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This UCSD-TV program is presented by University of California Television.
Dr. Eric Sperling explores how historical oxygen level changes shaped ocean life evolution and adaptation over geological time.
Key Takeaways
- Oxygen levels have fluctuated dramatically throughout Earth's history, profoundly affecting marine evolution.
- The Great Oxidation Event was a pivotal moment that introduced atmospheric oxygen about 2.4 billion years ago.
- Modern ocean oxygen minimum zones provide insight into how low oxygen environments influence species adaptation.
- Geological and chemical evidence helps reconstruct past oxygen conditions and their evolutionary consequences.
- Understanding past oxygen changes is crucial for predicting future ocean health under global change.
Summary
- Dr. Eric Sperling, a postdoctoral researcher at Scripps Institution of Oceanography, presents on the impact of oxygen on evolution and adaptation in ocean life.
- The talk covers the history of atmospheric and oceanic oxygen changes over billions of years, including the Great Oxidation Event around 2.4 billion years ago.
- Oxygen levels in Earth's past varied significantly, influencing the evolution and survival of marine species.
- Geological evidence such as iron formations and redox-sensitive minerals like pyrite are used to infer past oxygen conditions.
- The presentation highlights how low oxygen events, such as fish kills, demonstrate oxygen's critical role in marine life sustainability.
- Dr. Sperling connects ancient oxygen fluctuations to modern oxygen minimum zones in oceans to understand evolutionary impacts.
- The talk discusses the timing of major evolutionary events, such as the rise of dinosaurs and humans, in the context of oxygen availability.
- Future implications of oxygen changes for ocean health amid global environmental changes are considered.
- The speaker’s background includes degrees from Stanford and Yale, postdoctoral research at Harvard and Scripps, and an upcoming professorship at Stanford.
- The presentation is part of the Jeffrey B. Graham Perspectives on Ocean Science speaker series at the Birch Aquarium, UC San Diego.
Full Transcript — Download SRT & Markdown
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ocean science speaker series my name is Cheryl peach and I'm a project scientist here at the Birch Aquarium Scripps Institution of Oceanography UC San Diego it's my great pleasure this evening to introduce our speaker dr. Eric Sperling Eric is with us here today as a
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paleontology and then wanting to be sure that he rounded out his academic training his professional training at the finest institutions he did a postdoc at Harvard and then his second and current postdoc here at Scripps Institution of Oceanography UC San Diego
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Welcome to the Birch Aquarium at Scripps and the Jeffrey B. Graham Perspectives on Ocean Science speaker series. My name is Cheryl Peach, and I'm a project scientist here at the Birch Aquarium, Scripps Institution of Oceanography, UC San Diego.
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expertise is in paleontology and Eric uses earth history to incorporate data from modern oceans and modern oxygen minimum zone x' to increase our understanding of how oxygen excuse me of how oxygen changes in oxygen levels can influence evolution both in the past and
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It's my great pleasure this evening to introduce our speaker, Dr. Eric Sperling. Eric is with us here today as a postdoctoral researcher at Scripps Institution of Oceanography, but he began his career as a scientist and a geologist at Stanford University, where he received his bachelor's degree.
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here all right well thank you all for for being here it's really great to have opportunity to talk and thanks for the organizers for inviting me you've all been staring at this fairly gruesome image for some time now as the talk got
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He subsequently attended Yale University, where he received a doctorate in geology with a specialization and emphasis in paleontology.
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we'll die I've been interested academically in the interaction between oxygen and evolution for quite some time but apparently I've been interested in oxygen for much longer so my parents just recounted this story to me last week this is me in the middle and we're
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Then, wanting to be sure that he rounded out his academic training, his professional training at the finest institutions, he did a postdoc at Harvard and then his second and current postdoc here at Scripps Institution of Oceanography, UC San Diego.
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and I filled it full of air in the trail lab which apparently just meant I closed it and then I threw my backpack so if we got up too high and there wasn't enough oxygen I have an emergency supply of air
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It's also my great pleasure to announce that Eric will be taking up his first formal professorship position at Stanford University this fall, so we're really quite pleased for Eric and his wonderful career thus far. As I said, his
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talk I'll be talking about how oxygen levels in the atmosphere and ocean the earth system have changed in the geological past and how these changes have influenced the course of evolution of life on Earth and finally I'll be
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expertise is in paleontology, and Eric uses earth history to incorporate data from modern oceans and modern oxygen minimum zones to increase our understanding of how oxygen—excuse me—of how oxygen changes in oxygen levels can influence evolution both in the past and
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we're going to be talking about a lot of ancient times and ancient oceans and parts of the geological timescale that most people probably won't be familiar with so I'm going to keep returning to this image into the geological time
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also possibly in the future. So please join me in a warm welcome for Dr. Eric Sperling and his talk titled "Breathless Through Time: How Oxygen Can Alter Evolution and Adaptation of Life in the Ocean." Eric, thank you very much for being
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we call percentage of P Al which is just present atmospheric levels so this 100 here represents the present levels so basically three main stages to the evolution of the Earth's atmosphere component the first stage in early part of Earth's history the atmospheres and
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here.
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event during this middle part of Earth's history atmospheric oxygen is thought to have remained relatively low and steady about 1 to 10 percent of present levels and then Auction rose to essentially modern levels about 600 million years ago and kind of fluctuated around that
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All right, well, thank you all for being here. It's really great to have the opportunity to talk, and thanks to the organizers for inviting me. You've all been staring at this fairly gruesome image for some time now as the talk got
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Canada about 4 billion years ago now the things we think about is old in the geological record typically things like the dinosaurs they actually occur right here so geological time is incredibly long and geologists have a metaphor that
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started, and I chose it. It's a fish kill from Redondo Beach Harbor that was probably caused or influenced by low oxygen, to illustrate the simple fact that animals need oxygen. It's our most fundamental requirement, and without it,
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around late February the dinosaurs don't show up to the very end of the year they show up around December 12th and they only exist for about two weeks before going extinct right after Christmas December 26th the earliest humans don't
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we'll die. I've been interested academically in the interaction between oxygen and evolution for quite some time, but apparently, I've been interested in oxygen for much longer. So my parents just recounted this story to me last week. This is me in the middle, and we're
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history about oxygen and evolution during these fairly long stretches of geological time that most people don't generally think about the first story will be the great oxidation event and the origin of atmospheric oxygen about 2.4 billion years ago then we'll talk
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on a hike. I grew up near Seattle, and we're on a hike into the mountains outside Seattle, and I was really worried. Somehow, I had heard that the air up at higher elevations had less oxygen in it, so I took a water bottle like this
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about the future of our oceans so we'll start first with the great oxidation event about 2.4 billion years ago now we know from a number of lines of geological evidence that the oceans of this time period contain no oxygen
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and I filled it full of air in the trail lab, which apparently just meant I closed it, and then I threw my backpack. So if we got up too high and there wasn't enough oxygen, I had an emergency supply of air.
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precipitated from the waterfall and if there had been any oxygen present this reduced iron would have just precipitated out and not be present now all these are interesting from a geological perspective they're more important to human history in the growth
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From well back. Now, I didn't need oxygen up at 4,000 feet elevation, but what this does illustrate is that oxygen levels vary throughout the earth, and they influence where and what kind of species can live in certain places. So in today's
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their modern expansion similarly its Precambrian iron formations a little younger in this case from the upper mid continent of the US which is provided all the iron for the steel for the Detroit iron makers so these old ancient
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talk, I'll be talking about how oxygen levels in the atmosphere and ocean, the earth system, have changed in the geological past and how these changes have influenced the course of evolution of life on Earth. And finally, I'll be
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important are what we call redox sensitive final grades so just pyrite or fool's gold and what we see is if we look at this chemical equation if there's any oxygen present pyrite is going to oxidize and disappear so basically in
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concluding the talk by talking about the implications of these ancient oxygen changes for the health of our future oceans undergoing global change. So this slide sums up what geologists think we know about the history of atmospheric oxygen on Earth, and today
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with all these rounded rocks little cobbles which indicates these sediments have transported a long way now if we look at the distribution of these through earth history what we see is that these detrital pyrites only appear before 2.4 billion years ago and after
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we're going to be talking about a lot of ancient times and ancient oceans and parts of the geological timescale that most people probably won't be familiar with, so I'm going to keep returning to this image, into the geological time
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that's just the oxidized iron and soils it's occurring under an oxidized atmosphere so 2.4 billion years ago is the time when we know that Auction first started becoming present in the atmospheres of oceans but now the question is if auction is present in the
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scale, at several points throughout the talk in order to reorient you. Basically, what this shows is this is a geological time scale from present back to about 4.5 billion years ago, and this axis is the atmospheric oxygen and what
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is created through photosynthesis and in this process phytoplankton or algae take co2 light and nutrients like nitrate and phosphate and cruise this to create organic matter and oxygen the surface of the oceans are what we call equilibrium with the atmosphere so this auction goes
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we call percentage of PAL, which is just present atmospheric levels. So this 100 here represents the present levels. So basically, three main stages to the evolution of the Earth's atmosphere component. The first stage, in the early part of Earth's history, the atmospheres and
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below this that oxygenated water can't penetrate and mix in so what happens is that these phytoplankton after they die they sink down and once they've sunk down below the mixed layer they start to decompose they do this through the process of respiration
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oceans contain basically no oxygen. That's what we call anoxic oxygen levels. Then, oxygen rose orders of magnitude but still to relatively low levels compared to the modern at about 2.4 billion years ago. This is what we call the Great Oxidation
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basically this decomposition of the organic matter is going to occur at the expense of oxygen so if we look at a graph of oxygen levels in the ocean with respect to depth we see they start out high in constant through the mix layer
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Event. During this middle part of Earth's history, atmospheric oxygen is thought to have remained relatively low and steady, about 1 to 10 percent of present levels, and then oxygen rose to essentially modern levels about 600 million years ago and kind of fluctuated around that
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a number of different levers that we can play with in order to get low oxygen in the oceans one of the easiest is simply to just have lower levels of atmospheric oxygen that you're mixing in this is particularly relevant for that middle
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level ever since. So let's zoom in here on this geological time scale again from 0 to 4.6 billion years ago, which coincidentally is the age of Earth's formation. The oldest rocks we have present on Earth are up in northwestern
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physical mixing process itself if we can create kind of density layers that make it physically harder to mix we can make it harder for that oxygen to mix in and replenish the levels that are lost to respiration and the final way and
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Canada about 4 billion years ago. Now, the things we think about as old in the geological record, typically things like the dinosaurs, they actually occur right here. So geological time is incredibly long, and geologists have a metaphor that
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can get more phytoplankton growth there will be more organic matter sinking down a board in opposition so we look now where we see these are processes occurring in the modern ocean that nutrient one occurs oftentimes an upwelling margin such as the California
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we try to use to explain the stretch of geological time, and what we do is we say we're going to compress this entire 4.6 billion years of history into one calendar year. So in this calendar year, these oldest rocks show up sometime
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deep water then rises back up to the surface to take the place of that water that's moved offshore and these nutrients feel that extra primary productivity and so if we look at a map of oxygen against depth this is at 250
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around late February. The dinosaurs don't show up to the very end of the year. They show up around December 12th, and they only exist for about two weeks before going extinct right after Christmas, December 26th. The earliest humans don't
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in the Indian Ocean well that's a natural process this also occurs in the modern ocean due to human influences if you just dump a lot of nutrients in you're going to get increased phytoplankton growth what we call eutrophication and a decrease in oxygen
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appear until New Year's Eve, specifically 11:48 p.m., and Stonehenge was built about 30 seconds before the ball dropped. So during today's talk, we're going to be talking about three different stories, some of the best stories in Earth
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levels are dropping almost to zero now this is a major problem worldwide and it's happening coastal and estuary systems all around the world basically anywhere there's a lot of people in a lot of agriculture and a lot of excess
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history about oxygen and evolution during these fairly long stretches of geological time that most people don't generally think about. The first story will be the Great Oxidation Event and the origin of atmospheric oxygen about 2.4 billion years ago. Then we'll talk
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estuaries or places like the Black Sea where it's harder to mix in so anytime you have a density difference due to temperature differences or salinity differences can be hard to physically mix the system and bring that new oxygen
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about the Cambrian radiation and the origin of animals in the fossil record at about 540 million years ago, and finally the Permian-Triassic mass extinction, when almost all life in the oceans went extinct about 250 million years ago. And finally, we'll be talking
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color of a rock if you see a really black black rock like this dark shale chances are it has of organic matter in it that organic matter has been fueling excessive decomposition and resulted in well auction and it's no coincidence that
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about the future of our oceans. So we'll start first with the Great Oxidation Event about 2.4 billion years ago. Now, we know from a number of lines of geological evidence that the oceans of this time period contained no oxygen.
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grapdelites that only live in the upper layers of the water column so if you see a rock like this one which only has fossils that are living in the upper water column and nothing living on the sea floor the benthos you can infer that
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One of the most striking ways we know this are these banded iron formations, such as this one, the Brockman Iron Formation in Western Australia. And what these are are simply reduced iron that is just rained out and
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that the level of oxygen can correlate with how diversify is present so as you go down an oxygen you lose these big forms you lose diversity and ultimately you're often left with just a single single species that can tolerate those
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precipitated from the water. And if there had been any oxygen present, this reduced iron would have just precipitated out and not be present. Now, all these are interesting from a geological perspective. They're more important to human history in the growth
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where it's basically just one bivalve species chloride that can tolerate tolerate the conditions it's not just the body fossils though that can be used to tell us about ancient all oxygen levels animals also burrow through the sediments and leave traces of their
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of our industrialized society. So this is a photo I took at Tom Price mine in Western Australia, where they're mining the Brockman Iron Formation, and it's this iron that's being used, shipped off to China to build the steel for much of
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plenty of oxygen in contrast rocks deposited underneath low to absent oxygen conditions have this perfectly flat laminated appearance with no disturbance to the laminations and finally they're geochemical methods to reckon or hypoxia I don't want you to freak out
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their modern expansion. Similarly, it's Precambrian iron formations a little younger, in this case from the upper mid-continent of the US, which has provided all the iron for the steel for the Detroit iron makers. So these old ancient
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colleagues this is a nice black shale that's overlaying by this grey shale that has all these trace fossils and that's what all these little squiggly lines are supposed to represent and you can see that the black shale is enriched
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iron formations are basically where our iron for steel comes from. But now, it's not just the oceans that were anoxic at this time; it's also the atmosphere. We know this again through many sour—
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details just to note that we do have geochemical fingerprints of low oxygen conditions also so with this background an oxygen in the modern ocean and how we recognize it in the ancient oceans we can now move to our second story the
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Cambrian radiation and this is the time period where the first big complex fossils show up in the fossil record my colleagues at work on the unicellular fossil record the fossil record of single-celled organisms will be a little insulted by this comment but there's
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basically nothing going on in the fossil record for billions of years of evolution and then suddenly at 540 million years we see animals for the first time first large things in the fossil record and the question is why
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and this is really one of the most perplexing things in evolutionary biology and in fact it really stumped Darwin and each suggested it was one of the prime challenges to his theory of evolution because the geologists at this
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time knew that all the fossils all the echinoderms that trilobite the bracket bones all showed up this one specific point in the rock record and there was nothing beneath it and Darwin who kind of believed in this slow and steady
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unfolding of evolution he thought this was a big problem so he writes in the Origin of Species there's another an allied difficulty which is much graver allude to the manner in which number of species of the same group suddenly appear in the lowest
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known fossil of first rocks now we've learned a tremendous amount about early animal level in the time since Darwin but the severity of the explosion the temporal time in which all these groups show up in the fossil record hasn't changed and
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goodness knows us not for lack of trying so just to illustrate this women talk a little bit about my fieldwork I'm fortunate enough to work up here in northwestern Canada in kind of this arcuate belt of rocks from the Alaska
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Yukon border down to British Columbia this is one of the most wild remote places still left in North America and it seemed very few geologists that have actually gone out look at these rocks so it's a great place to find new fossils
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so for instance last summer we flew into Whitehorse we drove down to Watson Lake which is a town of about a thousand people and it's mainly famous for its extensive signpost forest we then took a dirt road up here for about six hours
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and got into a little mining town called tungsten which has this little dirt airstrip and at this airstrip there's a helicopter then flew us out about an hour into the Mackenzie mountains dropped us off with full away unless
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just on this truly spectacular exposures of what's known to geologists as the Windermere supergroup which is this set of rocks that was deposited about in the two hundred million years before the Cambrian explosion it's a perfect place to find fossils if there were now most
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of our work out there is relatively basic it's mapping describing the sediments collecting samples that we bring back for geochemistry because it's hard to get money just purely for exploratory paleontology out there but you better believe it that we keep our
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eyes absolutely peeled when we're out there for any Precambrian animal fossils because if we did find any it'd be huge we'd be famous we're famous to like a certain subset of paleontologists but you know but year after year we go out
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to places like this where there having been geologists and we don't find any new fossils and there are other people going to every other unexplored Begg worldwide and not finding fossils this is just another picture of my colleague
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Justin Strauss that I do a lot of fieldwork up there and he's kind of forlornly looking at the middle member of the backbone ranges and hoping that there's going to be in nature paper worth of new Precambrian animal fossils
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in there but we've yet to find that in contrast you go just 40 million years earlier in the geological record into the Cambrian and there are fossils everywhere you go to any Cambrian deposit and you're probably going to
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find Shelly fossils like trial bites and brachiopods clams and so forth but what's truly spectacular the best record of the Cambrian explosion are in these places called Burgess Shale fat deposits and these are interesting because they not only preserve Shelly fossils but
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they preserve fossils with only soft parts as well the Burgess Shale itself is located here in British Columbia kind of on the British Columbia Alberta border and if you're ever up here in kind of the Calgary Banff Lake Louise
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area I would strongly suggest making a day trip to the Burgess Shale parts Canada and the Burgess Shale foundation do a fantastic job leading tours there I think it's one of the absolute coolest things you can do if you're interested
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in earth history and science this is our guide Tom a couple years ago and it's not just the science that's interesting here because the Burgess Shale is in one of the most beautiful and spectacular sites one could ever hope to find
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fossils in the world so you guys start this hike here down in the valley hike up here into the Alpine you have to take lunch at these kind of spectacular outcrops overlooking some amazing mountains and glaciers get up to the
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burgess shale itself and you're looking down on these amazing glacial lakes this is emerald lake and over again to some amazing glaciers and mountains and the great thing is there's fossils everywhere I should point out that this is kind of a hard hike this is about 14
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miles roundtrip with a decent amount of and gain but basically anyone can do it if you want hard enough this is my mom here in the Burgess Shale fire and she's in her late 60's so if she can do it I'm
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sure you can do it she's holding here what's a little brachiopod which is one of my favorite groups they have some spectacular examples in the Burgess Shale Brockie pods are a group of organisms which are related to and look
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like clams that have the same sort of bivalve shell but they actually evolve their shell independently this is a fantastic specimen of micro meet Mike micrometer showing these really nice seal spines there's also more familiar or organisms in the burgess shale for instance
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trilobite this is a little crustacean like organism called wap thea Pollock eat worms there's also some truly spectacular organisms that people still don't really understand like this opa binya which has five eyes on its head in kind of this
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law of grasping koala can reach out to grab organisms with so this is a artist reconstruction of the sea floor in the Burgess Shale what's what's truly interesting about the Cambrian radiation is not just the appearance of organisms
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in the fossil record but that basically every major animal phyla were made every major animal body planet we see in the modern ocean is present in the Burgess Shale so here's what's called it pre acted here's an arthropod that's that
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little crustacean wap dia there's a eat getting pulled out of its tube by this oppa binya with the five eyes on its head this is an early core date swimming around their sponges and bracket balls hanging off them there's basically every
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modern group but as I hopefully illustrated with our example of our work in Northwest Canada if you go just 40 or 50 million years earlier there's nothing there this graph just hopefully illustrates that a little more quantitatively what this is is just the
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cumulative appearance of every animal phyla in the fossil record in blue an animal class in yellow and you can think of these as just kind of bins the animal bins that texana must put animals in order to count diversity this is a
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geological time scale from 800 million years ago up to 450 million years ago with the Cambrian Cambrian boundary the stuff below that is known as the Precambrian Cambrian boundary right there what's really interesting about this is that what's shown here these arrows here
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point to the number of total living phyla and total living classes so what this illustrates is basically all the modern body plant diversity showed up in that first 20 or 30 million years of the Cambrian and the big question that is
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course is why did it happen and geologists have for decades related this causally to this second oxygen increase in Earth's oceans what happened which happened about the same time and so what people have suggested is that the rocks before or
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the oceans before the Precambrian simply didn't have enough option to enable large complex organisms to live in there and indeed if we look at the rocks we can see that so these are this is a picture of another my field areas up in
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northwestern Canada it's the Ogilvie mountains about 800 million years ago you can see that these rocks are jet-black and I've investigated the geochemistry of these pretty extensively and they show a clear low oxygen signal but another group of paleontologists
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have questioned this and they've said well I can understand why any recent auction would cause an increase of body size or perhaps a few more species but why would things evolve into this these vastly different body plans as different
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from each other as a Pollock eat and a mollusk if you just increase the auction levels so this famous painting or this amazing painting is Brueghel's big fish eat little fish and it's been used by Nick Butterfield in Cambridge to just
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talk so I've subsequently stolen it from them the next arguments relatively straightforward it's just a big fish eat little fish and in kind of in this ensuing struggle to either eat or be eaten animals develop these new body
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plans and morphological innovations to aid in this struggle and this makes a lot of sense what I found interesting in thinking about this is that the carnivore the act of an animal eating another animal what Nick's hypothesis is
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actually is a large cost of oxygen so there's the obvious one which is just this simply the energetic cost of capturing and subduing a print but there's a second cost which is a little less obvious it's what we think of as a
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food coma but in physiological terms its measured by the specific dynamic action it's the metabolic response to the company's meal of digestion and so when we hypothesized so is that if you're living in a low oxygen ocean it's going
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to be much easier to be something like a deposit feeder or filter feeder something I can kind of slowly reach out and bring small particles of food to yourself then a carnivore that has to chase down and capture its prey and then
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is sticking a huge bunch of food down that's down its neck and basically has to experience Thanksgiving dinner every time it feeds just to illustrate this I have this little movie and this movie is of an emergent which is one of the
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groups who thinks maybe the first predators present in the Cambrian and what it's going to do here is to just shoot out its proboscis and capture this poor light Paula key or you can see that this is not an easy struggle these
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organisms are fighting for their lives and this is an energetic option intensive battle what the Murray is going to do now is it's going to start shoving this eat hole down its mouth so this is basically the Marine equivalent of a
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snake swallowing an entire small amount and now it's going to start crawling away you can actually see little bits of the polychaetes sticking out within it so in order to test this hypothesis relationship between oxygen and feeding strategies particularly the ability to
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be a carnivore we actually turned to that other group of organisms the polychaetes we did this for several reasons first polychaetes are the most abundant organisms in deep-sea low oxygen environments second they're feeding biology is well relatively well
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known and finally they have a diversity of feeding modes within this group so for instance they're deposit feeders like this Tara ballads carnivores often with these well-developed jaws like this paula node filter feeders like this turbulence and even the famous
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chemosynthetic tube worms so to do this study I took published data and coded the likely feeding strategy for about eleven hundred different paula key species occurrences which is about as much fun as it sounded from 68 stations or areas in the world's ocean which are
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shown here the main low oxygen areas of the ocean is shown here in black this is the results of the study I don't want you to too caught up on the details what this is basically showing is the
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percentage of carnivorous individuals in an area of the ocean against four different oxygen levels and these red bars represent the median for each of those different oxygen levels what you see is that there's a clear increase in the percentage of carnivorous
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individuals at a station and as Auction levels go up we also looked at the number of carnivorous taxa are carnivorous species at a station and again we see an increase in carnivorous species present as you go up in oxygen
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levels so at least for pollock eats in the modern ocean there's a strong relationship between oxygen level and the ability to be a carnivore and I should note out note that just on this lowest oxygen station amazingly 14 of
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the 28 stations nearly 50% have zero predators whatsoever so I'm kind of summing up the Cambrian radiation this origin of the first large organisms in the fossil record basically all of our major animal plan this diversity I think that both
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these two camps of people are right I think that probably was these predator print arms races and these animals eating other animals and kind of the fight for survival that caused this burst of morphological evolution but I think the geochemists and some of the
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other paleontologists are also right that the oceans before there were probably oxygen limited for the presence of predators so without coming to our third point or third story on the geological time line which is the Permian Triassic extinction what this
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illustrates is The Last Story Illustrated that oxygen can giveth and this basically shows that oxygen can taketh away auction is one of the strongest controlling diversity strongest controlling factors on diversity in the modern ocean what I'm showing here is
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just some plots illustrating how oxygen affects diversity in the modern ocean so what we did is we took all those places where we had data for the polychaetes in that last study we took all the organisms that are not just the
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polychaetes we calculated a diversity index what's called the Shannon H prime index I don't want you to get too hung up on this basically you can think of low values of this as representing communities that are not very diverse
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perhaps only a few species and dominated by one particular species whereas high values represent communities with many more species and a more equitable distribution of individuals between one species we then did what are called random forest analyses and these allow
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us to understand how various factors in this case auction temperature and pco2 effective versity in the modern ocean don't worry about what these values represent but basically a higher value represents a better explanation of the control on diversity of the modern ocean
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so this suggests that oxygen is the strongest control of diversity in the modern ocean what's shown here is a partial dependent spot and so higher values here indicate higher diversity and you can see that diversity basically drops off a cliff below about 0.5
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milliliters per liter oxygen which is about 8% of modern the social levels so we'll now though now go to a brief introduction about the late permian world because this is probably unfamiliar world to most people during this time period all the
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continents were together in one supercontinent you guys may have heard of this Pangaea and there was one big ocean Panthalassa as well as this kind of smaller more restricted ocean the temples the ocean community of this time contained a number of fairly sessile
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slow-moving highly calcified organisms many of which persist to these days or to today but nowhere near the abundance that they existed in the Permian so these are things like crinoids brachiopods and the shale a monoids and nautiloids on land the funnel is
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dominated by synapsids or the mammal-like reptiles like this Dimitra dog and all of these look like dinosaurs they're actually more closely related to mammals at the end of the Permian these entire ecosystems fell apart disappeared the Permian Triassic mass extinction is
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the most catastrophic extinction in the history of the earth so what's shown here is that is the genus level diversity in the oceans through time from the modern back through the Cambrian at about 540 million years ago and this is the number
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of fossil jeanna general that we find in the fossil record and you can see here that by proportion the Permian Triassic extinction was the biggest drop in diversity in the last 540 million years so this is the Late Cretaceous
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extinction it's the one where the dinosaurs went extinct and you can see that a roughly similar level of general with extinct but proportionally it was far less so in the Permian Triassic mass extinction up to 80% of the general went
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extinct now we don't really have a good way to track how many species are in the ocean for various reasons but if you kind of back of the envelope calculations on how many species are usually present in the genus suggest
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that up to 96 percent of species basically all life in the oceans went extinct at this mass extinction the latest date suggests that this happened really fast in geological time in less than 200,000 years and it happened at the same time
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in both the marine and terrestrial realms so there's been a lot of debate about the causes of the Permian Triassic extinction it's kind of the classic geological whodunit but in recent years geologists have tended to focus on what's called the Siberian flood basalts
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what this is is basically a vast outpouring of lava up in Siberia in northern Siberia it's the biggest volcanic eruption on earth in the last 500 million years and its current extent covers about two million square kilometers which is about
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the size of Western Europe which also gives you some sort of a hint about how big Siberia is kind of the idea that most geologists have played with or or believed for how this have that happened was that there's volcanic activity the
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released an extraordinary amount of co2 and this is both from the volcanoes themselves and from interaction with the rocks through the wall that the lava was erupting through this co2 led to global warming like in the modern ocean but
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this wasn't the only thing this co2 release resulted in a number of different kill mechanisms at least three that we can see in the fossil record so this global warming increased what we call ocean stratification this is those
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density surfaces in the ocean that make it harder for oxygen to mix in and this resulted in anoxia or low oxygen zones throughout the world's ocean it also the co2 directly equilibrate with the ocean plunging ocean acidification or drop in
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pH in the ocean waters as well as what's known as hypercapnia stress which is basically the ability of organisms to deal with the co2 and regulate their acid-base balance but this wasn't the only thing the co2 release also
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interacted with this warm climate to cause intense weathering of all these new lavas that are erupted now it turns out lavas are really rich in nutrients like phosphorus that key nutrients are phytoplankton growth so what happened that is you have this increased pulse of
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phosphorus into the oceans the led to notifications and again 2n oxy and hypoxia and so now I'm basically just going to go through a few of the little bit of the evidence for this mass extinction event and evidence for the anoxia and global
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warming this is a stratigraphic column we're basically description of the sediments meter by meter through a Permian Triassic extinction section Spitsbergen and what do you see here is it the latest Permian sediments are these nice well oxygenated burrowed
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sediments and the latest Permian there sharply overlaying by these sediments here these perfectly laminated rocks with absolutely no disruption as well as other evidence for anoxia block Jew chemical evidence where we do find fossils in here though these are these
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chloride beds it's only one single by valve that can tolerate these conditions and so it's this mono specifical assemblage in this highly stressed environment as I said that wasn't just a anoxia that did in the late permian organisms this is a temperature map or a
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model temperature map of the late permian world these are these white areas our land and what you can see here is that it's a relatively hot world at least compared to modern this graph over here is showing the change in sea
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surface temperature with respect to the modern ocean so anything that's positive will be warmer than the modern ocean so much of the oceans is in fact warmer so this is already a hot world the thing is then there's evidence in the geochemical
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record for a further 6 to 10 degrees of global warming and so that people have suggested that the tropics here got up to 38 to 40 degrees Celsius which is well over a hundred degrees Fahrenheit that's incredibly hot there's basically
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very little to no animal life they can live in those conditions and that's what we see in the fossil record so this is a reconstructed map of the earliest Triassic world after those anoxic events and those kind of greenhouse hothouse
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events and what people suggested there's basically a dead zone throughout the entirety of the tropics where there's no tetrapods present no four legged organisms present on land and basically very little life in the oceans in the in the tropics and
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especially none of the bigger life things like marine reptiles or fish and sharks and these are only existing and of these high latitude or Fugit so with this in mind what caused the lake Permian extinction we can now move to
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conclude our talk with the future of the modern oceans so when we think about the killer for the Permian Triassic extinction we think of it as little flood basalts but it's really not just the flip assaults the real thing that
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caused all these problems is the co2 release and so instead we can think of this as being driven by a co2 driven perturbation to the Earth's system and it is indeed an earth system it's not just one cause-and-effect that did these
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organisms in it's a cause and there multiple effects and Makhan effects that created this deadly trio of global warming ocean acidification and anoxia and so once we're thinking about this is being caused by co2 driven perturbation it's not that hard to replace the
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picture of the volcanoes with human induced co2 and note the atmospheric co2 is now 400 ppm and growing rapidly and the rate of change is unprecedented in the last 25 million years there are some distinct differences with respect to the
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Permian for instance this whole weathering feedback wasn't operating but we have other really important things going on in the modern such as the nutrients from runoff and increased upwelling that are again causing eutrophication and further anoxia and hypoxia so I'm a paleontologist I'm not
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really an expert in modern global change but I'm just going to briefly go through some of this evidence for how oceans and environments are changing in the modern ocean now I'm putting together to talk I was looking for a good slide on global
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warming and I figured you guys had seen plenty of slides of increasing temperature through time so I thought instead I would just tell one little anecdote related to my research that's kind of illustrated by this cartoon of these two polar bears trying to adapt
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to a warming world where there's no sea ice and we're trying to fit in with this Camel shirt and this anecdote is that the Arctic is one of the places on the on the worlds that is that is
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experiencing the fastest warming and as it's warming actually the grizzly bears are moving farther north and as this is happening the Grizzlies are actually interbreeding and creating hybrids with the polar bears and this is colloquially called the Paisley Bear and it kind of
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looks like a smaller dirty polar bear with this funny little head on it and this is just one example of all the different changes we're starting to see as the world warms and it's particularly relevant to me because the last thing I
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knew I need when I'm doing northern fieldwork is a new type of bear that's trying to get into my camp so global warming is familiar to most people but the other two causes of a major global change might be a little less familiar
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the first is ocean acidification and this is relatively easy to understand into model and it's basically as we're increasing co2 in the atmosphere that co2 is equilibrate with the ocean and making the oceans more acidic so this is
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the record from the men Aloha observatory of atmospheric co2 as you can see it's going up in time and as it goes up in time the record of ocean co2 from the nearby station Aloha Observatory in the ocean is also going
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up in lockstep and the pH is reducing and this has real big implications for any organisms that make a calcium carbonate skeleton if things get bad enough of the pH gets low enough their skeletons will literally start to
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dissolve the final global change stressor might be a little harder to understand the different causes because as we talked about in those first slides there's so many levers we can pull to change the oxygen levels in the ocean so
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for instance the deoxygenation in the modern ocean could be due to ocean warming because oxygen is less soluble in warm water it could be due in some places to increase stratification because we're getting less mixing of oxygen into the oceans or in other
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places it could be due to increased upwelling intensity we're bringing more to the surface feeling that phytoplankton growth and more decomposition whatever the causes in different places we know from many data sets around the world the ocean deoxygenation has happen and this is
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just a famous map at least in scientific circles of the showing of the hypoxic boundary this is the 60 micro molar per kilogram oxygen level off of Southern California slow you can see in many places that this oxygen level is risen
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50 to 100 meters the issue here is that these combined causes of warming acidification and deoxygenation decrease the habitats available for any particular species so for most organisms now in the modern ocean they're living in some habitat regime between waters so
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this is for for organisms on the continental slope and slope and shelf between waters that are too warm on the surface and have too little oxygen below as we increase the warming of the surface ocean and increase the extent of
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the low oxygen levels below we're going to squeeze the habitat for these different species and for some species those habitats are simply going to disappear so thinking about back about what we've seen in the geologic record and throughout this talk we could
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suggest that many areas of the world are going to have lower diversity perhaps in worst cases bow down to these single mono specific assemblages like we saw in the aftermath of the Permian Triassic we also might predict that there will be
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fewer predators based on the polychaetes studies that I showed you or the very least very big changes to the food webs and the interconnections of marine organisms finally from a more practical level we'll see big changes to fisheries
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and this will particularly impact benthic Fisheries places where the auction spreads it will simply wipe out the habitat or the where the low auction spreads it will simply wipe out the habitat for those benefit fisheries and also for organisms like Bill fish and
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tuna that have really high oxygen requirements it's going to aggregate them all really small habitat margins and it's going to make them really easy to fish and unfortunately to overfishing finally these changes will cause big changes to biogeochemical cycles the
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redox landscape or the landscape of the modern ocean strongly controls the the biogeochemical cycles of different things like where carbon is buried with a nitrogen cycle which ultimately influences nutrients and food etc and so the point is that this is
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these changes are related to that earth system as we see changes co2 driven changes it's not just oxygen temperature and pco2 that will be changing but the entire Earth system so if we sum this up we can see that the permian-triassic
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mass extinction was driven by a co2 driven perturbation to the Earth's system and that it is this Earth's system that's the important thing and that as we change an increased co2 in the modern ocean we're seeing those exact same stressors of global warming
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ocean acidification in a anoxia and hyper hypoxia and there are a lot of differences between the modern ocean and the permian-triassic especially with respect to the time scale of co2 release but this provides kind of an analogue in
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a worst-case scenario for what might happen as we continue to increase co2 levels so I conclude simply with a with a quote from a recent review article on the Permian Triassic extinction the end-permian rock record cannot currently provide the temporal and spatial
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resolutions to make specific predictions about expected changes in the coming decades or centuries but increasing evidence that the inner Permian mass extinction was precipitated by a rapid release of co2 into Earth's atmosphere is a valuable reminder that the best and
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most sobering analogues for our near future may lie deeper in the Earth's past thank
Topics:oxygen evolutionocean adaptationGreat Oxidation Eventmarine paleontologyScripps Institution of OceanographyEric Sperlingpaleontologyocean scienceoxygen minimum zonesgeological time
