The bottom potential temperature distribution for the Pacific Ocean north of 11° S. is presented, based upon 495 data points derived from hydrographic stations, the Lamont thermograd, and an in-situ salinity-temperature-depth recorder. Although the entire range of potential temperature is only 1.2° C, an oceanwide pattern is apparent. The coldest bottom water (< 0.8° C potential temperature) occurs in the equatorial region between 160° and 180° W. This feature can be traced into the area north of Hawaii by paths both east and west of these islands with a warming of only 0.5° C.
In order to separate the effect of the decrease of potential temperature with depth (which occurs in the upper 4000 to 5000 m) from the bottom variation due to influx of cold water, the anomaly of bottom potential temperature is plotted. This parameter is defined as the difference between the observed bottom potential temperature for a particular station and the average bottom potential temperature for the North Pacific at the depth of the observation. The water between 160° and 180° W. has the largest negative anomaly, 0.3° C colder than the average t p found at corresponding depths. The water north of Hawaii has a positive anomaly, indicating that in this region the deeper water is relatively warm compared to that in the equatorial region between 160° and 180° W., even after the depth effect is removed. The bottom water over and east of the crest of the mid-ocean ridge at 120° W. has large positive anomalies, suggesting the possibility that this water is warmed by geothermal heating.
From the bottom potential temperature distribution and the anomalies of these values, together with recently obtained Lamont bottom current measurements, it is possible to trace the basic pattern of bottom circulation (which should also reflect the circulation for the water below 2000 to 2500 m). The sole influx of water is the Antarctic Bottom Water flowing northward along 175° W. from 20° S. to 16° N. This current is no doubt a continuation of the deep western boundary current along the Tonga Trench described recently for the South Pacific. From this point, the flow divides into two zonal branches. The eastern branch passes between the Johnston Island and Christmas Island Ridges and the western branch passes between the Marshall Islands and the Marcus-Necker Ridge. After trans-versing these respective passages, both flows turn northward, eventually converging in the North Pacific Basin between the Hawaiian and the Aleutian Islands, where deep upward transport is expected. It is estimated that the time necessary for the water to flow from 175° W., 10° S. to the center of the convergence area is 750 years.