Recovering 'Sea Spiders' and Heading Home
Lamont graduate student Natalie Accardo reports from the Pacific. Blog 4: Jan. 13, 2013
The NoMelt project is more than just a seismic experiment; it also has an important magnetotelluric (MT) component. MT instruments measure natural magnetic and electric fields on the seafloor, allowing scientists to estimate the electrical conductivity of the underlying rocks. Conductivity is highly sensitive to tiny amounts of water and molten rock within the upper mantle and thus can help distinguish whether the mantle is “wet” (and thus easy to deform) or “dry” (rigid and plate-like).
To obtain information concerning the conductivity of the mantle, six long-period MT instruments were deployed along with the seismographs from the R/V Langseth in 2011. These instruments, which appear more like sea spiders than scientific hardware, sit on the ocean floor and record electrical and magnetic fields approximately every minute. We recover these instruments in the same way that we retrieve the OBS (previous post), although they proved to be much more shy than the OBS in communicating with us. We welcomed back our first MT instrument on a dark and windy night, and over the course of two weeks we recovered five additional instruments without incident, displaying them in all of their neon-orange glory on the stern deck.
With the last instruments safely strapped down, we have put the NoMelt site in our rearview mirror and are steadily speeding to our final destination of Honolulu. Sunny skies and calm seas accompany the slowing pace of activity during our four-day transit to port. Behind the boat, we trail fishing lines with every color of bait in the hopes that a tuna or mahi mahi might take a bite. Deck chairs have snuck their way out from the shelter of the hangers and onto the sun-drenched back deck where we, like moths to a lantern, try to soak up every last ray of sun before we must head back to the chilly Northeast.
Today we passed close enough to the island of Hawaii to give us our first glimpse of dry land in almost a month. The crew poured onto the main deck to snap photos and hunt for the tiniest glimpse of cellphone reception. There may be no better way to be welcomed back to land than the awesome sight of Mauna Loa towering above the clouds. Overall, the trip has been a great success. Most of our instruments survived their year of solitude on the dark, cold seafloor and came back to us with a set of unique and priceless data. We consider ourselves lucky to have gotten the chance to visit this remote region of the world, which will likely not see comparable human activity for some time.
Until next time, Aloha!