Discuss the formation of the Gulf of Mexico dead zone. Why does ...

[Mollykgkg]

Discuss the formation of the Gulf of Mexico dead zone. Why does this area form in the warmer months of the year?
 
  What will be an ideal response?

Question 2

Why do algal blooms frequently occur during spring and fall in temperate oceans?
 
  What will be an ideal response?

[pocatato]

Answer to Question 1

Dead zones are areas of the oceans and rivers (or lakes) where there is little or no available oxygen to support life. Spring rains carry agricultural and urban run-off adding extra nutrients to the warmer waters (eutrophication) stimulating algal blooms. When the algae die and fall to the sea floor, there is so much of it that oxygen is used up by the bacteria trying to decompose it. This further depletes low oxygen levels creating hypoxic (dissolved oxygen < 2.0 ppm) and anoxic (no oxygen) areas.

Answer to Question 2

Algal growth is limited by nutrient availability (usually nitrogen and phosphorus), light availability, and dissolved carbon dioxide concentrations. Since available light levels in the spring and fall are less than in the summer, it is not the changing light levels that are responsible for spring and fall blooms. During the spring and fall, storms frequently mix the water column in shallow coastal seas bringing nutrients to the surface that stimulate algal growth.