While researching a topic, a student has taken the following notes:
- "Blue carbon" refers to carbon captured by marine ecosystems, including kelp forests.
- Marine ecologist Nadine Dupont investigates whether large-scale kelp cultivation can lock away atmospheric carbon.
- Kelp grows quickly and draws down CO2; some biomass can be sunk offshore.
- Critics warn that sinking seaweed in the deep ocean may cause local oxygen depletion.
- A 2023 study found that roughly 20% of kelp-derived carbon reaches long-term deep-ocean storage.
- Some pilot projects attach harvested seaweed to offshore lines for sinking beyond the continental shelf.
The student wants to introduce a paragraph that acknowledges both the promise and the uncertainty of kelp-based carbon sequestration. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions, translate the goal into required functions, such as presenting promise while qualifying it with uncertainty. Then compare the choices not only for relevant details but also for accurate relationships among those details, eliminating options that add unsupported causes, recommendations, or definitive conclusions.
Hints
Restate the goal
Look for a sentence that presents both a potential benefit of kelp carbon sequestration and a supported reason its effectiveness or effects remain uncertain.
Separate the evidence categories
Identify which notes establish kelp’s promise and which notes qualify that promise. The best choice should connect these categories accurately.
Check the relationships between details
Do not assume that two concerns mentioned in the notes have a causal relationship. Also avoid choices that add a recommendation or treat limited evidence as definitive proof.
Step-by-step Explanation
Identify the required balance
The introduction must acknowledge both the promise and the uncertainty of kelp-based carbon sequestration.
The best choice therefore needs to:
- Present a reason the strategy appears promising.
- Present evidence that its effectiveness or effects remain uncertain.
- Avoid conclusions or causal relationships not supported by the notes.
Classify the relevant evidence
The notes provide evidence of promise: kelp grows quickly, draws down CO2, and can be sunk offshore.
They also provide evidence of uncertainty: only about 20% of kelp-derived carbon reaches long-term storage, and sinking seaweed may cause local oxygen depletion.
Check how each choice connects the details
Choice C accurately combines the promise with both limitations without adding a claim. Choice A incorrectly presents oxygen depletion as the main cause of the limited long-term storage, though the notes give no such causal relationship. Choice B adds an unsupported recommendation to abandon cultivation, and choice D treats limited evidence as confirmation that the method works.
Select the most effective synthesis
Choice C most directly and accurately fulfills the goal:
Kelp’s rapid growth and CO2 uptake make large-scale cultivation a promising blue-carbon strategy, but the finding that only about 20% of kelp-derived carbon reaches long-term deep-ocean storage and concerns about oxygen depletion make its benefits uncertain.