Chapter 16: Coastal Oceans and Continental Shelves

Overview/Main Issues

This chapter is a thorough review of data available on carbon cycling and storage in ocean and coastal systems. In general, the summary is accurate and well supported by evidence presented here.

The Committee identified just a few ways that the chapter could potentially be strengthened. This chapter should make clear at the outset that the fluxes presented here are total (pre-industrial/background + anthropogenic) carbon cycle; i.e. in the absence of anthropogenic perturbations, there would still be a net flux to (or from) the atmosphere, and the net flux would be balanced by lateral transports. The authors need to figure out how the findings from this chapter should be integrated into the North American carbon budget (e.g. Figure ES5), which is commonly thought of as that related to anthropogenic perturbations.

Statement of Task Questions

• Are the goals, objectives and intended audience of the product clearly described in the document? Does the report meet its stated goals?

This chapter is in alignment with the overall goals and objectives of the report as stated in the Executive Summary and Report Preface. This chapter is generally well written and is scientifically sound.

• Does the report accurately reflect the scientific literature? Are there any critical content areas missing from the report?

In general, the Chapter is accurate and is well supported by scientific literature. The Committee did find a few content areas that could be expanded or included further. For example:

• Hypoxia is a linked process to much of what is discussed here, can it be reviewed and discussed here?
• Methane from coastal / continental shelf sources is not discussed. Should be introduced, explained, discussed, quantified.
• In ocean systems, one can trace anthropogenic vs. natural carbon perturbation/fluxes. Can a discussion of the parsing of these sources be added here?
• Hawaii & Pacific Islands are not discussed; nor is Caribbean (Puerto Rico should be included). These are included in the map in the Executive Summary, so should be incorporated here. Similarly, trends, fluxes and gaps in knowledge for the Arctic coastline should be further discussed.
• There could be a more specific connection to social science added here, as many of the economic impacts on people will be felt in coastal zones (recreation, fisheries, tourism).

• Are the findings documented in a consistent, transparent and credible way?

The Findings appear to be in alignment with the supporting text.

• Are the report’s key messages and graphics clear and appropriate? Specifically, do they reflect supporting evidence, include an assessment of likelihood, and communicate effectively?

Tables are effective and clear, and figures are appropriate.

The addition of one figure showing an example observational dataset from the coastal ocean would be beneficial.

The map needs to align with the Executive Summary regarding Pacific Islands and the Carribean.

Key Finding 2: What does “high confidence” apply to? The fact that the number is not well constrained?

• Are the research needs identified in the report appropriate?

The research needs and gaps were appropriate. The Committee expressed some concern that these and other key findings were not appropriately covered in the Executive Summary, so the authors should consider aligning with Executive Summary text.

• Are the data and analyses handled in a competent manner? Are statistical methods applied appropriately?

The authors appropriately summarize and cite published analyses.

• Are the document’s presentation, level of technicality, and organization effective? Are the questions outlined in the prospectus addressed and communicated in a manner that is appropriate and accessible for the intended audience?

The chapter is well written, very through, and a concise point of reference for the state of the science on coastal carbon cycling. The level of technicality is appropriate for an interested scientific audience (undergraduates, graduate students, or scientists from other fields).

• What other significant improvements, if any, might be made in the document?

While Chapter 1 (Key Finding 2) states that global average temperature increase is found to be 0.85 degrees C, Chapter 16 avoids mentioning ocean temperature observations, despite the fact that this is the prime driver of the observable poleward migration of marine species, and the fact that oceans take up ~95% of all anthropogenic heat generated. It would be best to add a note or disclaimer about these omissions.

There are ongoing efforts by industry to re-inject below the sea floor large amounts of CO₂ associated with oil and gas production (wells with 30% co-produced CO₂ are now common). Such efforts are on the upswing and today are the industry standard. The report should perhaps acknowledge this progress, although this is not specifically a North American phenomenon.

Note that ocean CO₂ uptake and loss is not credited to any nation under IPCC CO₂ accounting. Ocean uptake is viewed as a “public good” — so that land-locked nations and small nations with large EEZs are treated equally in this matter. The chapter should make this distinction more clearly and avoid sending a confusing message by commingling these coastal ocean uptake terms with other North American sectors (industrial, agricultural, forestry) that can absorb carbon.

Line-Specific Comments

P653, Line 27-32

The sentence (photosynthesis in the spring, and respiration in summer and fall) could easily lead a reader to conclude (wrongly) that the biological carbon cycle is seasonal. The biological pump is much faster—with continuous grazing the residence time of phytoplankton is two weeks or less.

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