 I tagged on the last preposition to my title recently so I'm gonna talk about creating bioavailable isoscapes. So strontium isotopes are now, they now seem to be part of the archaeological toolkit, fairly sort of standard for determining local versus non-local humans, animals, and other materials. And so I'm gonna in this talk discuss some of the issues of concern in developing strontium isotope baselines by giving you an overview of some past and new and ongoing bioavailable strontium projects in Sub-Saharan Africa. But first I wanted to remind you of the factors that we have to consider when characterizing bioavailable strontium. I think most people are aware of these and they're out in the literature but they are still, we don't have solutions to them all of the time. So first and foremost geology can be a primary source of bioavailable strontium but is not always in some cases. And the isotope ratios of soil are often quite different than that of whole rock. Surface sediment movement can mean that strontium in plants don't actually, that doesn't actually come from the underlying bedrock. If you've done a bioavailable strontium study and you see lots of big places on your map that are called paternary alluvium, those can be problematic. And then of course you get strontium in the biosphere from different types of water and from, and you can get it from local dust or intercontinental dust. And then there's increasing evidence for the importance of marine derived strontium near coastlines and then modern fertilizer as well. So we still have some questions when we're creating bioavailable strontium maps. For example, for the empirical data, what materials should be sampled and at what density? I vote for plants but people do several different things. And how should that empirical data be extrapolated then across the unsampled areas of the landscape? Okay, so I have a couple of maps like this that I hope I'm not leaving out some studies. But from my quick look of the people I know in the literature, these are some published bioavailable strontium isotope studies from sub-Saharan Africa, which are all in South Africa. So let's see, so Celi et al. And there are other people that have done bits of strontium sort of studies in South Africa early on. So this was in the early 90s when strontium was was like in its infancy. So in the early studies, they basically would collect a sort of a handful of modern animals. And they had some whole rock values and would try to use that to interpret the archaeological materials from the Cape region. And then let's see, so a little square right there, that was a study done by Franz Radloff, who published it in 2010. So a study on the De Hoop Nature Reserve, where he was interested in just looking at the small area and he used basically, he looked at the geological map. And he took to heart the idea that bioavailable strontium is potentially best characterized by using modern animals. So he set out rodent traps and trapped 48 rodents from the different total from the different geologies. So I think we've learned through experience that that's a very sort of takes a lot of effort. But he was able to get his some results and basically then just plotted the range of the rodents from each of the different formations. And with the sort of simplistic, like interpretation, well, this is the range for that geology and since the bioavailable strontium range for that geology and so forth. Which works, I think if you're in a very small area, but you wouldn't want to extrapolate that out too far. We now know. But we took a similar approach, I have to say, in our 2011 paper, where we were doing studies at the cradle of humankind. And we basically looked at the geological map, which you see on the left there, and went out to collect plants from each of the different geological zones. We made sure that we got at least a few plants from each zone. And then basically, here's the different geological groups sort of used the range of values from those plants to say, well, here is the potential range of values for the dolomite. And that's how we interpreted local versus non local fossil hominins from these caves. So that was also, I wouldn't take this approach now because I think we know that it's not probably wise to extrapolate so much from just a few samples. And so then in the study that we published in 2016 from the south coast of South Africa, which was a much bigger area, I think we're moving in the right direction here because we decided to now take plant samples across a broader area and more evenly sampled over space with the idea of then incorporating it into GIS and using creaking to create a predictive model of strontium across the landscape. So this is a geological map showing the different geological zones. And this is the coastline. And this is the colors here represent the the isoscape that was produced by incorporating our data into a predictive map in GIS. And so that was useful because if we had sort of assumed that the different geologies had different ranges, we would have missed the fact that being close to the sea seems to be more important in determining the bioavailable strontium, far more important than geology, especially along the coastline, because basically no matter what geology you're on, if you're near the coast, then your samples are around that of seawater 0.7092. So that is some of the published studies. But the good news is that there are a number of new and ongoing studies taking place in sub-Saharan Africa. And I have plotted the ones that I am aware of on the map here. Let me know if there are some that are not up here. So first, I'm going to talk about this one right here, which is basically an expansion of the one that I just talked about. So Andrew Zipkin and Eric Fisher and colleagues are expanded the study that we were doing on the south coast. And it's not published yet, but they're working on it. So basically, this is what we had sampled before. Now they've expanded the sampling of plants up into the Great Karoo. And this is an interesting plot that's basically going from south to north, so from sea inland. So you can see here how the effects that we found were close to the coast, you have sea-like values. But then, of course, once you get further inland, there's no more evidence of that marine input. And it's presumably more of a reflection of the geology. It's unfortunate for us wanting to interpret artifacts in the coast, because these values are very similar to most of those values. Okay, so back to this sort of summary map. So Andrew Zipkin and colleagues are also doing studies in Namibia and Botswana. And then there's a study going on Mackie and Ames near the Cape Town area. And those are the impetus for those studies is to try to understand the origin of ostrich excel beads, which are common artifacts in South Africa and are items that are known to be traded long distance for many thousands of years. And there are several other studies happening in the Karoo area of South Africa. This one, this large square, Brian Stewart and colleagues. So their area of interest, the main focus of interest is the Lesotho area. And so from that place, they are collecting plants and soils to create a sort of dense bio bioavailable map. But they've also are using museum specimens of animals from known locations to make to try to expand their bioavailable map to a much broader area. And so it'll be really interesting to see the results of that study, which is about to be submitted for publication. Oops. And all right, so I wanted to move quickly up to Uganda, where Marion Hamilton, who finished her PhD last year from New Mexico, is doing a bioavailable strontium study that's very different than the others, because she is, well, she's taken a lot of plant samples and other sort of samples. And she's comparing different habitats. But most interestingly, she also has the modern primates from Uganda, including chimpanzees. And so she's doing a study of how the strontium and the different primates relates to that of the different habitats and whether if and how strontium isotopes can capture sex dispersal. And she has two papers in review right now. So hopefully we'll see that soon. And then finally, the bigger square in East Africa is a study that is about to be submitted for publication as well. And Annika Janssen is the first author. And so she has brought together research that several people have been doing in East Africa over the past decade, including myself, had never gotten around to publishing our samples. So she's brought them all together to make a strontium bioavailable map for East Africa, which is, and so the samples that come from Northern Tanzania and Kenya include plants, soils, owl roost rodents, and animals. And the one of the co-authors is Clement Bataille, who has done a lot of the modeling in Europe. So he's applying the similar techniques where using GIS and forest regression modeling basically create a nice escape for East Africa. And again, for example, in the Serengeti, you have, even though you have ancient sort of geologies with really high strontium isotope values, those get swamped by the recent volcanics that sort of have a westward tending blow from where they rocked. So the point is that samples that are on really ancient bedrock that you might think would have high strontium isotope values actually have really low strontium isotope values because of the volcanic ash that swamps the bioavailable strontium. So that is the closest thing we have, I think in Africa, to some of the nice maps that are being developed in Europe and the UK. And hopefully we are, so we have that now for East Africa and working together with everybody in South Africa, we're trying to build a model like that as well. And I would like to thank my colleagues and friends.