Southern Annular Mode changes phytoplankton composition in the Seasonal Ice Zone
Thursday 7 September 2017, 3:54pm–3:54pm
This week's seminar will be presented by Dr Bruce Greaves. Bruce came to phytoplankton late in life whilst undertaking a Masters in Marine and Antarctic Science by course work at IMAS and the AAD with Andrew Davidson, Andrew Martin, Andrew McMinn, Simon Wright and Rick van Enden. He completed this work in June 2017. Bruce was awarded a PhD at the University of Tasmania in 1997, not in plankton but something more terrestrial. Bruce has not been south of 45°S. In his talk, Bruce will discuss the influence of the Southern Annular Mode on phytoplankton.
Phytoplankton is the primary producer of the ocean, absorbing CO2 from the atmosphere, feeding the living ocean with the subsequently stored solar energy, and shifting carbon out of the atmosphere to the deeper ocean via the biological pump. Phytoplankton stocks are declining globally.
The Southern Annular Mode (SAM) is an index that indicates the position and intensity of the vortex of the southern-most portion of the Earth's atmosphere below ~ 51°S. The SAM is strongly related to global weather including the amount of rainfall in south-eastern Australia; it is increasing.
Fifty-two samples of surface water, collected during resupply voyages of the MV L'Astrolabe over 11 consecutive spring-summers, from the Seasonal Ice Zone in the Pacific sector of the Southern Ocean, were surveyed using scanning-electron microscopy. Some 25 730 organisms were counted, 48 taxa were identified, many of them to species level, including 38 diatom taxa, coccolithophores, silicoflagellates, Parmales and Petasaria. Forty-five taxa were analysed of which 10 showed a statistically significant relationship between abundance and SAM on an individual pair-wise basis. The variation in SAM explains up to 31% of observed variation in taxon abundance across all samples. Cluster analysis confirmed that samples could be grouped according to the species abundance composition. Constrained analysis of principal (CAP) coordinates showed that variation in SAM in spring at the beginning of the season explained 9% of the total observed variance in phytoplankton observed in that spring-summer season. A multi-constraint CAP model that included SAM, the number of days through the season, and the time since sea-ice was present at each sample location, explained 38% of the total variation in the abundance composition of 33 taxa.
Please join us in the AAD theatrette on Thursday, 7 September, at 11.30 am.
We are looking forward to seeing you there! All welcome!
AAD Seminar team
Southern annular mode changes phytoplankton composition in the seasonal ice zone
Dr Bruce Greaves:
Thanks for having me here to do a talk.
Ok, so the Southern Annular Mode shows influence on the species composition of phytoplankton in the Seasonal Ice Zone. And my supervisors in this, Andrew Davidson, Simon Rudd, Andrew Martin and Andrew McMinn from UTAS. And I did this project as part of the UTAS IMAS Masters, and this research project and the literature review that went with it formed one-third of the assessment for this. So this bit of phytoplankton, well, half a bit of phytoplankton, it’s a diatom, fragilariopsis rombica. This is only one-half, the other half is either inside or over the top of it. Here’s a few more photos of the same thing. These are scanning electron microscope photos. It’s quite small, it’s five thousandths of a millimeter long. It’s related to fragilariopsis kerguelensis, which is pretty popular. And here’s the answer really. This is the Southern Annular Mode, which I’ll talk a bit more about later. So this minus, this plus, this is the abundance of fragilariopsis. This is 52 samples. Each dot is one sample spread across 11 years and it seems from this that when the Southern Annular Mode is alone, there’s a greater probability that there’s going to be more fragilariopsis arabica and when the Southern Annular Mode is high or positive, there’s a probability there’s going to be less fragilariopsis rombica. And this is the canonical analysis of principle coordinates hack, and so there’s fragilariopsis rombica up there. And I’ve got 33 species in here. Some of them have species groups. And there’s the Southern Annular Mode down there and the fact that this has got a blue arrow and it’s certain length means that it’s displaying 9% of the variance of this multi-species competition. And the other one here, the type of spring summer, is explained 15% of this variance multi-species variance. We’ll go through this a bit later, but the statistically significant clusters that came out of these 52 samples, I’ve just drawn these circles around them, that’s how they appear on the CAP diagram. So that’s really the answer. And you can probably go now if you’ve got all that.
I’m now going to go through this long and rambling talk about how I got to this point – some of which is about the things I’ve learnt along the way, not so much about what necessarily I discovered in this project. So I was unemployed and so I said to the government who were paying my wage at the time through the dole, can I go back to uni, and they said yeah, no worries about that. So I went back to UTAS IMS and did this professional Honours, eight subjects in one year, and that was pretty fantastic. And in that time, one of them was a phytoplankton subject, and Professor Andrew McMinn let me use the scanning electron microscope at UTAS, which I just found completely amazing. And this isn’t a diatom, this is silica flagellum, they’re quite famous. We see pictures of them everywhere. It’s really, really small, but it’s, you know, point to point, forty-thousandths of a millimeter across, four-hundredths of a millimeter. And that’s what it looks like. That’s a live one. Got this out of the river off the IMS Building the other day and that was the first time I’d ever seen a live one. So this is just the shell, which is made of silica, silico dioxide, quartz, glass.
At the completion of that professional Honours, I still didn’t have a job, so I said to Andrew Martin, “Look, I need to find a project to keep going and do this Masters”, and he said, “Go and talk to Andrew Davison” and he said, “Let’s talk to Simon” and Simon had detected a SAM signal in chlorophyll content. And so he was pretty excited about that and he said, “We’ve got all these samples and maybe you can look and see what you can find in there”. Well, I didn’t even know was SAM was, I’d never heard of it, but I did like taking photos of phytoplankton so that seemed like a good thing to do. And Rick let me use the scanning electron microscope, so thank you Rick. And so I took a heap of photos like this and I’ve given them out here. I’ve finished with them, they’re going in the recycle bin. So if you want them, take them home, marvel at them and put them in your own recycle bin another time.
So phytoplankton. I really enjoyed meeting these guys. Charismatic microflora. And so they actually don’t look like that. This is the thing with the scanning electron microscope image. The shells of these things – and this is all that’s left here, is the shells – the shells of these things are made of clear glass, quartz glass. And this is a light microscope one. I took this with my camera down the eyepiece of the microscope, so it’s a slightly dodgy picture, but you get the idea. I like them anyway. So that’s clear glass. And that’s what it looks like. That’s the end of one of these ones. And you can see all this detail that you couldn’t see except in the scanning electron microscope. There were are, made it clear, quartz glass. So what’s going on here? Why is this the case? Why do these look like this and not this? So, if this is the filter, imagine going off for miles in any direction, you’ve got hundredths of a millimeter here, and so on the filter the water is being drained through and all the little things are lying on top of here, they’re clear. So they’re all coated with metal, be it gold or platinum. And then a highly focused beam of electrons is fired at this filter and it scans across and as it touches the metal, it’s reflected and the reflections pick up like detectors and the system puts it all together and ends up with an image like this. It’s not transparent at all, it’s just a surface image. And this is another diatom. A chaetoceros species. This is the only one of these that I found so I can’t even tell you what species it is. And this one is off the IMS Building. Looks kind of the same anyway.
Now, the thing about this is they’ve got chlorophyll in them. And chlorophyll, well, it’s a solar panel molecule, that’s what I think of it as. And it makes sugar out of greenhouse gas and sunlight – which is pretty magic – and it stores the energy in chemical bonds with carbon. And everyone just wants the sunlight. That’s all we want. When we eat this stuff, we don’t each much of this, but when we eat other things, all we want is the energy, the sunlight stored between the carbon bonds.
So, now I’m going to tell you a bit about myself. Now, Clobs was going to do this, but he said, “give me your résumé”, look, I’ll just tell you. I started my working life as an electronics technician. Did that for a while. And then I went into forestry. And there’s a Victorian species growing in southern Chile and these are ten years old, magnificent trees, they grew them for swords, they grow twice as fast as they can be grown here. Sadly, the wood is rubbish. I’m going to tell you a bit about some of the papers that I’ve written. But when I put this together, I realised that was completely boring. So I’ll tell you a bit more about myself. I’ve got a beautiful daughter who’s the coolest chic in Hobart and still lets me go out with her sometimes. And I’ve had some beautiful dogs in my life. All these have gone to dog heaven now, but they were good. I’ve climbed Krakatoa and didn’t get killed. So I was going through Indonesia and picked up a friend in Jakarta and she’d been up the volcano, so we started around Krakatoa and climbed up there and there was no action. And we got to just over the top of this rise and took a few photos and she said to me, “You know, when we climbed a volcano in Vanuatu, they said if it throws rocks in the air, don’t run away”. Anyway, we turned to walk away and there’s this massive bang behind us and it threw a heap of rocks like combi vans in the air. And this is when I – all the rocks had come down and I’d stopped running. So I took a photo. And then we spent the next day and a half – I was anchored there, there’s the boat out there – and I don’t know if you know the story of Krakatoa, but in Lonely Planet it says it’s the closest we came to losing all life on earth in the last two million years when it went off in 1883. And this island here and this island here and there’s another one over here, that’s what’s left of the mountain that was Krakatoa when it exploded. And this one came out of the water in 1927, and this is called the Son of Krakatoa and it’s slowly coming up out of the caldera.
I’ve had other adventures. This is me breaking the mast in Indonesia 200 miles south of the equator. This is the mast. This is supposed to be up there. There’s only two wires here, there’s supposed to be three. So on a boat like this, there’s 12 wires holding the mast up. If one of them breaks, the mast breaks. And which one breaks determines where the mast breaks. This is the front side. I know this isn’t much about phytoplankton, but it’s better than looking at my references. This is me repairing the mast. And no one spoke English here and they didn’t have any high tensile aluminium. In fact, no aluminium on the island. But nonetheless, got it together. And this is the mast repaired back. And you can see here, I’ve actually lost about three millimetres in mast length. Such high tensile material, it snaps, it doesn’t bend. So I consider that an achievement.
Anyway, what else have I done? It’s the references in it. So I’ve written some other things before. Google says I’ve got 623 citations and an H-factor of 15, but I still quite don’t know what that means. So, look, exciting times. So “Breeding Objectives For Eucalyptus Globulus For Products Other Than Kraft Pulp”. So that’s been cited 120 times. What’s another one? Here’s a nice one. I’ve made submissions to the National Greenhouse and Energy Reporting System Technical Guidelines for the Estimation of Greenhouse Gas Emissions and Energy at a Facility Level. So I’ve done a bit of work with that a few years ago. I’ve written a remote sensing code back in 1993 before we had really good remote sensing. Mostly it was genetic stuff anyway. What else? Well, I’ve single-handedly cleaned a radiotelescope at the university, the one out at Cambridge. And, as you can see here, I’ve almost finished. There’s just this much to go. And so after all that stuff, I find phytoplankton and it just absolutely amazed me. How did I not know about these things before? Anyway, here we are. So you’ve probably seen this before. Certainly, I’ve seen this in almost every phytoplankton presentation I’ve ever been to. It’s come from someone here at the Antarctic Division. And the things I want to point out about this is how much there is, southern ocean, five million tons. It’s always an estimate, I get that. And the estimate is that there’s six thousand million tons of phytoplankton. And the point to remember is that the annual production of phytoplankton is sixty thousand million tons a year in the Southern Ocean. Everything needs to eat phytoplankton or eat something that is eating phytoplankton.
So what else do we know about it? Well, that’s how much – I’m not too interested in that. The bigger ones are the younger ones. This took a while to get my brain around. When I was looking at one of these plots, and I looked at lots of these, within a particular species, the bigger ones are the younger ones. And it’s not sort of quite true because they’re dividing. They start off full size again after six reproductions and then as they divide they get smaller and smaller and smaller. So here’s one I caught in the act of dividing. So the two halves of the phytoplankton – sort of the diatom that fit negatively over each other – they grow apart a bit and the it grows a new valve for each half inside. There’s one there and there. And this is about to come apart and be two phytoplankton diatoms there. So this process of doing this, it ends up with two. One is the same size as the original diameter and one is a bit smaller. So after the second division, you’ve got one full size and one, two, the next size down and one smaller again. And with each division, they’re just getting smaller and smaller and smaller. And so if you see a big one, it’s from a recent sexual event. And yet the smaller ones are after lots of divisions. That’s the point.
So phytoplankton, to me, the thing about it is it’s so important to the carbon cycle. It feeds everything. So I have to go through this stuff, otherwise you don’t get all that. So where’s the carbon on the earth? So we’ve got 830 petagrams of carbon in the atmosphere, of which 240 is ours. And a petagram is 10 to the 15 grams of carbon, or a billion tons of carbon. So there’s 830 thousand million tons of carbon in the atmosphere. There’s another thousand petagrams, a thousand million tons, underground we haven’t got out yet. There’s 1700 petagrams in the terrestrial environment – that’s like carbon in me, carbon in the table, carbon in trees, carbon in the soil. There’s three petagrams of carbon in the ocean life – life in the ocean – whales, phytoplankton. And there’s 39 thousand petagrams of carbon in the deep ocean. So I sort of felt I needed to call that the carbon pond because that’s how I needed to think about it. It’s a still place, and that’s where almost all the carbon on earth is, in the biosphere.
Next, we need to know where the carbon is going. So there’s nine petagrams of carbon a year at the moment being released by us anthropogenically, largely from the combustion of fossil fuel. Phytoplankton is taking in 50 petagrams of carbon a year. It’s feeding all the life in the sea, not just [inaudible], but just that’s all the life in the sea, which respire it back. So 37 petagrams of carbon ends up going back into the atmosphere or the surface-ocean atmosphere environment environment, leaving 13 petagrams of carbon, which is being exported to the deep ocean. So we’ve got this greenhouse problem because we’re releasing too much of this and it’s changing how much is in the atmosphere. And at the same time as we’re releasing nine, phytoplankton is dropping 13 out of the system. That’s not to say that that’s countering the nine and so there’s more to consider here. The ocean is also doing ocean circulation. And over here, this is happening in a few places, but imagine this is Antarctica and this is the Antarctic diversion, so the deep ocean is coming to the surface, and it’s just gassing off carbon dioxide. Like, this, like that. So the carbon dioxide is just coming out at this higher concentration of carbon dioxide to water and it’s just gassing off. I’ve been wanting to open that all day.
So interestingly, this gassing off, you can see it. This is a – the gas is shown between the sea and the air. And so if it’s green, there’s no net carbon exchange between the sea and the air. If it’s yellow or red, the carbon exchange from the sea is from the sea to the air. So this line all around here, yellow, red, yellow, red, that’s the Antarctic divergence. That’s where the deep ocean is coming to the surface and simply gassing off CO2. The other thing that’s going on is some of the surface ocean is going under and taking carbon dioxide that’s been absorbed into it with it. And so that’s happening in these blue and purple areas. And in the case of the Southern Ocean, this is a global thing, the world here, not just the Southern Ocean, but all around the Antarctic continent we’ve got gassing off. And all around the Antarctic continent further north, we’ve got seduction. And you can see here, these blue and purple areas through here, and that’s where CO2 is going back to the deep ocean. So all things considered, the oceans are taking in 80, which is the phytoplankton and the seduction, and they’re leading 078. So we’ve got a net take-up by the ocean of two, which is still a lot less than 9. And for completeness, the land is doing a similar thing – taking in 123, letting go 119, with an uptake of four. Now, the uptake of four is because we’ve got sort of reforestation going on, I suppose. And that’s going to come to a halt. We’re going to stop having any more areas we can grow more. So I would expect this to decline. So that’s the carbon dioxide. So you’ve got to know what this phytoplankton is doing. This is important business. Phytoplankton does less of this. We’re going to end up with more up here. And I got a lot of this information from the IPCC stuff and some of my own stuff. So I’ve done some work in emissions training before, so I sort of think about it. Like, the biggest is Australia’s greenhouse gas emissions which were reported. And so they’re broken up into all these different numbers. You know, station energy loads and power stations 26 million tons in total. Most of it is there. And over here, we’ve got the forestry and land use change. So because in Australia we’ve got an increasing forest estate, increasing forest, but this is a negative number. So Australia is actually taking in atmospheric CO2 in our forest. And so if we just look really simply at this exclusive economic zone that’s Australia’s around the Antarctic continent, it’s about two million square kilometers. And if we assume that phytoplankton is exporting from the surface into the deep ocean, 40 grams of carbon per square metre per year, that simply comes out to three hundred million tons of – this is CO2 now, by the way, not carbon – negative. Now, I’m not suggesting Australia, because of its exclusive economic zone, I’m not suggesting that we can offset out fossil fuel emissions with our phytoplankton in the Southern Ocean. But just as a scale thing, like, these are big numbers. We don’t want to miss phytoplankton because they’ve got a big job in the carbon side. So somebody, probably Simon, I don’t know, was it you, Simon, decided that or organised so that when L’Astrolabe did it’s trips up to four in a summer, every 12 hours, collected a water sample, did up to four voyages a year, did this for 11 summers, so we’ve got 1300 samples which we carefully analysed. That’s where Simon got his indication of Southern Annular Mode showing effectiveness. 550 of them already mounted on SEM sites here in the building. So how did this go? They collect 250mls of surface water, put it through a 25ml filter with really small holes, .8 thousandths of a millimeter into that, and wash it a few times and all the organisms get left on the filter and there they are. That’s the la ostrila collection. That 550 SEM stuff is in that cupboard. There’s a few out on the desk – that’s from one voyage. These little things end up in here. There’s one in there now. And then they go into this machine and then you can take pictures like that.
And so in trying to understand this, I sort of approached it like I was surveying the forest. And so I took these pictures which I consider are plots. And one of these plots is equivalent to two-thirds of a drop of seawater. It represents one seventh-thousandth or so of the area of the filter. So I could take seven thousand photos like this on the filter for full coverage and the image for you to take home, that’s one of these, .22 millimetres x .3 millimetres of filter area. So there’s a few on the desk. And if you imagine a block of water over this picture – this is higher than it is wide and long – well, you need 2,300 of those to make the volume of water which had the organisms that have ended up on that photo. So, it looks like there’s a lot of organisms on one of these, but at that rate, there’s only one of these organisms probably every 20 or 30 of these water bodies.
So, I was just going to show you. These four photos are all taken on the one stub, just so you get some sense of the variation across the stub. Look at that beautiful radial area up there. That’s zooplankton, that doesn’t photosynthesize. And those four. Now, that’s another sample, it’s a different stub. And this was the one with the most stuff on it, and I would have done a bad job at surveying this because there’s a lot of things underneath that I couldn’t see. And that’s another sample, quite different again. And I took a few photos at a lower magnification to try and pick-up some of the bigger things that were more scarce and so I used these images which represent 2.2mls of water. And on this image, that’s the size of the image that I considered the plots like these one I put out there. Now, I made myself a key, little photos of things that I had identified. Everyone that does this work makes their own key, I think at the start. And from all this counting, you can work out the species composition. And so these are the 33 taxa that I settled on and for this particular sample this is the estimated number of cells per ml. So fragilariopsis rombica – 122 of them per ml estimated. And I wasn’t able to – the other big photosynthesiser in the Southern Ocean is the [inaudible], which looks like that. And bear in mind, the holes here are point eight thousandths of a millimeter. So this is a very small thing. And sometimes they are pairing off but I couldn’t assume just because I couldn’t see them they weren’t there. The sampled area – well, I just used samples from the seasonal ice zone, south of 62, north of 64.5 degrees. So in winter, some ice cover, and in summer, no ice cover. So this sample I’ve been looking at, this is a figure of the latitude that the sea ice is at with time. And when I say the edge of the sea ice, it’s the edge defined as where the sea ice is 15% cover. So this particular sample was taken, you know, late in 2007 and it’s taken when the sea ice is still around. But we’re not talking – it’s only 15% sea ice. We see ice outside this line as well, but less than 15% cover. And so down here, there’s more sea ice, 25% cover. So, you know, if you get around this, the latitude of the sea ice in winter, summer, winter, summer, yeah. Okay. So that’s one sample. So I have 52 samples spread across 11 years and each one of these dots – don’t worry about what the colours are – but each one of these dots represents one sample and that’s where the ice was at the time. And so I’ve got some samples here where they never sort of got ice the previous winter or they never got as much as 15%. There are some samples that we’re taking within the ice down there. Still a lot of water around, but it’s only low level concentrates of ice. Some samples that are taken like near summer, where the ice is well past. So there’s all this variation going on, right. So all these images, many of them, I ended up counting 25,000 diatoms. I measured most of them as well because I had an idea that the volume would be more important than the simple number because they had such different size. And after that, I ended up with this table and this table has got 52 samples down here and 33 taxa across here. And in here are the estimated cells per ml. And you can feed that into a cluster system that identified nine statistically significant clusters, suggesting that the samples could, statistically, be separated on the basis of this species composition of 33 taxa. But the question was really what’s going on with the SAM? And I had all these environmental parameters for each sample – the year, the date, the time, the latitude, the longitude, the days after 1st October, which is a time through the summer if you like, the latitude that the ice edge was at that time, the minimum latitude of ice, the sea surface temperatures for attrition numbers, some chlorophyll numbers, I got some from satellite, and the sea ice was 20% covered. And all of these things might be giving you variation in the species composition of phytoplankton. The chlorophyll numbers, we won’t worry about them. Oh yeah, that could be interesting. So this particular sample, as I said, was taken – remember that previous diagram – it was taken just before the ice was finished here, not finished, but before the 15% threshold goes past. So this is the snapshot of the chlorophyll content at the time the sample was taken. The sample was taken here. This latitude, longitude. And you can see there’s been a bit of phytoplankton activity further south. There’s a gap opened up in the ice. But most of it is happening north of there. So that’s just a snapshot of the phytoplankton – the chlorophyll in the water at the time the sample was selected. And this is the snapshot of the – this is the chlorophyll at the location the sample was taken through time. So just in that square through time. And you can see the ice is about to disappear or go past any the phytoplankton, or the chlorophyll content, is going to bloom. So all these things are going to probably give me variation in the species composition of phytoplankton. But I was looking for the Southern Annular Mode. So I had to come to grips with what the Southern Annular Mode was, because I’d never heard of it. So I think it’s also called the high latitude mark and the Antarctic Oscillation. And there’s a northern annular mode as well. And I finally came to the point of understanding what it was like this. I imagined it’s about a donut of air in the atmosphere, the southern most portion of the earth’s atmosphere, which I imagine is like a donut of air, that is turning. Yeah? And it’s not really a donut because the atmosphere is really a lot thinner than a donut. This is the total atmosphere 150 kilometres deep and 80% of the mass is the atmosphere’s in that light. Okay. So probably a donut is a bit bulky. But nonetheless, I think the physics is kind of the same because we’re talking about a momentum of mass of air going around in this stuff. And so when we’ve got a positive SAM, what’s going on is the donut is smaller, but it’s more intense. Then I put more sprinkles on it, shows more intensity, and so the boundary of this mass of air that’s turning, and so it’s windier, it’s winder when you’re in there. So that’s when the Southern Annular Mode is positive. And the other thing about when we’ve got a positive Southern Annular Mode is this dragging sun. And when SAM is negative, it’s a bigger donut, so it’s more boring and not as many sprinkles and not nearly as intensive wind in there. So you can sort of work out where this is based on the Southern Annular Mode. It’s probably more complicated than that. I’ve showed this to a few people and no one has said that’s rubbish, so take it or leave it. But that’s how I visualised it. And so this is SAM since we started kind of calculating it. I think we started calculating it in the 80s, late 90s maybe. And so, look, it goes all over the place. It’s not an annual cycle. You know, there are maybe fours year here. And there’s been a trend of increasing SAM of maybe three-quarters of a SAM point since 1979. My samples were just in these 11 years here. And we’re not talking about the SAM, the Southern Annular Mode. I have just used principally the SAM in the three month period of spring – September, October, November.
There are two versions of SAM - you can get one from the British Antarctic Survey, that’s just on the web. They produce a three monthly number. You can get one from Noah in the US, they produce a daily number. When you put the numbers together, they’re only correlated at about .9. So they’re not even the same. But I use the Noah one. We can talk about that later.
So here we are, back to the first one – fragilariopsis rombica. I showed you this at the start. When SAM is positive, there’s a probability there’s less of them; when SAM is minor, there’s more probability that there’s more of them. Okay. The thing about this relationship is I’ve only got one low SAM here. So I’ve only got 11 years and the SAM is what it was. So not a design experiment. And I do have two high SAM years. But this low SAM year has got a lot of leverage on this relationship. So there’s a caveat there. But nonetheless, that’s how it looked. Oh yeah, so fragilariopsis rombica is up this side of the graph because it shows a negative relationship with SAM. So, all the species that are some distance from the origin are ones that are on this side, showing a negative relationship with SAM. And all of the ones like this one here and this one here, they’re showing a positive relationship with SAM. This is abundance with the SAM number. And this was quite orthogonal to the line for the times through the spring/summer. And so fragilariopsis rombica is this way of the origin. So that’s saying that later in the summer, there’s more likely to be more fragilariopsis rhombica. So, what that means is some of this unexplained variation in this pair-wise, this one parameter analysed, has got variation here due to time through the summer. So really the only way to do it is with this multi-factor, what we call that multi-parameter.
Here’s another one. The [inaudible]. It shows a similar sort of trend. Less in a high SAM year; more in a low SAM year. You know, these are not strong relationships. 18% of the variance is explained. The relationship says it’s significant there. I have some questions in my own mind about the stats underlying this. Given that SAM is a single annual parameter, should you be using the same stats? I wonder that. But years ago when I was doing my undergraduate, I remember talking to a Masters student and he said, “Man, look, you do all these stats, ask people how do I do this, how do I do this, can’t get any answers. But when you write it up, they come out of the woodwork.” So it’s time people came out of the woodwork and told me if this is any good or not.
Here’s another one, chaetoceros atlanticus and this is one with a higher SAM unit, there’s more likely more of them, and a low SAM unit, there’s more likely less of them. So the time through the spring/summer. So my samples were all collected from 10 October. The latest one was the last day of February. And so we know this is from somewhere on the Continental Shelf and it occurred to be sort of similar, this chlorophyll content. So there’s not much chlorophyll until the ice melts and then, suddenly, it’s off, lots of chlorophyll. As summer starts to drop away again, coming into Autumn, it drops away again. So that’s the response of chlorophyll. So it’s quite likely that the species composition has got to change through this time and certainly some of them show it. So this is the parmales. Now, they are more likely to be seen early in the spring/summer and much less likely to be seen later in the spring/summer. And fragilariopsis cylindrus or curta, I couldn’t separate these reliably so I combined them together. In the analysis, sometimes I could, but mostly I couldn’t. And it was the only one that statistically had a curved response where there was more likely to be more of them in mid-summer, or mid-spring/summer, and less at the start of the spring/summer and less at the end of the spring/summer. But still, they’re not strong relationships. 33% of the variance explained. Still the stats are saying it’s highly significant.
And chaetoceros dichaeta – very less likely to see them early in the spring/summer; more likely to see them later in the spring/summer.
So, the canonical analysis. I showed you this at the start. SAM is 29% of the total variance, multi-species variance, 33 taxa. And the time through the summer is explained 15%. This isn’t including the fragilariopsis curved or cylindrus as they occur. That’s just assuming it’s a linear relationship. So there’s a – not so good there. Oh, this is the variance table that I want to show you here. Okay, so the total model is explained 38% of this species composition variance with all these things. And it’s uni traits. Southern Annular Mode, here it is, 9%. And it’s also 9% in multi-parameter model but just fitting the Southern Annular Mode by itself, still on 29% of the variance. Then these are other SAMS for the same year. December, January, February there; March, end of May; in July – they don’t explain as much variance as immediately before SAM. SAM in the spring is showing influence on the phytoplankton species composition in the spring/summer.
Now, it’s really not a surprise in terrestrial systems. You know, as the climate is changing, species composition in passes is changing. So it’s not surprising to me you’ll see a change in composition when the weather is different. And I guess that’s all this shows really. I won’t worry about that. Won’t worry about that.
So the conclusion is the Southern Annular Mode shows influence of the species composition of phytoplankton in the seasonal ice zone, Southern Ocean. Ten of the 33 phytoplankton taxa show a statistically significant SAM influence. Some up, some down. The 33 taxa species composition shows variation in SAM, with 90% of total variance in species composition explained by SAM.
I could not detect having – like, it’s one thing to count all these diatoms, but to measure them all, that took a lot more time. And so I worked out the volume of each individual cell – some of them were inferred, so I didn’t measure every one and every dimension on every one – but I could find no influence of SAM on total phytoplankton volume. And that’s like as a surrogate for phytoplankton biomass. It’s not a good surrogate because you can sort of double the – as a phytoplankton – as a diatom is dividing, the valves are growing apart. It isn’t necessarily changing environments, it’s building new valves inside. And so maybe – and particularly in the summer the species are even, I guess it is. But so they might have been doubled in volume, but they really haven’t doubled in environment. So volume itself isn’t any way necessarily the best indicator of biomass, but it’s all I had. Anyway, volume didn’t show anything.
So one last thing. I’ve just taken the samples I looked at just on the seasonal ice zone, and this is where we’ve got the deep ocean current involved reaching the surface and gassing off. There’s still export going on there. But the bulk of the uptake by the Southern Ocean, you know, people say the Southern Ocean is taking up 40% of anthropogenic greenhouse emissions. Well, it’s not happening here, it’s happening in the northern part where this subduction is going on. And so it would be interesting to know if there’s any change in the species composition for phytoplankton up here on the rest of the transits because the last lot of samples were collected from Tassie.
And I’ll just leave you with what is probably the most beautiful photographs I think I took.