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East Pacific Rise — Current Experiment Coordination — Responses [ISS]

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1. PI-Project Information

Name: Andreas Thurnherr (with Lauren Mullineaux, Jim Ledwell)
Institution: LDEO
Email address: ant@ldeo.columbia.edu
Project Title: LADDER project
NSF-OCE number: ###
Upcoming cruise ID and dates: Atlantis, Oct. 2006, Dec. 2006, Nov. 2007

Please note that this email concerns only the mooring aspect of our program --- you should already have received or you will receive considerations regarding the biological programs carried out on our cruise.

The one thing that we are trying to avoid is that our moorings get snagged by anything towed through the water. We would like to do so without unduly restricting the work of other groups, of course. We are particularly worried about snagging our axial moorings because they are ballasted very lightly --- we had to do this in order to be able to re- position them with Alvin. (That does not mean that they can be moved from their current positions, though!) Therefore, it is likely that you might not even notice if you snag a mooring while towing an instrument.

After considerable additional discussions, in particular with Scott Worrilow, who is the head of our mooring operations and the owner of most of the mooring hardware, we have come up with the following requests, which we hope interferes as little as possible with planned operations, while ensure the safety of our moorings:

  1. Instruments towed at or lowered to 2300m or shallower: No restrictions.
  2. Unnavigated instruments (i.e. no transponders on the lowered bodies) towed or lowered vertically to depths below 2300m (including CTDs!): 500m horizontal standoff distance between the ship and the moorings. (500m is the maximum displacement distance for instruments lowered on the wire that we observed during our cruise while the ship was on DP.)
  3. Acoustically navigated instruments towed or lowered vertically to depths below 2300m: i) Keep the ship and the towed body on the same side of all moorings in the area at all times when the ship is less than 500m horizontally from any of the moorings. (I.e. Do not cross the mooring location with the towing wire, regardless how high in the water you think the towing line is.) ii) Keep at least 75m horizontal standoff distance between the towed platform and all moorings. Please note that while the position of the towed body is known, the position of the towing wire is not. Wire-drag models show that when a body is towed through the water the wire can be deflected significantly from a straight line connecting the ship and the towed body, depending on the currents and the towing- track and -speed.
  4. Alvin: Keep at least 30m standoff distance to the moorings. We are aware of a single low-temperature hydrothermal area that is closer than 50m to our sediment-trap mooring at 9:50 (and none within 50m of our current-meter mooring; biomarker 141 site is approximately 200m south of the closest of our moorings). We would appreciate it if the sub could remain 50m from our moorings unless work is to be done at the site that's 40m from the sediment trap.

We cannot preclude that these restrictions will affect towed operations in the area while the moorings are deployed (until November 2007). I would like to point out, however, that the longer one of our moorings at 9:50N is crucial for the success of our project, that our plan has been publicly available on the web since December 2004, and that it was presented to the EPR ISS community during the workshop held at Lamont earlier this year and that no protests were raised then.

We hope that this provides you with the information that you requested. Please let us know if you need further clarifications.

  • Andreas Thurnherr (LADDER co-PI)
  • Lauren Mullineaux (LADDER co-PI)
  • Jim Ledwell (LADDER co-PI)
  • Scott Worrilow (head, LADDER mooring operations)
Thurnherr experiment photo

Plot showing the LADDER moorings near 9° 50N. Red dots are sites from the R2K database. Orange dots are deployments sites of LADDER biological experiments associated with Mullineaux et al. (and, therefore, hydrothermal sources). NA is our 200m-tall mooring with current meters and a sediment trap. The disc around it shows our requested 50m ALVIN standoff circle. TrapL1 is our 70m tall sediment-trap mooring. The light-blue disc around it shows our requested 30m ALVIN standoff circle.

Please note that we have similar moorings at 9°30N and 9°10N. Complete information regarding those will be found in our cruise report.