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下面为大家整理一篇优秀的assignment代写范文- Harm of ocean acidification，供大家参考学习，这篇论文讨论了海洋酸化的危害。海洋酸化，指的是由于海洋吸收大气中过量的二氧化碳，使海水逐渐变酸。目前海洋每年吸收的二氧化碳都在80亿吨左右，虽然对于减缓气候变暖起到了重要的作用，但海洋也为此付出了高昂的代价。有结果表明，海洋酸化在古代生物灭绝中起到了极大的作用。如果海洋酸化的问题再不解决，我们可以预见到它对某些海洋生物的影响，其中贝类动物面临的风险最大。

More than 250 million years ago, the earth experienced one of the most dramatic extinction crises, with about 90 percent of Marine life and 70 percent of terrestrial life disappearing. Exactly what caused so many species to die off has long been a matter of debate.

Now, a new study offers important clues. Scientists believe that ocean acidification, caused by rising levels of carbon dioxide in the air, may have played a crucial role in the ancient extinction event. Marine life with calcium carbonate shells, in particular, is particularly vulnerable to acid conditions.

Ocean acidification refers to the gradual acidification of seawater as the ocean absorbs excess carbon dioxide from the atmosphere. The term "ocean acidification" first appeared in the famous British scientific journal nature in 2003. The oceans currently absorb about 8 billion tons of carbon dioxide a year, and while it has played an important role in slowing warming, the oceans have also paid a high price.

As atmospheric concentrations of carbon dioxide rise over the next few decades, and the seawater that absorbs the gas eventually becomes more acidic, the earth is likely to head toward another serious extinction event that could repeat the history of more than 250 million years ago.

Canada ocean physicist alvaro monte Montenegro said: "although compared with many other what is happening, the role of acidification of the oceans, in fact, it is difficult to quantify, but our results clearly show that ocean acidification in the ancient extinction events plays a major role, played a great role."

It is clear that humans have made and will continue to make the oceans more acidic, and we can expect it to affect some Marine life, of which clams, mussels and other aquatic shellfish are most at risk. The results suggest that life may not be able to adapt quickly enough to change the ocean's pH.

PH is a measure of the activity of hydrogen ions in a solution, which is generally a measure of the pH of the solution. The higher the pH goes to zero, the more acidic the solution. And the more we go to 14, the more alkaline the solution is. At room temperature, a solution with a pH of 7 is neutral.

The evolution of life is interspersed with many major extinction events, including the one that wiped out most dinosaurs about 65 million years ago. The sequence of the most extreme events so far goes back more than 250 million years. The Permian ~ Triassic extinction event is a mass extinction event that occurred between the Permian and Mesozoic Triassic about 250 million years ago. In terms of lost species, 70% of earth's terrestrial vertebrates and up to 96% of all sea life disappeared. The extinction also caused the only mass extinction of insects, with 57 percent of "families" and 83 percent of "genera" disappearing. It took millions of years for the terrestrial and Marine ecosystems to fully recover, longer than other mass extinctions. PTB is the largest of five mass extinctions in the geological era, so it's informally called a "mass extinction," or "mother of mass extinctions." It took at least 100, 000 years for the ocean to return to normal after an estimated 450 gigatons of dissolved carbon dioxide were blamed for an extinction event 65 million years ago.

Scientists know that giant volcanic eruptions send huge amounts of methane and carbon dioxide into the atmosphere at very high temperatures. Geological studies have shown that oxygen levels in parts of the ocean floor are very low, but it's still not clear what causes it.

In order to solve some of the mystery, alvaro monte Montenegro and his colleagues created a computer model, simulation and extinction in before extinction. The model includes a continent that is precisely aligned according to historical circumstances, and also the first time the ridg-strewn seafloor has emerged to create a lifelike pattern of flow circulation. After setting the temperature and carbon dioxide concentrations to the maximum levels they assumed existed at the time, the researchers looked at what would happen in the ocean. Their results confirm that warmer climates do not account for the record of changes in the oceans at PTB, and that high levels of carbon dioxide alone can cause a significant drop in the ocean's pH.

British geologist helwig Noel Paul said: "as for why the extinction of oxygen at the bottom of the ocean is so little, the model does not provide much evidence, it shows that we need to do a lot of research work, can we truly understand occurred in the biggest extinction event in the history of the earth."

But acidification, or lack of oxygen, is an impending crisis in the modern ocean. The fossil record shows that the aquatic shellfish were destroyed in PTB because the acidic environment made it difficult for them to secrete and feed their shells.

The severity of the problem has been exacerbated by the cold water, which means aquatic shellfish in the higher latitudes face the greatest threat today. According to the researchers' projections, the first casualties could be pteropods between 2030 and 2050. These snails live in surface waters at high latitudes, forming the lowest end of many fish and bird food chains. Between now and 2030, the southern hemisphere's oceans will corrode snails' shells. These mollusks are an important source of salmon in the Pacific, and if their populations decline or disappear in some areas, that could affect the salmon fishing industry. In addition, the loss of coral reefs in the sea's continental shelf, which generate billions of dollars a year for tourism, will be a major setback for tourism.

Today's oceans are more acidic as more carbon dioxide enters the atmosphere through fossil fuels and other sources and is likely to spread southward into warmer waters, threatening creatures such as clams, oysters and corals.

Since the industrial revolution, more than a third of the carbon dioxide released by human activities has been absorbed by the ocean, increasing the concentration of hydrogen ions in surface waters by 30 percent over the past 200 years and lowering pH by 0.1. The increasing acidity of sea water breaks the balance of Marine chemistry and threatens the Marine ecosystem. Many Marine organisms and even ecosystems that depend on the stability of chemical environment are faced with huge threats. The extinction of some shellfish is a strong proof of ocean acidification. Ocean acidification has also severely damaged biodiversity and caused the emergence of some invasive species. As the main force of photosynthesis in the ocean, phytoplankton species are numerous, their physiological structures are diverse, and their ability to use different forms of carbon in the sea water is also different. Ocean acidification will change the conditions of competition among species.

With so much carbon dioxide being absorbed, the oceans are acidifying at an unprecedented rate. At present, the only effective solution to the problem is to reduce carbon dioxide emissions.

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