If Earth’s oceans are carbon dioxide sinks, that means that carbon dioxide should remain in oceans infinitely. Is that accurate?

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BlackTom AI · Accepted Answer

The prompt asks us to evaluate the idea that Earth's oceans, as carbon dioxide sinks, would trap CO2 indefinitely. 
First, note that there are no answer options provided in the material to analyze individually. This means we cannot compare multiple choices directly, but we can still reason about the core claim and the provided correct statement. 
The central concept here is that while oceans absorb CO2 from the atmosphere, this uptake is not permanent. CO2 dissolves in seawater and can be stored as dissolved inorganic carbon or convert to carbonate minerals, but ocean circulation and chemical processes gradually move carbon between different reservoirs. 
One key mechanism is the deep ocean circulation (thermohaline circulation), which transports surface waters rich in CO2 down to the deep ocean. Over time, these deep waters can return to the surface through upwelling, where CO2 can degas back to the atmosphere. This exchange means carbon cycles on timescales of hundreds to thousands of years, not infinitely long times. 
Additionally, biological processes such as photosynthesis by phytoplankton and subsequent sedimentation can sequester carbon for longer periods, but these sediments can later be resuspended or dissolved, returning CO2 to the ocean or atmosphere. 
Therefore, the statement that CO2 would remain in oceans infinitely is inaccurate because: 
- Deep ocean CO2 is not permanently trapped; it can be released back to the atmosphere via upwelling and other circulation patterns. 
- The carbon cycle involves continual exchange among the atmosphere, surface ocean, deep ocean, and sediments, with residence times that are finite. 
- Ocean processes, including chemical equilibration with carbonate chemistry, buffering, and physical mixing, ensure eventual re-release of CO2 under changing conditions. 
In contrast, the presented correct statement asserts that CO2 assimilated into the deep Atlantic will eventually surface elsewhere and be released back into the atmosphere. This aligns with our understanding of ocean-atmosphere carbon exchange and the non-permanent nature of deep-ocean carbon storage. 
If one were to consider possible counterpoints, such as very long carbon storage times or regional variability, those would still not imply infinite sequestration; they would only describe longer but still finite residence times and pathways for eventual release. 
In summary, the accuracy of the claim relies on recognizing that oceanic CO2 uptake is part of a dynamic cycle with finite residence times, not a perpetual sink.

BIOEE1610 Lecture 19: Post-Lecture: C02 Cycle S22V2

If Earth’s oceans are carbon dioxide sinks, that means that carbon dioxide should remain in oceans infinitely. Is that accurate?

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