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This tutorial explores the Earth's carbon cycle, focusing on the slow, geological processes that operate over millions of years. Carbon is essential for life and plays a crucial role in regulating Earth's climate.
The carbon cycle involves various reservoirs (where carbon is stored) and fluxes (processes that move carbon between reservoirs). We'll explore these concepts using text, diagrams, and interactive simulations.
Understanding the long-term carbon cycle helps us comprehend past climate changes and provides context for current anthropogenic impacts.
1. Carbon Reservoirs
Carbon is stored in several major reservoirs. The amount of carbon in each reservoir and the time it stays there (residence time) vary greatly.
1.1 Atmosphere
Carbon in the atmosphere is primarily as carbon dioxide (CO2) and methane (CH4). It's a relatively small reservoir but highly active and crucial for climate.
1.2 Oceans
The oceans are a major carbon sink, holding significantly more carbon than the atmosphere. Carbon is present as dissolved CO2, bicarbonate, and carbonate ions.
Higher temperatures generally reduce CO2 solubility.
1.3 Land (Biosphere & Soils)
This reservoir includes carbon in living organisms (plants, animals), dead organic matter, and soils. Photosynthesis and respiration are key processes.
Higher activity means more CO2 uptake (conceptual).
1.4 Lithosphere (Rocks)
The largest carbon reservoir by far is the Earth's lithosphere, primarily in carbonate rocks (limestone, dolomite) and kerogen (organic carbon in sedimentary rocks). Carbon cycles very slowly through this reservoir.
Conceptual view of carbon locked in rock strata.
2. Key Processes (Fluxes)
Fluxes are the processes that move carbon between reservoirs. Over geological timescales, volcanic activity, chemical weathering, and organic carbon burial are dominant.
2.1 Volcanic Outgassing
Volcanoes release CO2 from the Earth's mantle and crust into the atmosphere. This is a primary natural source of atmospheric CO2 over long timescales.
2.2 Chemical Weathering
Silicate rocks react with CO2 (via carbonic acid in rainwater). This process removes CO2 from the atmosphere, eventually transporting it to the oceans where it can form carbonate sediments.
3. Long-Term Carbon Cycle Model
This simplified model simulates the interplay of major long-term carbon fluxes and their impact on atmospheric CO2 over millions of years. Adjust the parameters and observe the changes.
Model Controls
Arbitrary units representing relative CO2 input.
Higher values mean faster CO2 drawdown by weathering.
Relative rate of organic carbon being removed from the active cycle.
Simulation runs for a conceptual 100 million years.
Conceptual Earth & Atmosphere CO2 Level
Atmospheric CO2 Over Millions of Years
Interpreting the Model:
This is a highly simplified model. In reality, these processes are interconnected in complex ways, involving temperature feedbacks, tectonic cycles, and biological evolution.
- Volcanic Input: Adds CO2 to the atmosphere. Higher rates tend to increase atmospheric CO2.
- Weathering Efficiency: Represents how effectively CO2 is removed by chemical weathering. This process is thought to be sensitive to temperature and CO2 levels themselves (a negative feedback).
- Organic Carbon Burial: Sequesters carbon in sediments, removing it from the atmosphere-ocean system for long periods.
Observe how different settings lead to different equilibrium CO2 levels or how the system responds to perturbations.
Conclusion
The Earth's long-term carbon cycle is a complex system of reservoirs and fluxes that has regulated our planet's climate for billions of years. Processes like volcanism, weathering, and organic carbon burial operate on timescales of millions of years, shaping the atmospheric CO2 concentration and thus global temperatures.
While these natural cycles are slow, understanding them is crucial for contextualizing the rapid changes occurring due to human activities. The geological record shows that Earth's climate has varied significantly in the past, often linked to changes in the carbon cycle.
We hope this interactive tutorial has provided you with a better understanding of these fundamental Earth processes.