新TOEFL阅读真题详解:GREEN ICEBERGS 绿色冰山

　　Icebergs are massive blocks of ice, irregular in shape; they float with only about 12 percent oftheir mass above the sea surface. They are formed by glaciers—large rivers of ice that begininland in the snows of Greenland, Antarctica, and Alaska—and move slowly toward the sea. Theforward movement, the melting at the base of the glacier where it meets the ocean, andwaves and tidal action cause blocks of ice to break off and float out to sea.

　　Icebergs are ordinarily blue to white, although they sometimes appear dark or opaque becausethey carry gravel and bits of rock. They may change color with changing light conditions andcloud cover, glowing pink or gold in the morning or evening light, but this color change isgenerally related to the low angle of the Sun above the horizon. However, travelers toAntarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, morecommonly, close to the Amery Ice Shelf in East Antarctica.

　　One explanation for green icebergs attributes their color to an optical illusion when blue ice isilluminated by a near-horizon red Sun, but green icebergs stand out among white and blueicebergs under a great variety of light conditions. Another suggestion is that the color mightbe related to ice with high levels of metallic compounds, including copper and iron. Recentexpeditions have taken ice samples from green icebergs and ice cores—vertical, cylindrical icesamples reaching down to great depths—from the glacial ice shelves along the Antarcticcontinent. Analyses of these cores and samples provide a different solution to the problem.

　　The ice shelf cores, with a total length of 215 meters (705 feet), were long enough topenetrate through glacial ice—which is formed from the compaction of snow and contains airbubbles—and to continue into the clear, bubble-free ice formed from seawater that freezesonto the bottom of the glacial ice. The properties of this clear sea ice were very similar to theice from the green iceberg. The scientists concluded that green icebergs form when a two-layerblock of shelf ice breaks away and capsizes (turns upside down), exposing the bubble-freeshelf ice that was formed from seawater.

　　A green iceberg that stranded just west of the Amery Ice Shelf showed two distinct layers:bubbly blue-white ice and bubble-free green ice separated by a one-meter- long ice layercontaining sediments. The green ice portion was textured by seawater erosion. Where crackswere present, the color was light green because of light scattering; where no cracks werepresent, the color was dark green. No air bubbles were present in the green ice, suggestingthat the ice was not formed from the compression of snow but instead from the freezing ofseawater. Large concentrations of single-celled organisms with green pigments (coloringsubstances) occur along the edges of the ice shelves in this region, and the seawater is rich intheir decomposing organic material. The green iceberg did not contain large amounts ofparticles from these organisms, but the ice had accumulated dissolved organic matter fromthe seawater. It appears that unlike salt, dissolved organic substances are not excluded fromthe ice in the freezing process. Analysis shows that the dissolved organic material absorbsenough blue wavelengths from solar light to make the ice appear green.

　　Chemical evidence shows that platelets (minute flat portions) of ice form in the water and thenaccrete and stick to the bottom of the ice shelf to form a slush (partially melted snow). Theslush is compacted by an unknown mechanism, and solid, bubblefree ice is formed from waterhigh in soluble organic substances. When an iceberg separates from the ice shelf andcapsizes, the green ice is exposed.

　　The Amery Ice Shelf appears to be uniquely suited to the production of green icebergs. Oncedetached from the ice shelf, these bergs drift in the currents and wind systems surroundingAntarctica and can be found scattered among Antarctica’s less colorful icebergs.

　　Paragraph 1: Icebergs are massive blocks of ice, irregular in shape; they float with only about12 percent of their mass above the sea surface. They are formed by glaciers—large rivers of icethat begin inland in the snows of Greenland, Antarctica, and Alaska—and move slowly towardthe sea. The forward movement, the melting at the base of the glacier where it meets theocean, and waves and tidal action cause blocks of ice to break off and float out to sea.

　　1. According to paragraph 1, all of the following are true of icebergs EXCEPT:

　　○They do not have a regular shape.

　　○They are formed where glaciers meet the ocean.

　　○Most of their mass is above the sea surface.

　　○Waves and tides cause them to break off glaciers.

　　Paragraph 2: Icebergs are ordinarily blue to white, although they sometimes appear dark oropaque because they carry gravel and bits of rock. They may change color with changing lightconditions and cloud cover, glowing pink or gold in the morning or evening light, but this colorchange is generally related to the low angle of the Sun above the horizon. However, travelersto Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, morecommonly, close to the Amery Ice Shelf in East Antarctica.

　　2. According to paragraph 2, what causes icebergs to sometimes appear dark or opaque?

　　○A heavy cloud cover

　　○The presence of gravel or bits of rock

　　○The low angle of the Sun above the horizon

　　○The presence of large cracks in their surface

　　Paragraph 2: One explanation for green icebergs attributes their color to an optical illusionwhen blue ice is illuminated by a near-horizon red Sun, but green icebergs stand out amongwhite and blue icebergs under a great variety of light conditions. Another suggestion is thatthe color might be related to ice with high levels of metallic compounds, including copper andiron. Recent expeditions have taken ice samples from green icebergs and ice cores—vertical,cylindrical ice samples reaching down to great depths—from the glacial ice shelves along theAntarctic continent. Analyses of these cores and samples provide a different solution to theproblem.

　　3. Which of the sentences below best expresses the essential information in the highlightedsentence in the passage? Incorrect choices change the meaning in important ways or leave outessential information.

　　○One explanation notes that green icebergs stand out among other icebergs under a greatvariety of light conditions, but this is attributed to an optical illusion.

　　○One explanation for the color of green icebergs attributes their color to an optical illusionthat occurs when the light from a near-horizon red Sun shines on a blue iceberg.

　　○One explanation for green icebergs attributes their color to a great variety of lightconditions, but green icebergs stand out best among other icebergs when illuminated by anear-horizon red Sun.

　　○One explanation attributes the color of green icebergs to an optical illusion under speciallight conditions, but green icebergs appear distinct from other icebergs under a great varietyof light conditions.

　　Paragraph 4: The ice shelf cores, with a total length of 215 meters (705 feet), were longenough to penetrate through glacial ice—which is formed from the compaction of snow andcontains air bubbles—and to continue into the clear, bubble-free ice formed from seawater thatfreezes onto the bottom of the glacial ice. The properties of this clear sea ice were very similarto the ice from the green iceberg. The scientists concluded that green icebergs form when atwo-layer block of shelf ice breaks away and capsizes (turns upside down), exposing thebubble-free shelf ice that was formed from seawater.

　　4. The word penetrate in the passage is closest in meaning to

　　○collect

　　○pierce

　　○melt

　　○endure

　　5. According to paragraph 4, how is glacial ice formed?

　　○By the compaction of snow

　　○By the freezing of seawater on the bottom of ice shelves

　　○By breaking away from the ice shelf

　　○By the capsizing of a two-layer block of shelf ice

　　6. According to paragraph 4, ice shelf cores helped scientists explain the formation of greenicebergs by showing that

　　○the ice at the bottom of green icebergs is bubble-free ice formed from frozen seawater

　　○bubble-free ice is found at the top of the ice shelf

　　○glacial ice is lighter and floats better than sea ice

　　○the clear sea ice at the bottom of the ice shelf is similar to ice from a green iceberg

　　参考答案

　　1. ○3

　　2. ○2

　　3. ○4

　　4. ○2

　　5. ○1

　　6. ○4

　参考译文：

　　冰山就是巨大的冰块，它们的形状各不规则;他们在海面上所呈现出来的部分大概只有总量的12%。冰山是由冰川----从格陵兰岛, 南极洲, 和阿拉斯加的内陆降雪开始积累成为大河中的冰----然后缓慢流入海洋。向前的移动，在进入海洋的时候冰川底部的融化，和波浪与潮汐变化造成了冰块的断裂从而漂浮在海上。

　　冰山的颜色一般是从蓝到白，虽然有时会因为他们带有砂砾和石块而显得颜色很深或不透明。在不同情况的光和云量下，它们的颜色呈现可能会随之不同，如在早晨和傍晚的阳光下所呈现的耀眼的粉色或金色，但这个颜色变化大致与太阳位于海平面上的低角度有关。不管怎样，总会有到南极洲的旅游者们报告说在Weddell Sea看到了绿冰山，南极洲东部Amery Ice Shelf的附近则更为常见。

　　对于绿冰山的颜色的一个解释是由于纯冰被接近海平面的太阳所照射而造成的错觉，但是绿冰山在很多不同状态的阳光下都能从白色和蓝色冰山中区分出来。另一个解释就是，它的颜色可能与冰里面所含高浓度的金属化合物有关，比如铜和铁。进来的探险队从南极洲的冰架上带回了一些绿色冰山和冰核的样本----到达深度的垂直圆柱型的冰的样本。对这些冰核和样本的分析给问题提供了一个不一样的解决方法。

　　215米长的冰架核已经足够用来穿透由压缩的雪组成，并含有气泡的流动冰，并随后穿透在流动冰的底部由冻结的海水形成的清透的没有气泡的冰。这个清透的冰的性质与绿冰山上的冰十分相似。科学家总结出，绿冰的构成是在两层的架冰分开并翻转过来时，暴露出的没有气泡的海水冰。

　　一个在Amery Ice Shelf西部滞留的绿冰山呈现出了两个明显的层：含有气泡的白蓝色冰，和没有气泡的绿色冰，它们中间是由1米长的带有沉积物的冰分隔开的。海水的侵蚀决定了绿色冰的质地。由于光的分散，裂痕处的颜色是浅绿的;而没有裂痕的地方是深绿色。绿色冰中是没有气泡的，因为它是由冻结的海水所构成，而不是压缩的雪。沿着这个地区冰架的边缘，可以发现，带有绿色色素的单细胞生物非常多，而且海水里面含有它们丰富的分解有机物质。绿冰山虽没有包含很多这些生物体的微粒，但从海水中所积累的分解有机物质还是很多的。不同于盐，分解有机物质并没有在结冰过程中被排除掉。分析表明，分解的有机物质会从太阳光中吸收足够的蓝波段，从而使冰呈现出绿色。

　　化学证据表明冰的小盘(微小的平面部分)是在水中构成，然后共生并附着在冰架底部形成一个slush (部分融化的雪)。Slush被一种未知的原理压缩成冰，而这种固体，没有气泡的冰形成于可溶解的有机物质多的水。当冰山从冰架上分离并翻转过来时，绿色冰便呈现出来了。