What Has Been Learned About The Influences Of Ecosystem Changes On Climate?


Primary Productivity In The Equatorial Pacific May Be Driven By Ammonium Rather Than Nitrate, With Implications For CO2 Uptake By The Oceans

The Equatorial Pacific Process Study (EqPac) of the Joint Global Ocean Flux Studies (JGOFS) program has provided substantial new insights into the dynamics of primary production associated with the upwelling in the equatorial Pacific. The equatorial Pacific is the single largest oceanic source for carbon dioxide release to the atmosphere, and up to 50% of world ocean primary production occurs there. Both primary productivity and chlorophyll were found to be lower than expected for this high-nutrient area, and two hypotheses have been put forward to explain this anomaly--one related to grazing by the zooplankton and the other related to the input of the micro nutrient iron. In the spring, EqPac researchers found that 80% to 90% of the phytoplankton growth was consumed by grazing; during cold tongue conditions grazing remained unchanged, but primary production was boosted, leading to increased sedimentation of carbon to the deep ocean. The rapid turnover indicates a food web driven by ammonium rather than nitrate. The spatial distribution of dissolved iron suggests that this micro nutrient enters the food web both from upwelling and via atmospheric deposition, suggesting that current popular notions about iron limitation in this region should be re-examined.
References: Physical and Biological Controls on Carbon Cycling in the Equatorial Pacific, Murray, J. W., R. T. Barber, M., R. Roman, M., P. Bacon, and R. A. Feely, Science, Vol. 266, pp. 58-65, 1994.

Forests Species Respond Differently To Elevated CO2 And O3

Multiple stress experiments have shown that white pine, trembling aspen and yellow poplar grown in open top chambers demonstrate very different responses to elevated ozone levels, alone or in combination with exposure to carbon dioxide. In experiments with trembling aspen exposed to ozone, the addition of elevated carbon dioxide produced a strong negative interaction, illustrating the difficulty of generalizing about the likely response of ecosystems based on single factor experiments with a limited number of species.
References: (1) Photosynthetic Productivity of Aspen Clones Varying in Sensitivity to Tropospheric Ozone, Coleman, M. D., R. E. Dickson, J. Isebrands, and D. F. Karnosky, Tree Physiology, in press, 1995; (2) Carbon Allocation and Partitioning in Aspen Clones Varying in Sensitivity to Tropospheric Ozone, Coleman, M. D., R. E. Dickson, J. Isebrands, and D. F. Karnosky, Tree Physiology, in press, 1995; (3) Photosynthetic Responses of Aspen Clones to Simultaneous Exposures of Ozone and CO2, Kull, O., A. Sober, M. Coleman, R. Dickson, J. Isebrands, Z. Gagnon, and D. Karnosky, Canadian Journal of Forest Research, submitted, 1995.

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Last updated 04/10/96