EXPLORING VAILULU'U SEAMOUNT: BIO-, HYDRO-, AND LITHOSPHERE INTERACTIONS

Hubert Staudigel and Brad Tebo (SIO)

Link to NOAA Strategic Plan: NOAA's Mission Goal 1: Protect, Restore, and Manage the Use of Coastal and Ocean Resources through Ecosystem-based Management

RESEARCH OBJECTIVES AND SPECIFIC PLANS TO ACHIEVE THEM

Task 1 Document the volcanological setting and survey for hydrothermal vents.

Task 2 Characterize the water-column properties through CTD and Niskin Bottle sampling from Pisces and hydrocasts.

Task 3 Deploy current meters, temperature probes and recording LBSS, either by shipboard deployment and retrieval or by targeted deployment by submersible (e.g. a Falmouth Scientific Instruments Acoustic Doppler current meter) in the crater breaches and summit.

Task 4 Exposure experiments: deploy a set of synthetic oxidized and reduced basaltic glasses in various forms, as polished sections, for studying surface colonization and hydration rind thickness.

Task 5 Sample glassy margins, biofilms, volcaniclastics and microbial mats in different hydrothermal regimes and eruption exposure ages.

Task 6 Sample organisms for morphological and reproductive studies.

Task 7 Determine the effects of pulsed-water events on microbial and benthic communities.

In 2005, two cruises aboard the Kaimikai O’ Kanaloa were carried out during a four-day cruise in March/April and a nine-day cruise in June/July including a total of 12 scientists:  H. Staudigel (chief scientist); Brad Bailey, Sandra Brooke, Stan Hart, Lisa Haucke, Ian Hudson, Ray Lee, Adele Pile, Brad Tebo, Alexis Templeton and on the second cruise Richard Smith from the Australian Broadcasting Company was also included.  These dives were devoted to the exploration of the hydrothermal and biological systems of Vailulu’u and the deployment and retrieval of exposure experiments, current meters and temperature and light backscattering recorders.

RESEARCH ACCOMPLISHMENTS

We explored the crater and flanks of Vailulu’u seamount by submersible and discovered a new 300m tall, volcanic cone in the crater of this seamount that marks the location of the Samoan hot spot. This cone, named Nafanua, grew from the 1000m deep crater floor to a summit depth of 700m in less than four years and could reach the sea surface within decades. Hydrothermal vents fill Vailulu’u crater and the location of Nafanua coincide with a linear array of seismic epicenters that were observed in April-June 2000, possibly the precursor activity to the formation of Nafanua some time in the subsequent four years.  Hydrothermal vents fill the crater with a thick suspension of particulates and apparently toxic fluids that mix with seawater entering from the crater breaches. Low-temperature vents form Fe oxide chimneys in many locations and up to one-meter thick layers of hydrothermal Fe floc on Nafanua. High temperature (81°C) hydrothermal vents in the northern moat (945m water depth) produce acidic fluids (pH=2.7) with rising droplets most likely consisting of liquid CO2. The Nafanua summit vent area is inhabited by a thriving population of eels (Dysommina rugosa) that feed on midwater shrimp that, we suspect, are concentrated by anticyclonic currents at the volcano summit and rim. The moat and crater floor around the new volcano are littered with dead metazoans that apparently died from exposure to hydrothermal emissions.  Acid-tolerant polychaetes (Polynoidae) live in this environment, apparently feeding on bacteria from decaying fish carcasses. Vailulu’u is an unpredictable and very active underwater volcano presenting a potential long-term volcanic hazard. Although eels thrive in hydrothermal vents at the summit of Nafanua, venting elsewhere in the crater causes mass mortality. Paradoxically, the same anticyclonic currents that deliver food to the eels may also concentrate a wide variety of nektonic animals in a death trap of toxic hydrothermal fluids.