a - Ecosystem Ecology: Carbon Cycle Summary

Ecosystem Ecology and the Carbon Cycle

Ecosystems and Ecosystem Ecology

An ecosystem comprises organisms in a community and their physical environment, interacting over time. Ecosystem ecology studies the connections between the physical and biological components of Earth, focusing on how the environment shapes communities and vice versa. Key focus is on biogeochemical cycles, which describe how chemical elements move between Earth and its life forms.

The Centrality of Carbon

Carbon is fundamental to life's chemistry. Lipids, proteins, carbohydrates, and nucleic acids all rely on carbon atoms as their molecular backbones.

The carbon cycle is an intricate network of biological and physical processes that shuttles carbon among rocks, soil, oceans, air, and organisms, acting as a basic organizing principle for understanding life on Earth.

Photosynthesis and Respiration

All living organisms need both carbon and energy. Photosynthesis and respiration drive carbon cycling in ecosystems.

Photosynthetic organisms convert solar energy into ATP, which is then used to reduce carbon dioxide into sugars. Annually, they remove approximately 210 billion metric tons of carbon from the atmosphere, around 25% of the total atmospheric carbon dioxide.

Cellular respiration oxidizes organic molecules using oxygen, releasing carbon dioxide and water. Photosynthesis converts carbon dioxide to organic molecules, while respiration harvests the energy stored in organic molecules, releasing carbon dioxide and water.

Carbon moves through biological systems via consumption, starting with photosynthesizers and then passing to higher-order organisms.

Annual Patterns of Atmospheric Carbon Dioxide

Charles Keeling monitored atmospheric carbon dioxide starting in 1958. His observations revealed seasonal oscillations: carbon dioxide concentrations increase from winter through spring and decrease in early fall (Northern Hemisphere).

This pattern results from terrestrial geography (most landmasses in the Northern Hemisphere) and Earth's axial tilt (more sunlight in the Northern Hemisphere from late spring through early fall).

During winter, reduced photosynthesis allows carbon dioxide to accumulate. Increased sunlight from late spring through early fall boosts photosynthetic activity, drawing down atmospheric carbon dioxide.

Keeling's observations also show a steady increase in atmospheric carbon dioxide over the past 65 years. The increase has been more than 30% since 1958.

The short-term carbon cycle is influenced by photosynthesis, respiration, and human activities. Carbon dioxide is added by geological inputs (volcanoes, mid-ocean ridges), biological inputs (respiration), and human activities (deforestation, burning fossil fuels). Carbon dioxide is removed via geological removal (chemical weathering) and biological processes (photosynthesis).

Industrial Revolution and Carbon Dioxide Levels

Data from ice cores show that pre-industrial revolution, carbon dioxide levels were stable and lower than current levels.

The isotopic composition of atmospheric carbon dioxide confirms that increased burning of fossil fuels correlates with higher levels.

Carbon has three isotopes: carbon 12, carbon 13, and carbon 14. The ratio of carbon 13 to carbon 12 has decreased, indicating that the added carbon dioxide has less carbon 13. Fossil fuels have the appropriate ratio of carbon isotopes to account for the observed atmospheric changes.

Humans add about 4 billion metric tons of carbon to the atmosphere yearly, mostly from power plants, transportation, and deforestation.

Approximately half of the carbon dioxide released by human activities is stored in the oceans as inorganic carbon.

Long-Term Carbon Cycle

Over long periods, carbon dioxide concentrations have varied significantly, correlating with temperature changes. Carbon dioxide is a greenhouse gas, trapping heat and causing warmer temperatures.

Climate can change without human input, as shown by historical data. The atmospheric record in glacial ice extends back approximately one million years. Data from geological analyses and computer models provide estimates for earlier periods.

Carbon is stored in reservoirs, which include the atmosphere, surface and deep ocean waters, living organisms, soils, and sediments. The largest reservoir is sediments and sedimentary rock.

Fluxes describe the rates at which carbon flows between reservoirs. Photosynthesis removes carbon dioxide, while respiration and human activity add carbon dioxide to the atmosphere.

Atmospheric carbon dioxide abundance depends on the size of reservoirs and the fluxes in and out of them. Geological processes like weathering, burial of organic matter, and sedimentation accumulate carbon. Oxidation of coal, oil, ancient organic matter, and volcanism release carbon.

Human use of fossil fuels releases substantially more carbon compared to natural geological processes.