D. Fornari, F. Meana-Prado, J. Bryce, T. Shank, M. Lilley, K. Von Damm* (* - deceased 15 August 2008)

Fluid temperatures at high-T and low-T hydrothermal vents at the EPR have been monitored nearly continuously since 1993, following the volcanic eruptions in 1991-1992 using several types of self-recording loggers (e.g, HOBOs for high-temperature vents and Vemcos for low-temperature diffuse flow areas. Data from the EPR high-T loggers (HOBO™) and Alvin temperature probe measurements provide the most complete temporal histories of vent fluid temperatures for any global MOR hydrothermal site. HOBO™ data recorded prior to and during the 2005-06 EPR eruptions are being correlated and reconciled with geophysical, fluid chemistry and biological data that span the eruption period from prior to mid-2005 to early 2006 (Von Damm et al. in preparation). These data will be available at the 2010 meeting and have been submitted to the Ridge 2000 database at MGDS and may be accessed there by contacting the PIs and MGDS.  Upon submission of the paper in the coming few months, access to these data will be unrestricted.

It would be useful to compile and correlate other fluid temperature time series data collected at other ocean spreading center hydrothermal vents, both within ISSs and elsewhere, to investigate both general trends in vent temperature history with biological community evolution, and vent fluid chemistry where available.  Additional correlations to microseismicity data for discrete periods would also be important to include.  This type of synthesis can shed light on first-order correlations between controlling phenomena at MOR axial vents.

Figure 1. Reprinted from Figure 9 in Scheirer et al., [2006; Q03002, doi:10.1029/2005GC001094], showing both punctuated measurements of high-T vent fluid temperatures since the 1991 EPR eruption [from Von Damm, 1995 & 2000] and continuous (every 15-30 minutes) fluid temperature measurements made using HOBO loggers through 2002.

Figure 2. (A) Photographs taken from Alvin during At15-6 (RESET06) cruise in June 2006 when the HOBO logger was recovered from M vent. The presence of the logger was identified in TowCam photographs taken on the R/V New Horizon (NH06) ‘event-response’ cruise in May 2006 (logger housing is visible at bottom-middle of photo in B). Visual observations of the logger prior to recovery and photo-documentation carried out when the logger was deployed in 2004 using Alvin shows that the new lava covered the bottom ~1 m of the M-vent chimney, while the crust of the new flow was <0.25 m from the logger housing (top left photo above). M-vent was no longer active in late June 2006 and has remained inactive up through late 2007.

Figure 3. Data from 3 HOBO high-T loggers recovered by Alvin on the AT15-6 cruise (June 2006) post-eruption (K. Von Damm, unpublished data). M-vent data are the most compelling in terms of their potential to help correlate microseismicity data, Po age-dating of lava [Rubin et al.,  2006, 2008] and fluid chemistry variations pre- and post-eruption in order to help constrain eruption timing, episodicity and processes associated with the most recent, documented EPR eruption.  Blue lines show recordings from two separate platinum RTD (resistance temperature device) sensors and logging chips in the HOBO housing deployed at M-vent. Very stable temperatures in the vent are apparent from April 2004 to August 2005 (note times when record was perturbed by Alvin manipulation at the vent are shown by red arrows). Post August 2005, the fluid temperature at M-vent fluctuated with several sharp reductions followed by rapid recovery to the ~360°C level, which preceded the suspected onset of the 2005-06 eruptions [e.g. Rubin et al. 2006, 2008]. On January 11, both logging chips recorded a dramatic fall in temperature that occurs nearly instantaneously, falling below the 152°C minimum recording temperature of the RTDs used in these loggers. Clearly, the high-T fluid flow at M-vent was disrupted on Jan 11, 2006,  but surprisingly after about 2 weeks, the temperature climbed suddenly to levels above 360°C and increased over a ~2 week period by nearly 20°C to ~380°C after which the battery power in the logger fell below operating current and the recordings stopped. The Jan. 22 seismic crisis reported by Tolstoy et al., [2006] is shown and post-dates the steep drop in M-vent temperature by ~11 days. Drift in the HOBO logger’s clocks are of the order of a few minutes per month so the magnitude of the temporal difference between these events is not due to the instrumentation.  Correlation and modeling of the M-vent temperature record with the microseismicity data and fluid chemistry will help establish linkages between processes controlling high-T venting at the EPR and clarify possible timing of eruptive phases in the 2005-2006 time period. Data for Q vent and Ty vent are also shown.