Elisabeth Sikes

Your work focuses on the Southern Ocean's control on glacial and interglacial climate. Can you walk me through how you got into the field of paleoceanography?

Ironically, I began my master's degree focusing on coral reefs because of my fascination with carbonates. Carbonates, which are the components that make up limestone, are primarily composed of fossils, including microfossils and, in the case of corals, macrofossils. Studying corals reveals their interaction with sea level. Corals are animals with photosynthetic algae, requiring them to be close to the surface, typically growing around the bottom of low tide. So, sea level is really important.

However, on longer timescales, sea level is not constant. When studying coral reefs globally, we find fossil coral reefs are situated slightly above or below current sea levels. That longer term component of sea level is actually controlled by climate. Currently, the melting of glaciers is causing sea level to rise, but during the last ice age, an abundance of glaciers led to lower sea levels. This sparked my interest in the fundamental controls on coral reefs and so, on climate itself. This pushed me towards paleoclimate research. I transitioned to studying paleoclimate over longer timescales, focusing on deep-sea cores during my Ph.D. I work with sediment cores to gather climate records spanning tens of thousands to millions of years, concentrating on the 10,000-year timescale of glacial climate change.

My interest in the Southern Ocean began towards the end of my Ph.D. It was around this time that the oceanographic field began to recognize the Southern Ocean's critical role in the air-sea exchange of CO₂. Understanding the uptake and release of CO₂ in this region has been a focus of my research for a long time.

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That's super interesting. Thanks for walking me through that. So, you began thinking about the Southern Ocean towards the end of your Ph.D. When was the first time you went to Antarctica?

That was in 1991. It was during a WOCE cruise, which stands for the World Ocean Circulation Experiment. Just to clarify, oceanographers refer to their expeditions as "cruises," and people often think it means a pleasure cruise. I've learned to say expedition and voyage, but it is indeed a cruise. So, it was a WOCE cruise in 1991, back before autonomous vehicles. To examine the Southern Ocean in the winter, we had to go there on a ship. This particular cruise was in March, which is very late winter, but still winter. We were one of the first cruises to do this, and it was just brutal.

We were supposed to steam south from Tasmania to Antarctica, but we encountered intense winds that were blowing so hard we had to steam into the wind. You have to steam into the wind because if you steam with the wind on your beam, the ship can readily roll too far and capsize. The ship we were on, the Aurora Australis, was an icebreaker, so it didn't have a very deep keel. They had a tilt meter on the ship, and when it reached 42 degrees – since 45 degrees is halfway – they would steam us into the wind. We did this multiple times, facing in 40-foot (12-meter) seas, upwind with this gale coming at our bow. So, we spent a lot of time steaming into the wind. 40-foot seas, clear wind just blowing. It's a 300-foot vessel, and the wavelength was long enough, we were going down waves and then up again. Standing on the bridge is the best place because you can see everything. This bridge is 10 stories up, and there you are – you're looking up at the water. The thing about 40-foot seas is that the wave height is measured from where still water would be, so the waves are actually twice as high. It was an incredible experience.

However, it was also quite challenging. You have to brace yourself in the bunk because it's so rough that you're literally getting lifted out of the bunk by the waves and being slid around. Trying to sleep while braced to avoid falling out of the bunk was tough. I remember some nights just crying to the room, "All I want is to fall asleep." But then you reach the sea ice, and everything changes. It doesn't matter how hard the wind is blowing because the ice covers the water, making it calm. We started icebreaking, the conditions became calm, and we began deploying our instruments. And then, on top of all that, we got stuck in the ice.

Oh, no!

Only for a few days! It was my first Antarctic cruise, and I thought, "Oh, no!" But they reassured me, saying, "This happens all the time, we'll be fine." The way it works is if the wind is blowing as hard as it was, even though we were in the fast ice, it moves the ice around. So, leads will break open, and you can weave your way out along an ice lead. And yes, we had a lot of food, so there was no concern. We were resupplying one of the bases, so we had enough food for ourselves and everyone else for several months. It was never a situation of, "We're going to starve in Antarctica."

Where exactly was this in Antarctica?

...the prevailing consensus then was that the wind could only mix the surface layer of the ocean down to 100 or 200 meters. This was based somewhat on the depth of the mixed layer in lower latitudes and how deeply these well observed systems mix in winter. I remember one of the best scientific moments on that cruise was when one of the team members came running in and exclaimed, "The ocean is mixing to 600 meters!"

This was more or less due south from Tasmania, we’d stopped at MacQuarie Island, and we were heading for Casey Station. I was with the Australian Antarctic program at the time, and I was living in Tasmania. I have never set foot on Antarctica, but I figure if you see a bunch of icebergs and get stuck in the ice, it counts. Right?

For perspective, what was really remarkable is that we were out there observing the winter weather, and we encountered brutal conditions. Until that cruise, the prevailing consensus then was that the wind could only mix the surface layer of the ocean down to 100 or 200 meters. This was based somewhat on the depth of the mixed layer in lower latitudes and how deeply these well observed systems mix in winter. I remember one of the best scientific moments on that cruise was when one of the team members came running in and exclaimed, "The ocean is mixing to 600 meters!" We would never have guessed that. For us at the time, it was an incredible discovery. But now we have autonomous vehicles like Argo floats that have verified this many times across the Southern Ocean. It is now clear that because of the very small density differences across the water column in the cold Southern Ocean, such deep mixing in the winter is possible and common. With ARGO and similar technologies, no one has to endure such conditions for science. And it's probably just as well.

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That sounds like a pretty memorable experience. Is that your most memorable field experience, or would you pick another one?

Well, that was the most hair-raising, but I would choose a better one. I had a cruise back in 2018 where I was the chief scientist. We were at sea to take sediment cores, not water samples. When sampling sediments, which is my area of expertise, you handle around 1,000 pounds, sometimes four or five tons, of lead on top of a metal pipe that needs to be maneuvered over the side of the vessel without causing harm, and then driven into the ocean floor. So calm weather is incredibly important. We were out there in November and December. You might think it would be calmer in January, but in the middle of the Southern Ocean, where we were working, it's calmest in late November. That period was particularly memorable for the exceptionally good weather. As it was November, we were nearing the summer equinox, and we weren't south of 60° South. That WOCE cruise I was talking about went down to about 66° which is below the Antarctic Circle. But at 42° South in the summer the weather conditions were just beautiful. It is extremely memorable when you get the weather conditions you need to accomplish your work. It is so important.

We took so many pictures of the birds. When you're out at sea, your entertainment comes from the seabirds. You always see numerous albatrosses. The question is which ones you will see. When the wind is up, they fly downwind towards the vessel to observe what you're doing. They make a few laps around the ship and then continue on their way. But if you stop to take cores, they assume you're a fishing vessel – the only other type of vessel that stops in the Southern Ocean. They think you're pulling a line or net with fish in it and settle down, expecting, "So what's for dinner?" This allows you to get a really good look at them. During the 2018 cruise, we were around Île Amsterdam, which is slightly north of the Kerguelen Islands. There is a subspecies of royal albatross that nests there and looks somewhat different. The Île Amsterdam albatrosses were just finishing their mating season, so they were out in pairs, basically waiting for us to throw them some fish, which unfortunately they did not receive.

Since it was spring, we also saw whales, some of which I had never seen before. Near Antarctica, when you're on the shelf, you mostly see minkes. We saw many minkes and seals on the ice. But out in the open ocean, we saw Bryde's whales. These are large whales, about two-thirds the size of blue whales. They are truly large ocean-going whales, and few people have heard of them for a couple of reasons. One is that they don’t occur near the US, so they aren't frequently hit by boats, and they don't migrate through areas where tourists can see them. Everyone loves humpbacks because they breach and are very charismatic. Bryde's whales, on the other hand, come up, and you see this tiny fin. I mean, it's a hundred-foot-long animal, and the fin is quite small. But they are majestic. I think, because it was spring and we were the only boat out there, the whales were curious and came to see us. That was magical and very memorable. I believe we saw about 30 whales, and none of them were minkes, which was very special for me.

That sounds really cool. I live in Alaska now, and there are a lot of whales so I can imagine how special that experience must have been. Are you teaching right now?

Yes, I am. I teach two classes. One is the core course for undergraduates, and the other is an upper-level course called Coastal Biogeochemical Cycles in a Changing World. The main focus is on biogeochemical cycles, particularly carbon cycling. One of the best aspects of being an oceanographer is that another crucial part of the carbon cycle is carbonate, which includes fossils and limestones. I am still working with limestones many years later. The "changing world" part emphasizes our examination of current environmental changes. For example, one of the units covers coral reefs, where we discuss the carbonate chemistry and how ocean acidification and warming are affecting corals. It also relates to the organic carbon cycle.

The other class I teach, the core course for undergraduate oceanographers, is called Dynamics of Marine Ecosystems. Fundamentally, this course covers the same introductory material that I studied as a freshman. The traditional class, Introductory Oceanography, starts by building the ocean step-by-step. In that class you first cover the ocean basins (that’s the geology) part, add water and sprinkle in salt (chemistry of water), and then blow the wind over it (currents). Finally, you get to biology. However, we don't research the ocean in such isolated segments. As both a chemical and geological oceanographer, I use geochemistry as my tool. I need to know the current chemistry of the ocean to apply it back through time. So, we teach the Dynamics course in a more interdisciplinary way. It's really fun. Even if you're not a marine biologist, if you are an oceanographer you need to know about how a spring bloom occurs and know why and how the ocean stratifies and warms up. Dynamics is team-taught which means the students get expert lectures in each of the disciplines. The physical oceanographer demonstrates thermal stratification, I introduce the nutrients, and the biologist builds the ecosystem. We repeat this process through each unit. A great example is El Niño. This phenomenon is driven by physics, but the chemistry dictates the biology, causing the system to rise, fall, and crash. We teach interdisciplinary material in this way, and I really enjoy finding ways to help students understand these systems without losing their interest.

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That’s a very interesting way to teach a course. I would definitely take that course now if I could.

It's actually based on a book called Dynamics of Marine Ecosystems, which is about 30 years old. That book focused on physics and biology, but we've incorporated chemistry and conclude with a unit on climate change. I can tie this back to my work because CO₂ in the atmosphere controls the climate. There are underlying factors like Milankovitch orbital cycles, but essentially, more CO₂ in the atmosphere means a warmer climate. The amount of CO₂ in the atmosphere depends largely on the ocean, as the atmosphere is a very small reservoir, containing 700 to 800 gigatons of CO₂, depending on the day of measurement. This CO₂ is in equilibrium with the surface ocean. But the deep ocean holds 50 times more CO₂ than the atmosphere. CO₂ doesn't just dissolve into the ocean; it reacts with water to form bicarbonate and carbonate. If you're not familiar with carbonate chemistry, consider your soda water or seltzer. There are no bubbles in our soda when the cap is on, and it is under pressure. The bubbles in your open soda are there because it's not just CO₂ in the water. If it were only CO₂, once you open the top, it would fizz out in an instant, and that would be it. However, when CO₂ dissolves in water, it forms carbonic acid, which then releases protons and hydrogen ions. The bubbles that come out of your soda, beer, or sparkling beverage – personally, I prefer Prosecco – are from the reaction reversing slowly, once the pressure is released.

The reason I'm interested in the Southern Ocean is that I like to say the Southern Ocean is where the ocean exhales. There's photosynthesis in the surface ocean, just like with land plants. These organisms pull CO₂ out of the atmosphere, turn it into organic matter, and when they die and sink, that carbon – now no longer CO₂ – sinks into the deep ocean. There's always something down there that will consume it. If there's organic matter, it gets respired back to CO₂. It’s like how we consume food, which then turns back into CO₂. So, you have this shunt for CO₂ from the surface ocean, where it's more or less in equilibrium with the atmosphere, into the deep ocean. The thermocline in the ocean acts like the cap on a soda bottle, keeping CO₂ under pressure and allowing the deep ocean to hold much more CO₂. This is how there can be 50 times more CO₂ in the deep ocean than in the atmosphere. When that water comes back up to the surface, it will de-gas. If there's more CO₂ in that water, it will de-gas; but if there's less, it won't. That's the equilibrium part.

The Southern Ocean in the winter has more CO₂ than the atmosphere because of the lack of biological activity there. In the spring, there might be so much photosynthesis that the CO₂ doesn't escape. But the point is, the deep ocean holds a significant amount of CO₂. There are only a few places where the deep ocean comes to the surface, and the Southern Ocean is one of them. If you change the dynamic of how much CO₂ was sequestered in the ocean through the biological pump, the winds, the fronts, and the sea ice, you will change how much CO₂ can escape. We know that during the last ice age, CO₂ in the atmosphere was a third less than pre-industrial levels. The only way that could have happened was by capping the Southern Ocean.

I've spent a lot of time examining temperature in the Southern Ocean using biomarker compounds but also work with carbonate microfossils. I collect these microfossils from the mud and measure δ¹³C as a tracer for respired carbon. Essentially, we can use these carbon isotopes to estimate how much CO₂ was sequestered or released from the ocean on timescales of tens of thousands of years. I am particularly interested in the last deglaciation because it provides a valuable model for understanding the dynamics involved in the transition from a colder world to a warmer one, similar to what we are experiencing now.

Do you have any current projects you are focusing on?

Yes, my main focus right now is the cruise we were on in 2018. I must admit, I am quite envious of physical oceanographers because they go to sea and return with data, whereas I come home with samples. I have to take that core and, much like tree rings, slice down the core back through time. However, we do not know where we are in time until we perform what we call stratigraphy. First, we have to slice the core open, sample it, and run isotopes or other measurements to determine the stratigraphy. That is the essential first step, figuring out how old that sediment is. Six months after returning from the cruise, you might have just completed the stratigraphy and are beginning to decide which cores are the most promising. It's a long process. Even though it was four years ago, we are still working on those cores.

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Currently, we have one paper published and two or three papers in progress. For the one that is out, we used radiocarbon to determine where sequestered CO₂ was released from the ocean during deglaciation (Umling et al. 2024). We discovered that the area between the Kerguelen Islands and Île Amsterdam is a crucial spot for CO₂. The CO₂ that was sequestered in the deep ocean during the glaciation – meaning it wasn't in the atmosphere – was released into the atmosphere right there. Occasionally, you hit the jackpot and get a sample from the perfect spot. So, we're very pleased, and we're hoping that this paper gets through the review process. CO₂ is our main focus: is it coming out of the ocean? How fast is it coming out?

We are also examining sea surface temperature because the solubility of CO₂ in water depends on temperature. Gasses dissolve better in colder temperatures. If the temperature changes, how much of the CO₂ change is due to temperature variation, and how much is due to circulation changes? We gather various records, align them, and analyze them, asking, "Which one was first? Which one was leading, which one is lagging?" This is a big problem to tackle that I’ve been thinking about for so long and I feel is so important, that I recently wrote a review paper about it (Sikes et al. 2023). Someone once asked me when I entered this field, "Liz, do you really want to spend the rest of your life matching wiggles?" Yes, I do. I enjoy it. One of the questions that I am not addressing because it has already been answered is: when we exited the last ice age, did the planet warm up first because of orbital changes, or did the CO₂ come out of the ocean and then warm the planet? We are still discussing the details, but it appears to be a combination of both factors. So, feedbacks.

Could we spend some time talking about your involvement in SCAR? How did you first get involved?

Joining the Southern Ocean Regional Panel was a logical step for me, as an oceanographer concerned about my science, to contribute in a way that might help the broader community and advance our understanding of the Southern Ocean.

I joined the Southern Ocean Regional Panel (SORP) in 2017. I have lived in three different countries. As I mentioned earlier, I moved to Tasmania after completing my Ph.D. So, in addition to being scientifically excited about the Southern Ocean, I was also geographically close to it. After Tasmania, I moved to New Zealand and then back to the United States. In Hobart, where the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is located, I became more involved in thinking about how the Southern Ocean and Antarctica are governed. CCAMLR regulates fishing and related activities in the Southern Ocean.

One of the aspects of Antarctica that fascinated me is that no one owns it. I realized that this is a pretty special place on the planet. Before nations started claiming territories, they decided to keep Antarctica an international zone. You can have bases for scientific research, but you cannot build cities. Joining the Southern Ocean Regional Panel was a logical step for me, as an oceanographer concerned about my science, to contribute in a way that might help the broader community and advance our understanding of the Southern Ocean.

Part of my motivation to get involved in SCAR and other societies is the slow pace of data generation in my work. One of the constant challenges in paleoceanography is that you can spend three to five years working up data from a core. It involves a lot of steps from sample collection to final product. Take, for example, the WOCE cruise, where we sent the CTD rosette over the side and collected 36 water samples each time. This extensive sampling of the water column generates data in real time and samples that can be processed relatively quickly. However, four years after my last cruise, each core represents one hydrocast with two bottles – one at the top, which is my planktonic foraminifera, and one at the bottom, which is my benthic foraminifera. To improve on that, I do more; we take depth transects of cores which multiplies the time between collection and publication. Moreover, the impact of your work depends on getting the right core and being able to correlate findings across it. Having worked internationally and with colleagues who had cores from different places, I wanted to improve coordination and collaboration between scientists and countries. That is why I joined SORP.

Part of my motivation to get involved in SCAR and other societies is the slow pace of data generation in my work. One of the constant challenges in paleoceanography is that you can spend three to five years working up data from a core. It involves a lot of steps from sample collection to final product.

Then I was asked to step up to be co-chair. I would like to emphasize that I was co-chair because Torge Martin was the primary chair. He shouldered most of the work, and I served as the secondary chair. The beginning of the United Nations Decade of Ocean Science for Sustainable Development coincided with my stepping up to co-chair. Before the official launch, various regional groups convened to discuss their respective action plans for the oceans. Every other ocean has surrounding populations, such as the Pacific, Atlantic, and Indian Oceans. There is even a North Pacific and South Pacific, as well as a North Atlantic and South Atlantic. However, early on, there was no regional action plan for the Southern Ocean. The individuals working in the Southern Ocean – I did not initiate this; I joined in time to assist – recognized the need for a Southern Ocean action plan. We were essentially playing catch-up those first years. We had to identify the needs of the Southern Ocean and establish research priorities to achieve the UN Ocean Decade goals in time for the launch.

That took a lot of work. Anything you do with an international organization requires extensive effort. You need to present your proposals, allow for public comments, hold meetings for feedback, and provide time for interaction. I was involved in the Southern Ocean Task Force coordinated by SCAR that developed the Southern Ocean Action Plan, which referenced the Ocean Decade implementation plan. I really leaned into this task because I believed it was very important. The Southern Ocean has no obvious stakeholders. There are no populations relying on its sustainability for their livelihood. Although many people visit the area – remember, we had whalers, and there are still fishing activities – but these individuals do not represent the Southern Ocean as it is not their territorial sea. Why would someone extracting krill from the area want an action plan for sustainable fisheries?

And part of it is that the Southern Ocean is unique in that its largest border has no coast. If you look at atlases, they might indicate the Southern Ocean stops at 40° south. Its boundary is not at 40° south. There is a front that runs along its northern boundary. As an oceanographer, I know that north of the Subtropical Front, there is a permanent thermocline, whereas in the Southern Ocean, there is a seasonal thermocline. This allows deep water to upwell and de-gas. This front is influenced by bathymetry and winds, causing it to meander. It does not have a fixed border. In fact, I remember, back in the '90s when I first began publishing papers, it wasn’t an official ocean. We had to argue with the Paleoceanography journal to capitalize "Southern Ocean."

They insisted, "This is not an actual ocean." Yes, it is, it's just very different. This was around the time people began to recognize the importance of this ocean. Just getting it named was a bit of a journey. I think National Geographic only added it to its list of world oceans last year. It did not officially exist until now! So, we have made some progress. The fact that it lagged behind makes sense. It only has two boundaries – one around the north and Antarctica to the south. So, it's easy to overlook. Go, UN Decade of the Ocean!

When did the United Nations Decade of Ocean Science for Sustainable Development start?

Technically, the initiative started in 2021 and will end in 2030. However, there was some catching up to do initially. That period was my pandemic Zoom-fest for a year. I believe we managed to consolidate everything and submit our plans by the end of 2021. By 2022, we had established an Action Plan around which people could build regional projects and collaborations. I felt it was crucial to be involved in this effort.

Now that I have rotated off SORP, I am not as involved, but they are currently working on Ocean Prediction. Essentially, our goal is to achieve a predictable ocean, a sustainable ocean, and a healthy ocean. There are seven objectives within this framework, and prediction is a key one. We aim to predict things like hurricanes, storms, and whether the glaciers in Antarctica are going to melt and cause sea levels to rise. Ocean Prediction is now one of the primary focuses, coordinating efforts to improve our predictive capabilities. It is easier to understand the necessity of predicting hurricanes in the Atlantic Ocean compared to the Southern Ocean, but the importance is just as significant.

Absolutely. I think we may have talked about this already, but you received the 2022 SCAR Medal for Excellence in Antarctic Research. Can you speak more about that?

Yes. I guess the underlying question is: Why does the science I do matter? I’ve already discussed ocean sequestration of CO₂ and its impact on climate. That work involves stable isotopes and radiocarbon. I’ve also done a lot of work estimating past sea surface temperatures to quantify that climate change. For that, I primarily use biomarker proxies. I am also an organic geochemist, which tends to surprise people. There are a few phytoplankton species globally, and Emiliania huxleyi in the Southern Ocean, produces unusual compounds called long-chain ketones or alkenones. These compounds are just a single string of carbon, and the number of double bonds that the organism incorporates is linearly correlated with temperature, which is kind of cool. This relationship is useful because it is linear, not nonlinear, and quite straightforward to apply. These compounds are like waxes and behave similar to how oils and fats behave. The more double bonds a substance has, the more liquid it is at lower temperatures. This is why butter is solid at room temperature, while oil is not, because it’s multi-unsaturated or poly-unsaturated. These tiny organisms add more double bonds when it is colder, and we can extract these compounds from sediment to determine past temperatures. Being able to quantify temperature - to put a value on how cold or how warm it was - is essential. I like to say doing that is the baseline we can compare against to determine climate change in the present and future.

So, I work with both carbonate chemistry and organic carbon chemistry. My work takes in the whole carbon cycle: both organic and inorganic components. On land, plants primarily produce organic carbon, and that's it. In contrast, the ocean holds the largest reserve of inorganic carbonate in the form of limestone. The largest carbon reserve on the planet is carbonates. While we often worry about fossil fuels because they are combustible, the majority of carbon is stored in limestone. Think of the White Cliffs of Dover – that represents a significant amount of carbon.

That's interesting about the phytoplankton. So, you find them in the cores?

Yes, we find the remnants of their dead bodies. They serve as my sea surface hydrocast samples, the top of the ocean, the phytoplankton The benthic foraminifera at the bottom of the ocean that serve as my bottom samples.

Well, I've taken a lot of your time, but I usually end with the same question: if you think back to when you got involved in Antarctic research, what helped you? And what advice would you give early-career scientists wanting to get involved at this stage?

I can talk about this on two levels. First, everyone wants to go to Antarctica. It's a fascinating place, and the environment is incredible. We all get it, right? But you need to have a scientific question that interests you and can be answered there, or that requires research in Antarctica. Otherwise, it is not sustainable and becomes more of a boondoggle. As a scientist, you need to have a specific question. At the same time, many of us have expeditions and need assistance. If you really want to go and think you might be interested in this science, and you just want to get your toes wet, ask scientists going to the Southern Ocean or Antarctica if they have room on their team. There usually is room. If you're young and fit, there's often space for someone with limited experience. So, don't be afraid of your lack of experience or feel that you need to be an "Antarctic hero," as they say in Australia, to go. You'll become an Antarctic hero when you return, perhaps, but you don't have to be one to go. Just don't be afraid.

I managed to join the ship because I had a solid scientific reason, there were a few spare berths, and we were brave enough to ask. We turned that opportunity into an intriguing project and a good solid paper. And here I am, still working in the Southern Ocean 30 years later.

That's great advice. I was pretty inexperienced when I started my Ph.D., and yes, you just learn.

You just learn as you go. And you're still here because the science kept you engaged, right? That's important, too. Think about your question and your passion. I got on my first cruise because there was space on the ship, and I needed samples. I had been working with alkenones – sea surface temperature markers – and no one had measured them in very cold water. Scientifically, that was why I was there. We needed to go out and filter hundreds of liters of water. I spent hours watching these filters fill with tiny green bodies. But there was space on the ship, so I seized the opportunity to go. We produced the first calibration of these compounds for polar waters, and remarkably, that's still one of my highest-cited papers. So, there you go. I managed to join the ship because I had a solid scientific reason, there were a few spare berths, and we were brave enough to ask. We turned that opportunity into an intriguing project and a good solid paper. And here I am, still working in the Southern Ocean 30 years later.

That’s quite an accomplishment. Well, thank you so much for your time. It was great to talk to you.