Properties of Seawater

Nutrients Are essential for plant growth. Main nutrients in seawater are: nitrogen phosphorus silicon Nutrient concentrations are much higher in coastal areas and lower as you move toward the open ocean.

Gases The main gases in seawater are: nitrogen (N2), oxygen (O2) carbon dioxide (CO2), hydrogen (H2) O2 is required by animals for respiration. Main sources are diffusion from the air and plant photosynthesis CO2 is required by plants for photosynthesis. Main sources are animal respiration.

Implications for global warming???? Gases, cont’d Oxygen content of water changes with temperature. Warm water cannot hold as much oxygen as cold water. Implications for global warming????

Temperature The top several hundred meters of the water column is warmer and floats on the colder, denser water of the ocean depths. The area of rapidly changing temperature is called the thermocline. Surface waters are exposed to the seasons and thus fluctuate in temperature. Deep waters remain a stable <4ºC all year.

Why is this important for stabilizing climates worldwide? Temperature, cont’d Water has the highest specific heat capacity (the amount of heat it takes to raise 1 gram of water by 1ºC) of any substance. This means that water does not easily change its temperature. Why is this important for stabilizing climates worldwide?

Freezing Point Freshwater freezes at 0ºC. The salt in seawater lowers its freezing point to –1.91ºC. Solid water (ice) floats on top of liquid water – unlike most other substances. If ice sunk to the bottom, most sea creatures would be killed.

Salinity – salt content The average salinity of seawater is 3.5% (percent = parts per hundred) or 35 ppt (parts per thousand). Salinity varies with depth and pressure. More salt in water = greater density Icy Finger of Death http://www.youtube.com/watch?v=r4cX2EPt2zE

Density Density increases with salinity. Freshwater will float on top of saltwater. The area of rapidly increasing salinity is called the halocline. Density also increases with temperature. Warm water will float on top of cold water.

Sound Speed in air = 334 m/s Speed in water = 1500 m/s Marine life uses sound: to find and capture food (sperm whales, pistol shrimp, dolphins) to communicate with each other, even over long distances to make courtship sounds (humpback whales)

Handout and Questions Read the handout and answer the questions on the next slide based on the handout and the info you copied down today.