- [Announcer] This conference will now be recorded.

- Good morning, everybody. Happy Saint Patrick's Day. Peggy, I saw your note there, good morning and I hope you're feeling better today. Welcome to another EcoFOCI Seminar Series. This is part of our spring 2021 series. I am Heather Tabisola and Jens Nielsen is the co-lead with me for this series here. This is part of EcoFOCI's bi-annual seminar series focused on the ecosystems of the North Pacific Ocean, Bering Sea and U.S. Arctic to improve understanding of ecosystem dynamics and applications of that understanding to the management of living marine resources. Since 1986, the seminar has provided an opportunity for research scientists and practitioners to meet, present and provoke conversation on subjects pertaining to fisheries oceanography or regional issues in Alaska's marine ecosystems. You can visit the EcoFOCI webpage for more information at www.ecofoci.gov or.noaa.gov. So again, we sincerely thank you for joining us here today as we continue this all virtual seminar series. You can find the speaker lineup via the OneNOAA Seminar Series and also on the NOAA/PMEL Calendar of Events. We are here in March of this year at 10:00 a.m. on every Wednesday. And if you missed a seminar you can catch up on PMEL's YouTube page. It does take a few weeks to get these posted but all seminars will be posted. Please, double-check that your microphones are muted and that you were not using video. And during the talk please feel free to type your questions into the Chat. Jens we'll be monitoring the questions and both Bonnie and Calvin will give their separate presentations this morning, but we will address all questions at the end but please feel free to type them into the Chat and we'll make sure we go back and address those. So today I'm really excited to introduce Dr. Calvin Mordy and Dr. Bonnie Chang. And we're gonna take a dive into the Chukchi Sea nutrients cycling. Both Bonnie and Calvin are nutrient chemists at the University of Washington Cooperative Institute for Climate Ocean and Ecosystems here in Seattle, Washington. Calvin carries out several projects at PMEL including running the nutrient lab, working with the GO-SHIP repeat hydrographic program. He's also the co-leader with my other program the Innovative Technology for Arctic Exploration and is also of course, part of our FOCI family. Bonnie joined CICOES in the fall of 2013. She's interested in understanding how microbes in the ocean use nitrogen an essential element for life. And I really liked this fact, Bonnie, I took this out. You can add more later, but I liked that she's worked in every ocean on earth, has crossed the Arctic Circle once. The Antarctic Circle twice and the Equator four times while being on research ships. Five times now, oh yeah.

- Five times, one more last year.

- I think that's pretty cool. And with that, I am going to let Calvin start off and Bonnie and Jens, we'll all go off video.

- So this is, we're gonna take you through nutrient cycling in the Chukchi Sea. So I'll go first and then we're gonna have a little technology glitch and we're gonna just give it over for Bonnie. Sometimes my internet kicks out and if it does it'll just take a second for me to reconnect. So this is a map showing patterns of flow in the Chukchi Sea, most of you are familiar with this there's flow to the West that goes through Herald Canyon, flow up the middle through the central channel and to the East is the coastal current that kind of hugs the coast and EcoFOCI maintains the three main mooring sites, C1, C2, C3 on the Icy Cape line off of Icy Cape Alaska. C2 being the primary mooring there. And when we think about the Chukchi Sea and production in the Chukchi Sea, there's a few things that we know. We know that primary production is limited by light and the supply of inorganic nutrients. And that the primary limiting nutrient is nitrate and ammonium, is nitrogen, nitrate and ammonium. And in the Chukchi Sea in winter most of that is ammonium gets converted into nitrate as Bonnie will show you later. So in the wintertime, as we're setting up for the spring bloom it's primarily nitrate that we're interested in in the Chukchi. At least that's a pretty good assumption. The nutrients are largely consumed in the summer and then replenished in the winter. So we're gonna look in this talk mostly at the winter replenishment. And about 40% of the flow coming up through Bering Strait passes the Icy Cape line. And it takes four to six months depending on the winds to get from M8 which is the Northern Bering Sea to the Icy Cape line. So we have some unknowns that we know about. The past literature has shown that the pre-bloom nitrate concentrations and this is kind of what sets the stage for overall production of the spring bloom. Or do you have a lot of nutrients to support production or not? So the literature values of pre-bloom nitrate vary by about 50%. And that means when you estimate how much carbon you have it varies from 30 to 70 grams of carbon per meter squared per year for that spring production. Now this is a flow-through shelf. So in summertime you're bringing in some new nutrients, but also in summer the nutrients tend to be depleted through the upper water column as a result of early production. So the unknown is what is this a seasonal and inter-annual variability to be in organic nitrogen? Is it really plus or minus? Is it really vary by 50% or is it, is there other things that might be driving that uncertainty in the literature. And then so a recent publication from Lewis et al shows this trend of primary production in the Arctic. Now this is for the entire Arctic this plot is that's in the upper right. But this also is a similar trend of in the Chukchi Sea. What is the changes in nutrient supply that might be driving this? And the argument in Lewis et al was it was a result of changing nutrient supply. So are we seeing increased nutrients coming up through Bering Strait? What's that matches this trend? So that's another question. So in this talk, I'm gonna provide you evidence on the first bullet point of what is the inter-annual variability. And this second bullet point is currently being addressed by NOAA. And we won't get into that today. So right now the goal is to better understand the physical and biological processes of the control, the seasonal inter-annual variability of nitrate in the Chukchi. I'm gonna present some of these physical processes and Bonnie will step in later and talk about some of the biological processes. So this talk is based on a paper that was published last year in DSR II and there were a number of coauthors and I wanna acknowledge all these folks on the slide and it was funded by NOAA, UW, BOEM and North Pacific Research Board. I wanna specially recognize Eric Wisegarver and Peter Proctor, the folks that are always running all the nutrients in the nutrient lab. And so how do we do this? This is a image of a sensor code is the SUNA. It's an optical nitrate sensor. And in the circle, there's a little slot in the sensor and that measures the absorbance of the water at a large number of wavelengths. And then you sub sample a few of those wavelengths and you're able to distinguish the unique optical signature of nitrate and estimate what the nitrate concentrations are. And then this little, there's a wiper here that cleans the flow cell, swipes the flow cell with a wiper before each measurement. And these soon as we're deployed at C1, C2, C3. So we're gonna look and they collect hourly data. So we're gonna look at one of those prime series that we get. So this is a kind of a complicated plot. This is a deployment in September 2016. We do a CTD cast as we deploy it. And that's this black dots a discrete measurement that we use to calibrate the nitrate sensor. The nitrate trace is in blue. You can see a lot of variability. There's low concentrations in November, December increasing through the winter. And then that this is near the bottom. This is a few meters off the bottom. And still we see that the nutrients are drawn down there in summer. In green is the chlorophyll trace. And this is chlorophyll fluorescence converted into a concentration. And you can see that we even get this high chlorophyll on the bottom. And then the draw down of nutrients. Black is a ice coverage. So, ice disappearing typically in mid-May and the spring bloom is often mid-May. In fact, I've picked May 15th as kind of cutoff for spring pre-bloom concentrations. In some years that nitrate continues to increase after May 15th, but I just pick May 15th cause that's in some years that the nutrients drop off quickly after that date. And then in red is salinity. You can see it's also a little fresher later in the year as you've mixed thoroughly mix the water column and brought that fresh or nutrient depleted water to depth. And then that water is flushed out during the winter. And so we wanna look at this trend here. We're gonna focus on January through May 15th this increase in nitrate and look at the variability in this replenishment and the pre-bloom concentrations of nitrate that might support spring production. So that's what we'll look at. So we've had a number of deployments at this C2 mooring site. We had deployments, now this is, on the bottom you'll see this is January through it's jumping ahead. This is January through May. So we deployed in this plot B we deployed in 2010, and this is January, 2011 through May, 2011. So we have a time series in 2011, '12, '15, '16, '17, '18. We take the mean of all of the nutrient data and that's in blue here. That's the mean nitrate from those deployments. And then we also have the mean, oh, come on Calvin don't do that. We have the mean salinity. And then we have the anomalies for each of these. So this second plot B is the anomaly in 2011 with this pink being the salinity anomaly. And this gray being the nitrate anomaly. And I just want to point out that in some years in 2011 and then on the bottom of 2018 we get this really high nitrate anomalies. In other years, as in 2012 we have a negative anomaly and these are pretty large. These are quite significant anomalies. And then the second a series of plots on the right just shows that C2. Well, the signal we're seeing in C2 is consistent with the rest of it sensors along the Icy Cape line. So the top three panels here are from the 2017 deployment C1, C2, and C3 and they all have a very similar nitrate anomaly and salinity anomaly. Similarly in 2018, we and the bottom three we have, don't kill him. Don't do that. Lemme go back again. I'm moving my mouse and clicking on it at the same time. 2018, the bottom three panels we have C1, C2, C3. You can see that this positive nitrate anomaly was consistent across the Icy Cape line. So when we were thinking about the nitrate flux and these estimates of what production this nitrate might support NCP, we can assume that C2 is representative of the entire Icy Cape line. And then this bottom plot shows Alamo, which is like an Argo float it profiles that water column it was deployed in September of 2017. And this top plot is that drift track of that Alamo colored by bottom salinity. And it happened to take a turn and go right over the C2 mooring. And this bottom plot is the profiles of salinity, you could see the two layer system in September into October and then by mid-October and into November the system is fully mixed as prior to the arrival of ice. So our two assumptions is C2 is representative of the Icy Cape line and that these near-bottom measurements reflect the entire water column. So our patterns of flow. So this is a schematic showing this flow from our M8 morning up into the Icy Cape lines or what are the two types of things that might be influencing this inter-annual variability. Well, it's transport. This is three month mean transport across the top. That's September, October, November through March, April, May across the top. And then the different years along the y-axis. And the colors are the intensity of transport during those three months means. So in red is strong northward transport and then in blue is a weak, sometimes even reversed transport to the South. So that's one aspect of our flux calculations. And then of course the other is the source water. And we're looking at this water of M8 as much of our source water. There may also be water contributed from the Anadyr Current here. But we see that in M8 there's a lot of variability. Now these are CTD casts around M8 every year some years we have multiple cruises up there but there's a significant trend in decreasing DIN. Now, DIN is your nitrate plus nitrite plus ammonium. And we see that this decreased significantly between 2005 and 2016 and then the concentrations rebounded in more recent years. So we have these two things, this interplay of both the transport and then what is it that you're, what's the flavor in the water that you're moving? Is there, are there nutrients in that water that are moving North or not? So those are the two things we look at. So here's the same plot showing the variability of the DIN at M8. I just want to mention real quick what might be driving that. This plot here, I'm not gonna go into it too much except this is how much nitrogen is missing from the water column in the bottom water. And this is where you've actually taken nitrogen. And Bonnie will mention this, I think and you've converted into nitrogen gas and it's left the system. And along the shelf break here, these cooler colors means you're not missing much nitrogen but along the middle shelf where our moorings are. And then you get up to M8 it takes a long time for this water to move North. This has maybe a couple, this water is taking a couple of years to, has a very long residence time up here. And during that time, you've formed a lot of, you've denitrified the water. You've formed a lot of nitrogen gas and you have a real nitrogen deficit. So around M8, when we're taking samples around M8 sometimes we're capturing this middle shelf, older water and sometimes you get this stronger flow up onto the shelf. And so this, we think that's what's driving the variability that we see here in M8. And Kristina and Phyllis and I are looking at the, oh, excuse me looking at those processes right now. Try to understand what's driving that variability. All right, let's keep going here. So if we look at our source water and then so this is now on the x-axis of the plot on the right is this DIN in summer and fall at M8 and then on the y-axis is the concentration we see at C2 the following spring. So here's kind of the source water in summer and fall on the x-axis. And then what do we see up at C2? And there's a very strong relationship between those two. So it appears that whatever we see at M8 is what happens the following conditions in the spring at C2. But something strange is going on here in 2012 at C2 where we have very low concentrations. And that's because the transport was very low that year. And the Bering seawater never reached the C2 mooring until much later in the season. And it didn't quite reach the same concentration because there was a simulation going on there. Phytoplankton production was starting to suck down those nutrients. Okay, so now if we look at, okay I wanna get a few more minutes and I got us wrap it up. So if we look at the nitrate flux over all of November through April, the mean we see it's very low in 2011 to 2012 because we have this low transport that's circled. Also low in, these are actual flux numbers. This is kilomoles per second of nitrate. It's also low in 2016, 2017, because the source water there was not very much nutrients to be had at M8. And then when we look at the 2017, 2018, it's very high. And because we have very high transport and we had moderate to moderately high nitrate counts. DIN concentrations at M8. So we can also break this down per month. So these different colored bars are different months for each year. And we can see that from November to April on average it was three kilomoles per second of nitrate coming up through this C2 to the the Icy Cape line. But in a couple of years, we had a very strong nitrate flux through Icy Cape line. And that's because we have this high transport and moderately high concentrations in that source water at M8. So we're pumping out high nutrients up through the Icy Cape line during that time. And then in May, that's the dark green bars on the right hand panel. And generally the flux is higher in May. As that Bering sea water has reached the Icy Cape line and in all instances. We can then use use the values that we've have for our pre-bloom concentrations to calculate using various assumptions here in the top three bullets. We can estimate that the production varies indeed between 30 to 70 grams of carbon per meter squared per year based on the variability that we see in the M8 source water. So the answer to the discrepancy of the literature is, yeah it's real that variability that we see, the 50% variability that we see in the pre-bloom concentrations and in the NCP values captures the actual variability that we see at M8 and then at C2. So, but here's the figure that shows these nice comparison between M8 and C2. And I totally am the fat liar because that's not exactly what happened. In some years the nitrate concentrations continued to increase after after May 15th. And this might be because we have different water types coming in or because there's other biological processes that are adding nitrate to the equation. So Bonnie is gonna talk about it, so that's it for me.

- Awesome, okay thank you Calvin. And if you wanna go off camera and then I'm gonna swap over to Bonnie. All right, Bonnie you should see the presenter box.

- Ok, I think I, so I'm sharing my screen now. How's this working? Yep, great, okay. Okay, thanks Calvin. Lemme see how I keep that. Okay, that was great. So Calvin already did a lot of the introduction explaining why we're doing this right same thing. So Calvin talked a lot about the physical transport of nitrate, but what's interesting is just like on the Bering sea shelf you saw with the variability and the denitrification also there's gonna be interactions with the Chukchi shelf as it goes across and the water interacts with the Chukchi shelf and that causes modifications to the water before it actually goes onto the main Arctic Ocean. So what are these processes affecting nutrients? These are biological processes, by the way. And when I say nutrients, for this talk I specifically I'm going be speaking about nitrate. That's the, by far and away the majority of all biologically available nitrogen in the ocean is as nitrate. So that's why it's really important to talk about that specifically. Anyway, so on the y-axis here, I have this oxidation state which is not important to think about only that it's interesting to think about the transfer of electrons. That is to say energy in the system as all of these transformations are happening. So that's how I like to think about it but it is not necessary to think about the redox state here. So nitrate, one of the major processes consuming nitrate, Calvin already talked about some of this assimilation just uptake by phytoplankton and they reduce it and take it and convert it to organic nitrogen. And then that can be remineralized to ammonia which can go on and be taken up as well by assimilation. Also, this ammonia can go on and be oxidized by nitrifying microbes. And this is an energy yielding process. They use it to fix carbon. So these guys are using it as a nutrient and they use light as an energy source to fix carbon. They're in the surface waters. These guys use the oxidation of ammonia for energy. They also fix carbon. These guys rule in the deep ocean, dark these guys rule in the sunlit ocean. These guys also need to assimilate a little nitrogen but it's a very small amount. Okay, and then the final process that's consuming nitrate in the ocean. So we had this one consuming nitrification produces and then denitrification consumes nitrate as well. But it is a very specialized process. It has to be, it only occurs in places where there is no oxygen. So in the absence of oxygen, these guys are heterotrophs. They continue eating organic carbon, but there's no oxygen. So they use nitrate to breathe. Basically they use that oxygen on nitrate to oxidize organic matter. That's how they get energy. And then they end up reducing the stepwise to N2 gas like how Calvin was saying. And that ends up, this is basically inert. There's only one process that can take this back to something that other biological things could use. That's a nitrogen fixation. I'm not gonna talk about that in this talk. So this is all the processes we're gonna talk about today. Okay, so referring to the title, what's the new technology? The new technology is this, ITAE In situ incubator which was built by McLane Laboratories and it was the brainchild of Calvin Mordy. And here's a picture of it being recovered in Hood Canal. Basically it takes 48 samples and then it can poison, can take up to 48 samples and then it goes and sequentially poisons them at time points. And so you're basically like sacrificing samples at time points and what we use this to measure nitrification rates. So that was the oxidation of ammonia to nitrate. And so what I did was add this 15N labeled ammonia and then let nitrifiers go at it in the water and convert it to nitrate. And then that was measured by, or is in the process of being measured or actually gonna be measured by Laura Bristow at the University of Southern Denmark. She's one of the coauthors here today. And I'm sorry, I skipped past that title slide Laura Bristow and Julie Granger both coauthors as well here. So we deployed this in the Chukchi Sea 2019 to '20, also in Hood Canal. This was a different, this also looked at nitrification looking at the effect of ocean acidification on nitrification. So I have some interesting data from this. And then now this one is an ongoing, I haven't recovered it yet. But so we don't have any data from this quite yet. So actually today what I'm gonna talk about is old technology. But using this old technology, we got new insights. So this is actually Dave Butterfield's remote access sampler also built by McLane Laboratories. And what we did was set this out in Chukchi Sea at C2 from 2018 to '19. So before we got an incubator of our own I had it collect water samples every two weeks through the winter was just a time period just very under sampled cause it's ice covered. It's hard to get a ship there. They were filtered by this thing that's what's in the blue top here is filter preserved with the acid. And then the stabilized isotopes of nitrate were measured by Julie Granger at the University of Connecticut. So here's just, is that C2 which Calvin talked about it was at 37 meters of water and overall a 45 meter water column. And a special thank you here to Sarah Donahoe and Catherine Berchok who, there was a third person actually I realized this morning I didn't know who that was but that third person, thank you so much. I know that you guys did a lot of work to upon the recovery of taking all the samples out of it. Okay, so. Okay, so looking at some hydrographic data from that year that it spent out on the C2 mooring there was lots of other instruments out there. So this top lot temperature and salinity temperatures in black you can see basically what happens is early December it goes down to freezing temperatures and you start forming ice. And you can see that the salinity which is in this kind of like orangey color you could see you got brine formation during this time. So that's what's indicating to me that you probably have ice formation and then suddenly right here in early February, it drops off. So here's, so that's from a sensor continuous data. This is from the RAS, the remote access sampler. These are discrete data points. So this is the every two weeks. Well, I guess I didn't do every two weeks here. It was like, well, anyway, forget the interval. I took the discrete samples over the course and time and you can see first nitrate which Calvin already talked a bunch about could see that it increases. We have this very distinctive increase right here when the ice starts forming. And then we got bumps and wiggles and then come to the end. Then ammonia is interesting. It goes down. It has a big decrease right at this very same time that nitrate has this big increase bumps and wiggles that are kind of the mirror image in my opinion of nitrates. So that's interesting. Okay, so then I'm gonna show you the isotopes but before I show you the isotopes I'm not really sure what everybody's specialty is here. I just want to give you a little primer on just how do we talk about isotopes nomenclature and everybody who knows about this can just go get a cup of tea right now. Nitrate has two isotopes, the N and O isotopes. Let's see, where's my pointer? Okay, there it is. Nitrogen two isotopes N15 and N14. This is the, they're both stable. These are not radioactive isotopes. They're stable isotopes. 14 as you can see is the abundant one, this is the rare one. Then oxygen has the same thing going on, but three isotopes. So the interesting thing about this is that the reason why we're looking at this is because isotopes trace biological processes because I said that backwards which is that biological process we call it, we say they fractionate the isotopes. They do not take it up in the ratio of the starting pool. So if the ratio was 99.6 to 0.4 assimilation when it consumes it might take it up at say I'm go wild and just say it's like 50, 50, you know, so that it really. It changes the ratio of isotopes in the starting pool. And you can see that and trace processes based on this change. Okay, the way we talk about it is we use this Del notation because we actually use isotopic ratios. Our eyeballs would go blind because we'd be looking at 0.00001% change. So instead what we do is turn this into or not present ratio change. But what we do is turn this into a Del. It's a per mille is the unit. So instead of percent we do per mille per a thousand basically cause that's how tiny these changes are. And so I'm gonna be talking about the Del N15 of nitrate, the N on nitrate and then also the Del O18 on the oxygen of nitrate. Okay, so I don't talk about 17. That's all. So when I say that it's increasing when I say the Del N15 is increasing I'm saying we're enriching the rare isotope, enriching 15 relative to 14. And when it's decreasing, we're depleting less 15 to 14 ratio, lower 15 to 14 ratio. Okay, most biological processes by the way deplete they usually prefer the light isotopes. So anyway, that wasn't, let's look at the actual data now. So here's the data that goes with that. That's the Del N15 of nitrate. The Del is in purple and the Del O18 of nitrate is in orange. And the first thing that jumps out at you, well jumped out at me is that right here during this brine formation time or ice formation time I guess I've been thinking about was brine formation time but I could see that there's quite a distinctive change in the isotopes that go along with this change in nitrate concentration. And then same thing. Things go along with bumps and wiggles. And then right at the end, they both are enriched together. All right, so in order to figure out what the heck is going on here I gotta tell you a little bit about what are, how do these processes that I first talked about in the beginning. How do these affect the nitrate isotopes? Okay, so what we're looking is in N and O isotope space, this is the Del O18. So the oxygen on the nitrate and then this is the Del N15, the nitrogen on the nitrate. And I want, just want to tell you that assimilation uptake by phytoplankton and denitrification that's that nitrate reduction to N2 gas. They actually both, the fractionation affects for both nitrogen and oxygen they're equivalent. They're fractionating them. Like they are preferring taking up the light isotope but they're doing it proportionally. So if you were to plot this as if the nitrogen is consumed it enriches both of them. It's preferring to take the light isotope. However, it's doing it similarly to both of these isotopes. So if you see it on this plot it would go along a one-to-one line, both assimilation and denitrification would drive it in that direction. Nitrification so that's the oxidation of ammonia to nitrate that drives it, it does various things to the nitrogen but it only does one thing. It basically is always trying to drive the Del O18 of the nitrate. It's always trying to drive it to water which is approximately zero per mille. And the reason why is that that's where the oxygens come from on nitrate when you're oxidizing it from ammonia. They get those oxygens from water. They may get the electrons from oxygen but they get the atom of oxygen from water. So anyway, that's why that is. Okay, so I'm gonna lead us through this one little portion over here which is relatively easy to interpret before I get into the rest of it which is a little harder to interpret. Right here where I was talking about how you have this increase in both the isotopes with N and the O isotopes enrich at this time. And so if we look over here on our little I just turned it into a little thumbnail plot. That's the O and the N, you see what's enriching in both directions is either assimilation or denitrification. Well, I'll tell you that we can tell them apart because denitrification, you get anoxic conditions and we have tons of oxygen right now. So it's assimilation that's driving this. And I'll tell you that the slope of this line if I do it, this is the different plots. You know, this is by time. But if I do it in this space the slope ends up being about 1.6. So a little bit bigger than one but anyway it's close. Is indicating to us that this is from assimilation, okay? And if I take a quick look at PAR, photosynthetically active radiation, I see that that confirms my diagnosis of what this process is. That's consuming that little bit, you know there's tons of little bumps and wiggles and what are they from? Well, this bump, this wiggle right here. I'll tell you decisively. That is from assimilation. And then also we can look at the PAR to verify that. Okay, so that was an easy example. Okay, my eye got really drawn to this area right here obviously cause this is very distinct. You've got enriching nitrogen isotope depleting oxygen isotope. Okay, let's go over to our little thumbnail. What process enriches N and depletes O? I should have put a little example but it would go like this, right? A downward sloping line. There's no process. There's no single process that's affecting the nitrogen nitrate that will do that. So I'll tell you the answer at the end is that it's a combination of all of these processes. That's gonna give us a signal like this and I will kind of try to explain this to you in this talk. So this is an unusual thing except that it's not the first time, I'm not the only one to have observed this. Okay, so let's look at some previous work that's been done actually in the Chukchi Sea over June or July. So this is important cause I'm looking in the winter time. Cause I was just curious to see what goes on in the wintertime. Very little data, June and July, people have been there and this person, Zach Brown, published this in 2015. All I want you to take away here. This is the Del O18 of nitrate. This is the Del N15 of nitrate. Okay, as the nitrate is enriched the Del O18 depletes, okay? That's all I want to take away. Here we go. East Siberian Sea that's like if you go to the West as you come out the Nor--Chukchi Sea into the main Arctic and you go to the West. Yep, that's right. You hit the East Siberian Sea I don't have a good key here or legend but I'll tell you that same thing. You got the enriching nitrate isotopes coincident with these depleting nitrate isotopes. Again, we're in the, not again but August, September in the Beaufort Sea. Again, it's the summertime is what I just wanna say is that enriching nitrogen isotopes with depleting oxygen isotopes. This is a strange condition, basically. Okay, I do not have time. So I didn't even try to make this figure understandable to you guys, because I knew I wasn't gonna have time to really explain it. But the explanation that has been cultivated over the course of and actually it doesn't include Julie Granger's work in the Bering Sea in 2011 and also Moritz Lehmann's work in 2005 in the Bering Sea. But this has been a cultivated idea that it's all about sedimentary reprocessing of all this nitrogen. So all I just want to say here, and we can talk about this one-on-one later on if you want is that in the benthos, in the sediments we'll just go through, you've got this partial nitrification, got ammonia coming up from the sediments, organic matter remineralization. It's oxidized to nitrate, but only some of it. That's why it's partial. And then some of this ammonia diffuses and gets nitrify to the water column. And then the nitrified nitrite gets denitrified the sum of it all heavy nitrogen, light oxygen. That's the net takeaway from this, okay? We can talk about this later if you want to know more details about it. I didn't tell you anything about enough details to explain this diagram. Okay, so perhaps I skipped that at the beginning of the talk cause I was excited but that we're looking at how the water is modified as it moves from one of the big gateways of the Arctic which is from the Pacific side of the Bering Sea. How is that water modified as it goes across the Chukchi shelf? What actually gets delivered to the Arctic? So here we're basically we're starting the Bering Sea and we're moving our way off off shore kinda. Bering Sea, Chukchi shelf, slope. Then we go West is the East Siberia Sea, East is the Beaufort Sea. And then okay across the top, talked about nitrate. talked about the isotopes. You guys know what that is. Okay, these two things AOU is the apparent oxygen utilization, okay? Apparent oxygen utilization. That means the way to think about that is it's the amount of oxygen that's been consumed by respiration. So it's like a measure of how much respiration has gone on in the water column. Okay, oxygen aerobic, oxygen using. N*, forget the details. All you need to know is that this is kind of like this tracks oxygen to oxygen respiration, aerobic respiration this tracks denitrification anaerobic respiration, okay? So these are both just measurements of how how respired things are, how much respiration has gone on in this water bass? And so we look at this, first we look at the isotopes, okay? And this is what Julie Granger says it's coming out of the Bering Sea. And you can see, let's start with the nitrogen. You can see kind of gets it's a little, basically you're getting a little bit more enriched with time and then you get a little bit more depleted not with time, sorry, with flow path basically, with travel. You get a little more enriched and a little more depleted. Basically what you're seeing is these two are being driven apart that's by a more and more sediment reprocessing of this or fixed nitrogen of this bioavailable nitrogen and organic nitrogen and all the inorganic nutrients, all these things together. Try to drive these apart. They're very similar though. Okay, they're somewhat similar but we can see this sort of overall trend. If we look over here, wait, what do I wanna show you next? Okay, so actually I wanna show you my study, this study, our study in relation to this. And we can see we basically fall right there in, sorry right here is where we are in amongst Zach Brown's values. So he's in the summer, we're in the winter it's very similar isotopic values, okay? The thing that's really different about what we see and I actually should have extended this little box to include him. What's really different is these signals of respiration, right? We're very low, low AOU. That means there's not less. This has been ventilated. Also the indicator of denitrification also, well actually he doesn't show, he doesn't actually provide us with the value of that. It's kind of in the middle basically. This is what's actually out there in the Arctic Basin at the Pacific Hill. Oh, I didn't say that. I'm so sorry. The reason why we're looking at it at this Arctic halocline salinity this place is important because it's basically at a depth of the nutrient maximum in the Arctic Ocean. This is the nutrient maximum that's basically supplying the euphotic zone with nutrients. So that's why we're looking at this kind of salinity depths in the ocean. This is why we're looking at this kind of surface. I'm so sorry, that was right in the beginning of why am I looking at it at the salinity of 33.1? This is basically what I think is the nutrient max supplying it to the euphotic zone in the Arctic. Okay, so right keeps going. And so that's all I'm trying to say is that this is what it looks like out there. This is what it is in the wintertime. Okay, so all I just want to say is that it kind of gets the signature except that obviously this isn't the water out there. It's gotta get up to basically these values of AOU. And so this is not easy to read but I'll just read it to you. So this water that's formed during this ice formation period this brine high salinity water. This actually must stay on this Chukchi shelf. It doesn't go out off the shelf at this time. It's got to stay there where it can accumulate more signals of benthic and pelagic respiration, right? It's gotta drive the, it's kinda you've got to get this value to these values. So it's not very different, but it's a little different. And then you gotta get these values up to these values as well before heading off shelf. Brown, so this guy on the Chukchi shelf and slope he found based on his calculations of this he thought that a minimum of almost 60% of the the nitrate that's coming in through the Bering Sea or the Bering Strait, going to, says Arctic halocline that eventually supplies all the nutrients to the euphotic zone of the Arctic. He thinks that that was regenerated right there in the Chukchi Sea. So there's a ton of modification going on due to the shelf by the way. The actual sediments are what's doing the modification. Okay, so that was basically as far as I'm gonna get you guys today. The next steps are, there's lots of next steps for that data. And the next steps for new data is this new technology we're gonna actually get In situ nitrification rates. So what are the actual nitrification rates then? Not just like, guess what they are based on geochemical parameters. Like actually just directly measure them. So I'll just show you there's not that many. There's not that much direct measure of data up there. Direct measured rates in the Arctic period but like the winter there's none. And so here's one study that actually did do that. They just went off of Point Barrow. On the y-axis we have the nitrification rate. Okay, don't worry the x-axis is not important to our discussion here but that is amoA is the, excuse me the gene that actually carries out nitrification. Like actually is one of the steps of oxidizing nitrate or ammonia to nitrate. That's not important here. Winter and summer. This is all just I wanna show you is that dramatically different rates in winter versus summer for nitrification rates. So just gonna be really interesting to see when does all this nutrient reprocessing happen as well? Not just in the sediments but also how does that link to the water column? Because obviously that ammonia that diffuses out I didn't get into it but coupled partial nitrification, denitrification part of that is that the ammonia that escapes the sediments has to go on to be oxidized to nitrate in order for this all to work. So what are the rates of that? So, okay. So I think that, yes, that is it. I am done presenting and... Is everybody still there?

- Yeah, thanks Bonnie.

- Okay, okay.

- I will swap over the screen real quick.

- Whoo, okay good time! I was just like, how much.

- Sorry, this is really not as easy as it used to be.

- Oh, gee, there's all these chat questions. I didn't see a single one of them, thank goodness.

- Yeah, no worries.

- Okay, well that is during the talk. I will look now so.

- Yeah, no, no, no it's okay. We'll go through them. So we have about seven minutes until 11 and Libby yes I always do this for everybody in the seminar. Because you can't virtually hear it. So let's see, okay I'm gonna scroll back here, sorry. All right, so Calvin, I think this was during yours. So one of the questions was what drives, this is from Libby. What drives the variability in nitrate in the source water at M8?

- So I showed a little of that with the plot that showed the denitrification that goes on around M8 of whether you're pulling in this middle shelf water or whether you're getting slope water that comes up towards M8. So that's the study that we're after right now to try to explore that. And Phyllis is believing that it's the strength of the slope current that kind of determines whether that slope water is getting all the way up to M8 or whether you're getting more of the middle shelf component.

- Thanks, all right. I'm gonna swap to a question for Bonnie. And this is also from Libby. What organisms are responsible for the modification in the sediments?

- What organisms are responsible? Okay, that is, it's all microbes, first of all. So, and then at that point, I guess I'm not exactly sure the microbes and then the denitrifies and the aerobic respirers and the they're almost all bacteria. And then I know that nitrifiers the big splash on the scene was that archaea are actually doing most of the nitrification. So like a totally even separate, you got eukaryotes, prokaryotes. And now the prokaryotes divide into bacteria and archaea and that's a really big deal. They're closer to like, okay I shouldn't go there cause I don't know this, but I think is that the question? Then there's specific ones like denitric pseudomonas, denitrificans and stuff like that but I'm not too up on those details like that but that was that the answer that you were looking for?

- Libby, you can chime in if that's what you were looking for.

- Great, okay, good.

- Thanks Libby. Okay, I'm gonna jump back at Calvin. This was a question from Darren. Could you also look at the other DBO sites to further constrain the source water?

- Yeah, things get complicated when you're, in winter things are a little easier and we don't measure measurements of the other DBO sites because in spring and summer then you complicate things because you've got active production going on. So you're sucking down the nutrients as the same time they're being recycled. And you're also infecting more nutrients into the system. So I was just looking at winter to try to simplify the situation a little bit. But we don't sample along the DBO line for the most part during, except for the summer season.

- Darren says gotcha, thanks Calvin. Jens did I miss any questions?

- I don't think so. There was sort of two together from Libby but I think they were both covered, right?

- I think so too.

- So I'll just make one other pitch. Libby has been looking at benthic processes epifauna, infauna, how much oxygen demand and respiration is going on in the sediments. This kind of ties to what Bonnie is getting at is looking at their rates of respiration and influence that it has on isotopic signatures. So one of the directions we wanna go with working with Libby is to begin to do like benthic landers, benthic growers that type of thing to get at the changes, not just in the chemistry but also in the biota with using some imaging systems. So something we wanna expand more of our benthic working way through the RPA is what we're thinking.

- The Recruitment Practices Alliance for those that maybe don't know what the RPA is.

- I think there's also data on meiofauna respiration from some of the ASGARD cruises or I think Sarah Hardy's group that might be relevant for some of your stuff, Bonnie, maybe.

- Awesome, okay if we have no other questions, it is 10:58 and I will just remind everyone that we are back here again next week for another FOCI seminar. And that will be at 10 o'clock and reminders will go up. So thank you everybody for joining us today and thank you to Bonnie and Calvin for talking.