Ocean Acidification in the Florida Keys

Erielle B. Clark

ERM 440. Chemistry of the Environment: Air, Water, and Soil

Spring 2019

1. Introduction

Atmospheric carbon dioxide (CO2) has become the greatest human-outputted pollutant and is responsible for many horrific environmental declines, including ocean acidification. Ocean acidification has harmed most coral reefs around the world, including the Great Barrier Reef, Red Sea Coral Reef, and many more. This paper will focus specifically on the Florida Keys Coral Reef in the United States, and will demonstrate how CO2 is responsible for ocean acidification, how ocean acidification has affected the Florida Keys Coral Reef, and how the effects of this pollutant can be remediated.

Though carbon dioxide is necessary for life on earth, human production in recent years has greatly thrown off the balance of CO2 input and output. This excess CO2 is produced by activities such as the burning of fossil fuels (including the production of electricity, use of transportation, industrial processes, or residential use).12 In Florida, where citizens and tourists alike rely on fossil fuel-dependent technology to make the amazing fishing, boating, and snorkeling opportunities possible, high pollution levels are expected. The sheer number of vacationers means large numbers of hotels, residences, and vehicles are outputting high levels of CO2.

Figure 1: Increasing CO2 Levels5

The Florida Keys Coral Reef is the only living coral reef in the continental United States, earning it a status of great importance. The Florida Keys community relies on it for tourism, fishing, medicine, and as a barrier against natural disasters. The reef, however, has seen a significant decline in living coral (Figure 2). The decreased pH levels (from ocean acidification) lowers the rate at which coral can calcify and grow. So, the acidic waters effectively kill the coral.3

15%

10%

5%

0%

1996

2016

Average coral cover in the reefs in the Florida Keys

Figure 2: Coral Decline in Florida Keys8

2. Results

2.1. Chemistry of the Pollutant

Ocean acidification occurs when CO2 is absorbed into the seawater at very high rates.2 Excess CO2 in the Florida Keys is becoming more prevalent due to human activities, with severe effects on ocean wildlife.

So, when the human-produced CO2 reacts with Florida seawater, it creates carbonic acid:

CO2 + H2O → H2CO3

The carbonic acid then breaks down to form a hydrogen ion and bicarbonate:

H2CO3 → H+ + HCO3-

Finally, the bicarbonate ion dissociates into carbonate ions and a hydrogen ion.

HCO3- → + CO32-

Featured below in Figure 3 is a speciation diagram for carbonic acid, bicarbonate, and carbonate, showing the percentage of each species present at different acidity levels.

Figure 3: Speciation Diagram for Carbonic Acid14

Figure 4: Ocean Acidification Chemistry10

As seen in the chemical processes, the proton is liberated to the water, decreasing the pH (Figure 4). As more and more hydrogen ions are liberated, the ocean is quite literally acidified.

Coral reefs are extremely vulnerable to changes in acidity levels, so it is no surprise to see the Florida Keys Coral Reef ravaged by lowered pH levels. Calcium carbonate (CaCO3), the mineral that makes up coral skeletons, dissolves easily in acid.1 Below a certain pH, this dissolution happens faster than the creation of new calcium carbonate, so the reefs are unable to grow and to recover from erosion processes.16 Coral reefs are extremely important to marine and human life, and when they continue to die and erode, it greatly harms the ecosystem.

Since the Industrial Revolution, the ocean pH has dropped from 8.2 to 8.1, which constitutes a 30% increase in acidity. Furthermore, at current emission rates, ocean pH is on the path to dropping to 7.8 by the end of the century, creating the most acidic ocean in the past 100 million years.11 Further decreasing pH of the ocean would be detrimental to the Florida Keys Coral Reef, which would bleach, die, and deteriorate quickly and irrevocably. With greenhouse gas emissions continuing to rise in the Florida Keys, this suggests a bleak future for coral reefs over the coming decades. The reef would see reduced calcification and increased dissolution, unless measures are taken in the Florida Keys community to stop the excess CO2 emissions and therefore halt ocean acidification.

2.2 Remediation Techniques

Entirely reversing the process of ocean acidification is, unfortunately, not a process that could be completed in our lifetimes. In fact, to return the pH of the entire ocean to pre-industrial levels, it will take approximately 700 years. In the meantime, however, there are still measures that can be taken to slow, prevent, and feasibly reverse the ocean acidification process. In order to save the Florida Keys Coral Reef, the Florida Keys community will need to undertake several strict (but realistic) remediation techniques, such as measures to lessen atmospheric CO2, the implementation of coral restoration, and the elimination of acidity in the ocean.

CO2 Reduction and Prevention

Restrictions on CO2 emissions are the most obvious and most necessary way in order to protect the Florida Keys Coral Reef.7 The environment would benefit greatly from a reduction in this pollutant, and a mixture of preventative measures and reversal measures would see great change. In the Florida Keys, I propose strict measures to prevent further damage to the coral reef and to help slow the ocean acidification process.

1. Carbon Dioxide Removal (CDR)9 comes in many forms. If even a single one of these devices was implemented in the Florida Keys, it could have devastating results on the CO2 emission levels in the area. Viable types of Carbon Dioxide Removal include:

i. Bio-Energy with Carbon Capture and Storage (BECCS)15

BECCS is the process of: first, using biomass (such as trees and crops) for energy in factories; next, capturing the embodied CO2 before it is released back to the atmosphere; and finally, storing it either underground or in long-lived products like concrete. Since biomass would be used to fuel the factories, large forests would have to be planted, which in turn also helps to reduce the CO2 in the environment. If the CO2 is stored in one of these long-lasting items, it is thought to be able to last 1000 years with a 99% retention rate, therefore keeping it out of both the atmosphere and the ocean.

Figure 5: BECCS

Figure 6: Direct Air Capture

ii. Direct Air Capture14

Direct air capture is the process of chemically scrubbing carbon dioxide directly from the ambient air, and then storing it either underground or in long-lived products like concrete.

2. Restrictions on CO2 emissions from cars, boats, and surrounding factories: while this is more of a “preventative” method, if used in conjunction with some of the other remediation options, it could see real-time results. Reducing the amount of CO2 emissions within the Florida Keys area could lead to the Florida Bay slowing the rate of acidification. This could include:

i. Setting regulations on the type of vehicles (cars, boats, etc) allowed and providing deterrents for models that have high emission levels.

ii. Instigating stricter guidelines for CO2 emissions, which could especially be implemented on factories in the surrounding area.

Coral Restoration

The ocean continues to acidify as CO2 mixes with ocean water and creates carbonic acid, which in turn continues to deprotonate, further acidifying the water. This acidification affects the calcium carbonate (CaCO3) of the coral reefs, effectively bleaching and killing it.

Mote’s Coral Nursery, a lab local to the Florida Keys, has produced over 12,000 pieces of coral in four years with a success rate of 85-90% alive and growing.4 In particular, they have developed a micro-fragmentation and fusion method to speed the growth of brain, boulder and star corals, which are crucial reef-building.

Though this method of remediation is less directly associated with the chemistry of carbon dioxide, it has some crucial benefits. While the acidification of the ocean bleaches and destroys coral, the bicarbonate molecule (HCO3-), when mixed with calcium ions (Ca2+) could actually facilitate the growth of coral. When combined with the acidity-reducing method below, both the pH of the ocean could be lowered and coral could be encouraged to grow.

Reducing Acidity in the Florida Keys with Olivine

While it remains unlikely that the ocean’s pH can be reset to pre-industrial levels without extreme measures or extensive time, there are still measures that can be taken to raise the pH of the ocean. For the Florida Keys Coral Reef, it is feasible to undertake this remediation technique:

Olivine (Mg2SiO4) can be used to de-acidify the ocean.13 Mg2SiO4 is a magnesium silicate mineral that is mainly found in Earth’s subsurface and has been previously suggested as a way to soak up CO2 in the atmosphere. The amounts needed to make a difference globally are too great, but feasible amounts could be used to reduce ocean acidification locally. When it is placed in seawater, it gradually swaps its magnesium ions for protons, thereby helping to remove acidity, as seen through the reaction below: Mg2SiO4 + 4H2O → 2Mg²+ + H4SiO4 + 4OH-

4OH- + 4CO2 → 4HCO3-

When olivine is mixed with ocean water, it dissociates to a magnesium ion, silicate, and hydroxide. The silicate molecules are simply food for ocean life and are inconsequential. The extra hydroxide prevents any dissolved carbon dioxide from reacting with water, instead reacting with CO2 itself. This leaves no extra H+ molecules, therefore not further acidifying the water. Bicarbonate can also be combined with Ca2+ to create calcium carbonate (the main chemical component of coral).

Figure 7: Olivine Reaction in Ocean Water6

3. Conclusion

Carbon dioxide is a major pollutant and contributes directly to ocean acidification. The majority of the carbon dioxide pollution is human-caused and can therefore be reduced. The Florida Keys Coral Reef is currently suffering because this excess carbon dioxide lowers pH levels and is causing the bleaching and dissolution of the calcium carbonate corals. There are ways to feasibly prevent, reduce, and remediate ocean acidification.

The most effective and immediate remediation technique would be the addition of olivine to the Florida Keys’ seaboard, as it directly helps to reduce the acidity of the ocean. This method would be most effective in reversing the damage and raising the pH in this area. While the Carbon Dioxide Removal techniques are extremely useful in removing atmospheric CO2 and preventing further damage, the olivine method has the most direct and hands-on beneficial effects. In that line of thought, the coral restoration is an effective way to reconcile the damage done to the existing environment, and when this “damage control” technique is paired with the olivine technique, it could have significant positive effects.

All of these methods hold merit, and if combined, they could induce a monumental change for the better. I suggest the Florida Keys community 1. Place restrictions on CO2 emissions, 2. Implement at least one of the given Carbon Dioxide Removal devices, 3. Pursue the coral restoration route, and 4. Take measures to eliminate acidity through the addition of olivine to the local ocean. If these measures went into effect, the Florida Keys Coral Reef would see immediate and extraordinary results, including the slowing and reversal of ocean acidification in their coral reef.

3. References

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ways-remove-carbon-pollution-sky

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