Archive of September 27th, 2007

Teacher at Sea log for September 27, 2007 by Linda Sciaroni

Today I learned more about our technical crew. I interviewed Bruce Appelgate. He works in our Computer Lab. He has a doctorate degree and has traveled all over the world doing oceanographic work.

When we first came on board, Bruce trained us in how to stand watch as bathymetry is being measured. Each watch member kept a log of certain numbers every 15 minutes so that we could be certain that data was being recorded consistently and all the equipment was functioning as needed.

If you look at the home page of our web page you will see that the left side of the map of Hawaii has much less detail than the area around Honolulu. One of the goals of our cruise is to fill in as much detail in this map as we possibly can. There are twelve hour breaks between Jason 2 dives. During those breaks and along the way between dive sites, Bruce maps out way-points for the ship to travel. You will see on our map of our journey it looks like we have been traveling like a lawn mower over the sea around Kauai. Each time we pass over an area we increase the accuracy and precision of the map of the ocean floor. There are many sources of error in these measurements taken by the equipment that need to be accounted for. Many can be eliminated mathematically by the navigational measurements taken by the ship. These include the measurements of pitch and roll, Global Position System data, heading, speed through the water and course over ground.

There are other measurements that are taken to understand the sea water the signal is passing through. Yesterday I went out on the fantail of the ship to see Bruce launch an XBT (expendable bathythermograph). This probe is precisely dropped into the water and the water's temperature is measured as the probe falls through the water. The signal recieved by the launcher is sent back to the measuring instrument through a very thin wire. Water can have different densities and we can detect those densities far away by knowing the temperature of the water. The different densities will cause a refraction of the sonar signals and so it must be measured and accounted for.

Science Update by Todd Bianco

Jason 2 is equipped with four video cameras (the brow camera, the pilot's camera, the science camera, and the reverse camera) and a digital still camera, while Medea also has a camera looking down on Jason 2. We typically use our science camera to select and take pictures of our samples because it has the highest resolution image. Even with all of these cameras, it can be hard to tell what our samples will be when we get them to the surface.

As stated in previous science updates, our goal is to study Hawaiian volcanism; therefore we are searching for samples of basalt on the ocean seafloor. Further, we seek in place (or intact) samples, so that we know their origins are local to the sample site. Sometimes we think we have sampled intact basalt, but we find out when we slice the rock open that it is simply manganese-encrusted mud that was well cemented to an outcrop.

Today we are showing images of three samples; for each sample there is an image from the seafloor sample site and image of the rock sliced open in the lab. Two of our samples, J2-296-01 and J2-297-13 were correctly identified on the seafloor as basalt and sediment, respectively, as seen in the rock slice images. The other sample, J2-296-06 was incorrectly identified as basalt on the seafloor images, and was sliced open to reveal mud on the inside. Jason 2 can only handle a limited payload, so the team is patient and methodical when selecting rocks to bring to the surface in order to maximize the number of correctly identified samples.

Presented by the School of Ocean and Earth Science and Technology at the University of Hawaii, with financial support from the National Science Foundation.