VOA标准英语2011--Melting Arctic Could be Major Source of Greenhouse Gases

Melting Arctic Could be Major Source of Greenhouse Gases

 

The melting arctic permafrost could release methane¹-producing microbes with the potential to accelerate climate change, according to a new study published in Nature.

Lead author Janet Jansson, senior scientist at the Lawrence Berkeley National Laboratory in California says the trapped microorganisms in permafrost are still active.

Jansson and colleagues at the U.S. Geological Survey and the Joint³ Genome Institute at the Department of Energy set out to identify microbes in permafrost and find out what they would do once thawed⁵.

“They had never been cultured," Jansson says. "So more than 90 percent of those bacteria and other microorganisms in permafrost, we had no idea what they were.”

Billions of metric tons of climate changing emissions6 could escape from the Alaskan permafrost as temperatures melt the frozen soils.

The researchers analyzed⁷ three soil cores from the soft, peat floor of a black-spruce forest in central Alaska. A single gram of that soil could harbor thousands of different species and billions of cells.

Jansson says the fact that those microorganisms had never been grown in the laboratory made them difficult to study. What they did instead, she says, was to extract the total DNA⁸ from the samples. "We used a sequencing approach to get information about both the identities of the microorganisms and also all of the bio-chemical pathways that they had in the permafrost before and after thaw⁴.”

The team identified single-celled organisms that feast on organic material in the soil and produce methane, a greenhouse gas more potent² than carbon dioxide. Jansson says methane-eaters were also among the microbes in the thawed permafrost. “Some of the methane was being consumed by other microorganisms in the samples, and they in turn would release, CO2, carbon dioxide.”

Core samples for microbial analysis are retrieved9 from the Alaskan permafrost.

The scientists compared samples from the upper permafrost layer - which melts and refreezes seasonally¹⁰ - and the permanently¹¹ frozen permafrost in which microbes have been trapped for millennia¹².

While initially¹³ very different the two samples became more similar after thawing¹⁴, Jansson says. “Those two very disparate samples started to converge¹⁵, both the microorganisms that were present and also their functions started to converge and became much more similar to what we saw in the seasonally thawed active layer samples.”

Jansson says understanding how microbes respond during a thaw can help improve models that chart the earth’s climate.

1 methane   

n.甲烷，沼气

参考例句：

• The blast was caused by pockets of methane gas that ignited.爆炸是由数袋甲烷气体着火引起的。
• Methane may have extraterrestrial significance.甲烷具有星际意义。

2 potent   

adj.强有力的，有权势的；有效力的

参考例句：

• The medicine had a potent effect on your disease.这药物对你的病疗效很大。
• We must account of his potent influence.我们必须考虑他的强有力的影响。

3 joint   

adj.联合的，共同的；n.关节，接合处；v.连接，贴合

参考例句：

• I had a bad fall,which put my shoulder out of joint.我重重地摔了一跤，肩膀脫臼了。
• We wrote a letter in joint names.我们联名写了封信。

4 thaw   

v.（使）融化，（使）变得友善；n.融化，缓和

参考例句：

• The snow is beginning to thaw.雪已开始融化。
• The spring thaw caused heavy flooding.春天解冻引起了洪水泛滥。

5 thawed   

解冻

参考例句：

• The little girl's smile thawed the angry old man. 小姑娘的微笑使发怒的老头缓和下来。 来自《简明英汉词典》
• He thawed after sitting at a fire for a while. 在火堆旁坐了一会儿，他觉得暖和起来了。 来自《简明英汉词典》

6 emissions   

排放物( emission的名词复数 )； 散发物（尤指气体）

参考例句：

• Most scientists accept that climate change is linked to carbon emissions. 大多数科学家都相信气候变化与排放的含碳气体有关。
• Dangerous emissions radiate from plutonium. 危险的辐射物从钚放散出来。

7 analyzed   

v.分析( analyze的过去式和过去分词 )；分解；解释；对…进行心理分析

参考例句：

• The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
• The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程，因为对他来说，爱是个不可分析的迷。 来自《简明英汉词典》

8 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

9 retrieved   

v.取回( retrieve的过去式和过去分词 )；恢复；寻回；检索（储存的信息）

参考例句：

• Yesterday I retrieved the bag I left in the train. 昨天我取回了遗留在火车上的包。 来自《简明英汉词典》
• He reached over and retrieved his jacket from the back seat. 他伸手从后座上取回了自己的夹克。 来自辞典例句

10 seasonally   

参考例句：

• The price of vegetables fluctuates seasonally. 蔬菜的价格随季节变动。 来自《简明英汉词典》
• They moved seasonally among various vegetation types to feed on plants that were flourishing. 它们还随着季节的变化而在各种类型植物之间迁移，以便吃那些茂盛的植物。 来自辞典例句

11 permanently   

adv.永恒地，永久地，固定不变地

参考例句：

• The accident left him permanently scarred.那次事故给他留下了永久的伤疤。
• The ship is now permanently moored on the Thames in London.该船现在永久地停泊在伦敦泰晤士河边。

12 millennia   

n.一千年，千禧年

参考例句：

• For two millennia, exogamy was a major transgression for Jews. 两千年来，异族通婚一直是犹太人的一大禁忌。
• In the course of millennia, the dinosaurs died out. 在几千年的时间里，恐龙逐渐死绝了。

13 initially   

adv.最初，开始

参考例句：

• The ban was initially opposed by the US.这一禁令首先遭到美国的反对。
• Feathers initially developed from insect scales.羽毛最初由昆虫的翅瓣演化而来。

14 thawing   

n.熔化，融化v.（气候）解冻( thaw的现在分词 )；（态度、感情等）缓和；（冰、雪及冷冻食物）溶化；软化

参考例句：

• The ice is thawing. 冰在融化。 来自《现代英汉综合大词典》
• It had been snowing and thawing and the streets were sloppy. 天一直在下雪，雪又一直在融化，街上泥泞不堪。 来自英汉文学 - 嘉莉妹妹

15 converge   

vi.会合；聚集，集中；(思想、观点等)趋近

参考例句：

• The results converge towards this truth.其结果趋近于这个真理。
• Parallel lines converge at infinity.平行线永不相交。