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16 Sep 2014, 01:47
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Despite an abundance of major nutrients in the surface waters of parts of the ocean, extremely low concentrations of dissolved iron are believed to play a crucial role in limiting the biological productivity of these regions. Phytoplankton, the basis of freshwater food chains and the source of most of Earth's atmospheric oxygen, require iron for various biochemical processes. Thus, a lack of iron in surface waters has detrimental effects.
In temperate and tropical oceans, iron reaches surface waters via the dissolution of eolian-transported continental dust. Previously, little was known about iron distribution in the surface waters of non-temperate oceans such as the Arctic Ocean. Recent advances, however, have resulted in an analytical methodology capable of determining iron concentrations in ambient surface waters. Studies indicate that concentrations across the Arctic Basin are relatively high and quite variable, ranging from 3.2 nM in the western Arctic to 0.75 nM in the Nansen Basin.
The highest values of iron concentration occur in regions with ice floes containing significant quantities of surface sediment. The hypothesis that ice-rafted sediment is the source of high iron values is bolstered by the presence of large amounts of aluminum in the same regions. The entrainment of sediments from the edge of the basin into floes during the winter freezing process along with the subsequent advection and partial melting of the ice at the center of the basin provides a means of transporting reactive trace metals, such as iron, to the center of the basin. The partial melting of floes during the summer appears sufficient to transport high concentrations of iron to both surface and stratified waters. It seems, however, that any change resulting in the diminution of ice-edge freezing in winter might lead to significant changes in the nature and magnitude of primary productivity in the central Arctic.
In temperate and tropical oceans, iron reaches surface waters via the dissolution of eolian-transported continental dust. Previously, little was known about iron distribution in the surface waters of non-temperate oceans such as the Arctic Ocean. Recent advances, however, have resulted in an analytical methodology capable of determining iron concentrations in ambient surface waters. Studies indicate that concentrations across the Arctic Basin are relatively high and quite variable, ranging from 3.2 nM in the western Arctic to 0.75 nM in the Nansen Basin.
The highest values of iron concentration occur in regions with ice floes containing significant quantities of surface sediment. The hypothesis that ice-rafted sediment is the source of high iron values is bolstered by the presence of large amounts of aluminum in the same regions. The entrainment of sediments from the edge of the basin into floes during the winter freezing process along with the subsequent advection and partial melting of the ice at the center of the basin provides a means of transporting reactive trace metals, such as iron, to the center of the basin. The partial melting of floes during the summer appears sufficient to transport high concentrations of iron to both surface and stratified waters. It seems, however, that any change resulting in the diminution of ice-edge freezing in winter might lead to significant changes in the nature and magnitude of primary productivity in the central Arctic.
1. It can be inferred from the passage that an example of a detrimental effect in the highlighted text would be
(a) a decrease in the supply of Earth's atmospheric oxygen
(b) a decrease in the significance of phytoplankton in the food chain
(c) an increase in the rate at which phytoplankton perform biochemical processes
(d) an increase in the dissolution of eolian-transported continental dust
(e) an increase in biological productivity in the surface waters of parts of the remote ocean
2. The passage is chiefly concerned with
(a) arguing against the increased production of surface sediment in order to transport iron through surface waters
(b) presenting possible causes for and effects of variations in iron concentrations in surface waters
(c) advocating stricter regulations governing the preservation of phytoplankton in oceanic surface waters
(d) analyzing methods that can effectively measure the amount of iron in surface waters
(e) recommending ways to ensure that iron is transported throughout oceans based upon recent advances in analytical methodology
3. The passage suggests which of the following about surface waters of temperate oceans?
(a) They do not display an even distribution of iron.
(b) They did not contain iron before recent advances in the development of analytical methodology.
(c) They would display lower concentrations of iron if eolian activity decreased.
(d) They would display higher concentrations of iron if continental dust rose to the surface.
(e) They would not contain iron if ice-rafted sediment did not melt.
4. It can be inferred from the passage that which of the following would provide the LEAST support for the idea that surface sediment is responsible for increased concentrations of iron in the Arctic Ocean?
(a) The observation that significant quantities of sediment are present on the surface of ice floes in the western Arctic
(b) The observation that a warmer winter results in decreased concentrations of iron in the western Arctic
(c) Measurements taken in the central Arctic confirming that concentrations of iron increase when ice melts
(d) Measurements taken during the summer in the Nansen Basin displaying the highest concentrations of aluminum
(e) The observation that there are higher concentrations of aluminum in the Nansen Basin than in the western Arctic
5. The passage mentions each of the following about iron EXCEPT:
(a) The hypothesis that ice-rafted sediment is the source of high iron values is bolstered by the presence of continental dust in surrounding regions.
(b) Researchers believe that very low concentrations of dissolved iron are a major factor in limiting biological productivity in remote ocean surface waters.
(c) Studies show that, within the Arctic Basin, iron concentrations are relatively high but vary significantly.
(d) Phytoplankton, the main source of Earth's atmospheric oxygen, require iron to perform various biochemical processes.
(e) The highest iron concentrations are found in regions that have ice floes containing large amounts of surface sediment.
6. Based on the information in the passage, it can be inferred that which of the following is critical for human life?
(a) aluminum
(b) ice floes
(c) phytoplankton
(d) surface sediment
(e) continental dust
(a) a decrease in the supply of Earth's atmospheric oxygen
(b) a decrease in the significance of phytoplankton in the food chain
(c) an increase in the rate at which phytoplankton perform biochemical processes
(d) an increase in the dissolution of eolian-transported continental dust
(e) an increase in biological productivity in the surface waters of parts of the remote ocean
2. The passage is chiefly concerned with
(a) arguing against the increased production of surface sediment in order to transport iron through surface waters
(b) presenting possible causes for and effects of variations in iron concentrations in surface waters
(c) advocating stricter regulations governing the preservation of phytoplankton in oceanic surface waters
(d) analyzing methods that can effectively measure the amount of iron in surface waters
(e) recommending ways to ensure that iron is transported throughout oceans based upon recent advances in analytical methodology
3. The passage suggests which of the following about surface waters of temperate oceans?
(a) They do not display an even distribution of iron.
(b) They did not contain iron before recent advances in the development of analytical methodology.
(c) They would display lower concentrations of iron if eolian activity decreased.
(d) They would display higher concentrations of iron if continental dust rose to the surface.
(e) They would not contain iron if ice-rafted sediment did not melt.
4. It can be inferred from the passage that which of the following would provide the LEAST support for the idea that surface sediment is responsible for increased concentrations of iron in the Arctic Ocean?
(a) The observation that significant quantities of sediment are present on the surface of ice floes in the western Arctic
(b) The observation that a warmer winter results in decreased concentrations of iron in the western Arctic
(c) Measurements taken in the central Arctic confirming that concentrations of iron increase when ice melts
(d) Measurements taken during the summer in the Nansen Basin displaying the highest concentrations of aluminum
(e) The observation that there are higher concentrations of aluminum in the Nansen Basin than in the western Arctic
5. The passage mentions each of the following about iron EXCEPT:
(a) The hypothesis that ice-rafted sediment is the source of high iron values is bolstered by the presence of continental dust in surrounding regions.
(b) Researchers believe that very low concentrations of dissolved iron are a major factor in limiting biological productivity in remote ocean surface waters.
(c) Studies show that, within the Arctic Basin, iron concentrations are relatively high but vary significantly.
(d) Phytoplankton, the main source of Earth's atmospheric oxygen, require iron to perform various biochemical processes.
(e) The highest iron concentrations are found in regions that have ice floes containing large amounts of surface sediment.
6. Based on the information in the passage, it can be inferred that which of the following is critical for human life?
(a) aluminum
(b) ice floes
(c) phytoplankton
(d) surface sediment
(e) continental dust
16 Sep 2014, 01:47
Kudos
Bookmarks
Show SpoilerQuestion S93-01 explanation
We are asked to infer what a detrimental effect of a lack of iron in surface waters would be.
The surrounding text says that because phytoplankton are the basis of freshwater food chains and the source of most of Earth's atmospheric oxygen, a lack of iron in surface waters has detrimental effects. Thus, we can infer that the lack of iron negatively affects food chains and the oxygen in Earth's atmosphere. Our answer should describe this inference as it relates to food chains and/or atmospheric oxygen.
Choice A talks about a fall in the supply of Earth's atmospheric oxygen. This describes a negative effect of a lack of surface iron on atmospheric oxygen, making choice A correct.
Choice B references a decrease in the importance of phytoplankton to the food chain. Phytoplankton is said, in the passage, to be the "basis" of freshwater food chains. Although the phytoplankton population may decrease based on the lack of iron in the surface water, this does not mean that the plankton would become less important to the food chain; in fact, the implication is that the entire food chain may be affected.
Choice C talks about an increase in the rate at which phytoplankton perform biochemical processes. This is the opposite of a correct inference; a lack of iron would not cause an increase in the rate at which phytoplankton perform biochemical processes because the passage states that phytoplankton require iron to perform these processes.
Choice D talks about a rise in the dissolution of eolian-transported continental dust. This is an irrelevant portion of the passage because a lack of iron in surface waters does not cause eolian-carried dust to do anything.
Choice E references a rise in the biological productivity in surface waters. Like choice C, this is the opposite of a correct inference; the passage notes that low concentrations of dissolved iron limit the biological productivity of these regions.
The surrounding text says that because phytoplankton are the basis of freshwater food chains and the source of most of Earth's atmospheric oxygen, a lack of iron in surface waters has detrimental effects. Thus, we can infer that the lack of iron negatively affects food chains and the oxygen in Earth's atmosphere. Our answer should describe this inference as it relates to food chains and/or atmospheric oxygen.
Choice A talks about a fall in the supply of Earth's atmospheric oxygen. This describes a negative effect of a lack of surface iron on atmospheric oxygen, making choice A correct.
Choice B references a decrease in the importance of phytoplankton to the food chain. Phytoplankton is said, in the passage, to be the "basis" of freshwater food chains. Although the phytoplankton population may decrease based on the lack of iron in the surface water, this does not mean that the plankton would become less important to the food chain; in fact, the implication is that the entire food chain may be affected.
Choice C talks about an increase in the rate at which phytoplankton perform biochemical processes. This is the opposite of a correct inference; a lack of iron would not cause an increase in the rate at which phytoplankton perform biochemical processes because the passage states that phytoplankton require iron to perform these processes.
Choice D talks about a rise in the dissolution of eolian-transported continental dust. This is an irrelevant portion of the passage because a lack of iron in surface waters does not cause eolian-carried dust to do anything.
Choice E references a rise in the biological productivity in surface waters. Like choice C, this is the opposite of a correct inference; the passage notes that low concentrations of dissolved iron limit the biological productivity of these regions.
Show SpoilerQuestion S93-02 explanation
We are asked to choose an option that describes a primary concern of the passage.
The first sentence reads extremely low concentrations of dissolved iron are believed to play a crucial role in limiting the biological productivity of [ocean surface waters]. The text then describes variations in iron concentrations, problems of low concentrations, and reasons why some areas may have higher concentrations than others.
So, our answer should talk about the causes and effects of varying iron concentrations in surface waters.
Choice A talks about arguing against the production of more surface sediment to move iron through surface waters. This is the opposite of the correct assumption; surface sediment is mentioned as a reason that iron is introduced into some surface waters, and high concentrations of iron are good for phytoplankton.
According to choice B, the chief concern is presenting possible causes and effects surrounding variations in surface water iron concentrations. This answer talks about the causes and effects of varying iron concentrations in surface waters, so choice B is correct.
Choice C references regulations about the preservation of phytoplankton. Since phytoplankton are only discussed in two sentences in the first paragraph, they are not the primary concern of the passage.
Choice D talks about analyzing methods that measure the amount of iron in surface waters. This is too narrow; methods for analyzing the amount of iron in surface waters are mentioned in one sentence in order to present current information on the concentration of iron in surface waters.
According to choice E, the passage is concerned with recommending ways of ensuring that iron is moved through oceans in accordance with advances in analytical methodology. "Analytical methodology" is a word trap that refers erroneously to part of the passage; furthermore, the author does not recommend ways to ensure that iron is transported.
The first sentence reads extremely low concentrations of dissolved iron are believed to play a crucial role in limiting the biological productivity of [ocean surface waters]. The text then describes variations in iron concentrations, problems of low concentrations, and reasons why some areas may have higher concentrations than others.
So, our answer should talk about the causes and effects of varying iron concentrations in surface waters.
Choice A talks about arguing against the production of more surface sediment to move iron through surface waters. This is the opposite of the correct assumption; surface sediment is mentioned as a reason that iron is introduced into some surface waters, and high concentrations of iron are good for phytoplankton.
According to choice B, the chief concern is presenting possible causes and effects surrounding variations in surface water iron concentrations. This answer talks about the causes and effects of varying iron concentrations in surface waters, so choice B is correct.
Choice C references regulations about the preservation of phytoplankton. Since phytoplankton are only discussed in two sentences in the first paragraph, they are not the primary concern of the passage.
Choice D talks about analyzing methods that measure the amount of iron in surface waters. This is too narrow; methods for analyzing the amount of iron in surface waters are mentioned in one sentence in order to present current information on the concentration of iron in surface waters.
According to choice E, the passage is concerned with recommending ways of ensuring that iron is moved through oceans in accordance with advances in analytical methodology. "Analytical methodology" is a word trap that refers erroneously to part of the passage; furthermore, the author does not recommend ways to ensure that iron is transported.
Show SpoilerQuestion S93-03 explanation
We are asked to identify something that is suggested about the surface waters of temperate oceans.
The passage notes that iron reaches surface waters via the dissolution of eolian-transported continental dust. This is the only mention of these waters in the entire passage, so the correct answer should relate to this fact.
Choice A says surface waters of temperate oceans do not display an even distribution of iron. This describes what the passage says about the surface waters of the Arctic Ocean, which is not the same as what it says about the surface waters of temperate oceans.
According to choice B, the surface waters of temperate oceans did not contain iron prior to recent advances in analytical methodology. The passage says nothing about when iron was discovered or the effect of analytical methodology on this discovery in temperate waters.
Choice C says that the surface waters of temperate oceans would display lower concentrations of iron if eolian activity decreased. Since eolian activity carries the continental dust which delivers iron to the surface of the ocean, surface waters would display low concentrations of iron if there was a decrease in eolian activity. Choice C is correct.
According to choice D, the surface waters of temperate oceans would display higher iron concentrations if continental dust rose to the surface. The passage describes the delivery of this dust by means of eolian activity; however, it cannot be inferred that eolian activity has anything to do with rising to the surface. Moreover, it is difficult to see how dust would rise upward through an ocean.
Choice E says that the surface waters of temperate oceans would not contain iron if ice-rafted sediment did not melt. Similarly to choice A, this is what the passage says about the surface waters of the Arctic Ocean, not temperate oceans.
The passage notes that iron reaches surface waters via the dissolution of eolian-transported continental dust. This is the only mention of these waters in the entire passage, so the correct answer should relate to this fact.
Choice A says surface waters of temperate oceans do not display an even distribution of iron. This describes what the passage says about the surface waters of the Arctic Ocean, which is not the same as what it says about the surface waters of temperate oceans.
According to choice B, the surface waters of temperate oceans did not contain iron prior to recent advances in analytical methodology. The passage says nothing about when iron was discovered or the effect of analytical methodology on this discovery in temperate waters.
Choice C says that the surface waters of temperate oceans would display lower concentrations of iron if eolian activity decreased. Since eolian activity carries the continental dust which delivers iron to the surface of the ocean, surface waters would display low concentrations of iron if there was a decrease in eolian activity. Choice C is correct.
According to choice D, the surface waters of temperate oceans would display higher iron concentrations if continental dust rose to the surface. The passage describes the delivery of this dust by means of eolian activity; however, it cannot be inferred that eolian activity has anything to do with rising to the surface. Moreover, it is difficult to see how dust would rise upward through an ocean.
Choice E says that the surface waters of temperate oceans would not contain iron if ice-rafted sediment did not melt. Similarly to choice A, this is what the passage says about the surface waters of the Arctic Ocean, not temperate oceans.
Show SpoilerQuestion S93-04 explanation
We are asked to make an inference about the existence of surface sediment in the Arctic ocean. Specifically, we are asked to choose the option that would provide the LEAST support for the idea that surface sediment is responsible for increased concentrations of iron.
The passage says the highest values of iron occur in regions where the ice floes have significant quantities of surface sediment. The suggestion that ice-rafted sediment is the source of these high iron values in the surface water is further supported by the enrichment of aluminum in the same regions. So, the correct answer should be the option that provides the LEAST support for this idea.
Choice A talks about floes in the western Arctic having significant quantities of surface sediment. This supports the idea that surface sediment is responsible for increased iron because aluminum is also deposited when surface sediment melts.
According to choice B, warmer winters result in decreased iron concentrations in the western arctic. This supports the idea that surface sediment is responsible for increased concentrations of iron, because if greater quantities of sediment were present on the surfaces of ice floes, it would explain the greater concentration of iron.
Choice C says that central Arctic measurements confirm increased iron concentrations when ice melts. This would support the idea that surface sediment is responsible for increased iron concentrations. A warmer winter would result in a decreased amount of surface sediment, and this decreased amount of sediment would account for the decreased iron.
According to choice D, summer measurements indicate that the Nansen Basin has the highest aluminum concentrations. If the concentration of iron increases when ice melts, the idea that the iron is contained within the ice would be supported because, as its name implies, surface sediment consists of sediment on the surface of the ice and is the source of high iron values in the surface water. It doesn't matter exactly where in the Arctic this is observed; any areas with iron in the ice would lead to surface sediment.
Choice E talks about higher aluminum concentrations in the Nansen Basin than in the western Arctic. If the Nansen Basin displayed the highest concentration of aluminum, then this would support the idea that this area would also display the highest concentrations of iron if surface sediment were the reason for these high concentrations. However, there are higher values of iron in the western Arctic than in the Nansen basin, and the finding that there are higher concentrations of aluminum in the Nansen basin would not support the existence of surface sediment.
The passage says the highest values of iron occur in regions where the ice floes have significant quantities of surface sediment. The suggestion that ice-rafted sediment is the source of these high iron values in the surface water is further supported by the enrichment of aluminum in the same regions. So, the correct answer should be the option that provides the LEAST support for this idea.
Choice A talks about floes in the western Arctic having significant quantities of surface sediment. This supports the idea that surface sediment is responsible for increased iron because aluminum is also deposited when surface sediment melts.
According to choice B, warmer winters result in decreased iron concentrations in the western arctic. This supports the idea that surface sediment is responsible for increased concentrations of iron, because if greater quantities of sediment were present on the surfaces of ice floes, it would explain the greater concentration of iron.
Choice C says that central Arctic measurements confirm increased iron concentrations when ice melts. This would support the idea that surface sediment is responsible for increased iron concentrations. A warmer winter would result in a decreased amount of surface sediment, and this decreased amount of sediment would account for the decreased iron.
According to choice D, summer measurements indicate that the Nansen Basin has the highest aluminum concentrations. If the concentration of iron increases when ice melts, the idea that the iron is contained within the ice would be supported because, as its name implies, surface sediment consists of sediment on the surface of the ice and is the source of high iron values in the surface water. It doesn't matter exactly where in the Arctic this is observed; any areas with iron in the ice would lead to surface sediment.
Choice E talks about higher aluminum concentrations in the Nansen Basin than in the western Arctic. If the Nansen Basin displayed the highest concentration of aluminum, then this would support the idea that this area would also display the highest concentrations of iron if surface sediment were the reason for these high concentrations. However, there are higher values of iron in the western Arctic than in the Nansen basin, and the finding that there are higher concentrations of aluminum in the Nansen basin would not support the existence of surface sediment.
Show SpoilerQuestion S93-05 explanation
This question asks for something that the passage does NOT say about iron. With this type of question, the best approach is to eliminate each answer choice that contains something the passage says about iron.
Choice A says that the hypothesis that ice-rafted sediment causes high concentrations of iron is strengthened by the existence of continental dust in surrounding regions. The second sentence of the third paragraph reads "The hypothesis that ice-rafted sediment is the source of high iron values is bolstered by the presence of large amounts of aluminum in the same regions." Choice A is correct.
According to choice B, researchers think that very small amounts of dissolved iron are a significant factor in limiting biological productivity in remote ocean surface waters. This is stated in the first sentence of the first paragraph.
Choice C says that studies indicate that, within the Arctic Basin, concentrations of iron are large but vary a great deal. This is stated in the last sentence of the second paragraph.
According to choice D, phytoplankton, the source of most of the oxygen in Earth's atmosphere, need iron to perform various biochemical processes. This is stated in the second sentence of the first paragraph.
Choice E says that the largest concentrations of iron occur in regions with ice floes that have large amounts of surface sediment. This is stated in the first sentence of the third paragraph.
Choice A says that the hypothesis that ice-rafted sediment causes high concentrations of iron is strengthened by the existence of continental dust in surrounding regions. The second sentence of the third paragraph reads "The hypothesis that ice-rafted sediment is the source of high iron values is bolstered by the presence of large amounts of aluminum in the same regions." Choice A is correct.
According to choice B, researchers think that very small amounts of dissolved iron are a significant factor in limiting biological productivity in remote ocean surface waters. This is stated in the first sentence of the first paragraph.
Choice C says that studies indicate that, within the Arctic Basin, concentrations of iron are large but vary a great deal. This is stated in the last sentence of the second paragraph.
According to choice D, phytoplankton, the source of most of the oxygen in Earth's atmosphere, need iron to perform various biochemical processes. This is stated in the second sentence of the first paragraph.
Choice E says that the largest concentrations of iron occur in regions with ice floes that have large amounts of surface sediment. This is stated in the first sentence of the third paragraph.
Show SpoilerQuestion S93-06 explanation
This question asks for something that the passage implies is critical for human life. The best way to approach this type of question is to eliminate all of the answer choices that the passage does imply are critical to human life.
Choice A says aluminum. The passage says that large amounts of aluminum make it likely that sediment is the cause of large amounts of iron in arctic regions. This has nothing to do with human life.
Choice B says ice floes. Ice floes are mentioned several times in the final paragraph, but there is nothing to suggest that they are vital to human life.
Choice C says phytoplankton. The passage says that phytoplankton are the source of most of Earth's atmospheric oxygen, so it can be inferred that they are critical to human life. Choice C is correct.
Choice D says surface sediment. This sediment is mentioned in the third paragraph, but there is nothing to suggest that it is vital to human life.
Choice E says continental dust. This dust is mentioned in the second paragraph, but, again, there is nothing to suggest that it is vital to human life.
Choice A says aluminum. The passage says that large amounts of aluminum make it likely that sediment is the cause of large amounts of iron in arctic regions. This has nothing to do with human life.
Choice B says ice floes. Ice floes are mentioned several times in the final paragraph, but there is nothing to suggest that they are vital to human life.
Choice C says phytoplankton. The passage says that phytoplankton are the source of most of Earth's atmospheric oxygen, so it can be inferred that they are critical to human life. Choice C is correct.
Choice D says surface sediment. This sediment is mentioned in the third paragraph, but there is nothing to suggest that it is vital to human life.
Choice E says continental dust. This dust is mentioned in the second paragraph, but, again, there is nothing to suggest that it is vital to human life.
