海洋酸化：环境污染如何改变海洋化学及生态

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Do you ever think about how important the oceans are in our daily lives? The oceans cover two thirds of our planet. They provide half the oxygen we breathe. They moderate our climate and they provide jobs and medicine and food, including 20% of protein to feed the entire world population. People used to think that the oceans were so vast that they wouldn't be affected by human activities. Today, however, there is a serious reality changing our oceans, called Ocean Acidification or the Evil Twin of Climate Change. Did you know that the oceans have absorbed 25% of all the carbon dioxide that we have emitted to the atmosphere? This is a vital service, since carbon dioxide is one of the greenhouse gases causing climate change. But as we continue pumping more carbon dioxide into the atmosphere, more dissolves into the oceans, changing their chemistry. When carbon dioxide dissolves in seawater, it undergoes a series of chemical reactions. Essentially, as more carbon dioxide enters the ocean, the seawater pH drops, increasing ocean acidity, a process known as ocean acidification.

Scientists have been monitoring ocean acidification for over two decades. In Hawaii, an important time series shows a steadily increasing concentration of carbon dioxide gas in the atmosphere, directly due to human activities. Simultaneously, the amount of carbon dioxide dissolved in the ocean surface increases at the same rate. The resulting chemical changes show that seawater pH is decreasing, indicating rising ocean acidity. In Ireland, scientists at the Marine Institute and NUI Galway observe acidification at similar rates to global sites, proving this is a local issue as well. Monitoring involves collecting seawater samples during harsh winter conditions in the North Atlantic. Instruments are lowered from ships to measure temperature, dissolved oxygen, and other parameters at depths over 4 kilometers, sampling at regular intervals to the surface. Samples are then analyzed on board or in laboratories to track chemical changes.

Why should we care about ocean acidification? Already, ocean acidity has increased by 26% since pre-industrial times due to human activities. Without slowing carbon dioxide emissions, ocean acidity could rise by 170% by the end of this century, within our children's lifetime. This rate is ten times faster than any acidification in the past 55 million years, meaning marine life has never experienced such rapid changes. Historical natural acidification events occurred much more slowly and coincided with mass extinctions. Studies show some species may adapt, but many show negative responses. One major concern is the decrease of carbonate ions in seawater, which are essential for building shells and skeletons for many marine species, such as crabs, mussels, oysters, and corals.

As ocean acidity rises and carbonate ions decrease, species struggle to form shells; at extreme levels, existing shells can even dissolve. For instance, the sea butterfly, a crucial food source for species from krill to whales, experienced almost complete shell dissolution after 45 days in seawater with pH levels projected for the end of this century. This demonstrates that acidification could impact the entire food chain, affecting seafood on our plates. Cold-water corals off the Irish continental shelf support rich biodiversity and fisheries, but by 2100, 70% of these corals may face seawater capable of dissolving their structures. Tropical corals show similar vulnerability, threatening reefs that support 25% of all marine life globally.

The solution lies in reducing carbon dioxide emissions. Although oceans have already absorbed large amounts of CO2, we can still slow down acidification and global warming. Action is necessary for individuals, industries, and governments to maintain healthy oceans and a healthy planet for present and future generations. Protecting our oceans ensures sustainable ecosystems, food security, and the long-term balance of our climate.