Fires and Oxygen

The frequency of forest fires, all other factors being held constant, should vary with the level of atmospheric oxygen because fire is sensitive to oxygen concentration. The quantitative effect of varying O2 on fire ignition and spread has been studied extensively in the laboratory (e.g., Tewarson, 2000 Babrauskas, 2002), but only on commercial materials. Little attention has been paid to the effects of varying O2 on the burning of forest fuels. One such study examined the ignition of paper...

Proxy Methods

Carbon Cycle The Permian

A variety of independent tests of the modeling predictions as to levels of Phanerozoic atmospheric CO2 are available. Methods include determining 1 the S13C of carbonates in paleosols 2 the stomatal density Figure 5.14. Input function for volcanic degassing of CO2 and for CO2 formed by the oxidation of CH4 from methane hydrate decomposition at the Permian-Triassic boundary. After Berner, 2002. Figure 5.14. Input function for volcanic degassing of CO2 and for CO2 formed by the oxidation of CH4...

Carbonate Deposition and Degassing

Any transfer of carbonate deposition from shallow-water shelves and platforms to the deep sea should have resulted in increased rates of global degassing in the geological past. This is because deep sea carbonates rest on oceanic crust that undergoes subduction and possible degassing at active plate boundaries. In chapter 3 it was shown that the rise and spread of calcareous plankton, chiefly coccoliths and forams, should have caused a shift of carbonate burial from shallow to deep water...

Methane Degassing

Methane is a potent greenhouse gas, 30 times stronger per molecule than CO2, and it is produced during both the short-term and long-term carbon cycles. In the prehuman short-term cycle, it is produced mainly from wetlands and animal exhalation such as from bovids and termites. These organisms have bacteria located in their digestive systems that break down carbohydrates to methane. In wetlands and other water-logged, organicrich sediments, methane forms from a variety of microbial processes and...

Processes of the Long Term Carbon Cycle Degassing of Carbon Dioxide and Methane

Degassing of CO2 and CH4 to the atmosphere and oceans is the process whereby carbon is restored to the surficial system after being buried in rocks. Carbon dioxide is released by a variety of processes. This includes volcanic emissions from the mantle and metamorphic and diagenetic decarbonation of limestones and organic matter. Volcanic degassing can occur over subduction zones, at mid-ocean rises, on the continents, and in the interior of oceanic plates. Degassing can be sudden and violent,...

Plants and Weathering

Berner And Kothavala 2001

There is little doubt that land plants accelerate the chemical weathering of silicate minerals for a summary, consult Berner et al., 2003 . This is accomplished in a variety of ways. First, rootlets symbiotic micro- Figure 2.2. Plot of fR t versus time based on Sr isotope modeling and on the abundance of Phanerozoic terrigenous sediments sandstones and shales . The curve is a cubic fit to the sediment abundance data. The parameter fR t is a measure of the effect of physical erosion on Ca and Mg...

The A Priori Method

A third approach, not dependent directly on either rock abundance or carbon and sulfur isotopic data, has been used for calculating changes in atmospheric O2 over time. Most of the models consider the cycles of the nutrients, P and N, and how they bring about negative feedback stabilization of O2 level. Such feedbacks, as they affect marine organic matter burial, are illustrated in figure 3.1 of chapter 3. The model of Hansen and Wallmann 2003 for the past 150 million years uses the a priori...

Plants and Oxygen

Carbon Oxygen Cycle

Before the Miocene, plants of the geological past almost all utilized the C-3 photosynthetic pathway that involves the competition of O2 and CO2 for sites on the key enzyme, rubisco. Carbon dioxide is taken up by rubisco during photosyhthesis, and O2 is taken up during photorespiration. Fractionation of carbon isotopes is affected by the relative rates of photosynthesis and photorespiration. At high O2 CO2 more O2 is taken up on rubisco and less CO2. As a result, the CO2 builds up within the...

Plankton Carbon Isotope Fractionation

The fractionation of carbon isotopes by marine phytoplankton is a function of the concentration of dissolved CO2 in seawater Rau et al., 1989 Hinga et al., 1994 . If surface waters can be assumed to be in exchange equilibrium between dissolved CO2 and atmospheric CO2, then the frac-tionation could be used as a measure of the level of atmospheric CO2. This observation has led to the suggestion that the difference between the 813C of coexisting organic matter and CaCO3 in sedimentary rocks might...

Land Plant Evolution

The rise of large vascular land plants during the Devonian perturbed the long-term carbon cycle not only by accelerating the weathering of silicate rocks, but also by bringing about the removal of atmospheric CO2 and production of O2 by increased burial of organic matter in sediments. The increased burial was due primarily to the creation by the plants of a new microbially resistant form of organic matter, lignin. Lignin is unique to woody land plants, and it is decomposed only by a very...

Summary CO and Climate

Royer 2004 Co2

Both theoretical modeling and proxy estimates point to similar trends for CO2 over Phanerozoic time. High levels of CO2 in the early Paleozoic are followed by a large drop to low levels during the Permo-Carboniferous. A primary reason for this drop, based on GEOCARB modeling, and the models of Mackenzie et al. 2003 and Bergman et al. 2003 , was the rise of large vascular land plants, which accelerated the weathering of Ca and Mg silicates and later led to the burial of increased quantities of...

Metamorphic and Diagenetic CO Degassing

Often the discussion of global CO2 degassing has concentrated only on volcanic processes. This neglects additional processes that may be just as important globally. For example, the range shown in table 4.1 for estimated total mantle degassing can be distinctly lower than that estimated for CO2 consumption by silicate weathering 6 3 x 1018 mol my . The remainder must be metamorphic or diagenetic in origin Kerrick, 2001 . The pathfinding study of Barnes et al. 1978 pointed to the importance of...

Solar Radiation Cosmic Rays and Weathering

Solar Radiation With Time

As emphasized in the previous section, the rate of mineral dissolution during weathering is a function of the temperature of the land. Besides the atmospheric greenhouse effect, there is also the effect of changes in solar radiation on both global and land surface temperature. It is well documented by solar physicists Endal and Sofia, 1981 Gough, 1981 that the gradual evolution of the sun over geologic time has resulted in increasing levels of radiation reaching the earth. On a geologic time...

Summary

Organic matter burial is a major process for transferring carbon dioxide from the surficial system to the rock record. It is also the principal process for the production of atmospheric oxygen. Rates of burial have been calculated from the abundance of organic matter in sedimentary rocks as a function of time and through the use of the carbon isotopic composition of seawater as recorded by sedimentary carbonates. Both methods demonstrate that organic burial increased appreciably during the...

Paleosol Carbon Isotopes

Carbon Isotopes Carboniferous

The paleosol method Cerling, 1991 rests on the assumption that the carbon in pedogenic carbonate is precipitated in isotopic equilibrium with dissolved inorganic carbon in soil waters and with soil CO2. The isotopic composition of soil CO2 is the result of mixing respired CO2, with the 813C value of soil organic matter, and atmospheric CO2. The relative proportions of respired CO2 and atmospheric CO2 determine the 813C of the soil gas and, if exchange equilibrium is attained, also of soil...

Mountain Uplift Physical Erosion and Weathering

Global Erosion Rates

Within the past decade much attention has been paid to the effect of mountain uplift on chemical weathering and its effect on the uptake of atmospheric CO2, an idea originally espoused by T.C. Chamberlin 1899 . The uplift of the Himalaya Mountains and resulting increased weathering has been cited as a principal cause of late Cenozoic cooling due to a drop in CO2 Raymo, 1991 . Orogenic uplift generally results in the development of high relief. High relief results in steep slopes and enhanced...

Weathering of Organic Matter

Much less attention has been paid to the weathering oxidation of organic matter than to its burial. This is a shame because both processes equally affect the level of atmospheric CO2 and O2. Recently, experimental evidence has been presented that shows that the oxidation of coal as a representative of sedimentary organic matter in water results in the formation of oxygen-containing organic compounds before complete oxidation to CO2 Chang and Berner, 1999 . The kinetics of the coal-oxygen...

Modeling the Phanerozoic Carbon Cycle

Diagram The Carbon Cycle

Together the carbonate-silicate and organic long-term subcycles play the dominant role in controlling the levels of atmospheric CO2 and O2 over millions to billions of years. In this book I show how these subcycles have operated only over the past 550 million years, the Phanerozoic eon. The Phanerozoic is chosen because of the abundance of critical data such as abundant multicellular body fossils, relatively noncontroversial pa-leogeographic reconstructions, and relatively agreed-upon tectonic...

Atmospheric Greenhouse Effect and Weathering

Silicate Weathering Diagram

Changes in the concentration of greenhouse gases affect both the temperature and the hydrology of the continents, which in turn affect the rate of uptake of CO2 via silicate mineral weathering. The principal greenhouse gases of interest are CO2 and CH4. Although H2O is the strongest greenhouse gas, it is buffered by evaporation and condensation that is driven by external factors such as solar radiation and the CO2 greenhouse effect. The buildup of CO2 in the atmosphere can lead to higher...

Model Results

Results of rock abundance modeling Berner and Canfield, 1989 and isotope mass balance modeling Berner, 2001 for atmospheric oxygen over Phanerozoic time are compared in figure 6.5. The isotope modeling, designated here as RROD, is based on the carbon isotopic data of Veizer et al. 1999 with a minor positive excursion during the Silurian ignored see figure 3.3 , the sulfur isotopic data of Strauss 1999 , and rapid recycling RR and O2-dependent OD C and S isotope fractionation Berner, 2001 ....

The Rock Abundance Method

Berner Rock Abundance

The rock abundance method Berner and Canfield, 1989 , for Fbg and Fbp, is based on original global sedimentation rates of terrigenous sediments sandstones and shales and their organic carbon and pyrite sulfur contents. Most sedimentary organic matter and pyrite is found in shales. For this purpose terrigenous deposition over time is divided into three major categories Ronov, 1976 coal basin sediments, noncoal continental deposits mainly redbeds , and marine sediments. This leads to the...

Long Term Model Calculations

Silicate Weathering Cycle

Values of fluxes in the long-term carbon cycle can be calculated from the fundamental equations for total carbon and 13C mass balance that are stated in the introduction and are repeated here dMc dt Fwc FWg Fmc Fmg - Fbc - Fbs 1.10 d 5cMc dt SwcFwc SwgFwg SmcFmc 1.11 Mc mass of carbon in the surficial system consisting of the atmosphere, oceans, biosphere, and soils flux from weathering of Ca and Mg carbonates flux from weathering of sedimentary organic matter degassing flux for carbonates from...

Boron Isotopes in Carbonates

Dissolved boron in the oceans is present primarily as B OH 3 and B OH 4-, and these two species differ in the ratio 11B 10B. Field obser vations and experimental studies have suggested that the uptake of boron into biogenic calcium carbonate records the isotopic composition of B OH 4- with little isotopic fractionation Hemming and Hanson, 1992 Sanyal et al., 1996 . Because the relative proportions of the two dissolved boron species vary with pH, and the degree of isotopic fractionation between...

Lithology and Weathering

The dominant source of dissolved Ca and Mg during silicate weathering is Ca contained in plagioclase Mackenzie and Garrels, 1966 Garrels, 1967 , Mg in ferromagnesian minerals such as pyroxenes, amphiboles, and biotite, and both Ca and Mg in volcanic glass. Field studies of the rate of weathering of small areas of relatively uniform rock type, subject to similar climates and relief Meybeck, 1987 Taylor and Lasaga, 1999 , have shown that basalts weather faster then granites or other acidic...

The Isotope Mass Balance Method

Modele Garrels Lermann

The isotope mass balance method for determining the values of Fbg, Fwg, Fbp, and Fwp is based on variations over Phanerozoic time in 13C 12C and 34S 32S of the oceans as recorded by the isotopic composition of CaCO3 and sulfate-containing minerals mainly CaSO4 in sedimentary rocks Veizer et al., 1999 Strauss, 1999 . As discussed in chapter 3, changes in oceanic 13C 12C figure 3.3 , expressed as 813C, largely reflect changes in the burial flux of organic matter in sediments. Changes in oceanic...

Organic Matter Burial in Sediments

Feedback Short Term Organic Carbon Cycle

At present, sedimentary organic matter burial occurs in swamps, lakes, reservoirs, estuaries, and in the open marine environment. The ultimate sources of the organics are land vegetation and marine phytoplankton. Also, soil organic matter, which is intimately associated with clay minerals, is eroded and transported to the sea by rivers Hedges et al., 1994 . A major question is how much of the total global burial is of marine or nonmarine origin. Recent work has shown that organic burial on land...

Degassing Rate of CO

Estimates of present-day global volcanic degassing rates are under constant revision e.g., see Gerlach, 1991 Brantley and Koepenick, 1995 Sano and Williams, 1996 Marty and Tolstikhin, 1998 Kerrick, 2001 . A compilation of recent estimated rates of most degassing processes is shown in table 4.1. A constraint on estimates is that none can exceed total global degassing. The latter can be determined from the steady-state assumption that CO2 release by global degassing must be balanced by global...

Submarine Weathering of Basalt

The reaction of CO2 dissolved in seawater with Ca and Mg silicate minerals in basalt can result in the formation of calcium and magnesium carbonates within the basalt Staudigal et al., 1989 . This is an additional process that could affect atmospheric CO2, because oceanic and atmospheric CO2 are in exchange contact. Some carbon cycle models include this process as a major control on CO2 Brady and Gislason, 1997 Sleep and Zahnle, 2001 Wallmann, 2001 . The idea is simply that if atmospheric CO 2...

Carbonate Weathering

The most notable aspect of present-day carbonate weathering is that it is so much faster than silicate weathering. Silicate terrains, such as portions of the high Himalayas and the New Zealand Alps Blum et al., 1998 Jacobson et al., 2003 that contain only traces of carbonates are marked by water chemistries dominated by carbonate dissolution. On a much grander scale, although silicates cover most of the surface area of the continents, the global average chemical composition of river water is...

Stomatal Index

Stomatal Index Gingko

The density of stomata gas exchange openings on leaves can vary with the CO2 level in the atmosphere Woodward, 1987 . The density also varies with changes in water availability, called water stress. A simple way to eliminate the water stress effect is to normalize the density of stomata to the number of epidermal cells, which corrects for changes in cell size Salisbury, 1927 . The result is called stomatal index. Besides water stress, stomatal index is insensitive, also to illumination and...

The Long Term Sulfur Cycle and Atmospheric O

Long Term Sulfur Cycle

The long-term sulfur cycle is depicted as a panorama in figure 6.1. Sulfate is added to the oceans, via rivers, originating from the oxidative weathering of pyrite FeS2 and the dissolution of calcium sulfate minerals gypsum and anhydrite on the continents. Volcanic, metamorphic hydrothermal, and diagenetic reactions add reduced sulfur to the oceans and atmosphere where it is oxidized to sulfate. Sulfur is removed from the oceans mainly via formation of sedimentary pyrite and calcium sulfate....

The Long Term Carbon Cycle

Short Term Carbon Cycle Volcanism

Over millions of years carbon still undergoes constant cycling and recycling via the short-term cycle, but added to this is a new set of processes affecting carbon. This is the long-term carbon cycle, the subject of this book. What distinguishes the long-term carbon cycle from the short-term cycle is the transfer of carbon to and from rocks. This is illustrated in figure 1.2. Over millions of years carbon transfers to and from rocks can result in changes in atmospheric CO2 that cannot be...