6.2 Terrestrial and marine ecosystems in the carbon cycle
4 min read•july 22, 2024
Carbon storage in ecosystems is a crucial part of the global . Terrestrial and play different roles, with land storing more carbon in biomass and soils, while oceans have a larger active carbon pool due to CO2 solubility in seawater.
and are key processes that drive carbon exchange between ecosystems and the atmosphere. The balance between these processes determines whether an ecosystem acts as a carbon sink or source, influencing atmospheric CO2 levels and Earth's climate.
Carbon Storage and Cycling in Ecosystems
Carbon storage in ecosystems
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- Store carbon in living biomass including plants (, grasslands) and animals (insects, mammals) and in soils (organic matter, humus)
- Photosynthesis by plants absorbs CO2 from the atmosphere converts it into organic compounds (glucose, cellulose)
- Respiration by plants and animals breaks down organic compounds releases CO2 back to the atmosphere
- of dead organic matter by microbes releases CO2 and incorporates carbon into soils (peat, permafrost)
- Marine ecosystems
- Store carbon in living biomass such as phytoplankton (diatoms, dinoflagellates), algae (kelp, seagrass), and marine animals (fish, whales) and dissolved in seawater as dissolved inorganic carbon (DIC)
- Photosynthesis by phytoplankton and algae takes up CO2 from the atmosphere and surface waters converts it into organic compounds
- Respiration by marine organisms breaks down organic compounds releases CO2 back to the water and atmosphere
- Sinking of dead organisms and fecal pellets transports carbon to deep ocean sediments known as the biological pump (marine snow, whale falls)
- Comparison
- Terrestrial ecosystems store more carbon in living biomass and soils (1,500 Gt C) than marine ecosystems (40 Gt C)
- Marine ecosystems have a larger active carbon pool (38,000 Gt C) due to the high solubility of CO2 in seawater forming carbonic acid and bicarbonate ions
- Turnover of carbon is faster in marine ecosystems (days to years) due to rapid cycling in the surface ocean compared to slower turnover in terrestrial ecosystems (decades to centuries)
Photosynthesis in carbon cycle
- Photosynthesis
- Process by which plants and phytoplankton convert CO2 and water (H2O) into organic compounds (C6H12O6) using light energy captured by chlorophyll
- Removes CO2 from the atmosphere and surface ocean waters stores it in living biomass
- Produces oxygen (O2) as a byproduct released to the atmosphere and ocean
- Respiration
- Process by which organisms break down organic compounds (glucose) to release energy in the form of ATP
- Releases CO2 back into the atmosphere and ocean waters as a waste product
- Consumes oxygen (O2) in the process of cellular respiration
- Balance between photosynthesis and respiration
- Determines the net exchange of CO2 between ecosystems and the atmosphere on short timescales (diurnal, seasonal)
- Influences the concentration of atmospheric CO2 and the Earth's greenhouse effect and climate
- Excess photosynthesis over respiration leads to net CO2 uptake (carbon sink), while excess respiration leads to net CO2 release (carbon source)
Carbon Sequestration and Human Impacts
Carbon sequestration processes
- Soil
- Accumulation of organic carbon in soils through plant growth (roots, litter) and incomplete decomposition
- Influenced by factors such as climate (temperature, moisture), vegetation type (grasses, trees), and soil properties (clay content, pH)
- Can be enhanced through land management practices that increase plant productivity and reduce soil disturbance (reforestation, cover crops, reduced tillage)
- Ocean carbon sequestration
- Removal of carbon from the surface ocean and atmosphere by physical and biological processes that transport it to the deep ocean
- Physical processes: dissolution of CO2 in cold, deep waters (solubility pump) and formation of calcium carbonate minerals (CaCO3) that sink to the seafloor
- Biological processes: photosynthesis by phytoplankton that converts CO2 into organic matter and the subsequent sinking of dead organisms and fecal pellets (biological pump)
- Can be enhanced through ocean fertilization techniques that stimulate phytoplankton growth (iron fertilization) and alkalinity enhancement that increases the ocean's capacity to absorb CO2 (olivine weathering)
Impacts on carbon cycle
- Land-use change
- and conversion of natural ecosystems to agriculture or urban areas releases stored carbon from living biomass and soils into the atmosphere (Amazon rainforest, Indonesian peatlands)
- Reforestation and afforestation can increase carbon storage in terrestrial ecosystems by creating new carbon sinks (China's Grain for Green program, African Great Green Wall)
- Changes in land use can alter the balance between photosynthesis and respiration shifting ecosystems from net carbon sinks to sources or vice versa
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- Increased absorption of atmospheric CO2 by the ocean forms carbonic acid (H2CO3) lowers seawater pH and carbonate ion concentration
- Affects the ability of calcifying marine organisms to build calcium carbonate shells and skeletons (corals, mollusks, some plankton)
- Can reduce the efficiency of the biological pump by altering the composition and sinking rates of marine particles and organisms
- Impacts the ocean's capacity to absorb and store carbon from the atmosphere potentially creating a positive feedback to climate change
Key Terms to Review (20)
Autotrophs: Autotrophs are organisms that can produce their own food using sunlight or chemical energy, serving as the foundation of food webs in various ecosystems. These organisms play a critical role in the carbon cycle by capturing carbon dioxide from the atmosphere and converting it into organic matter through processes like photosynthesis or chemosynthesis. As primary producers, autotrophs support all other life forms by providing essential energy and nutrients.
Biodiversity support: Biodiversity support refers to the ecosystem services and benefits that diverse biological species provide, which contribute to the stability and resilience of ecosystems. This term highlights the importance of maintaining a wide variety of species in both terrestrial and marine environments, as they play crucial roles in nutrient cycling, habitat provision, and the regulation of climate. Healthy biodiversity enhances the ability of ecosystems to function efficiently and adapt to changes, particularly within the context of the carbon cycle.
Carbon Cycle: The carbon cycle is the process by which carbon is exchanged between the Earth's atmosphere, land, oceans, and living organisms. This cycle plays a crucial role in regulating the Earth's climate and supporting life by enabling the flow of carbon through various ecosystems and geological processes. Understanding the carbon cycle is essential for analyzing climate models and assessing how terrestrial and marine ecosystems interact with carbon in their environments.
Carbon sequestration: Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide to mitigate climate change. This process plays a crucial role in reducing greenhouse gas concentrations, and it can occur through both natural and artificial means, helping to stabilize ecosystems and promote food security.
Charles David Keeling: Charles David Keeling was an American scientist best known for his groundbreaking work in measuring atmospheric carbon dioxide levels. His development of the Keeling Curve in 1958 provided critical evidence of the increasing concentrations of CO2 in the atmosphere, significantly enhancing our understanding of the global carbon cycle and the role of carbon reservoirs in climate change. Keeling's research emphasized the importance of both terrestrial and marine ecosystems as they interact with atmospheric carbon, shaping our current climate narrative.
Climate regulation: Climate regulation refers to the processes and mechanisms that maintain the Earth's climate balance and stability over time. This involves natural systems, such as terrestrial and marine ecosystems, which play a crucial role in controlling greenhouse gas concentrations, influencing temperature, and shaping weather patterns. The interactions within these ecosystems, including carbon storage and sequestration, are essential for moderating climate and responding to changes in atmospheric composition.
Decomposers: Decomposers are organisms that break down dead or decaying organic material, returning vital nutrients back into the ecosystem. They play a crucial role in both terrestrial and marine ecosystems by facilitating the recycling of carbon and other elements, thereby maintaining the balance of the carbon cycle. Without decomposers, ecosystems would be overwhelmed with dead matter, disrupting nutrient availability and carbon storage.
Decomposition: Decomposition is the biological process by which organic matter is broken down into simpler substances, facilitating nutrient recycling in ecosystems. This process is crucial for returning carbon to the atmosphere and soil, influencing the global carbon cycle. By breaking down dead organic material, decomposition supports plant growth and contributes to the overall health of both terrestrial and marine ecosystems.
Deforestation: Deforestation is the large-scale removal of forest cover, often resulting in the conversion of forested areas into non-forest land uses such as agriculture, urban development, or pasture. This process has significant impacts on greenhouse gas emissions, contributing to climate change and altering ecosystems.
Forests: Forests are large areas dominated by trees and other vegetation, playing a crucial role in the Earth's ecosystems. They serve as vital carbon sinks, absorbing carbon dioxide from the atmosphere through photosynthesis and storing it in biomass and soil, which significantly impacts the carbon cycle. Additionally, forests provide habitat for countless species, influence local and global climates, and contribute to ecosystem-based adaptation strategies against climate change.
Heterotrophs: Heterotrophs are organisms that cannot produce their own food and instead obtain energy by consuming other living or dead organic matter. They play a crucial role in ecosystems as consumers in the food chain, directly linking the energy derived from producers, such as plants, to higher trophic levels, including carnivores and omnivores.
Marine ecosystems: Marine ecosystems are diverse aquatic environments that exist in oceans, seas, and coastal areas, characterized by their unique biological communities and physical conditions. These ecosystems play a crucial role in the carbon cycle, as they are involved in the absorption and storage of carbon dioxide through processes like photosynthesis by marine plants and phytoplankton, which in turn supports complex food webs and influences global climate patterns.
Net Primary Productivity: Net primary productivity (NPP) refers to the amount of organic matter or biomass that plants produce through photosynthesis minus the amount used for respiration. It is a crucial indicator of ecosystem health, as it quantifies the energy available to support herbivores and, subsequently, higher trophic levels in both terrestrial and marine environments. Understanding NPP helps illustrate how carbon cycles through ecosystems and indicates how effectively these systems can sequester carbon, ultimately affecting climate dynamics.
Nutrient Cycling: Nutrient cycling is the process by which essential nutrients move through ecosystems, including the soil, water, and living organisms, in a continuous loop. This process is crucial for maintaining ecosystem health and stability, as it ensures that nutrients are recycled and made available to plants and animals. Nutrient cycling plays a significant role in biodiversity, agricultural practices, and the functioning of both terrestrial and marine ecosystems within the carbon cycle.
Ocean acidification: Ocean acidification refers to the process by which the ocean becomes more acidic due to the absorption of excess atmospheric carbon dioxide (CO2). This increase in acidity can disrupt marine ecosystems, affect the carbon cycle, and has implications for sea level rise, as it impacts the health of marine organisms that contribute to carbon storage and coastal protection.
Oceanic phytoplankton: Oceanic phytoplankton are microscopic, photosynthetic organisms that float in the upper layers of oceans and seas, forming the foundation of marine food webs. They play a crucial role in the carbon cycle by absorbing carbon dioxide during photosynthesis and producing oxygen, making them essential for maintaining the balance of marine ecosystems and influencing global climate patterns.
Photosynthesis: Photosynthesis is the biological process by which green plants, algae, and some bacteria convert light energy into chemical energy, using carbon dioxide and water to produce glucose and oxygen. This process plays a crucial role in the global carbon cycle and influences various environmental systems by regulating atmospheric composition and supporting life in terrestrial and marine ecosystems.
Rachel Carson: Rachel Carson was an influential American marine biologist, author, and conservationist whose work is credited with advancing the global environmental movement. Her groundbreaking book, 'Silent Spring,' raised awareness about the dangers of pesticides and their impact on ecosystems, leading to significant changes in environmental policy and public perception of biodiversity and pollution.
Respiration: Respiration is a biochemical process in which living organisms convert glucose and oxygen into energy, carbon dioxide, and water. This process is crucial for maintaining life as it provides the energy necessary for cellular functions and also plays a significant role in the global carbon cycle by releasing carbon dioxide back into the atmosphere, where it can be utilized by plants during photosynthesis.
Terrestrial ecosystems: Terrestrial ecosystems are land-based environments where living organisms interact with each other and their physical surroundings. These ecosystems play a crucial role in the carbon cycle, acting as both sources and sinks of carbon dioxide through processes like photosynthesis and respiration, which link them closely to climate change and overall environmental health.