The role of oceans as a store and source of carbon dioxide.

Lesson Objective:

To examine the role of oceans

as a store and source of carbon dioxide

Before we do that, let´s remind ourselves of the CARBON CYCLE

http://bcs.whfreeman.com/thelifewire/content/chp58/5802002.html

10 minutes:

Get into pairs (or threes). Describe in your own words the different stores (reservoirs) and transfers (fluxes) of CARBON on your handout

(numbers are in gigatonnes. 1 gigatonne is a billion metric tonnes!)

And now for some facts....

But first - Why is carbon dioxide important to our planet?

Major carbon stores:

• Atmosphere (730 GT)
• Oceans (38,000 GT)
• Terrestrial plants and soils (2000 GT)

Most carbon removed from atmosphere by organisms and deposited into sediments on ocean floor.

Just as well for the temperature of our planet - why?

This bulk of ocean floor carbon cannot freely interact with the atmostphere (it does so mostly via sea-floor spreading (which is what?).

Deep oceans (below thermocline) contain 36,000 GT of carbon which can interact with the atmosphere. How did it get into the deep oceans? Think back a few lessons........

Thermohaline circulation ! (Great Ocean Conveyer Belt)

and biological pump.

IIt takes the carbon between 500 and 1000 years to circulate in this fashion!

This means that the deep oceans and ocean sediments are considered as reservoirs of fixed size - they change very slowly

and do not interact with the atmosphere in the short term.

Three reservoirs that can quickly exchange carbon are:

• atmosphere
• surface layer of ocean
• terrestrial plants and soils

These reservoirs have been in balance until humans arrived!

Over the last 420,000 years, carbon dioxide levels in the atmosphere have fluctuated from

180 to 300 parts per million

Since the Industrial Revolution we have tapped into reservoirs of carbon by making cement (needs lime which involves CO2 byproduct) and burning oil, gas and coal.

We add c. 6 GT of carbon into the atmosphere every year (100x that of volcanoes)!

So what does this mean for our planet?

Our planet maintains a fairly constant volume of carbon dioxide in the atmosphere through interacting with the oceans and biosphere.

As CO2 increases in the atmosphere we would expect the oceans to respond by taking up more carbon. But this does not happen. Why?

Photosynthesising organisms in the surface oceans take up CO2 - but the ocean already contains more than they need. Adding more C02 to the oceans will not mean an increase in photosynthesis!

Increase CO2 levels in the oceans also has another serious impact.

As human society adds CO2 to the atmosphere it serves to decrease the concentration of carbonate in the surface oceans (ask your chemistry teacher! (Chatetlier´s principle) ).

What does this mean?

This makes it more difficult for corals to form their skeletons and for animals such as foraminifera and molluscs to form their shells.

This means that within a few decades these animals will no longer be able to produce calcium carbonate!

This means the destruction of fragile coastal ecosystems.

Ecosystems that form the livelihood of millions of people worldwide

Activity: Revisit your description from the beginning of our lesson. Modify the descriptions based on what you have learnt today.

Over to you

Outline the role that the oceans play as a store and source of carbon dioxide (5 marks).

Tip: You can access this presentation online (address on your handout).

Due next Monday.

NOTE: I will not be here for Thursday´s lesson (Malta trip).

Extension work:

Using your handouts, outline negative feedback mechanisms and describe the three types found within the oceans.

Activity

You can use annotations!

Primary source of carbon in atmosphere from volcanoes (before humans!)