Why do the densest water masses of the oceans form at high latitudes in the Atlantic Ocean?
The Atlantic extends to higher latitudes in both the Northern and Southern Hemisphere than the Pacific. Thus, high-latitude surface waters are cold. In addition, the Atlantic is a little more saline than the Pacific. Two factors contribute to this. (1) Because of atmospheric circulation (Trade Winds), water vapor evaporating from the Equatorial Atlantic is transported to the Equatorial Pacific across Central America — the Atlantic is “exporting” water to the Pacific. (2) Saline water flows out of the Mediterranean and Caribbean to the Atlantic. There is no similar situation in the Pacific.
