Slow Carbon Cycle

Question 1

Overview

Answer 1

Transfers of carbon compounds over extensive timescales (possibly millions of years). This involves the sequestration of the remains of marine creatures and it involves chemical weathering. Lastly it involves the transfer of carbon between spheres due to tectonic processes and volcanic activity.

Question 2

1 Carbon sequestration

Answer 2

This is the storage of carbon over geological timescales. It refers to long-term sinks accumulating substantial carbon stores that are not released back into the global carbon system for millions of years. It describes the transfer of carbon from the atmosphere into the storage of plants, soil, sedimentary rocks, fossil fuels and oceans.

2 types: geologic and biological

Question 3

1 Geologic sequestration

Answer 3

Humans can capture CO2 at the source (e.g. power plants) and inject it in liquid form into stores underground such as a depleted oil reservoir. This is still at the experimental stage but could be important in the future as a huge carbon sink.

Oceans also sequester carbon by absorbing it, and within a few weeks to months the carbon sinks to the ocean depths. It can take thousands of years to reappear at the ocean surface.

Question 4

1 Terrestrial/ biological sequestration

Answer 4

This is where plants capture the CO2 from the atmosphere and store it as carbon in their stems and roots or in the soil. Deforestation/ burning/ wildfires can release this CO2 where it may then be part of the fast carbon cycle.

Question 5

2 Chemical.

Answer 5

When atmospheric CO2 is dissolved within precipitation it produces weak carbonic acid which reacts with certain unstable rocks exposed on the land releasing potassium, sodium, magnesium and calcium ions that eventually find their way into the ocean via rivers (links with water cycle here).

Here the calcium ions combine with bicarbonate ions to form calcium bicarbonate, which is absorbed by corals, plankton and shell-building creatures. These organisms convert it into secretions of solid calcium carbonate which eventually end up on the ocean floor where over millions of years layers of shells and skeletal remains are compressed to form rocks such as limestone.

Question 6

3 Burial and compaction

Answer 6

The ocean algae absorb CO2 from the atmosphere. Simultaneously, weathered calcium and bicarbonates are washed into the sea by rivers and used by microscopic marine life to form shells (Foraminifera, coccoliths or molluscs).

When they die, the shells sink to the ocean floor, is buried and finally compressed to form sediments of limestone and chalk. Carbon locked up in limestone can be stored for millions of years or even hundreds of millions of years.

Question 7

3 Burial and compaction (hydrocarbons)

Answer 7

Hydrocarbons (fossil fuels) are also created through burial and compaction.

However, it is important to note that carbon in fossil fuels is sequestered only until humans burn them through combustion – this then turns into a fast carbon flow.

Question 8

4 Tectonic Activity

Answer 8

Carbon is stored below the ocean in layers of limestone. Tectonic forces cause the plates to move, pushing the sea floor under continental margins in the process of subduction.

Sea floor deposits are pushed deep into the Earth where they heat up, melt and rise back to the surface as volcanic eruptions. This releases CO2 back into the atmosphere.