As proponents of ocean fertilization know, the ocean is a huge carbon sink. Some of this carbon is directly absorbed into the water, and some of it is captured in organic material, like phytoplankton and fish and, of course, poop. Poop is a critical component of the ocean’s ability to store carbon, but not all carbon-storage poop is create equal.
The ability of a given poop to store carbon depends on its sinking rate. The ocean is an average of 2 1/2 miles (or 4,000 meters) deep, and a poop has got to make it all the way down if its carbon is going to get stored. If the poop sinks slowly, there’s lots of time for it to get eaten or degraded by bacteria, which means that the carbon is released back into the water. If the poop is sinks quickly, more of that carbon will make it to the deep sea, where it has the potential to be stored for millennia.
The critter with the fastest poop in the sea is the noble salp. Salps are filter-feeders that float about in the open sea, feeding off whatever gets sucked into their siphons. (Incidentally, they are our closest invertebrate relative. They have a primitive spinal cord as a wee tadpole, but lose it on adulthood. There’s a metaphor in there somewhere.) And salps have seriously dense poop. Their poop can sink up to 1,000 meters a day, making it to the sea floor in a matter of a few days rather than weeks or months.
And there can be a LOT of salps. When conditions are right, they can form massive blooms that eat up to 75% of all the plankton they encounter. And that’s the problem – a salp bloom doesn’t leave much food for anyone else, particularly the tiny crustaceans favored by fish and whales. This is of particular concern in the Antarctic, where salps have increased while krill (what whales eat) has decreased.
So where does this leave climate change? The ocean fertilization people want to deliberately breed salps for their carbon storage capabilities. It is likely that a massive injection of salp poop would store a lot of carbon – but at what cost? Then again, all those little crustaceans may not be able to form their shells anyway in a couple years, so maybe salps are the future. I hear people eat salps in Korea – factory-farmed salp, anyone?
Thus with a whimper and a splash ends Poop Day. May your muffins be fibrous, your intestinal flora vigorous, and your bowels cheerful.