Friday, May 30, 2014

Research cruise in the Gulf: First sampling site

We arrived at our first sampling site at about noon local time—NT800. This is a position on the upper break of the Florida Escarpment previously sampled in September 2013. We deployed the multicorer and recovered seven out of eight cores. We suspect that the eighth core was released in the water going down. Processing each drop of the multicore requires almost two hours. Deck to deck time for the multicore lowering and recovery is about 30 min. We need a minimum of three lowerings to provide samples for all the investigators involved. Took a CTD profile while the cores were being processes. Then completed a second lowering with similar success. 

The third lowering failed, however. The tubes came up with their caps closed top and bottom, but with no mud. We use a video timelapse camera system to record the bottom at each station where we collect sediments. It gets turned on before the core goes over the side and runs while the core is lowered and lands on bottom to collect its samples. This proved very valuable after this failure because we could clearly see that the cores had closed in the water while the corer was being lowered to the bottom. What happens is if there is too much weight on the center part of the core, it has more mass and momentum than the frame. So when slack comes in the cable, the center continues down faster than the frame. If there was too much separation, the trigger that releases the covers are tripped before the multicore lands on the bottom. The cores lower into the mud, but with the covers in place, the can’t collect samples. The solution was to remove six of the lead bricks, lightening the load on the center of the corer. The next lowering succeeded. High fives! 

After our third multicore sample was on board, we deployed the MILET and completed a 5 hour photographic and subbottom survey of the NT800 site. This put us into the morning of the next day.

John Kaba and Curtis Okolovich sectioning a core from NT800

Caroline Johansen taking a break from data entry

Peter Lazaravich and Eric Howarth checking the MILET controls
during the bottom photographic survey

 Posted by:

Ian MacDonald
Florida State University

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