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.
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