Hydrothermal Activity at Vailulu'u Seamount, Samoa
Abstract
Hydrothermal activity was discovered at Vailulu'u seamount (Samoan Archipelago; 14.21oS 179.06oW) in 03/2000 using the USCG Icebreaker Polar Star and re-surveyed in 03/2001 using the USCG Icebreaker Polar Sea.. Our surveys included CTD hydrocasts, nephelometry, water sampling, Mn and 3He/4He ratios in water samples, a dye tracer release experiment and one - year temperature monitoring in the crater and on the crater rim. Vailulu'u shows strong nephelometry anomalies within the crater (peaks at 1.2-1.4 NTU) and a halo around the volcano (<0.9 NTU) at a depth range bracketed between the highest summit and the lowest breach in the crater rim. This anomaly was traced >7km away from the summit with anomalies up to 0.07 NTU. The distribution of particulates inside the crater and in the halo around the volcano are highly time variant from day to day, but the same sized anomalies were found in 2000 and 2001. Nephelometer readings display excellent correlations with Mn content (0.1 ppb - 4 ppb) and He 3/4 ratios that range from 1 to 8.6 (R/RA), whereby the upper 3He/4He value is within the range of magmatic He from fresh Vailulu'u glasses. Potential Temperature and Potential Density inside the crater show distinct variability, but it is relatively constant when compared to the steep thermal gradients in the upper ocean (approximately 1oC/100m depth at 600m). To a first order, water temperature inside the crater is determined by the ocean temperature at the depth of the lowest breach of the crater wall. A one-year temperature log shows a complex temperature time series that is distinct for summit and crater floor records. Summit recorders show very noisy records whereby power spectra show peaks at periods of 24, 12 and 6 hours, consistently and highly correlated between the three summit sites. These variations are probably due to tidal modulation of currents around the seamount, whereby the 0.4oC temperature amplitude suggests vertical water motion of 40 meters. Temperature records on the crater floor display a nearly isothermal record for extended periods of time, separated by "spiky" periods due to hydrothermal venting (up to 0.2oC). While crater floor and rim appear to be de-coupled on a time scale of hours to days, there is a strong, eddy-driven seasonal variation on time scales of about two months.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMOS41A0435S
- Keywords:
-
- 1045 Low-temperature geochemistry;
- 1050 Marine geochemistry (4835;
- 4850);
- 4832 Hydrothermal systems