tv France 24 LINKTV September 20, 2013 2:30pm-3:01pm PDT
narrator: oceans cover 75% of the earth's surface and impact life on our planet in profound ways. the tropical pacific spanning almost half the earth's circumference triggers el niño events affecting storm tracks rainfall and temperatures across the globe. on a quieter but no less important scale, the tropical oceans are teeming with what may be the smallest and most abundant organisms on earth. microscopic phytoplankton are the base of the food chain on which much ocean life depends. both processes are only partially
understood, yet they each have far-reaching effects on ocean systems and ultimately on the habitability of our planet for human life. fertilized by the upwelling of a cold, nutrient-rich current, the coastal waters of peru and ecuador bring an abundant and dependable harvest to the fishermen of south america. but, mysteriously, every few years, this cold current is replaced by warm waters severely depleting the fish population. this warmer current appearing usually around christmas time became known as el niño, or the christ child. but what the fishermen didn't know was that the local phenomenon they called el niño
was, in fact an immense interaction between the vast pacific ocean and the atmosphere causing torrential rains drought, and famine across the globe. mark cane, a scientist at columbia's lamont-doherty earth observatory, has been studying el niño for over 30 years. cane: when you have an el niño event there are things that happen around the world. they don't always happen but they usually happen, and they have some -- some bad consequences for people. there is typically a poor monsoon in india. there are droughts in southern africa droughts in ethiopia droughts in northeast brazil which is the poorest part of brazil. in peru and ecuador, you have catastrophic flooding in many places that washes out infrastructure. narrator: because of its devastating effects around the globe
scientists tried to accurately predict el niño in advance to help people prepare. these attempts were unsuccessful until the mid-1980s when cane and his colleague steve zebiak set out to create a physically based computer model to predict these phenomena. cane: here is this el niño phenomenon which i knew about because it had caused these anomalies in wintertime circulation over north america in '77, '78. and i was living in boston at the time and it dumped this incredible amount of snow on us. we kept geing hit by snowstorms. and then we finally got hit by the big one. so, these el niño events if we could forecast them and get this information out there there's the possibility of taking actions that will mitigate these impacts. narrator: to understand el niño,
it is first important to understand the dynamics of the pacific ocean. in the 1960s ucla meteorologist jacob bjerknes proposed that ocean-surface temperatures were linked to atmospheric winds. the evidence he found came from the variation in ocean temperatures on either side of the tropical pacific. cane: he noticed that the state that we consider normal is very odd because the western pacific is warm. like 30 degrees celsius -- high to mid-80s fahrenheit -- the kind of water even my wife would swim in, it's so warm. bathtub temperature. the other end, the eastern end of the pacific has temperatures like 20 22 degrees celsius -- around 70 fahrenheit. why this enormous temperature contrast? both ends of the ocean get about the same amount of sunlight -- you know, we're talking on the equator here. and the reason for it is the way the ocean responds to the winds.
narrator: when el niño is not present, the air over the warm waters of the western pacific is heated and rises. as this warm air moves upward, it's replaced by air converging from the indian ocean to the west and the pacific to the east. these pacific trade winds also push the warm surface waters along with them. the warm waters collect in the western pacific near asia, deepening the boundary between the warm surface layer and the cold ocean depths. back east, off the coast of south america the warm surface waters flowing toward the west are replaced by colder waters upwelling from the deep ocean. this cools the air above creating an even greater temperature variation, which in turn makes the trade winds blow even stronger. cane: in other words
this temperature contrast between east and west, which was generated by the winds was also helping to generate the winds. a positive feedback between the ocean and the atmosphere. narrator: bjerknes also realized that the feedback could operate in reverse. roughly every four to seven years, the easterly winds slow and the warm water that was piling up in the western pacific sloshes back toward the east. this creates a warm current of water that moves from west to east. as the tropical-ocean temperature gradient disappears, the trade winds slow or even reverse, allowing warm water to accumulate off the coast of south america. this is el niño, and its effects are far-reaching. cane: bjerknes noticed that el niño
which had been known to people on the coasts as a coastal warming actually extended out into the central pacific all the way from the coastline to the dateline. the pacific is big. that's a quarter of the circumference of the earth. that's a lot of area to change the water in. that's a big disruption in the temperature -- the thermal-boundary condition that the atmosphere sees. narrator: in 1982, conditions were building toward an el niño of unprecedented proportions. but the warning signs went unheeded. the conrad a research vessel from columbia's lamont-doherty earth observatory, noticed dramatic increases in sea-surface temperature as it steamed east along the equator. the temperatures were so high that computers in washington d.c., rejected the data because it was too much of an anomaly.
cane: i was in a meeting in the fall in 1982 and the prevailing sense of things was, "there's no el niño going on. there won't be an el niño," and so on. now, this was, say something like september if i remember right, and we were already well into what would be the largest el niño in 100 years, okay? and i thought, "what a great prediction problem to go after. "if i understand something "then i should be able to turn it into a set of equations "that i could put on a computer, "and they'll simulate the thing i understand. so, i'll be able to, in that sense, make a model of it." narrator: cane and zebiak began work on their computer model by simplifying the el niño cycle to its essential features. first, sea-surface temperatures were entered into the model to calculate wind speed and direction.
as the computer stepped through each cycle of the simulation the calculated winds were coupled to a model of the ocean and caused the border between the warm surface waters and cooler underlying water to move up and down. cane: if we started with a state that gave a good description of where this layer of warm water was -- where it was higher than normal and where it was lower than normal -- then if we could just initialize a model with those conditions, start it off in that state and let it go forward, simulating the world then it might well work to simulate what was going to happenext in the real world. and that, in essence is a prediction. narrator: to test their model, cane and zebiak used archival records going back to 1970
and entered this data into their model to see if it could recreate the conditions that led to the 1982 el niño. by programming data a few months at a time and then comparing the computer's results with what had really happened -- a process called retrospective forecasting -- the two researchers were able to verify the accuracy of their program. cane: we started from june, and we went ahead, and it worked. and then we went back and we tried it from april and it worked again. and we kept going back like three, four months in time. and all of those forecasts actually gave something like a very large el niño event. narrator: confident that their model was accurate, cane and zebiak were ready to forecast into the future and predicted an el niño for the end of 1986. cane: now what do we do? do we sit on the information on the grounds that, well you don't want to scare people? remember, this is four years after the 1982 el niño
had rearranged the shoreline in california, had washed out a lot of the transportation infrastructure in peru and ecuador. there was a huge forest fire in borneo, and that fire has never stopped burning. you couldn't talk about el niño in some parts of the world without getting people really frightened. on the other hand, there are things you can do to prepare for it if you know it's coming. the conclusion was "well, this is good science, so.let's do it." narrator: cane and zebiak announced their prediction in march and, as forecasted an el niño event did develop at the end of 1986. this success of the cane/zebiak model was the first time el niño had been predicted in advance. it led to policy changes in ethiopia that helped avoid famine the following year.
today, although many new climate models have become available since 1986 a new generation of researchers continues to rely on the simplicity of the original cane/zebiak model. and scientists hope to be able to use their predictions to lessen the effects of el niño. cane: so, one issue was how do you get people to use this? what are the implications for agriculture, for water management for tourism, for ecosystems? and if you know those implications what should somebody do about it? narrator: the warm currents of el niño are now understood to be part of a global, dynamic system that affects the lives and well-being of millions of people around the earth. surprisingly tiny organisms in our oceans also have a huge impact on the habitability of our planet.
the top layers of the oceans are teeming with a huge variety of single-celled microscopic organisms called phytoplankton. these tiny organisms play a key role in regulating atmospheric carbon dioxide. and as the bottom rung in the food chain, they are essential to ocean ecosystems. understanding the ecology of phytoplankton is the goal of penny chisholm at the massachusetts institute of technology. chisholm: what most people don't realize is that the oceans are responsible for half of the photosynthesis on earth and that is that they produce half of the oxygen that is produced through the photosynthetic mechanism. the organisms that do this are the microbes, the phytoplankton in the oceans. we call them the invisible forest. they are the plants of the oceans,
and they are the base of the food web. if they weren't there, there would be nothing else living in the oceans. narrator: another crucial role of phytoplankton is to regulate carbon dioxide in the atmosphere. chisholm: we think of the ocean ecosystem as a photosynthetic machine, in a sense. and a critical function of this machine is to steadily pump carbon dioxide from the atmosphere into the surface oceans and then export it to the deep ocean. narrator: phytoplankton are at the base of this ocean pump capturing co2 and converting it to sugars and proteins which are transferred through the marine food web. each step along the way, some co2 is released back into the atmosphere. but some of the organic carbon falls from the upper ocean making a slow rain of dead organisms
and organic waste products that gradually accumulate in the cold depths. here, because of the slow circulation of the deep ocean, the carbon remains out of contact with the atmosphere for a thousand or more years. chisholm: if there were no phytoplankton and if the pump didn't exist and the oceans all mixed top to bottom, and all of that co2 in the deep ocean equilibrated with the atmosphere, the concentration of co2 in the atmosphere would more than double. so that just gives you an idea of how much the deep ocean plays a role in the global-carbon inventory and how important the phytoplankton are in keeping that pumped -- pumping downward to keep that co2 in the deep part of the ocean. narrator: by regulating carbon dioxide and producing oxygen phytoplankton play an essential role in maintaining a habitable planet.
although the role of phytoplankton in the world's oceans have been studied intensively, surprisingly, the most abundant variety of phytoplankton was only recently discovered. prochlorococcus. chisholm: it's incredibly humbling to realize that we didn't know this cell existed until 15 years ago and we had models of the ocean processes and models of the earth. we thought we understood this pretty well. we always think we understand it pretty well and then along comes something that just completely changes the way we think about these systems. narrator: prochlorococcus was finally discovered when an instrument used for biomedical research a flow cytometer was brought onboard an oceanographic-research vessel to test its usefulness in the study of phytoplankton. the flow cytometer breaks an extremely narrow stream of water
into individual drops -- each one only slightly larger than the cells under investigation. the drops are illuminated by a laser and if a desired cell is present in one of the drops it will give off a particular wavelength of light. a tiny force can then be applied to sort that droplet from the others. chisholm: we started working with this instrument and we realized that it would be really useful for studying plankton. rob olson was a postdoc in my lab at that time. he's a scientist at woods hole now. and we started studying a group of plankton called synecococcus which are interesting in that they fluoresce orange. most plankton, if you shine blue light, fluoresce red. as time went on, we started seeing some very, very tiny signals that were fluorescing red but scattering much less light than, um...
than any known phytoplankton cell would scatter -- which said that they were extremely small. and we thought that was electronic noise. but rob persisted in looking at this and, ultimately, it started taking on characteristics that were alive and that it changed with depth in the oceans and, um... so, we started focusing on these little signals with the flow cytometer and ultimately were able to isolate the prochlorococcus. and that turned out to be a very important component of the ocean ecosystem. narrator: prochlorococcus is the smallest and most abundant photosynthetic organism on earth. although only one-half micron in diameter, so small that about 200 could fit across a human hair, the single-celled prochlorococcus is the most efficient light absorber of all known photosynthetic cells.
chisholm: if the oceans are responsible for half of the photosynthesis on earth and prochlorococcus are a significant fraction of that that makes this one particular group of organisms an important photosynthesizer on a global scale. narrator: in addition to being the smallest in size prochlorococcus also has the fewest genes of any photosynthetic organism. chisholm: over time we've come to learn that prochlorococcus is a very special phytoplankton. with the smallest number of genes, it can convert solar energy, co2, and inorganic compounds into organic carbon. so, i think of it as the minimal life form. coleman: with these very few genes, they're able to do photosynthesis in parts of the oceans that are really, really low in nutrients. and these tiny cells with very few genes are really able to capitalize on that.
narrator: to learn more about the role prochlorococcus plays in the ocean ecosystem researchers from the chisholm lab routinely take samples of ocean water from a range of depths around the world. the big question they are trying to answer is why the population of prochlorococcus remains fairly constant over time. what factors regulate its birth and death? chisholm: the interesting thing out prochlorococcus is how stable it is in the deep-blue ocean. that is, in the warmer waters of the open ocean, you find on average, and fairly stably, about 10 million cells per liter of seawater. and there are some fluctuations in their numbers but not dramatic. and they double about once every one or two days, so that means they're eaten as fast as they're growing and they're growing relatively fast for ocean phytoplankton in the middle of the ocean.
narrator: prochlorococcus reproduces by cell division. dividing once a day, the population will double every 24 hours unless the cells are killed off as fast as they are born. this delicate balance is maintained week after week, year after year. so, it's a very stable system and yet very dynamic in how fast the cells are growing. so, we think that this system is playing an important role in regulating the stability of the ocean ecosystem. narrator: to help understand how the population of prochlorococcus is maintained, the research team has been investigating viruses that infect the organism. chisholm: it turns out the oceans are teeming with viruses that infect microbial cells in the system, and so it's not a surprise that there
are viruses that infect prochlorococcus. narrator: matt sullivan, a researcher in chisholm's lab has been working on isolating these viruses. so far, the team has identified three different viruses affecting the population. using dna sequencing the team then determines which genes are in these viruses and how they affect the prochlorococcus host cell. surprisingly, they are finding that viruses may not only be helping to kill off these cells, but also to help their hosts adapt to different conditions. sullivan: so, my goal's all in understanding right now the kinds of viruses that are there and how the interaction between the virus and the host cell happens. and wh's intesti about that is that we can interpret from the genes that are there what processes they're interacting with the host with. so, in one instance, some of these viruses contain core photosynthesis genes.
they're actually able to boost photosynthesis during infection in these particular hosts. narrator: a virus infects its host by injecting its genetic material into the cell causing the cell's biochemistry to switch over to making more virus particles. sometimes dna from the two sources gets mixed up, and the host takes away some of the genetic makeup from the virus. sullivan: so, is the virus just lysing and killing those host cells or are they also perhaps taking genes from the host and moving those genes back into the host after they've changed a little bit in the viral population? narrator: maureen coleman has been studying the genetic composition of several prochlorococcus strains. she was able to identify signatures in their genomes to suggest that viruses are actually important in moving genetic information between host cells. and this transfer of genetic information
leads to diversification within the population. even though everything looks similar if you look at it under a microscope or in a culture tube -- they all look like small green cells -- it turns out that all of these prochlorococcus are actually quite different from each other. this is med-4, and the "med" stands for "mediterranean." so, this one has adapted to really high-light conditions in the oceans. and so, if you were to go out to the ocean you would find a strain like med-4 at the surface -- so, right on the top layers of the water. and then these other strains... um... these ones grow deeper and these are low-light adapted. so, you wouldn't find these at 5 meters depth because they can't cope with the high light. but you might find these at 150 meters depth because they're much better at harvesting the very small amount of light that is available down there and doing photosynthesis with it. so, now that we have a genome sequence, you can actually see that there are
genes specific for this low-light environment. they have a lot more genes that are involved in harvesting light, for instance, than the high-light-adapted strains do. the high-light-adapted strains on the other hand, have genes for dealing with u.v. radiation, and so these guys that live deep don't ever see that much u.v. radiation so they don't need those genes. chisholm: it's a very complex story and has sort of changed our view of the role of viruses in the oceans that maybe it isn't just that they're there to kill prochlorococcus but more that, yes they do cause cell death but they are also moving genes around between different strains. and we think that that's very important in maintaining the global prochlorococcus population because it maintains genetic diversity in this group of cells. so, i've started to think of it as some kind of a symbiosis more than a predator/prey relationship which is really heresy and maybe completely
wrong but they've been working on that story and figuring it out. narrator: since prochlorococcus is an integral part of the ocean's food chain, knowing how it functions is key to a better understanding of the carbon cycle. without prochlorococcus and the things like it that do photosynthesis and produce oxygen then we wouldn't be able to survive. i'm trying to do my part to understand things at the most basic level. and then eventually someday we might be able to predict how these systems will respond to environmental problems. but right now we know so little about the basic science that that's really where we need to start. chisholm: my hope for prochlorococcus is that we will have a lot of people focusing on understanding this one organism and that it will serve as a model system for what i call systems biology, and that is the study of one organism
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