GREEN ICEBERGS
Icebergs are massive blocks of ice, irregular in shape; they float with only about 12 percent of their mass above the sea surface. They are formed by glaciers—large rivers of ice that begin inland in the snows of Greenland, Antarctica, and Alaska—and move slowly toward the sea. The forward movement, the melting at the base of the glacier where it meets the ocean, and waves 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 because they carry gravel and bits of rock. They may change color with changing light conditions and cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the Sun above the horizon. However, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, more commonly, close to the Amery Ice Shelf in East Antarctica.
One explanation for green icebergs attributes their color to an optical illusion when blue ice is illuminated by a near-horizon red Sun, but green icebergs stand out among white and blue icebergs under a great variety of light conditions. Another suggestion is that the color might be related to ice with high levels of metallic com¬pounds, including copper and iron. 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 the Antarctic continent. 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 to penetrate through glacial ice—which is formed from the compaction of snow and contains air bubbles—and to continue into the clear, bubble-free ice formed from seawater that freezes onto the bottom of the glacial ice. The properties of this clear sea ice were very similar to the ice from the green iceberg. The scientists concluded that green icebergs form when a two-layer block of shelf ice breaks away and cap¬sizes (turns upside down), exposing the bubble-free shelf 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 layer containing sediments. The green ice portion was textured by seawater ero¬sion. Where cracks were present, the color was light green because of light scattering; where no cracks were present, the color was dark green. No air bubbles were pres¬ent in the green ice, suggesting that the ice was not formed from the compression of snow but instead from the freezing of seawater. Large concentrations of single¬celled organisms with green pigments (coloring substances) occur along the edges of the ice shelves in this region, and the seawater is rich in their decomposing organic material. The green iceberg did not contain large amounts of particles from these organisms, but the ice had accumulated dissolved organic matter from the seawater. It appears that unlike salt, dissolved organic substances are not excluded from the ice in the freezing process. Analysis shows that the dissolved organic material absorbs enough 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 then accrete and stick to the bottom of the ice shelf to form a slush (par¬tially melted snow). The slush is compacted by an unknown mechanism, and solid, bubble-free ice is formed from water high in soluble organic substances. When an iceberg separates from the ice shelf and capsizes, the green ice is exposed.
The Amery Ice Shelf appears to be uniquely suited to the production of green icebergs. Once detached from the ice shelf, these bergs drift in the currents and wind systems surrounding Antarctica and can be found scattered among Antarctica’s less colorful icebergs.
Icebergs are massive blocks of ice, irregular in shape; they float with only about 12 percent of their mass above the sea surface. They are formed by glaciers—large rivers of ice that begin inland in the snows of Greenland, Antarctica, and Alaska—and move slowly toward the sea. The forward movement, the melting at the base of the glacier where it meets the ocean, and waves and tidal action cause blocks of ice to break off and float out to sea.
Directions: Mark your answer by filling in the oval next to your choice.
1. According to paragraph 1, all of the following are true of icebergs EXCEPT:
O They do not have a regular shape.
O They are formed where glaciers meet the ocean.
O Most of their mass is above the sea surface.
O Waves and tides cause them to break off glaciers.
Icebergs are ordinarily blue to white, although they sometimes appear dark or opaque because they carry gravel and bits of rock. They may change color with changing light conditions and cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the Sun above the horizon. However, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, more commonly, close to the Amery Ice Shelf in East Antarctica.
2. According to paragraph 2, what causes icebergs to sometimes appear dark or opaque?
O A heavy cloud cover
O The presence of gravel or bits of rock
O The low angle of the Sun above the horizon
O The presence of large cracks in their surface
One explanation for green icebergs attributes their color to an optical illusion when blue ice is illuminated by a near-horizon red Sun, but green icebergs stand out among white and blue icebergs under a great variety of light conditions. Another suggestion is that the color might be related to ice with high levels of metallic compounds, includ¬ing copper and iron. Recent expeditions have taken ice samples from green icebergs and ice cores—vertical, cylindrical ice samples reaching down to great depths—from 3 the glacial ice shelves along the Antarctic continent. Analyses of these cores and sam¬ples provide a different solution to the problem.
3. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?
Incorrect choices change the meaning in important ways or leave out essential information.
O One explanation notes that green icebergs stand out among other icebergs under a great variety of light conditions, but this is attributed to an optical illusion.
O One explanation for the color of green icebergs attributes their color to an optical illusion that occurs when the light from a near-horizon red Sun shines on a blue iceberg.
O One explanation for green icebergs attributes their color to a great variety of light conditions, but green icebergs stand out best among other icebergs when illumi-nated by a near-horizon red Sun.
O One explanation attributes the color of green icebergs to an optical illusion under special light conditions, but green icebergs appear distinct from other icebergs under a great variety of light conditions.
The ice shelf cores, with a total length of 215 meters (705 feet), were long enough to penetrate through glacial ice—which is formed from the compaction of snow and contains air bubbles—and to continue into the clear, bubble-free ice formed from seawater that freezes onto the bottom of the glacial ice. The properties of this clear sea ice were very similar to the ice from the green iceberg. The scientists concluded that green icebergs form when a two-layer block of shelf ice breaks away and cap¬sizes (turns upside down), exposing the bubble-free shelf ice that was formed from seawater.
4. The word “penetrate” in the passage is closest in meaning to
O collect
O pierce
O melt
O endure
5. According to paragraph 4, how is glacial ice formed?
O By the compaction of snow
O By the freezing of seawater on the bottom of ice shelves
O By breaking away from the ice shelf
O 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 green icebergs by showing that
O the ice at the bottom of green icebergs is bubble-free ice formed from frozen seawater
O bubble-free ice is found at the top of the ice shelf
O glacial ice is lighter and floats better than sea ice
O the clear sea ice at the bottom of the ice shelf is similar to ice from a green iceberg
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 layer containing sediments. The green ice portion was textured by seawater ero¬sion. Where cracks were present, the color was light green because of light scattering; where no cracks were present, the color was dark green. No air bubbles were pres¬ent in the green ice, suggesting that the ice was not formed from the compression of snow but instead from the freezing of seawater. Large concentrations of single¬celled organisms with green pigments (coloring substances) occur along the edges of the ice shelves in this region, and the seawater is rich in their decomposing organic material. The green iceberg did not contain large amounts of particles from these organisms, but the ice had accumulated dissolved organic matter from the seawater. It appears that unlike salt, dissolved organic substances are not excluded from the icc in the freezing process. Analysis shows that the dissolved organic material absorbs enough blue wavelengths from solar light to make the ice appear green.
7. Why does the author mention that “The green ice portion was textured by seawater erosion”?
O To explain why cracks in the iceberg appeared light green instead of dark green
O To suggest that green ice is more easily eroded by seawater than white ice is
O To support the idea that the green ice had been the bottom layer before capsizing
O To explain how the air bubbles had been removed from the green ice
8. The word “accumulated” in the passage is closest in meaning to
O collected
O frozen
O released
O covered
9. The word “excluded” in the passage is closest in meaning to
O kept out
O compressed
O damaged
O gathered together
Chemical evidence shows that platelets (minute flat portions) of ice form in the water and then accrete and stick to the bottom of the ice shelf to form a slush (partially melted snow). The slush is compacted by an unknown mechanism, and solid, bubble¬free ice is formed from water high in soluble organic substances. When an iceberg separates from the ice shelf and capsizes, the green ice is exposed.
10. The word “accrete” in the passage is closest in meaning to
O advance
O transfer
O flatten out
O come together
11. Which of the following is NOT explained in the passage?
O Why blocks of ice break off where glaciers meet the ocean
O Why blocks of shelf ice sometimes capsize after breaking off
O Why green icebergs are commonly produced in some parts of Antarctica
O Why green icebergs contain large amounts of dissolved organic pigments
12. The passage supports which of the following statements about the Amery Ice Shelf?
O The Amery Ice Shelf produces only green icebergs.
O The Amery Ice Shelf produces green icebergs because its ice contains high levels
of metallic compounds such as copper and iron.
O The Amery Ice Shelf produces green icebergs because the seawater is rich in a particular kind of soluble organic material.
O No green icebergs are found far from the Amery Ice Shelf.
Icebergs are ordinarily blue to white, although they sometimes appear dark or opaque because they carry gravel and bits of rock. They may change color with changing light conditions and cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the Sun above the horizon. However, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, more commonly, close to the Amery Ice Shelf in East Antarctica. One explanation for green icebergs attributes their color to an optical illusion when blue ice is illuminated by a near-horizon red Sun, but green icebergs stand out among white and blue icebergs under a great variety of light conditions. Another suggestion is that the color might be related to ice with high levels of metallic com¬pounds, including copper and iron. Recent expeditions have taken ice samples from 3 green icebergs and ice cores—vertical, cylindrical ice samples reaching down to great depths—from the glacial ice shelves along the Antarctic continent. Analyses of these cores and samples provide a different solution to the problem.
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
Scientists have differed as to whether icebergs appear green as a result of light conditions or because of something in the ice itself.
Where would the sentence best fit?
O. Icebergs are ordinarily blue to white, although they sometimes appear dark or opaque because they carry gravel and bits of rock. They may change color with changing light conditions and cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the Sun above the horizon. Scientists have differed as to whether icebergs appear green as a result of light conditions or because of something in the ice itself. However, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, more commonly, close to the Amery Ice Shelf in East Antarctica.
One explanation for green icebergs attributes their color to an optical illusion when blue ice is illuminated by a near-horizon red Sun, but green icebergs stand out among white and blue icebergs under a great variety of light conditions. Another suggestion is that the color might be related to ice with high levels of metallic compounds, including copper and iron. 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 the Antarctic continent. Analyses of these cores and samples provide a different solution to the problem.
O. Icebergs are ordinarily blue to white, although they sometimes appear dark or opaque because they carry gravel and bits of rock. They may change color with changing light conditions and cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the Sun above the horizon. However, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, more commonly, close to the Amery Ice Shelf in East Antarctica.
Scientists have differed as to whether icebergs appear green as a result of light conditions or because of something in the ice itself. One explanation for green icebergs attributes their color to an optical illusion when blue ice is illumi¬nated by a near-horizon red Sun, but green icebergs stand out among white and blue icebergs under a great variety of light conditions. Another suggestion is that the color might be related to ice with high levels of metallic compounds, including copper and iron. 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 the Antarctic continent. Analy^ ses of these cores and samples provide a different solution to the problem.
O Icebergs are ordinarily blue to white, although they sometimes appear dark or opaque because they carry gravel and bits of rock. They may change color with changing light conditions and cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the Sun above the horizon. However, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, more commonly, close to the Amery Ice Shelf in East Antarctica.
One explanation for green icebergs attributes their color to an optical illu¬sion when blue ice is illuminated by a near-horizon red Sun, but green icebergs stand out among white and blue icebergs under a great variety of light condi¬tions. Scientists have differed as to whether icebergs appear green as a result of light conditions or because of something in the ice itself. Another suggestion is that the color might be related to ice with high levels of metallic compounds, including copper and iron. 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 the Antarctic continent. Analy¬ses of these cores and samples provide a different solution to the problem.
O Icebergs are ordinarily blue to white, although they sometimes appear dark or opaque because they carry gravel and bits of rock. They may change color with changing light conditions and cloud cover, glowing pink or gold in the morning or evening light, but this color change is generally related to the low angle of the Sun above the horizon. However, travelers to Antarctica have repeatedly reported seeing green icebergs in the Weddell Sea and, more commonly, close to the Amery Ice Shelf in East Antarctica.
One explanation for green icebergs attributes their color to an optical illu¬sion when blue ice is illuminated by a near-horizon red Sun, but green icebergs stand out among white and blue icebergs under a great variety of light condi¬tions. ■ Another suggestion is that the color might be related to ice with high levels of metallic compounds, including copper and iron. Scientists have differed as to whether icebergs appear green as a result of light conditions or because of something in the ice itself. 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 the Antarctic continent. Analyses of these cores and samples provide a different solution to the problem.
14. Directions: An introductory sentence for a brief summary of the passage is pro¬vided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Several suggestions, ranging from light conditions to the presence of metallic compounds, have been offered to explain why some icebergs appear green.
Answer Choices
1. Ice cores were used to determine that green icebergs were formed from the compaction of metallic compounds, including copper and iron.
2. All ice shelves can produce green icebergs, but the Amery Ice Shelf is especially well suited to do so.
3. Green icebergs form when a two- layer block of ice breaks away from a glacier and capsizes, exposing the bottom sea ice to view.
4. Ice cores and samples revealed that both ice shelves and green icebergs contain a layer of bubbly glacial ice and a layer of bubble-free sea ice.
5. Green icebergs are white until they come into contact with seawater containing platelets and soluble organic green pigments.
6. In a green iceberg, the sea ice contains large concentrations of organic matter from the seawater.