The oceans absorb the carbon dioxide that the world emits into the atmosphere, causing changes in seawater chemistry and, in turn, in some marine ecosystems and organisms.
The main change is the gradual acidification of the oceans due to increased emissions of carbon dioxide (CO2), the main driver of climate change, is a threat to some marine organisms, such as clams and other molluscs, and will make it more difficult for them to form their shells or skeletons. This is bad news not only for the organisms themselves but also for the people who depend on them.
As acidity levels in the oceans rise, some organisms absorb and accumulate more radionuclides or metals than others, grow more slowly, or need more food to survive. To better understand the effects of acidification and climate change, and as a first step to combat the problem, scientists around the world are tracking all these changes in clams, corals, sea snails, mussels, oysters, etc. with nuclear and isotopic techniques.
Isotopic techniques and the effects of ocean acidification on calcifying marine organisms
Ocean acidification includes some changes in seawater chemistry, such as a decrease in pH, indicating that acidity is increasing. These changes are quantifiable: since the start of the Industrial Revolution, the average pH of the oceans has decreased by 0.11 units, equivalent to an increase in acidity of about 30%.
While it is difficult to estimate the full impact of ocean acidification on marine life, we know that below a certain pH and corresponding carbonate concentration, conditions become corrosive to calcium carbonate, a key component used by many organisms to form their shells and skeletons. This can hinder the ability of these organisms to generate shells and bones, so they become fragile and their chances of survival diminish. Some corals, tiny sea snails (pteropods), clams and mussels (bivalve molluscs), and calcifying phytoplankton appear to be particularly sensitive to these changes.
Nuclear and isotopic techniques use radioactive isotopes, such as calcium-45 or carbon-14, as precise tracers to measure, for example, the quality of calcification and the rate at which it occurs in calcifying organisms, such as mussels, clams, or oysters, which form their shells or skeletons from calcium carbonate, a naturally occurring mineral found in the ocean.
To do this, they pour a known amount of calcium-47 into an aquarium filled with seawater in which there are also, for example, clams. By measuring the amount of radiolabelled calcium carbonate absorbed by these organisms over time, scientists can assess this calcification process and use this information to closely examine the consequences of ocean acidification.
The acidification of the oceans makes it more difficult for clams and mussels to find the material they need to create and maintain their shell as calcium carbonate reacts with the acidity of the water.
Studies, such as that of the Radioecology Laboratory of Istanbul University (Turkey), found that, exposed to slightly acidified seawater conditions, clams absorbed twice as much cobalt as they would under balanced control conditions, while other marine organisms, such as oysters, have shown a higher degree of resilience.
Cobalt is a heavy metal necessary for the human body in trace amounts, but in high concentrations it is toxic, so this shows that ocean acidification poses a risk not only to clams, but also to the people who eat them.
This situation may have wider socio-economic consequences for coastal communities such as those in Turkey, which rely on seafood for local consumption and export to European countries.
