The average salinity of the world's oceans is approximately:
A15%
B25%
C35%
D45%
Answer:
C. 35%
Read Explanation:
- Salinity Definition: Salinity refers to the total amount of solid material dissolved in seawater. It is typically expressed in parts per thousand (ppt or ‰).
- Average Value: The average salinity of the world's oceans is consistently accepted as 35 parts per thousand (35‰), meaning there are 35 grams of dissolved salts in 1,000 grams of seawater.
- Primary Composition: Sodium Chloride (NaCl), or common table salt, is the most abundant salt in seawater, accounting for about 77.8% of the total dissolved salts. Other major ions include magnesium, sulfate, calcium, and potassium.
- Factors Influencing Salinity:
- Evaporation: Higher rates of evaporation increase salinity (e.g., in the Red Sea).
- Precipitation/Freshwater Input: High rainfall, river discharge, or melting glaciers decrease salinity (e.g., near the mouths of large rivers like the Amazon).
- Temperature: Higher temperatures usually correlate with increased evaporation, raising surface salinity levels.
- Regional Variation: While the global average is 35‰, salinity varies by latitude:
- Equator: Salinity is lower due to heavy rainfall and cloud cover reducing evaporation.
- Subtropics (20°-30° latitudes): Salinity is generally highest due to high evaporation rates and low precipitation.
- Polar Regions: Salinity is lowest due to the freezing of water (which excludes salt) and the melting of sea ice (which dilutes water).
- Measuring Unit: Historically measured in ppt, modern oceanography also utilizes the Practical Salinity Scale (PSS), which is based on the electrical conductivity of seawater and is dimensionless.