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Observations of the distributions of tritium and helium-3 in the Pacific are revealing many interesting features about ventilation, circulation and intergyre exchange. The penetration of tritium as a dye-like tracer provides information on decade time scales, whereas combining the two tracers to compute a tritium-helium age yields ventilation ages ranging from seasonal to decadal.
A large portion of bomb tritium was deposited in the northern hemisphere, where the bulk of the atmospheric weapons tests occurred. This has resulted in an asymmetry between the two hemispheres, with a sharp front in tritium at the equator. Maps of tritium on isopycnals reflect this asymmetry, but also show the equatorward invasion of this tracer in both hemispheres, separated by a large equatorial tongue of tritium deficient waters extending from the eastern boundary. This is seen even more dramatically in the meridional sections, particularly in the mid-basin, where one also sees the penetration of northern subtropical water into the tropics. The corresponding helium section shows similar features, but more strikingly the upwelling of subtropical waters in the tropics (note the helium isopleths crossing isopycnal surfaces).
In the upper waters, my main areas of interest include
The deep helium-3 distributions are also very exciting. Zonal sections at 10°N and 32°S show the tongues of helium-3 associated with hydrothermal venting at mid-ocean ridge crests. These tongues provide unique clues about abyssal circulation.
This is work in progress. Most of the tritium measurements have been completed, and the helium measurements should be complete this autumn. The reader is invited to visit our web site to learn more about using tritium and helium-3, and specifically our WOCE data page which presents sections and maps of the data.
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