Should We Store CO2 in Our Oceans?

Some ocean scientists are advocating for storing captured CO2 emissions in the deep ocean. Nope, this ain’t a scene out of a Matt Damon movie, it’s legit and not so ‘far out’ as you would imagine. Now, I’m all about those ‘natural’ vibes and never shy away from an enviro-fuelled verbal bit of jousting. I wear my green emoji heart on my sleeve and bleed my creeds colours. Well, at least that’s what my bamboo toothbrush reassures me of at night whilst whale noises play in the background. 

A couple weeks ago, I was taking the edge off my ‘Anthropocene’ induced depression down at my local when I got into a debate with a guy who was, no joke, referred to as ‘PPC’. Why I entertained a guy who was nicknamed after a cement company, I don’t know. It was probably something in my DNA, just screaming inside for me to throat punch the guy. Anyway, you get the picture I didn’t think much of PPC and his discourse. But through his ignorance and sarcasm, he inadvertently acted as the proverbial carrot in me writing this piece by shouting out “well, umm, why don’t you take your CO2’s and 3’s and shove them down your ocean hole”. Yes, he really said that. 

Featured image: Blair Austin © Shot Bru

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But, PPC got me thinking. Can we actually do that? Can we use the immense pressure of the depths to store carbon? What are the potential impacts it could have on the marine environment? 

The reality is, even if we somehow managed to magically stop emitting CO2 today, a tremendous amount in the atmosphere will still impact global processes and contribute to climate change for centuries to come. What does this mean? Well,  in addition to decarbonization, the world needs to pull excess CO2 from the atmosphere and do something with it. But what? That’s the question! Enter carbon capture and storage.

Our blue-green-brown world has such mechanisms set in place to store CO2 emissions, natural carbon sinks, such as plants, soil and marine algae. The oceans are one of the largest sinks on the planet, absorbing roughly 25% of the atmospheric CO2 we emit. Every year. But natures mechanics operate on a much slower clock, taking their sweet-ass time. As a result, mother nature can’t keep up with our kinds emission levels. Like that professor at varsity you never bothered to listen to, I point you to the facts: global atmospheric CO2 concentration in 1960 was 317 part per million (ppm), by 1990 was 354 ppm, by 2010 it was 390 ppm, and today it is 408 ppm.

 

Atmospheric CO2 concentrations are at their highest levels ever. Source: NOAA Climate.gov

It seems counter-intuitive: the oceans are turning more acidic due to too much CO2, yet here we come wanting to put more CO2 in there?  To be clear, this is not a solution to climate change, but perhaps a way to avoid the worst of it? Maybe?

Traditional storage techniques trap CO2, storing it as a liquid or gas deep underground in specific geological features and require a non-porous plug to prevent release. With ocean storage of CO2, the gas is intentionally injected into the deep ocean and is either allowed to diffuse or is trapped in a specific location.

Three general methods could be used to directly inject carbon dioxide into the ocean for storage. First, a pipe that runs from the shore to the ocean depths. This pipe would receive a stream of carbon dioxide from a capture or some other storage facility on the coast, directing it offshore for long-term storage. 

Then there’s the dispersal by ship method, where CO2 stored on board would be ejected at great depths using a long hose or pipe towed behind the vessel, bringing about the rapid diffusion of the CO2 into the surrounding seawater. The third method would be to use a stationary vessel or platform to send CO2 on a permanent vacation to the ocean floor.

The way in which CO2 is stored in the ocean depends on its phase state and the depth at which it is injected. Remember, pressure increases with depth, and we can use this fact to our advantage when it comes to ocean carbon storage.

At depths deeper than 3,000 meters the weight of the water column compresses the liquid CO2 making it denser than seawater, sinking slowly to the seafloor. As a solid, it will also sink but will dissolve as it descends in the water column. Once the carbon dioxide sinks to the seafloor it forms an underwater pool at the bottom of the ocean, trapped in place by its own density. If carbon dioxide had feelings, I would be like: “Damn, that’s cold”. Here I use cold in a metaphorical sense, although it must be cold as hell down there!!

 

Brine Lakes at the bottom of the sea. This is similar to what CO2 lakes would look like.

By utilizing the depths we are benefiting from time and space. Currently, 70% of  CO2 emissions will eventually wind up in the ocean. Prior to the Industrial Revolution, the CO2 exchange rate between the ocean and the atmosphere was pretty well balanced. But ever since we began emitting CO2 the ocean has been trying to catch-up with the atmosphere and failing.

The ocean has to isolate CO2 from the atmosphere for a long time before it can be viewed as effective. Ocean currents carry surface waters to the deep and vice versa. Thus a mixing effect takes place and is more pronounced near the surface, generally decreasing with depth. In the deepest parts, it can take between 300 to 1,000 years for seawater to go through a complete turnover. So where to store the carbon, deep, deeper is better. 

Another perceived advantage of ocean storage is capacity and availability. If our current annual emissions stay constant, we have about 25 to 50 years left before our toes are hanging off a cliff. On land, we do not have enough capacity to continue with the old ‘business as usual’ model. Ocean storage of CO2 could buy us more time and help us avoid peak concentrations of atmospheric CO2, perhaps avoiding the worst of climate change.

So is the lemon worth the press? The ocean has historically been slightly basic, with an average pH of 8.2. Due to the CO2 emissions over the last 200 odd years, the average pH has dropped 0.1 units. Imagine I told this to PPC, he would laugh at me. But again, his ignorance would be his undoing. The pH-scale is logarithmic, so this seemingly tiny change is actually a 30% decrease. Yeah, that surprised me too. If we were to store C02 in the ocean, it would almost certainly lead to a lower pH, but where in the water column and by how much.

The deep ocean is not well understood, 80% of the ocean floor remains unmapped, unobserved and unexplored. What deep-sea organisms and marine ecosystems are down there waiting to be discovered is anyone’s guess. For all we know, Tupac, Elvis and JFK could be playing backgammon down there. Probably not, although that shit would be so sick!

The ocean is going to absorb the majority of our CO2 emissions over the coming centuries anyways, but in the process, the atmosphere and ocean surface waters will be subjected to unprecedented warming and acidification. On the other hand, vast quantities of CO2 could be isolated in the deep sea, driving down atmospheric and ocean surface concentrations in the short term. This could help stabilise the climate. The cost, however, would be untold damage to sensitive deep-sea ecosystems that we know very little about. It’s an uncomfortable choice, but it’s one that we may have to seriously consider as our carbon budget goes kamikaze!