By Avigayil Kadesh
The levels of carbon dioxide (CO2) in air and water -- a toxic result of man-made emissions from the use of fossil fuels -- have increased dramatically during recent decades. And that has many scientists concerned for animal populations on land and in the seas and oceans.
Researchers from Israel have now devised a better way to quantify the effect on marine ecosystems when accumulating gas acidifies the surface waters, thereby making it harder for shelled organisms like corals and certain open-sea plankton to build their calcium-carbonate skeletons. Those skeletons are what make up coral reefs.
Getting an accurate measure has been complicated until now because the effect of ocean acidification on the rates of calcium produced by marine organisms is highly variable and specific to each individual species. Scientists tend to use local and site-specific field measurements, surveying reef environments and open-sea environments separately. These measurements provide a local snapshot of the situation rather than an overall picture.
To widen the focus, the group of researchers from the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University of Jerusalem studied a 5,000-kilometer-long strip of ocean reaching from Eilat to the Seychelles, crossing the Red Sea, the Gulf of Aden and the Western Indian Ocean.
This is the first study that demonstrates the feasibility of quantifying data on the effects of rising carbon-dioxide levels on an oceanic basin scale.
Because of its great significance in understanding potentially devastating changes going on in the marine ecosystem, the research won financial support from the Israel Science Foundation, the Bill and Melinda Gates Foundation and the Israeli Ministry of Science and Technology.
A crucial milestone
The researchers were interested in simultaneously assessing the overall calcification rates of coral reefs and pelagic (open-sea) plankton over a whole oceanic basin, based on variations in surface water chemistry.
These variations happen because organisms that produce calcium carbonate skeletons tend to replace some of the calcium in their skeletons with other elements – such as the element strontium -- depending on varying conditions in their environment.
This means that corals produce calcium carbonate with a different chemistry than do calcareous plankton, and their overall effect alters the chemistry of the ocean water.
According to the results of this
survey, published in the Proceedings of the National Academy of Sciences (PNAS), the group estimated that pelagic plankton account for about 80 percent of the Red Sea calcium carbonate, whereas coral reefs precipitate only about 20%.
“This data is a crucial milestone if we wish to track the effect of anthropogenic activity originating from human actions, since it is not possible to quantify change without having objective baseline conditions,” said
Prof. Boaz Lazar, who led the expedition along with Jonathan Erez and Ph.D. student Zvi Steiner, together with Prof. Amitai Katz.
Also participating in the comprehensive study were Prof. Aldo Shemesh and Dr. Ruth Yam of the Weizmann Institute of Science in Rehovot.
“The results of this study suggest that variations of major ions on a basin scale may potentially help in assessing long-term effects of ocean acidification on carbonate deposition by marine organisms,” according to Lazar.
Monitoring the variations in coral and plankton growth rates every few years can provide essential information regarding rates of environmental change in tropical and subtropical seas like the Red Sea, Caribbean and South China Sea.
Marine researchers across the globe will therefore be making use of the new Israeli method to assess the effects of dangerously rising CO2 in the world’s waterways.