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NASA: the ocean's carbon balance

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"For eons, the world’s oceans have been sucking carbon dioxide out of the atmosphere and releasing it again in a steady inhale and exhale. The ocean takes up carbon dioxide through photosynthesis by plant-like organisms (phytoplankton), as well as by simple chemistry: carbon dioxide dissolves in water. It reacts with seawater, creating carbonic acid. Carbonic acid releases hydrogen ions, which combine with carbonate in seawater to form bicarbonate, a form of carbon that doesn’t escape the ocean easily.

Crew members aboard the R/V Roger Revelle retrieve a CTD rosette from the frigid waters of the Southern Ocean. As the device is lowered into the ocean, electronic instruments measure salinity, temperature, and depth. Each of the white bottles collects seawater at different depths for detailed analysis. (Photograph ©2008 Brett longworth.)

As we burn fossil fuels and atmospheric carbon dioxide levels go up, the ocean absorbs more carbon dioxide to stay in balance. But this absorption has a price: these reactions lower the water’s pH, meaning it’s more acidic. And the ocean has its limits. As temperatures rise, carbon dioxide leaks out of the ocean like a glass of root beer going flat on a warm day. Carbonate gets used up and has to be re-stocked by upwelling of deeper waters, which are rich in carbonate dissolved from limestone and other rocks.

In the center of the ocean, wind-driven currents bring cool waters and fresh carbonate to the surface. The new water takes up yet more carbon to match the atmosphere, while the old water carries the carbon it has captured into the ocean.

The warmer the surface water becomes, the harder it is for winds to mix the surface layers with the deeper layers. The ocean settles into layers, or stratifies. Without an infusion of fresh carbonate-rich water from below, the surface water saturates with carbon dioxide. The stagnant water also supports fewer phytoplankton, and carbon dioxide uptake from photosynthesis slows. In short, stratification cuts down the amount of carbon the ocean can take up."

Good article about the scientific research that goes into determining the natural and human factors behind Co2 absorption and balance in our oceans. And as this article illustrates, humans will have to mitigate their emissions of Co2 in order for our oceans to continue to be able to balance Co2 in a way that sustains them, our planet, and all species that depend on them for life.
JanforGore

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