Nutrient Cycles in Marine Ecosystems Part I

Section 4

Surface Layer of Ocean

• Dissolved nutrients• Recall: algae require light for

photosynthesis• Intensity of light as depth• Restricted to surface layer (photic zone)

• Depth 30 m to 150 m• Obviously less in turbid water (high turbidity)

What is an ion?

• atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive (+) or negative (-) electrical charge.

SOME Surface Layer Ions

1. Copy this table on the next page of your notebook.2. Create a legible bar graph from the information above

Surface Ions• Those ions, together with nitrate and

phosphate ions form nutrients for growth of algae and other producers

• RECALL: ppm• Nitrate and phosphate ions occur in low

concentrations in seawater• Nitrate = 0.5 ppm• Phosphate = 0.07 ppm

Replenishment of dissolved nutrients (3)

• 1. Upwelling – movement of water from deep in the ocean to the surface layer, where nutrients become available to primary producers

Causes of Upwelling

• Deflection of deep water currents upwards• Nutrients sunk to sea floor brought back up

to surface of ocean• Movement of water away from the coast

by wind

2. Run-off from land• Part of hydrological cycle• Water leach nutrients (including nitrates

and phosphates) from soil

3. Atmospheric Gases• CO2 dissolved in seawater forming

hydrogencarbonate ions (HCO3-)

• AKA bicarbonate• Makes CO2 available for fixation in

photosynthesis for primary producers• N gas is fixed by blue-green algae in intertidal

zones• Forms nitrogen-containing organic compounds• How nitrogen enters marine ecosystems

Intertidal ZoneArea above water during low tide but underwater during high tide

Nitrogen Cycle

Recycled

• Nutrients like nitrates and phosphates are recycled at the ocean surface by excretion from zooplankton

Depletion of dissolved nutrients

• Uptake by primary producers like phytoplankton• Synthesis of organic substances

• Example: nitrate ions used for synthesis of amino acids and proteins• Phytoplankton zooplankton small fish

• Proteins passed to next trophic level and so forth

Recall