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Question

Difficulty: MediumStrengthening or Weakening Author Assertions

Passage:
For decades, marine geologists hypothesized that cold-water carbonate mounds—large undersea structures built from the skeletal debris of cold-water corals—formed primarily through the upward seepage of hydrocarbon-rich fluids from the seabed, which provided chemical energy for microbial mats that fueled coral larvae settlement. However, recent oceanographic surveys across the North Atlantic margin present a different picture. Researchers analyzed sediment cores from several prominent mound complexes and discovered that while deep subsurface methane leaks were occasionally present, they did not coincide temporally with the key initiation phases of mound development. Instead, high-resolution acoustic profiling and isotopic analysis revealed that mound growth spiked during periods of heightened bottom-current activity and enhanced surface water productivity. The authors of the recent study assert that cold-water carbonate mound formation is governed predominantly by hydrodynamic delivery of organic nutrients from surface waters rather than by benthic hydrocarbon seepage.

Which of the following, if true, would most weaken the authors' assertion regarding the primary cause of cold-water carbonate mound formation?

  1. Radiocarbon dating of coral skeletons within the earliest foundational layers of several major Atlantic mounds shows that initial reef colonization occurred exclusively during geological intervals when seabed hydrocarbon seepage reached peak intensity.Answer
  2. B
    Sediment samples taken from oceanic regions with weak bottom currents contain significantly lower concentrations of cold-water coral fragments than samples taken from high-velocity current channels.
  3. C
    Commercial deep-sea fishing trawlers operating in the North Atlantic have damaged up to fifty percent of shallow coral reefs, drastically reducing organic nutrient transport to deep-sea benthic ecosystems.
  4. D
    Mounds located in ocean regions with high surface water productivity host more diverse benthic organisms than mounds located in nutrient-poor surface waters.
  5. E
    Earlier marine geologists lacked the high-resolution acoustic profiling tools required to detect deep subsurface methane leaks in sediment layers.

Answer

The statement showing that initial coral colonization occurred exclusively during intervals of peak seabed hydrocarbon seepage weakens the authors' assertion.
The correct answer provides direct evidence that initial mound colonization coincided strictly with peak seabed hydrocarbon seepage. This directly refutes the authors' key premise that methane leaks did not coincide with initiation phases of mound development, thereby severely weakening their assertion that surface hydrodynamic delivery is the primary cause.

Step-by-Step Solution

1
Identify the author's main assertion and premises
The authors assert that cold-water mound formation is driven predominantly by hydrodynamic delivery of surface nutrients rather than benthic hydrocarbon seepage, based on the premise that subsurface methane leaks did not coincide with initial mound development phases.
To weaken an assertion, one must target the logical link between the evidence provided and the main conclusion drawn by the authors.
2
Evaluate potential counter-evidence
Finding that foundational coral layers actually colonized exclusively during periods of peak hydrocarbon seepage provides direct empirical counter-evidence.
If the initiation of mound growth occurred exclusively during peak seepage, the authors' claim that seepage did not coincide with initiation phases is undermined, bolstering the alternative explanation.

Key Concept

Weakening Author Assertions in Reading Comprehension
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Topics

Strengthening or Weakening Author Assertions

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