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Interview 2:00 - 9:58 Play 2:00 - More
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Tony Coates, Jeremy Jackson  

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Geology; Paleoecology; Recorded 26 of March, 1995  

Environmental Recording 12:46 - 26:00 Play 12:46 - More
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Village ambi  

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Time of Day: 0620; Geology; Paleoecology  

Interview 37:58 - 1:00:05 Play 37:58 - More
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Tony Coates, Jeremy Jackson  

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Geology; Paleoecology  

Environmental Recording 1:02:01 - 1:04:12 Play 1:02:01 - More
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Quiet river ambi  

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NPR/NGS Radio Expeditions
27 Mar 1995

    Geography
  • Panama
    Darién
    Locality
  • Union Choco
    Latitude/Longitude
  • 8.13809   -77.61566
    Habitats
  • River
    Channels
  • Stereo
    Sampling Rate
  • 48kHz
    Bit Depth
  • 16-bit
    Recorders
  • SONY TCD-D7
    Microphones
  • Sennheiser MKH 30
  • Sennheiser MKH 40
    Accessories
    Equipment Note
  • Stereo=1; Decoded MS stereo; Sennheiser MKH40 Cardioid Mid Mic and MKH30 Bidirectional Side Mic

NPR/National Geographic
RADIO EXPEDITIONS
Panama - Dar1en
DAT #6 -AX

41:49 -58:40 AC: Could I ask you again about biodiversity and the Isthmus? and the things that bring you to this river.
*JJ: What we are trying to see is how the diversity of shallow marine environments in tropical America changed through time, knowing in advance that there is at least one major event that must have disturbed the general pattern and that's the separation of what was once one continuous and probably fairly environmentally homogenous system into two rather different systems. Here we are actually looking at material that was deposited in a channel -in a sea passage between the islands that were forming, the isthmus, that eventually became Pacific, but really at that time they were neither Pacific or Atlantic, but isthmian archipelago deposits...So, what we are looking to see is how that fauna changed, how diversity changed, how the nature of the organisms changed through time...Our primary focus in the beginning was to say that the pivotal event must have bee the formation of the barrier... Indeed the barrier did have a very significant effect in isolating the biotas, and contributing to environmental differences on either side with an increase in the total number of species, because there were now two oceans instead of one...Aside from that the -at least in many groups of organisms -the changes were not as great as we expected, and the real surprise in our work was the discovery that the most dramatic changes we preserved were rather quick and post-dated the final closure of the isthmus by at least one million years. So one the one hand it's gone as expected if some what less of a change than anticipated, on the other hand, very much a surprise. These units are very important for what we are trying to do, because they document the nature of the biota that was living around this archipelago that was slowly developing into a barrier, and therefore represent a genuinely isthmian fauna, that presumably should have been more or less the same, be it on the Caribbean or the Pacific side of this chain of islands much like the Aleutian Arc, or the whole -the Lesser Antilles, or the Indonesian Archipelago -a string of islands with good marine communication across them but clearly a developing barrier.

JJ 45:08 So what we - if we were in slightly younger material than we would expect to say it has a more Pacific signature or a more Caribbean signature. But this material is probably old enough that it would simply have a isthmian signature, and it wouldn't make much difference whether you were on the Caribbean or the Pacific side, and ... up in Bocus del Toro, in the western end of Panama, where we know a lot more what we are talking about than here where we are still groping, that's indeed true, the faunas from the late Miocene, roughly 5 -7 million years ago, even into the early Pliocene just after that are really quite similar on opposite sides. Although there's already signs of divergence. You get into the late Pliocene 3 million years ago and younger, and there is just no question. You look at it and say this Caribbean, this is Pacific in its general nature. But still those changes are not so great in mollusks until the big turn over event that occurred 2 million years ago.

TC 46:17 But there is another group of organisms that have in fact covered quite different pattern. For example our colleague Laurie Collins who works on these tiny calcified single-celled animals, foraminifera, that live in the bottom of the sea. She notices well before the isthmus is finally closed but during the time it's a growing submarine sill that she is getting differential extinction and occurrence of species that are becoming more associated with carbonate -limestone -or perhaps reef environments. She notices that perhaps 5, 6, 7 million years ago and yet -I think I am right in saying Jeremy -that her groups go through your turn over with very little effect.

JJ 47:09 We don't really know because she only studied the common species, and so we have no idea whether or not there was evolutionary consequences for rare forms. She studied the most abundant, universally distributed form.
TC 47:21 But they do not turn -
JJ 47:23 They don't show much of an effect at all. But for example coral reefs which are presumably the source of much of the carbonate, they don't develop -really flourish and increase in the Caribbean until rather later than her foram (foraminifera ?) seem to indicate the same thing. SO clearly our discussion here is a reflection of the fact that we are groping towards a picture for each of these different groups being obtained by different specialists...The grand synthesis of it all is probably about five years away when we actually have real confidence in the patterns of for the different groups, and we can say, ok what does this group show versus that. After all, there is no reason to expect that every group of organisms would respond in the same kind of way to the same event. It might be the case, and it might not be. And because we all have collected our data -even with our attempts at standardization in this project -we have still gone about the analysis of our data in rather different ways. And now that we have come to realize that we're going to have to knock our heads together and say let's standardize even more to try to say --I am doing that with Ann Bud, who works on coral reefs in the Caribbean...We are trying to go back and look at the ways that we divided up faunas over time to ask whether or not an apparent discrepancy in the timing of this evolutionary turn over between reef corals and mollusks is an artifact of the way we analyzed our data or is a real difference in the timing of an evolutionary event...That's something we can now resolve because Tony just went on a trip to refine the dating of the critical beds in Costa Rica that are key to our interpretation of this.
TC 49:07 But that different organisms that have different life histories -¬in other words different ways of growing, different ways of dispersing their larvae, etc., are going to respond differently to the same event -¬seem to have been born out in that paper that we did a few years ago, in which we compared the corals today on either side of the isthmus to say the bryozoa...There is not one single species of coral which is common to both sides of the isthmus now. Where as I think there are several, or many species -
JJ 49:38 Well, there are many putative species. They are clearly not the same, but they are so similar that the earlier taxonomists couldn't tell them apart. And that's absolutely correct. The relative amount of differentiation is very great indeed. But as we discussed yesterday the problem with interpreting the coral record as we have practically none for the Pacific side so we don't know when they disappeared, how they responded or what have you. The pattern certainly holds that you can look at different groups of organisms on opposite sides of the isthmus and see in some cases very similar biotas, and in other cases entirely different biotas. Putting that into context and explaining it, is still very much controversial.
*TC 50:28 See the isthmus is strikingly asymmetrical geologically. It's as if you've got two different geological worlds on either side. These would normally be separated by quite a wide continent in other situations. But here you've got the Pacific plate --actually two plates --going down underneath the Caribbean plate. That's a tectonically very active zone. It depresses the crust of the oceans several thousand meters down into the ocean. It's highly seismic there's sediment pouring in huge thicknesses into that trench in a set of sedimentary environments that are continuously active and extremely rapid in their processes, and that's not a good place for the -say coral reefs to establish themselves. Whereas on the Caribbean side it's what we would call the trailing -or the passive margin -and its got a sloping continental shelf that goes out into the sea. It doesn't have the ferocious sort of seismic activity and volcanic activity that the Pacific side has.
AC 51:42 Does the Pacific side actually have enough -is it active enough so that a coral reef .... what would be the life of a coral reef it's not going to exceed a thousand years, is it?
JJ 51:54 Coral reefs -the life time of coral reefs is a function of the rate of change of sea level. Coral reefs, the last few million years, have been relatively short lived, because sea level has bounced up and down like a yo-yo. So reefs get left high and dry or they get drowned by rapid rise of sea level in times of much slower fluctuation in sea level reefs, not the individual corals that make them but reefs, almost certainly persisted for much longer periods of time. Hundreds of thousands of years rather than ten thousand years. But what Tony is saying is that geologically an environment with mountains of sediment being eroded off at very high rates and dumped into the coastal environment means that the immediate environment of the coast line is inhospitable for reefs regardless of any other ways that oceanic conditions might have changed due to upwelling and the things we were talking about before. So, it's very possible that since -first of all it's a bad record because much of it has been dragged under the crust and a very destructive area but it's also true that is inhospitable to coral reefs just because of the amount of sediment being dumped in and whatever. there are large areas of Indonesia with in the rich tropical western Pacific area with the highest diversity of corals in the world that have rather poor coral reef development when they are adjacent to very large amounts of sediment being eroded off the mountains and dumped into the coast. Those are areas of great development of mangroves, but not as great development of coral reefs. So you can imagine therefore that just because the geology is different on the opposite sides we could have an absence of coral reefs, and that would have nothing to do with all these other things we have been talking about of diverging oceanographic conditions. Corals are sensitive to that. Mollusks are not. Therefore, the fact that mollusks are much more similar on opposite sides of the isthmus than corals maybe simply due to that difference in the immediate geological environment and may not have a more pervasive oceanographic explanation. To separate out those different factors we need to go to go to places where we don't have the great inundation of sediment, and simply have the oceanographic conditions effecting it -like the Gulf of California, perhaps -
TC 54:29 Or a good example, even with in the Caribbean is the fact that you have no reefs from Florida to Vera Cruz in Mexico because of the Mississippi come pouring sediment into the Gulf of Mexico, and so that geologically would be a facies (?) change -a change in the environment ¬and clearly the Caribbean in many other areas is perfectly suited to growth of coral. It's just the geological set of circumstances in that place prohibits them.
JJ 54:55 And that's the issue of replication. If you're only measure of modern Caribbean environments was from the coastal plane of Texas of Louisiana, you would say -oh this was a time that was inhospitable to coral reefs. In spite of the fact in just a thousand kilometers to the south in the Yucatan Peninsula, are some of the greatest development of coral reefs in the Caribbean. That's why this issue of replication on a geographic scale is absolutely critical to any sense of how biotas change through time.
TC 55:31 Now having said that, it may well be in addition to that, that reefs even were the Pacific margin stable. They might not be able to grow because there is a twenty foot tidal range, or because the Pacific is very high in nutrients. So there are many different factors that can contribute to whether or not the organism is present, other than whether they can live in that ocean.
JJ 55:54 But this is resolvable. Now that we have established the frame work that says there is a record of life in the sea over this period of time -hey folks, you can come and study it. Now we are in the position of attracting the isotope chemists and the geochemists and paleo-oceanographers who have the skills that we don't have, to try and unravel exactly these different variables and questions that Tony is enumerating. So it's not hopeless and all arm waving. We do stand a chance now in this second phase of this research of reconstructing environmental conditions in a much more sophisticated way than we two personally are capable of doing, and thereby having an independent set of data to our biological data that will be able to compare to ask whether or not any changes that they may observe paleo-oceanagraphically correspond in an intelligible way to the biotic changes, the changes in diversity and ecological composition that we're documenting, and of course that independence of the sources of data is crucial...We will be in that position I would guess in about five or ten years.
TC 57:14 A good example of that is we're getting closer to the point with say the benthic foraminifera we can make estimates of depths of oceans on either side of the isthmus for several time slices up through the completion of the barrier. We could therefore give each of those three dimensional reconstructions of the sill when it was a thousand meters, a hundred and fifty meters and at fifty meters, and give it to a physical oceanographer to model ...Then the physical oceanographer can tell us what kinds of tidal patterns would be flowing through the -

JJ 57:52 what kind of upwelling regimes (1) would necessarily exist, etc., and then we can go back and collect animals for isotopic analysis of the shells and then those geochemists can do that kind of work and so on, and so on, and so on, as a feed back process between us. But we are really just at the beginning of the exponential phase of having demonstrated that the system is tractable. That there is enough of a record preserves, and there is enough of a biota preserved in it to attract the attention of all of these different people. Now they now its worth their while to do the extraordinarily expensive chemical analyses, and time consuming analyses to do that kind of work properly because there is a chance in getting something out of it for them.

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