A Petrologist at sea

August 20, 2013

We are in port in Newport for three days. Lots of R&R will be had, some of the science party and crew will swap out, and the ship will be refueled and restocked with fresh food. We depart again on Friday and the regular blogs will resume. Brian Dreyer has some thoughts to share today.

— Jenny Paduan

A Petrologist at sea

When people find out that I participate on research cruises, they often ask, “What do you do all day at sea?” Here is a typical day (though most days have surprises so hardly any day is “typical”). I’m a petrologist, which means that I study rocks and how they form. My particular interest on this cruise concerns the origin of submarine lavas. At MBARI, we use high-resolution AUV maps to guide our ROV dives and collect samples from a very well located and imaged portion of the seafloor. The combination of these techniques is a major advantage over seafloor exploration in past decades.

8:00 a.m.-9:00 a.m.: Check on previous day’s samples. This includes bagging and storing the lava samples we processed last night.

9:00 a.m -10:45 a.m.: My first watch on the VARS station. VARS is MBARI’s Video Annotation and Referencing System, the software and database system we use to record high-definition video and voice commentary during ROV dives. At the station’s computer, we manually input text annotations and take many “framegrabs” (from the Science Camera, see below) to document and catalog sample collection and visual dive observations of the seafloor. We also record location (latitude, longitude, depth), time, and a description of the activity, sample, and observations. This watch is also responsible for swapping tapes into the video deck every hour to ensure that all the action is recorded. All of this information becomes part of the permanent archive to which interested scientists will refer for years to come.

10:45 a.m.-11:30 a.m.: Continue processing the previous day’s samples. This typically includes cleaning glass chips that we removed from the outer rind of the lava samples. We make chemical analyses on the lava glass (rather than the lava interior) because the composition of the glass most closely matches that of the molten magma that formed at depth beneath the Earth’s surface.

11:30 a.m.-12:30 p.m.: Lunch and lunch relief. The entire science crew pitches in to make sure each of us has a meal while still maintaining coverage on each of the four concurrent watches.

12:30 p.m.- 2:15 p.m.: Second watch on the VARS station.

2:15 p.m.- 4:00 p.m.: Further processing of the previous day’s samples. I usually have a bit of unscheduled time in the late afternoon during which I may exercise and shower, relax, check email, or do laundry or cleaning if needed.

4 p.m.- end of the ROV dive: Science camera watch. The primary duty of the person who controls the science camera is to direct the execution of the ROV dive, narrate the dive, and communicate the science plan to the ROV pilots. The video and audio narration are another critical piece of the dive’s archive. The science camera watch is probably the most exciting watch because it requires constant interpretation of seafloor observations and quick processing and clear communication of multiple streams of information between the science and ROV teams. Although our ROV dives are planned well beforehand based on clear objectives, it’s quite common to modify these plans during the dive based on observations, sampling needs and capability, and resources. The ability to develop real-time contingencies can vastly improve the dive results.

Dave Clague in ROV control room

Chief Scientist Dave Clague operates the science camera in the ROV control room. ROV Pilot Mark Talkovic is in the background. The darkness of the ROV control room helps our eyes see greater detail from the live HD video. Here Dave is focused in on dark grey rounded “pillow” lavas that have very little sediment.

6:00 p.m.- ROV on deck: The ROV ascends towards the sea surface (at about two to three kilometers per hour) as we eagerly await the arrival of the rock and sediment samples we collected from the seafloor. A lot of activity occurs during this time in preparation: gathering sample bags and note cards, setting up the camera, preparing sample vials, etc.

ROV sled

Most of the seafloor samples are stored on the sled attached to the bottom of the ROV; the sled is extended in front of the ROV in this image. Rocks are stored in the box with rectangular partitions (you can see one particularly large sample protruding above the box). Pushcores (sediment samples) are stored in the tubes in the right side of the image. The main HD camera is visible in the top center of the picture.

6:30 p.m.-11:00 p.m.: Samples processing. Dave and Jenny perform the initial processing of samples to ensure that each sample is correctly matched to its identifying information. Once properly identified, a crew goes to work carefully rinsing mud and seawater from the rock samples, and Linda Kuhnz checks for biological material. Another part of the team goes to work on the pushcores. Once cleaned, rocks are photographed and we record our initial descriptions. We measure the size of each lava rock and note the degree of freshness or alteration. We also determine whether each rock has visible crystals or bubbles, and describe the overall appearance, shape, and texture of the sample. Next we carefully remove small pieces of the outer glass rind. Although the samples have been rinsed, we clean them further in a sonic bath. This breadbox-sized instrument is similar to the kind used to clean jewelry. This process can remove mud, rust, and other undesirable coatings from the glass. This cleaning step is necessary prior to analyzing the glass. We typically have a snack and play music while working into the night. The evening is also the time we do rock coring. Once all the samples are processed, I check email and usually try to get some other computer work done. We begin to unwind and settle into a sense that a good day’s work is nearing completion. I make a short call home on the satellite phone and then it’s time to turn in for the night.

photo of lava sample

A photograph of a lava sample. Note the index card with the sample’s ID and the scale bar below. Glass that has already fallen off this fragile sample is kept in the hexagonal white tray.

heart-shaped lava

Lavas come in a wide range of shapes. I particularly like this heart-shaped pillow “bud.” Many lavas are black and shiny and lack mineral crystals, but this sample has a high abundance of crystals called plagioclase feldspar (see the light-colored specks on the broken surface on the upper right side of the heart). Lavas containing crystals often enhance a petrologist’s ability to interpret the origin of the rock.

Image of ROV sonar display

Image of the ROV sonar display in the ROV control room while we were in the deep crater on Friday.

— Brian Dreyer