welcome to the science for the public lecture series science for the public is an organization committed to bringing the science information issue to the general public this is our website for our program observed actually from space settle lights the oceans themselves and by means of the phytoplankton absorb about one third of the c o two in our atmosphere and for that reason these plumes in our oceans play a fundamental role in maintaining the climate and the ecological health of the planet despite their importance what triggers the blooms is very complex and not fully understood one of the people instrumental to unraveling that mystery is doctor dave on a senior scientist in physical oceanography at the woods hole oceanographic institution in massachusetts she's also a fellow this year at the radcliffe institute for advanced study at harvard dr my hut yvonne received her ph d from stanford university and she joined the woods hole oceanographic institution  twenty eleven her research focus is the relationship between the physical and biological processes that shape the oceanic environment and contribute to earth's climate dr mahadev on is program with her collaborators post doctoral science scientists and ph d students in the mit woods hole oceanographic joint program we are very pleased to be able to learn about the relationship between the ocean physics and phytoplankton from a scientist who has contributed so much to this field of study start asking you if you would please give us a little background about the ocean how it works with the c o two and then the role of the phytoplankton so i thought i'd show start by demonstrating with this little video clip here which is actually constructed from  that you see in the oceans of course it's changing seasonal lisa just as you have seasons on the land the ocean chlorophyll increases during the summer months in most places not always but spring and summer and and then decreases about the times some of them can swim but many of them are sort of passively built around by the currents of the water and those organisms just like lamp plants they take up c o two the take up c o two that's dissolved in the they located in preferred areas in the oceans or are they through hell so you find phytoplankton everywhere you know if you take a bucket of water anywhere in the oceans and you look under the microscope it's richard find a plaque from and you'll see most diversity of these organisms so we're just barely understanding even what's out there and then there's you know a lot more to understand as to why the there who's there when it's there and and all kinds of sort of things in their life cycle a succession the diversity is as i said is enormous also in size you find an enormous range of  so so so these organisms as i said there they're free floating they take up c o two they respond to some light so they need sunlight and so when you asked me where they are in the oceans the prefer to be in the surface o say you know bloom is hard to define because if i were to ask you about your lawn when does a bloom you know in the spring it turns green but there isn't a given day and then if you wanted to define a day when it starts to bloom you would have to set some sort of atlantic you know around sixty degrees north you see an immense seasonal transition and that seasonal transition you know it's very you know sunlight north of sixty north in the winter  surface mix layer is deep mixed so you keep cooling the surface ocean when you cool the surface ocean you drive convection because colder waters heavier than warmer water it starts to sink and so it gets mixed down to depth of several hundred meters and when that happens if you're a little organism in the surface ocean you just don't find enough light but what's good is that by all this mixing you get a lot of nutrients to come up in the winter but the light is insufficient because you hardly have sunlight and if you're fried plantain been pushed down to six hundred meters every now and then every day just not see enough light so the light sunlight dk is with depth in the ocean you get a lot of sunlight  exponentially with air so by the time you get one hundred meters it's very little light in the ocean so these organisms just don't find enough light in the winter to grow and when the spring comes they start seeing enough light and you see nutrients so now what happens is that there's plenty of light in the spring and summer but the nutrients get consumed by the phytoplankton and when they run out of nutrients the oceans are very poorly mixed in the world to cool and it's very hard for them to bring those nutrients up when it's not when you start warming the oceans then you create a warm water the surface and that warm water stays trapped at the surface because warm water is lighter than heavier than a hold water and so in fact it doesn't mix in the summer very easily and that in fact is an issue in many regions of the oceans so if you look at further south like south of you know around thirty degrees north for example you have light all year round yes but you don't have the mechanisms to bring the time whereas the oceans for a large part of the time you're heating them from above and so the tropical oceans for example are heated from above the order womyn's but it doesn't sink because it's one of yeah i want to share a little bit this experiment of got this position in the middle i don't want to create something like a demo ocean so i'm going to put salt on one side of the tank and then i'm going to just open the sport rishon it so it's going to create a layered fluid in which you know the salty water is heavier so it's going to sink below the the fresh water and that's in fact so it's going to sink below that other side that the other side doesn't have solved that's right oh isn't that clever and so you will see and you can see that the water that sort years kind of stays in the bottom in the oceans it would be both sold  temperature that creates this and in fact you're generating these waves which are the interface of yes so the ocean is leered and there are waves at the surface there are waves at the interface of these different layers those are called internal waves just like like you have surface those waves break or get it get sort of energized and you get some sort of mixing but one of the big problems or i should say the problem is one of the things that we find about the ocean is that the oceans are forced to the surface of the oceans are in motion because the wind is blowing at the surface and that wind blowing at the surface sets up a lot of currents and and those currents are all getting the energy from the surface from the wind or even if you heat the ocean it's at the surface but the ocean is very strongly layered and that layering prevents things from mixing vertically a little bit further that i've just you know did this with two layers but you can imagine that if i now put something in here and mix it maybe it's a little less intuitive for you to think what will happen to this l so when i open this it's going to try to find its own density at which it's comfortable water really off another density and those that are the density o seem to interleave and form these layers and i can show you that you know in an image of what it looks like the ocean when you make some measurements like that just look at this graphic of the ocean here and what you're looking at is a section of vertical section slice taken through the ocean and so this is temperature and you can see that the red colors means that it's warmer the blue colors means it's denser and we're looking at the upper two hundred meters in this case of the ocean this is the indian ocean in fact and you can see that the warm waters of the top the colder waters lying below and those black lines are contours of density so booked nutrients and light so that's where the ocean physics comes in because the physics either helps to move things up or down bring the nutrients up in one case or in another case in the winters and this that one mechanism that does it all and although we found one mechanism that mechanism plays out with think at certain times and we think it's very widely prevalent we measured it or saw evidence  of it in one place in the north atlantic a lot more what needs to be done to figure out is that mechanism prevalent in other places there are other mechanisms that people have proposed and those two are active and so the question of trying to decide  sea glider that you're seeing in the image there it's a little robotic instrument about that size and it's really like a glider airplane it's got some batteries yes but which should adjust the angles of the wings and this robotic glider have these sorts of instruments and then there's another instrument which is a float in a sort of going around and these gliders are sort of following this and trying to follow a patch of water in which we want to observe my colleagues want to bloom is that as i said this surface is cooling everything's been mixed very deep and phytoplankton don't see enough light because they've been pushed to depths of several hundred meters and what they're waiting for is some form of comes out it starts to warm the surface ocean and when you warm the surface ocean you create a warm layer on top and that's where phytoplankton get trapped and then they start to bloom because now they are near the surface they already had nutrients and they get sunlight but what they noticed there in this experiment in the north atlantic is that the bloom started after the water column had become little but before the sun was really warming the surface so the oceans were still being cooled because there was a strong wind and strong loss of heat from the surface but they saw that the oceans started to layer up and so the question was why did it start to layer and once it started to l found is that in fact this is a very three dimensional process so if i create a water of different densities and in fact in the north atlantic we have the situation you have cold water and you have warmer water these warm and the reason that you can have this in the ocean where you have warmer water next to colder water is because the earth isn't it is spinning and because the earth is spinning the flow in the ocean and so because of that you can have when you have differences between warm water and cool water the flow is in the direction of those temperature controls or those density controls so that prevents these waters from sort of completely mixing but at the same time the flow when it's starting to go in this direction it starts to wiggle ok and when it starts to wiggle it's called an instability it forms eddies and i'm going to water and so what you do is you come you start with an ocean in which the contour surfaces of density are vertical then you form eddies and these eddies take the warm water and  put them that's right where they were they want to go ok great if you can the show was so i wanted to show you you know a picture of the global ocean and the global ocean is filled with whole multitude of scales of eddies and so you can see that there are strong currents what you're looking at here the white tells you where the current side fact it's the magnitude of the velocity that's been plotted in white and you can see that the ocean is full of these sort of  currents which are set up the way they are because of certain boundaries i was lucky to find an image on the nasa website today which shows you a piece of the ocean this is the south china sea that you can see and it let me ask you here very quickly is it is this something new that you've been able to do it sounds like your equipment for one thing just not the computer models yet but just the equipment is very sophisticated and it sounded from what i read that you have numerous both so you're know and very well coordinated could you've done this or like fifteen years ago you know yeah yeah so so what's new is there's several things i mean one is  able to make measurements at very high intensity you can remember to have multiple robots going into the ocean making die watching what's happening so we're able to piece together what's happening at much higher resolution in space and time so with time our understanding of the oceans has increased previously our measurements were very sparse even now they're sparse compared to the size of the oceans year but we can go in and observe a piece of the ocean and fairly well with multiple instruments it's again it's expensive and depending on how much money we put into it you know exactly what solutions will generate a great deal of interest but after they get the data so they get the data and it sounds like mountains of data possibly then you they go back to the lab and you develop some computer model that's right and you tell us about that how you do yes so so the data is always going to be sparse and that's because you may measure a profil the ocean time but you don't have a full three dimensional picture of how things are evolving in space and time and that's where i developed models to try and give us a picture of what is happening and in the model we don't have just one observation of one sample or one so imagine that you want to look at this table and your eyes are closed with you able to take one spot here one spot here and things are changing in the ocean all the time and yeah  and now you want to piece it all together and understand what processes are leading to those observations that you make and that's where sort of my specialisation comes and i develop the models which are solving integrate them forward in time and we're able to see how these ocean eddies are evolving and how they change one state of the ocean into another state so what we did is we took a state of the ocean that was observed by these up by these robots of these gliders we put it in the model and approximate state again we don't have an exact state and we run the model forward in time and we see it evolve and then we keep comparing with the observations that we had later in time and these observations didn't capture the evolution of the eddies or didn't show them what's happening but now we can say oh look that's what we saw there and it's probably due to an eddy doing that so you then can sort of developing this more so so here we looked at the beginning of the bloom what brings about the bloom another very important piece of the what happens to all this plankton that's produced in the surface so are now sinking very gradually out of the ocean they get attacked by bacteria and they get the dissolved nitrate and the carbon is released into the ocean but some of these little particles gets down there so have you done that part yet or just heard that one of our little bit has been done and just as part of this experiment they were able to observe the sinking of these diatoms which is what the beginning of the actually going in to do look at the exports part of this more detail can i go back for the carbon itself or the c o two rather very quickly here and now that we have pumps so much c o two and it keeps increasing it doesn't have any place to go and in addition warming in the ocean does this kind of change this process so yes so we've put out a lot of c o two in the atmosphere it's higher than we've known you know probably millions of years certainly we have a very clean record for the last six hundred fifty thousand years and it's much higher and it's not as high as it would have been without the oceans the oceans have already taken a up about a quarter  shells and so the big concern is that if the organisms cannot form their little caps in carbon and shells then they may not be as good at sinking and so we would change what's called this biological pump which is taking carbon from the surface and putting it down well ok now we don't it's a little too early for us to to make some sort of conclusive statements about this event because there's lot to be understood in terms of to about the oceans but all of these kinds of dynamics then change a lot of the other work that you are doing right in terms of understanding the physics of the that's the right thing here so yes these things are all  r for a longer period of every year the summer months there's a lot of regions which are ice free so the summer ice has really decline what does that do with now exposing the arctic to winds which would cross never exposed to before  sunlight where you have more blooms less proves these are things people are very interested in trying to understand or study it sounds as though you will be busy for quite a while here but it's very interesting very admirable work and at this point i'd like to talk support but we have a lot of students in here tonight and i think they'd like to talk with you as well so i will stop here and so that they can do some questions and answers and thank you attempt for people to say that they can initiate the first of all the oceans are immense and vast and you know the most we can do is try to initiate a boom in a small way somewhere and the place in which this is been taken gone with the ship and dumped in dust in the ocean and the response in response they see you know the growth of the plank but there was really very difficult for them to prove or showed that this fire the plankton th but the bacteria sort of act on it and it gets releases its nutrients again and produce dissolved carbon and that dissolved carbon may just come back up so we don't know whether we can successfully u spines and these spines can sort of inflict damage on other organisms that ingest them those are the sort of common reasons for what i think in some places it's observations for long so there's a lot of where variability and so most people will say that you know when you see two or three years of data it's difficult to say is that climate change or is it so there's a lot of variability in the ocean one year you may have a warmer gulf of maine another to really conclude significant data that yes some people have been interested in blooms for more than fifty years in the fifty's itself people were looking at you know what starts a bloom or what causes a bloom one of the most to the now we have better observations but again the observations that are made in the ocean are still sparse satellite observations certainly help us to fill in the things so you know we're ten or twelve years of satellite plausible data we can go in and look at some region of the ocean and that they are stimulated by nitrate that comes out in the mississippi river because of our culture and often the blooms become so large that when that organic matter starts to sink it becomes a huge sink for oxygen because that