Topic 15 - Nutrients and Dissolved Gases in the World's Oceans


What Are Nutrients?
Inorganic compounds that are used by bacteria and plants to build organic material
Nutrients include:
phosphates (PO4)
nitrates (NO3)
Ammonia (NH4)
Silica (SiO2)

How Are Nutrients Used?
Photosynthesis or Chemosynthesis 6CO2+6H2O+energy=C6H12O6+O2
Respiration C6H12O6+O2=6CO2+6H2O+energy

Nutrient Cycles
Unlike conservative dissolved salts in sea water, nutrient are rapidly used and recycled in the marine (and global) environment
Least common nutrients limit biological productivity in the world's oceans

Nitrogen Cycle
Nitrogen occurs in a number of nutrient compounds: N2, NO3, NH3
Nitrates and nitrogen gas enter the oceans from the atmosphere and rivers
Bacteria and plants absorb these and form carbohydrates and ammonia
Other bacteria and animals breakdown carbohydrates and recycle nutrients

Vertical Distribution of Nutrients in the Oceans
Nutrient content is low in the surface ocean
Nutrient content increases below photic zone due to scavenging and decomposition by animals
nutrient content of deep ocean waters is high due to decomposition and limited biological productivity

At mid to high latitudes, there is a marked seasonality to surface nutrient supply
During winter, low sunlight levels limit biological productivity - nutrient level increases
During spring, high sunlight and nutrient levels lead to high productivity
Limited in time while nutrients last

Gases in the Oceans
Gases occur in surface ocean in same proportion that they occur in air
Gases are used in biological processes just like nutrients - and are also recycled
More gasses can be absorbed in water as temperatures decrease
Oxygen minimum zone occurs in all oceans due to organic decomposition below photic zone


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