In recent years, the problem of marine waste has attracted considerable attention. Zheng, a researcher at the Biodiversity Research Center of China Academy of Sciences, formed a team to analyze marine floating garbage in seven marine regions of the world in the past 25 years by using big data calculation. The results show that both wind resistance effect and ocean current will affect the distribution of waste, and gradually transfer from subtropical zone to tropical zone and polar zone, among which the marine waste in the Pacific Ocean is the most serious, and 50% of the waste continues to drift at sea. The paper was published in Environmental Research Letters on June 6, 2020.
Where does the floating garbage come from?
Zheng, who grew up with the sea, was deeply saddened by the pollution of the sea. "Before we went out, we all went diving by boat, and the sea was very clean. Everyone only pays attention to whether there are whales, dolphins or seabirds. It's different now. At first glance, the sea surface is almost garbage! " Especially in some areas, there is more garbage. For example, the Pacific Garbage Patch is located in the Pacific Ocean, with an area nearly 50 times that of Taiwan Province Province in China, and it is still expanding. These rubbish are semi-floating in the sea and can't be seen from the plane.
Zheng has witnessed the changes of the world's oceans for decades and pointed out that marine garbage is the most serious environmental problem at present. The picture shows plastic garbage floating on the sea surface, taken underwater. iStock
There are many kinds of marine garbage, 20% will float and 80% will sink, such as fishing nets. It is estimated that 4.8 million ~ 1.27 million tons of floating garbage will flow into the sea every year, of which 50% may be washed ashore by wind and waves, and the rest will continue to float, and will be weathered, decomposed, broken into plastic particles and even become nano-sized. After being eaten by tiny zooplankton, it will be eaten by small fish, shrimp and big fish, spread through the food chain and accumulate in biological viscera and muscles.
Many scientists are studying the effects of plastic garbage and particles on marine life. A famous example is the "midway island" in the Hawaiian Islands. The local albatross mistook plastic for food and swallowed it. Parents feed their young birds with plastic. Scientists dissected dead albatrosses and found that their stomachs were full of rubbish. Other creatures, such as whales, sea lions and seals, also have a lot of rubbish in their bellies.
The green turtle thought that the plastic bag was a jellyfish, and swallowed it in one gulp, but it had no taste, could not be said, could not be spit out, and accumulated in his stomach. Professor Cheng Yijun from Ocean University of Taiwan Province Province, China has been studying green turtles for a long time and found that the dead green turtles had all kinds of garbage in their bellies. iStock
In addition, plastics contain plasticizers, which will cause harm to organisms when dissolved in the sea. At the same time, it is also an environmental hormone, which will shrink male shellfish and feminize animals. "However, because plasticizers have no acute toxicity, plastic particles will not die immediately, and many people are indifferent to marine garbage and are fearless. Zheng said to him.
Establish an analysis model from Dongsha Island
The research team of floating garbage in the sea consists of Zheng, Xin Yijia, a researcher at Academia Sinica, and Ke Jiayin, an associate professor at National Taiwan University Fisheries Institute. Establish an analysis model from Dongsha Island. Why choose Dongsha Island as the inspection site? Zheng said, "I have been to Dongsha Island more than 50 times. It was clean more than 20 years ago, and now there is so much garbage floating in the sea! I want to know where the rubbish comes from. 」
Zheng found an amazing amount of garbage floating on Dongsha Island. The picture shows the garbage floating on the shore of Dongsha Island. a surname
Moreover, although there are troops stationed in Dongsha Island, littering is prohibited. Team Zheng believes that the garbage in Dongsha Island comes from other places, which is a good place to establish a marine garbage tracking model. They are on a beach in the south and north of Dongsha Island. Every month, colleagues from the Marine National Park Management Office, Shangdao's research team and soldiers from the Coast Guard help to investigate the floating garbage in the sea and analyze its composition. After identification, it was found that most of them came from China or Southeast Asian countries.
In order to find out the source of floating garbage, colleagues from the Ocean National Park Management Office, a research team from Shangdao and soldiers from the Coast Guard assisted in investigating floating garbage and analyzing its composition. After identification, it was found that most of them came from China or Southeast Asian countries. a surname
Then the team collects data from countries or relevant units through the Internet, such as collecting global ocean current and wind direction data of the National Oceanic and Atmospheric Administration (NOAA) for 25 years, collecting seawater temperature of the Meteorological Bureau, and collecting fishing boat operation sites of the fishery department for big data analysis.
In Dongsha Island, there is northeast monsoon in winter and southwest airflow in summer. There is more garbage from China in winter and more garbage from Viet Nam in summer. The team threw all the collected data such as ocean current and wind direction into the computer, established a model, traced the floating garbage in Dongsha Island in the opposite direction, and compared it with the garbage source actually investigated in the local area, and found that it was consistent with the above data, indicating that this theoretical model was established.
Global analysis of marine floating garbage
After the success of Dongsha Island's model, the team found that the floating garbage came from all directions, so they began to understand the motivation of global floating garbage, and then used data simulation to analyze the trend of global floating garbage. The research team divided a latitude and longitude into three grids, simulated throwing 10 garbage into each grid in the global sea area, and observed where they would be taken by ocean currents and winds from 1993 to 20 17. Associate researcher Xin Yijia explained that wind resistance effect is an important factor to push marine garbage to shore and coast, which is the first time in the world to add wind resistance effect to analyze the trend of marine garbage.
The drag coefficient (Cw) of marine floating garbage is 0~0. 1. Garbage with high resistance coefficient may be blown ashore by the wind, and garbage with low resistance coefficient may float on the sea surface. The higher the Cw, the greater the resistance to the wind, such as large styrofoam, which is easy to run to the shore with large wind surface; Plastic slippers with Cw of 0 will not sink and the wind will not move, unless there is a big wave, they will be swept ashore. I have something to study.
As can be seen from the following figure, in the marine area with low wind resistance coefficient, the proportion of marine garbage discarded is greater than that of water, and it is mainly accumulated at 30 north latitude and 25 ~ 50 south latitude; Sea drifts with medium and high wind resistance coefficient, such as styrofoam and Bote bottles, have smaller specific gravity than seawater and are easy to drift with the wind, at the north latitude 10 and >: area 60. In addition, coastal garbage is not easy to be affected by wind, regardless of wind resistance, it is concentrated in tropical areas between north latitude 10 and south latitude 5 ~ 15.