Carbon Fluxes, Stores, and Human Impacts

Carbon fluxes, which are measured in Petagrams (Pg) or Gigatonnes (Gt) of carbon per year, occur over various time and spatial scales. The largest fluxes typically occur between the ocean and atmosphere or between land and atmosphere, involving processes like photosynthesis and respiration.

Highlight: While processes like photosynthesis, respiration, combustion, and decomposition can transfer carbon in minutes, hours, or days, carbon sequestration in sedimentary rocks or the ocean can take millennia.

Sedimentary rocks, such as limestone, contain the vast majority (99.9%) of Earth's carbon. These rocks form through two primary processes: the compression of dead organic matter covered by silt and mud over many years, resulting in shale, and the lithification of dead marine organisms at the ocean bottom over millions of years, forming rocks like limestone.

Fossil fuels, while containing only 0.004% of Earth's carbon, play a significant role in the carbon cycle due to human exploitation. They form when organic material is deposited and accumulates faster than it can decay, eventually transforming into oil, natural gas, and coal.

Example: Chemical weathering is a geological process that releases carbon into the atmosphere. Atmospheric carbon reacts with water vapor to create weak carbonic acid, which, during condensation, forms acid rain that dissolves calcium carbonate in rocks.

Outgassing, particularly through volcanic eruptions, is another natural process that releases stored carbon into the atmosphere. Combustion, both natural (e.g., wildfires) and human-induced (e.g., burning fossil fuels), rapidly transfers carbon from biomass or fossil stores to the atmosphere.

Vocabulary: The fast carbon cycle refers to the relatively rapid movement of carbon through the biosphere, atmosphere, and upper ocean, typically occurring over days to decades.

The ocean's role in carbon sequestration is crucial and involves three interconnected systems known as pumps: the biological pump, the carbonate pump, and the physical pump. These processes move carbon between the atmosphere, surface water, and deep ocean, playing a vital role in regulating atmospheric CO2 levels and global climate.

Definition: Carbon capture and storage refers to the process of capturing CO2 emissions from industrial processes or power generation and storing them long-term, typically underground, to mitigate climate change.

Understanding these complex interactions and processes within the carbon cycle is essential for assessing and addressing the impacts of human activities on global carbon balance and climate change.

The Carbon Cycle: Key Concepts and Processes

The carbon cycle is a fundamental biogeochemical process that regulates the movement of carbon through Earth's various systems. This page introduces key terminology and concepts essential for understanding the carbon cycle's mechanics.

Vocabulary: Sequestration refers to the capture of carbon from the atmosphere by oceans, vegetation, or sedimentary rocks where it is stored.

Carbon sources and sinks play crucial roles in the cycle. A carbon source releases more carbon than it absorbs, while a carbon sink absorbs more carbon than it releases. These concepts are vital for understanding the balance of carbon in different Earth systems.

Example: Photosynthesis, represented by the equation Carbon Dioxide + Water → Glucose + Oxygen, is a key process in the carbon cycle that removes carbon dioxide from the atmosphere.

The ocean plays a significant role in the carbon cycle, with phytoplankton serving as the foundation of marine food chains and contributing to carbon sequestration. Sedimentation occurs when dead organisms on the ocean floor create sediment rich in calcium carbonate, further storing carbon.

Definition: Thermohaline circulation refers to the movement of ocean currents based on their density, which is influenced by temperature and salinity.

Two important processes in ocean carbon cycling are downwelling, where warm water cools and absorbs more CO2 before sinking, and upwelling, where cold water rises to the surface, bringing CO2 that can be absorbed by phytoplankton.

Highlight: The carbon cycle operates as a closed system, meaning that while there are inputs and outputs of energy, the total amount of carbon within the system remains constant.

The carbon budget of a subsystem is determined by the difference between carbon inputs and outputs. This balance dictates whether a subsystem acts as a carbon source or sink, with sudden releases of carbon (e.g., from volcanic eruptions or wildfires) potentially disrupting this balance for extended periods.