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.

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