The is a fundamental process in Earth's systems, involving the movement of carbon between various reservoirs. This topic explores the key components of the cycle, including , fluxes, and biogeochemical processes that drive carbon exchange.
Understanding the carbon cycle is crucial for geochemists studying climate change and environmental impacts. The notes cover natural and , , and modeling techniques used to predict future scenarios and inform policy decisions.
Carbon reservoirs
Carbon reservoirs play a crucial role in the global carbon cycle, storing and exchanging carbon between different components of the Earth system
Understanding carbon reservoirs is essential in geochemistry for tracking carbon movement and predicting climate change impacts
The four main carbon reservoirs interact dynamically, influencing atmospheric CO2 concentrations and global climate patterns
Atmosphere
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Contains approximately 750 gigatons of carbon, primarily as CO2 and CH4
Atmospheric carbon concentration has increased from ~280 ppm to over 410 ppm since the Industrial Revolution
Serves as a critical link between other carbon reservoirs, facilitating rapid exchange
Influences global climate through the
Hydrosphere
Largest active carbon reservoir, storing about 38,000 gigatons of carbon
Carbon exists in various forms (dissolved CO2, carbonic acid, bicarbonate, carbonate ions)
Oceans act as a significant carbon sink, absorbing about 25% of anthropogenic CO2 emissions
Carbonate chemistry in oceans regulates pH and influences marine ecosystem health
Biosphere
Stores approximately 2,000 gigatons of carbon in living and dead organic matter
Terrestrial vegetation accounts for the majority of biospheric carbon storage
Carbon flux in the driven by , , and
Plays a crucial role in short-term carbon cycling and climate regulation
Lithosphere
Largest carbon reservoir, containing over 75,000,000 gigatons of carbon
Carbon stored in sedimentary rocks (carbonates, fossil fuels) and Earth's mantle
Exchanges carbon with other reservoirs through weathering, volcanism, and tectonic processes
Operates on geological timescales, influencing long-term climate patterns
Carbon fluxes
represent the movement of carbon between different reservoirs in the Earth system
Understanding carbon fluxes is crucial in geochemistry for quantifying carbon cycle dynamics and predicting future climate scenarios
Carbon fluxes occur at various spatial and temporal scales, from local ecosystems to global atmospheric circulation
Natural vs anthropogenic sources
include volcanic eruptions, wildfires, and respiration from living organisms
Anthropogenic sources primarily stem from and land-use changes
Natural carbon fluxes have been in relative balance for millennia
Anthropogenic emissions have disrupted this balance, leading to increased atmospheric CO2 concentrations
Current anthropogenic CO2 emissions exceed 35 gigatons per year
Deforestation contributes an additional 5-10 gigatons of CO2 annually
Terrestrial carbon exchange
Involves carbon exchange between the , vegetation, and soil
Photosynthesis removes approximately 120 gigatons of carbon from the atmosphere annually
Plant and soil respiration release about 60 gigatons of carbon back to the atmosphere
Net terrestrial carbon uptake estimated at 3 gigatons per year
Influenced by factors such as temperature, precipitation, and land-use changes
Ocean-atmosphere exchange
Oceans and atmosphere exchange about 90 gigatons of carbon annually
Driven by differences in partial pressure of CO2 between air and sea surface
Cold, high-latitude waters tend to absorb CO2, while warm, equatorial waters release CO2
transports carbon from surface to deep ocean through marine organism activity
Phytoplankton photosynthesis in surface waters
Sinking of organic matter and carbonate shells
Weathering and sedimentation
Chemical weathering of silicate rocks consumes atmospheric CO2 over geological timescales
Carbonate weathering temporarily sequesters CO2 in ocean waters
Sedimentation of organic matter and carbonate minerals in marine environments
Burial of carbon in sediments represents a long-term carbon sink
Estimated 0.2 gigatons of carbon buried annually in marine sediments
Biogeochemical processes
Biogeochemical processes drive the cycling of carbon between different reservoirs in the Earth system
These processes are fundamental to understanding carbon dynamics in geochemistry and their impact on global climate
Involve complex interactions between biological, geological, and chemical systems across various spatial and temporal scales
Photosynthesis vs respiration
Photosynthesis converts atmospheric CO2 into organic compounds using solar energy
6CO2+6H2O+light energy→C6H12O6+6O2
Respiration breaks down organic compounds to release energy, producing CO2 as a byproduct
C6H12O6+6O2→6CO2+6H2O+energy
Balance between photosynthesis and respiration regulates atmospheric CO2 concentrations
Influenced by factors such as temperature, water availability, and nutrient levels
Decomposition
Microbial breakdown of dead organic matter releases CO2 back to the atmosphere
Rate of decomposition affected by temperature, moisture, and organic matter composition
Produces soil organic carbon, which can be stored for varying periods
Contributes to nutrient cycling in terrestrial and aquatic ecosystems
Release of nitrogen, phosphorus, and other essential elements
Carbonate formation
Precipitation of calcium carbonate in marine environments
Ca2++2HCO3−→CaCO3+CO2+H2O
Biogenic by marine organisms (corals, foraminifera, coccolithophores)
Abiotic carbonate precipitation in warm, shallow marine environments
Represents a significant long-term carbon sink in the ocean
Organic carbon burial
Deposition and preservation of organic matter in sedimentary environments
Occurs in both terrestrial (peatlands, permafrost) and marine (continental shelves, deep ocean) settings
Influenced by sedimentation rates, oxygen availability, and biological productivity
Forms the basis for fossil fuel formation over geological timescales
Coal, oil, and natural gas deposits
Carbon cycle timescales
Carbon cycle operates on multiple timescales, from seconds to millions of years
Understanding these timescales is crucial in geochemistry for interpreting past climate changes and predicting future scenarios
Different processes dominate carbon cycling at various temporal scales, influencing atmospheric CO2 concentrations and global climate
Short-term carbon cycle
Operates on timescales of days to decades
Dominated by biological processes such as photosynthesis, respiration, and decomposition
Rapid exchange between atmosphere, biosphere, and upper ocean
Seasonal fluctuations in atmospheric CO2 concentrations
Northern Hemisphere growing season causes annual CO2 drawdown
Respiration and decomposition dominate during winter months
Long-term carbon cycle
Functions on timescales of centuries to millennia
Involves slower processes such as ocean circulation and soil carbon accumulation
Carbon exchange between atmosphere, deep ocean, and terrestrial reservoirs
Influenced by climate feedbacks and changes in ocean chemistry