Eastern Pacific is rapidly becoming more acidic

In 30 years, the limit for sublimation with carbonate could be reached

Satellite image of the East Pacific, photograph of the US weather satellite GOES-11 (GOES-L), 2010. © NOAA / NASA GOES Project
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The ocean off the west coast of the US could become so sour in 30 years that many organisms no longer have enough lime dissolved in the water. The simulation of an international team of researchers shows that the limit to calcium carbonate supersaturation could be reached by 2040, the lower layers of water and by 2050, all the offshore seawater. Based on these results, the researchers expect a strong change in the ecosystem, as reported in "Science".

The waters off the west coast of the United States are known worldwide for their wealth of wildlife. The reason for this is that the north wind carries the surface water away from the coast and thus ensures that particularly nutrient-rich water reaches the surface from the deep. However, offshore waters also have a generally low pH and are therefore particularly vulnerable to the widespread phenomenon of ocean acidification. The acidification of sea water is a direct consequence of the increased CO2 concentration in the atmosphere, as the oceans absorb about one third of the carbon dioxide produced by humans.

The CO2 dissolves in seawater, increases its acidity and thereby also lowers the carbonate saturation content. If the water is more acidic and undersaturated, already existing lime dissolves spontaneously and newer can not form. That could have serious consequences for many creatures. For example, animals are endangered, the Kalkschalen or Kalkskelette form, such as snails or coral.

Scientists led by Nicolas Gruber, a professor at the Institute of Biogeochemistry and Pollutant Dynamics at ETH Zurich, have now investigated how acidity and carbonate saturation along the west coast of the US will develop in the future. With the help of high-resolution model simulations they simulated the circulation of the coastal area. These combined

them with models of ecosystems and the carbon cycle, taking into account in particular the exchange of CO2 with the atmosphere. This enabled them to create projections for different climate scenarios by 2050. The results are presented in the current issue of the journal Science. display

CO2 dissolves in the seawater, increases its acidity and thus lowers the carbonate saturation content. The graph compares the current situation with projections for the year 2050. Nicolas Gruber / ETH Zurich

Limit to subjugation in 30 years exceeded

The simulations show that even in an optimistic climatic scenario, the saturated carbonate saturation level in the studied region drops rapidly, exceeding the important limit of subsidence. While today the water masses in the top 200 meters are still saturated, such water masses can only be found in the top 60 meters in summer in 30 years. In the year 2050, the seawater will no longer have a sufficient degree of saturation throughout the year. This is particularly alarming because the lives of many organisms are in the top 100 meters of the water.

The most obvious manifestation of acidification is in the coastal 10 km of the ocean. There, the pH will fall in 2050 to 7.8. "Strong changes in the ecosystem along the western coast of the US are inevitable, " explains Gruber. However, the scientists do not dare to forecast how this change will be made concrete. Although they were able to calculate the chemical and physical aspects of sea acidification very precisely, they still know too little about which organisms will be affected as much. Not all organisms are equally affected by the ocean, and a few species may even benefit from it. "However, it appears that mussels suffer the most from acidification, especially in early stages of development, says Nicolas Gruber.

However, the scientist is worried that acidification will increase so much in such a short time. Nicolas Gruber expects that the limit of undermining will be reached in the next 20 to 30 years. Considering how much CO2 emissions have increased in recent years, development will be difficult to avert: Our study is an example of how human beings limit the bounds of what cosystem can tolerate, has already maxed out.

(ETH Zurich, 18.06.2012 - NPO)