Radiocarbon age calibration of marine samples back to 9000 CAL YR BP (original) (raw)
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The variability in the carbon sinks as reconstructed for the last 1000 years
Geophysical Research Letters, 1999
The atmospheric CO2 and 5iac records for the last millennium have been analyzed to reconstruct the evolution and the temporal variability in the terrestrial and oceanic carbon sinks and to identify natural variations in the marine carbon cycle. Reconstructed natural variations in sinks are usually less than 4-0.2 Gt C yr-1 on time scales of decades to centuries and thus one order of magnitude smaller than the sink fluxes driven by the anthropogenic perturbation. The natural oceanic carbon cycle was generally close to steady state on a multi-decadal time scale. A large anomalous oceanic carbon sink is found around 1940 that is attributed to a higher than usual E1 Nifio activity. Interannual variations in the oceanic sink as reconstructed for the 1980-1996 period are around 4-I Gt C yr -1 and are significantly correlated with the Southern Oscillation. The relatively low atmospheric CO2 concentrations between 1600 and 1750 were caused by an additional terrestrial storage of 40 Gt C. The land biota acted as a carbon source between 1750 and 1950 and as a sink afterwards. Terrestrial changes can be explained by land use emission up to 1920. Then, additional mechanisms such as CO2 fertilization are responsible for an estimated terrestrial sequestration of 100 Gt C between 1920 and 1996. study, Global Biogeochem. Cycles, 7(4), 843-878, 1993. Trudinger, C. M., I. G. Enting, R. J. Francey, D. M. Etheridge, and P. J. Rayner, Long-term variability in the global carbon cycle inferred from a high precision CO2
Global Biogeochemical Cycles, 1997
We have updated earlier deconvolution analyses using most recent high-precision ice core data for the last millennium lEtheridge et al., 1996] and direct atmospheric CO• observations st'arting in 1958 [Keeling and Whorl, 1994]. We interpreted nonfossil emissions, that is, the difference between the increase in observed atmospheric plus modeled oceanic carbon inventory and fossil emissions, as biospheric carbon storage (release). We have assessed uncertainties in the CO• ice core data using a Monte Carlo approach and found • 2-a uncertainty for the nonfossil emissions (20-year averages) of 0.2-0.4 GtC yr -•. Overall uncertainties of the nonfossil emissions were estimated to be 0.5 GtC yr -• before 1950 and •1 GtC yr -1 during the last decade. We found a large and rapid change of-0.8 GtC yr -• in the nonfossil emissions (approximate net air-biota flux) between 1933 and 1943• Before 1933• the land biota acted as carbon source of order 0.5 GtC yr -• in agreement with independent estimates of carbon emissions by land use changes [Houghton, 1993a]. After 1943• the land biota was a net sink of about 0.3 GtC yr -•.
Carbon dioxide and climate over the past 300 Myr
… Transactions of the Royal Society of …, 2002
The link between atmospheric CO 2 levels and global warming is an axiom of current public policy, and is well supported by physicochemical experiments, by comparative planetary climatology and by geochemical modelling. Geological tests of this idea seek to compare proxies of past atmospheric CO 2 with other proxies of palaeotemperature. For at least the past 300 Myr, there is a remarkably high temporal correlation between peaks of atmospheric CO 2 , revealed by study of stomatal indices of fossil leaves of Ginkgo, Lepidopteris, Tatarina and Rhachiphyllum, and palaeotemperature maxima, revealed by oxygen isotopic (δ 18 O) composition of marine biogenic carbonate. Large and growing databases on these proxy indicators support the idea that atmospheric CO 2 and temperature are coupled. In contrast, CO 2 -temperature uncoupling has been proposed from geological time-series of carbon isotopic composition of palaeosols and of marine phytoplankton compared with foraminifera, which fail to indicate high CO 2 at known times of high palaeotemperature. Failure of carbon isotopic palaeobarometers may be due to episodic release of CH 4 , which has an unusually light isotopic value (down to −110 % % , and typically −60 % % δ 13 C) and which oxidizes rapidly (within 7-24 yr) to isotopically light CO 2 . Past CO 2 highs (above 2000 ppmv) were not only times of catastrophic release of CH 4 from clathrates, but of asteroid and comet impacts, flood basalt eruptions and mass extinctions. The primary reason for iterative return to low CO 2 was carbon consumption by hydrolytic weathering and photosynthesis, perhaps stimulated by mountain uplift and changing patterns of oceanic thermohaline circulation. Sequestration of carbon was promoted in the long term by such evolutionary innovations as the lignin of forests and the sod of grasslands, which accelerated physicochemical weathering and delivery of nutrients to fuel oceanic productivity and carbon burial.
The author has enhanced the original one dimensional semi-empirical atmosphere-ocean-biosphere model 1DAOBM based on the four-box presentation. The improved 1DAOBM-2 contains two major parameters, which have been tuned to adjust the total CO 2 net flux rate and the anthropogenic net flux rate from the surface ocean into the deep ocean based on the observed values. The surface ocean part is based on the known dissolution chemical equations according to Henry's law depending on the atmospheric CO 2 concentration and the surface ocean temperature. Simulations have been used to calculate the dynamic responses to the step changes from the actual fossil fuel rate to zero in 1964. The results show that the anthropogenic CO 2 decay rate follows very accurately the observed decay rate of radiocarbon 14 C having the residence time of 16 years. This is the expected result according to nature of anthropogenic CO 2 in the system of the atmosphere, the ocean and the biosphere. The decay rate of the total CO 2 in this system is much longer having the residence time of 55 years matching the adjustment time of 220 years. The simulations of the atmospheric net CO 2 rate by 1DAOBM-2 from 1960 to 2013 confirms the earlier results that the coefficient of determination r 2 = 0.75 (r 2 = 0.81 eliminating the Pinatubo eruption effects). The simulations also show that the present anthropogenic CO 2 fraction in the atmosphere is 8.0%, and it explains the observed δ 13 C value of-8.4‰ extremely well. The problem of the sink Original Research Article
Introduction to Special Section: Ocean Measurements and Models of Carbon Sources and Sinks
Global Biogeochemical Cycles, 2001
This issue of Global Biogeochemical Cycles contains a remarkable set of papers, which critically evaluate a variety of model-and observation-based approaches addressing the oceanic distribution, storage, and transport of CO2. Three of the papers are concerned with observation-based estimates of excess (or anthropogenic) CO2 [Coatanoan et al., this issue; Sabine and Feely, this issue; Chen, this issuel. They focus on the approaches, assumptions, and uncertainties involved in detecting the excess CO2 signal above the ocean's large and variable natural dissolved inorganic carbon (DIC) background. A further paper [Orr e! al., this issue] deals with modeling of the uptake of excess CO2, including a comparison of model results with observation-based estimates. A companion article published in the previous issue of this journal by Sarmiento e! al. [2000] addresses the preindustrial or "natural" carbon cycle and.particularly the role of the ocean in transporting carbon between the Northern and Southern Hemispheres. 2. Storage of Excess CO• The term "excess CO2" refers to carbon inventory or concentration differences within an environmental reservoir (e.g., the ocean, atmosphere, fossil fuel reserves or the terrestrial biosphere) relative to inventories or concentrations that existed during the preindustrial era. Analyses of high-resolution ice cores [Smith et al., 1999; Indermuehle et al., 1999] reveal that atmospheric levels of CO2 have varied by no more than-20 btatm (1 btatm-0.101325 Pa) through most of the Holocene. Around the year 1750 atmospheric levels started to rise from the late-Holocene level of-280 uatm, initially owing to excess CO2 released by land use changes and later owing to fossil fuel combustion. It is generally assumed that prior to 1750 the global carbon cycle was in a steady state that has now been significantly perturbed as a direct result of human activity. Hence the preindustrial era against which excess CO2 levels are assessed ended around 1750. In estimating or modeling oceanic levels of excess CO2, it is almost invariably assumed that changes in the ocean's dissolved carbon content since 1750 have been caused exclusively by an increased net air-to-sea flux driven by the anthropogenic increase of the pCO2 of the atmosphere. The uptake of excess CO2 by the oceans during the 1980s was-2 Pg C yr-• [Siegenthaler and
Biogeosciences Discussions
Release of CO 2 from surface ocean water owing to precipitation of CaCO 3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a model that gives the quotient θ = (CO 2 released to the atmosphere)/(CaCO 3 precipitated). The surface ocean layer is approximated by a euphotic zone, 50 m thick, that includes the shallower coastal area and open ocean. θ depends on water temperature, CaCO 3 and organic carbon mass formed, and atmospheric CO 2 concentration. At temperatures between 5 and 25 • C, and three atmospheric CO 2 pressures-195 ppmv corresponding to the Last Glacial Maximum, 280 ppmv for the end of pre-industrial time, and 375 ppmv for the present-θ varies from a fraction of 0.38 to 0.79, increasing with decreasing temperature, increasing atmospheric CO 2 content, and increasing CaCO 3 precipitated mass (up to 45% of the DIC concentration in surface water). For a surface ocean layer that receives input of inorganic and organic carbon from land, the calculated CO 2 flux to the atmosphere at the Last Glacial Maximum is 20 to 22×10 12 mol/yr and in pre-industrial time it is 45 to 49×10 12 mol/yr. In addition to the environmental factors mentioned above, flux to the atmosphere and increase of atmospheric CO 2 depend on the thickness of the surface ocean layer. The significance of these fluxes and comparisons with the estimates of other investigators are discussed. Within the imbalanced global carbon cycle, our estimates are in agreement with the conclusions of others that the global ocean prior to anthropogenic emissions of CO 2 to the atmosphere was losing carbon, calcium, and total alkalinity owing to precipitation of CaCO 3 and consequent emission of CO 2. Other pathways of CO 2 exchange between the atmosphere and land organic reservoir and rock weathering may reduce the imbalances in the carbon cycle on millenial time scales.