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Conductivity- Temperature-Depth Graph

Meridian Passages, Volume XIII, Number 29

Central Pacific Edition

Sound Advice

Is There an Echo in Here?

CTD (Conductivity-Temperature-Depth)

The amazing images we are seeing from the ocean floor are derived from echoes of sound bouncing off the undersea terrain and returning to our sonar. Making sense of this information depends critically on the speed of sound in the water. This varies quite a bit depending on conditions, so the REMUS is equipped with a CTD (Conductivity- Temperature-Depth) sensor that is used to calculate sound speed. Although we are only interested in the speed near the bottom, the sensor operates as soon as it hits the water and so will give us measurements all the way down. We took the opportunity to look at this “sound velocity profile” to see what it might tell us.

Under standard lab conditions, sound travels about 1,560 meters per second in seawater (much faster than the 340 meters per second in air). That’s just about a mile per second. But it varies quite a bit as the elasticity* of the water changes in response to changes in temperature, depth, and to a lesser extent, salinity. The biggest effect is temperature, which has a very complicated influence on elasticity due the the unique structure of the H2O molecule. With most fluids, sound speed decreases with temperature, but with water it actually increases by about 3 m/sec for every 1 °C increase. Sound speed also increases with depth (because the pressure increases and changes elasticity) by about 1.7 m/sec for every 100 m change in depth.

Conductivity-Temperature-Depth Graph
The measured temperature and calculated sound velocity changes as the REMUS descended to the depths on one of its missions.

The plot on this page shows how the measured temperature and calculated sound velocity changed as the REMUS descended to the depths on one of its missions. This is a classic profile. The temperature at the surface was a balmy 27.5°C (82°F), but dropped sharply to about 5°C just 1,000 m down. By the time REMUS reached 5,500 m it was a bone chilling 1.3°C, just above freezing. Influenced by the temperature, the sound velocity dropped sharply down to the first 1,000 m. At that point, the relentless increase in pressure with depth took over as the temperature stabilized, and the sound velocity rose back to and above its surface value. (Salinity effects were also calculated but were small.) The sound speed changed by more than 4% over this range.

Besides its effect on the sidescan sonar, changes in sound velocity cause the paths sounds travel to vary, much like a lens alters the path of light. As a wave of sound passes through the water, some parts of the wavefront move faster than others causing the sound to bend away from areas of higher velocity. A particular consequence of this can be seen if we look at the shallower (first 200 m depth) of this plot. Mixing of surface water warmed during the day to deeper regions, and subsequent cooling at night, will typically cause an “isothermal” (constant temperature) layer near the surface, or even a temperature “inversion,” where it gets warmer as one goes deeper, to a point. This can occur in tropical waters thanks to intense solar heating and strong wave action. Below that layer, the temperature will drop as described earlier. This thermal layer can cause large variations in sound wave propagation. Submariners take advantage of this as a submarine lurking just below the layer can be “hidden” from sonars listening at the surface, since its sounds will bend to greater depths. On the other hand, a ship on the surface may escape the attention of the submarine below the layer since its sounds may remain confined to shallower regions. In some cases, the sound can be trapped in a “surface duct” and propagate for many miles horizontally, while making not a whisper below the layer.

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This dramatic sidescan image mosaic shows an underwater landslide with material flowing from higher elevations on the upper left to flat terrain below. The feature is about a mile across and lies at a depth of about 18,000 feet.

Meridian Passages, Volume XIII, Number 28

Central Pacific Edition

In the Zone

Elgen Tells More Than You Wanted to Know About Time

Harrison’s First Marine Clock, H1, 1735
Harrison’s First Marine Clock, H1, 1735

There is a direct but unconnected relationship between the measurement of time and the world in which we live. Daily time is tied to the movement of the sun, but time standards are a human construct. Believe it or not, the United States did not have official universally accepted time zones until Congress passed The Standard Time Act of March 19, 1918, and that was just 9 years before I was born. Yikes! I’m nearly as old as our times zones in the United States!

In the centuries when the world was believed to be flat, and it was thought that there was nothing but water to the west between Europe and China there was little transportation or commerce between the few people then on earth, and little need or desire to keep track of time. The sun came up, and the sun went down, and for those living so went the days of their lives.

Marco Polo, Christopher Columbus, Magellan, and several other adventurers discovered there was a very large world out there that could supply things that would add wealth to their countries’ coffers. This immediately stimulated transportation to acquire the wealth overseas that could be had for the taking, and ships in the oceans needed a standard means of telling time to be able to navigate precisely across those oceans to access that wealth.

Greenwich Mean Time (GMT) was established when the London Royal Observatory was built in 1675. I t provided a standard time connected to the stars that ships needed so they could navigate across the oceans to provide the means of commerce. That spawned the need for clocks that were able to keep accurate time aboard ships in order to calculate longitude. The first useful marine chronometer was invented by John Harrison in 1761. His story is told the the book Longitude by Dava Sobel, a classic tale of the founding of an accurate chronometer for ships. Another excellent (and more technically accurate) source i s Plotting the Globe by Avraham Ariel.

Except for ships at sea, there was little need for a standard time zone as most people in the United States and around the world were happier to have their time controlled locally. Communities of any size had the their own observatories that would measure exactly when the sun was highest and everyone would then set their clocks to 12 o’clock noon. Locally it worked great and everybody was quite content with it.

Even at seaports around the world the local observatory’s time worked very well for the ships in the harbor. Before ships carried radios, most major ports in the world had a ball like the one in Times Square (used on New Years Eve) that could be seen from almost anywhere in the harbor. At noon every day the harbor city’s local observatory would countdown to the handler of the ball so that it would reach the bottom at exactly 12 o’clock noon. If a ship’s navigator knew when the local time was exactly high-noon he would know what his longitude was, and vice-versa.

Decades before the U.S. Congress ever assigned the official time zones for our country the railroads had already found out that each city having its own special time was unworkable. So in the latter part of the 19th century the railroads divided the country into railroad time zones with most of the borders passing through the railway stations of major cities.

In 1883 on November 18 each railroad station clock was reset as standard time noon was reached in each time zone. This became known as “the day of two noons.” Detroit was the last major city to leave its local time zone. On the boundary between zones, the city adopted Central Time in 1900 and finally settled on Eastern Time with the rest of the state in 1916, two years before the congressional act that ended the confusion for good.

During the early part of the 20th century various countries accepted the GMT system with (usually) regional even-hour offsets, though there are some exceptions that use a half-hour offset and even a few locales with quarter-hour offsets. Nepal was the country last to join in 1986 with an offset of 5 hours and 45 minutes.

I have not mentioned the use of UTC (Coordinated Universal Time) which is “Z” or Zulu time, and will save that topic for the next time we meet.

— Elgen Long

REMUS Image of the Day

This dramatic sidescan image mosaic shows an underwater landslide with material flowing from higher elevations on the upper left to flat terrain below. The feature is about a mile across and lies at a depth of about 18,000 feet.
This dramatic sidescan image mosaic shows an underwater landslide with material flowing from higher elevations on the upper left to flat terrain below. The feature is about a mile across and lies at a depth of about 18,000 feet.


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Meridian Passages, Volume XIII, Number 27

Central Pacific Edition

The Team

Cast & Crew

Note: Photographer Bill and two members of the
crew not pictured – someone had to steer the ship!

The Meridian Passages staff have fielded requests for a list of personnel aboard. Included here are the 36 folks sailing on Mermaid (counting Alan who was with us March 4-14) and the Nauticos team ashore providing regular & critical support. Of course, there are also folks at WHOI, MMA Offshore, U. of Hawaii, ship agents, crews of SauVage & Machias, CARC Cedar Rapids, NOAA, NASA, and helpers scattered around the hemisphere, not to mention our friends & families at home who are missing us and helping in many ways.

Roles listed here are primary duties, though everyone pitches in to get the job done.

Alan Eustace – Expedition Leader

Dave Jourdan – Coordinator & Publisher

Elgen Long – Advisor



Spence King – Operations Manager

Tom Dettweiler – Technical Manager

Greg Packard – AUV Team Leader

Jeff Morris – Chief Sonar Analyst

Joe Litchfield – Ship liaison & Seadog

Christopher Griner – AUV Operator

Neil McPhee – AUV Operator

Mark Dennett – AUV Operator


Radio Communications

Tom Vinson NYØV – Comms

Rod Blocksome KØDAS – Comms Media

Bill Mills – Director of Photography

Bryan McCoy KAØYSQ – MacGyver


Education & Outreach

Sallie Smith – Teacher

Marika Lorraine – Journalist

Sue Morris – Imagery & Ops Support


At-Sea Support

Jon Thompson – Exhibitionist

Pam Geddis – Doctor & Impersonator


Ashore Support

Charlotte Vick – Ashore Logistics & PR

Louise Mnich – Negotiator & Legal-beagle

David Kling – Master of Coin

Jenne James – Ashore Coordinator

Bethany Lacroix – Website & Comms


Mermaid Vigilance Crew

Noe Flores Armenta – Master

Lania Kurniauan – Chief Officer

Rifky Harimadya – 2nd Officer

Oleksandr Baybak – Chief Engineer

Andriyanto – 1st Engineer

Samsul Bachri Leorima – 2nd Eng.

Sergiy Stepanov – ETO

Iksan Natta – Bosun

Abdullah Mahmud – AB

Ahmad Derita – AB

Burhan Andi – AB

Kasmawir – Oiler

Kasman Sonne – Oiler

Jan Pieter – Chief Cook

Mardan Andi Kanna – 2nd Cook

Susanto Doni – Steward


Message from SauVage

[In reply to our farewell message sent yesterday…]

Thanks for those sweet words. We never thought that our old sheet padding fabric would be so much appreciated! Enjoy the wines. We wish you the best for the research and we feel honored to have been part of this exciting mission. We read the books! So interesting! And meeting Alan is great. We are sailing in optimal conditions, no swell, good beam winds, smooth glide. Still 480 NM to go.

Cheers, Sophie, Didier, Cloe, Nino, Alan

The Fate of the Itasca

We know that the US Coast Guard procured ten cutters of the Lake class commissioned starting in 1928. Each carried the name of a lake in the United States. My research shows the US Government transferred the cutters to Great Britain in 1941 under the lend-lease program. The British rechristened the ships with new names and refitted the ships for war.

The Pontchartrain (HMS Hartland) and Mendota (HMS Walney) were both sunk by gun fire on Nov. 8, 1942 off the coast of Oran, North Africa and the Sebago (HMS Culver) was torpedoed and sunk by the German sub U-105 on Jan 31, 1942. The remaining seven former Lake class cutters (Chelan, Tahoe, Champlain, Itasca, Saranac, Shoshone, and Cayuga) were returned to the United States after the war – probably nearly worn out. The trail of Itasca (HMS Gorleston) ends in 1950 with it being sold for scrap.

My family once owned a 1950 Ford sedan. Perhaps it contained some of the Itasca’s steel?

— Rod Blocksome

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Meridian Passages, Volume XIII, Number 26

Central Pacific Edition


Alan Begins Journey Back to Civilization

We were sorry to see Alan depart today on the sailing vessel SauVage, bound for Funafuti, then Fiji, then the Mainland and eventually to Lancaster, PA. It will take him about five sailing days to cover the over 600 nautical miles to the Funafuti atoll south of here, and considerably less time to make it the rest of the way to Pennsylvania.

Unfortunately, owning to timing and short scheduling window of this expedition, Alan was unable to spend the entire search mission on board. However, the ten days he spent with us were a great experience for all. He was able to immerse himself in our operations, catch up with details of the analysis work that underpins our search having all the experts at hand, and dive into the technology of REMUS and our sonar analysis tools. In a few short days he became an integral part of the team and said he enjoyed the camaraderie. Before he left, he thanked the Captain and crew for their hospitality and left us with some words of support and encouragement.

Spence reported feeling separation anxiety in response to losing a shipmate. Doc Pam examined him, expressed only mild concern, and prescribed a dose of Oreos. Pam herself was seen trying to climb over the rail as the sailboat departed, but was restrained by Bryan who slapped a running taut line hitch around her wrist.

The crew of SauVage took on a load of fuel from us, and returned the favor with a swag bag of goodies. Included was a lube oil filter for the Engineer, a SauVage t-shirt, some fancy scarves, a postcard, and three bottles of spirits. Doc Pam immediately took custody of the alcohol, and said she would inventory it in her cabin. She expressed “concern” that it be administered properly. (Did we mention this is a “dry” ship?) After departure, we sent the following message to the Captain and crew of SauVage:

Thank you for your kind gift of nice wines, liqueur and colorful fabrics. These things thrilled our team. Our captain was most pleased at the sight of the fuel filters; our ladies were most excited for the chance to improve fashion around here; and we all are looking wistfully at the wines and liqueur. The vessel owners did not think to provide us any cork pullers. But we have engineers, so don’t worry about us.

We hope you get off to a good start and have a safe trip to Funafuti.

For Alan:

From all of us here we join together to say thank you for sharing time with us and showing your support in so many ways. We all share the passion for discovery, and we’ll pursue the truth wherever the facts lead us until the sea finally gives up her secret. We’re proud to sail for the Eustace Earhart Discovery Expedition. And yours was the most memorable arrival and departure we’ve seen yet.

The Eustace-Earhart Discovery Team

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