are suggested to be about one million years old so this is the really long term sediment flux and as you can see that actually does increase steadily towards the south there might be some local influence of that is determined by the position of submarine canyons and adjacent rivers but in generally there’s an increase in sediment fill in the trench towards the north the south i’m sorry and so what that means is that the sediment volume here sort of does positively correlate with the increase in precipitation during this margin and here we are seeing the bathymetry offshore the chilean margin so we can look at the trench a little bit better and you can sort of see that the trench is filled here down in the south and as you go towards the north the transport trend trench becomes deeper and it’s also less smooth so there’s less sediment in here you cannot already tell by the by the bathymetry and because of that local gradient where these the entire trench is slightly tilted towards the north there’s also sediment transport going on here that’s directed towards the north so there’s an axial channel a nice termite channel in here that that is that continues over several hundred kilometers and then actually tapers out in here let’s zoom into this a little bit so we can appreciate it a little bit more this is the super nice um channel here within the trench that funnels sediment towards the north and then if we zoom into this northern part we can still see that channel running along and then we are actually getting into the we are where the juan fernandez which is subducted um underneath the south american continent i’m sorry and um and the trenches actually not filled anymore and the turbulent channel is also not present anymore so as you can see that this this whole depositional system here offshore is a very open system so sediment can be deposited along the continental slope you can see that the continental slope here in this realm is characterized by the big four arc based on that sediment field but also a bunch of smaller basins that are nested within this equationary prism here there’s a few large submarine canyons that can funnel sediment directly into the trench but there’s also these little mini basins that can store sediment that’s similar here in the south there’s a big canyon going down the continental slope directly that lowering sediment to the trench but also many different mini basins that can fill up with sediment so we cannot use this natural laboratory to actually close sediment budgets right it can go anywhere it can go in the little basins it can go along the canyon and then it can actually go northward within the trench because of this regional gradient so this is something we cannot do but we quantify or similarly quantify the sediment input by using individual gravity course okay and since we are already talking about the onshore and offshore geomorphology of this margin and how this changes along the gradient let’s look at into this a little bit more this is a block diagram here of the northernmost area those dots are gravity cores that we used for the studies i will introduce a little later on and we can see that the the onshore gradients are quite steep and the rivers drain the high end knees and then the shelf is actually quite narrow so you can also appreciate this in this map where the shelf edge is shown by this gray line and here in the north the shelf is really very narrow to almost absent so sediment during holocene sea level high stand cannot be efficiently stored along this very narrow shelves

however if we go to the south we see that the shelf actually increases in width quite a bit and this is the block diagram here in the south you see those big canyons coming down the canyon the itra basin or the interslope basins here and a shelf that’s up to 60 maximum 80 kilometers wide so this is this is not white when you look at passive margins where they can easily easily be 200 kilometers wide but um in this case along the subduction margin this is actually quite wide good and to constrain um offshore depositional patterns and sediment flux we used a bunch of sediment gravity cores and we looked at the sedimentation rates but also at the frequency of turbidite deposits so how often did the turbidity current come down the slope and actually exported coarse grained or sand sized sediment along the slope here and we splitted our estimates here in different time periods the holocene the glacial and the last glacial maximum but for now we will just focus on the yellow dots which represent the holocene and as you can see here in the semi-arid northernmost area the holocene turbulent frequencies which are given here in turbidites per thousand years actually quite low so there’s almost no turbidites coming down um into the marine rearm here and also not doing the same semiarid um within this uh this the study site which is actually of mediterranean climate so um the the peak in in erosion rates we can’t actually see that in the turbidites down here in this particular forex basin if we go down here to the south we actually see turbulent frequency up to eight turbidites per 1000 years and these weights are or this frequency frequencies are highly variable because that really depends on the deposit position outside your sampling so similar pattern that we just look at the sedimentation rates within those cores very low sedimentation rates all along here and then these shoot up to very high actually more than 5 meters per thousand years offshore the southern chilean margin here so in the north there’s little to no activity of turbidity current that exports sediment ii into the ocean during the holocene even though the shelf is very narrow and to almost absent right so there’s it’s not because this the sediment is actually stored on the shelf during the current holocene high stand it’s simply not delivered to the margin anymore and here in the south turbidity current um activity transport central that mud to the deep ocean even though the shelf is quite white and the sediment if it’s not directly funneled into a canyon the sediment could could be stored on on these relatively white shelves so there must be or there should be a mechanism that actually drives this and in order to highlight this mechanism let’s have a quick look at the current current patterns or the large scale current patterns of short chile there’s two surface currents that are directed towards the north which is the chilean coastal current and the infamous to chile current or the humbled current that brings cold water from the polar region towards the north however there’s also a southward directed current which is not a surface current but an undercurrent that flows at around 200 to 400 meters of water depth and we will zoom into this area of shore conception to look at some high resolution bathymetry of the shelf here that gives us clues into what’s actually going on here and this shows you that the burbear river actually discharges directly into the head of the submarine canyon the bubur submarine canyon so much of that bobo river ceremony can be directly funneled into the trench as the canyon leads directly into the trench that still doesn’t necessarily explain us the high sedimentation rates or the relatively high turbulent frequencies in on the continental slope so let’s zoom into the inner shelf here and when we do this this is very high resolution bathymetry the it’s about 2 meters per grit cell so much higher than our usual rhythm that we out there and we can see that the inner shelf is

actually quite smooth and we interpret this as being covered by loose sediment however if we zoom into the outer shelf area here we see a completely different pattern so this is out here is the shelf edge you could sort of guess those gullies that start incising into this shelf edge here and we see a bunch of rigid bedrock widgets that are partly folded and this rigid surface is partly covered by these smooth areas which we interpret as loose sediments and you can see that the sediment is reshaped into those elongate sediment drifts um here for example but it’s also windowed out or eroded into these scours here the direction of the scours sort of implies a south westward direction sediment transport directions direction of this of the sediment and the good undercurrent actually coincides with the depth of the shelf here and transports the sediment or sweeps this loose sediment over the shelf edge or into those gullies or onto the container and dot slope and um and causes these high sedimentation rates and also delivers sediment in order to trigger turbidity currents offshore here okay so to summarize this quite offshore north central chile the low sediment supply actually precludes a significant sediment export to the sea or through the continental slope it’s not very surprising um but that is the case although the shelf is narrow and the offshore gradients are steep so there’s still intermittent storage of sediment happening here however offshore south central chile we have the positive pairing of high sediment supply and a wide shelf but the sediment doesn’t stay on that white shelf at least not in this outer part because the water depth of that shelf of the outer shelf coincides with the gunter undercurrent that is fast enough or strong enough to actually export sediment over the shelf edge and sweeps it onto the continental slope so we get high sedimentation rates here even though sea level is high during the holocene so in general white shelves do not necessarily preclude the delivery of the original sediment to the deep ocean during sea level high stand in fact the export of sediment to the deep ocean via undercurrents can be especially efficient during high stance when these currents flow along flooded sediment covered continental shelves and we really need to make sure that we integrate those three-dimensional aspects into sediment mass balances and budgets and in our depositional models when we look at you know deeper time straighter and this is actually quite similar to the scenario along the nile river and the living margin that was introduced by uri shatner’s talk a few way weeks back where he also showed that the nile sediment can be transported towards the israeli coast via storm currents only when sea level is high and the shelf is actually flooded so this is not a unique situation that might be quite common good so i talked about why we can use the chilean continental margin as a natural laboratory on the spatial scale using this climate gradient but we can also use it as a natural laboratory on the temporal scale and so we can use the well-defined climate change from the last glacial maximum to present to analyze the effects of changing climate on sediment export to the ocean in different climate zones over time and what actually happened here is the following so we have the semi-arid study site up here in la serena a mediterranean study site offshore valparaiso and then a humid study site down here just south of concepcion and the reason why it’s humid down in chile it’s because the westerly winds they blow onto the continents in these latitudes and they bring moisture from the pacific ocean onto the continent and during the last glacial maximum the core of the westerlies was actually moved towards the north by about 5 degrees and so

with this the entire precipitation gradient was actually shifted towards the north by 5 degrees so along our study sites here everything got wetter or more humid and after the lgm and doing the glacial the westerly or the westerlies or the core of the vessel is actually shifted back down for about these five degrees so in doing the d glacial everything became drier along this um this margin because the entire gradient was shifted back south so we are talking about you know a climatic change towards less humid conditions in all of those distinct climatic zones so the research question we’re trying to answer here is how is the glacial electrification manifested in marine classic deposits under changing climatic and geomorphic boundary conditions and in order to understand how we developed our working hypotheses i would like to introduce you to two way you know quick concepts and the first one refers to how cyclic cyclical precipitation changes are thought to propagate into sedimentary sinks and there’s a bunch of numerical models out there that predict how this might work and we’re looking at an input signal here which is the water discharge or changing precipitation if you want and the sedimentary response in terms of sediment supply here and if you pick a diffusive one-dimensional model of armitage um he showed that well if the cyclicity is quite or the periodicity of the cyclicity is quite um quite high sediment flux may respond during the first few cycles and then it just sort of tapers out and you don’t actually see a signal in the sedimentary sink anymore there are other models out there that propose the opposite that such signal might be amplified in the erosional zone or if you pick yet another model by simpson in castletoy it might be amplified by river transport feedbacks meaning that if you put more water into the system then within the transport zone which in larger weather systems you can re-mobilize more sediment from this floodplain because you have more water available and you can amplify the sediment supply signal so depending on which model you choose or which one you think is more most applicable to your study area you might not see a signal or you might see a signal and we would just looking really at that precipitation decrease during the deglacial just as a half cycle if you want the second concept i would like to introduce is the concept of connectivity and connectivity describes how efficient a certain portion of sediment can be transferred from one compartment from one part of the sediment routing system to the next and generally um systems or sediment routing system is highly connected when a high amount of sediment can actually make it through so here in that northernmost study site the onshore gradients are quite steep you can see that on this onshore slope map then the shelf is narrow to absent i talked about this earlier and then the core locations that we are looking at are here within the continental along the continental slope because there’s very little sediment out there in the trench and so we think that this system up or these systems up here are highly connected and another term that we use for this is that these are reactive system and it’s a term coined by philip ellen in 2008 the geomorphology looks quite different if we look at the south here where the gradients are steep in the andes but then you get into the zone of the central valley which obviously has low gradients because it’s a valley and because the the coastal cordial um we go on to this white shelf the equation of a questionary prism out here is quite big so it has a bunch of smaller inter interbasins in here and then the core locations we chose are actually out here in the trench and on the incoming plate because the sedimentation rates are so high on the christian bosom or on the continental slope that we um within gravity course we never captured the last glacial maximum actually so um the distinct geomorphology is due to a steeper subduction angle

out here so there’s active volcanism as well and then that big central valley that develops here there’s also a bunch of glacial lakes over the glacial valleys here at the foothill of the andes so we think that this system is less connected and therefore more buffered so there’s a decrease in connectivity because the gradient is decreasing but there’s also an increasing size of potential transient sediment things towards the south and this includes the glacial lakes the great valley the white shelves but also the indo-sloped basins on the slope here so the working hypothesis that we came up with is that the d-glacial precipitation decrease is probably most prominently preserved in the marine records offshore that northernmost semi-arid studded study said because that’s a very reactive sediment routing system and that the signal or the sedimentary change due to climate change will be much less pronounced and occur with a significant lag time in that unit study site where the system is more profit so let’s see if that’s actually true so what we did now is we took a bunch of sediment cores that were caught by the arizona but we also included an odb core we quantified turbidite frequency and thickness in here we took a bunch of previous studies and extracted the paleoclimatic proxies from here that constrain the climatic change we computed or we computed the h-depth model to quantify the age uncertainties because we want to compare the timing of the environmental change or the climate change to the marine turbidite record this is the first glimpse at the data i’m leaving out this intermediate study site for time constraints where we can see in this northernmost study site that’s the orange curve of here and this is turbidite frequency now in turbidites per 500 years against age and we can see that around 16 to 15 000 years before present the turbidite frequency drops quite significantly here in the northern study site and it does so a little bit earlier at the humid study site there’s the steep decline in turbine frequencies in the course that we looked at now we want to compare the change in an offshore turbidite depositional pattern to environmental change proxies and so we come up with these plots in always i’m not going to get into this detailed plot but we basically want to compare the timing of curve change for different proxies um towards our sedimentary record oops and this becomes quite messy if you look at this this way and we also need to quantify the uncertainties so this is not a great way to look at this and we try to come up with a more intuitive way which um i hope i can explain in here so we um we plotted the h models against the proxy of interest be it be turbidite record or whatever climate proxy and we did that for each markov chain monte carlo simulation out of the h model so when you model h depth models with the baker and r software of the blog then um it actually does that by modeling many many thousands monte carlo markov chain monte carlo simulations so we took each one of these and we determined first the steepest or the the maximum change within the curve which is the steepest gradient of the proxy craft those are the black dots and then we also quantified the temporal duration of proxy curve change so that means when the curve changes its gradient and back again so that’s the transfer duration of the change in the proxy and we did this for every monte carlo simulation whoops now this is going clearly and and we just got rid of the curse and remained with the quantification of the steepest change or the maximum change and the tempo duration of this change so what you’re going to see from now on is black dots and the duration in a gray bar so we did this for all the proxies and our sedimentary proxies so the black dots again are the maximum change the gray bars are the tempo alteration of this change and we can see that turbidite frequency in this northernmost study area declines quite steeply around 16 to 15 000 years for present and the temperature duration of this change um actually goes on until about 11 000 years before present turbulent thickness takes a bit longer and if we compare this to humidity proxies in different sites but also offshore proxies we can see that the changes in proxies and the changes in the turbo diet record occur contemporaneously at the same time with

similar duration durations so within the resolution of the of the h models and down here we can look at um sea level that also changes of course but it didn’t have too much of an effect up here because the shelf is narrow to absolute now by looking at the south we can see this very steep decline in turbulent frequency um a little bit earlier about 17 000 or so before present and that occurs very abruptly and it also con occurs temporaneously with the changes in proxy so these are pollen changes this even slightly post-states this maybe a little bit at least in the steepest gradient but the other proxies are just in line with the change in turbulent frequency so everything happens at the same time so our working hypothesis that you know this the glacial precipitation decreases most prominently preserved just in the northern study site is actually not necessarily true because we can see that the special temple temple of turbulent pattern mirrors the glacial humidity decrease and the warming that comes with it over a wide range of climate zones and geomorphic settings basically all three sites that we tested lag times are not resolvable so they might be present but they must be below the resolution of our age models and turbidite decline is not mainly controlled by post glacial sea level rise as in the southern um study area sea level rise actually post states the change in turbidity currents and in the semi-arid side we think that high system connectivity or reactivity is responsible for the rapid manifestation of the glacial eredification here in you know seen in the decrease in offshore turbulent deposition so this is in agreement with our working hypothesis however the south seems to be functioning somehow differently and here the turbidites shut off also at the same time as the proxies show the steepest change or the steepest climatic change and we think this is actually due to a different process or at least partly due to a different process once we look down here at the map we can see there’s a couple of really big lakes that intersect the river systems down here those are over deep in glacial valleys that have been flooded by melt water and this is the biarica volcano here in the background of one of those legs so of course these legs became partly ice-free doing during the glacier as well so all of the sudden you open up this big efficient sediment trap in at the foothills of the andes which swallows a whole bunch of sediment that then doesn’t make it out to the uh to our core locations anymore so that would actually mean that this is a decrease in connectivity in the system that’s in the end responsible for signal propagation offshore so we conclude that high connectivity but also a rapid loss of system connectivity within the sediment routing systems can result in rapid manifestation of a climate signal in the downstream sedimentary system and it may create meaningful and quite similar stratigraphic patterns in the sink so for us as sedimentologists or stratigraphers that’s quite encouraging because we can see in in this particular area that climate change is um recorded in the sediment depositional patterns offshore so the turbulent deposition is dramatically reduced during the same time as the proxies indicate the climate change in all study sites along the entire gradient and that is of course encouraging because that’s what we usually try to do as sedimentologists right we try to take a sedimentary record and invert it into changes in the upland river catchments and so you know even though this is this is quite quite a nice result as i think um the the really interesting question behind this is the following so what are the sequence of processes that actually lead to this reduction of sediment supply especially when we think about the northern area does first chemical weathering reduce and then because there’s less loose material available erosion will reduce and that leads into the decreased export of sediment or is it simply that we don’t have enough water in the rivers

that um that decreases the the river transport capacity and so their sediment is available on sure it just cannot be transported offshore anymore and how does this sequence of you know different processes that change in the sequence with climate change differ between climate zones and this is a question that we are trying to address in a in a project that just started about a year ago and this project is part of the larger research consortium which is called earth shape it’s a german chilean research initiative that aims at looking at how microorganisms animals and plants so biota influences the shape and development of earth of the earth surfaces and a shape as well it’s making use of the steep climate gradient along the chilean margin to look at the influence of biota on the earth’s surface and the project that we have within this you know bigger research framework is called the seco cheetah project and that includes the coupled vegetation weathering erosion and sediment export response to climate change and we take a bunch of relatively novel proxies to constrain these so pis are helen whitman the ducks and patrick frings from the gfc potsdam and myself and then we have two very talented phd students that is charlotte lloyd lee down here and nestor gaviria who are taking up this challenge and the philosophy behind this project is such as we know that precipitation is changing from the lgm to the holocene over the glacial and what we would like to constrain is how does the hydrology change afterwards which we constrained by delta deuterium in leaf waxes then we are interested in how the vegetation changes after that precipitation changes we would hypothesize that it takes a little bit of a lag time for the vegetation to change but not much and we um also measure a bunch of parameters in leaflex biomarkers to constrain this then we look at the change in chemical weathering by looking at lithium isotopes and we would hypothesize that chemical weathering changes after the vegetation change we will then look at erosion rates and paleolith locate using cosmogenic look lights and then we already constrained the sediment or the change of sediment export to the ocean so we really want to get at the sequence of processes that are happening here and this is a first glimpse of the types of data that charlotte and nestor are acquiring those days and i won’t go too much into the details of this these particular data i just want to show the concept of the study and they sampled soil and river sediment on shore and they also have a bunch of surface sediment cores offshore um that can be used to calibrate those novel proxies and then charlotte actually takes marine gravity core to look at the the sedimentary record from the last glacial maximum to present to really look at how this climate change evolved in in this particular course and in order to do this these proxies actually have to be calibrated in modern sediment along the margin and this is what’s shown here the proxy that i’m plotting here against latitude is the average chain length of n alkanes so this is the number of carbon atoms in um in n alkanes of hair plant so how many you know carbons are within this one compound and you can see that this particular proxy is actually most sensitive here in the north where we transition from the arid to a semi-arid site and then it becomes um sort of scattered and maybe a little a little bit less sensitive once we get into the humid area so we are looking at these types of proxy vessels that we thresholds that we can then apply to the paleo worker to really constrain what happened in terms of these surface processes in the past following the lgm to present climate change all right so the take-home points um just very generally are basically that the chile margin can be used as a natural laboratory to analyze the response of sediment routing systems to changing climatic and geomorphic boundary conditions and we can do that in space in the modern world and also back in time by tracing this past climate change

millennium-scale erosion rates and sediment flux show the response of a transient landscapes a landscape whereas the million million sediment flux generally increases with the modern day precipitation gradient and during the holocene the river sediment input and shelf bottom currents control the sediments applied to the continental slope and trench and that’s really the interplay of the two you need to have size sediment input but you also need those undercurrents in order to increase your sedimentation weights on the continental slope the glacial climate change is reliably reserved in marine sediment archives on the continental slope and that is true for a wide range of climate zones so all the study sites that we tested show that same thing however the geomorphology of the onshore catchment plays a very important role in this type of signal propagation and distinct geomorphic processes can result in the same stereographic pattern so need to watch out which geomorphic process you actually want to invert from your sedimentary record all right and with this i will leave you with this beautiful image here from the bob river mouth that discharges sediment directly into the big bob or canyon that gets funneled towards the trencher and i’m very happy to take your questions. fantastic thank you very much anna and so let’s see if from the audience if any question you know tom bianchi left a message a question he has he has to leave earlier for another meeting so anna could you click the chat and see the question read the question yeah wait i i have to ah here’s the chat okay so there’s a question from reemail do you think lithology also could have some control on the sediment flux variation in the study area yes i i think there’s definitely a lithology control we do not have a good idea on how in terms of you know quantification how the lithology controls sediment flux if you look at the nature and the texture of the sediment offshore you can definitely see the in the um the influence of the of the catchment pathologies so in the north it’s mostly plutonic rocks also from the coastal coral that provides sediment for this for this area so you see um higher grain sizes if there is any coarse grained sediment because there’s quartz in those plutonic works and feldspar as well whereas in the south there’s active volcanism going on right because the subduction um the subduction angle is still um is deeper down there you can actually melt the crust and have active volcanism so we see a whole we see generally finer grain sizes and higher amounts of mud in there because we can make those volcanic and acidic rocks preferably whether into finer grain sizes and they don’t form um a whole lot of sand really so yes that would be the short answer i guess okay anna could you also see that the up one tom bianchi one oh there’s there’s one more down here he asked you know in addition to the in addition to glacial lakes how about the florjd also contribute to the buffering effect and how important earthquake earthquakes  0 in contributing to turbidites yes um so this is this is a very good um a question that equally two questions in one right and so i haven’t um talked much about the fjord area at all um um do you still see my screen noah yes oh okay and let me enhance this gave me a funny message here um so if you look at the coastline down in here and i remember our southernmost study site was somewhere in here but um if we go down here you can see that this entire coastline is heavily influenced by glaciation um during the last glacial maximum and earlier you can still see the remnants of the ice sheet here the southern patagonian ice sheets that are used to carve it are you sharing your screen oh okay let’s see it gave me a several minutes so i wasn’t sure um

here we go are you seeing it now yes great so again our study area we saw the most study was somewhere in here but then um this region is highly influenced by glaciation from the remnants of the ice sheet down here and so there’s a bunch of fjords and of course much of the sediment here is trapped in those fjords so if you actually look at the the trench full volume as you go further down to the south the volume actually decreases again i didn’t show that to you because it wasn’t the focus of the study but the trench volume actually goes back down and that is because a lot of the sediment actually stays within those uh within those fjords so there’s definitely a um influence of that and then i have to look up the the second question here because my chat window is gone could you go ahead and ask your question yes can you hear me yes uh hi hi great talk thank you um can you explain a little bit more about the long long shore along margin currents how they uh contribute because it’s um the the margin is quite a narrow and um i i don’t really understand if the sediments arrive into the margin and then they go from one region with one climate to to the other how how it affects the sedimentation um well we also don’t actually know that unfortunately um so what we need in order to constrain this better would be more high resolution bathymetry on the shelf however the dataset i showed you is the only one we have it was shot after the 2008 mauler earthquake in that region to see if there’s fault ruptures on the shelf and so the only thing that we do have is measurements out there so adcp measurements that show that the undercurrent is actually flowing along the outer shelf towards the south and we see the response of the loose sediment on the outer shelf so what we think is happening is that there’s those big sediment plumes that i showed at the beginning that um that hemipelagically distribute sediment over the shelf and then that gets reshaped by this current the amount we don’t actually know um we you know it’s quite logical that the influence should get less towards the north just because the shelf is not very very white so there’s not much sediment to be retransported here but in the south it should be quite significant we also know that the gunter undercurrent that’s name of that current um flows um quite a long ways until you know the southern part of southern chile as well so we think it has an influence but we can’t quantify it without that type of data but it seems like because sedimentation rates are so high on the continental slope that up to almost 6 meter meters during the holocene per 6 meters per thousand years um this is really high so you need a process that um that gets it down there and the connection of submarine canyons and rivets like the biobio canyon that i showed this is just an explanation for how you get sediment into the trench but not onto the small basins in the continental slope so we think it’s important however we can quantify it due to the lack of data which i guess is always the problem okay conduction yeah wonderful and i have a couple questions could you move to the slide maybe the last slide to show the Biobio river the the canyon yeah also the very last one uh yeah so oh yeah i might have to exit this because it’s going to take too long good too so yes this one so my question is this is on the shelf in the shelf right yes so how deep of that canyon cut down here here on the shelf um i i don’t we have a paper about it i would actually need to look this up but it’s several hundred meters i’m not sure if it no several hundred meters i’m not sure if actually it already cuts down to about a kilometer in this region but it does along its pathway so it’s really it’s a big big canyon it’s

if you were standing at the edge of it you would be um you would be thinking grand canyon wow and also the canyon head all the way extends almost connected to the estuary to the river mouse right yeah um it’s that has been shown so there’s we have a little bit of a data gap in here so we can but this is just a couple of hundred meters and but it seems like it actually goes all the way back onto the coast here so it must have incised quite a bit in the holocene as well you can see this um this other canyon head over here which is located at a water depth of minus 120 meters so this was connected to the coast during the last station maximum and when the the sea level was low and this was actually all this entire bay was land so this used to be connected but then this um continued eroding backwards towards the um the bobo or the the river mouth and if you look at the kenyan head very carefully in the higher resolution with symmetry you can also see that there is bed forms cyclic steps that um that are thought to be formed by turbidity currents so it seems like there’s a direct discharge of turbidity currents in terms of maybe hypycnal flows from the biobio into that river into the canyon because the you know the bed forms is very commonly to see in the monterey bay exactly this looks exactly the same wonderful so this is also just like the keys in in south western taiwan they called the gold pink canyon so the canyon had all the way connected to the river mouse so that’s a wonderful maybe future can do a comparison study so i think you know the gauping canyon is one of those crazy canyons because it receives so much sediment from this very steep slopes here the steep uh the slopes and shore are not that steep but um it seems to be enough to actually backward erode a canyon head and keep the connection of of the mouth so yeah these are very important canyons they’re not that many out there of this type but i think they are absolutely key in sediment transport towards the ocean during sea level high standard so you mentioned about the turbidity mainly around 15 000 years ago there’s a high peak 15 16 000 years ago so how about the modern day could is any morning sediment discharge to that subduction you know the trench do you have any evaluation any estimate how much those kind of riverine sediments reach to the trench you know the deep trench yeah so we don’t know in terms of quantities during the modern day the problem is that the trench uh the water depth at the trench is you know five six thousand meters deep and this is below the ccd so you dissolve foraminflora below this at this water depth which we use in order to date the sediment so we have severe trouble in dating sediment cores in the trench just because you dissolve all the carbon that we use for c14 dating it doesn’t work you know at least some more than i don’t know hundred years ago is any you know like at least Pb-210 able to i may be too slow i don’t know you know people do any sediment trap for the you know over there not that i know of that would be a very interesting thing to do and then 210 pb would would definitely be another option so there’s a study in this area onshore that determines sedimentation rates on the shelf which are quite high but the trench is still missing but i would absolutely love to do that it’s deep yeah i have more i have more question maybe we can ask you is uh you know uh after the meeting but okay i have two more questions from edilic edlic do you want to speak and leak could you i’m new to yourself and speak question is how the wheeze you know how wide of the canyon you know the one you just talk about yeah well this changes along the course of the canyon and um so it’s several hundred meters to even a kilometer wide um down down in here and then of course it’s less wide when when it comes to the uh to the coast so there is a 2015 paper in geomorphology where we show all the different the development of the width and the depth of the canyon

um along its entire pathway so if you’re interested in the in the numbers along its way you can look that up in that paper or email me so i can send you a copy if you like but it changes along the way a couple of hundred meters at the most at the most and the lake do you have more questions want to see at lake yeah uh can you hear me yes yeah i’m ethnic um yeah i have a i’m quite interested look at this canyon all right um i later posted an email the speaker and i request maybe for more information but another question i have is on the canyon floor do you see any kind of deep pool uh features not evidence of maybe some kind of turbulent very turbulent flow that create deep pools i don’t see any deep pools or scours that you you are referring to yeah yeah yes yeah yeah yeah so what we do see is um nick points in that you know that might retweet over a time so that would be an indication of flow but also those question shaped bed forms that paul mentioned before or cyclic steps that are pressure present in the canyon in the kenyan head indicate quite turbulent flow okay thank you so uh mr tang chung do you want to speak out your question go ahead champagne yeah i can also read the question um the question is the sediment flux to the ocean is much lower in the north semi arid and i wondered if most of the sediments were just accumulated in the continent such as the piedmont area so yeah that was one of the questions that we’re addressing in further research so if you look at if you quantify you know sediment storage just from remote sensing digital elevation models then it doesn’t seem like there’s a whole lot of sediment stored in there however this doesn’t answer your questions because we need to date that sediment in order to know how much sediment is stored during the holocene so we don’t actually know that yet however when you remember the geomorphology up there there’s over over longer timescales there’s just not many sediment things up up in there right there’s not no deep valley there are no big glacial lakes that actually can take up a whole lot of sediment however you can store a sediment of course in the river valleys and also on the hill slopes um that might just not be transported so in what we are testing in our new project is what’s actually responsible for um the decrease of sediment flux to the ocean during that climate change by looking at you know whether it’s really just transport capacity if the rivers cannot transport that loose sediment down there anymore or if it’s simply not produced because you also reduce chemical weathering and erosion during the aerification so we are still in the testing phase of this interesting thank you so uh anna you should you show a lot of high resolution for symmetry uh multi-beam data but you didn’t show uh much seismic or chirp, sparker you know that kind of a sequence stratigraphic profile is the still processing is some of your colleagues doing that part or um so there’s a bunch of high resolution echo sounding that was taken when the cores are um taken and they haven’t um shown that that’s correct but the problem is that for my purposes as i want to constrain the the sediment flux offshore it’s not very useful in the sense that you know the system is so open even if you constrain the sediment flux to one small into a slow basin you are not taking um all the un the other interslope basins into account so it’s very questionable how much the the analysis of of this actually tells you about the entire sediment budget the trench flow fill volumes are based on deeper you know multi-channel seismic reflection data but yes i haven’t shown that there is some but for the purposes of the studies that i presented it was just not very useful okay because the slope is so dissected and there’s so many little basins you could look at other other crazy crazy thought and so during the during the last maximum duriling the glacial time you know the big ice sheet mountain how much the death the deformation change that

could be pushed down among the land on shore part how much this deformation could change the sediment routing or even because the pressure coming down from you know the uplifting is any change the volcano earthquake activity i mean it’s just crazy i don’t know how much that kind of so in terms of earthquakes so one of the original um ideas for for this data set was to test whether we can re reconstruct past earthquakes um from from this particular from the turbidite record and it it turns out that there’s many big earthquakes for example in the northern study areas during the holocene during historical times so we have constrained on those but they don’t trigger termites so we cannot because there’s not not enough sediment delivered to the ocean margin so you cannot trigger a turbidite so you won’t you know you won’t get mass movement during doing earthquake shaking um so doesn’t um quite work work out well very well and um i guess what you are referring to in in your second part of the question is um the deformation that is caused by the subduction and how it determines the geomorphology is that correct not the subduction of course production can cause but during the glacial period the big ice load oh the i saw that possible push up down the the land portion you know i don’t know about that kind of geode aerodynamic deformation yes um absolutely so in in the um in the places that i looked at or that i showed you actually the that was just the northern tip of the the patagonian ice shield and even further north in the semi-arid study site there was very minor glaciation in the um in the andes so i have not quantified the ice volumes or the isostatic rebound that might come with a glacial melting however this process is most probably much more important in the south where the big fjords are and that huge patagonian ice shield actually reached all the way towards the coast of the pacific ocean so in this particular area that we are looked at we think it’s marginal uh it’s it’s not so important but in the south it will be very important as glaciation was massive down the end of your region very good the time flied very quickly thank you anna very very very much for this very interesting talk in that active chile margin i think that we have more questions we can discuss later and but once again so next week next wednesday steve kuehl and next friday rebecca all talk about the global river and the delta sediment and the carbon so please mark your calendar and come back and so thank you very much for today and i hope thank you anna thank you all the audience so still here so i hope you can have a great weekend