GY1431 Biogeochemical cycling C cycle

  • Biogeochemical cycles are crucial for understanding how elements move through ecosystems.

  • Focus on the carbon cycle as a key component in the evolution of Earth's systems.

Earth's Atmosphere Comparison

Atmospheric Composition:

  • Venus:

    • CO2: 96.5%

    • N2: 3.5%

    • Minor components: SO2, Ar, H2O, CO, He, Ne.

  • Mars:

    • CO2: 95.32%

    • N2: 2.7%

    • Additional gases: Ar, O2, CO, H2O.

  • Earth:

    • N2: 78.084%

    • O2: 20.946%

    • Trace gases: Ar, CO2, Ne, He, CH4, Kr, H2, H2O.

Key Observations:

  • During the Great Oxidation Event (GOE), the percentage of N2 in Earth's atmosphere increased significantly.

Biogeochemical Cycles Overview

Carbon Cycle:

  • The carbon cycle involves the movement of carbon through biological (organic) and geological (inorganic) systems.

  • Carbon is essential for life; without it, biogeochemical cycles would not exist.

  • Regulates climate through the carbon-silicate cycle (C-Si cycle) on short timescales.

Forms of Carbon

Distinction Between Carbon Types:

  • Organic Carbon: Found in living organisms (e.g., sugars).

  • Inorganic Carbon: Found in carbonates (e.g., CaCO3).

Bonding Characteristics:

  • Ionic bonds are weaker and easily broken (salts and minerals).

  • Covalent bonds are strong, providing energy stored from the sun.

Photosynthesis and Carbon Capture

  • Photosynthesis plays a crucial role in carbon removal from the atmosphere, converting CO2 into organic molecules like glucose.

    • Reaction: 6 CO2 + 6 H2O -> C6H12O6 + 6 O2 (with light energy).

  • Organisms use glucose as a primary food source.

CO2 Release and Respiration

  • Organisms respire aerobic processes converting organic carbon back to CO2:

    • Reaction: C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + ATP.

Decomposition of Organic Matter

Components of Organic Matter:

  • Includes sugars, cellulose, lignin, and more. Each contributes differently to soil and carbon content.

Temperature Effects:

  • Decomposition is influenced by temperature; it is fastest at optimal conditions. Extreme temperatures slow down microbial activity.

Oxygen Requirements:

  • Oxygen is required for aerobic respiration; insufficient oxygen leads to slower decomposition.

Carbon Pool Dynamics

Key Points:

  • Soil organic matter can accumulate if soil respiration is lower than the rate of photosynthesis.

  • Examples of carbon storage include peat, coal, and oil.

Nutrient Ratios and Decomposition

  • Carbon to Nitrogen ratios (C:N) influence decomposition rates:

    • High C:N indicates low nitrogen, limiting decomposing bacteria and slow decomposition.

    • Low C:N (e.g., 20 or less) promotes faster microbial growth and decomposition.

Anthropogenic Effects on Carbon Cycle

Observations of CO2 Levels:

  • Increasing CO2 levels documented at Mauna Loa Observatory highlight the impact of human activities.

Carbon Sinks vs. Sources

Function of Carbon Sinks:

  • Seasonal photosynthesis, biomass increase, ocean CO2 uptake, and long-term carbon burial (e.g., peat, coal).

Carbon Sources:

  • Seasonal respiration and destruction of biomass release CO2 back into the atmosphere.

Role of Oceans in Carbon Cycling

  • Oceans contain a large pool of dissolved CO2, contributing to the biological inorganic carbon cycle.

  • Phytoplankton photosynthesize, while all organisms respire, cycling CO2.

Long-Term Carbon Reservoirs

  • Long-term burial of carbon occurs through geological processes leading to shell formation and sediment deposition over millions of years.

Weathering Impact

  • Weathering of limestone removes CO2 from the atmosphere, returning it to the ocean as bicarbonate.

Carbon Pools on Earth

Pools and Their Sizes:

  • Atmosphere: 750 Gt (fast cycle)

  • Ocean (Near Surface): 1200 Gt (fast)

  • Deep Ocean: 40,000 Gt (slow)

  • Terrestrial Biomass: 600 Gt (fast)

  • Sediments/Rocks: 10 million Gt (slow)

Carbon Cycle Dynamics

Terrestrial Biosphere:**

  • Flux in and out of the atmosphere is balanced (net primary productivity - NPP).

  • CO2 residence time is very fast, contributing to spatial variations of atmospheric CO2 concentrations.

Climate Influences on Carbon Cycle

Weather and Temperature Effects:

  • Changes in temperature will impact carbon solubility and cycling.

    • Colder conditions increase CO2 solubility (positive feedback during cooling).

Anthropogenic Impact on Carbon Cycle: The Seuss Effect

  • Plants exhibit a "fingerprint" in CO2 with lower d13C due to fossil fuel utilization.

Conclusion

  • Understanding these cycles is essential for predicting changes in Earth's climate and ecosystem health.