Tales from the Green Sands (4)


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.


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.


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.



Tales from the Green Sands

green sand at mahana

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 ?


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.

Sour seas stump coral growth

As it was predicted in various models and observed in many laboratory tests, so it has been demonstrated in the real world. Mimicking the increase in acidity of the world’s oceans in response to the ever increasing CO2 in the atmosphere, marine scientists from Australia and the US have performed a field experiment in circular reefs along the Great Barrier Reef, in which they increased the pH of the seawater to pre-industrial levels. As a result, the corals in those “pre-industrial” reefs were reported to grow some 7% faster than in seawater with a pH that is normal nowadays.

Mussels muscle back…?

Mussels can adapt to their acidifying ocean by changing the composition of their hard parts. In an ever more corrosive environment, mussels changed the mineralogical makeup of their calcareous shells. Shells normally consist of calcium carbonate which is ordered in a crystalline fashion, with strong and resistant properties. However, under ocean acidification conditions, with a lower pH, the calcium carbonate of these experimental mussel shells consisted of much more amorphous calcium carbonate, leaving the shells more vulnerable to predation by crabs and seagulls and the crushing forces of waves. This is a very strong example of secondary effects of ocean acidification, where organisms suffer from the consequences of climate change in an almost cryptic way. The danger sits in the fact that these changes on an organism level might go by unnoticed, until it is too late.



Global Warming’s Evil Twin

Loligo bubbles

By now, everyone has heard of global warming, or climate change in one way or another. The International Panel on Climate Change (IPCC) has even established that it is caused by humanity’s continuous emissions of fossil fuel-derived carbon dioxide. Global warming would cause more intense and more frequent stormy weather and of course the rising of the global sea level, by melting the polar ice caps.

Another effect of anthropogenic or “man-made” climate change is Ocean Acidification (OA). Both historical and ongoing carbon dioxide (CO2) emissions flow from our smokestacks to the atmosphere. As the atmosphere constantly balances itself with the world’s oceans, any excess of CO2 in the air will quickly (in a matter of one to two years) end up in the surface seawater. If it would not be for our oceans sucking up a LOT of CO2, we would be in real trouble. However, because the oceans store such enormous amounts of CO2, the seawater is slowly acidifying.

Marine organisms have adapted and evolved over millions of years and are dependent on the chemistry of the seawater being within certain bounds. It is difficult for them to respond to rapid changes in its chemistry, such as is happening nowadays. Mainly organisms that produce calcium carbonate, those being calcareous body parts, are threatened by Ocean Acidification (OA). Shellfish and corals are among the best known that suffer from OA, but there are many other organisms that are under threat in an ocean that turns acidic ever more rapidly.

As our seas are souring up, Global Warming’s Evil Twin is not only threatening all sorts of marine organisms, it also decreases the ocean’s capacity to take up (more) atmospheric CO2, so effectively diminishing our planet’s self-regulating carbon-storage.