Ningbo, a coastal city in Zhejiang province, is bringing into play the potential of its ecosystems to achieve carbon neutrality, as 2,340 metric tons of "blue carbon" credits were auctioned off in the city on Tuesday.

The concept was introduced in the report Blue Carbon: The Role of Healthy Oceans in Binding Carbon by the United Nations Environment Programme in collaboration with the UN Food and Agriculture Organization and the UN Educational, Scientific and Cultural Organization in 2009.

It refers to carbon that is absorbed from the atmosphere and stored in coastal and marine ecosystems. Scientific studies show that the ocean stores 50 times more carbon than the atmosphere, and 20 times more than land plants and soil combined. Mangroves, tidal marshes and seagrasses are recognized as three major blue carbon sinks as both their plants and sediment below can sequester and store large quantities of carbon.

Based on the quantity of carbon they absorb and store, the ecosystems generate blue carbon credits that are sold to buyers who want to offset their carbon emissions.

The market for blue carbon credits is relatively new in China. Those sold on Tuesday were generated by three varieties of algae — kelp, seaweed and sea lettuce — at Xihu Port in the city's Xiangshan county.

"Algae is part of marine fishery carbon sinks. Due to accounting difficulties, it has not entered the international carbon markets. It's a blue ocean of blue carbon trading," said Yan Xiaojun, the Party secretary of Zhejiang Ocean University.

It was the first time a blue carbon credit has been auctioned in China.

He Congying, an associate researcher at Ningbo Institute of Oceanography, stressed that such auctions will promote the development of ecological products, and encourage company engagement in protection efforts.

Wang Yuan, a manager at Zhejiang Yiduan Precision Machinery, which won the auction, said the blue carbon credits will be used to offset the company's carbon emissions.

Zhu Wenrong, general manager of Xuwen Seaweed, sold nearly 200 tons of blue carbon credits at the auction.

"The sea lettuce that we raise is a great carbon sink. Now we can turn its ecological value into cash."

Zhu said the income from the auction will be used in research on sea lettuce cultivation and its carbon sequestration.

"I hope Xiangshan's blue carbon economy and coastal economy will receive more attention," he said.

In June, Ningbo released a strategy to reach peak carbon emissions and carbon neutrality, which included improving blue carbon ecosystems and tapping the market for blue carbon credits.

Ding Dewen, an academician at the Chinese Academy of Engineering, said, "It will serve as a model for the development of blue carbon projects in coastal cities across the country."

Yu Yincontributed to this story.