The "Iceberg" Correction

Since leaving the Chilean coastline, the THOR team has been exploring the sea floor… with sound.  Similar to the way that sea mammals communicate with each other over long distances and submarines avoid obstacles, scientists use sound to “see” the bed surface and ultimately map the ocean bottom.   Sound waves are generated from beneath the ship from an instrument called a multibeam echo sounder – it is in effect a giant loud speaker pointing downwards and away from the vessel on either side. 

Here’s how it works. The multibeam sends a “ping” (like you hear in the movies about submarines); a pulse of high-pitched sound that moves down and away from the bottom of the ship.  Each ping contains 432 individual depth soundings (which is why it is called multibeam) that in the shape of a fan. The angle and trajectory of each sounding, the time traveled and distance away from the source of sound combined with the properties of the ocean (temperature and salinity) are used to calculate the velocity of sound through water.  The result is a swath “image” of sound velocity, where the swath’s width is the maximum angle the outermost depth soundings have achieved as they travel some distance to the seafloor and back.

Each “ping” is displayed as a line of points. This image shows multiple pings. Each “ping” line is composed of 432 depth soundings – you may even be able to see the individual points.  )

Each “ping” is displayed as a line of points. This image shows multiple pings. Each “ping” line is composed of 432 depth soundings – you may even be able to see the individual points. )

So for deeper water, the swath will be wider and for shallower water, the swath will narrow.  Each of the reflected soundings are then processed to show a continuous colorful ribbon, or snail trail of the seafloor below the ship. The colors are equivalent to the distance the sound wave has travelled through the depth of the water, where the longest distances, which are blue, represent the deepest parts and the red colors are shallower features.  Collectively they “paint” a picture of the seafloor’s surface in 3-dimensions.

Most oceanographic research vessels employ the multibeam echo sounder whenever they can, the combined results of which can paint a detailed picture of processes that we could never witness ourselves through the depths of the ocean. Marine geologists, oceanographers and glaciologists studying Thwaites Glacier will use this information to unravel the processes operating between the ocean and the ice shelves.  Features such as furrows and plough marks indicate past movement of the ice shelf and icebergs dragging along the sea floor, channels show where water flowed beneath past ice sheets, and high ridges or peaks may have been places where ice was once “grounded” (or resting on) the sea bed, a situation which may act to stabilize an ice shelf or glacier, and allay or even stop its’ backwards retreat.

Seafloor bathymetry off of the Cosgrove Islands, Antarctica. This broader image is assembled from many transits by the ship, each with a sonar image of the seafloor below.

Seafloor bathymetry off of the Cosgrove Islands, Antarctica. This broader image is assembled from many transits by the ship, each with a sonar image of the seafloor below.

Ali Graham and Kelly Hogan examining bathymetry data.

Ali Graham and Kelly Hogan examining bathymetry data.

The science team also use these echo sounders to make decisions about where to gather samples from the sea floor by producing an image of the layers of muds, sands and rocks just below the surface. The samples help to decipher a longer term history of how ice interacted with the ocean, and ultimately how the ice will behave in the future.  The accuracy of the data is critical to ensuring that the location where those samples are taken will not be in a place that might damage the instruments (coring devices)  used to collect the samples. 

An important part of collecting accurate multibeam data is accounting for a variety of physical parameters. On the ship, we are effectively a bobbing cork in the ocean. Combined with the echo sounder, a set of reference points are made with each “ping” to account for this unpredictable motion.  Similar to how a gyroscope works, the reference point data accounts for real time conditions such as roll (side to side) pitch (forward and backward motion), heave (the up and down motion) and yaw (the horizontal or side to side motion). The data processing software then applies clever  corrections to make sure that the data accurately represent the true position and orientation of each sea floor sounding. 

Two days after the ships passage through rough seas, THOR team members Kelly Hogan and Ali Graham noticed that the seafloor bathymetry data output suggested that the seafloor had a tilt when they knew it should have been flat.  In order to understand if the tilt was real, they needed to do an experiment.  They would have to go back over area that had already been scanned, but in the opposite direction.  The difference in the two data sets would show an equal and opposite tilt (if they were right that the tilt was in error) and it would help them calculate the degree of that error.  In order to accomplish this, the seafloor would have to be flat and they would need about an hour’s worth of backtrack scanning of the same flat seafloor.

Icebergs are made of freshwater ice and compacted snow. They typically originate from the breakup of glaciers and ice shelves that terminate in the ocean.

Icebergs are made of freshwater ice and compacted snow. They typically originate from the breakup of glaciers and ice shelves that terminate in the ocean.

Enter the icebergs.  The first significant iceberg that appeared was close enough to provide a terrific photo opportunity for the passengers, and the crew of Nathaniel B. Palmer made a spontaneous viewing loop around the iceberg. The ship had also entered the Bellingshausen Abyssal Plain in the Southeast Pacific Basin, the flattest area of the transit before reaching the Antarctic continental shelf.  So the sea floor conditions were optimum. 

Sonar image of our maneuver around the iceberg!

Sonar image of our maneuver around the iceberg!

 Another iceberg on the horizon looked to provide the appropriate distance and time it would take to conduct the necessary scan.   Using that iceberg as a goal post, they made the first multibeam swath, rounded the second target iceberg (which was as photogenic as the first), and retraced the initial snail trail long enough to determine the degree of error and apply the correction.

These icebergs which originated from Antarctica may be at least a year old, but their location in warmer waters will melt them very quickly, as much of their rounded surfaces are already showing.

These icebergs which originated from Antarctica may be at least a year old, but their location in warmer waters will melt them very quickly, as much of their rounded surfaces are already showing.

Two icebergs later, the problem was solved and the colorful ribbon of seafloor bathymetry was returned to its horizontal self. These kinds of corrections are not uncommon and ensure that the data are good for when the THOR team reach Thwaites itself, where the accuracy of the sea floor measurements will be important for selecting the best sea floor to sample and interpreting its history.

Here are some of the other icebergs we have seen on our traverse through the Amundsen Sea. Icebergs are categorized by shape, age and how they formed. 

This is classified as a tabular berg - a blocky, multi-year, freshwater ice berg because of its steep sides and flat top.

This is classified as a tabular berg - a blocky, multi-year, freshwater ice berg because of its steep sides and flat top.

Drift sea ice is young flat ice floes formed from sea water at the sea surface that can move with current or winds.

Drift sea ice is young flat ice floes formed from sea water at the sea surface that can move with current or winds.

Other iceberg pics….

Sea ice (foreground) with an iceberg protruding and more bergs on the horizon.

Sea ice (foreground) with an iceberg protruding and more bergs on the horizon.

As icebergs age, they melt and crumble to produce amazing sculpture.

As icebergs age, they melt and crumble to produce amazing sculpture.

Penguins! Penguins like ice. Ice makes them happy.

Penguins! Penguins like ice. Ice makes them happy.

Here’s the Palmer nosing its way through sea ice. Icebreakers like the Palmer do not crash through ice, but ride up on top of it and crush the ice with the ship’s weight. Sometimes it takes several tries, and you can see here where the Palmer rode up onto this ice leaving an impression from the hull and long cracks through the ice.

Here’s the Palmer nosing its way through sea ice. Icebreakers like the Palmer do not crash through ice, but ride up on top of it and crush the ice with the ship’s weight. Sometimes it takes several tries, and you can see here where the Palmer rode up onto this ice leaving an impression from the hull and long cracks through the ice.

Landfast ice or “Fast” ice is multi-year flat, solid ice made of both seawater and fresh water (from snow) that is attached to the far continental margin and can include grounded icebergs such as the one in the background). Note the penguins in the foreground!

Landfast ice or “Fast” ice is multi-year flat, solid ice made of both seawater and fresh water (from snow) that is attached to the far continental margin and can include grounded icebergs such as the one in the background). Note the penguins in the foreground!

The J-Team

None of the field-based science conducted on board and beyond the Nathaniel B. Palmer would be possible without the support of the marine technicians.  They are in charge of on-board deck operations, ship to shore operations, and the safe deployment and recovery of scientists, scientific tools and equipment.

Within a day after leaving Punta Arenas, marine technicians Jennie Mowatt and Joee Patterson were tasked with the recovery of a state-of-the-art Autonomous Underwater Vehicle (AUV) that was being field tested in the Straits of Magellan prior to its deployment in the Amundsen Sea.

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Jennie Mowatt (Left) will celebrate 4 years in her position in May; Joee Patterson (RIght), 3 years in May.  They love their jobs and the great opportunity to problem solve. The work is always different, sometimes hugely frustrating but also hugely satisfying.  They appreciate seeing Antarctica in ways most people never do.  “We have seen the entire profile of the ocean around Antarctica - from the top to deepest depths. I have put my hands on creatures from 1500 m deep below the surface.” -Joee Patterson

The pressure is on for the successful launch and retrieval of this “torpedo of science”, which can accommodate up to 20 different sensors, including an obstacle detection sonar instrument in the nose cone.  The design is based on devices used by the petroleum industry and for national defense purposes, taking advantage of its ability to dive deep (up to 1000 meters), but with payloads that will measure a variety of characteristics of the ocean, map the seafloor under Thwaites Glacier and collect information on what is happening at the interface of both. Something that was not possible until now.  Much was riding on this early test.

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The morning of the test was perfect.  Cloudless skies were mirrored by the nearly still water of a small cove in the Straits of Magellan. The Hugin, built by the Kongsberg company (who also happen to provide the technology for multibeam bathymetry), is named for one of Odin’s ravens that travel the world to gather information.

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Prior to launch, the science team meets with the entire Marine technician support group to go over safety and the sequence of activities. Jonas Andersson, one of the TARSAN scientists that manages the Hugin, rolls out the AUV from a specially made garage.

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Once the bridle was attached and rigging set to lift Hugin off the ship, Joee and Jennie hopped in the zodiac to prepare for Hugin’s deployment.

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Once Hugin is in the water, the ship moves away and Jennie and Joee move in to watch over the AUV as it takes on water (shedding buoyancy) in preparation for diving.  Once it disappears, they return to ship.  Four hours later, the weather has turned ominous.  The skies are heavy, dark and spitting rain.  The winds have picked up and the sea surface is rough and rolling.  Hugin’s bright orange skin is spotted and Joee and Jennie are off in the zodiac to begin the process of bringing Hugin home.

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Unbeknownst to those of us observing on deck, the marine technicians (known as the MT’s) had met and devised a plan, to include several contingencies for the AUV’s retrieval based on changes in the environment or equipment condition.  The first unplanned situation was the unexpected presence of a South American fur seal who found the AUV interesting.

“The seal was doing acrobatics while we were out there, and I thought it might jump in the zodiac. He came at us quickly and so I scooted the boat away, and then he just disappeared”, said Joee.

Their first step was to attach the bridle system using the hooks on top that would be used to hoist the AUV onto the ship.  The plan was that one person would be in charge of maneuvering the lighter weight and buoyant zodiac while the other wrangled the two ton AUV.

Assuming that the AUV would move more slowly and that the wind and the swells would impact the zodiac, their plan would take advantage of the zodiac’s maneuverability. The goal would be to tie the AUV to the side of the zodiac, which is a typical way of using a smaller thing to tow a
larger thing. “Once we got out there, we figured out that our plan where one person did the maneuvering and one person to do the wrangling was not the optimum situation. The contingency was then to tow it astern of the zodiac. This presented other challenges.  The Hugin acts an anchor so we have to put a lot of power on the zodiac to get the Hugin to move at all.  Then once you get the Hugin moving you don’t want to get it moving so fast that it moves past you.  Add to that the swell and wind working against us as we try to keep a heading and keep it trapped behind us.”

Jennie summarized the complexity of the situation, “It was our first time working with the bridle system and we didn’t know how well the zodiac would travel with the AUV.  I definitely would not have predicted its hydrodynamic behavior as we tried to tow it behind the zodiac. That was the thing that we couldn’t have predicted until we were actually doing it.”

Following the successful delivery the Hugin to the deck, Jennie and Joee discussed adding a third person for next retrieval, even if the conditions are calmer.  “It would be good to have more hands to pull the lines, and to use extra slip lines on the vehicle itself.  The weight of the bridle makes it want to sink, so keeping that in the boat will enable better control of the AUV.”

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I was amazed at their perseverance and their calm under what was obviously difficult environmental conditions.  Yet for the J-Team, it was another Friday at the office, and problem solving is why they are MT’s for science.

A Room with a View

I was going to write the next blog on THOR science activities to be conducted during  NBP1902 , but the struggle to not bury myself in my bunk as the seas got rougher and rougher forced me to seek a room with a view.  Since I needed to focus on the sea to avoid seasickness, I decided the sea should be the focus of this next post. 

NBP ‘s current path approaches the second of two low pressure systems. Waves approaching 15 feet are regularly inundating both the lower deck and the main where our berth is located.  Viewing the maelstrom from the large windows  of the aft winch control room where I’m sitting, I can forget the sea sickness for a bit as I watch the incredible power and beauty of the sea, eyes fixed on the distant horizon as a rocking and rolling NBP slowly but very steadily works its way south.

 Large wave on the starboard side of the aft deck.

It is after noon, and I realize I have missed lunch when suddenly from the radio comes a message that everyone outside needs to come in due to heavy seas.  Feeling somewhat normal and wanting to know how fast or how close the ship is moving into the upper areas of the low (very cyclonic looking in my opinion)  I head to the bridge.  You wouldn’t know that the NBP is 6,800 long tons (15,232,000 pounds, or 6.9 million kg) in mass with 3000 10’ x 40’ (3 x 12 m) steel plates (the bow plates are 1 9/16 inches or ~4 cm thick) carrying 425,000 gallons (1.6 million liters) of gas. It was moving around with all the ease of a cork in a bath tub.

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Left: A computer model of the low pressure system driving the waves.  The NBP is the red target between 1016 and 1012 pressure contours. Right: This image shows the ship’s traverse to the Amundsen sea.

Meanwhile below deck, science planning and activities persevere.  

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Left: The monitors show the depth to the seafloor using a multibeam generated sound wave - 4426 meters (13,278 feet) with the reflected signal in two views. The range of colors indicate depth-blues are deepest and reds are shallowest.  Right: Chris Linden, the NBP multibeam manager and expert, points out the location of the transducers that generate the sound waves and the instruments that will receive the signals that have been reflected off the seafloor.

The THOR team and NBP multibeam specialist Chris Linden set up the EM122 multibeam echo sounder to start gathering bathymetry information. As soon as the ship passed beyond the legal border of Chile, they would take advantage of the adjusted ship traverse to gather high resolution seafloor bathymetry from an area that hasn’t been mapped previously. There will be some challenges to acquiring the return signal to include the slow ship speed and the rough seas. The waves impact the ship’s hull to create interference (bubbles, for example) around the receivers, impacting the quality of the data.

Other ITGC scientists whose constitutions are more stalwart than mine, sit at workstations and tabletops that are festooned with pieces of anti-slide fabric (much like rubber carpet pads) utilizing predrilled holes for eye-screws that you tie bungee cords to; these go over top of your valued electronics to hold them in place.

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Author Elizabeth Rush is ready for the rough sea crossing!

Back on the bridge of the NBP,  I stumble around, still developing my sea legs as the motion of the ship is amplified due to its height off the water.  Yet the near 360 degree view of the waves are both captivating and hypnotic, helping to subdue some of the seasickness.  In fact, sitting on one of the control chairs is like having an unlimited ticket on the earths most incredible amusement park ride.  But as we roll upwards of 20 degrees each way,

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 Tilt-o-meter and barometer on the bridge of the NBP

knowing that the larger sea is coming, the amusement fades for a few moments.  THOR team member and PhD student Victoria Fitzgerald adds “There is no getting off this ride”. According to Chief Mate Rick Wiemken, there is a buoy in the area that has measured a wave height of 80+ feet. That is the highest wave ever recorded!  

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NBP pitches forward into a large wave.

One would think TARSAN’s successful deployment of the Hugin AUV would appease Ran (which is the AUV’s unofficial name) the Nordic goddess of the seas. The crew of the ship reassure us that the storm will still pass in front of us.  And while we will see a couple more days of rough seas, the Palmer (with 80 research cruises since coming into service in 1992) will handle it. We will have gained a deep appreciation and respect for the amazing people who are taking care of us, and the forces of nature around us that we hope to better understand.

Departure Update!

#NBP1902 is declared fit and will depart at 3:30 pm (Punta Arenas time)!

Straits of Magellan, here we come!

White boards are the information superhighway of the NBP.

White boards are the information superhighway of the NBP.

We are finally getting underway, heading west instead of east to cross the Drake passage.

For the next 24 hours, we should be able to get emails fairly easily, so now is a really good opportunity to submit your questions: Linda.welzenbach.guest@nbp.usap.gov

Your name, where you are from and your question (and our answers) will be posted on the blog. The best question (and I don’t yet know how they will be judged) will be announced at the end of the cruise along with an Antarctic swag prize!

Rice University’s EEPS staff Linda Welzenbach’s office (a room with a view!!) on board #NBP1902.

Rice University’s EEPS staff Linda Welzenbach’s office (a room with a view!!) on board #NBP1902.

First Things First...

After 24 hours of travel from Houston, Texas to Punta Arenas, Chile, I arrived exhausted yet excited (and perhaps just a wee bit anxious of the unknown) to be part of something very unique.  My name is Linda Welzenbach and my role on this expedition is to share the scientific discoveries that will come from our journey to Antarctica on board the RVIB (research vessel/ice breaker) Nathaniel B. Palmer (NBP).  Akin to a spacecraft exploring new frontiers beyond Earth, the Nathaniel B. Palmer and her marine operations specialists will navigate safe passage through Antarctica’s icy waters for the 26 ITGC scientists and the wide array of science activities they have planned over the next two months. 

This first post will bring you aboard to see what she has to offer, and how scientists become seafaring explorers.  NBP’s origins and history will be highlighted in a later post.

Welcome to the Nathaniel B. Palmer! She is a beautiful ship, with commodious berths…if you can find the one green door among many that is assigned to you.

Welcome to the Nathaniel B. Palmer! She is a beautiful ship, with commodious berths…if you can find the one green door among many that is assigned to you.

The NBP’s vitals can be found on the USAP website HERE

Radio journalist Carolyn Beeler models the steel toed boots needed to work on deck and onshore.

Radio journalist Carolyn Beeler models the steel toed boots needed to work on deck and onshore.

Upon arriving Sunday evening, we discover that the ship would be leaving a day early. The NBP was thirsty and if we wanted to stay on schedule, we would need to leave for the “gas station” Monday evening.

Prior to departure, we head to the U.S. Antarctic Program warehouse for orientation and distribution of the necessary Extreme Cold Weather (ECW) gear.

We are on board for just a couple hours, yet the first task will be to participate in a simulated exit. As part of that exercise, we must be able to put on flotation suits, which are required for situations that call for abandoning ship (below). During the cruise we will practice several more drills of this nature, to build muscle memory in the event of a real emergency.

In anticipation of an evening departure, we met in the laboratory to unpack and sort through all the core processing supplies, stowing them securely in anticipation of the rough seas that characterize Drake’s passage. To see live weather, and forecasts, click HERE.

Interpretive dance is the best approach for getting into the flotation suit.

Interpretive dance is the best approach for getting into the flotation suit.

Dr. Rebecca Totten Minzoni (left) and her Ph.D. student Victoria Fitzgerald successfully complete the flotation suit challenge.

Dr. Rebecca Totten Minzoni (left) and her Ph.D. student Victoria Fitzgerald successfully complete the flotation suit challenge.

There are two covered life boats for passengers- each one can hold the full complement of scientists.

There are two covered life boats for passengers- each one can hold the full complement of scientists.

THOR scientist Dr. Alastair Graham in the surprisingly comfortable life boat.

THOR scientist Dr. Alastair Graham in the surprisingly comfortable life boat.

THOR team members (l to r)- Rebecca Totten Minzoni, Alastair Graham, Rachel Clark, Rob Larter- sort through and distribute core processing supplies in the core processing lab. All drawers and cabinets have dog-locks to ensure they do not open during passage through rough seas.

THOR team members (l to r)- Rebecca Totten Minzoni, Alastair Graham, Rachel Clark, Rob Larter- sort through and distribute core processing supplies in the core processing lab. All drawers and cabinets have dog-locks to ensure they do not open during passage through rough seas.

A bit after 7pm, #NBP1902 left Punta Arenas to refuel. As of this posting, we are back in Punta Arenas, and remain here until maintenance activities have been completed. For more information about that, go HERE.

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Linda is the science communications specialist in the Department of Earth, Environmental and Planetary Sciences at Rice University. She is a geologist and veteran of two expeditions to collect meteorites from Antarctica. Her role for THOR is public outreach, and so she will communicate science activities during the first scientific cruise in 2019-NBP19-02 and serves as the project webmaster.

Sea Ice!

Like all good explorers who are preparing for the unknown, I went looking for information about what to expect in the place where we will spend the better part of two months. Thanks to Rob Larter who had tweeted information about the sea ice in December, I found Sentinel-1 SAR imagery imagery that shows the coverage as of TODAY! You can go see this for yourself at: https://www.polarview.aq/antarctic . #ThwaitesGlacier (on the grid at 75°30′S106°45′W) is the slight tongue extending out along the 106W gridline, and the area in front of it looks to be breaking up.

IMAGE FROM POLAR VIEW

IMAGE FROM POLAR VIEW