Ecology and Oceanography in the Gulf of Mexico

Part I – The ProblemSue’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 helpDead Zone: dissolved oxygen levels in

the water get so depleted the water cannot sustain life.

Mississippi River Drainage Basin

Detail of the Dead Zone in the Gulf of MexicoRed shows lowest O2 levels

Part II – What affects the Dissolved Oxygen?Paula predicts a physical cause

1. Conditions that limit amount of oxygen that can be dissolved from the atmosphere

a. Temperatureb. Salinityc. pressure

2. Conditions that facilitate the transfer of oxygen across the air-surface interface

a. Boatsb. Wavesc. Wind

3. Conditions that are the result of advection (transfer of a property – by mass movement of water)

a. Ocean currentsb. Upwelling/downwellingc. River outflow

Part II – What affects the Dissolved Oxygen?Zack predicts a biological cause

1. Photosynthesis by producersa. Adds oxygen

2. Cellular Respirationa. Plants &animalsb. Uses oxygen

Fluctuation over the seasonsPhysical influences

Temp changes seasonallyMississippi discharge peaks in the springStorms and strong winds are more common in

the autumn and winterBiological influences

Reactions occur faster in warmer temperaturesDay length increases in spring through mid-

JuneAvailability of food or nutrients

Part III – How do the Gulf Waters Change with the Seasons?

1. Temperature of deepwater does change, but not as dramatically as the surface water

2. Huge volume of freshwater that enters the Gulf via the Mississippi River in April due to snow melt and spring rains

3. Mississippi discharge is lower in September and the fall winds and storms agitate and mix the water.

4. Hypoxic layer increases in size extending up to 12 meters

Let’s Talk Water – Required for LifeUnique Structure

Gives rise to some unique propertiesFor this study: a universal solvent

Ex. Salt (NaCl)

Density Relationships of H2OTemp vs. Density – Inverse relationship*

*as long as temp stays above 4C

What About Dissolved Oxygen?As terrestrial organisms we need O2 from airAquatic organisms need O2 also! How?

Dissolved OxygenMicroscopic bubbles of O2 gasAmount of D.O. varies

Depends on physical and chemical make up of water

Marine Food Web