This is a recording of the May 2024 seminar in the Southern Ocean Observing System (SOOS) Southern Ocean Indian Sector (SOIS) Regional Working Group Webinar Series.
Speaker 1: Anvita U. Kerkar (Portland State University)
“Primary Productivity in the Indian Sector of the Southern Ocean: Observations from Three Austral Summers”
Speaker 2: Annie Foppert (UTAS)
“Multidisciplinary Investigation of the Southern Ocean in 2024 Summer”
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https://soos.aq/activities/rwg/sois
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yeah okay hi good afternoon good morning all and today as Elizabeth said we have two talks and the first talk will be by Dr Anita ker and who was a PhD student at NCP National Center for Polar and research and after her PhD and she is presently working at Portland University in us and uh she has been working in the Indian sector of Southern Ocean on the topic of f plant production and biooptics and uh today’s talk anas will be the work she has carried out during her PhD degree so with this short introduction uh I would like to invite an to give her talk Amita the floor is yours thank you um is my screen VIs yes that’s perfect great uh yeah so thank you for the introduction and U thanks for having me here today uh I would be uh presenting my talk on the primary productivity in the Indian sector of the Southern Ocean and I would be discussing my observations from three austral Summers so um just before I begin I would like to give a brief introduction of my present work I’m working as a poster doctoral researcher at the department of biology Portland State University in Oregon and currently I’m studying The Selective feeding responses between the gelatinous grazers and Pico phytoplancton and I’m using molecular methods like qpcr to quantify these interactions prior to this I was working as a posto at Florida uh Atlantic University and I was studying the applications of digital holography in planton ecology and prior to this I was a student PhD student with uh Dr sharat tiati at National Center for Polar and ocean research that brings me to my present topic on phytop plantant productivity and biooptical variability in the Southern Ocean and Coastal Antarctic region I have been a part of two scientific expeditions to the Southern Ocean and I would be discussing the observations which have been a part of my PhD thesis so a brief outline of my presentation is I would be starting with a brief introduction to the Southern Ocean primary productivity and its potential controlling variables and my observations on the measurements of primary productivity and an inter comparison of the primary productivity estimates from different methods I would be very briefly going through the potential modulators focusing on the biooptical variables and grazers or the copy ports in the region so I a few weeks ago I came across this interesting model uh that was developed by MIT that shows the global distribution of phytop planton and um it was very interesting to see these diverse and teeny tiny cells which have a great impact on the globe which by by accounting around 50% to the global photosynthesis these tiny cells are so responsive to the surrounding physiological and biological variables and these give invaluable insights in the changing oceans so um by this as all of us are aware today the climate change is a triple threat for the oceans making them warmer less oxygenated and more acidic so several impacts such as sea level rise bleaching of calcarius organisms corals recurring toxic algal blooms habitat loss for several species in several aquatic ecosystems acid acidified water and economic disruption of fisheries and several other sectors is um becoming more and more evident over the years and Southern Ocean plays a critical role in this scenario so the Southern Ocean is characterized by several unique properties such as Oceanic frontal structure the contribution to Total Global primary production that’s mark That’s remarkable it hosts large stocks of zooplankton and has a profound influence on the climatic system system it’s also regarded as the high nutrient low chlorophyll region and it’s an unused repository of micronutrients Southern Ocean forms a critical component of the carbon cycle and it’s a carbon dioxide zinc it stores huge quantities of heat and carbon dioxide and also connects three oceans that’s the Indian Atlantic and Pacific Oceans and the topic of my today’s dist discussion is it’s contribution to Global primary production so coming to the fundamentals of the process primary productivity can be defined as building up of organic matter from inorganic elements and this process is mediated by primary producers which are right at the base of the marine food web so the rate at which primary production occurs is defined as primary productivity and these primary producers occupy the base of the trophic pyramid and as we can see the Tropic pyramid is fueled Tropic pyramid is fueled right by the primary producers so therefore primary production is the source of the all organic biomass that leads to the carbon production and Export over the entire food chain primary productivity is controlled by several variables some of the major ones are light uh the water column is basically constituted of phytoplankton and non- phytoplankton comp components and the optically active properties of these constituents are assessed to study the impact of optical field on the primary production the second one is the nutrients the micronutrients such as nitrates phosphates silicates and the other micronutrients have a profound influence on the biomass and Community type of the phytoplankton in every ecosystem another one is grazing by the Predators and the immediate level of prime consumers that can be represented by some abundant class like copor or gelatinous grazers are the immediate ones which clear the phytoplankton community and another controlling variable is the phytoplankton physiology or the health of the phytoplankton community so some of the variables such as furacin or the photochemical yield are proxies for the physiology of phytoplankton so in my study I uh measured the phytoplankton productivity variability and made a made an intercomparison of the productivity estimates using more than one methods so um basically the sampling was carried out in the Indian sector of the Southern Ocean during three ustal Summers and this was the uh Transit of sampling and the annotations indicate the postal summer of sampling so the productivity was measured um through incubations in a deck tank and the controls were of course filtered immediately and the samples were packed in appropriate light filters to simulate the oceanic depth from which they were collected Oceanic PP has been measured through several methods and approaches to to date and it could be evolution of oxygen or incorporation of Isotopes or active fluorometric methods or the satellite based methods but all of these methods have a basic aim of improving the estimation of primary production at the global scheme so I used three of these methods firstly it was the 14 C or the radioactive carbon based isotope method which measured the disintegration per minute or the DPM values which were converted into the daily rates of primary production secondly it was the stable isotope method which converted the Delta 13 C values to the rates of primary production I’m sorry and uh the next one was an instantaneous method to measure primary production which through this equation calculated the instantaneous rates of primary production and along with it it also measured the physiology of the phytoplankton community so the proxies were derived through the ratios between the variable and the maximum fluoresence and some similar parameters which gave an indication about the phytal physiology at the time of sampling so uh some of the factors which were evaluated were the variability of chlorophyll a and primary productivity across the water columns so this showed a significant correlation at several station and several depths so in general the chlorophyll a and primary productivity um inured a north to south increasing concentration gradient at most of the stations and there was a presence of photo inhibition effect which was assessed through par PB relationship uh for the community and in general the correlation between PP and chlorophyll a was significant over the region in during the second ustal summer uh the frontal stations were evaluated for biooptical variability as well as primary productivity and some of the key findings were the frontal station being consistently less productive and these could be attri this could be attributed to lower uh estimates of chlorophyll a and also the silicates were low in this region there was also um a package effect or the pigment packaging effect that was prevalent at the frontal stations so these all together could be linking to the differences or variability in primary productivity during these austral Summers there was another interesting uh factor that was measured by comparing the pp estimates from different techniques during this third austral summer so the primary productivity was measured using fast reputation rate fluorometry and these rates showed a strong correlation with the radioactive based method measurement of primary production as well as the stable carbon isotope method and these range of estimates was also compared with the letter which was seen to show an agreement and there was a low magnitude of discrepancies between the estimates that were op obtained therefore one could say that FF could be a potentially reliable tool to estimate primary productivity in the Indian sector of the Southern Ocean however um one should be cautious about the sample size technical differences and assumptions that are associated with every technique of primary productivity estimation the F frrf sorry the F frf was also used to evaluate the photosynthetic efficiency and the other photophysiological parameters of phytoplankton so both the variable and maximum fluoresence ratios were shown to decrease exponentially across the water column so this is an indication of generally General low photosynthetic efficiency of the phytop planton community in the region so the values ranged between 0.1 to4 and this is a typical low photosynthetic efficiency of phytoplankton and as it is seen it’s a characteristic of Southern Ocean phytoplankton to be acclimatized to low light so this can be a further uh validation to the results to infer the pp estimates showed a north to south increasing gradient photo syn photo inhibition was evident through par PB relationship and further this could be also linked to the low photosynthetic efficiency of the Southern Ocean phytop planton and in case of interc comparability of the pp Vari PP estimates the 13c and F frrf PP Trend continued to be reliable over the Indian sector of the Southern Ocean coming to the biooptical assessment of this region biooptical oceanography basically relies on the interactive interactions between the light and life in the ocean so it’s measuring the biooptical constituents across the water column so these are typically the phytol blancon non- phytol blancon total suspended matter and the chromophoric dissolved matter so all these are measured to get a picture of the absorption that occurs in the water column and this can have great implication on the primary productivity of the ocean so the characteristic absorption properties of each of these optically active colum substance is measured from the absorption Spectrum so here basically the absorption of particles was measured using an UV visible spe using a UV visible spectr photometer and further the samples were treated with methanol and remeasured in order to get the non- phytoplankton component on a filter paper so when the non-f phytoplankton component was sub subtracted from the total total particle component it led to the absorption by phytop plankin so this is how the three variables were derived and parall the acome or the chromophoric dissolved organic matter was also measured using the UV visible spectr photometer so coming to Spectra from the filter papers this is just a gist of different absorption spectra during the ustal Summers and the Peaks at specific wavelengths were further evaluated to get a flavor of the biooptical variability in the region bringing the Spectra to graphs the pp was better explained by the absorption by phytoplankton compared to the biomass or the chlorophyll the primary productivity and AP at 443 nanometer ratio declined as we progress to the Deep chopy maximum from the surface and the pigment packaging effect was prominent at the frontal and Coastal domains so definitely it was something uh constant and modulating the primary productivity throughout the Indian sector of the Southern Ocean these um interactions were evaluated over all the austral Summers they were pretty constant and the AAR pH and chlorophyll relationship indicated pigment packaging effect at discrete depths starting from the surface also at the DCM and also in between and the pigment packaging effect was also validated further through the B by R ratios let me come to that so the phytop planton community was characterized so basically the validation was kind of a two-step validation firstly it was the B by R ratio and U it’s the ratio that’s used to classify the dominant uh Comm the dominant phytoplankton functional groups or classes based on their size so this was the ratio between the absorption of phytoplankton between 440 and 675 nanometers which divided the phytoplankton Community into Pico micro and nanophytoplankton this was also validated by applying the data to an absorption based model which was used to classify the dominant phytoplank in sizes uh here the slope of AP at 44 3 was something that was examined to get a picture of the phytoplankton Community the observations were constant and the phytoplankton size structure showed uh that the most dominant Community type was of microf phytoplankton followed by nanophytoplankton and the least were picop phytoplancton so uh this was constant over both the Summers and however there was an observation that the model in general captured microf phytoplankton or the largest Siz phytoplankton lesser in case of both the tests so to infer uh most of the stations were dominated by larger phytoplankton type and that could be a reason why the P pigment packaging effect was was more prevalent across the Indian sector of the Southern Ocean also um this was validated through the negative relationship between the AAR pH and chlorophyll a which again corresponds to package effect and the absorption by phytoplankton was a better predictor of primary productivity in the surface waters in the region also the global absorption model was seen to capture the smaller Siz phytoplankton however it was not as efficient in evaluating the larger phytoplankton or microf phytoplankton therefore this could be one important recommendation or highlight what which which recommends necessity of region specific modifications in case of Indian sector of the Southern Ocean and this would have uh implications for future model-based primary productivity studies so this um observation these observations um are a start point for region specific ocean color models or ecological models which would be aiming to derive the phytoplankton size structure uh or maybe physiological effects of phytop physiological status of phytoplankton in the Comm in the region I will quickly run through this um this was a very initial attempt to um evaluate the traffic link between the primary and secondary producers through a theoretical carbon based approach so uh mesocosm or grazing studies were something not which were were not conducted during any of these experiments this was just to check uh the first step in energy flow from phytoplankton to the Z Plankton community in the Indian sector of the Southern Ocean and um some of the highlights of oh let me come to the methods first um the estimation of carbon biomass of the copor community was done through morphometric equations the specimens were counted in bov’s chamber and identified using some authentic taxonomic keys and the carbon was further estimated using the imaging software and established prome length measurement based equations and also the equations that helped in measuring Tropic link between the primary and secondary producers was applied to the data sets species specific carbon content could be evaluated using these equations and this was done for two ustal summers so these are in general the contributions of each of the species and this can of course at a cumulative level be extrapolated to the class level carbon stocks or even Community level carbon stocks and these studies are extremely scanned in the Indian sector of the Southern Ocean further U there was a strong correlation between the carbon stock of phytoplankton and the Zoop planton and there was a clear variation in Tropic efficiency seen between these two communities so it indicates uh as a as an important method to evaluate the effective transfer of energy between the producers and The Zo Plankton uh in the community another highlight of the technique was it allowed the sample preservation so the samples are still in the laboratory and can be utilized for any thing else or any different kind of experiments so it also told the amount of carbon available for the next trophic level and amount and amount of carbon that was contributed by each species of copico and the entire copico Community during the study so the species specific carbon estimates in general are extremely extremely sparse at a global level and these are very essential in pred predicting the uh pre Predator interactions and several other ecological interactions at uh Regional as well as temporal levels so the such estimates could help a long-term monitoring and um clearance rates and the changing climate or changing water conditions and definitely improvise the uh picture of the food web in the Aquatic ecosystems so these are also a start Point uh I would say to the studies because right now the ecological models do not account for such interaction especially when it comes to uh small phytoplankton so these studies if tweaked to smaller phytoplankton communities can definitely be uh very helpful so to summarize the study the estimates of f frrf were closer to the stable isotope based primary production so this could be uh potentially promising technique to estimate primary production at a relatively High high resolution uh in the Indian sector of the Southern Ocean further it could also be um stand used in standardizing the stable carbon isotope technique uh which is a non-invasive U way to estimate primary production and uh it could also have an impact over the current measurements which include radioactive contamination and potentially solve the problem of spars PP estimates in the Indian sector of the Southern Ocean F frrf along with the primary productivity estimation can also help in getting a better picture of the photochemistry and the physiology of the Southern Ocean phytoplankton at an extensive scale and coming to the biooptical characterization the results have suggested a necessity in Regional modifications for the absorption based models when applied to the Indian sector of the Southern Ocean especially emphasizing on the AAR pH and chlorophyll a relationships and the size structure of the phytoplankton that was evaluated from the spectral absorption also has suggested some cautions especially like while mapping the larger phytoplankton in the Southern Ocean before the models are applied to the global uh absorption models and um the species and Community carbon estimates could be evaluated at a non from a non-destructive technique so this could be a start point to monitor the carbon flux at Regional levels or specific time points and get a better picture of the traic link between the phytoplankton and zop Plankton and food web in general with this I would like to extend my thanks to Seuss and Southern Ocean Indian sector studies I would like to uh thank Dr shararti Who has been my uh PhD adviser and uh Dr Sabu Dr Pandi and benut Rana for their contribution uh during my PhD the entire ocean science group at ncpr uh the funding agencies captains and crew and all the collaborators my family and friends thanks for this wonderful opportunity and thanks for the patient hearing thank you Anita for your nice talk and uh may I request Elizabeth if there is any questions in the chat box May kindly read out or can I take the questions uh Elizabeth uh can you hear me yes I can hear you yeah I think um if anyone has a question I don’t know that we’ll be able to see raised hands but we can try yeah yeah that will be fine if anybody has any questions please please feel free okay uh Rob please can you hear me yeah yeah uh okay oh yes thank you yeah please go ahead oh thank you very much indeed hi Mita thank you very much for a wonderful talk there that was really interesting I’m uh I’m coming from a sea I perspective and I was just wondering um what to what extent SE I has influenced your findings and measurements and relationships are the species that you’ve been measuring related specifically to Sea ice in any way at all please oh thanks Rob that’s an interesting question and the influence of c i in particular was not measured in the study so I’m not sure how that can be answered and secondly the phytoplancton community type or the functional groups were basically coming from the spectral measurements so that was not a direct measurement so um yeah that’s all I can say yeah thank you thank you very mucher I I was wondering as well if if within the Indian program whether anybody is looking at the sea ice and its influence on primary production all right yeah yeah that would be really interesting yeah yeah Rob at present I think no one is looking that we are looking C there are people working on CIS of course but as you rais this question this is very interesting nobody’s looking into that in fact but we should be doing it soon thank thank you very much Sarat and thank you again and please thank you uh thank you very much for many information on the primary production in this assumtion so so you were you studied about your relationship between their so FF and their carbon 1 or carbon 14 primary production so the so in the final slide you said that uh you will use FF uh to derive the primary production uh in carbon as a car amount so do you plan to use the just only the frf or uh so still continue the uh carbon based measurements simultaneously uh please correct me if I wrong if I’m wrong but um from what I understood you asked if I used F frrf to compare the primary productivity through carbon so that was um I mean f frrf measures the productivity in an indirect way so it takes into account the electron transport rate and that is further converted to the estimates of carbon and U so in this way it was kind of an extrapolated attempt to get the rate of primary productivity and this was compared to the carbon based estimation from the 13c and 14c um techniques and this is still in progress so I’ll be again working reworking this uh stuff yes I think so so the and also uh maybe the fight Frankton group is gradually changing and the climate change so the relationship between the carbon and foren information uh will maybe changed so the yeah I I recommend you to continue there so boss FF and carbon measurements for the primary production yeah thank you very much thank you very much yeah thank you Professor actually Prof was asking our comparison result is so robust do you think that you can only measure and rely on it so I not we have to still continue with carbon measurements that was the question and yeah I’m sorry a long way to go thank you thank you so um I can’t see all the hands I don’t think but I might just ask you and thank you very much for your presentation to stop sharing your screen and we can of course um continue in the chat but we might now switch to our next speaker thank you can can sign thank you so next up we have Annie fer who will there she is um and so I’m very pleased to introduce Annie so Annie is a research associate at the University of Tasmania which is just next door to where I am here in Hobart um and she is of course um contributing to an Australian program called the Australian Antarctic program partnership and most recently a nice line that she has added to her CV was a a heroic task of of being the chief scientist or the voyage leader on on a recent Voyage to the Southern Ocean which I believe is going to be the focus of her presentation today so I will hand it over to you Annie okay thank you Elizabeth and thank you uh oh my screen’s all messed up um thank you to Elizabeth Kay and Sarat for organizing this webinar um it’s really great to be able to talk to people about what um I and many others have been doing uh here in Hobart so um yeah most of this talk will um be kind of about the research plan and strategy uh and approach and not so much on the results although I hope to have time to get to some of the results at the end um mainly because this is about a voyage that um we undertook this Summer that we’ve only been back for um a little over two months now so um results and analyses are um underway um but I think it’s a really nice framework to think about the Southern Ocean and the atmosphere above it um and how they’re all linked and how they affect the earth’s climate so um yes the voyage was a multi multidisiplinary investigations of the Southern Ocean um or or miso uh and the goal was to link the physics bio geochemistry Plankton aerosols clouds and climate um so no no menial task here um as Elizabeth said I was um the chief scientist on board uh Steve was Chief scientist providing Shore support um and there was a whole team of pis and people on board and on Shore that helped make this voyage happen um I am a physical oceanographer at um university of Tasmania and Australian Anar program partnership so I’m not an expert on all of the biod chemistry plankt in airs clouds and climate part of it but um I hope that um I’m able to articulate um the importance of all those things as well um I guess our mission statement is kind of could be thought of to be the goal of miso is to understand to improve understanding of how the Southern Ocean influenced the Earth system and used this knowledge to improve climate projections um I’m kind of preaching to the choir here but I’ll go through some background anyway uh we know that the Southern Ocean has a profound influence on global climate um biogeochemical cycling and biological productivity um it takes up anthropogenic heat and carbon dioxide but that also means that it’s going to have a large influence on sea level rise and ocean acidification um and the Southern Ocean is um adjacent to the Antarctic ice sheet and that that ice sheet is the largest and importantly the most uncertain contributor to Future sea level rise uh and so the Southern Ocean plays this crucial role in the earth system and yet um Earth system models currently have large and persistent biases over the Southern Ocean here is a picture of um short W shortwave Cloud radiative bias um between the Australian atmospheric model the access model and um observations and you can see that over most of the Southern Ocean um we’re not getting the the atmosphere right and it’s thought that that’s mainly due to um we’re not getting the right cloud formation and the right types of clouds forming over the Southern Ocean and and so um our big picture SS questions are um and so our goal is is to fix those biases in in the climate model so that we can make better um uh projections of future climate um and so the big picture science questions are um what physical and biological processes and interactions account for The Unique aerosol Cloud precipitation radiation interactions over the Southern Ocean so clouds in the Southern Ocean form um a bit different than they do um over the rest of the globe mainly because there’s not um Continental sources of not many continental sources of of dust and aerosols so they um it’s thought that the uh biology in the Southern Ocean actually produces precursors releases gases that then um turn into aerosols in the atmosphere that the clouds can form on so we want to understand that connection um which is kind of that second point there that what are the controls on the primary production productivity and the community compositions and um how do those affect the um production of these biogenic aerosols or or precursors um we want to know how and why the ocean inventories of heat and carbon are evolving in time um so large scale um uh overturning circulation kind of questions here um and what are what are the impacts on climate and sea level rise and a big focus of this project is on the high latitudes Southern Ocean um how it’s changing and the implications for the stability of the iishi the formation of Antarctic bottom water and the Deep overturning circulation cell which we know are all um very important for future and so the fully coupled research questions that I’ve just presented you um require a fully integrated multidisiplinary disciplinary approach in order to answer them um and so this Southern Ocean is quite special because everything is really linked to together and so for example um if you have a change in the overturning circulation here you um will change the anthropogenic Heat and carbon inventories in the ocean but not only that you’ll change the iron and nutrient the macro and micronutrient supply to the surfaced ocean um which uh uh in turn affects the uh biological product primary productivity and Community compositions at the surface those um Community compositions and um Banting communities could impact the different biogenic sources of these Cloud condensation nuclei that are released into the atmosphere mainly deyl um diyl dimethyl sulfide DMS um which form these aerosols for the clouds to form on uh changes in the cloud then influence the Earth’s radiative budget which which then affects the um amount of heat and uh going back into the ocean so everything is sort of is linked together um and it’s really difficult to understand how the Southern Ocean influences the Earth climate by only looking at one of these um um aspects at a time so the picture on the right there shows um sort of a a bit of a tangled web of how all these things are connected and and that’s really what um all what I want you to get from that is that there you’d be hard pressed to find one of those that isn’t linked to at to all of the others if not um four of the five other um bubbles over there and we need to observe the system to understand it and we then need to um develop and Implement new parameterizations to improve the Earth System model so that’s the big goal um and we set out in January uh to collect the observations to do the first part of that um process and so our research strategy um was complicated uh but we um did 65 days on the RV investigator the syro and Marine National Australia Marine National facilities research vessel um starting in Hobart and going to the Antarctic margin region and then Westward along the along the slope there and then back up the goip repeat section of I9 South to free mantle in Western Australia um along the way we had um kind of a five pronged approach to um observation the observations so we had the underway data that the ship is collecting um all the time including physical bio geoch IAL and biological parameters we also had atmospheric measurements going um pretty much all the time measuring the cloud precipitation and radiative properties we and we were launching radios son um to understand the meteorology and we also had onboard um se- spray generation tanks to um understand uh how um different uh biological controls um and physical properties of the water affected how much sea spray um was generated um to produce Cloud nuclei we did um repeat stations um which included con the goip and geotraces um I guess standard St stations uh and so this was the first time that the I9 or the um gs05 is the G trac’s name for that line was um occupied um to do the trace elements Trace element and Isotopes um both dissolved and particulate so we had both a trace metal clean rosette and Institute pumps that were deployed at multiple depths um at several at many of the stations um and then the hydrography the um ctd L adcp that is um well known uh novel um aspect of the Misa Voyage was um four multi-day process stations um so some work has shown that you can that some of these processes that control um the um biological um communities need more than just a single occupation to understand so we had uh roughly 3-day stations we occupied stations for 3 days which incl included um deckboard incubations to look at for example um ocean acidification ocean alkalinity uh enhancement experiments and then we also had um two th000 lit mosm incubations on the front deck where that we filled with Trace metal clean water and Infused one of the tanks with iron um and it was totally sealed and then um we were able to sample both the water and the the head space the air in the head space above it to directly quantify um the release of these biogenic precursors um that were uh being released in the tanks with and without iron so you could see how um the effect of nutrients were directly um influencing the the bio biological release of these precursors that the clouds conform on um we also had 22 autonomous FL that we deployed we did 10 um biogeochemical Argo floats from the socom project in the US and um 12 deep Argo floats four um deep arvor floats from France that had um were also equipped with O oxygen sensors and eight deep solo floats that um Australia provided uh the AAP provided so that um is very exciting as well um and last we use remote sensing to um not only choose where these process stations would be but to um help us uh make decisions along the way uh okay and so just in the last um five or 10 minutes now uh I’ll talk about probably the one that the one the one of these questions that I’m the most comfortable talking about which is how is the high latitude Southern Ocean changing and what what are the implications for uh I’m particularly interested in Antarctic bottom water and the Deep overturning circulation and so um just a bit of background on that is that um we know that Antarctic bottom water is of global importance it makes up the lower limb of the over overturning circulation it forms near Antarctica in only four locations despite making up um 40% of the global ocean volume um as it sinks into the abyss it takes heat and carbon with it um storing it for Millennial uh time scales and it brings it also brings oxygen into the deep ocean and so um the picture here just shows the fraction of Antarctic bottom water in the deepest uh uh CD sample and unsurprisingly it’s mostly found it’s found in the most um highest concentrations near uh Antarctica um but even um far far north in the um Pacific and Indian basins it’s it’s found all the way to the most northern parts of the Basin the North Atlantic it um sort of dwindle away where you have North Atlantic deep water forming um again I’m kind of preaching to the choir here but the Southern Ocean is notoriously harsh especially in Winter um and and to measure antartic bottom water you need to get to the bottom of the ocean um and so it’s outside of the core Argo capabilities um this picture shows hydrographic profiles reaching deeper than 2100 meters so noncore Argo float profiles um in particular and you can see as we know the Southern Ocean is a real um data desert um and so we rely on these Hydro graic sections to track changes in Antarctic bottom water and I’ve highlighted there in purple um the kind of miso area that we were covering so from 150 East um repeating the southern end of sr3 and then up I9 um and we rely on these sections to tell us uh not only how the ocean is changing but why and so this is a picture from um Van Wick and r tool in 2014 that shows um how how the ocean the antar bottom water is changing with the blue bars representing freshening and the red bars representing warming at a bunch of repeat um locations um and the uh miso Voyage tract crosses um this pathway in five locations so we have um also the longstream evolution of how that bottom water is changing um we know that uh bottom water especially um has especially strong signal of change in the last couple decades which is um strongest in the Australian Antarctic Basin which is where we are um focused and we see that that layer has contracted uh by about 50% since 1970 to the early um 2010s and that’s along I9 which we repeated this this this year earlier this year uh this is a modeling study um that shows again this uh slowdown of the overturning circulation as seen by freshening and warming of the Abyssal ocean you can see those changes are again super strong near um uh in the Australian Antarctic Basin and it’s driven by the glacial melt so the freshening um the the freshwater Budget on the Shelf is what’s controlling um the production and export of these properties uh the bottom water and so um we we want to be able to track how that’s going in time and then quickly I think um most people wouldn’t be familiar with deep Argo but deep Argo is a fairly new um program that has has floats that can um profile down to 6,000 M or 4,000 M depending on the um type float type um and so um the uh Australian deep Argo or Argo program along with um International collaborators started a pilot array in the Australian Antarctic Basin in 2018 which provides year round full depth profiles um feeling that that seasonal bias in the Southern Ocean and um they also safely profile under sea ice so um they go under the sea ice for the winter they continue to profile and then as the ice melts um they relay the data back bya satellite once they are um able to get to the surface again and just in the first five and a half years of this pilot array which started as 12 floats and has been continually uh receded as as the years have gone on um so as of April last year um the array has provided over two and a half times the number of deep profiles and 10 times the number of deep winter profiles in that southern sector of the um Australian Antarctic Basin compared with the world ocean database so this is um really changing the way that we understand the variability uh of the deban on um as as short time scales as even daily um and seasonally and then adding filling in the gaps in that in the multi- decadal uh time series and so um in order to study bottom water on this Voyage um it fit in in these five sections along the uh bottom water outflow pathway which included stations on repeat sections at the southern end of P11 and sr3 um the 132 section and 123 that have are nearby other um historical uh cgd stations and the southern end of I9 and we deployed the 12 deep floats in this Southern sector uh we also had three shelf stations um there in the green um triangles that uh were in or very close to the adeli depression which is where um a Deli Land bottom water one of the two flavors of bottom water this region is formed um and so that was uh very exciting as well uh sorry I’ll just go quickly through this I realize I’m running out of time um so this is adding to this time series of um contraction of bottom water along I9 so this is I9 section all the way from uh the southern end to the Northern end uh and you can see from the green to the orange to the red to the purple that that bottom water layer as defined by a um particular isop pigal is is um Contracting so is sinking um and that is even occurring uh on the on the Northern side of the southeast Indian Ridge so in the in the Basin to the north as well that South Australian Basin you can see again in different colors um that the red line is the shallowest of all of those so that again the top of that bottom water is is depressing if we look at in TS space so in temperature salinity space this is the long 150 um this is all preliminary data um that was calibrated on board um but is not the final version of the data set um calibrated to within goip standards on board though so uh these are good data um you can see that um from the 90s through to um 2010 2012 where the the Ross sea bottom water now is just freshening continuously freshening um had a large Rebound in salinity in 2018 and it is starting to um freshen again so we can see that interannual variability playing out um in in these properties and in as a function of latitude it looks like this so you have fresher Rossy bottom water than what was found in 2018 so that red compared to that light lighter Orange um is so you can see a continuation of the long-term freshening Trend excuse me with a um small [Music] um uh salinification in the in the mid-2010s and then it’s continuing to freshen again uh this is looking at all uh five of those short Antarctic margin sections and you can see that there’s a lot to pick apart here um and so we have kind of our work cut out out for us but one thing that immediately jumps out is that 130 um looks very different this year the red dots than it did many all the other years and the um this is the salinity there is very fresh compared to other years and looks looks a lot more like the um bottom water properties are usually found at 140 so that’s something that definitely jumps out at us immediately and you can see that 130 transect is fresh um and it’s also very high in oxygen compared to previous occupations um suggesting that it’s a newer newer um bottom water so it’s been on the Shelf more recently perhaps than than other years um and then uh we were in the deli depression um and we found that it’s cold compared to most recent years so those orange dots and higher in oxygen um so again just preliminary data and no real um inferences and implications uh that enita was having it’s more of just a a show and tell kind of situation here um and so this is the last SL um we take an grated and multi disconary approach to understand the Southern Ocean influence on Earth’s climate um it was a very ambitious we kept being told and highly successful is what we say research voyage that um occurred earlier this year so of course a big thanks to the captain and crew the support staff and everyone who helped make it possible um both on Shore and on the ship um and we see some some changes in Antarctic bottom water uh some that are expected like the continuing contraction um and maybe some that were were not so expected like the unusually fresh and high oxygen water at 130 um and so um that is all I have I hope I didn’t go too far over time not at all okay does anyone does anyone have any questions it’s hard for me to see H so please jump in either in the chat or just go for it um because I can’t see everyone all at once I have a comment which which is that it’s wonderful to see it’s wonderful to see the data even if it’s preliminary and I can think of lots of of um things that we could dig into potentially with some of the um budg chemistry data from repeated stations really far south too so very exciting to see it and I would I would Echo that it it was definitely a lot a ton of work um and say thanks back to you on behalf of those of us who did not get on the ship for 60 days and and a big success so rat I see you have your hand over up yeah uh thanks an for your nice presentation it’s interesting to know how the ABW has is impacting the overturning circulation or it’s going to impact but my question is slightly different um when you do on De incubation do you maintain the temperature or or how it happens like for example you take sample from subsurface do you maintain temperature or um so the the deck Port incubations were taken using surface waters for the most part um uh and the large misoc cosm experiments on the front deck we did not maintain the temperatures um in fact they got quite warm at some point um um and the smaller incubation experiments again I do not think that we are able to maintain the temperatures but I can’t say for sure so don’t quote me on that thank I don’t see hands but if someone has a question please just I think has one question yeah yeah wait oh H my my video doesn’t work but anyway uh yeah I’m very interested in about the colder and higher oxygen share Waters is there any report show saying that some anomalous High dens for the production or CS production around there um yeah that’s a great question question uh I haven’t looked into it yet um in terms of the CI uh State at the time or in the past couple years um but that’s definitely something uh that we’re interested to to unwrap yeah I’m very interested in this these things so thank you thank you and any other questions for Annie no all right well um then I will just take the last opportunity to thank both of our speakers and also everybody who attended and spread the word I see that kah was trying to put some of that stuff into the chat so we are um aspiring to have more frequent webinars as part of the um Indian Ocean sector Regional working group and there’s also a newsletter where we Aspire um saywe it’s most K to to get um a publicity of people’s work out to the general community so if you have papers that you have published or that your students or colleagues have published that you think would be of interest to the broader Community please let us know so that we can promote them in our newsletter and if you would like to volunteer to give a webinar or you’d like to volunteer a student or a colleague please also do that um and you can get in touch with us via the sus website um we’re trying to build a a more collaborative Community it’s a large region it’s often difficult but I think this is a great first start so thank you very much Deone for being here and toah in particular for helping us to organize it