The Ocean’s Unseen Carbon Engine

Michael Thompson

Welcome to the show -- Emily, I want to start with a number that should make people sit up: Australia’s ocean system is estimated to sequester roughly 175 to 220 million tonnes of CO2 a year in its Exclusive Economic Zone. That is not a rounding error. That is climate work on a national scale, and most of it is treated like invisible background flux.

Emily Carter

The 175 to 220 million tonnes is the bit that sticks for me, because if you said a forest was taking up that much carbon, there’d be policy papers, branding, probably a minister in a hard hat. But because it’s the sea, we sort of shrug and go, well... currents happened.

Michael Thompson

Exactly. And the ocean is already the planet’s largest carbon sink. One source here puts its capture rate at about 30% of annual carbon emissions. So the provocation is simple: if a living system is already storing carbon at that scale, why do our accounting systems behave as if it has no managed climate value?

Emily Carter

And the accounting mismatch is VERY specific. In the Australia example, only coastal blue carbon -- about 26 to 29 million tonnes of CO2 per year -- is counted in national accounts. Open-ocean sequestration, estimated around 11 to 29 million tonnes a year in that same material, is ignored entirely. So we’re counting the neat, shoreline-adjacent bit and waving away the messy offshore bit because it’s harder to measure.

Michael Thompson

That’s the heart of it. In ocean science, we’ve long treated these processes as fluxes -- real, important, but diffuse. And from a governance standpoint, diffuse often means politically invisible. The Ocean Dividend framing says, no, this is not just background chemistry. It may be an environmental and economic asset that has been left unmeasured, uncredited, and unmanaged.

Emily Carter

I’ll admit, Michael, this is where I flinch a little. The phrase “asset” makes me nervous. The ocean is not a spreadsheet cell. The paper itself says, very pointedly, “The ocean is not a resource to be extracted. It is a living system to be activated.” And I quite like that distinction because history is full of people calling nature an asset right before they wreck it.

Michael Thompson

I don’t disagree with the warning. But I think “asset” can be empowering if it forces governments to value what they currently ignore. If Australia’s EEZ is already doing carbon work equal to something like 30 to 40% of national emissions -- again, from the source material -- then refusing to count that has consequences too. Neglect is also a choice.

Emily Carter

Right, but the phrase you used there -- 30 to 40% of national emissions -- that’s exactly why we’ve got to be careful. Because once you put that kind of number on the table, investors, carbon markets, ministries, everyone piles in. And then the question becomes: are we restoring an ecosystem, or are we inventing a new excuse to financially engineer the sea?

Michael Thompson

Fair push. And this is why the debate gets interesting fast. The bottleneck, according to the Ocean Nourishment and Ocean Dividend material, is not primarily whether the ocean matters. It’s whether you can build an approved MRV methodology -- measurement, reporting, and verification -- that proves what happened, how much carbon was removed, how long it stayed there, and whether the intervention was environmentally safe.

Emily Carter

So let me try to say that back. The scandal is not that we forgot the ocean stores carbon. We know that. The scandal is that we’ve built climate accounting systems that only reward what can be boxed, audited, and sold. And the open ocean is biologically doing the job already, but without a credible paper trail, it doesn’t count.

Michael Thompson

That is very well put. In climate policy, if it can’t be measured credibly, it tends not to exist. Which is maddening when you’re talking about the biggest carbon sink on Earth.

Emily Carter

So here’s the proposed fix, and it is... slightly audacious. Ocean Nourishment, and the related Ocean Dividend concept, want targeted nutrient balancing in low-nutrient, low-chlorophyll zones -- LNLC zones -- to stimulate phytoplankton. Basically, give parts of the ocean a carefully calibrated vitamin shot, not a chaotic dump, so you boost productivity and strengthen what’s called the biological carbon pump.

Michael Thompson

And that mechanism matters. More phytoplankton means more primary production. Some of that carbon-rich organic matter then moves down through the water column, and the goal is to increase export to more durable storage, including verified seabed flux. Their proprietary biostimulant is called PhytoPlus, and the proposed deployments are from ships or offshore platforms, with the possibility of integrating with renewable energy.

Emily Carter

PhytoPlus is a very polished name, I have to say. But the detail I care about is LNLC zones, because that tells you they’re not talking about just chucking nutrients everywhere. These are low-nutrient, low-chlorophyll waters where the argument is that carefully targeted micronutrients can produce additional productivity with, they say, minimal ecological disturbance.

Michael Thompson

And they’re trying to operationalize that with ODAMS -- an AI-governed platform for site selection, nutrient delivery, bloom modelling, current modelling, monitoring, and regulatory reporting. Biology, physics, engineering, AI control, MRV -- it’s a whole stack. The pilot they describe, AUSPICE-1, is offshore from Coffs Harbour in an ocean gyre, intended as a minimal viable product to prove the full pathway: uplift productivity, measure it reliably, satisfy regulatory thresholds, and generate creditable carbon value.

Emily Carter

AUSPICE-1 off Coffs Harbour is one of those details that makes this feel less like a thought experiment and more like a test case. But this is where I want to slow us down. Because the source says the primary competitive advantage is not the nutrient idea itself. It’s building the MRV methodology. That is a huge tell. The real race is not just “can you grow phytoplankton?” It’s “can you prove additional, durable, environmentally safe carbon removal?”

Michael Thompson

Yes. And that word “additional” is doing a lot of work. You need to show carbon removal beyond what would have happened without the intervention. Then “measurable” -- a full chain from productivity uplift to export flux. Then “durable” -- they talk about export below the permanent thermocline and verification against seabed sediment burial rates. And then, crucially, “environmentally safe” and “compliant.” If any one of those fails, the credit claim gets shaky very quickly.

Emily Carter

Which brings us to the comparison with ocean alkalinity enhancement -- OAE -- and this is where my British marine-biologist caution siren starts blaring. OAE aims to increase seawater alkalinity so the surface ocean can absorb more CO2. There are ground mineral approaches, electrochemical approaches, even photochemical ones. On paper, elegant. In practice, the source material is full of warnings.

Michael Thompson

Including the International Maritime Organization saying marine geoengineering technologies, OAE included, have the potential for deleterious effects that are widespread, long-lasting, or severe. That’s a strong phrase. And the concerns aren’t abstract: temporarily high pH can be dangerous to marine life, impacts on biodiversity and food chains are unpredictable, and some pathways require massive mineral extraction or energy-intensive processing.

Emily Carter

The “hundreds of years” point is the one I can’t shake. In the source, CO2-depleted water may only absorb atmospheric CO2 when it rises back to the surface and meets air, which can take hundreds of years. Hundreds. So when a company says, oh yes, carbon credit now, long-term certainty later... that gap matters.

Michael Thompson

And some projects are already commercially ambitious. Equatic, for example, has been testing in Singapore and Los Angeles and wants tens of millions of dollars in revenue from offsets. Boeing has signed a pre-purchase agreement in that ecosystem. Ebb Carbon has sold to Stripe’s carbon market. So the market appetite is ahead of full ecological certainty in some cases.

Emily Carter

That’s the tension, isn’t it? Money is flowing into marine carbon removal because climate pressure is real, and shipping rules from the IMO are tightening. But if the revenue story outruns the ecology story, you end up doing old extractive behaviour in a very modern carbon-removal accent.

Michael Thompson

Which is why the Ocean Dividend people are trying to distinguish themselves from OAE by emphasizing reversibility, ecological risk assessment, BBNJ-compliant environmental impact assessment, sovereign EEZ governance, and an auditable MRV chain. They’re basically saying: don’t just change chemistry and hope. Show the baseline, show the uplift, show the export, show the safety.

Emily Carter

And maybe show humility, too. Because phytoplankton are not widgets. Whales, incidentally, are part of this story as well. The WhaleX work in the XPRIZE Carbon Removal space is built on the idea that whale waste naturally fertilizes the ocean, supporting phytoplankton that may capture something like 40% of CO2 produced, according to that source. Their experiments in mesocosms suggest 300 litres of artificial “ocean nourishment” could sequester about one tonne of CO2. Fascinating -- but still, experiment first, scale later.

Michael Thompson

That’s the right posture. Learn from nature, but don’t romanticize intervention. I think the cleanest version of the question is this: can we treat the ocean as a climate asset only when we can prove the intervention is restoring ecosystem function rather than exploiting it? If the proof is robust, this could be important. If the proof is flimsy, the ocean becomes just another place where we hid the ledger.

Emily Carter

And that, I think, is the line I’d leave people with. Not “is ocean carbon removal good or bad?” Too blunt. The real test is whether “verified, additional, durable, environmentally safe” is a scientific standard... or just very expensive poetry. See you next time.