On the temperature, salinity, and density differences between the Atlantic and Pacific oceans in the upper kilometre

Abstract

The surface of the Pacific Ocean stands about 40 cm higher than the Atlantic Ocean with respect to the 1000-decibar surface, and the North Atlantic and North Pacific stand respectively about 14 and 17 cm higher than the South Atlantic and Pacific. The North Atlantic is warmest and saltiest, the South Atlantic is coldest and densest, and the North Pacific is least dense and least salty.

The extreme values in temperature and salinity of the North Atlantic are probably related to the formation of the deep water there, which carries away from the upper layer the cold water of relatively low salinity. If this water spreads into the South Atlantic at depth and is replaced with warm saline surface water from the South Atlantic via the South Equatorial Current and the Gulf Stream, then the South Atlantic should be substantially cooler and less salty.

The difference in density and sea level of the Atlantic and Pacific oceans may stem from the difference in latitude of the southern tips of America, Africa, and Australia, and the constriction of the west wind drift at Drake Strait. Only the densest surface waters of the Pacific pass through to the Atlantic, while lighter waters from lower latitudes of the South Atlantic pass eastward south of Africa. Further, the constriction of the flow by Drake Strait may result in a higher sea level on the Pacific side through the effect of Windstau (Montgomery, 1938).

The density difference between the southern and northern oceans may be partly a consequence of the west wind drift around Antarctica. This is the greatest current of all oceans. Its flow is approximately geostrophically balanced and the surface slopes down to the south. The northern west wind drifts are not so strong, are at lower latitudes, and the high latitude flow is westward with slope upward to the north.

These differences are not confined to the upper thousand metres. The average density difference between the Atlantic and the Pacific from the surface to the bottom is about 17 × 10⁻⁵ g/cm³. Referred to some deep surface such as 4000 decibars, the Pacific stands about 68 cm higher than the Atlantic.