6.1.B Carbon Cycle types

Question 1

What is the geological carbon cycle and how does it move?

Answer 1

the geological carbon cycle is a natural cycle that moves carbon between land, oceans and atmosphere. This movement involves a number of chemical reactions that create new stores which trap carbon for significant periods of time. There tends to be a natural balance between carbon production and absorption within this cycle. However, there can be occasional disruptions and short periods before the equilibrium is restored, such as when major volcanic eruptions emit large quantities of carbon into the atmosphere, or when natural climate changes occur

Question 2

What is the difference between geological and biologically derived carbon?

Answer 2

geological carbon results from the formation of sedimentary carbonate rocks - limestone and chalk - in the oceans, and biologically derived carbon is stored in shale, coal and other sedimentary rocks

Question 3

How can volcanic eruptions maintain the carbon equilibrium?

Answer 3

the impact of emissions from volcanic eruptions is to send extra CO2 into the atmosphere, which leads to rising temperatures, increased evaporation and higher levels of atmospheric moisture. This, in turn, leads to increased acid rain, which weathers rocks and creates bicarbonates that will eventually be deposited as carbon on the ocean floor. The process is slow - perhaps a few hundred thousand years - but this chemical weathering process slowly rebalances the carbon cycle

Question 4

What does the bio-geochemical carbon cycle determine?

Answer 4

biological and chemical processes determine just how much of the carbon available on the earth’s surface is stored or released at any one time. That’s why it’s often referred to as the bio-geochemical carbon cycle. The role of living organisms is critical in maintaining the efficient running of this system, because they control the overall balance between storage, release, transfer and absorption

Question 5

What are the four key processes in the carbon cycle?

Answer 5

photosynthesis - removing CO2 from the atmosphere to promote plant growth
respiration - releasing CO2 into the atmosphere as animals consume plant growth and breathe
decomposition - breaking down organic matter and releasing CO2 into soils
combustion of biomass and fossil fuels - releasing CO2 and other greenhouse gases into the atmosphere
together these four processes continuously transfer carbon from one store to another. the time period over which the carbon stays in any one store is important, and - since the Industrial Revolution - deeply buried stores of carbon have been exploited and burnt, releasing CO2 into the atmosphere.

Question 6

Stats showing carbon released as CO2 being the main driver of climate change

Answer 6

-2015 began a year of record global average temperatures
-By 2016, the longest hot spell in 137 years had occurred - 0.9 degrees Celsius hotter than the average for the twentieth century

Question 7

What is the largest carbon store

Answer 7

The largest carbon store is geological

There is over 100 million Pg of carbon in the lithosphereMost lithospheric carbon is concentrated in the sedimentary rocks of the crust

Question 8

How is sedimentary rock formed?

Answer 8

Sediment is deposited in layers in a low-energy environment E.g. lakeE.g. sea bed
Further layers are deposited and sediment undergoes diagenesis

Diagenesis - the physical and chemical changes that occur during the conversion of sediment to sedimentary rock

The lower layers become compressed and chemical reactions cement particles together

The conversion of loose, unconsolidated sediment into solid rock is known as lithification.

Question 9

What is limestone?

Answer 9

Com​posed of calcium carbonate, and is 40% carbon by weight
80% of lithospheric carbon is found in limestones
Limestone is formed when calcium carbonate is deposited on the ocean floor.

Question 10

How is limestone formed?

Answer 10

1) limestone formed in the oceans
The Himalayas form one of the Earth’s largest carbon stores. This is because the mountains started life as ocean sediments rich in calcium carbonate derived from crustaceans, corals and plankton. Since these sediments have been upfolded, the carbon they contained has been weathered, eroded and transported back to the oceans.
2) carbon 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 bottom 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.

Question 11

How can the carbon cycle be fast and slow?

Answer 11

the quickest cycle is completed in seconds, as plants take carbon from the atmosphere through photosynthesis. they then release it by respiration. sunlight, temperature and moisture all control the speed of these processes. if it’s too dark, hot or cold they decrease. low levels of CO2 in the atmosphere also reduce the speed of the cycle
dead organic material in soils may retain carbon for years - or even centuries - waiting to be broken down. note that the tree on the left in figure 5 is alive and therefore taking in co2 from the atmosphere, and the one of the right is dead, so the co2 it holds eventually makes its way to the sea via the soil and decomposition. some organic materials may become buried so deeply that they don’t decay at all - instead transforming into sedimentary rocks, such as limestone, or coal or alternatively into hydrocarbons (commonly referred to as oil and natural gas). CO2 is then only released when these are burned, or when limestone is used industrially, e.g. when making cement

Question 12

Explain the geographical patterns of the carbon cycle

Answer 12

since regional climates influence rates of photosynthesis and respiration, its not surprising that co2 fluxes vary with latitude. levels are always higher in the Northern hemisphere because it contains greater landmasses and temperatures than in the Southern Hemisphere

Question 13

What geological processes can release carbon?

Answer 13

Geological carbon can also be released into the atmosphere through geological processes:
carbon dioxide in the atmosphere reacts with moisture to form weak carbonic acid. When this falls as rain, it reacts with some of the surface minerals 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 pockets of carbon dioxide exist in the Earth’s crust. Volcanic eruptions and earthquakes can release these gas pockets. 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.