Whose CO₂ is it Anyway? Ocean Fizz or Smokestack Blame

Picture this: it’s a hot day, and you grab a soda can that’s been in the sun. You crack it open—psssht—and CO₂ fizzes out, tickling your nose, maybe spraying your shirt if you’re slow. It’s a tiny chaos, a burst you can’t control. Now imagine that fizz across the ocean’s sun-warmed surface, covering 71% of Earth, bubbling CO₂ into the air we breathe. Wild, right? A bit mad. I reckon it's a missing piece of the climate puzzle.

The IPCC pins it all on smokestacks—11 billion tonnes of carbon a year from fossil fuels. Even skeptics like the CO₂ Coalition echo this, leaning on guys like Ferdinand Engelbeen who do their maths by the consensus numbers on this issue of CO₂ origins.

But they might have it all back to front and be leaving out ocean chemistry and biology. In fact, I’m convinced they are.

The Keeling Curve—CO₂’s climb from 280 to 420 ppm—carries their blame. But what if the ocean’s fizzing more than they think? Their rock-solid evidence could be mostly myth.

I’ve been digging into this with Ivan Kennedy, my second guest for the webinar series ‘Towards a New Theory of Climate Resilience’. That was back in February and I’m still to process the audio from this discussion.

Instead, my focus has been on writing technical papers. Ivan and I are working through a hypothesis that could perhaps flip the climate script.

Engelbeen claims fossil fuels’ isotopic fingerprint—light ¹²C (isotope C12) dragging the air’s ¹³C-to-¹²C ratio from -6.5‰ (per mille)* to -8.5‰ since 1850—is proof of coal and oil’s guilt. Ocean CO₂, averaging 0‰ from deep waters, should nudge it up—not down. Case closed.

Except. That ¹²C/¹³C tale’s shakier than they admit. What if the ocean’s surface, warmed by the sun, fizzes CO₂ richer in ¹²C than the deep oceans 0‰?

Calcification—limestone forming in seawater—might churn out CO₂ at -10‰ or lower, diluting that delta 13 signal just like fossil fuels. It’s not the deep ocean I’m on about—it’s the top 65 meters, the mixed layer, where sunlight and warmth cause biological action. So much action that it has built the biosphere’s great carbonate deposits, even the White Cliffs of Dover.

Ivan and I talked some of this over—Great Barrier Reef, North Pacific—during our webinar (soon my first podcast—thanks for waiting!). Calcification’s no sleepy trick; it’s a biological buzzsaw—corals, algae, phytoplankton like coccolithophores churning limestone. In summer blooms, they might pump out tonnes of CO₂, light on ¹³C. Our Thermal Acid Calcification (TAC) hypothesis says nature’s pitching in more than you might think.

Ponder this next time you sip a soda: could the ocean be bubbling up a CO₂ twist?

TAC’s perhaps a second plank in my New Theory of Climate Resilience. Subscribe for irregular updates, and to know about next webinars.

In churn and current, me with that silver scuba air tank at the surface above the mixing layer at the Great Barrier Reef. And the top/feature image is of my scuba buddies diving off the edge from Myrmidon Reef that is already at the edge, photographed by underwater photographer, scuba buddy and boat skipper Jenn Mayes.

This is Part 2 of How Climate Works. Part 1 was with Bill Kininmonth. I never properly processed the audio from Part 1, and I accepted the AI summary of our meeting click here.

Postscript

From a paper by Werner Berner et al. 1980. In Radiocarbon, Vol 22, No.2. pgs. 227-235. Suggesting higher carbon dioxide levels just a few thousand years ago.

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When we say deep ocean carbon is 0‰ (per mille), we're talking about its carbon isotope ratio, specifically the δ¹³C value. This is a measure of how much carbon-13 (¹³C) is present relative to carbon-12 (¹²C), compared to a standard reference.

In this case, 0‰ doesn’t mean there’s no carbon-13 in the deep ocean—it means the ratio of ¹³C to ¹²C in deep ocean dissolved inorganic carbon (DIC) is about the same as the standard reference, which is usually the Vienna Pee Dee Belemnite (VPDB). A δ¹³C of 0‰ indicates no enrichment or depletion of ¹³C relative to that standard.

Now, why is deep ocean carbon around 0‰? It’s because the deep ocean is a massive, well-mixed reservoir of carbon that’s been cycled through various processes over long timescales. Surface ocean carbon starts with a δ¹³C of about +1 to +2‰ due to photosynthesis, where phytoplankton preferentially take up ¹²C, leaving the surface water slightly enriched in ¹³C. But as organic matter sinks and decays, it releases carbon back into the deep ocean. This process, along with the mixing of water masses, balances out the isotopic signature. The deep ocean ends up with a δ¹³C close to 0‰ because it reflects a long-term average of all these inputs—biological, physical, and chemical—without much net fractionation.

In terms of carbon-13, this means the deep ocean has a pretty stable and "neutral" amount of ¹³C compared to the global carbon cycle. It’s not heavily skewed like surface waters or organic matter (which can be -20‰ or lower due to that photosynthetic preference for ¹²C). So, a δ¹³C of 0‰ tells us the deep ocean is kind of a baseline, a big pool where carbon isotopes have settled into equilibrium over thousands of years.