How do people sink in the ocean?

The sea is going sour

Everyone is talking about climate change. Everyone knows by now: The greenhouse gas carbon dioxide, which comes primarily from the burning of coal, crude oil and natural gas and from the destruction of forests, is the main driver of the changes in the climate system, which are becoming increasingly noticeable. Much less well known is a second global environmental problem, which is also caused by the hundreds of billions of tons of CO2 which man has produced and continues to produce since industrialization: the acidification of the seas.

Not only the atmosphere, but also the oceans and seas absorb carbon dioxide. Researchers estimate that around a third of CO2- Freight, which is additionally emitted from chimneys, exhaust pipes or through slash and burn of primeval forests, is stored there.

This is not without consequences. The gas dissolves in the water, creating carbonic acid and reducing the pH of the water. It doesn't literally get acidic, but the drop in pH changes the living conditions of many marine life.

Since the beginning of the industrial revolution, the pH value in the uppermost layer of the oceans has already dropped from 8.2 to 8.1. This means that the acidity has increased by 26 percent. By 2100 it is expected that up to 105 percent will be added. The acidity in this water layer would be higher than ever in the past 50 million years.

The seas and oceans cover around 70 percent of the earth's surface, making them the largest habitat for animals and plants on the globe. Acidification mainly affects species that depend on lime - such as corals, shellfish and starfish. At lower pH values, they have problems with the structure of their skeletons and shells.

According to forecasts, for example, almost all tropical coral reefs could be destroyed by 2050, although in addition to the pH value, the warming seawater and pollutants that are discharged into the oceans via rivers also play a role. Molluscs (oysters, mussels, pteropods) and their larvae as well as lime-dependent microorganisms are particularly affected by acidification.

Food security is at stake

Fish are apparently fundamentally less susceptible to acidification than stationary organisms - they are able to compensate for falling pH values ​​in their blood. However, fish populations could also be harmed in the future, as scientists from the German research association "Bioacid" have shown in tests for the important edible fish species cod in the Baltic Sea and in the Barents Sea north of Northern Europe.

The experts examined what happens when fertilized eggs and larvae in sea water with CO2-Concentrations are maintained as they are expected to be reached by the end of the century. Result: The mortality rate of fish offspring has increased significantly compared to today - with serious consequences, because according to "Bioacid" the offspring production could drop to a quarter to a twelfth of the previous value.

Another study with clownfish - a species that lives in coral reefs in the Pacific - showed that their visual perception, hearing and sense of smell are impaired by the more acidic water. A British study on the olfactory sense of sea bass recently came to similar results.

There are also some species that can cope well with the lower pH values ​​- this has been proven, for example, for phytoplankton and seagrass species, which benefit from stronger photosynthesis in more acidic waters. Overall, however, the experts assume that many marine organisms cannot adapt to the changes quickly enough.

The studies make it clear: Acidification not only threatens the biodiversity of the world's oceans, it can also have serious consequences for world nutrition. A destabilization of the marine food chain would be dramatic, since almost 60 percent of the approximately 7.6 billion people on earth currently live in coastal regions and in many countries fish and other marine animals are an important source of protein for the diet.

"Biggest undetected challenge of our time"

The IUCN, the International Union for Conservation of Nature, is very pessimistic about the situation. Warming and acidification are probably "the greatest unrecognized challenge of our generation," according to an IUCN report from 2016, on which 80 scientists from twelve countries collaborated. The warming of the oceans leads to the impoverishment of the ecosystems, warn the researchers. Sensitive species are threatened with extinction, while more resilient species could spread around the world.

The nature conservation experts are calling for more attention to be paid to the threat to the seas posed by climate change and for marine protected areas to be expanded faster than before - especially on the high seas. That could help to stabilize the ecosystem services of the oceans. The IUCN warns that action must be taken quickly.

The absorption capacity of the oceans for CO2, which has been slowing down the heating of the atmosphere so far, threatens to decline sharply. Warming and acidification of the water reduce this effect. The Intergovernmental Panel on Climate Change (IPCC) expects that the "CO2-Sink "ocean will gradually lose this function by the end of this century.

The climate-relieving effect is therefore continuously decreasing - another argument in favor of a courageous climate protection policy that quickly reduces the globally still rising emissions of greenhouse gases to net zero.