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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 9, NUMBER 9, SEPTEMBER 1996

PROFESSIONAL PUBLICATIONS...
CARBON CYCLE

Item #d96sep7

"Global Net Carbon Exchange and Intra-annual Atmospheric CO₂ Concentrations Predicted by an Ecosystem Process Model and Three-Dimensional Atmospheric Transport Model," E.R. Hunt Jr. (Dept. Bot., Univ. Wyoming, Laramie WY 32071; e-mail: erhunt@uwyo.edu), S.C. Piper et al., Global Biogeochem. Cycles, 10(3), 431-456, Sep. 1996

Used a generalized terrestrial ecosystem process model to simulate the global fluxes of CO₂ that result from photosynthesis, autotrophic respiration and heterotropic respiration. Predictions agreed to an encouraging degree in phase and amplitude with observed atmospheric CO₂ concentrations for 20° to 55° N latitude, the zone where most data are available. In the tropics and high northern latitudes the agreement was poor. The methodology presented here allows terrestrial ecosystem models to be tested globally, not by comparisons to homogeneous plot data, but by seasonal and spatial consistency with a diagnostic vegetation model and atmospheric CO₂ observations.

Item #d96sep8

"Modeling Carbon Stores in Oregon and Washington Forest Products: 1900-1992," M.E. Harmon (Dept. Forest Sci., Oregon State Univ., Corvallis OR 97331), J.M. Harmon et al., Clim. Change, 33(4), 521-550, Aug. 1996.

This new model for estimating carbon stored in forest products considers the manufacture of raw logs into products and their fate during use and disposal. Pools examined were long- and short-term structures, paper supplies, mulch, open dumps and landfills. Of the 1,692 Tg of carbon harvested during the selected period, only 23% is currently stored, mostly in long-term structures and landfills.. Most carbon release has occurred during manufacture and this may help to account for the lack of sensitivity of forest products models. The fate of paper and wood wastes appears to be a key focus for future research.

Item #d96sep9

"An Efficient and Accurate Representation of Complex Oceanic and Biospheric Models of Anthropogenic Carbon Uptake," F. Joos (Physics Inst., Univ. Bern, CH-3012 Bern, Switz.; e-mail: joos@climate.unibe.ch), M. Bruno et al., Tellus, 48B(3), 397-417, July 1996.

Proposes an ocean mixed-layer pulse response function that characterizes the surface to deep ocean mixing in combination with a separate equation describing air-sea exchange. This avoids the problem arising from nonlinearities of carbon chemistry and gives more accurate results. Found that difference between the complete Princeton 3-D model and its pulse substitute is better than 4% for cumulative uptake of anthropogenic carbon for the period 1765 to 2300.

Item #d96sep10

"A Feasible Global Carbon Cycle Observing System: A Plan to Decipher Today's Carbon Cycle Based on Observations," P.P. Tans, P.S. Bakwin (ERL R/E/CG1, NOAA, 325 Broadway, Boulder CO 80303; e-mail: pbakwin@cmdl.noaa.gov), D.W. Guenther, Global Change Biology, 2(3), 309-318, June 1996.

One of 14 papers selected from a workshop, Strategies for Monitoring and Modelling CO₂ and Water Vapour Fluxes over Terrestrial Ecosystems (Mar. 1995, Valle d'Aosta, Italy). Presents a design to continuously monitor transfers of carbon between the atmosphere and the terrestrial biosphere and oceans on large spatial scales. Considering the expected signal-to-noise ratio, a cost effective method would be to perform repeated measurements of the mixing ratios of trace gases at more sites than the present geographical coverage, a process that can be done by applying existing technology.

Item #d96sep11

Two related items in Clim. Change, 33(1), May 1996:

"Accounting for the Missing Carbon Sink with the CO₂ Fertilization Effect," H.S. Kheshgi (Corporate Res. Labs., Exxon Res. Co., Annandale NJ 08801), A.K. Jain, D.J. Wuebbles, 31-62. Estimates the magnitude of the biospheric sink with a simple carbon cycle box model, assuming that the past missing carbon sink was due to the CO₂-fertilization effect. Then uses the model to project the future role of this sink in the carbon budget under a variety of scenarios, finding that it could rival the oceanic sink in the next century.

"The CO₂ Fertilization Factor and the 'Missing' Carbon Sink: An Editorial Comment," A.A. Keller (Stanford Univ., Stanford CA 94304), 63-68. The role of simple carbon cycle models such as the one used in the previous paper is to point us in the correct direction, by defining the magnitude of the response and to provide interim answers to policy makers. But closing the "missing carbon sink" debate will require high resolution models with multiple components.

Item #d96sep12

"Moving the British Cattle Herd," P. Smith (Soil Sci. Dept., IACR-Rothamsted, Harpenden, Herts AL5 2JQ, UK), J.U. Smith, D.S. Powlson, Nature, 381(6577), 15, May 2, 1996.

A commonly suggested solution to the U.K.'s crisis involving bovine spongiform encephalopathy ("mad cow disease") is to move all cattle to new pasture after eradication of the disease. This article attempts to quantify the possible impact of this scenario on soil carbon content and on nitrate leaching. If permanent grasslands were plowed for arable crops there would be significant and long-lasting environmental effects, including losses in soil organic carbon.

Item #d96sep13

Two related items in Nature, 381(6579), May 16, 1996:

"A Quickening on the Uptake?" M. Bender (Grad. Sch. Oceanog., Univ. Rhode Island, Kingston RI 02881), 195-196. The following paper is the second landmark contribution from Keeling et al. on the distribution of oxygen concentration in air and its implications for the CO₂ budget. The flux terms they calculate (using the O2/N2 ratio) are in good agreement with estimates from tracer methods. Possible causes for rapid uptake in northern biota they find include CO₂ fertilization of land biosphere, nitrogen fertilization from industrial emissions, and warmer temperatures and increased precipitation.

"Global and Hemispheric CO₂ Sinks Deduced from Changes in Atmospheric O2 Concentration," R.F. Keeling (Scripps Inst. Oceanog., La Jolla CA 92093), S.C. Piper, M. Heimann, 218-221. Carbon sinks are missing in both the global and the Northern Hemispheric carbon budgets, suggesting that northern land biota may be missing sink. This study presents an extensive data set for the ratio O2/N2 which shows simultaneous trends in this ratio in both Northern and Southern Hemispheres. For 1991-1994, the global oceans and the northern land biota each removed the equivalent of ¸30% of fossil fuel CO₂ emissions, while the tropical land biota were not a strong source or sink.

Item #d96sep14

"A Latitudinal Gradient in Carbon Turnover Times in Forest Soils," M.I. Bird (Sch. Earth Sci., Australian Natl. Univ., Canberra, ACT 0200, Australia), A.R. Chivas, J. Head, Nature, 381(6578), 143-146, May 9, 1996.

Analyzes carbon isotope contents and ratios in particulate organic carbon samples from low altitude, non-water-stressed forests. A marked latitudinal gradient supports the proposition that high-latitude forest soils have the capacity to act as a net sink for anthropogenic CO₂ on decadal time scales.

Item #d96sep15

"Significance of Ocean Carbonate Budgets for the Global Carbon Cycle," P.M. Holligan (Dept. Oceanog., Univ. Southampton, Southampton SO17 1BJ, UK), J.E. Robertson, Global Change Biology, 2(2), 85-95, Apr. 1996.

A commissioned review that examines the role of biologically driven fluxes of organic and inorganic carbon in modifying the carbon dioxide chemistry of the oceans, and the corresponding implications for partitioning of CO₂ between atmosphere and ocean. Some of the topics presented are: recent estimates of and uncertainties in marine carbonate fluxes; the need to account for the carbonate pump and subtle interactions between organic and inorganic carbon cycling in addition to accounting for the role of ocean biota; the significance of carbonate formation and dissolution; and the effects of global change on the marine carbonate system.

Item #d96sep16

"Rapid Exchange Between Soil Carbon and Atmospheric Carbon Dioxide Driven by Temperature Change," S.E. Trumbore (Dept. Earth System Sci., Univ. California, Irvine CA 92717), O.A. Chadwick, R. Amundson, Science, 272(5260), 393-396, Apr. 19, 1996.

Comparison of 14C in pre-1963 and contemporary soils along an elevation gradient in the Sierra Nevada, California, revealed rapid (7-65 years) turnover for 50-90% of the carbon in the upper 20 cm. Carbon turnover times increased with elevation (decreasing temperature), a trend, consistent with that from other locations, indicating that temperature is a dominant control of soil carbon dynamics. When extrapolated to large regions, the observed relation between carbon turnover and temperature suggests that soils should be significant sources or sinks of atmospheric CO₂ in response to global temperature changes.

Item #d96sep17

Two related items in Nature, 379(6566), Feb. 15, 1996:

"Iron Grip on Export Production," A. Longhurst (Biological Oceanog., Bedford Inst. Oceanog., Dartmouth NS B2Y 4A2, Can.), 585-586. The following paper and one by Kumar et al. (Nature, 1995) have added to our understanding of the factors that control the rate of oceanic carbon uptake by phytoplankton, showing that over some of the ocean the controlling factor is iron. We need to understand how this occurs in order to predict phytoplankton response to even higher levels of CO₂ than those already being produced from anthropogenic sources. Models of algal growth must also include iron transport and supply to quantify the response of the ocean to changing global climate regimes, or to predict where iron limitation may occur in the larger regions now thought to be nitrate limited.

"Control of Community Growth and Export Production by Upwelled Iron in the Equatorial Pacific Ocean," K.H. Coale (Moss Landing Marine Labs., POB 450, Moss Landing CA 95039), S.E. Fitzwater et al., 621-624. Surface water measurements show that the main iron source to equatorial waters at 140° W is from upwelling waters, not solely from atmospheric deposition as has been suggested.

Item #d96sep18

"Coral Reefs and Carbon Dioxide," Science, 271(5253), 1298-1300, Mar. 1, 1996.

Comments and a reply by H. Kayanne concerning his suggestion that coral reefs might serve as a sink, not a source, for atmospheric CO₂.