Posts Tagged ‘oceanography’

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Salinity Processes in the Upper Ocean Regional Study (SPURS): Prawlers, Engineers, and the Future of Oceanography at Sea

October 5th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

A number of the instruments deployed during SPURS are “works in progress.”  They work well, but need exercise in new or more challenging environments to perfect them. The whole of SPURS is an experiment, taking salinity measurement in the ocean to an entirely new level. Extended deployment of sensor webs in hostile and distant environments is something NASA needs to perfect for the future of Earth System Science research and for planetary exploration.  One of the overarching goals for those involved is to advance the use of autonomous measurement platforms for real-time global oceanography.

The Prawler (Profiler + Crawler) instrument from NOAA Pacific Marine Environmental Laboratory (PMEL) is one example of SPURS exercising a work in progress. It is also a place where we can see common goals between NASA and NOAA in physical oceanography.

Prawler closed on the laboratory bench.

The Prawler is a wave-powered subsea instrument that eliminates the need for multiple sensors on a mooring line. During descent, it makes a profile using whatever sensors have been installed and communicates those via inductive modem to the surface buoy (from there they are communicated via satellite to shore). Once the Prawler falls to the pre-determined bottom depth (arount 1,640 feet, or 500 meters), a micro-processor activates a ratcheting mechanism and harnesses the wave motion of the mooring to crawl back up the mooring line.

Diagram showing the ratchet mechanism on Prawler that allows it to climb the mooring wire.

The Prawler has been years in development and testing. This expedition we deployed two NOAA moorings where the Prawler is the primary instrument. The Prawler will make from five to 30 profiles per day (the average is about 20 profiles per day). For SPURS, the Prawler measures temperature, conductivity, and pressure. Those are core variables that are easily conversed to temperature, salinity, and depth.

An example (from a prior test of Prawler in the Pacific Ocean) of how many profiles one can expect to make using one Prawler during the course of a year. Provided by Billy Kessler, NOAA PMEL.

Billy Kessler at NOAA PMEL and University  of Washington is leading a NOAA SPURS project to test the Prawler technology. Billy and I were in graduate school at University of Washington together in the early 1980s and shared the same PhD mentor, Prof. Bruce Taft. It’s wonderful to be working with Billy again after all these years!

John Shanley and Andrew Meyer (aboard the Knorr) are two NOAA PMEL engineers who have been involved with Prawler mooring design tests for the last 3 years. They have already participated in some major tests of Prawler on moorings (a 7-month and a 4-month deployment in Hawaii, each time with two Prawlers, and many tests in Puget Sound). SPURS offered a great opportunity for a full year deployment near the heavily-instrumented Woods Hole mooring whose deployment I described in an earlier post.

John Shanley.

Andrew Meyer.

John and Andrew are fortunate to work in a small group of engineers where they get to work on all aspects of the Prawler, from design input to the actual fabrication of the instruments, to testing materials and components, to full ocean deployments. “From art to part,” as the boss likes to say! The NOAA PMEL mooring shop has a long history of excellence providing products that meet both researcher and operational requirements.

Seeing the Prawler used in SPURS after years of development is the light at the end of the tunnel for John and Andrew. This project has been a cumulative effort involving their entire engineering group. There have been four radically different versions, countless numbers of modifications, long days and weekends of machining parts. They have seen Prawler grow from just a few scribbles on a white board to deployment of the “finished” product over the stern of Knorr on this voyage. They both describe persistence as the key to success.  It almost brings a tear to your eye to hear Andrew describe to me “the last few touches before deployment as we assemble and ballast, to bolting it on the mooring line and dropping it into the ocean, bring a great sense of accomplishment.”

For Andrew and John being out here on Knorr to deploy the Prawler is just icing on the cake. The interaction with people from other institutions and seeing many different ways and means of measuring salinity truly puts the Prawler capability in a new perspective. They are both standing watches and working with the other teams to expand their ocean instrumentation expertise. They certainly now know that they too are on the leading edge of global real-time ocean observing in the 21st century. From interactions aboard ship they go home energized with ideas for the next innovation!

Salinity Processes in the Upper Ocean Regional Study (SPURS): What is ocean microstructure and why study it?

October 4th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

“The techniques I developed for studying turbulence, like weather, also apply to the stock market.”
Benoit Mandelbrot

If Mandelbrot’s statement is true, maybe oceanographers studying ocean microstructure (caused by turbulence), besides writing journal articles about mixing in the ocean also work on padding their retirement accounts with stunning stock market acumen?

Jokes apart, how does ocean microstructure work? The microstructure component of SPURS features measurements of very small-scale (inch or smaller) variations of temperature, salinity, and velocity, used to infer mixing rates due to turbulence and convection in the upper ocean.

Profiles of Temperature, Salinity, two channels of small-scale temperature gradient and two channels of small-scale shear from a dive of the Vertical Microstructure Profiler (VMP). The depth intervals with the strongest variations in temperature gradient and vertical shear are the places where the ocean is mixing the strongest. These raw data are carefully processed to tell us how much of the salinity change that we see is due to the vertical mixing rates. They can also tell us which processes are causing the mixing, such as shear instability or salt fingers.

Lou St. Laurent, together with Woods Hole Oceanographic Institution colleagues Carol Anne Clayson and Ray Schmitt, are the scientists principally focused on these issues. Their work is supported by the National Science Foundation and is another good example of the inter-agency cooperation spanning SPURS.

Ken Decoteau, a WHOI engineer, leads the microstructure group’s sea-going effort. Together with James Reilly, a research technician from UMass-Dartmouth/SMAST, Oliver Sun, a WHOI postdoctoral investigator, and Alec Bogdanoff, a graduate student in the MIT/WHOI Joint Program for Physical Oceanography, they run 24-hr operations of two instrument systems, a vertical microstructure profiler (VMP) and turbulence-sensing gliders (T-gliders).

Ken Decoteau.

Jim Reilly.

Oliver Sun.

Alec Bogdanoff.

The first, a vertical profiler (Rockland Scientific VMP5500), is lowered into the water and released. In its pressure housing, it carries batteries and electronics. The data collected by the external sensors is recorded to a disk drive inside the instrument. The steel ballast weights it carries cause it to sink to a pre-set depth. Upon reaching this depth, a trigger mechanism is fired, causing the weights to be released, and the instrument to float back to the surface. The instrument is then recovered, the data downloaded, and preparation for the next deployment begins. Although the instrument is capable of profiling to a depth of 18,000 feet (about 5,500m), most of the profiles on this expedition are being done to a depth of 4,000 feet (1,200m). These deployments take about one hour from the time we release the instrument until it re-surfaces.

The Vertical Microstructure Profiler, ready for deployment.

A second kind of measurement (of longer duration) is conducted using two Teledyne-Webb Slocum Gliders (T-gliders), each carrying a Rockland Scientific MicroRider. The MicroRider is similar to the VMP, but is much smaller in size since it is not designed to go as deep, and does not carry its own batteries and CTD; it draws battery power from the glider. The T-glider does not utilize direct propulsion (as in a motor), instead changing its buoyancy to move up and down in the water column and using wings to translate this motion from vertical to horizontal (a.k.a. gliding). This low power design means microstructure data can be collected continuously over a time period covering weeks, even months, with minimal intervention.

Small boat crew filming a T-glider in trial deployment.

During SPURS, one T-glider is covering the upper 230 feet (70m) of the water column while stationed in a small area close to the highly-instrumented WHOI mooring, while the other T-glider is covering the upper 660 feet (200m) of the water column while doing continuous transits between the WHOI mooring and PMEL-N mooring.

So far, more than 30 VMP microstructure profiles have been taken by two twelve-hour shifts working 24/7. With the minimal additional amount of effort required to deploy and to periodically checkup on the two gliders, we have collected over 700 additional profiles of the upper ocean from the gliders. Utilizing these two different platforms simultaneously has a dramatic positive effect on our sampling efficiency, and illustrates why autonomous sampling techniques have become much more common in recent years.

The measurements of microstructure variations in temperature, salinity, and velocity are crucial to SPURS estimating the salinity balance.  We need to know how the less saline waters to the south and south are mixed with the saltier waters near the salinity maximum in the North Atlantic.

Maybe, after all, it is like the stock market! The “value” (measurement) of our “commodity” (salinity) depends on a complex global “marketplace” (a salinity balance equation) forced by wind, evaporation and precipitation and “trading” in complex oceanic processes (circulation and eddies) acting in the end through “derivatives” (turbulent mixing) to determine the values we see.  Maybe these oceanographers are in fact sitting on a gold mine!

Truth be told, their mathematical wizardry is focused on understanding the ocean and the water cycle, not the stock market and the business cycle. However, old Benoit Mandelbrot was entirely correct! A few brilliant men like him can live in both worlds and we all profit.

Salinity Processes in the Upper Ocean Regional Study (SPURS): Starting A Career In Oceanography And The Global Water Cycle

September 27th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

The SPURS work has renewed interest in the broader community in studying the ocean to better understand the global water cycle, heating and cooling of the oceans, and oceanic mixing.

Julian Schanze of Woods Hole Oceanographic Institution/MIT is about to complete his Ph.D. in physical oceanography under the supervision of Ray Schmitt. Julian and Ray are on the Knorr to study ocean salinity, the water cycle and mixing in the ocean.

Julian Schanze at work.

Raymond Schmitt on the Knorr.

For his Ph.D. project, Julian is trying to estimate how much mixing occurs in the ocean. For this, he is using satellite datasets on surface fluxes of heat and fresh water and a concept known as power integrals. This is a mathematically complex subject, so let’s avoid the technical details and consider it in simpler terms.

Consider that, broadly speaking, the Earth is heated near the equator and cooled near the poles. For the equatorial and polar regions to not heat up or cool down, respectively, the excess heat must be transported away from the equator and towards the poles through mixing. The same approach can be used for the water cycle (which creates salt differences) as well such as ocean density and other, let us say “weird” ocean variables. For example, oceanographers consider the “spiciness” of ocean water as a measure of how warm and salty it is. So Julian is doing something really cool and looking at not just at heat moving through the ocean, but density and spiciness fluctuations as well. These are directly related to vertical and horizontal mixing in the ocean.

The equations that govern these power integrals relate the production of heat and salt variance (in our example, heating at the equator and cooling at the poles) to the destruction of variance (mixing) in the interior ocean. However, Ray and Julian found something curious: Under the right circumstances, the ocean interior can produce density variance rather than destroy it. The reason for this is double diffusion or salt fingers. When warm, salty water is found atop cool, fresh water, heat is diffused faster than salt in the ocean, leading to the formation of cold and salty “salt fingers”. These salt fingers transport salt downward and can create sharp density gradients. The SPURS region is top heavy in salt and therefore a likely place to find salt fingers.

On this SPURS cruise, Julian is trying to extend his understanding of mixing in the oceans from theoretical studies to hands-on work with the data. He is hoping the data will help him constrain uncertainties in the global maps of the water cycle and the heat budget that he has assembled. But while the approach he has taken in his dissertation allows him to calculate the total sum of mixing in the ocean, it does not constrain where the mixing occurs. This is where instruments deployed in SPURS enter the picture. Some of the SPURS instruments specifically allow for mixing in the ocean interior to be estimated by recording miniscule changes in temperature, salinity, and velocities in the ocean. The Vertical Microstructure Profiler and several of the gliders equipped with similar technologies allow oceanographers to estimate mixing quite precisely.

Night deployment of Velocity Microstructure Profiler.

Sensor package on VMP.

On board, Julian is in charge of the Lowered Acoustic Doppler Profiler (LADCP), an instrument lowered on a wire that records horizontal velocities in the ocean by pinging sound waves off small particles that float in the water. This requires him to prepare the instrument for deployment, charge its batteries and process the data after the retrieval.  The LADCP helps identify good sites for mixing by measuring where the velocity changes most rapidly with depth.

How did Julian get to be such an intelligent man? He tells me that at age seven, he moved close to the North Sea in Germany and became fascinated by the ocean. He soon became a keen sailor and decided to complete a four-year B.S./M.Sci. degree in oceanography at the University of Southampton in England. While his research has been largely focused on using satellite data to estimate the global water cycle (80-90 percent of which occurs over the ocean), he is thrilled at being able to go on a month-long research cruise to get in touch with the subjects he has been studying for the last 9 years. His fascination with satellite remote sensing and his research in oceanography are perfectly combined in NASA’s work on SPURS and the advent the Aquarius satellite, to measure sea surface salinity from space.

Everyone on Knorr believes that Julian has a stellar career in front of him!

Salinity Processes in the Upper Ocean Regional Study (SPURS): Engineering of R/V Knorr

September 25th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

The proud R/V Knorr engineering staff in the ship’s control room.

The Research Vessel Knorr is a fantastically capable oceanographic research vessel. She has traveled over 2 million miles and explored all the major oceans in her around 40 years of service.

As a visiting oceanography research crew, we have our space on the ship, for which we have free run. We are mostly in the main labs, on deck, or in the mess (getting fed very well indeed!) Much of the ship is off-limits to personnel other than the crew. I asked for a tour so I could give you a quick view of some “hidden” portions of the ship that make everything work. The daily routine is for the scientists to request that the ship, with her propulsion, station-keeping, cranes, winches, and capstans, to go here, stop there, stay still, lift this, pick up that… and so on, with only vague appreciation of the engineering feats behind these daily miracles.

I was privileged to get a tour of Knorr’s engineering space from the Chief Engineer Steve Walsh. He has been with Woods Hole Oceanographic Institution and aboard the Knorr for many years and participated in the vessel’s complete refit in 1991.

In 1991, the ship was basically cut in two pieces and 34 feet were added to her mid-section. The new engine room was placed in the new section and the space freed up in the after section (the old engine room) is now used as a workshop, welding room, and scientific cargo space.

Knorr’s machine and welding shop.

Knorr still has the old engine order telegraph connected to the bridge.

At the noisy heart of the ship are the engines (3500 Series Caterpillar). These run the four generators that supply 600V energy for all the ship’s electrical needs (which are many). The voltage is stepped down for various different purposes to 480V, 220V, and 120V (like in your house). The generators drive electric motors for primary propulsion, thrusters, and supply power for air conditioning, refrigeration, cranes, winches, lighting, computing, navigation and the coffee machine. According to Steve the most critical elements by far are the air conditioning and the coffee machine.  OK, he’s half-joking…but I know he is serious about the coffee machine!

One of the electric motors for propulsion.

Upper deck crane on R/V Knorr.

It seems to me like the Knorr is, in some ways, like my all-electric home back in Maryland. When the power goes out, it’s a hollow, dark, cold shell of a place. Except on Knorr, we have the power company living in the basement using diesel engines to run the generators to keep our lights on. And unlike my house, the Knorr can also get up and go wherever oceanography takes her and use a crane to pick up the garage and car (or 10,000-lb mooring anchors) to go along for the trip.  Knorr has all the comforts of home, work, and play for our 33 days at sea. They are all in one awesome package. All powered by home-grown, engineer-maintained, electricity.

Coffee anyone?

Knorr Chief Engineer Steve Walsh enjoys a cup of coffee.

Salinity Processes in the Upper Ocean Regional Study (SPURS): Life in the Sargasso Sea

September 24th, 2012 by Maria-Jose Viñas

By Eric Lindstrom

John snags a flying fish in mid flight.

There are not many places in the open ocean that get their own special name as a “sea.” Most seas are what we call marginal seas – offshoots of the major ocean basins.

The Sargasso Sea, as a vast track of the western subtropical North Atlantic Ocean is known, has a special characteristic – something noted by Portuguese sailors for centuries and even visible from space. It is the home waters of Sargassum, a genus of brown macroalgae (seaweed) that inhabit the open ocean. The sea is named after the seaweed and it seems that small clumps are nearly always within sight of the ship (we have yet to see giant mats of the stuff in the SPURS region). Anyway, the Sargasso Sea is special because of a plant. Well, it is more complicated than that!

A patch of Sargassum at the surface (Photo: Julian Shanze.)

Sargassum, up close.

Closeup of Sargassum.

In my opinion, the really cool thing about Sargassum is that each clump can be a teeming ecosystem by itself. Several varieties of fish (e.g. Sargassum fish and flying fish), crabs , and nudibranchs live in close association with the weed. Each clump is a complex island of life floating free at the surface of the deep ocean. When you are out here in the vast emptiness of the open ocean, it is just hard to imagine how this intricate web of life came to be, survived, and actually thrives. Every time I am in the Sargasso Sea, it seems such a wonder.

A flying fish.

Barnacles on French glider recovered by Knorr.

We had spectacular sunset last night and I was reminded of the old adage: “Red sky at night, sailor’s delight. Red sky in morning, sailor’s warning.” Here we are still in proximity to Hurricane Nadine and is this saying true, or is it just an old wives’ tale? Like the answer to most questions, there is a web site for that. In fact I think it may be true for us; we are well south of the hurricane weather and forecasts have good weather for in days ahead.

Sunset sen from the Knorr.

An interesting sidebar to today’s blog topic is another kind of life we have found in great abundance at our SPUR study location. It was a mystery for a few days – we were seeing lots of floating microscopic reddish dusty particles. Some said it looked a little like sawdust (but where are the trees?), and some wondered whether it was floating dust from the Sahara. Well, thank goodness for the Web again. I discovered that it’s a bloom of an important nitrogen-fixing bacterium (Trichodesmium) also known as “sea sawdust.” It certainly reinforces the idea that a key to identification is a good description!

Trichodesmium in a bucket of sea water.

A Trichodesmium bloom in the Pacific Ocean seen from space.

Trichodesmium, it turns out, just loves these sea conditions – just as much as SPURS oceanographers love the North Atlantic salinity maximum!

Notes from the Field