Frank Hubacz: Unimak Pass, May 4, 2013

NOAA Teacher at Sea
Frank Hubacz
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.

Unimak Pass
Unimak Pass

 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.

 

CTD Unit
CTD Unit
Here I am in my hot rain pants helping to deploy the CTD
Here I am in my hot colored rain pants helping to deploy the CTD.  Notice the niskin bottles?
Monitoring the drop with Peter
Monitoring the drop with Peter
Monitoring the CTD deployment
Data screens in the lab

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.

The sampling begins!
The sampling begins from a niskin bottle!
Filling the sampling vials to be stored for later analysis
Filling the sampling vials to be stored for later analysis
Peter placing samples in the freezer
Peter placing samples in the freezer
Scott preparing the chlorophyll samples
Scott preparing the chlorophyll samples

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.

Personal Log

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.

IMG_7099
View as I traveled to work!
Islands of the Aleutians.
Islands of the Aleutians.
IMG_7055
Island hopping!
IMG_7029
Not all islands are completely snow covered.

 

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Frank Hubacz: ADCP Deployment, May 2, 2013

NOAA Teacher at Sea
Frank Hubacz
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 2, 2013

Weather Data from the Bridge:

Partly sunny, WindsN 5-10 knots
Air Temperature 1.3C

Relative Humidity 60%

Barometer 1008.2 mb

Surface Water Temperature 2.8C

Surface Water Salinity 31.37 PSU

Science and Technology Log

As I described previously, one of the instruments being deployed on this cruise is an Acoustic Doppler Current Profiler (ADCP), which measures speed and direction of ocean currents across an entire water column using the principle of Doppler shift (effect).  The Doppler Effect is best illustrated when you stop and listen to the whistle of an oncoming train.  When the train is traveling towards you, the whistle’s pitch is higher. When it is moving away from you, the pitch is lower. The change in pitch is proportional to the speed of the train.  The diagrams below illustrates the effect.

Doppler Effect
Doppler Effect
Another view of the Doppler Effect
Another view of the Doppler Effect

The ADCP exploits the Doppler Effect by emitting a sequence of high frequency pulses of sound (“pings”) that scatter off of moving particles in the water. Depending on whether the particles are moving toward or away from the sound source, the frequency of the return signal bounced back to the ADCP is either higher or lower. Since the particles move at the same speed as the water that carries them, the frequency shift is proportional to the speed of the water, or current.

The ADCP has 4 acoustic transducers that emit and receive acoustical pulses from 4 different directions. Current direction is computed by using trigonometric relations to convert the return signal from the 4 transducers to ‘earth’ coordinates (north-south, east-west and up-down. (http://oceanexplorer.noaa.gov/technology/tools/acoust_doppler/acoust_doppler.html).  The most common frequencies used on these units are 600 KHz, 300 KHz, and 75 KHz.  The lower the frequency the greater the distance that the wave can propagate through the ocean waters.

Determining current flow helps scientist to understand how nutrients and other chemical species are transported throughout the ocean.

Typical 4 beam ADCP sensor head. The red circles denote the 4 transducer faces.
Typical 4 beam ADCP sensor head. The red circles denote the 4 transducer faces.

Prior to sailing, ADCP mooring locations are selected by various research scientists from within NOAA.  Next, engineers develop a construction plan to secure the unit onto the ocean floor.  Once designed, the hardware needed to construct the mooring is sent to the ship that will be sailing in the selected mooring locations.  Prior to arriving at the designated location it is the responsibility of the science team to construct the mooring setup following the engineering diagram shipped with each ADCP unit. ADCP moorings can be constructed to hold a wide variety of measuring instruments depending upon the ocean parameters under study by the research scientist.

ADCP Construction Diagram
ADCP Construction Diagram

The moorings are built on the ship’s deck starting with an anchor.  The anchor weight is determined based upon known current strength in the area where the mooring will be located.  Anchors are simply scrap iron railroad train car wheels which bury themselves into the sediment and eventually rust away after use.  The first mooring unit that we assembled had an anchor composed of two train wheels with a total weight of 1,600lbs.  Although this mooring was built from the anchor up this is not always the case.  When setting very deep moorings the build is in the reverse order.

Selecting the anchor
Selecting the anchor
Anchor on the back deck
Anchor on the back deck below the gantry

Next, an acoustic release mechanism is attached to the anchor by way of heavy chains.  This mechanism allows for recovery of the ADCP unit as well as the release mechanism itself when it is time to recover the ADCP.  The units that we are deploying will remain submerged and collect data for approximately 6 months.

Acostic Release Mechanism
Acoustic Release Mechanism
Bill attaching the acoustic release mechanism
Bill attaching the acoustic release mechanism

Finally, an orange closed-cell foam and stainless steel frame containing the actual instrumentation is connected to the assembly and then craned over the back deck.  The stainless steel frame has a block of zinc attached to it which acts as a sacrificial anode.  Sacrificial anodes are highly active metals (such as zinc) that are used to prevent a less active metal surface from rusting or corroding away.  In fact, our ship has many such anodes located on its hull. Once the entire unit is in position, a pin connected to a long chord is pulled from a release mechanism and the unit is dropped to the ocean floor.  Date, time, and location for each unit are then recorded. 

Hoisting ADCP
Hoisting ADCP
ADCP unit assembly
ADCP unit assembly
Assembling mooring unit
Assembling mooring unit
Ready for launch
Ready for launch

To recover the unit, an acoustic signal (9-12 Khz) is sent to the ship from the sunken mooring unit to aid in its location.  Once located, a signal is used to activate a remote sensor which powers the release mechanism to open.  The float unit then rises to the surface bringing all of its attached instruments along with it.  The stored data within the units are then secured and eventually sent along to the research scientist requesting that specific mooring location for ocean current analysis.

Recovering a mooring with a rope lasso
Recovering a mooring with a rope lasso

Personal Log

On my first day of “work” I was able to watch the science teams deploy three different ADCP moorings as well as conduct several CTD runs.  I will discuss CTD’s in more detail in future blogs.  I was impressed by the camaraderie among all of the science team members regardless of the institution that they represented as well as with members of the deck crew.  They all work as a very cohesive and efficient group and certainly understand the importance of teamwork!

Adjusting to my new work schedule is a bit of a challenge. After my work day ended today at 1200 hours, I fell asleep around 1500 hours for about 4 hours.  After trying to fall back asleep again, but to no avail, I decided to have a “midnight” snack at 2000 hours (8pm).  I finally fell asleep for about 2 more hours before showering for my next shift.  I think I now have more empathy for students who come to my 8am chemistry class and occasionally “nap”!

A wide selection of food is always available in the ship’s galley. I have discovered that I am not the only one taking advantage of this “benefit”!  I will definitely need to reestablish an exercise routine when I return home.  We are currently heading for Unimak Pass which is a wide strait between the Bering Sea and the North Pacific Ocean southwest of Unimak Island in the Aleutian Islands of Alaska.

Did you know that since the island chain crosses longitude 180°, the Aleutian Islands contain both the westernmost and easternmost points in the United States. (172° E and 163° W)!

180 longitude