How does rising atmospheric CO2 affect marine organisms?

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Volume 3 Number 10:  15 May 2000

Global Ocean Warming: How Much and Why?: The discovery that the world's oceans have warmed a smidgen over the past half-century has brought forth claims of vindication for climate model predictions of CO2-induced global warming.  Of course they are unfounded.

Journal Reviews
Tidal Cycles as Agents of Millennial-Scale Climate Change: Changes in the strength of the ocean tides on millennial time scales are hypothesized to be a major driving influence of earth's climate.

Extraordinary Warmth in the 20th Century?: Tree ring records from Siberia reveal several warm and cold oscillations over the past 2200 years, among which are the Medieval Warm Period and Little Ice Age.  In addition, the authors note that the warming experienced in the 20th century is "not extraordinary" and that "the warming at the border of the first and second millennia was longer in time and similar in amplitude."

Rapid Climate Change: Past and Future: A review of what is known and hypothesized about the role of the global ocean's thermohaline circulation suggests that it can reorganize itself and dramatically affect earth's climate; but not enough is known about the subject to make responsible predictions about the future.

Assessing Volcanic-Induced Climate Forcing: The probability of a major climate-altering volcanic eruption occurring in the next decade is estimated by the authors to be between 35 and 40 percent.

Soil Carbon Storage: The authors review the significance of soil to the biosphere and conclude that enhancing soil organic matter is of paramount importance to improving its ability to do its life-sustaining work.  We note that atmospheric CO2 enrichment is one of the most effective means for accomplishing this goal.

Response of Mature Spruce Trees to Elevated CO2: In a branch bag study conducted for four complete growing seasons on mature Sitka spruce trees, current-year needles on CO2-enriched branches displayed photosynthetic rates that were twice as great as those reported for needles on control branches flushed with ambient CO2, while in second-year needles the stimulation was 43%.  Branch growth parameters, however, were unaffected, most likely as a consequence of the export of photosynthetically-derived sugars from the CO2-enriched branches to other sinks within the tree.

Effects of Elevated CO2 and Light on Four Weedy Species: Four weedy species common to European grasslands were grown from seed to senescence in glasshouses receiving combinations of ambient and elevated atmospheric CO2 concentrations and full and reduced levels of light.  Elevated CO2 elicited a significant positive vegetative and reproductive growth response in only one species, while reduced light significantly decreased these growth types in all four weeds.  Moreover, the reductions in growth caused by shading were much greater in magnitude than growth increases resulting from atmospheric CO2 enrichment.  Thus, it is unlikely that these weeds will proliferate and dominate ecosystems in the next hundred years, as often predicted by individuals propagating the view of CO2-induced biological anarchy (of weeds).

Effects of Elevated CO2 and Nitrogen Supply on a Legumious Tree: After six weeks exposure to elevated CO2 and a wide range of mineral nitrogen concentrations, the leguminous tree Acacia melanoxylon did not exhibit any change in symbiotic nitrogen fixation as a function of the air's CO2 content.  However, the proportion of symbiotically-fixed nitrogen in ambient and CO2-enriched seedlings decreased with increasing nitrogen availability.  Thus, nitrogen fixation in this species is more dependent upon nitrogen availability than it is upon atmospheric CO2 concentration.  Nonetheless, seedlings grown at 700 ppm CO2 displayed significantly greater rates of net photosynthesis and total leaf nonstructural carbohydrate contents than seedlings grown at 350 ppm CO2.  These phenomena likely contributed to greater biomass production in CO2-enriched seedlings, which were consistently twice as great as those of their ambient counterparts, in all but the most nitrogen-deprived systems.

Effects of Nocturnal Elevated CO2 Treatment on C4 Species: Only one of four C4 plants responded positively to diurnal atmospheric CO2 enrichment by increasing both its photosynthetic rate and biomass production.  The other three plants may not have responded favorably to elevated CO2 due to the short duration of this three-week experiment.  Nonetheless, nocturnal CO2 enrichment of the one positively responding plant indicated that its significant growth response to elevated CO2 was not driven by reductions in dark respiration or more efficient internal leaf water balancing.  Thus, the mechanisms responsible for elevated CO2 responses in C4 species remain to be elucidated.

Effects of Elevated CO2 and Water Stress in Alfalfa: CO2-enriched water-stressed alfalfa plants produced significantly more total plant and nodule biomass than well-watered control plants grown at ambient CO2 concentrations.  In addition, water-stressed plants grown at 700 ppm CO2 contained significantly greater amounts of total plant nitrogen than did well-watered plants grown at 400 ppm CO2.  Thus, atmospheric CO2 enrichment completely ameliorated the growth-reducing effects of water-stress on biomass production in this important forage species.