HUMAN BIOLOGY

prinCiples of eCology 467

What is the global carbon cycle?

• In the global carbon cycle, carbon is released by the metabolic
  processes of organisms, by decomposing organic material, by
  fossil fuel burning, and by geologic events.


• Much of Earth’s carbon moves into the atmosphere (as carbon
  dioxide gas) and becomes dissolved in the oceans.


• Carbon may be buried in deep sea or land-based sediments for
  millions of years before cycling back into organisms.

taKe-Home message

Figure 24.11 A “loop” of moving ocean water delivers carbon

dioxide to carbon’s deep ocean reservoir. The CO 2 sinks in

the cold, salty North Atlantic and rises in the warmer Pacific.

(© Cengage Learning)

warm,^ le

ss^

sal

ty,^ s

hallow^ c

urrent

cold, salty, deep^ curr

ent^

bicarbonate

and carbonate

dissolved in

ocean water

marine food webs

producers, consumers,

decomposers

marine sediments, including

formations with fossil fuels

photosynthesis aerobic

respiration

death,

sedimentation

incorporation

into sediments

diffusion between

atmosphere and ocean

burning of fossil fuels

uplifting over

geologic time

sedimentation

land food webs

producers, consumers,

decomposers

terrestrial

rocks

peat,

fossil fuels

volcanic action

burning

of fossil

fuels

deforestation

death, burial, compaction over geologic time

weathering

leaching,

runoff

soil water

(dissolved carbon)

atmosphere

(mainly carbon dioxide)

photosynthesis aerobic

respiration

combustion

of wood (for clearing

land; or for fuel)

A B © Cengage Learning

long-standing reserves of gas, petroleum, and coal, which

we humans have been tapping for use as fossil fuels.

Human activities, including the burning of fossil fuels,

are putting more carbon into the atmo sphere than can be

cycled to the ocean reservoir. This factor is contributing to

global warming and climate change, topics we return to in

Chapter 25.

many millions of years in deep sediments until part of

the seafloor is uplifted above the ocean surface through

geologic forces. Other buried carbon is slowly converted to

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