L7 - The carbon cycle

Question 1

Why are global biogeochemical cycles important?

Answer 1

They play roles in climate change, biodiversity, food security, hydrology, air quality, and interactions between these areas.

Question 2

What are the Earth’s system ‘spheres’?

Answer 2

Atmosphere, hydrosphere, lithosphere, terrestrial, oceanic, pedosphere, and cryosphere.

Question 3

What roles does the biosphere play in the Earth system?

Answer 3

Physical: Storing/moving material, erosion control

Chemical: Changing chemical forms and reactivity

Radiative: Converting solar energy, altering surface albedo

Question 4

What are the three key organism types in biogeochemical cycles?

Answer 4

Producers (e.g., photosynthetic organisms)

Consumers (e.g., animals)

Decomposers (e.g., fungi and bacteria)

Question 5

What elements are essential for life?

Answer 5

Macronutrients: C, H, N, O, P, S, Ca, Na, K, Mg, Cl

Micronutrients: Fe, B, Cr, Cu, I, Mn, Se, Zn, etc.

Question 6

How do humans perturb the biosphere?

Answer 6

Pollution, land use change, overharvesting, monocultures, species relocation, genetic modification, altered nutrient/water cycles.

Question 7

What are some effects of human perturbations on the biosphere?

Answer 7

Reduced biodiversity, altered ecosystem stability, species extinction, promotion of harmful species, and increased greenhouse gas emissions.

Question 8

What is a global biogeochemical cycle?

Answer 8

The transport and transformation of substances in the natural environment across various time and space scales.

Question 9

What is the UK Earth System Model (UKESM)?

Answer 9

A comprehensive model developed by the Met Office and NERC to simulate Earth’s systems and support IPCC reports.

Question 10

Which sub-models are included in UKESM?

Answer 10

UM (atmosphere), JULES/TRIFFID (land), NEMO (ocean), CICE (sea ice), UKCA (atmospheric chemistry), MEDUSA (marine biogeochemistry), BISICLES (ice sheets), OASIS (coupler).

Question 11

What is a reservoir in the context of Earth systems?

Answer 11

A reservoir is an entity within the Earth system that contains an amount (burden) of a substance of interest.

Question 12

What is the ‘burden’ of a reservoir?

Answer 12

The burden is the amount of a substance within a reservoir, usually measured by mass.

Question 13

What are the four types of reservoirs?

Answer 13

Physical, phase, chemical, and biological reservoirs.

Question 14

What defines a physical reservoir?

Answer 14

It confines an element to a specific location, like a lake or atmosphere.

Question 15

What defines a phase reservoir?

Answer 15

It is defined by the phase of a material, such as ice, liquid water, or vapor

Question 16

What defines a chemical reservoir?

Answer 16

It is based on the chemical form of a substance, e.g., NH₃ vs HNO₃.

Question 17

What defines a biological reservoir?

Answer 17

It involves material being taken into or released from living biomass.

Question 18

What is a flux in biogeochemical terms?

Answer 18

The quantitative rate at which a substance enters or leaves a reservoir, usually measured in mass per time.

Question 19

What are sources and sinks?

Answer 19

A source adds to a reservoir’s burden, while a sink removes from it.

Question 20

What is a coupling in the context of reservoirs?

Answer 20

When a sink from one reservoir serves as a source for another.

Question 21

What is the formula for turnover time (τ₀)?

Answer 21

τ₀ = M / S, where M is burden and S is sink rate.

Question 22

How is total turnover time calculated for multiple sinks?

Answer 22

τ₀,tot = M / (S₁ + S₂ + … + Sₙ)

Or: 1/τ₀,tot = Σ(1/τ₀,i)

Question 23

Why might fluxes be out of balance in a model?

Answer 23

Due to changing burdens from natural variability or anthropogenic effects.

Question 24

What is needed to understand and predict biogeochemical cycles?

Answer 24

Understanding reservoirs and fluxes

Knowing magnitudes and changes

Assessing couplings, interactions, and feedbacks

Quantifying human impacts

Question 25

What is the ultimate goal of learning about reservoirs and turnover times?

Answer 25

To make quantitative predictions about current and future changes in Earth’s biogeochemical systems.

Question 26

What are the major categories of carbon in the Earth system?

Answer 26

Elemental, inorganic, and organic carbon.

Question 27

What are common forms of elemental carbon?

Answer 27

Diamond, graphite, fullerenes, graphene.

Question 28

What are examples of inorganic carbon?

Answer 28

CO, CO₂, carbonic acid (CH₂O₃), carbonate (CO₃²⁻), carbon black, coal, soot

Question 29

What makes organic carbon unique?

Answer 29

Its ability to form complex molecules with many elements; it's the basis for all life on Earth.

Question 30

What are some reservoirs of organic carbon?

Answer 30

Biomass, soils, sediments, particulate organic carbon (POC), dissolved organic carbon (DOC), fossils, and oil.

Question 31

What are VOCs and where do they come from?

Answer 31

Volatile organic compounds, produced by plants (e.g. isoprene) and human activities like combustion and industrial processes.

Question 32

What happens to VOCs in the atmosphere?

Answer 32

They undergo oxidation, often converting to CO₂ and H₂O or particulates.

Question 33

What is methane’s role in the Earth system?

Answer 33

Produced by anaerobic bacteria Major greenhouse gas (~1.8 ppm) Lifetime ~10 years Increased by human activities like farming and fossil fuels

Question 34

How does carbon affect climate?

Answer 34

CO₂, CH₄, halocarbons trap outgoing radiation (warming) Aerosols can cool by scattering light Indirect effects include water vapor increase and cloud formation

Question 35

What is black carbon and why is it important?

Answer 35

A form of soot that absorbs radiation, causing warming Reduces albedo when deposited on snow/ice Possibly second most significant warming agent after CO₂

Question 36

What complicates the net effect of black carbon?

Answer 36

It is often emitted alongside cooling agents like organic carbon aerosols, making the total climate impact complex.

Question 37

What key points did the 2013 IPCC report highlight about carbon?

Answer 37

Need to resolve methane budgets Carbon’s large climate impact Importance of reservoir and lifetime models for understanding carbon

Question 38

What are the three parts of the Global Carbon Cycle?

Answer 38

Short-term organic carbon cycle (biosphere-atmosphere) Long-term organic carbon cycle (fossil fuels, sediments) Long-term inorganic carbon cycle (carbonate rocks)

Question 39

How does the short-term organic carbon cycle work?

Answer 39

It involves rapid exchanges of carbon between the atmosphere and the biosphere (land and ocean).

Question 40

What is the long-term organic carbon cycle?

Answer 40

Small fraction of organic matter is buried to form fossil fuels and sediments Human fossil fuel burning releases carbon much faster than natural burial

Question 41

What is the long-term inorganic carbon cycle?

Answer 41

Carbon injected by volcanoes forms limestone deposits (CaCO₃) Processes like weathering and subduction recycle carbon over millions of years

Question 42

What chemical reaction forms limestone?

Answer 42

Ca²⁺ + 2HCO₃⁻ → CaCO₃ (shells) + CO₂ + H₂O

Question 43

How does cement manufacturing affect the carbon cycle?

Answer 43

Cement production releases CO₂ CaCO₃ → CaO + CO₂

Question 44

What role does the ocean's biological pump play?

Answer 44

Photosynthesis in the upper ocean captures CO₂ Organic material sinks, decomposing and releasing CO₂ at depth

Question 46

What is primary production?

Answer 46

Gross Primary Production (GPP): Total carbon fixed by photosynthesis Net Primary Production (NPP): GPP minus carbon respired by plants

Question 47

How does terrestrial biosphere carbon compare to marine biosphere carbon?

Answer 47

The terrestrial biosphere is larger due to trees and soil organic matter.

Question 48

What causes the seasonal variation in atmospheric CO₂?

Answer 48

Seasonal differences in photosynthesis and respiration, especially in the northern hemisphere.

Question 49

What is the turnover time for carbon in litter?

Answer 49

About 1.5 years on average.

Question 50

How does temperature affect litter decomposition and carbon storage?

Answer 50

Above ~30°C, decomposition exceeds litter formation → little soil carbon storage Below ~25°C, litter accumulates → more soil carbon storage

Question 51

What happens to soil carbon with warming climates?

Answer 51

The balance point moves north, potentially releasing more carbon into the atmosphere.

Question 52

How do land use changes impact the carbon cycle?

Answer 52

Deforestation and agriculture can rapidly release stored biomass and soil carbon.