The ocean, our super hero ? Will those vast expanses of salty water, reaching down to lightless depths, be our planet’s saviour ? In an interview with Eos magazine, none other than our own Phil Renforth (yes, the same with whom we walked the rugged shores of Hawai’i), explains in a very accessible way how the ocean may assist us in combating effects of climate change. More specifically, Phil explains how raising the ocean’s alkalinity -it’s acid buffer capacity- may help to sequester more CO2 from the atmosphere. This is of course a shared research interest, as we collaborate on several fronts. The interview in Eos was done to accompany a scientific article Phil published in the journal Reviews of Geophysics, on the same subject. It would be silly to repeat what Phil has to say, so I invite you sit down and read it here. Enjoy !
Another publication of our work has made it to the scientific press ! This time, it is a so-called “review”. A review is a type of scientific publication in which the authors make a compilation of what is known on a certain subject, and expand on it with knowledge and scientific opinions of their own. As any other scientific publication, reviews also go through a rigorous peer-review process to ensure that the reasoning follows the scientific “rules” in a proper way.
The review we wrote is on how to use enhanced weathering of olivine in seawater, in order to combat ocean acidification and ultimately, to soak up CO2 from the atmosphere. In this review we discuss and explain the mechanisms of enhanced olivine weathering in seawater, the latest findings and potential future applications. Also, we shine a light on subjects that need strong research focus, if these approaches and techniques are ever to be implemented in the real world. As it is a scientific publication it is rather technical, but much less so than the paper in our last post. We therefore invite you to read it and share it, and get back to us if you have any questions. The article is Open Access and can be viewed and downloaded here.
Yes ! We did it ! After a lot of concerted effort, working with a team of scientists from all over Europe, each specialised in different aspects of enhanced weathering, we published a scientific paper on the effects of enhanced weathering of olivine in seawater. The paper was published in the journal Environmental Science & Technology (ES&T, in short), and can be found on their website. I think it is safe to say that we managed to publish the most complete work on this subject up till now. Of course, at the end of the day, we are still left with numerous questions, but we’ve experimentally proven that it works ! Olivine dissolution increases the pH (lowers the acidity) and increases CO2 uptake by the seawater. The article is Open Access and can be obtained here.
For those readers who are not scientists (marine, climate, geo-engineering or otherwise) and who are wondering what the paper actually is about, I will try to explain our research in a more accessible way (please do let me know whether I succeeded in doing so…).
There are numerous claims that if olivine is ground to the size of fine sand grains and dumped in the ocean, it would actually enable the sea to take up more carbon dioxide from the air, while at the same time combating ocean acidification. However, this process has only been proven in model simulations or under ideal -and thus unrealistic- conditions. What we have done is taken certain quantities of olivine sand grains of ca. 150 micrometer (15% of a millimeter, see picture at the end of this post) and let those dissolve in bottles of seawater, while the bottles were constantly shaken on a rotational shaker table. A rotational shaker table is a piece of laboratory equipment (picture below), on which you can place bottles or jars or other containers in a fixed manner. The table part with the bottle holders can then be set to freely turn in circles (rotate) with a given number of rotations per minute (rpm) so that the contents of the bottles are constantly mixed.
Then, we opened the bottles at regular times (every 2 to 7 days) and took a bit of seawater out, so we could analyse its composition and chemistry. Our first and most important finding is that we actually could measure the fact that over time a) the seawater became less acidic and b) the CO2 buffer capacity also increased, leading to more CO2 being captured by the seawater from the air.
Of course, we made sure that we used a proper control group. In the context of a properly conducted experiment, this means that you introduce a group to control for the effect of the olivine. In other words: how do you know the effect you measure comes from the substance/treatment you introduced, if you do not have a control group ? So, in order to make sure that it was the olivine that was causing the seawater de-acidification and increase of its buffer capacity, we also dissolved another mineral in seawater at the same time. For this, we used pure quartz minerals. Quartz is a highly inert mineral, meaning that it hardly reacts or dissolves in (sea)water. Ordinary beach sand is basically quartz, and does not have the properties that olivine has, in that it does not (should not) influence the seawater chemistry. When we analysed the seawater of the control (quartz) group, we found just that: no changes in either acid-level or buffer capacity. Conclusion: olivine has indeed the capacity to make our seas less sour.
The second part of our study, was essentially a repetition of the first part. Only now, alongside bottles of natural seawater, we used a series of artificially made seawater mixtures, in which we dissolved the olivine sand. The artificial seawater mixtures had a different composition, meaning that we replaced certain compounds for others. The reason seawater is so salty, is that it has (surprise !) a whole lot of different salts dissolved in it. Rain (fresh water) falls on land, and dissolves a tiny amount of the rocks and earth minerals it runs past. The ultimate fate of all fresh water is to arrive in the world’s oceans, where it eventually evaporates as fresh water, while the dissolved compounds stay behind in the ocean. After millions of years of dissolving rocks and evaporation-rain cycles, the concentration of dissolved compounds can even be tasted as different types of salts. By far the most common salt in seawater is sodium chloride, yes table salt ! But there are also several other salts in seawater, that contribute to the salty-ness, mostly magnesium and calcium salts. So, what we did in the second part of our experiments, is replace the calcium and the magnesium salts for sodium salts. In that way, the artificial seawater would be as salty as before, but made with different kind of salts. What we wanted to know, is if olivine would dissolve in a “different type of seawater”, would it also display a different dissolution “behaviour”
And what we observed was indeed different. We first replaced only calcium and saw that the dissolution went faster, which translated into faster de-acidification and more CO2 taken up from the air. When we also replaced magnesium, the dissolution went about 2 to 4 times faster ! The response of the seawater was off the charts: the pH increased with more than 0.1. The pH scale is a logarithmic scale, meaning that from pH = 6 to pH = 7 is a ten times increase, while from pH= 6 to pH = 8 is a hundred times increase. To place it in perspective: the ocean’s acidity has decreased by about 0.1 in recent years, which gave rise to the concern of many marine and climate scientists. In our experiment, we managed to actually counteract part of that pH change. Also, as a consequence of us replacing magnesium in the artificial seawater mixture, the CO2 buffer capacity increased much more than in natural seawater. Of course, we cannot take out all the magnesium from seawater, nor do we need to, but it shows us that magnesium in seawater seems to put a brake on the effects of olivine in seawater.
All in all, it seems that the olivine dissolution we measured in our experiments lines up pretty well with what had been predicted in all sorts of model simulations in the literature, and even is a tad faster. But we are the first ones to prove it experimentally !
And now for the remaining questions and challenges. What about the secondary (or side) effects of olivine dissolution on the marine ecosystem ? The main reaction products of olivine dissolution are increases in pH, buffer capacity (alkalinity), dissolved CO2, dissolved magnesium, dissolved silica and dissolved nickel. Now the first three are actually the desired effects, in terms of climate change mitigation. Even number four, an increase in dissolved magnesium in seawater, is not expected to cause any negative effects, because the natural concentration of magnesium in seawater is already much higher than what olivine would add.
Dissolved silica is used by certain groups of microscopic algae in seawater. In turn, these algae would benefit from this “fertilisation” effect, grow faster and would then suck up more CO2, right ? Hmm, yes… But, imagine a sudden (much) higher silica concentration in the seawater. This may (not necessarily, but possibly) cause more intense growth of these groups algae. Algae do not have eternal life and such sudden bursts (also called “algal blooms”), have a tendency for massive die-offs. If such amounts of algae suddenly die, it means a lot of food for bacteria, who will use a lot of oxygen from the seawater to eat up all that dead organic matter. In some areas in the world’s oceans, this already happens in a more or less “natural” way, and really lowers the oxygen concentration in the sea. This leads to the development of so-called “dead zones”, because you can imagine that not a lot of sea organisms (fish, shrimps and crabs, clams, worms etc.) are able to live in under such conditions. I am not saying that this will happen, but it is definitely something we need to find out, before thinking about applying olivine in natural systems.
The sixth and perhaps most pressing, consequence of olivine dissolution is a marked increase in nickel. Nickel is officially counted as a heavy, and potentially toxic, metal. Although there is some research on whether and how toxic nickel is to marine organisms, the overall effect is not very clear. Nonetheless, the potential impact of nickel needs to be clarified as soon as possible. The last thing one wants to do is to try and solve a climate problem, only to find that another aspect of that solution is just as damaging for the ecosystem one is trying to protect.
In the last part of our study, we investigate how well our results would do in a real-life situation. We take the example The Netherlands, a country famously known for the fact almost half of it is below sea level and protected from the sea by a large system of dunes. To maintain the coastline, and prevent the hinterland from being exposed to the wrath of Neptune’s, the Dutch government is required by law to perform yearly supplements of sand along the coastal zone. In the last decade, the yearly volume of sand used to maintain the coastline was 12 million cubic meter (424 million cubic feet). That volume is already becoming more because of sea level rise due to climate change. We made a calculation, using the values on how fast the olivine dissolves in seawater, and how much carbon dioxide (CO2) it captures as a consequence. We then imagined that those 12 million cubic meter sand actually consisted of the same olivine sand we used in our experiments. Using the calculation mentioned before, we found that the yearly “olivine sand supplements” along the Dutch coastal zone could capture about 5 % of the yearly CO2 emissions of The Netherlands. This may seem a bit low at first sight, but there are many natural processes in that sandy sea bottom that would considerably speed up the olivine dissolution. It is thus very likely that those 5 % would turn out higher. In any case, we think it would be very important to have a look at those naturally occurring coastal processes, and investigate how they influence the olivine dissolution when applied to a truly natural situation. But that is a story for another (upcoming) publication !
Our take home message ? Dissolving olivine in seawater indeed counteracts ocean acidification, by increasing the alkalinity, and consequently sucks up CO2 from the atmosphere. It sounds like the perfect medicine against climate change, but it is very important to realise that there are secondary effects, which need to be investigated in detail. It is also very important to answer the question whether olivine dissolution would be feasible to apply at a (very) large scale.
For more information on how olivine dissolution may be used in seawater, we expect a review article to come out quite soon. Keep an eye on this website for the latest news and research outcomes. If you have any questions, or want thing clarified, please drop us a line via the contact form !
It has been quite a while since I updated the blog. So, let’s pick up where we left last year… With media attention for geo-engineering, and enhanced weathering in particular.
In a recent editorial, the scientific journal Nature Geoscience turned the spotlight directly to enhanced weathering and its potential to contribute to negative emissions, the net removal of CO2 from the atmosphere. Click here for the direct link. In the last post, I found out that the popular science website IFLScience picked up on an interview in the New Scientist, when I was visiting a conference on Ocean Acidification in Tasmania. Again, I cannot say it often enough how nice and important it is to be covered by more popular science media. In this way, a far larger -and in essence, more important- audience is made aware of what is achieved in the realm of Academia.
As such, I wanted to put down a list of media that have covered our story in the past years. Just to show that the use of enhanced weathering of olivine against ocean acidification, both from a scientific and climate change mitigation standpoints, is considered an interesting option. Also, I wanted to provide useful links, with extra narratives, that makes those articles so much easier digestible than your average scientific article.
Being a scientist I have to stress here -and stress it I will- that I do not endorse or dismiss any climate engineering action per sé. What I DO promote, wholeheartedly, is research into these approaches. How else are governing bodies going to decide whether to pursue a certain path of climate change mitigation approaches, if they do not have the scientifically checked facts on the table ? I know that the last sentence might even sound a bit odd in the “post-truth” era we appear to be living in, but I stand by my point.
Anyhow, without further ado…our media coverage during the past years:
2015: One of the bigger Dutch national newspapers, de Volkskrant, publishes an article on olivine
2014: During a very interesting, multi-disciplinary conference on climate engineering in Berlin, several media approach us and cover the story of how olivine works against sour seas and sucks up CO2. The scientific journal Nature published an editorial in the News section, and the well-known US-based newspaper The New York Times published a long article.
Also, I was once asked for some comments on an article in Geology about how ant colonies enhance underground olivine rocks and so increase CO2 uptake. These were done in a German newspaper (Sueddeutsche Zeitung) and a Swiss one (Neue Zuercher Zeitung).
The currency of science is (sadly, sometimes…) publications. “Publish or perish” is the oft-used adagium, to illustrate how much of a Red Queen we have to be as a scientist. Think of researchers needing to publish for scientific survival, as a person running on a conveyor belt at full speed… If that person (the scientist) stops running (publishing), (s)he will fall and be whisked off the stage. Harsh ? Hmm, yes… Unfair ? No, not really. Because, science needs to stay as up-to-date as possible to provide well-founded facts and answers to questions big and small. Of course, publications in high-impact journals constitute the biggest trophy one can proverbially shoot. But, how many people read such publications actually ? Not that many, is the fair answer. That is why I find it so incredibly cool that the popular (but accurate) scientific website IFLScience has picked up on the interview in New Scientist and published an article about our work. With the sole purpose of explaining and distributing real science to real people, IFLScience uses no-nonsense language, straight to the point, without dumbing it down.
Being home for only some weeks after our Hawai’ian adventure, I had to pack my bags again by the end of April. This time, I would travel entirely to the opposite end of the world, to the Tasmanian capital of Hobart (Australia). A colleague of mine, Dr. Andrew Lenton, of the Australian research institute CSIRO, had asked me to come and give a talk at the Fourth International Symposium on The Ocean in a High-CO2 World. Andrew works with large-scale biogeochemical models and because we knew each other from the climate mitigation research community, he told me this symposium would be the perfect stage to give a presentation on how olivine could be used against ocean acidification. I did not have to think too long before I accepted. Of course I wanted to be a week long among the greatest minds involved in researching the ocean’s future trends !
The entire conference was a big success. Apart from bringing together hundreds of scientists from all over the world, the symposium comprised a public townhall meeting, in which climate change and ocean acidification was explained to the general public. This was a very special experience, as the plenary hall filled up to the rim with “normal” people, who came to listen to scientists (also known as “not so normal people”), doing their best to deliver an interesting, yet accessible story. The turnout was enormous, and the questions were both plentiful and valid. I for one had the impression that people were not being told by your (stereo)typical scientist about climate change, but rather educated and informed on a voluntary basis, with genuine interest on both sides.
Walking among these researchers who had dedicated the last decade(s) of their careers to researching the state of the ocean and listening to the talks in the beginning of the week, the main message appeared grim: “We are facing unprecedented rates of warming and acidification, on top of the environmental pressures which have been going on for almost just as long: pollution and over-fishing.” However, as the week took shape, I managed to talk to many of these great researchers, hailing from many different sub-disciplines, becoming more and more confident that my presentation was going to fit in very nicely. It felt a bit odd, though. It was almost missionary, to bring this message of hope against Ocean Acidification. Sure, our experiments were done in the laboratory or in simplified systems, but still…the results were so consistent and the implications so compelling, that I felt very excited to present them. Finally…the hour had come to bring my work to the stage. On the one-but-last day of the conference, I stepped up unto the dais and gave my presentation, which was well received, I might add. Apart from some nice questions right after the presentation, I received many positive reactions. Also, people seemed very much surprised that there is a possibility for remediation at all, even though research into this subject is still very preliminary. To my surprise, the attention for my presentation even spread further than the conference. I was contacted by the science journal, New Scientist, to comment on the work we are doing with olivine against ocean acidification. And by the next week, the interview appeared in their new issue. Very nice to have the research receive such attention !
All good things…well, you know…they end. And I wish I could say that that’s for the best, but in the case of doing fieldwork on Hawai’i, I will make an exception. It has been an absolute blast doing fieldwork here. The days were long, and the work was hard, but rewarding. I know, I know…sometimes it looks like we’re playing with sand on the beach, snorkelling in warm Pacific waters to get some bottles of seawater and prying sea urchins off the rocks. And then I would have to say you are almost right…we filled countless tubes with seawater to be analysed in the laboratory back home. Bags and bags and bags of sand from two different bays. Black sand, white sand and mostly: green sand. Saying that no animals were harmed in conducting this research, would be a blatant lie. But rest assured that we followed all the protocols in place. While the sand and seawater will shed light on how fast the Hawai’ian olivine dissolves and how this affects the CO2 in the seawater, the animals and algae will tell us a bit more about how its reaction products potentially bio-accumulate through the marine foodweb.
Although we did most fieldwork alone, it would not have been possible without the financial, logistic and administrative support from several agencies and institutions. Our main sponsor was the Royal Geographic Society, who awarded us a grant to pay for this fieldwork. The Department of Land & Natural Resources of the State of Hawai’i, assisted us in obtaining the permits to work in the field and collect samples needed for our research. The University of Hawai’i at Hilo, and Dr. Tracy Wiegner in particular, assisted us with all sorts of fieldwork equipment. Along the rugged southern Ka’u coast of Big Island, we were greatly helped by the local community members, who organise the transport to and from Papakolea/Mahana beach. Their normal fare consists of tourists, but when we needed to bring in large boxes of fieldwork equipment, they stepped in and accommodated our needs perfectly ! And of course, an extra thank you goes out again to our science-minded diving friends at Kona Diving Company !
It is strange. After so many days, weeks, toiling with bags of sand and tanks of water, walking around Papakolea bay and snorkelling in its warm waters, we became so intimately acquainted with our fieldwork location. We felt we knew every corner, every nook and cranny, both above and below the water. After such an intense period, we felt sad to say goodbye to the place we visited almost daily. We took one more long walk along the coast and took as many pictures as we could. It’s not a location one reaches easily, but with a bit of luck and good results, we may be able to repeat our visit and even expand our research. Who knows ? For now, it is mahalo (thank you) from us and aloha ! Until we meet again !
Science is not magic, nor does it work any. A scientific experiment is only any good if you build in a control group. In any scientific experiment you hope to measure an effect of the experimental treatment you have imposed onto your subjects. This can be the effect of certain chemicals on eating behaviour in rats, the effect of psychological stress on decision making in humans, or even a model simulation of average global temperature changes under different CO2 emission scenarios. However, without the control group, the values you measure can be as good as any. Rather, if you have a similar group of subjects, which pass through the experiment unaware of any treatment you have bestowed onto the others, you have yourself an experimental control group. That control group provides a baseline, that tells you what the background values are of the process you are trying to investigate. And when you know the background values of your control group, you can demonstrate what the effect is of the particular treatment you are investigating.
In our case, we were investigating the effects of the presence of naturally dissolving olivine on the environmental chemistry of an entire bay on an island in the Hawai’ian archipelago. To incorporate a control group, we would need an entire bay, without dissolving olivine, preferably on the same island. The best control group we could have is a typical tropical white sand beach, which consists almost entirely of calcareous sand. “That should not be too hard on a tropical island, right ?”, I hear you exclaim. Well…sort of…yes, or rather: no. It is harder than one might think. White sand beaches are normally formed by…coral reefs. Yes, the tiny sand grains on tropical white sandy beaches once were colourful corals. How ? Well, there is a group of fish that eats the calcareous skeleton of corals, in order to reach microscopic algae that live INSIDE the coral skeleton. That’s right, corals do not only have algae in their soft parts, but also inside their “bones”. These highly specialised fish, called parrotfish, have strong teeth that look like a parrot’s beak to grind the coral skeleton, so they can reach their food. What happens inside the parrotfish’ body stays inside the parrotfish’ body. But what comes out is freshly ground coral, in tiny white, calcareous sand grains. Next time you are snorkelling around a tropical coral reef, keep a look out for parrotfish. You are bound to see one pooping, which looks like it has a fast-sinking, white smoke trail behind it. Tropical white sand beaches are actually parrotfish poop, people…get used to it !
So, what does this have to do with finding an experimental control group, while investigating an olivine beach on Hawai’i ? Well, most land masses on Earth are hundreds (if not thousands) of millions of years old, which is plenty of time for organisms to settle and evolve. In contrast, the Hawai’ian islands are relatively young. The oldest islands, located in the North-Eastern tail of the archipelago, already exist for several million years, while Hawai’i (Big Island) is only max. 400.000 years old. Now, think of the beautiful, but rather violent manner in which these volcanic islands are born: enormous volumes of red-hot molten rock are pushed from the fluid belly of the planet through fault cracks in the massive crust, only to solidify once it comes into contact with seawater. This is still going on on the south coast of Big Island. Every year, the island grows towards the south-east, by lava flowing into the Pacific Ocean. The newly formed rocks cool down, and -after a while- become colonised by living organisms, like corals. Given enough time, both parrotfish and pounding waves will grind corals into white sand beaches. But when an oceanic island in the center of the largest water body on the planet has only just been born, there has simply not been enough time to form white sand beaches. Luckily, the north-western parts of Hawai’i are old enough to have some stretches of white beach, and we had secured a permit to go sampling on Makalawena Beach. Unluckily, however…the ocean was much (MUCH !) rougher than you see on the regular websites praising this secluded paradise.
Although very nice for surfing, it was impossible to snorkel out and safely collect samples from further into the bay, as we had done at Papakolea/Mahana. Because the sea state did not quiet down during the entire period, we had to modify our plans somewhat. We were able to collect water, sediment, algae and rock-based animals close to the beach…always keeping one eye on the huge waves rolling in.
Being able to stay under water for much longer, we could take samples of sand from the deeper parts, which were located further out into the bay. Also, we were able to sample the pore water in the sediment itself, without removing it and bringing it to the lab, so as to get snapshots of the chemistry in the sand in its natural setting. The sand is extracted with tubes of ca. 30 cm long, so-called “cores”. What we do with those cores is push out the sand, and slice it at predetermined, regular intervals. Each slice is weighed and dried and later analysed. In this way we obtain a depth profile of different locations in the bay.
While diving the deeper parts of the bay, we collected thumb-sized fragments of live coral. Why would we take coral, you ask ? Well, as the olivine dissolves, it releases both silicate and metals into the seawater. Most of the metals are either magnesium or iron, http://www.youtube.com/watch?v=wm790hF6Wogwhich are both in ample supply in natural seawater. Part of the saltiness of seawater is actually caused by magnesium salts. No, what is of interest to us researchers is nickel. Nickel occurs in very low concentrations in olivine. However, if you have an entire olivine beach, the amount of nickel leaching out of the olivine sand is expected to be considerable. For many organisms, including ourselves, nickel is of vital importance to certain physiological processes. However, as with many metals, it tends to become toxic in higher concentrations. So, the main reason we sampled corals in Mahana Bay is to investigate whether we can find traces of nickel (coming from the olivine) in the corals. We not only collected corals, but also other organisms that spend their entire life living in close vicinity of dissolving olivine and may even ingest it on a regular basis, like sea urchins and sea snails. Mind you, this would just tell us something about the incorporation of dissolved metals from the olivine into the tissues of living organisms. Whether that is bad thing in itself remains to be seen.
To be able to distinguish whether the metals may be accumulating in different parts of the coral, we need to separate the soft coral tissue from the hard calcareous skeleton. This can be done by using pressurised air, and literally blowing the soft polyps off the hard skeleton. It does sound a bit gruesome, and it actually is…but it is the only way. Like this, we get a really clean calcareous skeleton and a gooey substance which can be analysed separately, enabling us to say whether corals store the metals in their hard skeleton or in the soft body tissue. Because both the skeleton and the soft tissue each serve as food for different animals higher up in the food chain, stronger accumulation of metals in either of them, may affect different parts of the ecosystem.
By now we had sampled the basics of our field site: seawater of the surface and along the bottom, olivine sand from the beach and the surf, and even the pore water from the space in between the sand grains (see previous post). Now it was time to move into newer territory. Sampling-wise, that is… Our next objects of attention were located in the deeper parts of the bay. And by deeper, I don’t mean hundreds of meters, but a mere 4 to 9 meters deep. It is fairly easy to train yourself to draw a deep breath and snorkel to such depths, especially using diving fins. However, to be doing actual sampling work while down there, without getting too stressed by the lack of oxygen is another sport. Simply put, we would have to go sampling, doing SCUBA diving. But for SCUBA diving, one needs quite some gear. For two persons, mind you, because one does not dive alone. Not to mention that one would need to transport said gear to the actual field site. And recall that our particular field site was located rather off the beaten track.
We have been extremely lucky in finding a diving company in Kailua-Kona willing to help us with our mission. The manager-on-duty at Kona Diving Company, Katie, is a trained marine biologist herself. After explaining our project to her, she was more than willing to make us a very nice deal. In the name of science, her colleague Ian, set us up with the much-needed gear, ready to dive Mahana Bay. Thanks Katie ! Thanks Ian ! Thank you, Kona Diving Company !
As said before, the diving gear obviously enabled us to stay under for much longer. We were able to plant a pressure meter in the center of the bay, and left it there for an entire day. Because there is more water on top of you under the crest of a wave, and again less water when the wave passes by, the water pressure builds up and decreases again as waves come and go. By measuring the water pressure, we could get an idea of the number and the height of the waves passing through the bay throughout the day. In the movie below you see my dive buddy, dr. Diana Vasquez, diving down in the center of the bay and anchoring the pressure meter (inside the bag she is holding) in the sediment, next to a small rocky outcrop with a coral colony.
Upon reaching our underwater sampling stations, Diana provides the tools to extract both sediment and pore water. In the video below, she hands me a large PVC tube, with a diameter of ca. 25 cm. This tube will be inserted into the sand and the sand inside dug out. The big tube has small holes at pre-determined intervals. These holes serve like little windows, through which we can again insert our rhizon samplers to suck out the pore water at a particular depth into the sediment. In this way, we obtain a similar chemistry profile as we did with the extracted cylinders of sand described in the former post. It basically serves like an inverted version of those incubation cores. This particular station is located at about four to five meters deep. Behind Diana, you can see large, dark-coloured sand ripples along the bottom. These are ripples that consist largely of olivine and basalt grains and are rather stable. The lighter-coloured sand around those ripples is mostly old volcanic ash and much lighter than either the olivine of the basalt. Although the waves on the sea surface can really be felt at the bottom, and we really needed to hold on to our equipment for fear of it washing away. Those same waves cause the formation of the sand ripples. As the heavier material is hardly moved by the waves, you can clearly see the lighter volcanic ash being moved over large distances along the bottom.