Thursday, September 27, 2012

Deep-C Geomorphology/Benthic Studies Cruise - Fall 2012

Ship’s Blog:  Weatherbird II (WB1305)
27 September 2012

Map of Cruise Progress (as of 27 September)
 


We have had 36 hours of great working conditions and continued success with our equipment.  We have been working our way southwest down the DeSoto Canyon, so that each sampling station is deeper than the next.  This afternoon we reached the deepest point at 2300 m in a site called XC4. 

Interestingly, the viewing conditions on the bottom have been improving with deeper water.  At earlier stations, suspended sediments made for cloudy viewing, but at this site it all cleared out.  The animal life continues to be scarce, although their trails and burrows are everywhere.  We particularly notice the circular patterns of holes made by a burrowing shrimp and chalky white mounds with a bulls eye hole right in the center.  

Holothuroids (sea cucumbers) rule the deep.
The ocean below 1500 m is sometimes called the kingdom of the holothuroids--after the numerous, sometimes very colorful sea cucumbers that become abundant at depth.  We like the bright purple species that sometime appear in clusters of two or three.  Although they are able to creep slowly across the bottom, they have a faster means of travel when they choose.  Sea cucumbers can expand and contract their tissues and can expand enough so that they become buoyant and rise off the bottom to swim.  

Samira flies the  MILET platform, which is
hovering 2 m above the sea bottom at the end of 2500m cable.
The way the cameras are set up, the still camera is ahead of the video and is set to take a picture every 12 seconds.  So often we see things in the video by do not manage to capture them in the high resolution camera.  Every once and a while it works out though and we capture a fish or crab perfectly centered in the picture.  Sights like these relieve the tedium of having to "fly" the MILET about the height of a person by carefully reeling in or playing out the winch cable.  You have to concentrate or the bottom will creep up on you and suddenly appear very large in the monitor.

Sunken vegetation,  like these water lilies,
can be a significant source of nutritive carbon in the deep sea.
The cruise days have been going by fast as we work long days and nights.  Saturday is our last full day at sea and Sunday morning Weatherbird will tie up in Panama City for a crew change.  But we saved the most exciting sites for last.  One of our objectives has been to find natural hydrocarbon seeps so we can study the effects of oil and gas in the deep sea environment.   We had scheduled a visit to a site we are calling Seep C, which is a known seep.  But because our schedule was going well, we decided to sneak in an extra survey at a site we are calling Peanut Mound (site 10 on the chart).  The Okeanus Explorer had detected gas bubbles here in 2011, so we thought there might be some active venting.  Lo and behold, as we maneuvered MILET up the flanks of a mound we call Peanut Hill, we spied several patches of bacterial mats and an unmistakable lump of natural asphalt.  Bingo!

A unexpected patch of asphalt on Peanut Hill indicates natural hydrocarbon seepages.


 Post Author:
Dr. Ian MacDonald


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