Ocean Chemistry Research

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Professor Ariel Anbar of ASU’s School of Earth and Space Exploration talks discusses how ASU and the University of Cincinnati are planning to use a new geo-chemical technique to study ocean chemistry in an effort to study a mass extinction that hit the Earth 250-million years ago.

Ted Simons: Theories abound as to what caused the earth's most substantial mass extinction some 252 million years ago. Researchers at Arizona state University and the University of Cincinnati are using a new geo chemical technique to study the ocean's chemistry in an effort to discover what at the time wiped out 90% of ocean life. Here now to talk about all this is professor Ariel Anbar of ASU's school of earth and space exploration. And from the same school, joining us, Dr. Greg Brennecka. Good to have you both here.

Dr. Greg Brennecka: Thank you.

Ted Simons: Did I get that right? 250 million years ago, 90% of ocean life went kaput?

Ariel Anbar: Yes. Greatest mass distinction in earth's history.

Ted Simons: What are the general theories?

Ariel Anbar: There are a number of ideas. A period of volcanic eruption, there have been ideas about a big meteorite impact like wiped out the dinosaurs, and there's been an idea that has gathered steam that a change in ocean chemistry was instrumental in making this happen.

Ted Simons: That was instrumental in getting you guys to start working on this research. Talk to us about what you looked at and what you were looking for.

Dr. Greg Brennecka: We looked at carbonate rocks that deposited over the same time period, and uranium isotopes and thorium-uranium ratios in these rocks to tell us a little bit about the ocean chemistry of the time they were deposited.

Ted Simons: What were these ratios tell you if you saw them?

Dr. Greg Brennecka: If it was a major change at a certain time period it would tell us when there was a change in the ocean chemistry.

Ted Simons: And did you find it?

Ariel Anbar: He did. He's the lead author in the study. He found a substantial shift in the uranium isotopes and thorium uranium ratios, and that tells us the amount of oxygen in the oceans decreased just before this extinction.

Ted Simons: So basically what you saw was what happened right prior to and during the extinction?

Dr. Greg Brennecka: Yes. We saw a marked shift, the uranium isotopes and thorium-uranium ratios right before or immediately after the extinction of them.

Ted Simons: Did this method of study break new ground? I get the impression this was a unique way of looking at this particular problem, or this issue.

Dr. Greg Brennecka: It definitely is. Professor Anbar's group has been working over the last many years about new novel techniques to look at changes in ocean chemistry, which this was the latest element that they use to tackle this big problem.

Ted Simons: What got you going on this element?

Ariel Anbar: This particular element? We focused on chemical elements whose abundance and chemistry in the ocean is sensitive in the amount of oxygen. Uranium was sort of next on the list of elements we could measure, and whose chemistry should be strongly affected by oxygen. And it was particularly well suited to this problem.

Ted Simons: Why is this research important?

Ariel Anbar: A bunch of reasons. First of all, just trying to understand how we got here. If that extinction hadn't happened, evolution would have gone a different way. And dinosaurs -- that extinction paved the way for the rise of dinosaurs, which paved the way for the rise of us. From a fundamental standpoint it's important. There's also interest in this kind of question because of global climate change. I don't want to overplay this, but as temperatures get warmer, one of the things that happen is parts of the ocean start to lose their oxygen or the amount of oxygen decreases. There's generally an interest in whether or not how changes in oxygen in the oceans affect biology. So this is the granddaddy of changes in ocean chemistry affecting life.

Ted Simons: Were some of these ideas at play with you when you did this research and led this particular effort, or were you just looking at hard science trying to get hard facts?

Dr. Greg Brennecka: There are always a lot of different reasons you do research projects, and being part of our lab, understanding history of oxygen in the ocean is always a big goal. And looking at these samples to understand a mass extinction event, that plays into different aspects. You look at what's going on now in the ocean, maybe some of these changes, we can draw parallels to what's going on. And what could be happening.

Ted Simons: Did you expect to find what you found?

Dr. Greg Brennecka: That's a good question. No. Not necessarily. We expected to see changes as drastic as they were, I don't think I expected to see that. Honestly I didn't really know what to expect going into this. This is a very new technique that's being explored and it was just a good table set to do this on, and this is kind of a novel technique to use.

Ted Simons: Did it surprise you at all?

Ariel Anbar: Yeah. We were expecting to see a shift. We picked this period in earth's history because we knew ocean chemistry changes, broadly there's been theories about it. So we thought we could test it and expect to see a shift. We didn't expect it to be so close to the extinction. That's what surprised us, because the previous thinking was the ocean chemistry changed long before and was -- and oxygen was low in the ocean for quite a while leading up to the extinction. We found there was a big shift just benefit extinction, which affects the timing.

Ted Simons: How does this affect the idea, the theories? How does this come into play?

Ariel Anbar: I think it strengthens the idea that the change in ocean chemistry caused the extinction, because there is this substantial increase or decrease in oxygen just before the extinction, that suggests there really is a cause and effect relationship there. Previous to this, there was evidence of a change in ocean chemistry, but it was not as extreme and it was much earlier. So the thought was, well, maybe it's connected, but there was more room for debate. I think it makes it more solid.

Dr. Greg Brennecka: I think the sharpness of the change we saw is important too. It happens very quickly in geologic time. It's just a very sharp change in uranium isotopes as well the uranium thorium ratios.

Ariel Anbar: The other thing the technique allows us to do, we build a pretty strong case what we're seeing represents the global oceans, even from measuring one location. And that has been unclear before whether this change was global.

Ted Simons: All right. We've got to stop you right there. Fascinating stuff. Thanks for joining us.

Ariel Anbar: Thank you.

Dr. Greg Brennecka: Thank you very much.

Ariel Anbar:Professor, ASU School of Earth and Space Exploration; Greg Brennecka:Doctor, ASU School of Earth and Science Exploration;

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