User:Shanell.lovelace/Ocean acidification in the Arctic Ocean

=== Outline: ===

• Rewrite the introducing section to make it more clear and concise as to what we're talking about.
• Effects of Ocean Acidification on Arctic Organisms
  • "Organisms in Arctic waters are live in a very challenging environment with stressors including extreme cold temperatures. It is thought that because of this challenging environment, additional stressors such as ocean acidification, will cause ocean acidification effects on marine organisms to appear first in the Arctic." Doesn't make a whole lot of sense, they were literally evolved to live there.
  • Make separate sections about the different kinds of animals (calcifying organisms, non calcifying, etc.)
  • Maybe also make sections about the affect on the different stages of life (current article discusses larvae in great detail).
• Using this sentence to add some references

*****I reworked the intro to make it more concise and obvious what the topics would be*** Also, new pic!

Arctic drift ice, with a popular arctic organism, the polar bear

The Arctic ocean has experienced drastic changes over the years due to global warming. One of these changes is in the acidity levels of the Arctic ocean, which have been consistently increasing at twice the rate of the Pacific and Atlantic oceans. The increased acidity in the Arctic Ocean is a result of a variety of mechanisms, and is negativity impacting the Arctic Ocean ecosystem, as well as the organisms that live within it.

Reduction of sea ice is an important contributor to the acidification of the Arctic Ocean. The protective nature of the sea ice decreases without as much area being covered, causing carbon dioxide levels to increase in the water, and pH levels to decrease, leading to ocean acidification. The decrease in sea ice has also allowed more Pacific water to flow into in the Arctic ocean during the winter, this is called Pacific winter water, which further increases CO₂ levels in the Arctic.

Another important factor that affects how the Arctic Ocean is affected by acidification is the cold water's ability to absorb higher amounts of carbon dioxide compared to warm water. The solubility of gases decreases in relation to increasing temperature. Cold water bodies absorb the increasing amount of carbon dioxide in the atmosphere and become known as carbon sinks. The increasing amount of carbon dioxide in the water puts many organisms at risk as they are affected by the increase of acidity in the ocean water.

With these changes in the chemistry of their environment, arctic organisms are challenged with new stressors. These stressors can have damaging affects on these organisms, with some being affected more than others. Calcifying organisms appear to be the most impacted by this changing water, as they rely on carbonate to survive, a compound that decreases with increasing CO₂.

Effect of Sea Ice on Ocean Acidification

Arctic sea ice has experienced an extreme reduction over the past few decades. The lowest area of sea ice in 2019 was 4.32 million km², a sharp 38% decrease from 1980, when the lowest area was 7.01 million km². Sea ice plays an important role in the health of the Arctic Ocean, and its decline is causing acidifying effects to the chemistry of arctic water. As in all ocean ecosystems, the atmosphere equilibrates with ocean water. Specifically, carbon dioxide equilibrates with oceans in a reaction that produces hydrogen ions and carbonate ions, which lower the pH of the water. Sea ice limits the air-sea gas exchange with carbon dioxide by protecting the water from being completely exposed to the atmosphere, keeping the levels of carbon dioxide gas exchange low. With less sea ice cover to limit this carbon dioxide exchange, carbon dioxide levels have increased in the water, resulting in lowering the pH of the arctic water. This change in the chemistry of the Arctic Ocean causes ocean acidification. Low carbon dioxide levels are important to the Arctic Ocean due to intense cooling, fresh water runoff, and photosynthesis from marine organisms.

Effects of Methane Hydrates on Ocean Acidification

Climate change is causing destabilization of multiple climate systems within the ocean. One of these systems is methane hydrates. Methane hydrates are located along the continental margins, and are stabilized by low and high pressure fluctuations, as well as temperature. Climate change has begun to destabilize these methane hydrates within the arctic ocean by fluctuating pressure and increasing temperature, allowing methane to be released into the arctic waters. When methane from methane hydrates is released into the water, it can be used in anaerobic metabolism by microorganisms in the ocean sediment, reach the top of the water and enter into the atmosphere, or be used in aerobic oxidation by microorganisms in the water column. Most impactful to ocean acidification is aerobic oxidation by microorganisms in the water column. Carbon dioxide is produced by the reaction of methane and oxygen in water. This carbon dioxide then equilibrates with the water, producing bicarbonate, which then reacts with water to produce hydrogen ions and carbonate ions. The ultimate production of hydrogen ions and carbonate ions from the initial release of methane by methane hydrates contributes to ocean acidification in the Arctic Ocean.

The decrease in sea ice has also allowed more Pacific water to flow into in the Arctic ocean during the winter, this is called Pacific winter water. The Pacific water flows into the Arctic ocean carrying additional amounts of carbon dioxide by being exposed to the atmosphere and absorbing carbon dioxide from decaying organic matter and from sediments. - ***Thinking of adding this to this section, someone else can do it if I don't get to it***

*****I copied and pasted the below part so we can rework it into smaller sections, and make it more clear****

***It def needs more resources***

Effects of Ocean Acidification on Arctic Organisms[edit]

Organisms in Arctic waters are under high environmental stress such as extremely cold water. It is believed that this high stress environment will cause ocean acidification factors to have a stronger affect on these organisms. It could also cause these effects to appear in the Arctic before it appears in other parts of the ocean. There is a significant variation in the sensitivity of marine organisms to increased ocean acidification. Calcifying organisms generally exhibit larger negative responses from ocean acidification than non‐calcifying organisms across numerous response variables, with the exception of crustaceans, which calcify but don't seem to be negatively affected. This is due, mainly, to the process of marine biogenic calcification, that calcifying organisms utilize.

Calcifying Organisms

Carbonate ions (CO₃²⁻) are essential in marine calcifying organisms, like plankton and shellfish, as they are required to produce their calcium carbonate (CaCO₃) shells and skeletons. As the ocean acidifies, the increased uptake of CO₂ by seawater increases the concentration of hydrogen ions, which lowers the pH of the water. This change in the chemical equilibrium of the inorganic carbon system reduces the concentration of these carbonate ions. This reduces the ability of these organisms to create their shells and skeletons.

The two polymorphs of calcium carbonate that are produced by marine organisms are aragonite and calcite. These are the materials that makes up most of the shells and skeletons of these calcifying organisms. Aragonite, for example, makes up nearly all mollusc shells, as well as the exoskeleton of corals. The formation of these materials is dependent on the saturation state of CaCO₃ in ocean water. Waters which are saturated in CaCO₃ are favorable to precipitation and formation of CaCO₃ shells and skeletons, but waters which are undersaturated are corrosive to CaCO₃ shells. In the absence of protective mechanisms, dissolution of calcium carbonate will occur. Because colder arctic water absorbs more CO₂, the concentration of CO₃²⁻ is reduced, therefore the saturation of calcium carbonate is lower in high-latitude oceans than it is in tropical or temperate oceans.

The undersaturation of CaCO₃ causes the shells of calcifying organisms to dissolve, which can have devastating consequences to the ecosystem. As the shells dissolve, the organisms struggle to maintain proper health, which can lead to mass mortality. The loss of many of these species can lead to intense consequences on the marine food web in the Arctic Ocean, as many of these marine calcifying organisms are keystone species. Laboratory experiments on various marine biota in an elevated CO₂ environment show that changes in aragonite saturation cause substantial changes in overall calcification rates for many species of marine organisms, including coccolithophore, foraminifera, pteropods, mussels, and clams.

Although the undersaturation of arctic water has been proven to have an effect on the ability of organisms to precipitate their shells, recent studies have shown that the calcification rate of calcifying organisms, such as corals, coccolithophores, foraminiferans and bivalves, decrease with increasing pCO₂, even in seawater supersaturated with respect to CaCO₃. Additionally, increased pCO₂ has been found to have complex effects on the physiology, growth and reproductive success of various marine calcifiers.

Life Cycle

A sea urchin, cracked open to reveal the eggs inside. These eggs hold the embryo stage of this organism.

CO₂ tolerance seems to differ between various marine organisms, as well as differences in CO₂ tolerance at different life cycle stages (e.g. larva and adult). The first stage in the life cycle of marine calcifiers which are at serious risk by high CO2 content is the planktonic larval stage. The larval development of several marine species, primarily sea urchins and bivalves, are highly affected by elevations of seawater pCO₂. In laboratory tests, numerous sea urchin embryos were reared under different CO₂ concentrations until they developed to the larval stage. It was found that once reaching this stage, larval and arm sizes were significantly smaller, as well as abnormal skeleton morphology was noted with increasing pCO₂.

Similar findings have been found in CO₂ treated-mussel larvae, which showed a larval size decrease of about 20% and showed morphological abnormalities such as convex hinges, weaker and thinner shells and protrusion of mantle. The larval body size also impacts the encounter and clearance rates of food particles, and if larval shells are smaller or deformed, these larvae are more prone to starvation. In addition, CaCO₃ structures also serve vital functions for calcified larvae, such as defense against predation, as well as roles in feeding, buoyancy control, and pH regulation. Another example of a species which may be seriously impacted by ocean acidification is Pteropods, which are shelled pelagic molluscs which play an important role in the food-web of various ecosystems. Since they harbor an aragonitic shell, they could be very sensitive to ocean acidification.Laboratory tests showed that calcification exhibits a 28% decrease at the pH value of the Arctic ocean expected for the year 2100, compared to the present pH value. This 28% decline of calcification in the lower pH condition is within the range reported also for other calcifying organisms such as corals. In contrast with sea urchin and bivalve larvae, corals and marine shrimps are more severely impacted by ocean acidification after settlement, while they develop into the polyp stage. From laboratory tests, the morphology of the CO₂-treated polyp endoskeleton of corals was disturbed and malformed compared to the radial pattern of control polyps.

This variability in the impact of ocean acidification on different life cycle stages of different organisms can be partially explained by the fact that most echinoderms and mollusks start shell and skeleton synthesis at their larval stage, whereas corals start at the settlement stage. Hence, these stages are highly susceptible to the potential effects of ocean acidification. Most calcifiers, such as corals, echinoderms, bivalves and crustaceans, play important roles in coastal ecosystems as keystone species, bioturbators and ecosystem engineers. The food web in the arctic ocean is short and simple. Any impacts to key species in the food web can cause exponentially devastating effects on the rest on the food chain as a whole, as they will no longer have a reliable food source. If these larger organisms no longer have any source of nutrients, they too will eventually die off, and the entire Arctic ocean ecosystem will be affected.