麻豆淫院

Organic particles that settle on the seabed ensure CO₂ stays locked. However, natural gel-like substances slow down this process. Such microscale mechanisms play a crucial role in enhancing climate predictions.

Divers are familiar with marine snow, tiny particles of dead algae and other microorganisms that slowly sink to the bottom of the ocean. In total, the enormous accumulation of organic particles deposits over 50 gigatons of carbon at the bottom of the oceans every year.

This process plays a crucial role for the climate, as the carbon bound in the particles remains on the sea floor for thousands of years before resurfacing in the form of CO₂. Consequently, it is important to understand what happens to these particles during their descent.

A research group led by Roman Stocker is exploring this topic. The ETH team works at the intersection of various disciplines, including microbiology, physics, mathematics, microfluidics, and oceanography.

In a study in the journal Nature Communications, the researchers demonstrate for the first time that natural biogels significantly reduce the sinking rate.

The faster the fall, the fewer CO₂ emissions

"The speed at which the particles sink determines how much carbon is retained in the sea," explains Stocker. This is because marine snow serves as a food source for bacteria as it slowly descends to the ocean floor.

All the carbon that is metabolized in the process quickly ends up back in the atmosphere as CO₂. According to current calculations, only about 1% of the sinking biomass reaches the seabed.

Until recently, researchers believed marine snow sank at rates between 10 and 100 meters per day. But Stocker's team has now found evidence that some particles may descend even slower.

Biogels鈥攖ransparent, gelatinous substances secreted by bacteria, algae and other living organisms鈥攁re responsible for this. These gels have various functions, from protecting organisms against predators to capturing food, and often drift in vast quantities through the ocean.

One study in the Atlantic near Bermuda, for instance, found up to two billion biogel particles per liter of seawater. Stocker's team proposed that these gels become entangled with organic particles, reducing their falling speed.

Tracking a particle for days

A single particle cannot be tracked in the open sea over several days. This is why postdoctoral researcher Uria Alcolombri, now a professor at the Hebrew University of Jerusalem, has developed a unique piece of laboratory equipment: a 20-centimeter-high glass column filled with seawater, containing a single particle suspended in the middle.

A counter-rotating water flow equalizes the particle's sinking, ensuring it remains in the same place. The speed of the counterflow corresponds to the sink rate.

The researchers used this to simulate the sinking of a single particle for several days, both with biogel and without it. Aggregated fragments of the shell of diatoms served as the particles. The team produced the biogel themselves using a marine bacterium.

As predicted, the gel-like substance slowed the particle's descent. It actually slowed it even more than expected. In the presence of biogel, the particles fell to the ground almost 50% more slowly.

"We were amazed at how big the effect was," says Stocker. This means that the more biogel there is, the less carbon reaches the seabed because bacteria have more time to metabolize the carbon.

This braking effect stems from the low density of biogels. When entangled with organic particles, the gel acts like a buoy, reducing their sinking speed. It also spreads out like a parachute and forms filamentous threads, which increase drag and further slow the motion. The team confirmed these dynamics with a mathematical model.

"We expect these processes to occur similarly in the ocean," says Stocker. However, there will be significant variability in the open seas. Different organisms in different marine areas generate differing quantities of biogel, which also differ in composition. "We are trying to predict this better with our mathematical models."

According to Stocker, it makes sense to gradually incorporate such mechanisms into climate forecast models. "There are many more processes like this that take place on a very small scale." Some of them might even have the opposite effect, but far too little is known about this.

"We need to open this black box and find out in detail exactly what is happening in the ocean at the microscale."