ScienceMatters - Season 3, Episode 10 - The Physics of the Ocean
The new dean of the Georgia Tech College of Sciences, Susan Lozier, is continuing her physical oceanography research as she takes the reins of her administrative duties in Tech Tower. She talks about her studies of “the global ocean conveyor belt,” her plans to get back to the ocean in 2020, and her commitment to mentorship.
Renay San Miguel: Hello and welcome to ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m RSM.
The new dean of Georgia Tech’s College of Sciences, Susan Lozier, has moved into her office in Tech Tower.
That would be her — landlocked —office at the midtown Atlanta campus. It’s a nice office, but she has another unofficial office, and it’s a bit farther away.
Renay San Miguel: She may have grown up in Indiana, but the ocean has been calling Lozier since her days in graduate school. Back then she was studying chemical engineering, and she earned a Bachelor’s of Science degree in at Purdue University.
A quick note to listeners: During our interview, Lozier would sometimes pound the table with her hands for emphasis. That’s the bumping noise you’ll occasionally hear during her answers.
Susan Lozier: And then when I found my way to graduate school, I was attracted to the Pacific Northwest and ended up going to University of Washington for my master's degree. Now chemical engineering, particularly the part that I was studying, it's all about fluid dynamics and thermodynamics. And so I happened to be taking my courses, my first year, taking a course in applied mathematics studying partial differential equations. And the instructor, the professor that I had in that class, had a joint appointment in the School of Oceanography as well as School of Mathematics. And every example he was giving of these partial differential equations was applied to ocean physics, or physical oceanography, ocean circulation. And so I thought, “Wow! I can study fluid dynamics in the ocean instead of fluid dynamics in a pipe.” And so I went and took a course in physical oceanography and just decided to—finished up that master’s and went right into the Ph.D. program in physical oceanography.
Renay San Miguel: That set her on a different academic course, which has led to her new title as the Betsy Middleton and John Clark Sutherland Chair of the College of Sciences. But Susan Lozier is also a working scientist. She’s the president-elect of one of the largest scientific organizations in the world. She’s the lead investigator for a major international ocean research project that will take her back out on the water in 2020.
Lozier is an award-winning physical oceanographer whose research examines ocean currents and how they are affected by climate change.
You may not have known that there are different kinds of oceanography; chemical, biological, geological. Then there’s physical, which is as it sounds: It involves the physics of the ocean.
Susan Lozier: And the physics of the ocean can run anywhere from people studying about waves at the shoreline all the way to what I do which is study the very, very large-scale ocean circulations. So I'm interested in currents that move from Antarctica up to the northern North Atlantic, or what we would say the global ocean circulation.
Renay San Miguel: Those currents are a lot like the air streams that wrap around the planet in the atmosphere. Just like in the atmosphere, evidence of humanity’s effect on the planet can be found in its waters, underscoring the importance of Lozier’s research.
Susan Lozier: I found it very sobering myself when I realized that the anthropogenic carbon dioxide—the man-made carbon dioxide that we had put into the ocean since the industrial revolution—put into the atmosphere since the Industrial Revolution—I found it sobering that you can see signatures of that at 4,000 meters depth in the ocean.
(2016 Los Angeles lecture)
Susan Lozier: In the winter at high latitudes, the surface waters lose their heat to the atmosphere, they become very dense, they sink, and they spread equatorward. They fill the deep ocean with these cold waters, and in time those waters must upwell and return to those deep water formation sites. This is called the ocean overturning circulation, or popularly called the global conveyer belt.
Renay San Miguel: That is Susan Lozier from a 2016 lecture in Los Angeles. At the time, she was the Ronie Richelle Garcia-Johnson Distinguished Professor of Ocean Sciences at Duke University, where she was on the faculty for 27 years. The named chair is the highest honor that Duke can bestow on a faculty member.
Lozier isn’t just fascinated by the rivers moving within the ocean, like the Gulf Stream. She also relishes the history of scientific efforts to study these deep waters. A story she likes to tell involves a historical figure known for his studies involving lightning.
Oh, and for his work helping to create the United States.
Susan Lozier: So Benjamin Franklin was the postmaster general of the colonies, and during that time he noticed that the ships that were carrying the mail from the colonies back to England would get there much quicker—a matter of a couple of weeks quicker—than the ships that were returning from England and bringing the mail back to the colonies. And it frustrated him because he knew that the sea captains were taking the same route and he couldn't account for it by differences in weather or anything. And so he finally wrote to a cousin of his, Timothy Folger, who was a whaler from Nantucket, and asked him if the whalers knew any reason to explain this.
And then of course, several weeks later the letter comes back from his cousin and his cousin said, “Yes, of course, everyone knows that you take advantage of the Gulf Stream which is the river in the sea moving from the colonies to England,” you know, “but that on the way back you must avoid it.” And so Benjamin Franklin made one of the first maps of the Gulf Stream as postmaster general by just dipping wooden buckets over the side and he put a little thermometer in and because the Gulf Stream, they’re exceptionally warm waters because they're coming up from the tropics.
Renay San Miguel: There’s more history behind the discovery of the so-called global ocean conveyor belt.
Susan Lozier: There was also someone, a Reverend Stephen Hales over in England who was very curious about what the deep ocean temperatures were. this is the mid-18th century, and everybody thought the deep ocean was void of life, dark, very, very cold. And so he asked a colleague of his who was a ship captain of a slave trader moving from West Africa over to the colonies and asked him at one point to stop in the middle of the Atlantic and take measurements of the deep ocean temperatures. And so this is Captain Henry Ellis, and so on one of his transits, he stopped in what they called the “torrid zone,” what we now call the tropics.
Renay San Miguel: Ellis’ team figured out a way to use a wooden bucket to capture water at specific depths. He recorded the results in a letter back to Hales.
Susan Lozier: And so in this letter he says that, “Well, we first found out that the water sitting at the surface is the same temperature as the air temperature as expected,” which was 83 degrees Fahrenheit at the time. And then he said, “As we lowered that bucket further and further and pulled that water up, we found that the temperature decreased proportional to depth.” So that's good; this is what we would expect.
He said, “Until we got to a depth,” and I think it's something like 600 or 700 fathoms which is the unit of depth they used there, he said that, “The temperature we recorded was 53 degrees Fahrenheit, and it didn't matter how much further we went, the temperature was always 53 degrees Fahrenheit.”
So he's writing all that all this down and he's also making some scientific interpretations because he's also saying “We think those waters were actually colder than 53 degrees Fahrenheit, 00:08:43.76 But the fact is that the waters were cold and colder than they expected. So the part of the story I like is the very end. He says, “We don't know if this is of any scientific interest to you, but it really doesn't mean that much to us scientifically. But we're very happy to have found a source of cool water for our wines and baths in this hot climate.”
Susan Lozier: So it was really funny I thought. A very practical people, they just cared that there was a source of cold water.
So that letter went back to Reverend Stephen Hales. He sent it on to the Royal Society of London, and it sat there until the year 1800 when Count Rumford picked up this letter. he was so intrigued by this because he couldn't figure out how that deep ocean in the equatorial regions, or the torrid zones, why cold waters would be there, right? Because the expectation was that if that, you know, at the surface, all the heat from the solar radiation should have penetrated and those waters should be warm, right? Even in the winter, the water shouldn’t be that cold. And so he pondered on this. And he then came up with the idea. He said, “I can think of no other supposition to account for the cold at depth in the torrid zone that those deep waters were once at the surface at very high latitudes.”
And then he said “If those deep waters at depth in the equator, torrid zone, were once at the surface at the very high latitudes in the polar regions, then we must have some waters from the surface moving up there.”
And so he described in two sentences what we call today as our “global ocean conveyor belt” or the “meridional overturning circulation.” So in the winter at very high latitudes up by where we call the Labrador Sea, the Norwegian Greenland Sea, the Irminger Sea, the atmosphere is very cold. The ocean loses a tremendous amount of heat to the atmosphere during the winter. When the ocean loses heat, the waters become very dense. Cold water is more dense. So that means that surface water becomes more dense than the water below it. And those waters sink because of that density. And those cold waters are denser than any waters equatorward, and those waters then start moving equatorward at the bottom.
Almost all these waters, 90 percent of the deep waters in the world's oceans form in the North Atlantic, and they spread throughout the global ocean. And then they upwell, and then they have to return to the northern North Atlantic.
Renay San Miguel: The warm waters of the Jet Stream and the global conveyer belt, mix with rising temperatures caused by climate change for what could be a devastating combination for the environment.
Susan Lozier: So there’s two things there. One is even without any circulation, the water warming in and of itself, you know, we've documented that, that's going to melt ice. And in fact, we know that the warmer the water, the warm water has a more impact on the ice melt than actually the warm air, right. So but then the circulation does bring, can bring, warmer waters and can make a difference as well. But the real why we're concerned about the overturning circulation is not just because of its impact— I should back up a little bit and say that even before we got into climate change, for 100 or more years we've known that this overturning circulation redistributes heat on our planet. And the best example of that is that in the North Atlantic, if you think about the weather and climate, I should say, over Great Britain and Northern Europe, it's much more hospitable than the climate in comparable latitudes over in Labrador and the Maritime provinces in Canada. And that's because of these warm waters that are coming back as part of the upper limb, the surface limb, of the overturning, and then the westerlies moving from west to east across the North Atlantic pick up all that heat and they deliver that heat and moisture to Great Britain and the British Isles and northern Europe.
Susan Lozier: The British Isles are very rainy because of all that moisture that’s picked up from the ocean.
Renay San Miguel: Is the ocean conveyor belt mostly what you spend your time on with your research?
Susan Lozier: I do now, you know. I would say the past 10 years it's been a major focus of my work. And I'll just tell you that, in addition to redistributing heat, so we're interested in that if the conveyor belt is overturning circulation slows. And why we think it might slow is because I mentioned to you earlier that during the winter, the waters become very cold and they sink. Well if we have winters that are increasingly warmer, right, and so that's always been—that's the concern. And lots of climate models lead us in that direction.
Renay San Miguel: Is this just a part of the ocean sciences story that you think isn't being focused on enough?
Susan Lozier: Sea level rise is you know very easy for people to think about. It's easy for people to think about the fisheries impact.
But I'll tell you though, the real concern about this actually has to do with the increasing levels of carbon dioxide. And so I think the main untold story here is the ocean's role in the uptake of carbon. So since the Industrial Revolution, we have had a good measure of how much carbon dioxide we have emitted by the burning of fossil fuels—“we” meaning not you and I, Renay, but the global population, primarily the industrialized countries. But starting in the ‘70s or ‘80s, scientists understood that the amount of carbon dioxide that was in the atmosphere did not quite match up with what the estimates of how much had been released. And it turns out that's because the ocean and the terrestrial domain have been taking up some of the carbon. the ocean has been up taking about 30 percent of the carbon dioxide that's been emitted in the atmosphere. So that's good news for the atmosphere, right? That's bad news for the ocean.
Alot of that carbon dioxide—over half of it is in the deep ocean because of this conveyor beltSo when those surface waters go to depth, they carry that carbon dioxide with it.
Renay San Miguel: What is it doing to ocean life?
Susan Lozier: So that leads, yes, to ocean acidification. And so that's, you know, now there's very early indications of ocean acidification. It's not at the point where it is alarming—we're starting to study it—but if this trend continues, it will have a strong impact. And so what motivates me to study the overturning circulation is not just how will changes in the overturning impact the amount of heat that's delivered to different places, but if the overturning circulation slows, it means that the carbon dioxide will build up more in the atmosphere. So there's a lot of feedbacks there. So as a physical oceanographer, I'm very interested in understanding what are the changes in the overturning circulation and what can we expect in the years ahead, and that's why we have this international observing system in the North Atlantic.
Renay San Miguel: That international observing system is called Overturning in the Subpolar North Atlantic Program, or OSNAP. Lozier has a ticket to ride with them in the summer of 2020. As we said earlier, Lozier is the international lead investigator for this six-nation effort to learn more about the global ocean conveyor belt.
Susan Lozier: there's six countries that contribute to this but the United States has the largest components funded by the National Science Foundation. And in the water right now taking measurements are instruments that are strung off the shelf and slope of Labrador off that Canadian coast, and then all the way to the western coast of Greenland. Then, starting on the east coast of Greenland, we have instruments going all the way over to the Scottish shelf. And so every other summer we go and pull those instruments off, refurbish them, put them back in, and take all sorts of other measurements along the way.
We do have autonomous gliders that are involved in the program. And so those are remotely operated and they get their instructions, you know, via satellite. But they're going on their paths taking measurements of temperature and salinity along the way. So we have floats, current meters measuring salinity, temperature; gliders; we use satellite data, so there's all sorts of ocean observations.
Renay San Miguel: That’s not the only big scientific assignment awaiting Lozier in the next couple of years. She is set to take over as president of the American Geophysical Union in 2021. The AGU boasts more than 60,000 members from 130 countries.
Susan Lozier: So anybody that is Earth, ocean, atmosphere planetary sciences is a member of AGU. So it is a professional society in that it organizes meetings for all these different scientists, has publications—I think we have 26 different journals. But also, yes, it has a strong outreach component to let people know what Earth, ocean, planetary scientists are doing, and is involved how it makes policy statements as well, involved in educational programs, mentoring programs, so it really galvanizes the Earth and space science community, you know, to work with partners to really work toward a sustainable future.
Renay San Miguel: In addition to her research and administrative duties, Lozier wants to make sure there are enough women physical oceanographers following in her footsteps.
Susan Lozier: I will say that I, at a certain point, realized that I owed a lot of whatever success I had in my career, I owed a large fraction of that success to my mentors. Starting in high school, I had a fantastic, you know, chemistry teacher who just made a huge difference to me. In large part, I think that's why I ended up, you know, in science. But also going through an engineering program and also going through the oceanography program, I looked around and realized that a number of my colleagues who were going through the same program didn't always make it through the program. And it just in large part, just from my personal experience, I realized that there was just the lack of support. And just when I—after I had been recently tenured and I was—just realized that it was important to me to increase the representation of women—at that time, I was really focused on—in science. And I knew from my own experience that mentoring and mentoring networks could make a big difference.
And so I went to the National Science Foundation. In fact, I got funding from five different federal agencies for proposals to set up a mentoring program called Empower which was mentoring physical oceanography women to increase retention. And importantly, I told everybody that this wasn't a women's issue, that it was a community issue. And I told the funding agencies that they had spent a lot of money on graduate education for women and that they would do well to invest some money in mentoring programs to retain them in the field.
And I've been very proud of this program because it really has changed the needle on the retention of women in that field. But I've also gone on, and through AGU, have established mentoring programs for Ph.D. students who are interested in careers other than academia because oftentimes those students don't get the same support for the careers they're looking at than those who are interested in academia. I think it’s vital to any science that we be open to ideas from all people.
Renay San Miguel: My thanks to Susan Lozier, Dean and Betsy Middleton and John Clark Sutherland Chair of the College of Sciences.
Lozier’s School of Earth and Atmospheric Sciences website is at lozier-dot-eas-dot-gatech-dot-edu.
Siyan Zhou, a former research associate with the School of Psychology, composed our theme music.
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This is ScienceMatters, the podcast of the Georgia Tech College of Sciences. I’m RSM. Thank you for listening.