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 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
[spoiler]OA:E[/spoiler]
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 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
[spoiler]OA:E[/spoiler]
