Dive and Discover : Daily Updates

Last night the Towed Camera Sled took 1,753 photos of many different kinds of terrain on ocean floor. So far, the tally is 11,484 digital pictures taken on this cruise! The images taken last night included old, extinct hydrothermal sulfide deposits and chimneys, crabs, starfish and many different lava flow types and collapse structures. Some of the photos were a little too close! The Sled “kissed” the seafloor three times!

The Night-Owl Camera Team may make it sound like it’s easy to tow the Sled from behind RV Atlantis, but it’s definitely harder than it looks. The Sled is attached to a 1/2” steel wire that is spooled on an oceanographic traction winch mounted under the fantail of the ship. The seafloor here on the East Pacific Rise crest is at about 2550 meters depth but because the ship is moving at about 1/2 knot (or about 15 meters per minute) the wire does not go straight to the bottom. If you have ever been trolling for fish, the principle is the same; the wire ends up being at an angle, so it takes a bit more wire for the Camera Sled to reach the bottom . In general, when the Sled is at its towing altitude, about 7 meters, above the seafloor, its position is about 100-200 meters behind the ship. Hauling in the steel wire or lowering it down is how they change the position of the Sled above the seafloor.

The Sled has a 12 kHz (that’s the frequency of the sound that it sends into the water) pinger mounted inside the frame that sends out a sound signal that allows the scientists onboard Atlantis to measure how close the Sled is to the seafloor.

Unlike many of the camera tows done on this leg that traversed relatively flat terrain, last night we were surveying down in the Axial Summit Trough (AST) of the East Pacific Rise. The AST is full of many interesting features, including tall lava pillars, active and inactive hydrothermal sulfide chimneys, and walls that can be 5-8 meters tall.

To visualize the technique that the Night-Owls are using to tow the Sled, and the challenges they face, imagine a stage, like the auditorium in most schools, with tall paper cups randomly distributed on the stage floor. Now, imagine that you are up in the catwalks, where they have the lights, dangling a ball on the end of a string just above the cups. Position the ball only an inch or two above the cups-no higher and no lower. Now try to walk all of the way across the catwalk keeping the ball at the same distance, 1-2 inches above the cups. Easy? Not really!

The “Night Owl” crew was faced with this type of scenario last night as they used the traction winch to keep the Sled above most of the pillars using the pinger trace to tell them how high they were off the bottom. They missed nearly all of the pillars, but a few got “bumped”. The sturdy Towed Camera Sled was built to last, however, and showed only a few minor scratches when it came on deck! It went back into the water tonight at 1830 hours for the last tow of this cruise.

One popular past time amongst the Atlantis’ crew is fishing, but the fish have been few and far between on this leg. After the bridge spotted some birds feeding, the crew cast their fishing lines and - success - the fish were biting! Check out today’s slide show and see what Ed Popowitz and Bruce Strickrott were able to catch!

After lunch, the scientists and crew gathered in the library to listen to Julie Barber speak about her experiences as the “Our World Underwater Scholarship Society” (OW-USS) Scholar. The OW-USS was established in 1974 to promote educational activities associated with the underwater world. Each year a Scholar is chosen who then participates in a variety of hands-on activities and unique opportunities in underwater related fields. Julie is on the last leg of her year-long journey, having traveled across the US and to such amazing places as Egypt, Northern Ireland, and her personal favorite-the Galapagos Islands!

While folks on board were enjoying the sunset, it suddenly got very dark as a squall moved towards the ship. It was our first rain of the cruise! The downpour sent many people on the fantail scurrying for cover-but not quite all! A few of the scientists and crew enjoyed the refreshing rainfall as they relaxed in the pool after a hard (and hot) day’s work. After all, they were already wet!

Dive Summary
On Bottom: 0929 hours
Off Bottom: 1506 hours
Maximum Depth: 2543 meters

Today's trip to the bottom in Alvin was the final geophysical dive of this cruise. Dan Fornari, and graduate student Del Bohnensteihl of Lamont-Doherty Earth Observatory went to the bottom with pilot BLee Williams. They ran a 1.5 kilometer-long line from South to North that crossed 10 of their previous East-West lines, and then they continued to collect data on an additional 5 East-West traverses.

The North-South “tie-line” will give them important data to determine the precision and repeatability of their continuous gravity measurements. Basically, the concept of crossing lines when doing geophysical surveys is the same as any experiment where you repeat it several times to be sure you get the same results. Jim will analyze the data to check that he has calculated the same gravity value at each crossing point.

The geophysical data recording in Alvin, which by now is routine thanks to Dana’s logging programs and the reliability of the sensors and recording system on Alvin, went very well and about 7.5 kilometers of track were run. At the beginning and end of the dive, rock samples were taken of curtain-folded sheet flows. The last sample was recovered from inside the east wall of the Axial Summit Trough near 9° 38’N Latitude. We also collected a feather starfish that was attached to one of the rocks.

Upon Alvin’s return to the deck of Atlantis, Margo, Greg, Julie, and Paul gave Del, who had just had his first Alvin dive, a warm (or rather chilly) reception! After being soaked with iced sea water, Del had to take a quick swim in the pool in order to rescue his laundry. Congratulations on a successful first dive, Del! And many thanks to the Alvin group and crew of RV Atlantis for all of their help in making the collection of the geophysical data a great success.