Seamounts Cruise
May 7, 2004, Day 11

Today was our last dive of the expedition. We returned to Rodriguez Seamount and green water rich with "marine snow" (particles of molts, mucus, fecal pellets, and bits of dead plankton drifting down from the sunlit surface waters, which provides food for the critters in the dark deep-sea where photosynthesis does not occur). We dove on the southern flank of Rodriguez, whereas our first dive of the trip had been on the northwestern flank of the same seamount. It was sunny and so calm this morning that organic slicks were continuous on the sea surface from horizon to horizon. It is rare that the Pacific Ocean is so pacific! The wind picked up in the afternoon, kicking up some swells. We have now an 18-hour steam to Moss Landing, where our ETA is 17:00 tomorrow (Saturday).
--Jenny PaduanMay7205.jpg (59943 bytes)

A baby octopus (probably Graneledone spp.) hides under a rock, while a larger octopus (also Graneledone) glides around just outside. Whether the larger one was protecting or hunting or even aware of the smaller one, we will never know.


We returned to Rodriguez Seamount for a second dive during this cruise, and our sixth including the four last October. The dive was designed to examine and collect rock samples from a series of volcanic cones on the south flank between about 1550 and 1000 meters depth. One of these cones is the second largest cone on Rodriguez and since we had crossed the largest during a dive last October we wanted to compare the two. We began on a deeper, smaller cone that consisted entirely of pillow and blocky lava flows. We then moved up the slope of the larger cone, which was almost entirely composed of volcaniclastic deposits, as was the largest cone explored in October. The next three smaller cones were mostly volcaniclastic deposits, but some blocky lava flows were also observed and collected. The saddles between cones had strong currents and little sediment, although the slopes of several cones had considerable light brown sediment, filling in between the rocks and even on the tops of rocks. The abundant sediment suggests that currents are not strong enough to prevent sediment deposition. The final cone was sampled only at the base since we were out of time and the surface was covered in talus, the sonar showed the same pattern upslope, and the slope of the cone was constant from top to bottom. We decided that the entire slope was probably covered by talus and that samples from the base would simply have to do. We worked our way up the flank of each cone and around its summit, sampling and making observations. We then had the ship move quickly ahead and flew the ROV through the midwater to the next cone, lowered the ROV to the seafloor again, and worked up the next slope. This strategy was used because it is very slow to work downslope since the ROV must crab down the slope to be able to see anything and to prevent damage to the stern of the vehicle, which commonly hits the bottom. It also May7202.jpg (46273 bytes) allowed us to extend the length of the dive track. We decided that since most of the cones we have explored are fairly symmetrical and the two slopes are similar in composition, we would not miss important observations or samples by skipping one slope. The dive was more striking in terms of the biology since the first several cones had familiar assemblages of sponges, crinoids, anemones, urchins, and cucumbers, but a single cone in the middle of the dive had abundant large Paragorgia and bamboo corals similar to the summit of Davidson Seamount. The surfaces on the first few cones also had shell fragments or entire valves of the seamount clam, but living specimens were rare until the top of the second cone, by which time we had spent considerable time searching for and collecting a half dozen that we plan to return alive to MBARI for respiration measurements.  The patchy distribution of animals on the seamounts, even from cone to cone, is striking to say the least. 

May7203.jpg (46684 bytes) There were also two wonderful midwater encounters today. The first occurred just as we were approaching the bottom at the end of a midwater run between cones. We came across a 6-8 feet long sleeper shark (Somniosus pacificus) that allowed us to video her (apparently a she, since she looked pregnant) as she swam by and explored the ROV. The second encounter was May7201.jpg (29936 bytes) with a large, nearly spherical jelly that we first discovered several years ago on Gumdrop Seamount north of Monterey Bay. This jelly was described by George Matsumoto at MBARI who named it Tiburonia granrojo (Tiburon Big Red) in honor of the ROV Tiburon. We also passed by a second Tiburonia granrojo later in the dive, but time limitations cut short our documentation of this encounter.
--Dave ClagueMay7208.jpg (31686 bytes)


The sleeper shark investigated the Tiburon then swam off.



May7206.jpg (48314 bytes)A kelp holdfast is a meal for the dinner-plate-sized purple pancake urchin, Tromikosoma. (An anemone and sponge are also in the photo.) The kelp must have drifted out from coastal waters. We lifted the holdfast and examined it for any rocks that it may have transported with it, but found only pebbles. We suspect that kelp holdfasts may be a source for the many continentally-derived cobbles we find on the seamounts.

Working in an office and lab at the U.S. Geological Survey, I don't get the chance to do field work very often, so when I received an invitation on MBARI'S Western Flyer for my very first research cruise I was stoked! My objective on the cruise was to collect ferromanganese crusts that grow on the seafloor, but I gained an enormous amount more! In less then two weeks, I met interesting, caring, and very intelligent people who have been a pleasure to work with, I've viewed the ocean floor at 3000 meters water depth, I've seen spectacular creatures I was unaware even existed, and forged lasting friendships. The remarkable science occurring before my very eyes, the marvelous ship carrying us to a new dive spot each day, the cooperation and camaraderie of the entire ship's and ROV's crews has been a pleasure to be apart of. The atmosphere on the ship has been so stimulating, the numerous science discussions, the exciting and wondrous exploration of the seafloor everyday, the questions that arise after every dive. My love of exploration and passion for science was reawakened while sitting in the ROV control room and taking my first glimpse of the seafloor for the first time opened my eyes to a whole new and fascinating world. Who knew there were so many animals in a light-less world, and that they would be so vibrantly colored and ornate! When I saw my first deep-sea cephalapod, the Vampyroteuthis, dance around and look at our camera with its blue eyes, I felt honored to have experienced something that most will only read about. It's a bittersweet feeling heading home after such an adventure! I will savor the last dive of the cruise…the last time I'll see the mysterious and wonderful seafloor, my last navigation watch, the last dinner with the crew and science team who I've come to think of as pals, I will definitely treasure these memories I've been afforded, for this has been a trip of a lifetime. Thank you MBARI. This may have been my first research cruise, but I promise it won't be my last! The entire trip has been truly amazing!
--Brandie McIntyre

May7204.jpg (31081 bytes)

Brandie and Jim take a hacksaw to a large rock with a thick ferromanganese crust, so they can measure the thickness of the crust and subsample the accreted layers. The rest of the group wanted to know what kind of rock was inside, obscured by all that manganese!



May7207.jpg (52708 bytes)A crab (family Lithodidae) has a tiny snailfish (fam. Liparidae) cleaning its leg.


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