2.1.6 The global carbon cycle

What is the global carbon cycle

The movement of carbon between the atmosphere biosphere hydrosphere and lithosphere through interconnected processes

Why is the carbon cycle a closed system

Carbon is not created or destroyed only transferred between stores

What are the four main carbon stores

Atmosphere biosphere hydrosphere and lithosphere

How much carbon is stored in the atmosphere

About 800 gigatonnes of carbon mainly as CO2 and methane

How much carbon is stored in the biosphere

About 560 gigatonnes of carbon in vegetation and soils

How much carbon is stored in the hydrosphere

About 38 000 gigatonnes of carbon mostly as dissolved CO2 and bicarbonate

How much carbon is stored in the lithosphere

Around 100 million gigatonnes of carbon in rocks fossil fuels and sediments

What are inputs to a carbon store

Processes that add carbon such as respiration combustion and volcanic activity

What are outputs from a carbon store

Processes that remove carbon such as photosynthesis and ocean absorption

What is mass balance in the carbon cycle

The idea that in a balanced system inputs equal outputs

Why is there carbon imbalance today

Human activities add carbon faster than natural sinks can absorb it

What human activities disrupt carbon mass balance

Fossil fuel combustion deforestation and land use change

What is the fast carbon cycle

Short term carbon exchanges operating over seconds to years

What processes dominate the fast carbon cycle

Photosynthesis respiration decomposition and combustion

What is photosynthesis

Plants absorb CO2 and convert it into glucose using sunlight

How much carbon does global photosynthesis fix annually

About 120 gigatonnes of carbon per year

How much CO2 can a mature tree absorb annually

Around 22 kilograms of CO2 per year

What is respiration

The release of CO2 back into the atmosphere by plants animals and soils

How much carbon do plants respire

Around 40 to 60 percent of the carbon they fix

What is decomposition

The breakdown of organic matter releasing CO2 via microbial activity

How much carbon can forest litter release annually

Around 1.5 to 2.5 kilograms per square metre

How does combustion affect the carbon cycle

It releases stored fossil carbon rapidly into the atmosphere

How much CO2 does burning one litre of petrol release

About 2.3 kilograms of CO2

What is carbon sequestration

The long term storage of carbon in biomass soils or sediments

How much carbon can grassland soils sequester

Up to 0.3 tonnes per hectare per year under good management

What role do oceans play in the carbon cycle

They act as major carbon sinks absorbing atmospheric CO2

What is diffusion in the ocean carbon cycle

The physical exchange of CO2 between ocean surface and atmosphere

How much anthropogenic carbon do oceans absorb annually

About 2.5 gigatonnes of carbon per year

Why do cold oceans absorb more CO2

CO2 is more soluble at lower temperatures

What is biological absorption in oceans

Uptake of carbon by phytoplankton through photosynthesis

How much carbon do phytoplankton fix annually

About 50 gigatonnes of carbon per year

What happens to carbon after marine organisms die

It sinks and contributes to long term ocean storage

What is ocean acidification

The lowering of ocean pH due to dissolved CO2 forming carbonic acid

How much has ocean pH fallen since 1750

About 0.1 units representing a 30 percent increase in acidity

What is the slow carbon cycle

Long term carbon transfers operating over thousands to millions of years

What processes dominate the slow carbon cycle

Chemical weathering river transport and sedimentation

What is chemical weathering

CO2 reacts with rainwater to form carbonic acid that breaks down rocks

How much carbon does chemical weathering remove annually

About 0.3 gigatonnes of carbon per year

Why is the Himalayan region important for weathering

High rainfall and uplifted silicate rocks enhance carbon drawdown

What is the River Exe example used for

Showing how small rivers transport organic carbon to the ocean

How much rainfall does the Exe catchment receive annually

Over 1 200 millimetres per year

What is the role of rivers in the carbon cycle

They transport dissolved and particulate carbon to the oceans

How much carbon do rivers transport globally each year

Around 1.1 gigatonnes of carbon

Why is the Amazon River important to the carbon cycle

It delivers about 0.1 gigatonnes of carbon annually to the Atlantic

How does rainfall link the water and carbon cycles

Rainfall mobilises carbon through runoff and weathering

How much rainfall does the Amazon Basin receive annually

Over 2 000 millimetres per year on average

What happens to carbon once it reaches the ocean long term

It is buried in sediments forming limestone and carbonate rocks

How much carbon is sequestered in marine sediments annually

About 0.2 gigatonnes of carbon

What geological feature shows long term carbon storage

The White Cliffs of Dover made from carbonate shells

Why is the carbon cycle important for climate regulation

It controls atmospheric CO2 concentrations and global temperatures

Why is understanding the carbon cycle important

To manage climate change and maintain carbon balance