NOAA Teacher at Sea
Onboard USCGC Healy
August 7 – September 16, 2009
Mission: U.S.-Canada 2009 Arctic Seafloor Continental Shelf Survey
Location: Beaufort Sea, north of the arctic circle
Date: September 7, 2009
Weather Data from the Bridge
Latitude: 790 ’24N
Longitude: 1540 27’W
Science and Technology Log
Today we deployed our first dredge in hopes of collecting some samples of bedrock from the Arctic Ocean. A dredge is a basket made of metal chain link with a sharp edged bottomless tray on top. A wire cable connects this dredge to the Healy. Our echosounding instruments show us what the sea floor looks like. Maps reveal ridges, seamounts, flat abyssal plains, and raised continental shelves. But, how did all these features form? How old are they? What type of rock are they made from? What kinds of forces created this ocean surrounded by continents? Where are the plate boundaries? Collecting rock samples will help us to answer some of these questions.
FOR MY STUDENTS: Can you predict what type of rock we might find by sampling oceanic crust? Continental crust?
Here is how dredging works:
- The dredge is deployed over a seafloor feature with a steep slope. Lowering the dredge takes a long time as the huge spool of cable unwinds. The top speed for the cable is 50 meters/minute. Today, the cable with the dredge attached rolled out 3850 meters before it stopped. The Healy then moves slowly up the slope dragging the dredge behind. The metal plates at the top of the dredge catch on rock outcrops as it is dragged up the side of the slope. Pieces of rock and sediment fall into the basket. The dredge is pulled up by the cable and lowered back on to the deck of the Healy. The dredge is dumped and scientists pick through all the mud and find the rocks.
This first dredge brought back 400 pounds of mud and rock. Unfortunately, most was mud and only 10% was rock. Dredging is tricky business. Sometimes the dredge gets stuck and needs to be cut free. Sometimes it collects only mud and no bedrock. We will be dredging at different sites for the next few days in the hope that good examples of bedrock will be collected. The rocks we find will be catalogued and the chemistry of the rocks will be analyzed. Hopefully, the rocks will help to answer some of the questions we have about the geologic history of the Arctic Ocean.
When you work at a school, you get used to drills. Fire, severe weather, and intruder drills help to ensure that students and teachers will know what to do in the event of a real emergency. The Coast Guard has drills each Friday to ensure the Healy will be ready to handle any emergency. I have observed the crew practicing what to do in the event of fire, flooding, collision with another ship and various other scenarios. Last Friday, I was lucky enough to watch the crew in action.