• Why Do We Care About Ocean Alkalinity Enhancement?

Recently, global temperatures have risen by 1.35°C above pre-industrial average levels, highlighting the increasing urgency of tackling climate change. The need to remove excess CO₂ from the atmosphere is undeniable. So, when I first heard about the concept of Ocean Alkalinity Enhancement (OAE), I was immediately intrigued. Could this be a viable solution? Could I contribute to turning this carbon removal concept into a real-world action?

OAE is inspired by the natural process of rock weathering, which releases alkalinity into seawater. This alkalinity acts as a buffer, allowing the ocean to absorb significantly more CO₂ than it normally would. Without this buffering capacity, our planet would face even more extreme heat and climate crises. The fundamental idea behind OAE is simple: more alkalinity in seawater = more CO₂ absorption from the atmosphere.

However, alkalinity is not the same as pH. While pH directly reflects the concentration of hydrogen ions (H⁺) in seawater, alkalinity is a more complex parameter. According to Zeebe and Wolf-Gladrow (2001), alkalinity is defined as:

Total Alkalinity = [HCO₃⁻​] + 2[CO₃²⁻​] + [B(OH)₄⁻​] + [OH⁻] − [H⁺]

This equation shows that alkalinity can be increased in multiple ways—by adding hydroxide (OH⁻), bicarbonate (HCO₃⁻), or carbonate (CO₃²⁻). However, different sources of alkalinity can lead to drastically different environmental impacts.

People often ask me, "Do you think ocean alkalinity enhancement will work?" But the answer isn’t a simple yes or no. The type of alkalinity source, the amount used, the location of application, and the timing—all of these factors influence its effectiveness and environmental consequences. The only way to truly understand OAE’s impact is through real-world experiments.

(On-deck incubations underway during a research cruise aboard the RV Sonne.)

• The Journey to the West

"Would you like to go on a voyage across the Pacific Ocean?" my supervisor asked me one day after I completed an OAE experiment in a coastal region.

At that time, I had been hoping to shift my research from coastal waters to the open ocean to see how different OAE substances would affect plankton communities. However, my original plan to conduct research in the Southern Ocean was cancelled due to budget cuts. Just when I thought I had lost the opportunity, this new voyage came at the perfect time!

"That sounds amazing!" I replied without hesitation.

I was incredibly lucky—another scientist had cancelled their spot just three months before departure, and I was able to take their place. With such short notice, all the logistics had already been finalized. I had to plan my experiments wisely, using only what I could borrow from the scientific team onboard and what I could fit into two pieces of luggage on my flight. To make room for more than 240 sample bottles, I packed fewer clothes and personal items. Thankfully, the research vessel had a small convenience store selling T-shirts, snacks, and soft drinks, and the food/dessert onboard was delicious—so surviving 50 days at sea wasn’t a problem! The journal from Guayaquil, Ecuador to Townsville, Australia turned out to be amazing.

(Sailing across the Pacific Ocean aboard the research vessel Sonne. Photo credit: Ze Chen.)

• The Science at Sea

During the voyage, we tested three popular OAE substances: sodium hydroxide (NaOH) solution, olivine particles, steel slag particles.

We collected seawater samples from the surface of the Pacific Ocean and incubated them for 48 hours. Every time I analysed the samples; it felt like a lottery reveal moment. Would we see a change? A decrease in chlorophyll? No effect at all? Nature, as always, was full of surprises.

Sometimes, I observed a reduction in phytoplankton, but in other cases, the effects vanished. These results reinforced an important lesson: nature is incredibly complex, and simple rules rarely apply in every situation. That’s why we didn’t just test these substances once—we repeated the experiments multiple times, moving westward from Ecuador to Australia across the Equatorial Pacific Ocean.

After months of analysis and writing, our findings became clear. This study highlighted the potential of NaOH as a safer OAE option in the Pacific Ocean but also raised concerns about the unintended effects of using particulate substances like olivine and steel slag.

So, if you were to ask me again, "Will OAE work?" my answer would still be: "It’s too early to say for sure, but we’re working on it." And next time we talk about OAE, we should specify which substance we’re discussing—because their methods and impacts can be drastically different.

(Jiaying Guo (right) and colleague Anne working in the clean tent, known as the “bubble”.)

• Fun Fact: Living on a Floating Time Machine

Since our research vessel was moving westward, we occasionally crossed time zones. This meant that our clocks had to be adjusted every now and then.

Our experiments were mostly conducted at night, right after sunset. Why? Because this way, we could get consistent measurements of phytoplankton photosynthesis while these tiny, hardworking organisms were finally relaxing after a long day of photosynthesis. The sun is the best clock.

 (CTD deployment at sunrise during the RV Sonne expedition. Photo credit: Xuegang Chen.)

• Final Thoughts

This journey across the Pacific was more than just an experiment—it was an adventure, a challenge, and a learning experience. OAE is a promising approach for carbon removal, but its real-world application requires careful consideration. By conducting more experiments, we can move closer to answering the big question: Can OAE be a safe and effective climate solution?

One thing is certain: the ocean still holds many secrets, and we’re just beginning to uncover them.

Check our article for more details 👉 Effects of ocean alkalinity enhancement on plankton in the Equatorial Pacific | Communications Earth & Environment https://rdcu.be/egM0x