Speed 11.4 knots (kts) Course 247° Location 71.54° N, 157.08° W, approx. 14 nm offshore from Barrow. Depth 116 meters
SPECIAL FEATURE DISCUSSION:
(see previous journal for the questions.)
When we measure in miles on land we nearly always use statute miles. At sea we use nautical miles (nm.) A statute mile is 5280 feet long. **A nautical mile is 1/60 of one degree of latitude. That turns out to be about 1.15 statute miles. **
Aboard a ship the term knot doesn't always mean a way of tying rope. It is also an abbreviation for a nautical mile per hour.
TODAY'S JOURNAL:
The ocean acidification study team (Chris Dufore, Sherwood Liu, and Mark Patsavas ) has several state-of-the-art water chemistry analysis systems aboard. They are setting new precedents for high-resolution pH measurements at sea, using spectrophotometric analysis to obtain results that are accurate to ± 0.0004 pH units. (Spectrophotometric measurements involve shining light through a water sample and then measuring the resulting spectrum of light reaching the other end which yields a very precise pH value.)
In preparation for another CTD cast (Conductivity, Temperature, Depth) Chris Dufore readies Niskin Bottles by setting the top and bottom stoppers. Upon command from the ship the spring-loaded stoppers on each end of the bottle are tripped closed, capturing a sample from that particular level in the water column.
Besides the onboard lab equipment that the team uses, they have two automated continuous pH profilers that go onto a CTD rosette for the ride down and back up. In preparation the crew removes a Niskin Bottle from the CTC rosette and puts a pH profiler in its place. The device pumps water through its analysis system throughout the round trip (up to 1000 meters deep), adding a carefully metered amount of indicator solution into the stream (remember that indicators change color depending on the pH level.) The water then flows into a tube where calibrated light is passed through the sample. A light detector at the other end measures the resulting spectrum and from that data the computer can determine a precision pH value. All of this is done automatically and when the CTD rosette is back aboard in the staging area the data from the automated pH profilers is downloaded onto a laptop.
Sherwood Liu and Mark Patsavas mount the automated pH profiler onto the CDT rosette. A Niskin Bottle has been removed and the profiler is put in its place on the array.
The automated pH profiler mounted on the CTD rosette and ready to put overboard.
This is the first time such automated pH profilers have been used in the Arctic Ocean. Without them measurements can only be made in surface water, so these devices open up a whole new dimension for tracking pH changes at the 'top' of the world.
Just prior to putting the gear overboard the automated pH profilers are switched on by Chris Dufore and Mark Patsavas. MST Lee Brittle coordinates the deck operations, signaling to the aftcon for a-frame and winch movements.
MST Daniel Purse controls the a-frame crane and winch from aftcon (the aft control center.) Dale Chays (at monitor), Sherwood Liu, and Mark Patsavas monitor conductivity, temperature, depth, and oxygen levels as the CTD descends. The data profiles collected as the CTD descends can be used to plan water collecting levels on the way back up.
Upon its return, Mark Patsavas and Sherwood Liu download data from the automated pH profiler onto a laptop.
SPECIAL FEATURE:
As acidity increases, does pH increase or does it decrease?
Why are the Niskin Bottles typically tripped on the way back up to the ship instead of on the way down?
Why are Niskin Bottles still used when the automated pH profiler already records data from the water column?
That's all for now! Best- Bill