Sea surface salinity refers to the amount of dissolved salts present in the water at the ocean's surface. It's a key characteristic of seawater that influences density, currents, and marine life. Generally, sea surface salinity is measured in practical salinity units (psu), which are roughly equivalent to parts per thousand (ppt).
Understanding Salinity Ranges
Open Ocean Salinity
- The salinity of the open ocean typically varies from 32 psu to 37 psu.
- This range is due to the balance between processes that add fresh water (like precipitation and river runoff) and those that remove fresh water (like evaporation and ice formation).
Factors Affecting Salinity
| Factor | Effect on Salinity |
|---|---|
| Evaporation | Increases salinity |
| Precipitation | Decreases salinity |
| River Runoff | Decreases salinity |
| Ice Formation | Increases salinity |
| Ice Melting | Decreases salinity |
Variations in Sea Surface Salinity
- High Salinity: Regions with high evaporation rates, like the subtropics, tend to have higher salinity.
- Low Salinity: Areas with significant freshwater input from rivers or precipitation, or with melting ice, usually have lower salinity.
- Regional Differences: Coastal areas often exhibit greater salinity variation compared to the open ocean due to local freshwater sources.
Why Sea Surface Salinity Matters
- Ocean Circulation: Salinity affects the density of seawater, which plays a crucial role in driving ocean currents.
- Marine Life: Salinity is vital for marine organisms, as they have adapted to specific salinity levels.
- Climate: Salinity variations influence the Earth’s climate by affecting heat distribution in the oceans.
Practical Example:
- Consider the Mediterranean Sea, which has a high evaporation rate and relatively low freshwater input; thus, it exhibits high surface salinity values.
- Conversely, the Arctic Ocean receives significant freshwater from melting ice and river runoff, resulting in lower surface salinity.
