🌿 APES Topic 1.4: The Carbon Cycle

What is the carbon cycle?

This describes how carbon moves through Earth's parts: air (atmosphere), living things (biosphere), water (hydrosphere), and rocks/soil (geosphere). Carbon atoms and molecules transfer between carbon sources (release carbon) and sinks (absorb and store carbon).

What is a carbon sink?

It's a natural or artificial reservoir that absorbs more carbon from the atmosphere, hydrosphere, or geosphere than it releases, acting as a net absorber. Examples: oceans, forests, soil.

What is a carbon source?

It's a natural or artificial reservoir or process that releases carbon into the atmosphere, hydrosphere, or geosphere, making it a net emitter. Examples: volcanic eruptions, burning fossil fuels.

What are carbon reservoirs?

Major places on Earth where carbon is stored for varying times. These include the atmosphere, oceans, living organisms (biosphere), and geological formations, with carbon moving between them.

What are short-term carbon reservoirs and their typical residence time?

Components that store carbon for brief periods (years to decades). Examples: atmosphere, living plants (during photosynthesis), and surface ocean layers.

What are long-term carbon reservoirs and their typical residence time?

Components that store carbon for extended periods (thousands to millions of years). Examples: fossil fuels, carbonate rocks, and deep ocean waters.

Define photosynthesis and its role in the carbon cycle.

Green plants, algae, and some bacteria convert light energy into chemical energy. They absorb carbon dioxide (CO_2) from the atmosphere or water to produce glucose and oxygen, removing carbon from the atmosphere and acting as a carbon sink.

Define respiration and its role in the carbon cycle.

A metabolic process where organisms break down organic molecules to release energy. Carbon dioxide (CO_2) is released into the atmosphere or water as a byproduct, making it a key carbon source.

Explain the role of decomposition in the carbon cycle.

Decomposers (bacteria and fungi) break down dead organic matter. Aerobic decomposition releases carbon dioxide (CO_2). Anaerobic conditions produce methane (CH_4). This returns carbon to the atmosphere or soil.

Define combustion and its impact on the carbon cycle.

A rapid chemical reaction (burning) with an oxidant, usually oxygen, producing heat and light. In the carbon cycle, burning organic matter or fossil fuels quickly releases large amounts of stored carbon as carbon dioxide (CO_2) into the atmosphere.

Describe oceanic uptake and exchange in the carbon cycle.

Continuous movement of carbon dioxide (CO_2) between the atmosphere and oceans. (CO_2) dissolves in surface waters, forming carbonic acid. Marine organisms use this carbon. The ocean acts as a major carbon sink, despite releasing some (CO_2).

How do volcanism and geological processes contribute to the carbon cycle?

They release carbon from Earth's crust and mantle over long geological timescales. Volcanic eruptions release (CO_2) and other gases. Rock weathering also consumes atmospheric (CO_2), leading to carbon deposition in sediments.

Describe the fast carbon cycle.

Rapid exchange of carbon between atmosphere, oceans, and living organisms over days to decades. Key processes: photosynthesis, respiration, decomposition, and oceanic exchange.

Describe the slow carbon cycle.

Movement of carbon through rocks, soil, and deep ocean over millions of years. Includes: fossil fuel formation, rock weathering, and volcanic activity, which slowly release or sequester carbon.

How do human actions act as significant carbon sources?

Human activities significantly impact the carbon cycle by adding carbon. Burning fossil fuels for energy releases vast amounts of (CO_2). Deforestation removes trees that absorb (CO_2), reducing carbon sinks.

Explain the greenhouse effect and its link to increased atmospheric carbon dioxide.

A natural process where atmospheric gases ((CO_2), methane, water vapor) trap solar heat. Increased (CO_2), mainly from human activities, intensifies this effect, causing global warming and climate change.

What is ocean acidification and its impact on marine life?

Ongoing decrease in ocean pH due to absorption of anthropogenic (CO_2). (CO_2) forms carbonic acid in seawater, increasing acidity and reducing carbonate ions. This threatens marine organisms that build shells and skeletons.

What is the fundamental difference between carbon reservoirs/sinks and carbon sources?

Reservoirs/sinks store carbon, removing it from active circulation (e.g., oceans, forests). Sources release carbon into the atmosphere or other parts of the cycle (e.g., volcanic eruptions, combustion).

Define residence time in the context of the carbon cycle.

Also called turnover time, it's the average duration a carbon atom/molecule stays within a reservoir before transfer. Short times: years to decades (atmosphere, surface ocean). Long times: thousands to millions of years (deep ocean, fossil fuels).

What are carbon fluxes in the carbon cycle?

Processes by which carbon moves between reservoirs (fast or slow). Major fluxes include: photosynthesis (atmosphere to biosphere), respiration (biosphere to atmosphere/hydrosphere), decomposition (dead organic matter to atmosphere/soil), and combustion (organic matter/fossil fuels to atmosphere).

What is the crucial role of the ocean in the global carbon cycle?

The ocean is a significant carbon reservoir, regulating atmospheric (CO_2) levels. It exchanges (CO_2) with the atmosphere and absorbs much anthropogenic (CO_2). However, this absorption causes ocean acidification, impacting marine ecosystems.

What are anthropogenic changes to the carbon cycle?

Alterations primarily caused by human activities. Burning fossil fuels, deforestation, and industrial processes increase (CO_2) and other greenhouse gases, disrupting the natural carbon balance and accelerating climate change.