A Level Edexcel Carbon Cycle Enquiry Question 1

[6.1A] What is the carbon cycle?

The biogeochemical is the cycle by which carbon moves from one sphere to another (atmosphere, hydrosphere, lithosphere, and biosphere). It acts as a closed system made up of linked subsystems that have inputs, throughputs, and outputs.

- Biogeochemical. = biological (living plants), geological (erosion), and chemical (reactions under heat and pressure.)

[6.1A] What are the stores in the carbon cycle?

Hydrosphere (oceans), atmosphere, lithosphere, and the biosphere.

[6.1A] What is the hydrosphere store?

This refers to oceans and bodies of water, and carbon dioxide is dissolved by oceans from the atmosphere.

- Most CO2 is in intermediate and deep water.

[6.1A] What is the atmosphere store?

Volcanic activity, respiration, wildfires and outgassing emit carbon dioxide into the atmospheric store.

- Human emissions is also increasing this by 3%.

[6.1A] What is the lithosphere store?

Carbon is trapped is trapped in rocks, particularly sedimentary rocks like limestone, oil and coal.

[6.1A] What is the biosphere store?

Carbon atoms are trapped in living and dead organisms.

[6.1A] What are carbon stores, processes and fluxes?

Carbon Stores:

- These function as sources (adding carbon to the atmosphere) and sinks (removing carbon from the atmosphere).

Processes:

- The physical mechanisms that drive the flux of material between stores.

Fluxes:

- The movement of carbon between stores.

[6.1A] How is carbon measured?

Petagrams are the units used to measure carbon. One pentagram, also known as a gigatonne is equal to a trillion kilograms.

[6.1A] What are terrestrial stores?

These are land-based stores.

[6.1B] Where is most of the earth's carbon stored?

Most of it is geological, so it is stored in rocks. There is over 100 million Pg of carbon in the lithosphere.

[6.1B] How is sedimentary rocks formed in the geological carbon cycle?

- These are formed from calcareous ooze (calcium carbonate mud) that collect at the bottom of oceans.

- Marine creatures such as phytoplankton absorb carbon from seawater, and when their remains collect on the seabed, the calcium carbonate is compacted by the weight of new layers about them and cemented together form an organic limestone.

[6.1B] How is carbon biologically derived from shale, coal, and other rocks?

Carbons derived from plants and animals in shale, coal and other rocks. These rocks were made up to 300 million years ago from the remains of organisms. These remains sank to the bottoms of rivers, lakes and seas and were subsequently covered by silt and mud. As a consequence, the remains continued to decay anaerobically and were compressed by further accumulations of dead organisms and sediment. The subsequent burning of these fossil fuels has released the large amounts of carbon they contained back into the atmosphere.

[6.1C] What are key processes in the geological carbon cycle?

Weathering, decomposition, transportation, sedimentation, and metamorphosis.

[6.1C] What are the types of weathering?

Mechanical Weathering:

- The breakup of rocks by frost; shattering and exfoliation produces small, easy-to-transport particles.

Chemical Weathering:

- The breakdown of rocks by carbonic acid in rain, which dissolves carbonate-based rocks.

Biological Weathering:

- Burrowing animals and the roots of plants can break rocks up.

[6.1C] What is decomposition and transportation?

Decomposition:

- Decomposition - When living organisms die, they are broken down by decomposers (such as bacteria and detritivores) which respire, returning CO2 into the atmosphere

Transportation:

- Rivers carry particles to the ocean, where they are deposited.

[6.1C] What is sedimentation and metamorphosis?

Sedimentation:

- When the animals die, they decompose, and their remains become sediment, trapping the stored carbon in layers that eventually turn into rock or minerals.

Metamorphosis:

- Deep burial of sedimentary rocks combined with compression due to plate tectonics, which causes sedimentary rocks to be altered by heat and pressures into metamorphic rock.

[6.1C] How can chemical weathering release carbon from silicate rocks?

Carbon dioxide in the atmosphere reacts with moisture to form weak carbonic acid (carbon dioxide in the air). When this falls as rain, it reacts with some of the surface minerals such as calcium carbonate and slowly dissolves them. This is chemical weathering: the decomposition of rock minerals in their original position by agents such as water, oxygen, carbon dioxide and organic acids. It is carried by water or released as a gas.

[6.1C] How can volcanic outgassing release carbon from silicate rocks?

- There are pockets of CO2 found in the Earth's crust, such as limestone. Following tectonic activity, CO2 can be released.

Outgassing is the release of gas, previously dissolved, trapped, frozen or absorbed in some material (e.g. rock).

- It occurs mainly along mid-ocean ridges, subduction zones and at magma hotspots.

[6.2A] What is sequestering and pumping?

The natural storage of carbon by physical or biological processes such as photosynthesis. It is held in solid or liquid form.

Pumping is simply the movement of carbon around.

[6.2A] What are the carbon cycle pumps?

These are pumps operating in oceans to circulate and store carbon. There are three types: biological, carbonate and physical. This is oceanic.

[6.2A] What is phytoplankton?

These are mostly microscopic single-celled plants found in the warmer surface waters of oceans. These plants photosynthesise. They take in carbon and turn it into organic matter. As they are the base of the marine

food web (half of the planet's biomass consist of phytoplankton despite their microscopic size) when

they get eaten, carbon is passed through the food chain.

[6.2A] What does the biological pump do?

- This is the sequestration of CO2 to oceans by marine plants called phytoplankton.

- The small plants float near the surface, so they can taken in sunlight to photosynthesise.

- The phytoplankton have rapid growth rates.

- Carbon is then passed up the food chain by consumer fish and zooplankton.

- Most of the carbon dioxide is taken up by the phytoplankton and is recycled near the surface.

- However, some dead phytoplankton and their predators sinks into deeper waters. They are decomposed or turned into sediment, such as calcium carbonate.

[6.2A] What does the physical pump do?

- This is based on the oceanic circulation of water, including upwelling, downwelling and the thermohaline current.

- Downwelling occurs in parts of the ocean where cold, denser water sinks.

- These current bring dissolved carbon dioxide down to the deep ocean.

- Once there, it moves in a slow-moving deep ocean current, staying there for years.

- The deeper ocean currents part of thermohaline circulation return to the surface by upwelling.

- The cold deep ocean water warms as it rises towards the ocean surface and some of the dissolved carbon dioxide is released back into the atmosphere through respiration.

- The colder the water, the more potential for CO2 to be absorbed and stored.

[6.2A] What does the carbonate pump do?

- Carbonate pumps form sediments from dead organisms that fall to the ocean floor (sedimentation).

- Marine organisms may utilise calcium carbonate (CaCO2) to make hard outer shells and inner skeletons, such as some plankton species, coral, oysters and lobsters.

- When organisms die and sink, many shells dissolve before reaching the sea floor sediments.

- This carbon becomes part of the deep ocean currents.

- Shells that do not dissolve build up slowly on the sea floor, forming limestone sediments.

[6.2A] What is thermohaline circulation?

It is the global system of surface and deep water ocean currents and is driven by temperature and salinity differences between ares of oceans. It circulates carbon around the system. This helps transfer CO2 from equatorial ocean source area to polar sink areas.

- The foundation of the planet's food chain depends on the cool, nutrient-rich waters that support algae and seaweed growth.

- This is vital to the global carbon cycle.

[6.2B] How do terrestrial primary producers sequester carbon?

- Plants (primary producers in an ecosystem) sequester carbon out of the atmosphere during photosynthesis. In this way, carbon enters the food chains and nutrients cycles of terrestrial ecosystems.

- When animals consume plant matter, the carbon sequestered in the plant becomes part of their fat and protein. Respiration, particularly by consumer animals, returns some of the carbon back to the atmosphere.

- Waste from animals is eaten by micro-organisms (bacteria and fungi) and detritus feeders (e.g. beetles).

- As a consequence, carbon becomes part of these creatures. When plants and animals die and their remains fall to the ground, carbon is released into the soil.

Forests sequester the most carbon.

[6.2B] How does carbon fluxes within ecosystems vary?

Diurnally:

- During the day, fluxes are positive - from the atmosphere into the ecosystem. The reverse applies at night when respiration occurs but not photosynthesis.

Seasonally:

- During winter, carbon dioxide concentrations increase because of the low levels of plant growth. However, as soon as spring arrives and plants grow, these concentrations begin to decrease until the onset of autumn.

[6.2C] How can biological carbon be stored in the soil, and what does it depend on?

Soils store between 20% and 30% of global carbon.

- They sequester about twice the quantity of carbon as the atmosphere and three times that of terrestrial vegetation.

- Dead organic matter decomposed, taken up by plants or released into the atmosphere.

The actual amount of carbon stored in some soil depends on:

Climate:

- This dictates the rates of plant growth and decomposition; both increase with temperature and rainfall.

Vegetation Cover:

- This affects the supply of dead organic matter.

Soil Type:

- Clay protects carbon from decomposition, so clay-rich soils have a higher carbon content.

Land Use:

- Cultivation and other forms of soil disturbance increase the rate of carbon loss.

[6.3A] What are the greenhouse gases?

Methane, and carbon dioxide.

[6.3A] What is the greenhouse effect?

The greenhouse effect is what controls the temperature system of the earth. It has been found that the Earth's average temperature has changed with the changes in concentration of atmospheric carbon.

- The earth's climate is driven by shortwave solar radiation.

- Without the atmospheric greenhouse gases, there wouldn't be enough heat to warm the planet with the sun alone.

- Approximately 31% of solar radiation is reflected by clouds, aerosols, and gases in the atmosphere and by the land surface.

- The remaining 69% is absorbed, almost 50% is absorbed at the earth's surface.

- Much of this radiation absorbed at the surface is re-radiated as long wave radiation.

[6.3B] How is ocean and terrestrial photosynthesis important in regulating the composition of the atmosphere?

- Photosynthesis regulates the composition of the atmosphere by balancing oxygen (20.94%) and carbon dioxide (0.03%).

- It plays an essential role in keeping carbon dioxide levels relatively constant thereby helping to regulate the Earth's mean temperature.

- The amount of photosynthesis varies spatially, particularly with net primary productivity (NPP). (This is the amount of organic matter that is available for humans and other animals to harvest or consume).

- NPP is highest in the warm and wet parts of the world, particularly in the tropical rainforests and in shallow ocean waters. It is least in the tundra and boreal forests.

[6.3B] How is soil health influenced?

- Soil health is an important aspect of ecosystems and a key element in the normal functioning of the carbon cycle.

- Soil health depends on the amount of organic carbon stored in the soil.

- The storage amount is determined by the balance between the soil's inputs (plant and animals remains, nutrients) and its outputs (decomposition, erosion and uptake by plant and animal growth.)

- Organic matter helps retain soil moisture and nutrients (fertility), which in turn improves the productivity of an ecosystem by providing water and dissolver nutrients.

- Carbon gives soil its structure, retention capacity, and fertility.

[6.3C] How has fossil fuel consumption increased?

It is estimated that about half the extra emissions for carbon dioxide since 1750 have remained in the atmosphere. The rest has been fluxed from the atmosphere into the stores provided by oceans, ecosystems and soil. Fluxes have also increased. This is as result of the industrial revolutions globally, increasing worldwide temperatures.

[6.3C] What are the implications of higher fossil fuel combustion for the climate?

- Temperate and tropical areas may have stronger storms because of more heat energy and moisture in the atmosphere.

- Fewer extreme cold events but more hot events due to average temperature increase.

- Precipitation patterns will change, causing it to be higher near the poles and decreasing in the subtropics as warmer air can hold more moisture.

- More evaporation and precipitation.

- Less snow and more rain for some regions.

- Sea level rise.

[6.3C] What are the implications of higher fossil fuel combustion for ecosystems?

- Ecosystems help regulate carbon and hydrological cycles, so they are important.

- Global warming may be the dominant direct driver of changes in these services and in biodiversity.

- Sea level rise brought about higher climate will mean many ecosystems are under threat.

- 80% of coral reefs could become bleached by warmer seawater and suffer chemical weathering.

- 10% of land species face extinction due to an inability to adapt or move when climate conditions change.

[6.3C] What are the implications of higher fossil fuel combustion for the hydrological cycle?

- Increased evaporation rates, so there will be more moisture circulating through the cycle, leading to intense precipitation events.

- Cryosphere store will decrease as glaciers retreat or ice sheets melts.

- Change in precipitation in the type, particularly spring melt which will occur earlier.