The ocean acts as a huge carbon sponge. Organic matter sinks into the deep and gets stashed away from the atmosphere for a long time. The process is called the “biological pump” and it’s one reason why climate change isn’t already worse. (Iron fertilization attempts to artificially enhance the biological pump.)
Unfortunately, we seem to be breaking the biological pump. Scientific American reports that the ocean (along with terrestrial plants) absorbed significantly less carbon in 2006 than in 2000. Scientists have known of this positive feedback loop for a long time - the main culprit is likely to be increased stratification. It goes like this:
1) CO2 & other greenhouse gases trap heat in the earth’s atmosphere.
2) The ocean gets warmer from the top down. The surface layer (say, down to 100 feet or so) is mixed by wind and waves and becomes uniformly warm. Below that remains cold. This is stratification - you’ve probably felt it during the summer, when it’s so pleasant to swim on the surface but your feet get really cold when you put them down.
3) All the nutrients in the warm mixed layer get incorporated into critters. The critters sink, taking their nutrients with them.
4) The warm mixed layer can no longer support much photosynthesis. Phytoplankton and bacteria become efficient recyclers, keeping organic material in the surface layer to be reused. There’s not enough net growth to suck carbon out of the air. Very little carbon sinks to the deep sea.
Now, this is the normal state of things in tropical places - they have crystal clear water because there’s relatively little phytoplankton. But in temperate places, this should be only seasonal. Winter conditions - storms, winds, cold temperatures on the surface - should mix up the layers, bringing nutrients back to the surface. But with global warming, the temperate oceans are stratified for longer periods of time, reducing their carbon export.
That’s bad. The ocean is the largest carbon sink on earth - more than trees, more than soil, more than everything. If the ocean’s ability to remove carbon is compromised, we’re going to have to reduce emissions more drastically than ever, at least if we care about having a pleasant and comfortable planet with a few neat non-human things to look at.
