Ocean’s acidifcation is repeatedly referred as the evil’s twin of global change.


Global warming is not just heating up the globe, the increase of carbon dioxide levels are messing with the chemical makes up of the oceans, leading to a constant acidification of the water. In fact, I would rather refer to ocean acidification as the daughter of global change that enhances the negative impact of global warming with serious and fast processes. These processes are a menace towards many system, from coral reefs to the feeble poles.  It also seems like the polar oceans will be the first to principally suffer from ocean acidification effects.

Keep me cool, let’s move to the poles

It is predicted that climate change will affect marine biodiversity at a higher rate, compared to terrestrial organism. In order to mitigate the rapid effects of climate change on marine biodiversity and to predict how species will respond to shifts over time, it is essential to estimate the magnitude at which the process will develop in the next 100 year.

Marine organisms have long been classified as being stenothermal. Thereby, to avoid extinction and to fight off the effects of climate change as well as ocean acidification, marine organism have had to find multiple ways to combat the staggering consequences. Enhancing their physiological capacity and flexibility, migrate to different areas or acclimatise. According to a recent study in Australia, driven by Elvira Polocanska, marine organisms are heading to the poles looking for a cooler environment. Oceanic species are shifting towards cooler latitudes; they are seeking a more suitable climate that is no longer available where they live. Marine life is moving quickly but, will it be quick enough to avoid deplorable consequences?

Ocean Acidification 101- the chemistry behind it

When Carbone dioxide (CO2) dissolves in seawater, it combines with water molecules (H2O) creates a weak acid – carbonic acid (H2CO3). When the acid is diffused in the water, the molecule breaks apart, producing Hydrogen (H+) and bicarbonate ions (HCO3). At stable seawater pH between 7.5 and 8.4, some of the free hydrogen ions will decrease the pH, making the water more acidic. The excess of hydrogen ions, simultaneously, will search for carbon ions to create additional bicarbonate ions HCO3, reducing the carbonate ions pool (Figure 1).

Where is the issue?

Due to a increase of Carbon dioxide concentration of sea water pH and calcium carbonate is declining. Using a climate change modelling IS92a ‘business-as-usual’ scenario, J. Orr et al. (2005) predicted a change in chemical components in the Southern Ocean surface waters as a result of the forthcoming carbon dioxide emissions from humans. According to this study, the ocean surface will start to undersaturate towards metastable aragonite, a soluble form of calcium carbonate. This process will influence both benthic and planktonic calcifying biota. By 2100 the chemical parameters of the ocean will have over passed a threshold recognised as aragonite undersaturation (Figure 2), where the level of aragonite will extremely dropped down, generating an environmental challenge for the organism living in the ocean. This process is known as: ocean acidification.

Figure 2:Simulated surface aragonite saturation (top) and atmospheric CO2 concentration in ppm (bottom). Image: Friedrich Tobias

As the acidity of seawater rises, the saturation level of aragonite drops down and extracting CaCO3 which is used to build shells, making the process more challenging and resulting in a higher energetic cost. As a consequence, survival is more difficult due to smaller protection against predators and more arduous capacity of mobility. In polar oceans, the accessibility of calcium carbonate rate is already demanding, with polar oceans having a lower rate than the tropics, these predictions will influence the entire rich communities of marine animals, including aragonitic-pteropods (Figure 3) and cold-water corals. Therefore, when the predicted undersaturation will occur, it will firstly affect the Antarctic peninsula.

Pteropod image showing acidification results
Figure3: Pteropod’s shell when placed in seawater with pH and carbonate levels projected for 2100. Image: David Liittschwager/National Geographic Stock.

Regime shift

Global warming is also challenging the Antarctic peninsula with a return of crushing predators, like crabs which cannot stand cold waters and follow the warming and shallow water flow of the Southern Ocean.  Crabs, such as the King crabs, Paralithodes camtschaticus (Figure 4), are now, natural invaders. Cold water controlled crabs invasion from the Antarctic sea for 30 million years. The warming income current followed by the predators, is now slowly changing the Antarctic ecological regime. Dr C. Smith at al. in 2012 published evidences of 1.5 million crabs inhabiting the Antarctic Peninsula. Due to the Ocean Acidification effects on marine organism’ shells, their resistance to predators is highly reduced -this phenomena will increase in a temporal scale, as sources of CaCO3 are depleted. As a consequence of climate change, we will see ecological shift occurring in multiple ecosystems.

King Crab
Figure 4: A King crab invading the Antarctic coast.Image: Alexander Semenov

Regime Shift can be seen in two different ecological impacts: shift in species ranges or shift in phenology– the time of biological activities that occur seasonally. One factor may, however, include the other. When a species migrate between different latitudes, different scale of day, and diverse temperature, might confuse their seasonal activities such reproduction. Resulting in mismatches with food abundance at the right time when the larvae or the young are released.

A critical lesson from the Southern Ocean:

In order to prevent serious damage to the ecosystem, it is essential to further our knowledge on the possible consequences the oceans are going to face. Antarctic was taken as a example to describe what consequences our oceans are and will suffering. Global warming and ocean acidification are two sides of the same coin. If not actions will be made at the current time, critical outcomes are likely to occur in the near future. Scientists are devoting their lives and time to predict the future changes and to prevent the problems from becoming unmanageable. The human race should be vigorously encouraged to be conscious of the function which the ocean plays in attenuating the dynamic movement of climate change.

Account:Kalle Ljung


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