Hydrothermal Exploration of the Society Islands Hot-Spot

Chris German, Geology & Geophysics
Jeff Seewald, Marine Chemistry & Geochemistry
Sean Sylva , Marine Chemistry & Geochemistry

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2015 OEI Funded Project

Abstract

This project seeks to explore for and locate new sites of seafloor hydrothermal activity associated with the Society Islands hot-spot near Tahiti in the South Central Pacific Ocean.  The project is highly leveraged because two weeks of shiptime to conduct the work has already been offered aboard the RV Falkor in Spring 2016, provided by the Schmidt Ocean Institute who would also fund all costs for the WHOI AUV Sentry team to participate in the cruise, in support of our research, as part of SOI’s “facility-provider” funding model.  What is unique about the Society Islands as a target for hydrothermal exploration is that our recent US GEOTRACES work spanning the SE Pacific Ocean has revealed that both dissolved and particulate biogeochemical tracers extend all the way from the southern East Pacific Rise, for more than 4000km, to the vicinity of the Society Islands hot-spot.  While that result is already extraordinary and exciting for trace element geochemistry, what we can now ask is: Does the physical dispersion of the Southern EPR plume, replete with biogeochemical nutrients, also have the potential to transport larvae from the southern East Pacific Rise to the Society Island hot-spot and, if so, could they colonize any vents that are found there?
 
To answer that question, we first need to locate and characterize any active vent-sites within the Society Islands hot-spot area and we have already made a crucially important breakthrough.  In 2013, a lone CTD cast occupied above the sea-mount closest to port at the end of a 60 day US GEOTRACES cruise revealed compelling evidence (from both in situ sensors and Fe concentrations) for an active black smoker system – at a site where only diffuse flow had previously been reported when the same seamount was last visited in 1987, following an episode of seafloor volcanic eruptions.  We now know that an active high-temperature site exists.  Further, because it sits atop an active seamount, its location is already sufficiently constrained that we can immediately implement a well-established protocol with the Sentry AUV – an approach that will allow us to map and locate the source of venting, precisely, and then obtain first photographs of the vent-site together with any chemosynthetic ecosystem that it may host.  Over the course of a 2 week cruise we will also prospect for signs of hydrothermal venting in the water column at 5-9 additional hot-spot seamounts, leaving sufficient time to track at least one and ideally two more water-column hydrothermal plumes to their seafloor vent-source(s).  Ultimately, we seek to both locate new sites of venting and obtain sufficient supporting information to enable both ourselves and others to write compelling NSF research proposals to return to this area to conduct more detailed multi-disciplinary research programs in future using HOV Alvin and/or ROV Jason.