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Tales from the Green Sands (8)

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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 !

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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 !

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Tales from the Green Sands (7)

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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 !

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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.

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Tales from the Green Sands (6)

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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.

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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.

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Tales from the Green Sands (5)

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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 !

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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.

 

 

Tales from the Green Sands (4)

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After a couple of intense first days of sampling Mahana bay, we needed to hold our horses somewhat and allow some time to process the material we had gathered. As you can see at the top of this post, Phil is very busy analysing samples in our holiday home laboratory. It is funny, starting so enthusiastically, one always forgets these simple truths of fieldwork life: you have to empty the bottles you use, lest you can take more samples. Until that point, there is no going on.

One of the things we needed to find out, is what compounds are released by the olivine. Recall that the olivine on Mahana / Papakolea beach is thought to take up CO2 while it (slowly) dissolves in the seawater. The olivine itself is what mineralogists would call quite “pure”. That is, it is made up of only a few different elements, and apart from its main constituents, it does not contain many extra elements, sometimes referred to as “contaminations”. Typical (forsteritic) olivine contains three main compounds: mostly magnesium (Mg), some iron (Fe) and lots of silicate (SiO4). “Normal” sand, which is found on your “average” beach is made up of mainly silicium dioxide (SiO2). There are some “extra” metals, that occur in the olivine mineral, but only in very low concentrations. Some of these metals normally set off a lot of alarm bells, like chromium and nickel, but luckily these occur only in very low concentrations. Nonetheless, when olivine dissolves, all those mentioned compounds, including the metals, are supposed to be released from its solid form and go into solution. At the same time, the dissolving olivine should provoke the uptake of CO2 by the seawater. Exactly this is one of the reasons why we want to measure the concentration of dissolved compounds and CO2 in the seawater.

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In the picture above, you see me (Francesc Montserrat) preparing to take samples of the seawater we collected from both the surface and along the bottom of the bay, while snorkelling. These samples will be preserved and later analysed for dissolved CO2.

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As the beach sand contains a lot of olivine, the real chemistry is of course happening in the water that fills the space between the sand grains, aptly called the pore water. Because pore water is not as diluted as the constantly moving seawater on top of the sediment, it typically has higher concentrations of the dissolved compounds we were after. One way to analyse the dissolved compounds in pore water, is extract a column of sand from its original place, take it to the laboratory and and suck out the water in between the sand. In the picture below, you can see a PVC cylinder, containing sand from Mahana beach. In the wall of this cylinder, we drilled some holes at fixed intervals. In the holes, we stuck little flexible tubes, which are coated with a sort of filter. These filters, called “rhizon samplers”, are connected with little tubes to syringes with which we suck out the pore water. The filter coating on the rhizon samplers filters the pore water we are sampling, and so provides a snapshot of the chemistry at a particular depth in the sediment.

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Tales from the Green Sands (3)

On our first real sampling trip, we walked along the Papakolea coast, to Mahana “Greensand” Beach… As you can see, the coast is rugged, and the low vegetation belies strong winds during most of the year. The first time we walked in, we brought only the most necessary field work equipment, including goggles, a snorkel and a pair of fins. The wide-open spaces of this coast are beautiful and wild, with the typical moon-like landscapes of a volcanic desert, while the waves of the mighty Pacific pound the shore.

The walk in, from the last car park to the beach, took about an hour…a bit more on the way back, when we were literally loaded with water and sediment samples from Greensand Beach.

Tales from the Green Sands (2)

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Mahana beach is located at the southern tip of Hawai’i. It is a natural coastal system with an olivine beach, constantly being reworked by waves rolling in from the vast Pacific Ocean. Mahana beach was formed when lava poured from the volcanoes that make up Big Island, into the Pacific, and cooled off in rains of fine cinders. These cinders contained high concentrations of very pure forsteritic olivine crystals, like those crystals in the lava shown in the header picture for this post. The accumulating cinders formed a coastal hill, which eroded into the ocean, forming a green olivine beach.

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Because this beach lies in the tropical Pacific it has several advantages for studying its chemistry and biology. First of all, seawater temperatures are relatively high, some 26-27 degrees Celsius, so all chemical reactions are naturally faster. Second, because of its location in the tropics, we expect not only to find your “normal” marine coastal biota, like seaweeds, shellfish and shrimps, but also some more exotic and interesting groups like corals. The interesting part is here is that corals make their calcium skeleton from the seawater. Corals like it when their seawater is less acidic and more alkaline, so an entire beach of dissolving olivine spells good news for them. However, olivine also contains metals, which leach out into the seawater during the dissolution process.

Are the waters in this bay measurably affected by the presence of an olivine beach ? Is the seawater indeed more alkaline ? What is the fate of the dissolving metals from the olivine ? Do they accumulate in the food web ? How do the different marine organisms fare in these waters ? These are some of the questions we hope to answer, and hopefully use this information for when -in a possible future- artificial olivine beaches may be constructed to protect coasts from rising sea levels, while they slowly absorb the CO2 that is the cause of that same sea level rise

Tales from the Green Sands

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Our uncontrollable hunger for energy has led to unprecedented emissions of carbon dioxide. More, higher, faster, we exhaust, with no end in sight. Recently, the scientific community has reached an equally unprecedented consensus, stating that to avert dangerous climate change, mankind needs to take back its emissions from both atmosphere and ocean.

As long as there have been carbon dioxide, water and rocks, mineral weathering has been the geological control button on Earth’s climate. Mineral weathering constitutes the dissolution of minerals (rocks) by water and dissolved CO2, better known from your soda pop drinks as carbonic acid. One of the fastest dissolving silicate minerals is olivine. Olivine has been shown to consume protons in solution, which pulls down the acidity and effectively draws more CO2 into the solution in which it is dissolving. This is exactly the desired effect of depositing olivine in seawater: the consumption of protons would counteract ocean acidification, while sea-air equilibration processes draw more CO2 into the seawater, which in turn can be neutralised by the olivine. To observe how this would work in reality, is what we had in mind when we planned this field campaign. Together with Dr. Phil Renforth from Cardiff University (UK), we travelled to Hawai’i to investigate enhanced olivine weathering in a marine environment and the effect it has on the surrounding ecosystem.

After a series of flights, crossing the Atlantic, the US mainland and half of the Pacific Ocean, we arrived in Hilo, the capital of Big Island. Mauna Kea and Mauna Loa, the two enormous volcanoes that essentially make up Hawai’i (as Big Island is officially called), separate the island into roughly two parts: a cloudy, rainy side with lush tropical vegetation, and a dry and sunny side, reminiscent of the southern Mediterranean. Hilo is an old colonial town with a quaint atmosphere, located on the wet, eastern side of the island. Here, all the moisture evaporated from the surface ocean and carried by the north-easterly tradewinds, accumulates against the flanks of the volcanoes, draping the capital in clouds. Although the sun can be brutal on tropical Hawai’i, exactly these clouds make Hilo’s micro-climate very pleasant.

In Hilo, our first stop would be the University of Hawai’i at Hilo. Dr. Tracey Wiegner, a faculty member of the Department of Marine Science, had graciously offered local assistance for our field campaign. She provided some equipment that was simply to bulky to bring from Europe, and offered us space in the laboratory, should we need it. Doing research on ocean alkalinity himself, Also at the Marine Science department, Dr. Steven Colbert was able to provide us with much-needed knowledge on the Hawaiian coastal system and its geochemistry. After exchanging ideas and loading our car with borrowed fieldwork equipment, we set course for Naalehu, our home for the weeks to come.

Naalehu is a small community, located a convenient 15 minute-drive from Greensand Beach, known in Hawaiian as Mahana beach. That is, where the normal road to Mahana ends and one needs to walk for about an hour along the coast to reach the olivine beach. That, or get a shuttle service in an old-but-trusty 4WD car, provided by members of five local Hawaiian families. As they have been fishing the waters off this southern tip of Hawai’i for several generations, they have intimate knowledge of the coastal region. They know this rugged, wind-swept coast like the back of their hands, long before any tourist had ever heard of the mysterious Green Sands Beach.

On our first day in, we met up with prof. dr. Jens Hartmann, of the University of Hamburg, who had been doing his own field campaign in the lava tubes around the volcano. Like us, prof. Hartmann is interested in enhanced weathering and its use in CO2 sequestration and together we set off to do a first reconnaissance into our field site along the wild and beautiful Papakolea coast.

What is going on at Green Beach ?

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Yes ! It is almost that day that we fly to Hawai’i. We, that is Dr. Phil Renforth from Cardiff University and myself, Dr. Francesc Montserrat of the Netherlands Institute for Sea Research. Why is it interesting for you to read about two researchers going to the Big Island of that famous archipelago in the central Pacific Ocean, you ask ? Obviously, we are not going there to sunbathe…no, we are going there to do a three-week field research on a natural olivine beach. Papakolea Beach on the southern tip of Big Island is a beach that consists mainly of olivine grains. We are very much interested in the incredible capacity of this green mineral to capture CO2 from both atmosphere and seawater and potentially counteract climate change effects, such as ocean acidification. Before ever coming close to trying this out in real life we wanted to investigate how this works in a natural setting, where olivine has been weathering for hundreds, no thousands of years. We are going to Papakolea Beach to try and measure the effect this dissolving mineral has on both the chemistry of the ocean and the state of the surrounding ecosystem. Please keep following this blog for the coming weeks, as we will try and update it regularly.