Nouveaux instruments

New seafloor instruments for WP1 :                                                                                                                       

Hot vent chlorinity + temperature sensor : chloride is one of the very few chemical compounds in deep sea end-member vent fluids for which there is an operational monitoring tool (Larson, Lilley et al. 2007 ; Larson, Lilley et al. 2009). We will build this instrument in collaboration with M. Lilley (University of Washington) and adapt its electronics for connection to the EMSO SeaMon system at the Tour Eiffel site, allowing for near real time data transmission. These transmissions will be a first at a deep sea observatory and a major improvement compared with the discrete sampling of hot fluids performed so far at Lucky Strike. It will allow us to monitor changes in end-member fluids chemistry and temperature on the same time scales as seismicity, and the other time-series data acquired at the observatory. We do not expect difficulties with building and connecting this tool.

Hot vent automated fluid sampler : we also request funds to build a completely new instrument that will collect and store on demand up to 12 distinct samples of hot fluids from a given vent in gas-tight titanium bottles, for later on-shore analyses. We have already obtained ˜2/3 of the funding from CNRS (INSU call for « Equipment » and CNRS call for « Instrumental Challenges at extreme conditions »). This is a challenging technical objective and we propose a phased approach. In a first phase, we will build this prototype with preset sampling times scheduled over a one-year deployment. This preset sampler will already be a significant progress compared to present fluid sampling methods that require the use of a submersible. In parallel, we will evaluate phase 2 solutions to connect this prototype to the EMSO SeaMon system at the Tour Eiffel site, allowing for sampling to be triggered from shore based on, for example, the reception of data indicating significant variations in fluid chlorinity and/or temperature. If successful, this part of the project will be a remarkable progress in monitoring the chemistry of deep sea hot vents.

New or upgraded seafloor instruments for WP2 :                                                                                               

OBH micro-array . This prototype will comprise 4 hydrophones, one on a central frame with the electronics and power supply, and 3 connected by 100 to 200 m-long cables to this frame and distributed around the Tour Eiffel-Montsegur vent sites. The sampling rate for this system will be at least 250 samples/sec, 4 times higher than that for the surrounding OBSs. This should allow us to detect and relocate very small seismic events that may occur due to shallow (<100-200m) hydrothermal circulation and fluid-rock reactions. We plan to connect this OBH micro-array to the EMSO SeaMon infrastructure and will develop an adapted event detection system that will send microseismic alerts to shore (see WP5).

Chain of thermistances. A simple and low cost tool made of ~100 thermistances encased in a flexible tube about 50 m-long and spaced by a few centimeters near the fauna and more widely outside the assemblages. This chain will provide high frequency measurements of the temperature in the gradient zone at the seafloor, linking the measurements performed by autonomous T-probes in diffuse vents and at the studied maicrohabitats. We anticipate the connection to the EMSO SeaMon system to be straightforward (see WP5). A similar tool is currently deployed at a diffuse venting area at the Neptune Canada observatory.

Upgraded Chemini analyser. Chemini (Chemical miniaturised analyser) is a tool built by Ifremer that is currently operated by a submersible and is widely used to measure in situ iron and sulphur concentrations in deep sea hydrothermal ecosystems (Vuillemin et al., 2009). The objective is to improve the reliability of the system by exploring new technologies (e.g. new pumping devices, microfluidics; Beaton et al. 2011, 2012; Fukuba et al. 2011) to decrease the reagent and power consumption for long term moorings, and to enhance the analytical performance. We plan to deploy the new prototype connected to the SEAMON East node and associated to the Tempo observing system (see WP5).

Off-the-shelf additional instruments :

 - Additional temperature probes (built for us at WHOI, USA). These probes will be placed in venting fissures next to the chain of thermistance, allowing us to link the temperature of the diffuse effluents with those in the gradient zone (measured by thermistances).

 - One additional oxygen Aanderaa optode (there is currently a connected optode on the TEMPO station) will be equipped with an NKE data logger for autonomous recording during one year and placed at a selected maicrohabitat, next to the thermistance chain.

Instruments operated by our international collaborators :

 - Autonomous Ocean Bottom Tiltmeter-accelerometer (OBT; Applied Mechanics Inc., 2003; Collaboration with H. Villinger). This instrument was deployed at Lucky Strike in 2010-2011 and recorded two significant variations in seafloor tilt. Work on these data is ongoing, in relation with the seismic data recorded for the same period. The OBT was also used at the Logatchev vent field (Mid-Atlantic Ridge) where it detected a periodic signal interpreted as due to geyser-type overpressure of the hydrothermal system (Fabian et al., 2008). Deployed next to Tour Eiffel, the OBT will allow us to detect similar signals, if any, and will complement the seismic record for lower frequency ground motions.

 - Autonomous video velocimeter (camera to monitor venting velocity ; E. Mittelstaedt, University of Idaho). This instrument was developed by E. Mittelstaedt et al. at WHOI following a seafloor experiment with us at Lucky Strike (Mittelstaedt et al., 2010 ; 2012). It computes the fluid flux at vents from video records of the motion of particles entrained in the fluid. It is currently deployed at the Juan de Fuca ridge.