Washing away the by-products
The researchers colonised the alginate particles with genetically modified, green-glowing bacteria. These broke down the particles much faster when water flowed through the chamber; the breakdown takes about ten times longer in still water. This is because the flowing water washes away the degradation products, leaving the bacteria’s enzymes to get to work directly on the particles, without having to spend time on decomposing molecules that have already split off.
Drawing on these observations, Alcolombri and his colleague François Peaudecerf have designed a new model of the biological carbon pump that considers how the sinking influences the degradation of the marine snowflakes. The model calculations suggest two things: Firstly, that the enhancement of particle degradation due to sinking reduces the theoretical transport efficiency of the carbon pump twofold. And secondly, that much of the dead algae is decomposed in the uppermost layers of the ocean – which is consistent with measurements of real carbon flux in the sea.
Tiny things, enormous impact
The team’s research was not aimed at boosting the performance of the biological carbon pump: “We’re interested in gleaning a fundamental understanding of natural processes; we wanted to know how the biological pump works,” says Alcolombri. “For this is essential if we’re to predict more accurately how our oceans will respond to climate change”.
It turned out that the degradation rate of marine snow – and indirectly, the global carbon dioxide content in the atmosphere – is determined by microscopic transport dynamics. Which shows, once again, how even the tiniest things in the environment affect the big picture.