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Nature Of Ocean Acidification

What Is Ocean Acidification In Marine Life?

Ocean acidification refers to a reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere. For more than 200 years, or since the industrial revolution, the concentration of carbon dioxide (CO2) in the atmosphere has increased due to the burning of fossil fuels and land use change.

The ocean absorbs about 30 percent of the CO2 that is released in the atmosphere, and as levels of atmospheric CO2 increase, so do the levels in the ocean. When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less abundant.

Carbonate ions are an important building block of structures such as sea shells and coral skeletons. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.

These changes in ocean chemistry can affect the behavior of non-calcifying organisms as well. Certain fish's ability to detect predators is decreased in more acidic waters. When these organisms are at risk, the entire food web may also be at risk. Ocean acidification is affecting the entire world's oceans, including coastal estuaries and waterways. Many economies are dependent on fish and shellfish and people worldwide rely on food from the ocean as their primary source of protein.

Ocean Acidification Benefits Some Marine Organisms

While research has shown that ocean acidification threatens many invertebrate marine species, such as clams and corals, by hindering their ability to grow shells and exoskeletons, a new study suggests that some species may actually benefit from increased acidity. As the ocean absorbs growing amounts of carbon dioxide from the atmosphere and becomes more acidic, not all organisms respond in the same way because they use different forms of calcium carbonate for their shells, says Justin Ries, a marine scientist at the University of North Carolina, Chapel Hill, and lead author of a study in the journal Geology.

After exposing 18 marine organisms to four levels of ocean acidity -including 10 times pre-industrial levels - Ries found that oysters, scallops, and temperate corals grew thinner, weaker shells as acidity levels were increased. Exoskeletons of clams and pencil urchins dissolved completely at the highest levels. But some species - including blue crabs, lobsters, and shrimp - grew thicker shells that could make them more resistant to predators. It is unclear, however, whether the energy spent coping with the higher acid levels detracted from other functions, such as immune responses, Ries said.

"The take-home message is that the responses to ocean acidification are going to be a lot more nuanced and complex than we thought," he said. Increasing levels of CO2 in the atmosphere are slowly causing the surface of the ocean to become more acidic. This is because the ocean absorbs some of the CO2, forming a weak carbonic acid.

At present, the ocean absorbs about a third of fossil fuel emissions, but this amount is likely to increase to 90% in the future. Over the last century, the average pH of the ocean has decreased, and there are hints that the current levels are beginning to impact organisms that make their shells out of the minerals aragonite and calcite (both composed of CaCO3). Aragonite is more susceptible to dissolution in more acidifc waters than calcite. Coral reefs that are made of the mineral aragonite and are particularly vulnerable to ocean acidification. A recent study has found, for example, that the area of coral covering the Great Barrier Reef in Australia has been cut in half since 1985.

However, coccolithophores and foraminifera, organisms that serve a vital role at the base of the marine food chain that are composed of calcite, are becoming increasingly susceptible. Moreover, the future appears to be even more bleak; some CO2 projections suggest by the year 2100 there will be a 150% increase in the ocean's acidity compared to preindustrial times. Here we review the chemical changes in seawater that result from increasing CO2, and then we discuss the impact on reefs and planktonic organisms in the ocean. Finally, we discuss the evidence for acidification in ancient oceans and its impact on life in the past.

Equation Of Ocean Acidification

The ocean contains a massive reservoir of dissolved CO2, hundreds of times more than in the atmosphere, and, actually, by contrast, the amount derived from fossil fuel burning is relatively modest. Since the beginning of the industrial revolution, about 340 to 420 petagrams carbon (a petagram or Pg is 1015 grams) in the form of CO2 has been emitted to the atmosphere, with about a third of that amount absorbed by the ocean, approximately 118 Pg.

Seawater today may already contain more CO2 than at any time in many millions of years. As we discussed in Module 5 on the Carbon Cycle, the absorption of CO2 in the ocean forms weak carbonic acid (H2CO3). Some of this acid dissociates in seawater releasing H+ ions, which make the water more acidic, as well as HCO3- (bicarbonate ions) and CO32- (carbonate ions). This reaction is as follows:

CO2(aq) + H2O = H2CO3 = H+ + HCO3- = 2 H+ + CO32-

Going back to your elementary chemistry course, you might remember that a pH of greater than 7 is regarded as alkaline whereas a pH of less than 7 is acidic. Surface ocean waters have a pH of between about 7.9 and 8.3, which means that they are, by definition, alkaline. Anthropogenic CO2 is thought to have decreased the mean pH of the ocean by 0.1 unit since 1800.

This may not sound like that much, but more ominous is the projection that if CO2 levels continue to rise unabated (i.e., projections based on SRES A2 "business as usual", pH levels will drop a further 0.3 by 2100. As we will see below, in parts of the ocean, these levels would be extremely damaging to organisms that build their skeletons out of CaCO3, which is very sensitive to CO2 addition.

CaCO3 is the dominant material used by invertebrate organisms to build their skeletons. There are two different minerals made of CaCO3, known as polymorphs: calcite and aragonite. These minerals have the same composition but different crystal lattice structure and thus their properties and behavior in seawater differ, including their ability to dissolve. To understand how CaCO3 dissolves and precipitates, we need to introduce a term Ω that represents the saturation state of the water.

Where waters are highly saturated with respect to CaCO3 and Ω is high, calcite and aragonite are less likely to dissolve than where these waters are less saturated or even undersaturated and Ω is low. Likewise, calcite and aragonite are more likely to precipitate under higher Ω values. The dissolution and precipitation reactions are as follows:

Dissolution reaction: CaCO3 (solid) = Ca2+ + CO32-

Precipitation reaction: Ca2+ + CO32- = CaCO3 (solid)

An increase in CO2 from the atmosphere presents a double whammy for skeletons formed from CaCO3, both aragonite and calcite. The H+ ions and carbonate ions (CO32-) that derive from the dissociation of carbonic acid combine to form bicarbonate ions (HCO3-). This rapid reduction in available carbonate ions decreases Ω and limits calcification by organisms with aragonite- and calcite-based skeletons. However, here we need to dispel two myths. The first myth is that the precipitation of CaCO3 is directly controlled by pH. In fact, precipitation is affected principally by the decrease in CO32, which is coincident with the addition of H+ ions, and reduction in pH.

The second myth is that precipitation of CaCO3 can occur in any water that is oversaturated with respect to the particular CaCO3 mineral. In fact, both corals and coccolithophores have been shown to have difficulty calcifying in environments when waters were actually oversaturated. Different organisms can calcify at very different Ω values, but for most the decrease in saturation that results from decreasing CO32- content is a direct threat to calcification.

Finally, it is key to move that aragonite is more susceptible to dissolution than calcite. Thus, shells made of the CaCO3 polymorph aragonite, including the corals, will be the first to dissolve, followed by those made of the polymorph calcite. The saturation of CaCO3 in the oceans is also a function of temperature and pressure. A delicate balance exists between the production of CaCO3 via the formation of skeletons in the shallow part of the ocean and the dissolution of this aragonite and calcite in the colder and deeper realms of the ocean where waters are less saturated. In most parts of the ocean, undersaturation occurs far below the surface.

However, recent increase in dissolved CO2 is leading to a shoaling of the saturation horizon of CaCO3, and, in the future, this will impact especially the organisms that live at depth or in colder waters as well as those that make their shells of the mineral aragonite, which is more soluble in seawater than calcite.

Who Discovered Ocean Acidification?

Climate scientists discovered ocean acidity called Ken Caldeira and Michael Wickett, who coined ocean acidification. Caldeira played a crucial role in discussing how acids occur in the ocean through the alteration of pH of ocean water and the injection of CO2 into the sea. The sea keeps soaking up carbon until it reaches the air's equilibrium, and reversing the acidification is impossible.

When Did Ocean Acidification Start?

It can be difficult to study ocean acidity from a long time ago. However, scientists know that the Industrial Revolution of the 1800s triggered an escalation of carbon dioxide levels in the atmosphere, which has continued to climb ever since. Ocean acidification is now thought to occur faster than it has been in the last 20 million years. In the past, similar changes in pH have happened naturally, but over much longer periods of time. If carbon dioxide emissions continue to accumulate at this rate, the ocean will keep absorbing more of the gas each year.

Reasons For Ocean Acidification

Are People Contributing To Ocean Acidification?

Yes. Over the past 200 years, the world's oceans have absorbed more than 150 billion metric tons of carbon dioxide emitted from human activities. That's a worldwide average of 15 pounds per person per week, enough to fill a train long enough to encircle the equator 13 times every year. Ocean carbon dioxide concentrations are now higher than at any time during the past 800,000 years, and the current rate of increase is likely unprecedented.

The atmospheric concentration of carbon dioxide has increased because of the burning of fossil fuels such as coal, gas, and oil along with land use change (for instance, conversion of natural forest into crop production). The oceans have absorbed roughly one-third of all carbon dioxide emissions related to human activities since the 1700s. Estimates of future carbon dioxide levels, based on business-as-usual emission scenarios, indicate that by the end of this century the surface waters of the ocean could be nearly 150 percent more acidic, resulting in a pH that the oceans haven't experienced for more than 20 million years.

What Causes Ocean Acidification

Ocean acidification is mainly caused by carbon dioxide gas in the atmosphere dissolving into the ocean. This leads to a lowering of the water's pH, making the ocean more acidic.

Carbon dioxide is being produced faster than nature can remove it, so increasing amounts are being absorbed by the ocean.

Why Are Carbon Dioxide Levels Increasing?

Many factors contribute to rising carbon dioxide levels. Studying ocean acidity in the past is difficult, but scientists know that an escalation in carbon dioxide levels was triggered in the 1800s by the Industrial Revolution. Currently, the burning of fossil fuels such as coal, oil and gas for human industry is one of the major causes. Deforestation results in fewer trees to absorb the gas. Also, when plants are cut down and burnt or left to rot, the carbon that makes up their organic tissue is released as carbon dioxide.

What Else Can Affect The Acidity Of The Ocean?

Some parts of the ocean are naturally acidic, such as at hydrothermal vent sites - underwater 'hot springs'. In the past, ocean acidification occurred naturally but over much longer periods of time. It is occurring faster now than in the last 20 million years. The primary cause of ocean acidification is anthropogenic CO2, responsible for about two-thirds of the decrease in pH levels. Other natural and human-related factors can also contribute to acidification, such as volcanic activity and agricultural runoff.

However, these factors are often temporary in comparison to the long-lasting, pervasive influence of CO2 emissions. As the concentration of CO2 in the atmosphere continues to rise, so does the urgency to mitigate the causes of ocean acidification. Ocean acidification is caused primarily by increased CO2 levels in the atmosphere, leading to a decrease in ocean pH. Anthropogenic activities such as burning fossil fuels are the main drivers of ocean acidification. Acidification affects a wide range of marine species, disrupting ecosystems and posing a significant threat to marine life.

Climate Change Impacts On Ocean Acidification

Ocean acidification is the process of oceans becoming more acidic, making it hard for some marine life to thrive. Increasing carbon dioxide levels in the atmosphere - mainly caused by burning fossil fuels - is driving ocean acidification. This is because oceans absorb carbon dioxide from the atmosphere, which makes them acidify. Ocean acidification affects ecosystems, the natural food chain, our food supply, our economy, and tourism and recreation.

Reducing carbon dioxide emissions is the best way to prevent further ocean acidification. Managing and reducing other pressures on ecosystems can also help them to cope with ocean acidification. For example, ocean acidification reduces the concentration of carbonate in sea water. Marine organisms - such as coral, shellfish, and some plankton - use carbonate to build their shells. Less carbonate in the water makes it harder for marine organisms to form their shells and skeletons. Existing shells may also start to dissolve.

Ocean acidification will affect estuarine and coastal ecosystems of NSW in different ways. This is because other factors such as ocean upwelling, salinity and heat have varying impacts on ocean chemistry. Also, different plants and animals have different capacities to adapt. So the impacts of ocean acidification are not the same for all regions and all plants and animals. For example, some algae and seagrass may benefit from higher carbon dioxide concentrations, as this may increase their photosynthetic and growth rates. But this growth may compromise the ability of other organisims to thrive.

How Ocean Acidification Is Affected By Climate Change In NSW

The oceans naturally absorb carbon dioxide, but the increased amount of carbon dioxide in the atmosphere means that oceans absorb too much. Since the Industrial Revolution in the early 1800s, the oceans have absorbed about one-third of the carbon dioxide that humans have released into the atmosphere. This has increased ocean acidification by nearly 30%, which is about 10 times faster than any other time in the past 50 million years. If carbon dioxide emissions continue at the current rate, the surface ocean pH could change from the current 8.1 to 7.7 in the next 100 years.

This means the oceans will become more acidic. The impacts of ocean acidification are amplified in coastal marine habitats. Runoff from acid sulfate soils can decrease the pH of nearshore ocean water. Sea level rise and flooding - driven by climate change - worsens the impacts of coastal acidification.

Adapting To Ocean Acidification In NSW

Reducing carbon dioxide emissions is the best way to prevent further ocean acidification. We can help organisms and environments cope with increasing ocean acidification. Managing the marine estate and catchment can reduce other pressures, such as acid sulfate soil run-off, turbidity and pollution.

What Are All Affected By Ocean Acidification

How Does Ocean Acidification Affect The Economy, (The Hidden Costs)

The vast ocean, often viewed as a boundless resource, is facing a silent threat: acidification. Driven by rising atmospheric carbon dioxide, the ocean's chemistry is subtly shifting, becoming increasingly acidic. While the consequences for marine life are well-documented, the ripple effects on our economy deserve urgent attention.

Reduced Food Security
Ocean acidification also has a direct bearing on global food security, particularly for communities heavily dependent on seafood:

Nutrient Disruption
Acidic oceans disrupt nutrient availability for marine life. This can lead to altered marine food webs, affecting the abundance and distribution of fish species that are vital for global food security.

Decreased Harvests
Diminished fisheries due to ocean acidification translate to decreased seafood harvests, which can strain the availability of affordable and nutritious protein sources for vulnerable populations.

Infrastructure Vulnerability
Ocean acidification has indirect consequences for infrastructure, as coastal communities face heightened risks from rising sea levels and extreme weather events:

Coastal Erosion
Weakened coral reefs and the degradation of coastal ecosystems due to ocean acidification contribute to coastal erosion, putting infrastructure such as roads, buildings, and utilities at risk. While less visible, acidified seawater can even corrode coastal infrastructure like docks, piers, and seawalls. This increases maintenance costs and can eventually lead to structural damage, impacting ports, transportation, and coastal communities.

Increased Maintenance Costs
Infrastructure in coastal areas must contend with more frequent and severe damage, increasing maintenance costs for governments and businesses.

Ocean Acidification Affects Beaches
At some point, if the ocean gets acidic enough, sandy beaches-specifically certain types of rocks in beach sands called carbonates-will start dissolving too. A big part of my research is trying to figure out when that will happen, and what the effect on water chemistry will be.

The main strategy for this research is exposing beach sands to current and "future" (i.e., acidic) seawater conditions. Last summer, most of the time doing these kinds of experiments in the lab. This summer, taking that work outside to see if lab results match more realistic conditions. The main way to do this is by placing "benthic chambers" on sand, underwater, These chambers use a spinning device to pump water through sand, just like it would do naturally from waves and current pressure. A few of these experiments already, and the results match last year's lab results pretty well.

How Is Ocean Acidification Expected To Affect Plants?

Ocean acidification can actually give ocean plants access to more carbon, helping them grow more quickly and mitigating the effects of the change in pH. A common problem with many plant nurseries is the lack of carbon dioxide as the plants absorb it quickly when provided with adequate nutrients. With ocean acidification the supply of carbon is greater, meaning this is no longer a limiting factor for the plants.

Changes in pH can, however, have a negative effect on plant growth as some types of plants grow best in a narrow pH range. Increasing carbon dioxide concentration in the ocean lowers its pH levels by adding carbonic acid, a process known as ocean acidification. Learn how the ocean is a natural 'sink' for carbon dioxide, and study examples of the chemistry changes in the ocean and the environmental effects noticeable in seashells.

How To Prevent Ocean Acidification

How Is Acidification Measured?

In chemistry 101, we learn that pH is a measure for how acidic or basic (alkaline) a water-based liquid is. A pH of 7, as in pure water, is neutral. Tart lemon juice has a pH of 2; a cup of coffee, a pH of 5. Ammonia and bleach, on the other hand, are basic, with a pH of 11 and 13.5, respectively. Our oceans support an abundance of life with an average pH level of 8.1, making seawater slightly basic.

But experts estimate that over the course of the 21st century, the pH of ocean water could dip down to 7.8. That may sound like a small change, but the last time the ocean pH was this low was some 14 to 17 million years ago, when the Earth was a very different place. Scientists predict the change will have serious ramifications for ocean ecologies, food security, and economies, big and small, that depend on marine industries.

Why Is Ocean Acidification A Problem?
The consequences of disrupting what has been a relatively stable ocean environment for tens of millions of years are beginning to show. Ocean acidification is literally causing a sea change that is threatening the fundamental chemical balance of ocean and coastal waters from pole to pole. For good reason, ocean acidification is sometimes called "osteoporosis of the sea." Ocean acidification can create conditions that eat away at the minerals used by oysters, clams, lobsters, shrimp, coral reefs, and other marine life to build their shells and skeletons.

Human health is also a concern. In the laboratory, many harmful algal species produce more toxins and bloom faster in acidified waters. A similar response in the wild could harm people eating contaminated shellfish and sicken fish and marine mammals. And while ocean acidification won't make seawater dangerous for swimming, it will upset the balance among the multitudes of microscopic life found in every drop of seawater. Such changes can affect seafood supplies and the ocean's ability to store pollutants, including future carbon emissions.

Is Ocean Acidification Bad For People?
Absolutely. Even if you don't have a shell, the impacts of ocean acidification can ripple through the entire food chain, in water and on land. Significant portions of our economy rely on the ocean's bounty in one way or another. The U.S. shellfish industry, for instance, plays a huge role in coastal economies, providing employment to thousands of people and generating millions of dollars in revenue each year. If ocean acidification is left unchecked, it is estimated that the industry can lose more than $400 million annually by the year 2100.

"As we transform the sea with our actions-by the burning of fossil fuels-we're interfering with the crucial role it plays for humanity, from stabilizing our climate and protecting coastal communities to providing food for billions of people around the world".

Which Communities Are Most At Risk Of Ocean Acidification In The United States?
A 2015 study co-authored by NRDC looked at which coastal communities around the nation are most vulnerable to ocean acidification. It found 15 states at risk of long-term economic harm as a direct result: Alaska, California, Connecticut, Florida, Hawaii, Louisiana, Maine, Maryland, Massachusetts, New Jersey, New York, Oregon, Rhode Island, Virginia, and Washington. Researchers took into consideration communities' dependence on the shellfish industry, ocean areas that are experiencing the most rapid chemical changes, and areas where shellfish are most vulnerable.

You can see whether your community is being impacted through NRDC's interactive map. Because CO2 dissolves faster in cold water, areas like the Pacific Northwest will see more serious impacts from acidification. Many communities there rely heavily on the shellfish industry, which supports some 3,200 jobs and has an estimated economic impact of $270 million annually.

Prevention Is Better Than Cure:
Even though ocean and coastal acidification may sound scary, there are simple steps you can take to reduce your contribution to the problem. Simple choices and small behavior changes add up over time and across communities. The first step is to get the facts and make sure your family and community are aware that this issue is real, measurable, and happening now. Anything that reduces energy consumption or increases energy efficiency is the right move because such actions ultimately help to reduce carbon emissions and pollution.

A lower ocean pH has a range of potentially harmful effects for marine organisms. Scientists have observed for example reduced calcification, lowered immune responses, and reduced energy for basic functions such as reproduction.

Ocean acidification can impact marine ecosystems that provide food and livelihoods for many people. About one billion people are wholly or partially dependent on the fishing, tourism, and coastal management services provided by coral reefs. Ongoing acidification of the oceans may therefore threaten food chains linked with the oceans.

The only solution that would address the root cause of ocean acidification is to reduce carbon dioxide emissions. This is one of the main objectives of climate change mitigation measures. Carbon dioxide removal from the atmosphere would also help to reverse ocean acidification. In addition, there are some specific ocean-based mitigation methods, for example ocean alkalinity enhancement and enhanced weathering. These strategies are under investigation, but generally have a low technology readiness level and many risks.

We can tackle ocean acidification on multiple fronts. First and foremost, since we know ocean acidification is caused primarily by carbon pollution from fossil fuels, we know we have to advance the global transition to clean energy. Pollution regulations for power plants and stronger fuel-economy standards for our cars can help with that. Government leaders can also step up conservation efforts to protect and enhance the resilience of our forests, wetlands, and other critical carbon sinks, through initiatives like the 30x30 pledge, which sets aside 30 percent of our lands and waters to let ecosystems recover and withstand these growing challenges. Policymakers-recognizing the job sectors and other economic engines at risk from ocean acidification-are introducing climate action plans that promote increased investments in monitoring, forecasting, and mitigation. Considering the scale and rate of change, we need to prepare ourselves and safeguard vulnerable industries.

"While ocean acidification's effects have a global reach, local factors also influence how at risk regions are,". Some managers of West Coast oyster hatcheries, for example, have invested in monitoring systems. When harmful acidic water upwells on the coast, they shut off their intake valves to prevent baby oysters from being exposed. Other solutions include cultivating ocean acidification-resistant strains of shellfish and diversifying aquaculture systems.

For example, scientists are teaming up with fishermen to see how cultivating seaweeds like sugar kelp can potentially buffer farmed oysters, clams, and mussels from acidification as they absorb carbon dioxide from the salty water. The changes in our oceans are startling, and we don't yet fully understand what's to come as oceans acidify. But we know we must act. "We both love and need our oceans,". "If they fail, we all do."

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