High (carbon) seas

A primary driver of mass extinction events, ocean acidification isn’t a popular topic – but is already affecting coastal ecology and economy

Hardest of elements as diamond and softest as graphite, with another 14 known allotropes (different forms of the same element) like graphene and graphenylene, and a further 500-odd theorized. Carbon forms more bonds than all the other elements in the periodic table combined except for hydrogen, with which it forms at least five million known compounds and another (at least) five million theorized.
It is carbon’s unique valency that makes it such a shape-shifter, and both the building block and energy carrier of all known life forms. All current transport fuels – gasoline, coal, natural gas, alcohols… everything except electric, nuclear, and hydrogen – are carbon-based.
Through history it has been both a giver of life, and a taker. The carbon cycle is an exquisitely tuned phenomenon that evolved with the planet and life in what is called a biogeochemical relationship. Carbon circulates through the biosphere into the atmosphere and aquasphere to be laid down as limestone and hydrocarbon deposits like coal and oil in the lithosphere – Earth’s crust and outer mantle. Life works with other environmental factors to keep the balance.

Carbon’s ancient footprints
Modern science has delivered many miracles that most take for granted, and some that few appreciate or respect: we can now read with great accuracy the tales laid down in the sediments and fossils from bygone epochs.
Besides having multiple shapes and forms, carbon also has 3 isotopes: C12, C13 and C14. Fossil carbon is C14 and we can tell its concentration in air and water with great accuracy. One of the big factors with “climate change” studies is how much CO2 (carbon dioxide) the ocean absorbs, and it turns out to be a lot: of the 1300 gigatonnes of carbon dioxide from anthropogenic emissions over the last 200 years, about 38% has already been absorbed into the oceans. The chemistry of ocean acidification is very simple and endlessly repeatable: add CO2 to water and it becomes carbonic acid. When we compare the data of observed CO2 increases in our acidifying oceans with the data on how much fossil fuel we’ve burned, there is no denying that our fossil carbon output is driving ocean acidification – and the historical analogs are bleak.

Around 250 million years ago in what is now Siberia, continuous volcanic eruptions in an area larger than Europe ignited massive coal beds – we know this because the formations are well known, Canadian scientist Stephen Grasby found the ash in the arctic in 2011, and the geological record shows a massive carbon spike at that time. The Earth’s crust has cooled since then and we’re unlikely to see those kinds of eruptions again, but we are now acidifying the oceans at a much greater rate than the lead-up to the Permian Triassic.

The Permian Triassic extinction, often referred to as “the Great Dying” occurred around the same time as the Siberian eruptions. It was the biggest known extinction event in history: around 95% of marine species disappeared, 70% of terrestrial species vanished, and it was the only mass extinction of terrestrial plants that should have otherwise thrived in the CO2-rich environment. We know that the oceans became acidic and anoxic (low in oxygen), and like a bad case of indigestion, the conditions favoured production of poisonous hydrogen sulfide gas.

For ten million years, no coal was laid down, quite simply because there were no coal-forming plants like peat moss to do so – this is referred to as the Permian Coal Gap. Ocean acidification played a role in all the other extinction events and has been identified as a major driver of such occurrences.

Struggling molluscs & acidification “refugees”

The northwest coast of North America is subject to an upwelling effect which makes this region a canary in the proverbial coal mine. Cold water, which holds more CO2, comes up to the surface when strong northwesterly winds push the surface water offshore. Washington state (and Puget Sound in particular) gets hit hardest, and its valuable oyster industry first started noticing unusual die-offs in 2005 – larvae survival was near zero at some farms. The next two years were no better, and by 2008 it was established that increasing acidity was the culprit. One company moved half of its operations to Hawaii in what has been called the first case of an ocean acidification refugee. Seed oyster producers have adapted by measuring acidity at the seawater intakes and shutting off supply pumps during upwelling events or adjusting pH – but wild oyster beds on the west coast have been experiencing reproductive failure because of the acidic waters.

Species with calcium carbonate-based shells are most at risk, with varying levels of sensitivity. Canada first felt the economic impact in 2013 when 10 million scallops died at a scallop farm on Vancouver Island. Of course, much more than our seafood supply is affected, the whole food chain is at risk. The southern resident orcas feed largely on chinook salmon, and Dungeness crab larvae are a major feed stock of young chinook. NOAA (US National Oceanic and Atmospheric Administration) studies show that larvae survival rates drop from 58% at “normal” pH levels down to 14% at pH levels already seen in Puget Sound during upwelling events.

Scientists are finding the changing pH may have unexpected effects: numerous studies show that more acidic water seems to interfere with salmon’s ability to smell. We observe that salmon stocks are declining, and the southern resident orca are malnourished.

Due to the way the oceans circulate, the corrosive water that surfaces off Washington and BC is the result of CO2 that entered the sea decades earlier. We are just starting to understand how carbon circulates through the oceans and it appears likely that even if we stopped emitting excess CO2 now, West Coast sea chemistry would worsen for several decades before stabilizing, unless we find ways to pull the carbon out.

Prevention is always preferable to reaction, and we have all the technology we need to rapidly complete the transition away from a fossil future towards what can be a happier, healthier, more egalitarian way.

Hal Hewett, Watershed Sentinel, 13 December 2019. Article.

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