Dredging!
September 3, 2008
An ocean mapping cruise is mostly about forward motion, trying to map as much territory, around the clock, as time allows. But other projects on board require us to stop from time to time (see, e.g. my entry #12 about the on-ice deployment of a NOAA/National Ice Center buoy). We have spent the last few days of the trip dredging at various sites to get a sense of what kinds of rocks are in different parts of the ocean. Getting the rocks is really only the beginning. From here they will be taken back to various campuses for analysis under the careful eye of a few geologists. Their analyses will contribute to the larger picture of what the Arctic Ocean floor is made of and how the ocean basin was formed.
Kelley Brumley (in pink hard-hat), our fantastic on-board tectonic geology scholar, led the rock end of the dredging effort with the help of Healy's Marine Science Technicians (see entry #9), Dale Chayes of Columbia's Lamont-Doherty Earth Observatory and Alex Andronikov (blue hard-hat) a volcanics expert from the University of Michigan Department of Geology. The actual dredging requires much planning and logistical coordination:
- Identifying the right dredge sites based on sparse mapping of the region,
- Finding the actual site and hoping there is not too much ice over it,
- Breaking any ice that is there,
- Conducting a drift test which helps with the next step,
- Keeping the boat stationary over the site for the two to three hours it can take to run a dredge two to three thousand meters down and haul it back up,
- Properly preparing and securing the dredge, which weighs 700 pounds empty! (it is not uncommon to lose them if they snag on some unseen formation hundreds or thousands of meters below).
- Briefing all participants, and ensuring their safety (keeping non-essential personnel clear of the fantail for the hour or two that the dredge needs to pulls up its load under very high tension).
- Once the dredge is hauled back up, weigh the contents, which can be over a thousand pounds! Lots of mud involved ---
- Hope for more rocks than mud,
- Once the crane empties the dredge onto the fantail, start hosing down the pile and sorting the rocks. This involves lots of water in cold temperatures, bending, kneeling, lifting bucket after bucket of rocks, drying them and transporting them into the lab for cataloging…
The picture below shows the safety attire (and proves that I am earning my keep – that’s me under the yellow hard hat, happy as a geologist in mud).
- Identifying the right dredge sites based on sparse mapping of the region,
- Finding the actual site and hoping there is not too much ice over it,
- Breaking any ice that is there,
- Conducting a drift test which helps with the next step,
- Keeping the boat stationary over the site for the two to three hours it can take to run a dredge two to three thousand meters down and haul it back up,
- Properly preparing and securing the dredge, which weighs 700 pounds empty! (it is not uncommon to lose them if they snag on some unseen formation hundreds or thousands of meters below).
- Briefing all participants, and ensuring their safety (keeping non-essential personnel clear of the fantail for the hour or two that the dredge needs to pulls up its load under very high tension).
- Once the dredge is hauled back up, weigh the contents, which can be over a thousand pounds! Lots of mud involved ---
- Hope for more rocks than mud,
- Once the crane empties the dredge onto the fantail, start hosing down the pile and sorting the rocks. This involves lots of water in cold temperatures, bending, kneeling, lifting bucket after bucket of rocks, drying them and transporting them into the lab for cataloging…
The picture below shows the safety attire (and proves that I am earning my keep – that’s me under the yellow hard hat, happy as a geologist in mud).
