We are glad to share with you our second blog post!
Polins Ifeanyichukwu Anyanwu, a participant of EVE’s Fall School 2024, summarised a part of his and Nomathamsanqa Moyo’s final paper on Ocan Acidification. You can read the full work here: The Changing Trends in Atmospheric CO2 and Global Increase in Ocean Acidification, their effects on Aquatic Ecosystems
We also remind you that you can read the full Post-Graduate Student’s Papers Collection 2024 and all the others EVE’s Publications on our website.
Thank you so much for following along,
EVE’s Team
Changing Trends in Atmospheric CO2 and Global Increase in Ocean Acidification, their effects on Aquatic Ecosystems
By, Polins Ifeanyichukwu Anyanwu
The Ocean has always been around us, and will continue to serve as a huge reservoir and resource base for the entire universe. It enhances transport, communication among nations, a source of food and nutrients and home to a diverse array of species of both plants and animals. Most importantly, the ocean plays a very important role in energy and nutrient circles. The ocean has been a blessing, but how long are we assured of this? Ocean acidification, which results from climate change, is caused by the increase in the amount of Co2 dissolved in the ocean water above the natural levels.
Ocean water is normally slightly basic, with a surface-water pH of about 8.2. pH (potential for Hydrogen ion) scale is a measure of the relative amount of free hydrogen and hydroxyl ions in water. The more the free hydrogen ions, the more acidic. A unit change in pH represents a tenfold change in acidity, base or alkalinity of water. Water that has a pH of 6 is ten times more acidic than water with pH of 7. The most acidic substance therefore has a pH of zero. Carbon dioxide (CO2) when absorbed rapidly into the ocean, reacts with water molecules (H2O) to form carbonic acid (H2CO3). The compound then breaks down into hydrogen ion (H+) and bicarbonate (HCO3–), and these hydrogen ions decrease seawater pH. Ocean Acidification results from the change in the pH level of the ocean, the lower the pH level, the more acidic is the Ocean. The enormity and the implications of the growing Ocean acidification has seemed to elude researchers because of the seemingly minute change in the pH scale, but in reality, it represents a major shift and has several implications for the ocean ecosystem and the global human population at large. The pH level of the entire world’s Oceans is now 50 times more than in pre-industrial times. The changing Ocean Acidification therefore represents an unprecedented shift in the natural balance in the global aquatic ecosystem.
The Ocean has been absorbing about half of the excess Co2 produced by man from the atmosphere since the 1850s. While this has helped slow down the overall impact of climate change, it did create another problem in the form of Ocean acidification which is known to impact many ocean species and microorganisms, which are very fundamental for the health of the ocean and sustenance of the livelihood of those that depend on the ocean for daily living. Creatures that make hard shells and skeletons by combining calcium and carbonate from seawater are unable to do so due to increased acidity of ocean water, a situation critically referred to as the Osteoporosis of the ocean.
Researchers have opined that the observed effects of ocean acidity on ocean plants and animals have gone far beyond the individual organisms, now challenging the entire marine ecosystem. Evidence indicate that Ocean Acidification is a direct result of anthropogenic (human caused) activities, thereby making man directly responsible and quite able to control the change.
Figure 1: A coral reef at the Palmyra Atoll National Wildlife Refuge in the Pacific Ocean. JIM MARAGOS/USFWS
Analysis of data from measurements of atmospheric Co2 and Ocean acidification collected by the National Oceanic and Atmospheric Administration (NOAA), covering a period of 37 years (1985 to 2022) showed a causal relationship, (Figure 2).
The relationship between atmospheric CO₂ and ocean pH levels was modeled using the following linear regression equation:
y=mx+c
Where:
- y represents ocean pH levels.
- x denotes atmospheric CO₂ levels.
- m is the slope of the regression line, indicating the rate of change in ocean pH per unit increase in atmospheric CO₂.
- c is the y-intercept, representing the estimated ocean pH when atmospheric CO₂ levels are at zero.
Statistical analysis showed a Correlation coefficient r of = -0.98651 showing a strong inverse relationship between Atmospheric Co2 and change in Ocean pH levels. Slope of the graph was = -0.0036, showing that for every unit change in Atmospheric C02, there was a corresponding drop in Ocean pH level by 0.0036, (0.1 change in pH level of the ocean is equivalent to 26 per cent increase in Acidity levels). The intercept of the graph was 8.1823, approximately 8.2, which is the standard pH level for the ocean when the excess Co2 level in the atmosphere is zero. The graph intercepts show that if the value of Co2 in atmosphere were normal, the Ocean pH will be 8.18. The coefficient of determination R2, showed the goodness of fit of the model and shows how well the model predicts the relationship between the variables. It had a value of 0.9732, indicating that variability observed in pH level and, by implication, Ocean Acidification, can be predicted with up to 90 per cent accuracy using the model.
Figure 2: Relationship between atmospheric Co2 and Ocean Acidification
The maximum CO₂ level of 37.15 ppm was recorded in 2022, and the minimum CO₂ level of 20.31 ppm was recorded in 1985. The minimum value of atmospheric CO2 was 20.31, while the maximum value was 37.15, a change of 16.84 units between 1985 to 2022, an increase of 0.46 units annually.
Several multinational agencies have been studying the change in the Oceans. The National Oceanic Atmospheric Administration (U.S.) has also developed an action plan, that stipulates steps to mitigate the impacts of Ocean Acidification. In Africa however, the knowledge and impact are still very elementary.
The effects of Ocean Acidification are profound, yet not clearly identified as such, especially in the third world economies. While a global coordinated effort is required to control Ocean Acidification, there is already a fallout of events and adverse weather conditions with prolonged impact on the global aquatic eco system as well as humans all over.