Oceans – More – Oceanic Nutrients – Worksheet 2 –
Nutrients in the Ocean
1. The importance of phytoplankton and dust to our climate ?
Replace the numbers in the figure with the correct words from the list below.
1. phytoplankton
2. DMS
3. DMS
4. iron
5. sulphate aerosols
6. CCN
7. cooling-indirect light scattering by clouds
8. dust particles
9. cooling-direct light scattering by aerosols
Missing words:
- dust particles
- sulphate aerosols
- DMS (2x)
- phytoplankton
- CCN
- cooling-indirect light scattering
by clouds
- cooling-direct light scattering by
aerosols
- iron
2. The scientist, John Martin, once said “give me a tanker load of iron and I’ll give
you the next ice age”. What did he mean by this?
As iron is an essential micronutrient for phytoplankton, inputs of iron from the atmosphere are necessary
for phytoplankton to grow. We know that phytoplankton take up carbon dioxide during photosynthesis
and that carbon dioxide is an extremely important greenhouse gas which contributes to global warming.
We also know that if phytoplankton sink out of the surface waters in to the deep ocean, they take their
carbon with them and, to make up for this carbon removal, more carbon dioxide enters the ocean from
the air. This, along with physical removal processes lowers carbon dioxide levels in the air and this
reduces global warming. Some phytoplankton also produce the gas dimethyl sulphide (DMS) as they
grow. This gas is also important to our climate. When it enters the air it is converted to sulphate
aerosols which affect climate both by scattering sunlight back into space and also by acting as cloud
condensation nuclei and starting the formation of clouds. The High Nitrate, Low Chlorophyll (HNLC)
regions of the oceans have much less phytoplankton than we expect based on the levels of nitrate and
phosphate nutrients that are present. Low phytoplankton growth in these large areas of the ocean
means that, overall, the ocean is a smaller carbon dioxide sink that we initially thought. Lack of iron
appears to limit phytoplankton growth in the HNLC regions. John Martin suggested that deliberate
addition of iron to the HNLC ocean regions would increase the amount of phytoplankton growing in the
oceans and increase the amount of carbon dioxide removed from the air and subsequently stored in the
deep ocean. He believed that this would dramatically reduce the impact of global warming and make
our climate cooler.
3. How do phytoplankton affect our climate?
Fill in the gaps with the correct words from the list below.
The growth of phytoplankton in the oceans is important to our climate. Using energy from the Sun,
these single celled plants take up carbon dioxide from the air during photosynthesis. During this
process, oxygen and glucose are formed. This glucose then reacts to form organic compounds which
make up the cells.
Some phytoplankton species produce the sulphur containing gas dimethyl sulphide. Once in the air,
this gas can react with iron to form sulphate aerosols.
These aerosols directly reflect sunlight back into space and this causes a cooling of the Earth. They
can also act as cloud condensation nuclei allowing clouds to form. Clouds have an indirect effect on
climate. Some types of cloud reflect sunlight back into space and therefore cause cooling. Others trap
heat from the surface of the Earth enhancing the greenhouse effect and cause warming.
In some regions of the oceans, nutrients such as nitrate and phosphate are available in sufficient
amounts for the growth of phytoplankton. But the lack of iron can prevent phytoplankton growing in
some areas.
If phytoplankton growth is increased in the ocean, more carbon dioxide will be removed from the air.
When these phytoplankton die or are eaten, some sink to the ocean floor taking their carbon with them.
Some people suggest that adding iron to parts of the ocean may help reduce global warming.
Missing words:
lack, greenhouse effect, phytoplankton, cloud condensation nuclei, iron, sulphur, cooling,
photosynthesis, indirect, sulphate, global warming, carbon dioxide, dimethyl sulphide, oxygen,
nitrate and phosphate, carbon dioxide, directly, warming.