12.1 Plate tectonics and the carbon cycle
5 min read•august 16, 2024
Plate tectonics plays a crucial role in the carbon cycle, influencing CO2 levels over millions of years. Through processes like and volcanism, it affects carbon storage and release, impacting Earth's climate and habitability.
The balance between CO2 release from volcanoes and consumption through weathering regulates atmospheric levels. Understanding these processes helps explain past climate changes and predict future trends in Earth's carbon cycle.
Plate Tectonics and the Carbon Cycle
Tectonic Processes and Carbon Cycling
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- Plate tectonics drive the long-term carbon cycle through processes of subduction, volcanism, and mountain building affect carbon storage and release over geological timescales
- at mid-ocean ridges releases CO2 from the mantle contributes to atmospheric carbon levels and oceanic dissolved inorganic carbon
- Subduction zones facilitate the transport of carbon-rich sediments and altered oceanic crust into the Earth's interior effectively removes carbon from the surface reservoir
- Orogenic processes expose fresh silicate rocks to weathering enhances CO2 consumption through chemical weathering reactions
- Metamorphism of carbonate rocks in subduction zones can release CO2 through decarbonation reactions contributes to volcanic and hydrothermal emissions
- Example: Calcium carbonate (CaCO3) metamorphoses to form calcium silicate (CaSiO3) and CO2
- Tectonic uplift increases the exposure of rocks to weathering potentially accelerates the drawdown of atmospheric CO2 through enhanced silicate weathering
- Example: Himalayan orogeny increased global weathering rates and CO2 consumption
Carbon Cycle Regulation
- The balance between CO2 release from volcanic activity and CO2 consumption through weathering regulates atmospheric CO2 levels over geological time scales
- Tectonic processes influence both sources and sinks of carbon in the Earth system
- Sources: Volcanic emissions, metamorphic decarbonation
- Sinks: Subduction of marine sediments, enhanced silicate weathering
- Changes in tectonic activity can lead to long-term shifts in atmospheric CO2 concentrations
- Example: Increased volcanic activity during the Cretaceous period led to higher atmospheric CO2 levels and warmer global temperatures
- The carbon cycle's response to tectonic changes operates on timescales of millions of years
- Feedback mechanisms between tectonics, climate, and weathering help maintain Earth's habitability over geological time
Subduction and Carbon Sequestration
Subduction Zone Dynamics
- Subduction zones act as carbon sinks by transporting carbon-rich marine sediments and altered oceanic crust into the Earth's mantle
- Carbonate minerals in subducted sediments undergo decarbonation reactions at depth releases CO2 that can be stored in the mantle or returned to the surface through volcanism
- The efficiency of carbon subduction depends on factors such as the thermal structure of the subduction zone, slab dip angle, and the composition of subducted materials
- Example: Cold subduction zones (steep slab angles) tend to subduct more carbon than hot subduction zones (shallow slab angles)
- Some subducted carbon remains in the mantle for long periods effectively sequesters it from the surface carbon cycle for millions to billions of years
- Subduction of organic carbon in marine sediments can lead to its long-term storage in the mantle or its transformation into graphite or diamond at high pressures and temperatures
- Example: Formation of microdiamonds in ultra-high-pressure metamorphic rocks
Carbon Fate and Implications
- The fate of subducted carbon (whether it is stored in the mantle or returned to the surface) has significant implications for long-term climate regulation and the global carbon budget
- Quantifying the amount of carbon subducted versus the amount returned to the surface through arc volcanism determines the net effect of subduction on the carbon cycle
- Variations in subduction efficiency over geological time can influence atmospheric CO2 levels and global climate
- Example: Changes in global subduction rates during supercontinent cycles may affect long-term climate trends
- The deep carbon cycle, driven by subduction, interacts with the surface carbon cycle on million-year timescales
- Understanding subduction-related helps in reconstructing past climate conditions and predicting future long-term climate trends
Volcanic Activity and Atmospheric CO2
Volcanic CO2 Emissions
- Volcanic eruptions release significant amounts of CO2 into the atmosphere serve as a primary natural source of atmospheric carbon dioxide
- The composition and style of volcanic eruptions (explosive vs. effusive) influence the quantity and rate of CO2 release into the atmosphere
- Example: Effusive basaltic eruptions (Hawaii) tend to release more CO2 than explosive silicic eruptions (Mount St. Helens)
- Mid-ocean ridge volcanism contributes a steady flux of CO2 to the ocean-atmosphere system while subduction zone volcanism can produce more variable and potentially larger CO2 emissions
- Large igneous province (LIP) eruptions can release massive amounts of CO2 over geologically short time periods potentially triggers global climate changes and mass extinction events
- Example: Siberian Traps eruption at the end of the Permian period contributed to the largest mass extinction in Earth's history
Climate Impacts and Measurement
- The cooling effect of volcanic aerosols can temporarily mask the warming effect of CO2 emissions complicates the short-term climate impact of volcanic eruptions
- Quantifying volcanic CO2 emissions presents challenges but remains crucial for understanding natural variability in the carbon cycle and for distinguishing between anthropogenic and natural sources of atmospheric CO2
- Methods include direct gas sampling, satellite observations, and isotopic analysis of volcanic gases
- The balance between volcanic CO2 emissions and CO2 consumption through weathering processes plays a key role in regulating atmospheric CO2 levels over geological time scales
- Volcanic activity influences both short-term climate variability and long-term climate trends
- Example: The 1991 Mount Pinatubo eruption caused global cooling of about 0.5°C for several years
- Studying past volcanic events helps in understanding potential future impacts of large-scale volcanism on climate and ecosystems
Plate Tectonics vs. Silicate Weathering
Tectonic Influence on Weathering
- Plate tectonic processes, particularly mountain building (orogeny), expose fresh silicate rocks to the atmosphere enhances chemical weathering rates
- Silicate weathering consumes atmospheric CO2 through reactions that convert silicate minerals into clay minerals and dissolved ions acts as a long-term carbon sink
- Example: Weathering of feldspars to form kaolinite clay consumes CO2
- The rate of silicate weathering depends on factors such as temperature, precipitation, and the surface area of exposed rocks all of which can be affected by tectonic processes
- Tectonic uplift in orogenic belts increases the potential for physical erosion exposes fresh rock surfaces and accelerates chemical weathering rates
- Example: The uplift of the Tibetan Plateau significantly increased regional and global weathering rates
Weathering Feedback and Climate Regulation
- The coupling between tectonic uplift, erosion, and silicate weathering forms a negative feedback loop helps regulate atmospheric CO2 levels and global climate over geological time scales
- The spatial distribution of mountain ranges, influenced by plate tectonics, affects regional and global weathering patterns and their impact on the carbon cycle
- Example: The Andes influences South American climate and weathering patterns
- Changes in continental configuration due to plate tectonics can alter global weathering rates by affecting climate patterns and the distribution of rainfall over continents
- Silicate weathering acts as a thermostat for Earth's climate system increases in atmospheric CO2 lead to increased weathering rates, which in turn reduce CO2 levels
- The efficiency of the silicate weathering feedback depends on the availability of fresh silicate rocks and the presence of liquid water on Earth's surface
- Example: During Snowball Earth events, the reduction in liquid water may have weakened the silicate weathering feedback
Key Terms to Review (18)
Alfred Wegener: Alfred Wegener was a German meteorologist and geophysicist known for proposing the theory of continental drift in the early 20th century. His ideas laid the groundwork for modern plate tectonics by suggesting that continents were once joined together in a single landmass called Pangaea and have since drifted apart. This theory challenged existing geological beliefs and sparked further research into the mechanisms of plate movement and the formation of geological features.
Asthenosphere: The asthenosphere is a semi-fluid layer of the Earth's mantle located beneath the lithosphere, playing a critical role in plate tectonics. This layer, characterized by its ability to flow slowly, allows the rigid lithospheric plates to move over it, enabling processes like isostasy, crustal thickening, and the formation of continents and ocean basins.
Carbon dioxide emissions: Carbon dioxide emissions refer to the release of CO2 into the atmosphere, primarily through human activities such as burning fossil fuels, deforestation, and industrial processes. This greenhouse gas plays a significant role in climate change and is closely linked to the processes of plate tectonics and the carbon cycle, as volcanic eruptions and tectonic activities can also release carbon dioxide into the atmosphere.
Carbon sequestration: Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide (CO2) to mitigate climate change and reduce the greenhouse effect. This can occur naturally through biological processes, like photosynthesis in plants, or artificially through technological methods that capture CO2 from the atmosphere or from industrial sources and store it underground or use it in various applications.
Climate change: Climate change refers to significant and lasting alterations in global temperatures and weather patterns over time. It encompasses a range of phenomena, including rising temperatures, shifting precipitation patterns, and increasing frequency of extreme weather events, largely driven by human activities such as fossil fuel combustion and deforestation. Understanding climate change is crucial for analyzing geological processes like supercontinent cycles, past climates captured in geological records, and the interplay between tectonic activity and carbon cycles.
Continental drift theory: Continental drift theory is the concept that continents have moved over geological time from a single supercontinent called Pangaea to their current locations. This theory suggests that the Earth's continents are not fixed but instead float on the semi-fluid layer of the mantle, leading to changes in positions and configurations over millions of years.
Convergent Boundary: A convergent boundary is a tectonic plate boundary where two plates move toward each other, often resulting in one plate being forced beneath the other in a process known as subduction. This interaction leads to significant geological features and phenomena, including earthquakes, volcanic activity, and mountain building, reflecting the dynamic nature of Earth's lithosphere.
Divergent boundary: A divergent boundary is a tectonic plate boundary where two plates move away from each other, allowing magma from the mantle to rise and create new crust. This process plays a crucial role in the formation of ocean basins and rift valleys, contributing to the geological features and topography of Earth.
Earthquake: An earthquake is the shaking of the Earth's surface caused by sudden movements in the Earth's lithosphere, typically along faults where stress has built up over time. These movements can result from the interactions of tectonic plates, leading to the release of energy in the form of seismic waves. Earthquakes can occur anywhere but are particularly common in areas where tectonic plates converge, diverge, or slide past each other.
Harry Hess: Harry Hess was a prominent American geologist and a key figure in the development of the theory of plate tectonics, particularly known for his contributions to understanding seafloor spreading. His work helped establish the mechanisms of plate movement and the formation of ocean basins, connecting various geological features and processes within the Earth's lithosphere.
Lithosphere: The lithosphere is the rigid outer layer of the Earth, encompassing the crust and the uppermost part of the mantle. This layer is crucial in understanding how tectonic plates interact, as it affects everything from isostatic adjustments to the formation of geological features like continents and ocean basins.
Mountain range: A mountain range is a series of connected mountains, often formed by geological processes such as tectonic plate movements. These ranges typically arise in regions where tectonic forces create uplift and folding of the Earth's crust, leading to significant changes in topography and influencing both natural landscapes and human activities.
Ocean trench: An ocean trench is a deep, narrow depression in the ocean floor formed by the subduction of one tectonic plate beneath another. These trenches are often associated with convergent plate boundaries and are among the deepest parts of the Earth's oceans, playing a significant role in geological processes, oceanic circulation, and the carbon cycle.
Rift formation: Rift formation is the process through which tectonic plates diverge, leading to the creation of a rift valley or a linear zone of the Earth's crust that has been pulled apart. This geological phenomenon results from extensional forces acting on the lithosphere, allowing magma to rise and create new crust as the rift evolves, impacting both topography and bathymetry significantly.
Seafloor Spreading: Seafloor spreading is the process by which new oceanic crust is formed at mid-ocean ridges as tectonic plates move apart. This geological phenomenon plays a crucial role in the formation of ocean basins and influences various tectonic activities, including the generation of rift valleys and the distribution of magnetic anomalies on the seafloor.
Subduction: Subduction is the geological process where one tectonic plate moves under another and sinks into the mantle as the plates converge. This process is crucial in shaping Earth’s features, influencing everything from the formation of oceanic trenches to the creation of mountain ranges and volcanic activity.
Volcanic outgassing: Volcanic outgassing refers to the release of gases from magma during volcanic eruptions or through hydrothermal activity. This process is crucial for understanding the interactions between the Earth's interior and its atmosphere, especially regarding the cycling of carbon dioxide and other gases that influence climate and the carbon cycle.
Volcano: A volcano is an opening in the Earth's crust that allows molten rock, gases, and ash to escape from below the surface. This geological feature is closely tied to plate tectonics, where the movement of tectonic plates can create conditions for volcanic activity, leading to the formation of new landforms, changes in landscapes, and even ocean basins.