Sunday, September 30, 2012

Deep-C Geomorphology/Benthic Studies Cruise - Fall 2012

Ship’s Blog:  Weatherbird II (WB1305)

30 September 2012
Map of Cruise (as of 30 September)

This is the final entry for the Deep-C geomorphology/benthic ecology cruise (leg 1).  We departed from St Petersburg on 22 September and returned to land in Panama City on 30 September.  Overall the cruise was highly successful.  We generated over 40 sampling events at 12 sampling sites, including 12 photo-surveys, 9 CTD casts, and 12 successful multicore deployments.  Everyone on board worked extremely hard to get a great deal done in just a few days.  We were helped by a top-notch captain and crew and by excellent weather.  We hope that future cruises will be equally successful, but this will be hard to top.  The next leg of the Deep-C cruise will be leaving on Tuesday 2 October, after a slight delay caused by rough weather offshore.

WB1395 Science Party 

Post Author:
Dr. Ian MacDonald

Friday, September 28, 2012

Deep-C Geomorphology/Benthic Studies Cruise - Fall 2012

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

Map of Cruise Progress (as of 28 September)

Scene on the Weatherbird’s work deck
as the last of 24 multicore tubes were processed.
The mud soirĂ©es have resumed as we wind down our sampling activities.  Previously today, we completed an extensive photosurvey of Seep-C.  This is a natural hydrocarbon seep situated on a mile-wide mound that rises in a plateau almost 200 m above the surrounding seabed.  We did our most sophisticated work to date with the MILET platform as we were able to complete 1 km long tracks over the mound, then fly the MILET up in the water while the ship came around to a new course, and finally play out cable to bring the vehicle in on track on the top of the mound.  This would not have been possible without the superb bathymetry collected for us by the Okeanus Explorer because we needed to have confidence that we would not hit the bottom turns and that we knew when we would begin to approach the bottom as we brought the vehicle on track.

Samira and Arvind log core photographs
and descriptions while Chris offers advice.
The result was that we have localized the area of active seepage to be on the southern edge of the mound in an area about 100 x 400 m.  This will allow the next leg to drop its sediment and water sampling right into the most active area.  A similar strategy will be possible for Peanut Hill, so this cruise has accomplished an important objective in confirming the location where our positive control sites for hydrocarbon “contamination” can be sampled.

Samantha, Patrick, Chris, and Nikki: happy to only have one more coring site to go.

Samantha does double duty working on both sediment and water samples.
Nikki, Patrick, and Chris.
The multicoring crew then got a chance to get back in action  after several shifts standing by.  They are getting faster at processing the cores, but it still takes almost 10 hours to complete a 3-drop set of multicores.  By the end, everyone is tired, muddy, and a bit giddy looking forward to a shower and a few hours of sleep.  Less than 24 hours to go before we have to head for Panama City and trade out our science party for the next leg.

Post Author:
Dr. Ian MacDonald

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