Evolution of the Southern East Pacific Rise Helium Plume over the Past 3 Decades

Abstract:

The recent GEOTRACES expedition completed in 2013 crossed the EPR at ~15⁰S following the same track as the 1987 Helios Expedition. A detailed suite of samples from the 1987 expedition were analyzed for helium isotopes, and similar detailed helium measurements were completed by the WHOI helium laboratory in 2013 at the same sample locations. This has allowed us to make a detailed comparison with the earlier 1987 work and assess the evolution of the extensive EPR ³He plume over the intervening 26 years. Additional information concerning the time scale for evolution of the plume comes from 1987 RAFOS float tracks, which show that the average westward transport in the core of the plume is about 0.3 cm/s. This translates to about 30 years for the hydrothermal helium from the EPR to reach the distal part of the plume at 150⁰W. While the δ³He profiles out at 150⁰W are essentially unchanged over 26 years, profiles closer to the EPR axis show significant changes. These differences may be due to oceanographic effects, or may reflect temporal changes in the hydrothermal input on the EPR axis.