The amount of salt in grams present in 1000 grams of water.
Explanation
Salinity is a fundamental property of seawater, representing the concentration of dissolved salts. It is a critical factor in determining the density of seawater and driving thermohaline circulation.
Analysis of the Definition
- Standard Definition: Salinity is scientifically defined as the total amount of solid material (salts) in grams contained in 1,000 grams (1 kilogram) of seawater.
- Expression: It is usually expressed as "parts per thousand" (ppt) rather than as a percentage (which is parts per hundred). The symbol used for this measurement is ‰.
- Average Value: The average salinity of the oceans is approximately 35‰, meaning there are 35 grams of salt in every 1,000 grams of seawater.
- Evaluation of Options:
- The amount of salt in grams present in 100 grams of water.: Incorrect because it refers to 100 grams of water, which would calculate percentage, not the standard parts per thousand.
- The amount of salt in grams present in 1000 grams of water.: Correct. It accurately states the mass ratio used in oceanography: grams of salt per 1,000 grams of water.
- The amount of salt in kilograms present in 1000 litres of water.: Incorrect because it uses kilograms of salt (too large a unit for the ratio) and litres of water (volume) rather than mass.
- The percentage of salt in the total volume of water.: Incorrect because percentage implies a ratio out of 100, whereas salinity is a ratio out of 1,000.
Key Takeaway: Salinity is defined as the weight of dissolved salts in grams per 1,000 grams of seawater and is expressed in parts per thousand (‰).