Lecture 14 – Biogeochemical Cycle

A reservoir in a biogeochemical cycle is

A space that contains a material

A positive feedback

Accelerates a change

The largest carbon reservoir on Earth is

Sedimentary rocks

In the short-term carbon cycle carbon moves via

Photosynthesis and respiration

Burial of organic carbon is important because

It removes CO2 and leaves O2 in the atmosphere and forms fossil fuels

Anoxia refers to

The absence of oxygen

Black shales form when

Organic-rich muds accumulate under anoxic conditions

Black shales are significant because

They are source rocks for petroleum and natural gas

Carbon's two stable isotopes are

12C and 13C

During photosynthesis organisms preferentially incorporate

More 12C than 13C

Respiration preferentially releases

12C

When organic carbon is buried the ocean and atmosphere become

Enriched in 13C

Burning fossil fuels causes atmospheric 13C 12C to

Decrease

Limestone records the 13C 12C ratio of

Ocean water

Chemical weathering removes CO2 by forming

Carbonic acid

Weathering products form

Carbonate minerals and limestone

Metamorphism of limestone

Releases CO2 back to the atmosphere

Mountain building affects the carbon cycle by

Exposing more rock to weathering which removes CO2

Higher temperature and precipitation

Accelerate weathering

Vegetation accelerates weathering by

Producing acids from roots

Methane hydrates represent

Positive feedback warming releases methane

Negative feedback between weathering and temperature works because

Higher temperatures increase weathering reducing CO2

Middle Paleozoic CO2 drop was caused by

Evolution and spread of land plants

Carboniferous CO2 decline was due to

Burial of organic carbon in coal swamps

Highest atmospheric oxygen occurred during

Carboniferous to Permian

Oxygen isotopes typically measured are

16O and 18O

More 18O in carbonate skeletons indicates

Colder temperatures

Microfossils used for ancient ocean temperatures

Planktonic foraminifera

H2O with 16O evaporates faster because

16O is lighter

During glaciation ocean water becomes enriched in

18O

Steady state means

Input equals output

A negative feedback

Acts to slow or counteract a change

Oceanic Anoxic Events

Enhance organic carbon burial drawing down CO2