Why the Gulf of Mexico Is Saltier Than Average Ocean Water

The Gulf of Mexico’s average salinity is about 36 parts per thousand (ppt), slightly higher than the global ocean average of 35 ppt. Three main factors drive this elevated saltiness:

High Evaporation

The Gulf lies in a subtropical zone with intense sunlight and warm temperatures, causing rapid evaporation. When water evaporates, dissolved salts remain, concentrating the remaining water.

Limited Freshwater Input

Although the Mississippi River empties into the Gulf, the overall freshwater influx is modest relative to the basin’s volume. The Gulf is semi‑enclosed by land on three sides, restricting exchange with the open Atlantic.

Warm, Salty Currents

The Loop Current carries warm, saline water from the Caribbean Sea into the Gulf, further raising salinity levels.

These combined effects make the Gulf’s water noticeably saltier than many other marine regions.