Phytoplankton could increase by 10-20% by 2100 in tropical seas

A team of researchers at the University of California at Irvine has calculated that by 2100 there will be a substantial increase in phytoplankton in the oceans. They obtained this result through a model performed with a neural network and the same conclusion proved to be “surprising” for researchers.

Phytoplankton populations will grow mainly in low latitude waters, an unexpected result that contrasts with the belief of many scientists in the international scientific community that the ongoing climate change will make large areas of the oceans, particularly tropical ones, not very hospitable for phytoplankton.

Phytoplankton is one of the components of plankton. It is made up of very small microorganisms (most of them cannot even be detected by the naked eye) but they are so numerous that they represent a fundamental part of ocean ecosystems all over the world.

In the new study, published in Nature Geoscience, it is explained how the traditional method of measuring plankton in the seas, the one made by measuring the chlorophyll in the water, is not very suitable to measure the whole quantity of plankton.

This is explained, in the press release presenting the study, Adam Martiny, senior author of the research and professor of oceanography: “The problem is that chlorophyll is not all that is found in a cell, and actually at low latitudes, many plankton are characterized by a very small amount; with so much sunlight, plankton only needs a few molecules of chlorophyll to get enough energy to grow. In fact, so far we have had very little data to actually demonstrate whether or not there is more or less biomass in the regions being stratified. Consequently, the empirical basis for less biomass in warmer regions is not so strong.”

The researchers, therefore, conducted a new type of census on phytoplankton in hot regions by analyzing water samples taken from 10,000 different locations around the world. With this method, they were also able to measure more efficiently the presence of the so-called “picophytoplankton,” consisting of microorganisms 10 times smaller in diameter than plankton microorganisms. According to the researchers, picophytoplankton microorganisms account for 80 to 90% of the biomass of the same plankton in most tropical and warm regions.

Using machine learning, the researchers then created a model to understand the changes in the amount of plankton in tropical areas between today’s date and 2100, noting a 10-20% increase in biomass. According to the researchers, one of the explanations could be that when plankton dies it does not disappear immediately but stays in the water a little longer if it lives in warmer, more tropical areas. For this reason, they can be food for other plankton which recycle these nutrients to build new biomass.