Surface seawater salinities largely reflect the local balance between evaporation and precipitation.
- Low salinities occur near the equator due to rain from rising atmospheric circulation.
- High salinities are typical of the hot dry gyres flanking the equator (20-30 degrees latitude) where atmospheric circulation cells descend.
- Salinity can also be affected by sea ice formation/melting (e.g. around Antarctica)
- The surface N. Atlantic is saltier than the surface N. Pacific, making surface water denser in the N. Atlantic at the same temperature and leading to down-welling of water in this region this difference is because on average N. Atlantic is warmer (10.0 C) than N. Pacific (6.7 C).
- This is mostly because of the greater local heating effect of the Gulf Stream, as compared to the Kuroshio Current. Warmer water evaporates more rapidly, creating a higher residual salt content
- The influence of surface fluctuations in salinity due to changes in evaporation and precipitation is generally small below 1000 m, where salinities are mostly between about 34.5 and 35.0 at all latitudes.
- Zones where salinity decreases with depth are typically found occur at low latitudes and mid latitudes, between the mixed surface layer and the deep ocean. These zones are known as haloclines.
The spatial distribution of salinity across oceans, is studied in two ways:
- Horizontal Distribution of Salinity
- Vertical Distribution of Salinity