How does rising atmospheric CO2 affect marine organisms?

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Carbon Sequestration in CO2-Enriched Forest Understory Trees
Naumburg, E. and Ellsworth, D.S.  2000.  Photosynthetic sunfleck utilization potential of understory saplings growing under elevated CO2 in FACE.  Oecologia 122: 163-174.

What was done
The authors measured photosynthetic rates in leaves of four hardwood saplings growing beneath the canopy of a Pinus taeda forest, several portions of which were exposed to either ambient or enriched (ambient + 200 ppm) atmospheric CO2 concentrations in a FACE study spanning two complete years.  The measurements were made under conditions of both low and high light intensity, which commonly exist beneath maturing forest canopies due to shading and intermittent illumination by sunflecks, respectively.  Hence, the authors studied the effects of elevated CO2 on sapling performance under the variable light conditions that prevail beneath the canopies of forests.

What was learned
Elevated CO2 increased the average steady-state photosynthetic rates of four hardwood understory saplings by 60 and 40% under high and low light conditions, respectively.  In going from shaded to lighted conditions, elevated CO2 had no effect on photosynthetic induction, with ambient and CO2-enriched species both reaching 90% of their maximal transient photosynthetic rates at approximately the same time.  However, in going from lighted to shaded conditions, elevated CO2 extended the time during which maximal rates of photosynthesis were maintained.  Thus, elevated CO2 slowed the rate of photosynthetic decline caused by the onset of shading.  Consequently, shaded leaves of CO2-enriched saplings maintained greater rates of photosynthesis for longer periods of time than did shaded leaves of saplings growing in ambient air, which allowed the CO2-enriched leaves to sequester greater amounts of carbon than was expected from photosynthetic measurements made under steady-state conditions.

What it means
As the air's CO2 content continues to rise, saplings growing beneath the canopies of larger trees will likely increase their rates of photosynthesis under both low and high light conditions characteristic of intermittent shading and illumination by sunflecks.  Moreover, because elevated CO2 concentrations allow saplings to maintain higher rates of photosynthesis for longer periods of time when going from lighted to shaded conditions, such trees should be able to sequester greater quantities of carbon than they do now.  So powerful is this phenomenon, in fact, the authors state that current estimates of the enhancement of long-term carbon gains by forests under conditions of elevated atmospheric CO2 "could be underestimated by steady-state photosynthetic measures."

Put another way, the results of this study suggest that carbon sequestration by future forests will probably be significantly greater than what is currently predicted by state-of-the-art models.  Hence, the planting of forests may be an even better means of removing CO2 from the atmosphere than what was originally thought when this policy option was first conceived as a means for slowing the rate-of-rise of the air's CO2 concentration.