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14 November 2012

posted Nov 15, 2012, 5:58 AM by Amy Waterhouse   [ updated Nov 15, 2012, 9:21 AM ]
Early hours of the 14th were spent doing a cross ridge transect across a steep slope of the Mendocino Ridge. During the survey, Ruth, Hanne, Julie, Felipe, Jonathan and Kris launched 13 XBTs over the side of the boat to get profiles of temperature and pressure over the hydraulic features that were being seen from the velocity of the ship board sonar. Someone in the lab might have shouted "Holy Overturns!" meaning that the ridge was causing the flow to be accelerated, plunging it down the lee side of the ridge, dissipating lots of energy through convective overturns and shear instabilities. Yay, this is what we came to find!

Felipe (L), Julie (M) and Hanne (R) all practice their aim (and looking tough) launching the XBTs.

With the ridge top survey finished at noon, we did a drift test just downstream of where we wanted to drop our last mooring. We were all set to travel up-current (against a 1.5 kt current) and started our final mooring deployment. Two current meters, over 20 temperature sensors
and 2 CT sensors were attached to the 485 m mooring. Vanessa dropped the anchor (birthday present!) and after triangulating the position, we had our 3rd mooring deployed. Here is where we put them

(L) Jonathan and Paul attaching a microcat to the wire (R) Bridge deck view of our mooring launch

(L) Our cheery work crew: Bob, Hanne and Liz.                      (R) Paul and Liz triangulating the moorings

At dinner, we celebrated Vanessa's 21st birthday with an amazing chocolate-peanut butter-jam layer cake prepared by the ever talented ship cooks. Here is Vanessa helping out with the mooring deployment on the air tugger.

After dinner and eating a lot of cake, we started with our next set of measurements: LADCP-CTD-Chipod profiles! What does this mean? We put 2 current meters on the CTD cage and a chi-pod to measure temperature at extremely small scales and started profiling up and down in 800 m of water, just south of the ridge. Initial velocity records from the ship board sonar shows a strong shear layer with a strong jet (1 m/s) coming off of the ridge at the surface which then grows with depth.

The lower plot here (generated by Ruth and Hanne) shows velocities from the ship board sonar. The shear layer (red vs green in the bottom plot) changes in time. More exciting data to come soon!

The LADCP-CTD-Chipod profiles will continue through the night and into tomorrow evening. We expect that there will be some interesting changes with the tide! With our night time stationary profiling, we had about 60 gulls joining us around the boat tonight catching fish, and Hanne spotted some possible siphonophorae in the water.