The Sour Truth about the Oceans in a High CO2 World

            Since the onset of the industrial revolution in the 18th century the atmospheric concentration of carbon dioxide has significantly increased owing to human activities including burning of fossil fuels, cement production, deforestation and land use changes. The current concentration of carbon dioxide in the atmosphere is close to 390 ppm and approximately 40% higher than the concentration observed at the onset of the industrial revolution.

Based on analysis of ice core records in Antarctica, we know for certain that the present CO2 concentration is the highest atmospheric concentration of carbon dioxide over the last million years, and it may be the highest concentration in as long as 50 million years. At the current rate of increasing CO2 emission, the present concentration will have doubled by the end of this century.

            Global warming will no doubt have a significant impact on the climate system and the lives of humans, and we are probably just starting to see some of the consequences at this time including melting and retreating glaciers, thinning ice caps, and rising sea level. Future projections suggest that the average temperature could increase another 1 to 6 degrees Celsius during this century, but the exact magnitude is highly uncertain and intensely debated because there are many feedback mechanisms, both positive and negative that we do not fully understand. Regardless whether the average temperature of Earth's surface will increase 1, 2, 3, or even 6 °C during this century, there is another problem linked to the rise in atmospheric CO2 that we are just starting to learn about. This problem has been named "the other CO2 problem" or more specifically ocean acidification .

            At present time, the oceans absorb 25-30% of the CO2 humans release to the atmosphere, 55% accumulate in the atmosphere and the remainder is taken up by the terrestrial biosphere. From a global warming standpoint this is good. Because if the oceans did not absorb this CO2, there would be significantly more CO2 in the atmosphere and consequently the average surface temperature of the earth would be higher. Unfortunately, this uptake of CO2 comes at a cost. When CO2 dissolves in seawater, it combines with water molecules and form carbonic acid. As the name reveals, this is an acid and as more CO2 is taken up by the oceans, the acid-base balance changes and the acidity of the oceans increases. The acidity of the surface ocean has increased about 30% since the onset of the industrial revolution and could increase by another 100% by the end of this century if the current increase in CO2 emission rate continues. Observations from the Bermuda Atlantic Time-series Study - BATS, which is the longest open ocean time series in the world, show clear evidence of increasing acidity in the surface ocean at this location between the early 1980s until present. This record is the best evidence and the "smoking gun" that ocean acidification is occurring.

            Ultimately, as the oceans become increasingly corrosive, calcium carbonate structures, reefs and sediments will become subject to increasing dissolution, that is, the chemical breakdown and disintegration of calcium carbonate minerals. At some point in time that may not be too far away in some places, coral reef ecosystem will transition from net accumulation to a net loss of calcium carbonate material. This process actually act as a negative feedback to rising CO2 and ocean acidification by increasing the buffer capacity of the ocean, but it will take thousands of years to neutralize the CO2 originating from human activities. Field and experimental results show evidence that marine calcifiers could become subject to dissolution under increasingly acidic seawater conditions anticipated in the future.

            At BIOS, several investigators are already pursuing research on the wide ranging effects of ocean acidification both on a local and on a global scale. However, because of the high risk of the Bermuda coral reef to ocean acidification we are currently trying to coordinate and expand these efforts to develop an ocean acidification research centre at BIOS. Bermuda and BIOS are especially suited for a centre like this because of the imminent threat to the Bermuda coral reef ecosystem; the absence of major industries and sources of pollution, which implies that the changes we might observe are most likely due to large scale global changes; the existence of Bermuda Atlantic Time-series Study, which helps us constrain changes observed on the reef; and the logistical support and expertise available at BIOS. In addition, there is a natural gradient in acidity across the Bermuda reef platform that allows for important experiments and comparisons in a natural environment across this gradient. We envision this research center, which we currently refer to as BEACON (Bermuda ocean acidification and coral reef investigation, having four different components including (1) a field component, continuously monitoring chemical conditions on the reef with concurrent observations of coral reef health; (2) an experimental component using  tanks and aquaria to manipulate and control environmental conditions and investigate the effect of future seawater conditions on various marine organisms; (3) a numerical modelling component used to forecast future scenarios and consequences to the Bermuda coral reef; and (4) an educational and outreach component involving local schools, students and the general public.

            In summary, I would like to reiterate that regardless of the magnitude warming the earth will experience in the next several decades owing to rising atmospheric CO2, the oceans will continue to absorb a significant fraction of this CO2 with all its consequences to marine organisms and ecosystems. Opposed to making predictions of the future climate, which is challenging, we can very accurately predict the chemical conditions of the surface ocean under given CO2 scenarios. The threat of ocean acidification is imminent but at this time we are only beginning to understand the potential consequences. In order to accurately direct future conservation and emission policies, the need for a better understanding of this problem is urgent. The only way we can stop or slow down ocean acidification is to reduce emissions of CO2 to the atmosphere.