Looking into the distance, it is the same color; Close up, is the blue waves, the feeling of the day high brow; Smell, its own slowly salty wind and come... In recent years, the seemingly unfamiliar term "acidification" has been creeping into public view in a different way.

So is the sea really turning sour? Why does it turn sour? Who are the victims of ocean acidification?

On April 15, the 4th International Symposium of the Global Ocean Acidification Observation Network (GOPN) was held in Hangzhou. More than 270 well-known experts, scholars and industry representatives from more than 60 countries gathered here, and a brainstorming session on global ocean acidification was launched.

Schematic of the effects of ocean acidification on shellfish and other organisms. Photos in this edition (except where indicated) are provided by Ocean Institute 2

Seawater pH over the last 200 years

Why the apparent decline?

What is ocean acidification? It's a long process of chemical change.

Chai Fei, a researcher at the State Key Laboratory of Satellite Marine Environmental Dynamics, explained that acidification is a phenomenon in which seawater absorbs excess carbon dioxide from the air, which dissolves in seawater and forms carbonic acid, resulting in a series of chemical reactions that lead to a drop in seawater pH.

PH is a major indicator of seawater acidification. In general, surface ocean water has a pH of about 8.2 and is weakly alkaline. Available scientific evidence suggests that the oceans have absorbed about 30 percent of human-produced carbon dioxide over the past 200 years, with about 50 percent remaining in the atmosphere. Carbon dioxide uptake by the oceans has minimized the effects of global warming, but it has also reduced the average pH of surface waters from 8.2 at the start of the industrial revolution to 8.1 today.

A change of 0.1 May seem like a trivial amount at first glance, but over a longitudinal time span of tens of millions of years, it is a significant number.

In fact, the pH value of seawater is not fixed. The pH value of high latitude sea is higher than that of low latitude, and the pH value of surface seawater is also higher than that of deep seawater. But in the context of the ocean as a whole, the change in pH is small, with a range of ±0.3 over 20 million years. Compared with the 0.1 drop in our ocean system in just over 200 years, the change is huge.

According to the Intergovernmental Panel on Climate Change (IPCC), the global average pH of seawater will continue to decrease by 0.3 to 0.4, from 8.2 to 7.9 or 7.8 by 2100. By then, sea water will be about 100 to 150 percent more acidic than it was at the start of the industrial Revolution. Based on this, the global average pH of seawater is likely to fall by about 0.5 by 2300.

In fact, there is no precedent in Earth's geological history for large changes in ocean pH.

55 million years ago, the melting of "combustible ice" at the bottom of the sea released huge amounts of methane, causing a sudden increase in greenhouse gases in the atmosphere. In just a few thousand years, the Earth's temperature rose by about 6 ° C. Two trillion tons of carbon dissolved into the ocean, the pH of the water plummeted, causing a massive dissolution of seafloor carbonates, which in turn led to the extinction of a large number of Marine benthic organisms. All four mass extinctions in Earth's history have been accompanied by acidification. The warning from past experiences is that the ongoing acidification of oceans should not be taken lightly.

And the "main culprit" of seawater acidification is the excessive emissions of carbon dioxide in human production and life.

Long-term monitoring at Mauna Loa and Aloha stations in Hawaii, USA, showed that atmospheric carbon dioxide concentrations were increasing at a rate of about 1.7 parts per million (PPM) per year through 2017, with increasing PCO2 at the ocean surface, while the pH of ocean surface waters continued to decrease. Moreover, the monitoring results of all monitoring stations around the world, including WHOTS buoy, KEO buoy and Papa buoy, showed a similar trend. The scientists also found that the acidification of the ocean today is unprecedented, and has not occurred during either prehistoric or interglacial periods.

"Ocean acidification is an important ecological problem facing mankind." Chen Dake, academician of the Second Institute of Oceanography, Ministry of Natural Resources.

Ocean acidification impacts shellfish farming

Since the scientific problem of "ocean acidification" was first proposed in Nature in 2003, the understanding of "ocean acidification" is changing from a simple and abstract academic term to a concrete and vivid one.

"Acidification is a progressive process that extends not only from the initial ocean surface to 500 meters and 1,000 meters below sea level, but also from the open ocean to the marginal ocean and the offshore ocean." "Said researcher Chai Fei.

The increasing acidity of sea water will change the balance of chemical properties of sea water, posing a great threat to Marine life and ecosystems that depend on the stability of the chemical environment, Prof. Chen said. Global ocean acidification is progressing at an unprecedented rate. Ocean acidification is also profoundly affecting the fragile Marine ecosystems of the Arctic and Southern oceans, two of the most important oceans on either side of the globe.

Professor Richard Feely, a famous American oceanographer, had a similar view. Ocean acidification will eventually lead to a series of chemical changes in the Marine system that will affect the physiology, growth, reproduction, metabolism and survival of most Marine organisms, he said.

Creatures with calcium carbonate bones are the first to suffer from a drop in pH. In the surface water, carbonate is saturated, and some Marine organisms can form calcium carbonate skeletons normally, but in deeper water, as pressure and temperature increase, the carbonate concentration becomes less saturated, and the pH of the water decreases, and the calcium carbonate dissolves. "Acidification is when the pH of the surface water goes down and carbonate saturation goes down. As a result, organisms that are protected or supported by calcium carbonate bones cannot survive." "Said researcher Chai Fei.

In the oceans, calcium carbonate skeletons are found in numerous organisms, from planktonic foraminifera and coccolithophores to mussels, oysters, echinoderms and crustaceans, which play a prominent role in maintaining biodiversity, and some of them are economically important.

"As far as human society is concerned, the first thing to be affected by ocean acidification is offshore aquaculture." "Said Professor Dai Minhan, academician of the Chinese Academy of Sciences and director of the State Key Laboratory of Offshore Marine Environmental Sciences. The impact is particularly significant for shellfish farming industries such as oysters along the Chinese coast and in California and Washington state.

In past studies, Chaifei has been impressed by young oysters raised in California that have failed to develop properly because of acidification. "In normal seawater, most of these baby oysters and oysters can develop normally; But in acidified water, they tend to be stunted and die in about 20 days." "Said researcher Chai Fei.

When we look from the global to domestic, we find that the negative impact of ocean acidification on shellfish farming is not limited to the United States and other countries. China is the world's largest aquaculture producer, accounting for more than 60 percent of global mariculture production, according to researcher Chai Fei. The aquaculture of shellfish accounts for about 30% of the world's total. Therefore, the impact of coastal seawater acidification on shellfish farming in China cannot be ignored.

Recent studies have shown that in addition to the impact on yield, acidification of seawater also changes the taste of aquatic products to a certain extent. A Swedish scientist has conducted controlled experiments with shrimp reared in different acidified environments. It was found that shrimp grown in acidified environment were significantly inferior to the control group in terms of meat quality and taste. The results of such experiments should be the most intuitive to the average resident.

However, experts say that despite the taste, there has been no evidence that eating seafood grown in acidified environments is harmful to human health.

The "smart ocean" system protects the Marine ecology

"If you want to stop this trend, the best way of course is to reduce the concentration of carbon dioxide in the atmosphere, but that is not easy." Says Bronte Tilbrook, co-chair of the Global Ocean Acidification Observatory (GOA-ON) at Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO).

In the opinion of Prof. Dai Minhan, the key to solving the problem of ocean acidification is to gradually clarify the driving factors of ocean acidification and to find solutions through more systematic scientific research. In 2016, the Ministry of Agriculture and Rural Affairs set the goal of "reducing pesticides and fertilizers", as well as the country's efforts to optimize the energy structure and green travel, which will help reduce carbon dioxide emissions and ease ocean acidification.

Many Marine scientists have reached a consensus that ocean acidification is a global ecological problem that requires global participation. The Global Ocean Acidification Observatory (GOA-ON) has carried out cutting-edge exploration and important practice in this field.

The Global Ocean Acidification Observatory (GOA-ON), established in 2012 by the National Oceanic and Atmospheric Administration (NOAA), the International Atomic Energy Agency (IAEA), the Intergovernmental Oceanographic Commission (IOC) and other agencies, is a platform for international cooperation ON global ocean acidification research. In recent years, GOA-ON has organized global ocean acidification related work, such as observing the state of ocean acidification in the open ocean, offshore and estuarine regions, assessing the impact of ocean acidification ON Marine ecosystems, analyzing the driving factors of ocean acidification, and providing high spatio-temporal resolution data to optimize ocean acidification analysis and prediction models. So far, 94 countries have participated, and China is a member of the organization.

Jan Newton, an oceanographer from the University of Washington and co-chair of the symposium, said that China is the initiator and participant of GOA-ON and has been actively involved in the organization and development of the international platform.

"The offshore sea and the deep sea are interconnected. Only by comprehensively understanding the overall situation of the sea can we better monitor and protect the offshore Marine environment and resources." "Said researcher Chai Fei, the organizer and co-chairman of the symposium. A few decades ago, China's Marine scientific research mainly focused on the Bohai Sea, the Yellow Sea, the East China Sea and the South China Sea due to limitations on the ability to go out to sea, the capacity of research vessels, and the staffing and training of research personnel. In recent years, the influence of the western Pacific basin from the equator to the Kuroshio, as well as the extension of the coast of Japan, on our shore has been gradually brought into the field of view of Chinese Marine science research. "In the last five to 10 years, with the strong promotion of China's Marine science research technology and training of Marine science and technology talents, China's Marine science research will gradually move from the offshore China to the deep sea." Researcher Chai Fei said this is the trend of Marine science research.

In addition, researcher Chai Fei also told reporters that the existing satellite remote sensing, numerical word simulation, three-dimensional monitoring and other technologies of his State Key laboratory can be used to monitor the Marine environment, which can be combined with ecology, biogeochemistry and other disciplines to jointly carry out the study of ocean acidification, which is also a major direction of his team's future efforts. "At present, scientists are building Marine monitoring systems in the East China Sea and the Western Pacific Ocean, and will further expand the coverage in the future, in order to build a 'smart ocean' system through big data and artificial intelligence, and better protect the global Marine ecological environment."

The rain has leveled the river sea blue. As the forces of all countries converge, the balance of Marine ecology may no longer be a difficult problem to solve.