Continuous sampling of hydrothermal fluids from Loihi Seamount after the 1996 event

Abstract

For at least 9 years prior to July 1996, hydrothermal fluids flowed from Pele's Vents on Loihi Seamount, Hawaii. In July-August 1996 a tectonic-volcanic event occurred that destroyed Pele's Vents, creating a pit crater (Pele's Pit) and several sites with hydrothermal venting. In October 1996 we deployed two new continuous water samplers (OsmoSamplers) at two of these hydrothermal sites and collected fluids using traditional sampling techniques to monitor the evolution of crustal and hydrothermal conditions after the event. The samplers were recovered in September 1997, and additional discrete vent fluid samples were collected. The OsmoSampler located along the south rift at Naha Vents captured a change in composition from a low-chlorinity, high-K fluid (relative to bottom seawater) to a high-chlorinity, low-K fluid. These changes are consistent with the fluid cooling during ascent and being derived from several different sources, which include high-(>330°C) and low- (<150°C) temperature components and a source of magmatic volatiles. The other OsmoSampler, which was deployed on the rim of Pele's Pit at Lohiau Vents, captured warm hydrothermal discharge that originated from a high-temperature source (> 330°C) into which magmatic volatiles were added. During the deployment, thermal and fluid fluxes decreased. At Naha the transport of heat and chemicals was decoupled. The chemical and thermal evolution of hydrothermal fluids after the event on Loihi is consistent with previous models based on events that have occurred along mid-ocean ridges. The event at Loihi clearly had an effect on the local hydrography; however, the integrated effect of chemical fluxes to global budgets from similar events is uncertain. Chemical fluxes from similar events may have a global impact, if ratios of chemical (e.g., CO2, Fe/Mn, Mg, sulfate, and K) to thermal anomalies greatly exceed, or are in the opposite direction to, fluxes from mid-ocean ridge hydrothermal systems. Copyright 2000 by the American Geophysical Union.