Jillian Worssam, July 19, 2008


NOAA Teacher at Sea
Jillian Worssam
Onboard U.S. Coast Guard Vessel Healy
July 1 – 30, 2008

Mission: Bering Sea Ecosystem Survey
Geographic Region: Bering Sea, Alaska
Date: July 19, 2008

Numerous times over the past two and half weeks I have mentioned the CTD, small ones attached to moorings, there is one on the MOCNESS, there are even CTD sensors aboard the HEALY, but what does this CTD really tell the scientists?

For every sampling station the CTD needs to be prepared ahead of time so that all the equipment is functioning fully.

For every sampling station the CTD needs to be prepared ahead of time so that all the equipment is functioning fully.

As a review, let’s remember that a CTD records the Conductivity of the water that when adjusted for Temperature gives us salinity. The Depth of each sample is recorded because the ocean is not static; it is constantly moving both vertically and horizontally, and changing as it moves. When you sample with the CTD you can add a variety of accessory sensors to measure other ocean parameters: O2 salinity, temperature, pressure, fluorescence, turbidity and on our specific cruise we are also collecting data in regards to micro-zooplankton, nitrates, iron, and radon.

Each line represents a different element that the CTD is measuring.

Each line represents a different element that the CTD is measuring.

Let’s stop for a moment and talk about ocean currents. There are three ocean currents that affect the ecosystems of the Bering Sea: The Alaska Coastal Current, heavily freshwater, colder runoff that shoots through Unimak Pass; The North Pacific Gyre, warmer(relatively) water that seeps through the entire Aleutian chain, like water through a sieve. And the deep ocean conveyor belt, this one actually comes from the Mediterranean…water that has not seen the surface for a thousand years or more! This dense and cold fluid flows through Kamchatka pass, and has traveled from the north Atlantic through the Pacific to get to the Bering Sea, and is really rich in nutrients. No wonder it takes a thousand years. Anyway here we have all this water filtering into the Bering Sea, and here on the HEALY we have the CTD to give us precise data on the composition of this water.

The scientists all getting their water samples out of the 30 liter bottles.

The scientists all getting their water samples out of the 30 liter bottles.

During the actual cast of the CTD at each recorded station 24 data points are collects each second, giving an excellent representation of each specific water column. It is Scott’s job to run the CTD and let me tell you this is no easy task. The electronic equipment has to be constantly calibrated, the physical instrument array maintained, and all the collected data cataloged and stored for transmission to all the scientists both during and at the end of this cruise. None of this is an easy task. I also find Scott’s role on the vessel fascinating. Scott is an engineer who works for Scripts out of California and is hired on as outside technical support. He is not technically one of the scientific team, not technically part of the U.S. Coast Guard, and the HEALY could not technically collect most of their data with out him!

Hamming it up, Scott shows us the real science behind the CTD.

Hamming it up, Scott shows us the real science behind the CTD.

Quote of the Day: If you plan for a year, plant rice. If you plan for ten years plant trees. If you plan for 100 years, educate your children. Chinese Proverb.

FOR MY STUDENTS: What is a pycnocline?