1. Ecology and Oceanography in the Gulf of Mexico
The Dead Zone
Ecology and Oceanography in the Gulf of Mexico

2. Part I – The Problem
Sue’s Dad has to travel further out into the gulf to fish.
Why do the fish disappear near the Louisiana shore in the summer?
Sue visits a Biology Professor for help
Dead Zone: dissolved oxygen levels in the water get so depleted the water cannot sustain life.

3. Mississippi River Drainage Basin

4. Detail of the Dead Zone in the Gulf of Mexico
Red shows lowest O2 levels

5. Part II – What affects the Dissolved Oxygen?
Paula predicts a physical cause
Conditions that limit amount of oxygen that can be dissolved from the atmosphere
 Temperature
 Salinity
 pressure
Conditions that facilitate the transfer of oxygen across the air-surface interface
Boats
Waves
Wind
Conditions that are the result of advection (transfer of a property – by mass movement of water)
Ocean currents
Upwelling/downwelling
River outflow

6. Part II – What affects the Dissolved Oxygen?
Zack predicts a biological cause
Photosynthesis by producers
Adds oxygen
Cellular Respiration
Plants &animals
Uses oxygen

7. Fluctuation over the seasons
Physical influences
Temp changes seasonally
Mississippi discharge peaks in the spring
Storms and strong winds are more common in the autumn and winter
Biological influences
Reactions occur faster in warmer temperatures
Day length increases in spring through mid-June
Availability of food or nutrients

8. Part III – How do the Gulf Waters Change with the Seasons?
Temperature of deepwater does change, but not as dramatically as the surface water
Huge volume of freshwater that enters the Gulf via the Mississippi River in April due to snow melt and spring rains
Mississippi discharge is lower in September and the fall winds and storms agitate and mix the water.
Hypoxic layer increases in size extending up to 12 meters

10. Let’s Talk Water – Required for Life
Unique Structure
Gives rise to some unique properties
For this study: a universal solvent
Ex. Salt (NaCl)
Density Relationships of H2O
Temp vs. Density –
Inverse relationship*
*as long as temp stays above 4C

11. What About Dissolved Oxygen?
As terrestrial organisms we need O2 from air
Aquatic organisms need O2 also! How?
Dissolved Oxygen
Microscopic bubbles of O2 gas
Amount of D.O. varies
Depends on physical and chemical make up of water

12. Marine Food Web