Biological Production in the Ocean

What are two macronutrients in the ocean? What are macronutrients?

Phosphorous and nitrogen. They are nutrients that are required in large abundance

Is the macronutrient cycle for phosphorous simple or complex? What about nitrogen?

Simple for P and complex for nitrogen

What is the limiting nutrient? Is phosphorous or nitrogen the limiting nutrient?

It is the one that shuts down productivity. Nitrogen is the limiting nutrient

What form of phosphorous is used by primary producers?

Phosphate (PO₄^-)

Describe the phosphorous cycle

1. Phosphate is produced by weathering of rocks on land

2. Phosphate comes down the rivers and moves out into the ocean where it gets used repeatedly (phytoplankton use it, they die, it gets regenerated, etc)

3. There is a little bit of leakage of phosphate into the sediment and then it gets buried in this sediment

4. Have to go through the whole plate tectonic cycle to uplift and repeat the phosphorous cycle again

What percentage of the atmosphere is made up of nitrogen? Is it the most abundant gas in the atmosphere?

78% and yes it is

Describe the nitrogen cycle

1. Nitrogen in the atmosphere makes it into the ocean by air sea exchange

2. Most primary producers can’t use nitrogen in the N₂ dissolved gas form in the water

3. Diazotrophs are able to convert N₂ into PON (particulate organic nitrogen) (fixation by diazotrophs)

4. A herbivore will then graze on the diazotroph and will excrete ammonium NH₄⁺ as a waste product

5. Also if diazotrophs have excess nitrogen they will excrete ammonium

6. Ammonium is available to primary producers to do their photosynthesis

7. Organisms eventually die and sink into the deep ocean

8. Ammonium is not used in the deep ocean because there is no photosynthesis taking place here

9. Bacteria go to work on that ammonium in a process called nitrification (ammonium is converted into nitrite (NO₂^-) and then to nitrate (NO₃^-))

10. Nitrate gets brought up to the surface and phytoplankton use it as fuel for primary production

11. If nitrate gets into low oxygen parts of the ocean then it gets converted back to N₂ by bacteria and this is called de-nitrification)

Can phytoplankton use ammonium? Do they excrete NH₄⁺?

Yes to both

Where are the low oxygen parts of the ocean?

Deep layer around 1000 meters or in the sediments

What does diazotroph mean?

Two nitrogen feeder (feed on 2 nitrogen (N₂))

What is phosphorous used in? Is it released quickly or slowly during decay?

Used in metabolism such as ATP and is released quickly during decay (usually around base of 1% light level)

What is nitrogen used in? Is it released quickly or slowly during decay?

Used in structural tissue such as proteins. They are more durable and don’t have to be broken down as quickly inside the cell so they are released slowly during decay (nitrogen is taken down to depths so that is why it is limiting)