Missing Carbon Sink Research Articles

Terrestrial sources and sinks of carbon inferred from terrestrial data

Two approaches have been used to calculate changes in terrestrial carbon storage with data obtained from terrestrial ecosystems, rather than with atmospheric or oceanographic data. One approach is based on the changes in carbon that result from changes in land use (conversion of forest to agricultural land, abandonment of agricultural land, harvest and regrowth). The other approach uses measurements of forest biomass obtained through forests inventories to determine change directly. These latter studies may also calculate changes in the amount of carbon stored in wood products and soil, but in this respect the two approaches are similar. If a significant fraction of the missing carbon sink is to be found in mid-latitude forests, one would expect direct measurement of biomass to show greater accumulations of carbon than analyses in which calculated accumulations result only from regrowth following previous harvests or abandonment of agricultural land. Data from Canada, the conterminous US, Europe, and the former USSR show this circumstance to be correct. Accumulations of carbon in biomass and soil are 0.8 PgC yr −1 greater than expected from past management practices (land-use change). In the tropics (where forest inventories are rare), the total net flux of carbon from changes in land use (1.6 PgC yr −1 ) is consistent with recent estimates of flux based on atmospheric data, but the geographic distribution of the flux is not the same. Globally, terrestrial ecosystems are calculated to have been a net source of 0.8 ± 0.6 PgC yr −1 during the 1980s. DOI: 10.1034/j.1600-0889.1996.t01-3-00002.x

In search of the missing carbon sink: a model of terrestrial biospheric response to land-use change and atmospheric CO2

In search of the missing carbon sink: a model of terrestrial biospheric response to land-use change and atmospheric CO2

In search of the missing carbon sink: a model of terrestrial biospheric response to land-use change and atmospheric CO<sub>2</sub>

Estimates of the net exchange of carbon between the terrestrial biosphere and the atmosphere may be too large because the models of carbon release from changes in land use do not allow for enhanced carbon assimilation by the terrestrial biosphere in response to increasing atmospheric CO 2 . We address this deficiency with a model of terrestrial biosphere that includes both ecosystem response to land-use perturbation and vegetation response to atmospheric CO 2 . Model inputs specify the areas affected by land-use change since 1700. The carbon dynamics of the affected areas are described by an area distribution function for vegetation carbon density and a compartment model of carbon in vegetation, litter, and soil. Vegetation growth is modeled as the difference between net primary production (NPP) and mortality. NPP, the net flux of carbon from atmosphere to vegetation, is a logistic function of vegetation carbon density. The response of NPP to atmospheric CO 2 is modeled with three response functions: a logarithmic, a rectangular-hyperbolic, and a response function derived from a biochemical model of C 3 photosynthesis. The response functions are parameterized by ecosystem type with data from CO 2 exposure experiments. Elevated CO 2 affects the NPP of both undisturbed and recovering ecosystems. We use the model to test the hypothesis that the CO 2 enhancement of terrestrial NPP explains the historical missing carbon sink of the global carbon cycle budget. Our estimates of the biosphere's CO 2 enhanced carbon flux are much smaller than the reconstructed missing carbon sink. We conclude that our model results do not support the hypothesis. DOI: 10.1034/j.1600-0889.47.issue4.9.x

A strategy for estimating the impact of CO2 fertilization on soil carbon storage

As soils are a likely candidate for the so called missing carbon sink, we explore the possible impact of CO2 fertilization on the global humus inventory. For any given greening‐induced enhancement of plant growth, the increase in soil carbon inventory will depend on the spectrum of turnover times with respect to oxidation. Here we develop estimates of carbon turnover rates based on soil radiocarbon measurements.

Terrestrial carbon storage resulting from CO2 and nitrogen fertilization in temperate grasslands

Abstract. A temperate grassland model has been used to simulate carbon sequestration under various environmental conditions. The results suggest that the CO2 and nitrogen fertilization that has occurred may contribute appreciably to the so‐called missing carbon sink, which it has been suggested must exist to balance the global carbon budget.

Resolving the intermediate and deep advective flows in the Indian Ocean by using temperature, salinity, oxygen and phosphate data: the interplay of biogeochemical and geophysical tracers

For computing large-scale advective flow in the Indian ocean (including the Indian-Antarctic sector), we use a box-model approach and perturbed inverse method. The top 400 meters is not considered in this study, in view of the dominant seasonal dynamics. We use 1244 hydrographic stations, to estimate mean values for temperature, salinity, oxygen and phosphate concentratons. Fifty perturbed inversions of steady-state tracers conservations and thermal-wind equations are done using box-averages standard deviations and a 25% perturbation on the thermal-wind coefficients. The mean solutions represent the large-scale advective flow and carbon-decomposition rates in which we are interested. Solutions with only advective processes are first considered. The broad features of the circulation in the Indian Ocean are resolved in the intermediate levels, but in deeper layers, an input from North Atlantic Deep Water (NADW) is not apparent. Inspection of oxygen and phosphate residuals reveals a biochemical signal. Therefore, we introduce in the oxygen and phosphate budgets a linear parameterization (Redfield ratios) for the organic-decomposition processes. The structure of the residuals for oxygen and phosphate is changed in that the biochemical signal vanishes. The advective solutions are nearly the same in intermediate waters; however, in deep layers the new solution shows an inflow of 11 (±8) Sv of NADW south of Africa. The calculated total organic decomposition of 0.93 (±0.25) 10 15g C year −1 is about one fifth of the estimated world ocean amount, but total residuals of oxygen and phosphate lead to an unexplained 0.5 10 15g C year −1 missing carbon sink. The new solution does contain unrealistic elements (e.g. large deep flow between Indonesia and Australia). Finally, to investigate this last result, we add one advective constraint at the Indonesia-Australia boundary. This addition changes the circulation in the northeastern part of the Indian Ocean. The circumpolar flow between 400 m and 27.65 (σo) remains unchanged at 20°E and at 80°E; however, at 130°E the constraint increases the advective flow by 20%. Total organic-carbon-decomposition rates are not affected by the additional inflow from Indonesia.

Resolving the intermediate and deep advective flows in the Indian Ocean by using temperature, salinity, oxygen and phosphate data: the interplay of biogeochemical and geophysical tracers

For computing large-scale advective flow in the Indian ocean (including the Indian-Antarctic sector), we use a box-model approach and perturbed inverse method. The top 400 meters is not considered in this study, in view of the dominant seasonal dynamics. We use 1244 hydrographic stations, to estimate mean values for temperature, salinity, oxygen and phosphate concentratons. Fifty perturbed inversions of steady-state tracers conservations and thermal-wind equations are done using box-averages standard deviations and a 25% perturbation on the thermal-wind coefficients. The mean solutions represent the large-scale advective flow and carbon-decomposition rates in which we are interested. Solutions with only advective processes are first considered. The broad features of the circulation in the Indian Ocean are resolved in the intermediate levels, but in deeper layers, an input from North Atlantic Deep Water (NADW) is not apparent. Inspection of oxygen and phosphate residuals reveals a biochemical signal. Therefore, we introduce in the oxygen and phosphate budgets a linear parameterization (Redfield ratios) for the organic-decomposition processes. The structure of the residuals for oxygen and phosphate is changed in that the biochemical signal vanishes. The advective solutions are nearly the same in intermediate waters; however, in deep layers the new solution shows an inflow of 11 (±8) Sv of NADW south of Africa. The calculated total organic decomposition of 0.93 (±0.25) 10 15g C year −1 is about one fifth of the estimated world ocean amount, but total residuals of oxygen and phosphate lead to an unexplained 0.5 10 15g C year −1 missing carbon sink. The new solution does contain unrealistic elements (e.g. large deep flow between Indonesia and Australia). Finally, to investigate this last result, we add one advective constraint at the Indonesia-Australia boundary. This addition changes the circulation in the northeastern part of the Indian Ocean. The circumpolar flow between 400 m and 27.65 (σo) remains unchanged at 20°E and at 80°E; however, at 130°E the constraint increases the advective flow by 20%. Total organic-carbon-decomposition rates are not affected by the additional inflow from Indonesia.