Antacids for the Ocean

Have you ever had a stomach ache? Did you take a Tums tablet to quiet that grumbling?

Tums neutralize the acid in your stomach (which is hydrochloric acid). Tums are made up of a mineral called calcium carbonate, found in things like chalk, limestone, and marble!

Calcium carbonate can also neutralize other acids – like carbonic acid – which forms when carbon dioxide (CO2) mixes with rainwater or seawater. Since the carbon dioxide in the atmosphere has been rapidly increasing from fossil fuel burning, there is a lot of CO2 gas around to interact with seawater – making lots of carbonic acid in the ocean.

So, can we give the ocean some Tums?

That is the question I am pursuing in my research in Will Berelson’s Lab. Hi, my name is Rucha Wani and I’m a rising 3rd year PhD student in the Ocean Sciences Program at USC.

The Earth’s climate system already uses limestone and other rocks like it as a natural antacid to draw down CO2 in a process called “weathering”. Limestone is an abundant rock in the Earth’s crust – so theoretically there is tons of limestone around to be dumped into the ocean.

But have you ever seen a Tums dissolve in water?  If we dumped a bunch of Tums into the ocean it could take a really long time to dissolve. Large scale weathering can take thousands of years to capture all the carbon dioxide. Humans only live a couple decades, so we need a way to speed up natural weathering.

Accelerated Weathering of Limestone (AWL) is a carbon capture technology that rapidly dissolves limestone with CO2 in seawater. The company Calcarea, Inc. has built a reactor right here at USC to test this technology. Their reactor functions like your stomach! The reactor is filled with limestone, seawater, and CO2 rich gas. After the reaction is complete the gaseous CO2 is converted to a dissolved carbon compound called bicarbonate. Turns out bicarbonate is already the most abundant form of carbon in the ocean! So, the product of AWL – bicarbonate rich seawater – is meant to go back into the ocean for longer term storage. In theory, this all sounds very promising for the fate of the climate. However, we still need to know how this reactor effluent will impact the ocean. 

This summer, as a Wrigley Fellow, I am taking small batches of reactor effluent and adding them into seawater on Catalina Island. In an attempt to recreate the ocean ecosystem at a small scale, we collect seawater in 6L bottles and add 10-40 mL of the reactor effluent – this is to mimic a cargo ship dumping effluent into the vast ocean. We then monitor the various states of carbon (solid, liquid, and gas) to track how carbon in the bicarbonate rich effluent may transform in the seawater. The carbon could precipitate and reform calcium carbonate (solid) but this reaction produces more gas CO2, the dissolved carbon could also degas back into carbon dioxide (gas), or it could remain dissolved as bicarbonate (liquid) which is ideal for long term storage.

However, the ocean isn’t just dictated by the laws of chemistry and physics – it’s full of life. So we also monitor changes in light, temperature, nutrients, oxygen, and microbial community composition to understand how the base of the ocean-food web may be impacted by limestone addition.   

Conducting multiple experiments and hauling many liters of seawater up the massive Wrigley hill is by no means an easy feat (having a golf cart really helped)! Luckily, I was assisted by a rockstar undergraduate researcher – Esther Lim! I’ve had the privilege to mentor Esther through the Zinsmeyer Summer Research Program. She is a USC Dornsife undergraduate student in the Environmental Studies program. Not only is it great to have an extra set of hands, but also to have a student that asks very intuitive questions about the research and is dedicated to her work.

Guiding Esther has helped me grow as a teacher and science communicator. By being a mentor and a Wrigley Fellow, I have been able to share my work with many people – visitors and students on the island. It’s been exciting to work with young kids exploring their relationship with nature.

The island life has been truly magical – we’ve successfully completed many experiments but also enjoyed existing in the sun and waves. Apart from short commutes, and amazing coworkers, my days have been filled with morning yoga, chasing quails, roasting marshmallows, and sunset snorkels!

I am grateful for the support provided by the Wrigley Institute – the Fellows program and the Faculty Innovation Award; this opportunity has been monumental to my research progress. With the uncertainty of future climate change brewing anxiety within us, it is motivating to create work that brings us closer to finding solutions.  

Rucha Wani is supported by the USC Dornsife Wrigley Institute Graduate Fellowship.