A FAR-FIELD HYDROTHERMAL PLUME FROM LOIHI SEAMOUNT

An extensive helium plume in the north central Pacific emanates from L oihi Seamount on the flanks of Hawaii. The maximum helium signal is fo und at a depth of about 1100 meters, the same depth as the near-field plume directly above Loihi Seamount. Although this helium plume is str ongest near Hawaii, where the He-3/He-4 ratio at a depth of about 1100 meters reaches values 28 percent above the atmospheric ratio, it can be detected quite clearly at latitude 24 degrees N, over 400 kilometer s to the north. Excess He-3 is also present on the same isopycnal betw een 15 degrees N and 20 degrees N at 135 degrees W, some 2000 kilomete rs east of the Hawaiian Islands.