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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.
It can be inferred from the passage that an example of a detrimental effect in the last sentence of the first paragraph 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
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.
It can be inferred from the passage that an example of a detrimental effect in the last sentence of the first paragraph 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
16 Sep 2014, 01:47
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Official Solution:
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.
It can be inferred from the passage that an example of a detrimental effect in the last sentence of the first paragraph 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
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.
Answer: A
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.
It can be inferred from the passage that an example of a detrimental effect in the last sentence of the first paragraph 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
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.
Answer: A
