A team of scientists have published maps depicting the most comprehensive picture yet of global ocean acidification, providing a global benchmark against which future changes can be measured.
The maps are a culmination of over four decades of data analysed by scientists at Columbia University’s Lamont-Doherty Earth Observatory and the University of Colorado at Boulder.
Using 2005 as a reference year, the maps track month by month seasonal and spatial variation in ocean acidity, as well as saturation levels of calcium carbonate minerals essential to shell building organisms.
The oceans have absorbed a quarter of human induced carbon dioxide in the last 200 years, resulting in a 30% increase in surface ocean acidity since the pre-Industrial era.
Lead author and geochemist Taro Takahashi said:
If the current pace of ocean acidification continues, warm-water corals by 2050 could be living in waters 25% more acidic than they are today.
Pictures paint 1000 words
The maps reveal that the greatest pH fluctuations occur in the colder waters between Siberia and Alaska, the Pacific Northwest and Antarctica.
In the spring and summer, plankton blooms absorb carbon dioxide and decrease acidity. However, in the winter upwelling of CO2-rich water from the deep ocean results in more acidic surface waters.
In contrast, tropical and temperate oceans show the least variation in pH (8.05-8.15).
Although the northern Indian Ocean is at least 10% more acidic than the Atlantic and Pacific, this has been attributed to its chemistry being heavily dominated by seasonal monsoon rains and the Eurasian super rivers draining into the ocean basin.
However, it is the polar waters near Iceland and Antarctica which are suffering the consequences of anthropogenic carbon dioxide. In these polar regions, the study found that waters were acidifying at a rate of 5% per decade.
These findings are consistent with recent estimates, including a 2014 study led by the Bermuda Institute of Ocean Sciences.
Significantly, these rates of ocean acidification correspond with the volume of carbon dioxide humans are emitting into the atmosphere.
Rik Wanninkhof, an oceanographer with the National Oceanic and Atmospheric Administration (NOAA) who was not involved in the study said:
This is exactly what we’d expect based on how much CO2 we’ve been putting in the air.
Ocean acidification threatens the sustainability of corals, mollusks and other calcium carbonate shelled based organisms. The loss of smaller calciferous organisms also threatens the sustainability of larger predators higher in the food chain.
According to a recent United Nations report, ocean acidification could be costing the global economy $3 trillion a year by 2100 due to losses in ecosystem services, fishing and tourism.