Dissolved noble gases in the east equatorial and southeast Pacific

Abstract

The presence of excess 4He in deep and bottom waters of the southeast Pacific Ocean, first indicated by results from the Carrousel expedition, has been confirmed in samples from the Piquero expedition of the Scripps Institution of Oceanography. The mean concentration of He in this part of the Pacific and in waters below 2000 meters depth is (4.54 ± 0.01) × 10−5 ml (STP)/liter. Helium gradients are observed close to the bottom and below the Antarctic Intermediate Water (AAIW). Their interpretation allows an estimate of the influx of He through the sediment-water boundary between 1 and 2 × 106 atoms/cm2 sec. All noble gases are highly supersaturated near the core water of the Equatorial Undercurrent, and the influence of this water is again evident in the Equatorial 13-C water. The generation of such supersaturated water is suggested to derive from areas of high evaporation although the details are not yet clear. While the mean concentrations of all gases in deep water are in good agreement with the results of the Carrousel expedition, mean surface supersaturations are from 1% to 2% lower, probably due to seasonal effects. Evidence for mixing within the thermocline is absent in the Piquero samples.