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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Weathering / Chemical weathering: CO2-driven dissolution and CO2 consumption

Chemical weathering: CO2-driven dissolution and CO2 consumption

Dissolution and alteration of minerals by water and acids: carbonic acid attacks carbonates and silicates, releasing cations, silica and bicarbonate to rivers. Silicate weathering is the slow geologic sink that regulates atmospheric CO2.

Boundary: where this process starts

Starts with: Soil CO2 (0.3-3 percent, 10-100 times air) dissolves to carbonic acid and lowers pH to 4.5-6

Boundary: where it ends

Ends after: Secondary clays and Fe-Al oxides precipitate; Si, Ca, Mg and bicarbonate leave in drainage; Lower atmospheric CO2 and cooler climate follow, then weathering slows

PARTICIPANTSRESOURCESWaterMineralsAtmosphereClimateSoilCarbonic acidCalciumSilicaCarbon dioxideWaterImpact +3 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.50% carbonate minerals (calcImpact +5 of 5. Click for details and evidence.35% silicate minerals (feldsImpact +2 of 5. Click for details and evidence.Impact +4 of 5. Click for details and evidence.Impact -3 of 5. Click for details and evidence.ions accumulate if flow is sImpact -3 of 5. Click for details and evidence.↻ balances · moderate · 0.3 slower dissolutiImpact -4 of 5. Click for details and evidence.CO2 draw-downImpact -3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.↻ balances · strong · 0.1 warmer and wetter Impact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.15% sulfide, evaporite and oImpact +1 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact -2 of 5. Click for details and evidence.Soil CO2 (0.3-3 percent, 10-100 times air) dissolves to carbonic acid and lowers pH to 4.5-6: makes Carbonic acidmakesSoil CO2 (0.3-3 percent, 10-100 times air) dissolves to carbonic acid and lowers pH to 4.5-6: uses up Carbon dioxideuses upSoil CO2 (0.3-3 percent, 10-100 times air) dissolves to carbonic acid and lowers pH to 4.5-6: uses up Wateruses upWhich minerals are attacked: uses Carbonic acidCarbonate dissolution: 1 mol CO2 consumed per mol Ca, released again on marine carbonate precipitation: uses up Carbonic aciduses upCarbonate dissolution: 1 mol CO2 consumed per mol Ca, released again on marine carbonate precipitation: makes CalciummakesSilicate hydrolysis: 2 mol CO2 consumed per mol Ca or Mg released, a net long-term sink: uses up Carbonic aciduses upSilicate hydrolysis: 2 mol CO2 consumed per mol Ca or Mg released, a net long-term sink: makes CalciummakesSilicate hydrolysis: 2 mol CO2 consumed per mol Ca or Mg released, a net long-term sink: makes SilicamakesSecondary clays and Fe-Al oxides precipitate; Si, Ca, Mg and bicarbonate leave in drainage: makes CalciummakesSecondary clays and Fe-Al oxides precipitate; Si, Ca, Mg and bicarbonate leave in drainage: makes SilicamakesDissolved ions build up near the mineral, slowing the reaction (rates drop near equilibrium): uses CalciumDissolved ions build up near the mineral, slowing the reaction (rates drop near equilibrium): uses SilicaWarmth and runoff speed weathering (roughly 2-fold per 10 K up to a plateau): uses WaterLower atmospheric CO2 and cooler climate follow, then weathering slows: uses up Carbon dioxideuses uplowers soil pHCarbonic acid: lowers soil pHdissolved into soilwaterCarbon dioxide: dissolved into soil watercarries the dissolvedacidWater: carries the dissolved acidattacks mineral surfacesCarbonic acid: attacks mineral surfacesconsumed in dissolutionCarbonic acid: consumed in dissolutionreleased from carbonatesCalcium: released from carbonatesconsumed in hydrolysisCarbonic acid: consumed in hydrolysisreleased from silicatemineralsCalcium: released from silicate mineralsreleased as dissolvedsilicaSilica: released as dissolved silicaexported in drainageCalcium: exported in drainageexported in drainageSilica: exported in drainageaccumulates and slowsthe reactionCalcium: accumulates and slows the reactionaccumulates near themineralSilica: accumulates near the mineralrunoff flushes reactionproductsWater: runoff flushes reaction productsdrawdown drives coolingCarbon dioxide: drawdown drives coolingStart: Chemicalweathering: CO2-drivendissolution and C…STARTStart: Chemical weathering: CO2-driven dissolution and CO2 consumptionEnd: Chemicalweathering: CO2-drivendissolution and C…ENDEnd: Chemical weathering: CO2-driven dissolution and CO2 consumptionSoil CO2 (0.3-3percent, 10-100 timesair) dissolves …📄1Soil CO2 (0.3-3 percent, 10-100 times air) dissolves to carbonic acid and lowers pH to 4.5-6Which minerals areattacked📄1Which minerals are attackedCarbonate dissolution:1 mol CO2 consumed permol Ca, released aga…📄1Carbonate dissolution: 1 mol CO2 consumed per mol Ca, released again on marine carbonate precipitationSilicate hydrolysis: 2mol CO2 consumed permol Ca or Mg release…📄1 ↗1Silicate hydrolysis: 2 mol CO2 consumed per mol Ca or Mg released, a net long-term sinkSulfide oxidation andother acids: weatheringthat does not take …📄1Sulfide oxidation and other acids: weathering that does not take up CO2Secondary clays andFe-Al oxidesprecipitate; Si, Ca, …👍1📄1 ↗1Secondary clays and Fe-Al oxides precipitate; Si, Ca, Mg and bicarbonate leave in drainageDissolved ions build upnear the mineral,slowing the reacti…👍1📄1Dissolved ions build up near the mineral, slowing the reaction (rates drop near equilibrium)Warmth and runoff speedweathering (roughly2-fold per 10 K up to…📄1 ↗1Warmth and runoff speed weathering (roughly 2-fold per 10 K up to a plateau)Lower atmospheric CO2and cooler climatefollow, then weatheri…📄1Lower atmospheric CO2 and cooler climate follow, then weathering slows
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Soil CO2 (0.3-3 percent, 10-100 times air) dissolves to carbonic acid and lowers pH to 4.5-6
SoilRootsMicrobesCarbon dioxideCarbonic acidWater
Evidence (1) · added by Quanta
  • Kump 2000, Chemical weathering, atmospheric CO2 and climate, Annual Review of Earth and Planetary Sciences, doi:10.1146/annurev.earth.28.1.611: Soil-air CO2 far above atmospheric levels drives carbonic acid weathering; plants and microbes raise it. (confidence 0.55)
⑂ Which minerals are attacked
WaterMineralsPrimary mineralsCarbonic acid
Evidence (1) · added by Quanta
  • Gaillardet 1999, Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers, Chemical Geology, doi:10.1016/s0009-2541(99)00031-5: Carbonates dominate dissolved bicarbonate in rivers though covering a minority of land; silicate share smaller; shares estimated. (confidence 0.45)
Carbonate dissolution: 1 mol CO2 consumed per mol Ca, released again on marine carbonate precipitation
WaterMineralsCalciumCarbonic acid
Evidence (1) · added by Quanta
  • Gaillardet 1999, Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers, Chemical Geology, doi:10.1016/s0009-2541(99)00031-5: Carbonate weathering CO2 is not a net long-term sink because it returns when carbonate precipitates in the ocean. (confidence 0.6)
Silicate hydrolysis: 2 mol CO2 consumed per mol Ca or Mg released, a net long-term sink
WaterMineralsCalciumMagnesiumSilicaCarbonic acid
Evidence (1) · added by Quanta
  • Gaillardet 1999, Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers, Chemical Geology, doi:10.1016/s0009-2541(99)00031-5: CO2 consumption by silicate weathering about 0.1 Gt C per year (about 8.7e12 mol/yr) from large rivers. (confidence 0.55)
Sulfide oxidation and other acids: weathering that does not take up CO2
WaterMineralsOxygenHydrogen ions
Evidence (1) · added by Quanta
  • Hartmann 2009, Global CO2-consumption by chemical weathering: what is the contribution of highly active weathering regions, Global and Planetary Change, doi:10.1016/j.gloplacha.2009.07.007: Other acids and evaporite dissolution alter apparent CO2 consumption estimates; classified as other. (confidence 0.4)
Secondary clays and Fe-Al oxides precipitate; Si, Ca, Mg and bicarbonate leave in drainage
MineralsWaterClay mineralsSilicaCalcium
Evidence (1) · added by Quanta
  • Riebe 2004, Erosional and climatic effects on long-term chemical weathering rates in granitic landscapes, Earth and Planetary Science Letters, doi:10.1016/j.epsl.2004.05.019: Chemical depletion fraction of granitic soils ranges from near 0 to about 0.7 depending on erosion and climate. (confidence 0.55)
Dissolved ions build up near the mineral, slowing the reaction (rates drop near equilibrium)
WaterMineralsSilicaCalcium
Evidence (1) · added by Quanta
  • Maher 2014, Hydrologic regulation of chemical weathering and the geologic carbon cycle, Science, doi:10.1126/science.1250770: Weathering flux depends on fluid residence time and saturation: rates plateau when fluids approach equilibrium. (confidence 0.6)
Warmth and runoff speed weathering (roughly 2-fold per 10 K up to a plateau)
ClimateWaterHeatWater
Evidence (1) · added by Quanta
  • White 1995, Effects of climate on chemical weathering in watersheds, Geochimica et Cosmochimica Acta, doi:10.1016/0016-7037(95)00078-e: Silicate weathering fluxes in granitic watersheds rise with temperature and precipitation; apparent activation energies of tens of kJ/mol. (confidence 0.5)
Lower atmospheric CO2 and cooler climate follow, then weathering slows
AtmosphereClimateCarbon dioxideHeat
Evidence (1) · added by Quanta
  • Walker 1981, A negative feedback mechanism for the long-term stabilization of Earth's surface temperature, Journal of Geophysical Research, doi:10.1029/jc086ic10p09776: Walker feedback: higher temperature increases weathering, which draws CO2 down, stabilising climate on 10^5 to 10^6 year timescales. (confidence 0.65)