NOAA Teacher at Sea
Aboard NOAA ship Oscar Dyson
April 29 – May 10, 2013
Mission: Pacific Marine Environmental Laboratory Mooring Deployment and Recovery
Geographical Area of Cruise: Gulf of Alaska and the Bering Sea
Date: May 5, 2013
Weather Data from the Bridge (0300):
Partly cloudy, S Winds, variable, currently 3.71 knots
Air Temperature 2.8C
Relative Humidity 73%
Barometer 1025.1 mb
Surface Water Temperature 0.10 C
Surface Water Salinity 31.66 PSU
Seas up to 5 ft
Science and Technology Log
Once we completed our mooring work from Gore Point through to Pavlof Bay, we sailed on to Unimak Pass, nearly 400 miles away, and then entered into the Bering Sea. Unimak Pass is a strait (wide gap) between the Bering Sea and the North Pacific Ocean in the Aleutian Island chain of Alaska. Upon arrival at our first station, we started the process of deploying our CTD sampling unit at predetermined points as well as MARMap Bongo casts(discussed in my next blog) when specified, within a region forming a rectangular “box” north of the pass. If you have been following my voyage using NOAA ship tracker, hopefully you now understand why we appeared to have been “boxed in” (I can hear the groans from my students even out here in the Bering Sea). It is important to understand the ocean waters of this region given that it is a major egress between the North Pacific Ocean and the Bering Sea. Therefore it serves as an important pathway between these two water bodies for commercially important fish stock as well as serving as a major commercial shipping route.
A CTD (an acronym for conductivity, temperature, and depth) is an instrument used by oceanographers to measure essential physical properties of sea water. It provides a very comprehensive profile of the ocean water to help better understand the habitat of important marine species as well as charting the distribution and variation of water temperature, salinity, and density. This information also helps scientist to understand how variations in physical ocean properties change over time. The CTD is made up of a set of small probes attached to a large stainless steel wheel housing. The sensors that measure CTD are surrounded by a rosette of water sampling bottles (niskin bottles) that individually close shut by an electronic fired trigger mechanism initiated from the control room on-board the ship. The rosette is then lowered on a cable down to a depth just above the seafloor. The science team is able to observe many different water properties in real time via a conducting cable connecting the CTD to a computer on the ship. A remotely operated device allows the attached water sampling bottles to be closed (sample collected) at selective depths as the instrument ascends back to the surface.
On this cruise, our CTD was equipped to collect real-time water column measurements of conductivity, temperature, density, dissolved oxygen, salinity, chlorophyll levels, and light as the unit traveled down through to a set point just above the ocean floor. Additionally, water samples for determining concentrations of nutrients (nitrate (NO3-1), nitrite (NO2-1), ammonium (NH4+), phosphate (PO4-3), and silicates (SiO4-4), dissolved oxygen, dissolve inorganic carbon, and chlorophyll were measured at specified depths within the water column as the unit was raised back to the surface. Replicate measurements of some chemical constituents measured on the ascent are completed to help support the reliability of the dynamic measurements of these same species made on the drop. All of the nutrient samples are then frozen to -80C and brought back to the lab on shore for analysis. Dissolved oxygen, dissolved inorganic carbon, and chlorophyll samples are also treated according to unique methods for later detailed analysis.
Our first CTD cast from the “Unimak Box” began with my shift, a bit after midnight, on May 3rd and ended 32 hours later on May 4th. The science crew worked nonstop as they completed 17 different CTD casts. Again, it was impressive to see the cooperation among the scientists as each group helped one another complete CTD casts, launch and retrieve Bongo nets, and then collect the many different samples of water for testing as well as the samples of zooplankton caught in the bongo nets. My task was to collect nutrient water samples from each CTD cast. As the water depth increased so did the number of samples that were collected. During our sampling water depths ranged from approximately 50 meters (5 samples) up to 580 meters (11 samples). On our last cast the air temperature was -2.3o C with water temperature reading 2.90 C. Seas were relatively calm and we were able to see many different islands in the Aleutian chain.
It was rewarding to be able to help the team collect water samples for nutrient testing, especially given that we are able to sample many of these same nutrient species in our chemistry lab at Franklin Pierce. I want my students to know that I practiced “GLT” when collecting nutrient samples making certain to rinse each sample bottle and sampling syringe at least three times before each collection. Want to know what “GLT” references…ask one of my students!
My most “interesting” time on board ship happened during our first night of CTD testing along one of the lines of the Unimak Box. At 2:45 am Peter, Douglas, and I were recording flow meter values from the previous bongo net tow on the side quarter-deck. I was writing values down on a clip board as Peter read the values off to me. I happened to glance over the deck towards the sea when I noticed an unusually large wave about 2 meters out from the boat traveling towards us. Suddenly it crashed on top of us knocking us to the deck floor. Water flooded all around us and through the doors of our labs. I immediately grabbed onto one of the ship’s piping units and held on tight as the water poured back off the deck. In an instant the sea was calm again after the “rogue” wave released its energy on our ship. Because Peter and I fell onto the deck our clothes became completely soaked with icy cold seawater. Upon standing, we checked on each other and then immediately began retrieving empty sampling bottles and other lab paraphernalia as they floated by in the water emptying off the deck. Douglas was able to hold-on to the CTD and remained standing and dry under his rain suit. This is the first, and I hope the last, “rogue” wave that I ever experience. Fortunately, no one was lost or injured and we were able to retrieve all of our equipment with one exception…the clip board of data log entries that I was holding!
I must admit that I am disappointed at the limited internet access while on board ship. I find it somewhat disheartening that I have not been able to write the consistent blogs promised to you telling of my adventures. Hopefully this will improve as we change course and you will continue to follow along.
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