Coastal upwelling and atmospheric CO2 changes

A transfer function relating diatom assemblages in surface sediments and primary production in the photic zone was used to calculate variations in primary production in hole ODP Leg 112, Site 681A over the last 400 kyr. Primary production off central Peru was enhanced during peak glaciations and it decreased during peak interglacials, but low and high production periods also occurred in both glacials and interglacials. The close resemblance of the primary production curve off Peru to the atmospheric CO2 Vostok record suggests a relationship between the Peruvian neritic biological pump and atmospheric pCO2.

Effects of elevated atmospheric CO2 concentration on leaf dark respiration of Xanthium strumarium in light and in darkness

Leaf dark respiration (R) is an important component of plant carbon balance, but the effects of rising atmospheric CO2 on leaf R during illumination are largely unknown. We studied the effects of elevated CO2 on leaf R in light (RL) and in darkness (RD) in Xanthium strumarium at different developmental stages. Leaf RL was estimated by using the Kok method, whereas leaf RD was measured as the rate of CO2 efflux at zero light. Leaf RL and RD were significantly higher at elevated than at ambient CO2 throughout the growing period. Elevated CO2 increased the ratio of leaf RL to net photosynthesis at saturated light (Amax) when plants were young and also after flowering, but the ratio of leaf RD to Amax was unaffected by CO2 levels. Leaf RN was significantly higher at the beginning but significantly lower at the end of the growing period in elevated CO2-grown plants. The ratio of leaf RL to RD was used to estimate the effect of light on leaf R during the day. We found that light inhibited leaf R at both CO2 concentrations but to a lesser degree for elevated (17–24%) than for ambient (29–35%) CO2-grown plants, presumably because elevated CO2-grown plants had a higher demand for energy and carbon skeletons than ambient CO2-grown plants in light. Our results suggest that using the CO2 efflux rate, determined by shading leaves during the day, as a measure for leaf R is likely to underestimate carbon loss from elevated CO2-grown plants.

Dependence of global temperatures on atmospheric CO2 and solar irradiance

Changes in global average temperatures and of the seasonal cycle are strongly coupled to the concentration of atmospheric CO2. I estimate transfer functions from changes in atmospheric CO2 and from changes in solar irradiance to hemispheric temperatures that have been corrected for the effects of precession. They show that changes from CO2 over the last century are about three times larger than those from changes in solar irradiance. The increase in global average temperature during the last century is at least 20 times the SD of the residual temperature series left when the effects of CO2 and changes in solar irradiance are subtracted.

A natural experiment on plant acclimation: lifetime stomatal frequency response of an individual tree to annual atmospheric CO2 increase.

Carbon dioxide (CO2) has been increasing in atmospheric concentration since the Industrial Revolution. A decreasing number of stomata on leaves of land plants still provides the only morphological evidence that this man-made increase has already affected the biosphere. The current rate of CO2 responsiveness in individual long-lived species cannot be accurately determined from field studies or by controlled-environment experiments. However, the required long-term data sets can be obtained from continuous records of buried leaves from living trees in wetland ecosystems. Fine-resolution analysis of the lifetime leaf record of an individual birch (Betula pendula) indicates a gradual reduction of stomatal frequency as a phenotypic acclimation to CO2 increase. During the past four decades, CO2 increments of 1 part per million by volume resulted in a stomatal density decline of approximately 0.6%. It may be hypothesized that this plastic stomatal frequency response of deciduous tree species has evolved in conjunction with the overall Cenozoic reduction of atmospheric CO2 concentrations.