Can We Engineer the Oceans to Help Battle Climate Change?

As the planet continues to warm, scientists are developing new tech to enhance the oceans’ natural capacities for carbon sequestration.

Climate change has already started showing its ugly face. Extreme weather events are becoming more common; we are experiencing droughts in places where precipitation used to be abundant; and previously semi-desertic landscapes are flooding, destroying economies, and even taking human lives. Under this scenario, we may reach a point where simply stopping carbon dioxide emissions isn’t enough. We may need to start sequestering carbon from the atmosphere. But if so, how?

One obvious (and weirdly less discussed) option lies beyond our shores — all our shores: the ocean.

Those reading my articles may remember that I’m an ecologist and a paleontologist. As such, I like looking into the past to understand the present and find answers about the future. Throughout Earth’s history, several periods have been marked by significant volcanic activity that contributed to elevated atmospheric carbon dioxide levels. These events triggered severe environmental and climatic changes. And every time, oceans have played a crucial role in moderating these changes by absorbing Carbon dioxide. Want some examples? Here you go:

1. The End-Permian Extinction (around 252 million years ago), often called “The Great Dying,” saw massive volcanic eruptions from the Siberian Traps, a large region of volcanic rock in present-day Siberia. These eruptions released vast quantities of CO2 and methane, leading to significant global warming and ocean acidification. The oceans absorbed some of this CO2, but the rapid change in ocean chemistry led to the extinction of about 90% of all marine species.
2. The End-Triassic Extinction (around 201 million years ago) is associated with the volcanic activity of the Central Atlantic Magmatic Province (CAMP), which involved massive eruptions that coincided with the break-up of the supercontinent Pangaea. These eruptions likely released large amounts of CO2, leading to a warmer climate. The oceans absorbed CO2, but as with the End-Permian, the rate of change led to severe marine extinctions due to increased acidity and deoxygenation.

You can read a comprehensive evaluation of those events in the link below.

What Caused Past Climate Change Events?

And what were the consequences? It’s time to talk fossils.

But how did the Earth manage to cool down after these events? Here’s where oceans really come in.

The Ocean as a Carbon Sequestrator

Oceans can absorb carbon dioxide through physical and biological processes. Physically, carbon dioxide dissolves in the surface water and eventually gets transported to deeper waters and the ocean floor via thermohaline circulation, which can sequester carbon for centuries to millennia. Biologically, phytoplankton consume carbon dioxide during photosynthesis, and when they die, the carbon in their bodies can sink to the bottom of the ocean, a process known as the biological pump.

Unfortunately, the ocean’s capacity to absorb carbon dioxide is not unlimited. It depends on various factors, including temperature, circulation patterns, and biological activity. Worse, when the absorption capacity is overwhelmed, as during massive volcanic events, the excess carbon dioxide may lead to ocean acidification and other ecological impacts (something we already see in many ocean ecosystems).

By studying the fossil record in coordination with studies in modern ecosystems, we can better understand the ocean’s capacity and mechanisms to absorb greenhouse emissions and mitigate climate change’s impacts. Scientists, engineers, and conservationists have been able to adapt some of these into potential interventions that could play a significant part in the climate battles to come. But how feasible are they? Let’s take a look at some of the leading contenders.

1. Seaweed Farming

You know how we talk about planting trees as a great strategy for carbon dioxide sequestration because, during photosynthesis, trees capture this greenhouse gas and release oxygen into the atmosphere? Algae are also photosynthetic organisms capable of sequestering carbon dioxide and releasing oxygen, so the idea is to use them to our advantage. About 70% of Earth’s surface is covered in ocean water, so their productivity and carbon sequestration potential is in fact greater than that of trees.

Macroalgae, red, green, and brown seaweed, can grow several centimeters daily. These photosynthetic organisms absorb carbon dioxide from the ocean to sustain their growth. Upon death, the algae sink deep into the ocean. At this point, the carbon can enter deep-sea food web cycles or get buried in sediments, possibly remaining there for several decades or centuries.

The image below shows the natural process scientists are trying to recreate at scale as food for us humans or livestock. This is a great alternative that’s been discussed for decades now. After all, farming seaweed can be a very sustainable alternative to traditional agriculture. Even more, kelp helps promote the growth of muscles, and may be one of the foods that becomes more popular as the planet warms. It doesn’t hurt that they are delicious (I grew up on the Mediterranean coast) and grow in tandem.

However, farming seaweeds is not necessarily a carbon sequestration solution, as the carbon dioxide returns to the systems instead of being locked away. Indeed, each technology has pros and cons that must be considered carefully.

2. Ocean Iron Fertilization

Phytoplankton, like terrestrial plants, need sunlight and nutrients. And this includes iron. Ocean iron fertilization is a carbon dioxide removal strategy that involves adding iron to ocean waters to stimulate phytoplankton growth. This method was proposed by John Martin in the 1980s, who observed that even a small amount of iron could trigger phytoplankton blooms, which would enhance the ocean’s ability to capture carbon.

Trials conducted from 1993 to 2009 showed that adding iron promotes large blooms, but these experiments needed to be longer to evaluate the long-term effects of carbon sequestration. Additionally, these experiments faced environmental concerns and criticism. But most recently, renewed interest due to the climate crisis has emerged. New research initiatives are trying to address past problems and explore the potential of this technique under current environmental conditions and regulations.

I know what you’re thinking: Aren’t algae blooms bad for us? The answer, as usual in biological sciences, is that it depends. Algae blooms are a natural process that helps keep ocean ecosystems healthy and functional. The problem arises when these blooms promote the growth of bacteria that are toxic to coastal species (i.e. humans themselves). These blooms are caused by human-created waste waters near the coast. If algae grow disproportionally and then die out, they can even deplete the water from oxygen, affecting entire ecosystems.

For this reason, scientists are being cautious before further exploring this technology, as it could have unprecedented damage. See the story below from NOAA (National Oceanic and Atmospheric Administration) for more information.

3. Artificial Upwelling and Downwelling

Naturally, nutrients tend to sink to the bottom of the ocean, rarely returning to the surface where organisms can use them to grow. Artificial upwelling involves mechanically pumping deep, nutrient-rich waters to the surface, promoting algal blooms that absorb atmospheric carbon dioxide. Conversely, artificial downwelling involves pushing carbon-rich surface waters into the deep ocean to lock carbon away. These methods could enhance other marine carbon removal strategies like seaweed farming and ocean iron fertilization.

However, upwelling and downwelling come with their challenges. These include the potential release of sequestered carbon from the deep ocean back into the atmosphere, unknown ecological impacts from altering benthonic communities (those that live at the bottom of the ocean), and high energy requirements that could release more carbon dioxide than what they sequester if not sourced from renewable energy.

4. Enhanced Rock Weathering

Enhanced rock weathering increases the ocean’s alkalinity and the water’s ability to neutralize acids or resist changes that cause acidity, maintaining a stable pH. Improving this capacity can help absorb atmospheric carbon dioxide and mitigate ocean acidification.

Rocks naturally erode over thousands of years. The minerals from these rocks eventually end up in the ocean and help regulate its acidity. Mimicking this natural process, scientists are trying to speed up this process by adding alkaline minerals like calcium hydroxide to seawater. The goal is to enhance the ocean’s ability to absorb carbon dioxide from the atmosphere.

Recent tests in places like Apalachicola Bay in Florida and Halifax Harbor in Canada have shown promising results. However, the process has raised concerns about the ecological impact of altering ocean chemistry, the environmental cost of mining and processing minerals, and the overall feasibility of expanding the approach.

5. Direct Ocean Capture

Direct ocean capture involves extracting carbon dioxide directly from seawater using an electrochemical process. This methodology involves pushing seawater through a membrane that facilitates a chemical reaction with a solution like sodium hydroxide, effectively removing dissolved carbon dioxide. The reaction also increases the water’s pH, increasing its capacity to absorb more atmospheric carbon dioxide.

However, this technology faces significant challenges, including high operational costs. There are also many environmental concerns, especially when it comes to the potential impact on marine life.

Making Waves

While all these ideas are promising, they also have several problems that must be addressed, and there is still much to be learned. Additionally, any large-scale intervention must be managed cautiously to prevent unintended repercussions that may disrupt marine ecosystems (always remember what happens when we engineer ecosystems like we did with the wolves of Yellowstone).

When we explore these technologies in greater depth, it becomes apparent that the ocean has the potential to be more than just a quiet hero in our climate story. We could maintain the ocean’s role as a reliable, steadfast ally in our battle against climate change. However, we need to do it cautiously and rely on the input of every expert involved. Because ultimately, we don’t want the solution to be a bigger problem than the problem itself.