VOA慢速英语2021--科学家致力于解开加勒比海海藻之谜

Scientists Work to Solve Caribbean Seaweed Mystery

Ten years ago, scientists were shocked when a huge amount of seaweed appeared in tropical waters in the Atlantic Ocean. The area where it was found usually lacks the nutrients¹ to feed such growth.

Years later, a group of U.S. researchers has identified one of the leading causes for the event: city and farm runoff carried by rivers to the ocean. This nutrient-charged outflow is just one of several likely suspects fueling an explosion of seaweed in warm waters of the Americas.

Scientists around the world say they suspect the cause involves a complex mix of climate change, Amazon rainforest destruction and dust blowing west from Africa's Sahara Desert.

"There are probably multiple factors" driving the growth, said Ajit Subramaniam. He is an ocean expert at Columbia University.

"I would be surprised if there is one clear villain²," he added.

Seaweed is a kind of plant that grows in the sea. The dark-brown seaweed is also known as sargassum.

A recent study examined the chemistry of sargassum from the 1980s up to 2019. The results of the study offered the strongest evidence yet that water coming from sewage and agricultural runoff played a major part in the expansion of the so-called Great Atlantic Sargassum Belt. The area now stretches for nearly 9,000 kilometers.

Nitrogen runoff

The study found that sargassum recently collected in coastal³ waters from Brazil to the southern United States contained levels of nitrogen that were 35 percent higher than in samples taken more than 30 years ago.

The study's findings appeared earlier this year in the publication Nature Communications.

Nitrogen is found in human and animal waste and in fertilizers. The results suggest that runoff flowing into rivers throughout the Americas and into the ocean is feeding sargassum growth. Ocean flows, or currents, carry much of this seaweed to the Caribbean Sea.

The researchers found that changes in the Amazon River have played a big part in the seaweed growth.

Brian Lapointe is one of the writers of the recent study. He is with Florida Atlantic University. He told Reuters that stronger rainstorms over the Amazon have led to more extreme flooding. This, he said, is likely pushing more nitrogen-rich runoff out to sea.

Experts note that extreme Amazon River flooding pushes a large amount of nutrients hundreds of kilometers out to sea during March and April. That is also when sargassum blooms appear. From there, currents push the seaweed around the coast of Venezuela into the Caribbean Sea. Sometimes, the seaweed makes it farther north into the Gulf⁵ of Mexico.

Climate change is also fueling stronger hurricanes. The ocean storms can pull more nutrients up from the seabed to possibly fertilize⁴ sargassum.

African dust and ash

Scientists have also suggested that dust from the Sahara Desert, along with smoke and ash, could play a part in the seaweed boom. As the particles are blown west over the Atlantic Ocean, they run into clouds. They then get rained down as iron and phosphorus deposits in the water.

It will take many more years of research to prove exactly how much each of these conditions may be contributing to sargassum's growth. But scientists say there are still things governments can do to make a difference.

"This phenomenon will continue until there is a change in public policy," said Carlos Noriega. He is an oceanographer at Brazil's Federal University of Pernambuco. Brazil, for example, could slow deforestation, which has led to a rise in cattle ranching⁶. Raising cattle leads to loose soil, waste and fertilizer washing into rivers.

Noriega also noted⁷ the rising human population in Brazil's Amazon area. The five largest cities in the area have grown by nearly 900,000 people since 2010. Much of the region lacks effective sewage treatment.

"Treating sewage and stopping deforestation, Noriega said, "that's the only way to control it."

Words in This Story

tropical - adj. of, relating to or happening in the tropics

multiple - adj. more than one, several

villain - n. someone or something that is blamed for a specific problem

sewage - n. waste material

sample - n. a small amount that is taken to get information

fertilizer - n. a substance that is added to soil to help plants grow

hurricane - n. an extremely large and powerful storm

phenomenon - n. something interesting that can be observed and studied

region - n. part of a country or world that is different than others in some way

1 nutrients   

n.（食品或化学品）营养物，营养品( nutrient的名词复数 )

参考例句：

• a lack of essential nutrients 基本营养的缺乏
• Nutrients are absorbed into the bloodstream. 营养素被吸收进血液。 来自《简明英汉词典》

2 villain   

n.反派演员，反面人物；恶棍；问题的起因

参考例句：

• He was cast as the villain in the play.他在戏里扮演反面角色。
• The man who played the villain acted very well.扮演恶棍的那个男演员演得很好。

3 coastal   

adj.海岸的，沿海的，沿岸的

参考例句：

• The ocean waves are slowly eating away the coastal rocks.大海的波浪慢慢地侵蚀着岸边的岩石。
• This country will fortify the coastal areas.该国将加强沿海地区的防御。

4 fertilize   

v.使受精，施肥于，使肥沃

参考例句：

• Fertilizer is a substance put on land to fertilize it.肥料是施在地里使之肥沃的物质。
• Reading will fertilize his vocabulary.阅读会丰富他的词汇。

5 gulf   

n.海湾；深渊，鸿沟；分歧，隔阂

参考例句：

• The gulf between the two leaders cannot be bridged.两位领导人之间的鸿沟难以跨越。
• There is a gulf between the two cities.这两座城市间有个海湾。

6 ranching   

adj.放牧的

参考例句：

• They cleared large tracts of forest for farming, logging and ranching. 他们清除了大片的森林以经营农耕、采伐与畜牧。
• This is a trade center in a ranching and oil-producing region. 这是一个牧场与产油区的贸易中心。

7 noted   

adj.著名的，知名的

参考例句：

• The local hotel is noted for its good table.当地的那家酒店以餐食精美而著称。
• Jim is noted for arriving late for work.吉姆上班迟到出了名。