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JULY
11:
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Sub pilot Ken O'Brien and research scientist Edie Widder in the sphere of the JSL preparing to dive. The sphere allows an almost 360 degree field of view.
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From left to right are the ISIT camera in its housing, the fiber optic unit and the LoLAR.
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This deep-sea fish was tested for UV reflectance and transmitance.
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A bottom profile shows the scattering layer of a large mass of organisms between about 1,200 to 1,800 feet deep.
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Dr. Tammy Frank calibrates her Electrophysiological prep for the wavelenghts of light she will use in her threshold response experiments.
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The Tucker trawl was launched off the stern of the R/V EDWIN LINK.
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Click below to learn a bit more about this advanced and versatile deep-sea research tool...
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Accomplished videographer Brian Cousin is doing double duty on the Gulf of Maine cruise. He's gathering footage for a video about bioluminescence, and he's bringing the Gulf of Maine to your desktop as our @Sea correspondent. Click below to learn more about Brian...
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Is there a question you'd like to ask our intrepid correspondent? Send us an email at
AskAtSea@hboi.edu.
Selected questions will be forwarded to Brian, and we'll post the answers online.
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DISPATCH 4: Getting Down To Business
@Sea correspondent/photographer, Brian Cousin
R/V EDWIN LINK Mate, Matt Skelly at the helm during submersible operations. The ship must maintain position close to the submerged JSL.
July 11, 10:30 AM --
Drs. Edie Widder and Tammy Frank are in the JOHNSON-SEA-LINK submersible ready to make the first dive of the mission. Winds are 16 knots and seas 2 to 4 feet. Excellent conditions considering we are diving in the Gulf of Maine.
A sub launch is pretty cool to watch, especially if you've never seen one before. Even those still coping with the ill effects of being on the water have braved leaving their cabins for the event. It's the first time since leaving port that the entire science contingent has assembled as a group.
The giant A-frame lifts the sub off its' cradle and eases back until it is poised over the water behind the ship. When everything is set, the Sub Ops. director gives the okay, and the sub is lowered into the water.
Tammy Frank is in the aft compartment with sub tech and pilot Tim Askew, Jr. They report a good seal around the hatch, which is located on the underside of the chamber. The instructions to blow the drop lock and release the tow cable are given, and the sub is floating free, dropping back from the stern of the research ship. The hatch seal around the top of the sphere containing Edie Widder and pilot Ken O'Brien is positive. All systems look good and the sub has permission to dive.
The first objective of this dive is to characterize the water in terms of its transparency, or its ability to transmit daylight. The second is to find the depths the animals they want to study are living at, based on the irradiance (brightness) and spectral distribution (color) of light in the water they are occupying.
To accomplish the first objective means diving with sub lights off, and when the water is very deep, diving in what appears to the human eye as pitch blackness.
Tammy and Edie do a vertical profile, collecting data in a controlled descent. Using a Low Light Auto Calibrating Radiometer (LoLAR) developed by Edie Widder and Harbor Branch engineers, they are able to measure light gradients as they descend into the ever-darkening depths.
The more transparent the water, the more slowly light is attenuated, or diminished. The less transparent, the more quickly light is attenuated.
In addition to LoLAR, the scientists use a fiber optic unit which channels outside light through the hull of the sub and into a spectrometer attached to a computer. This records the wavelength, or color, of light as the sub descends. The attenuation coefficients that are determined through this in-situ data collection will be used to indicate conditions in the water where the organisms are positioned, and compared with readings from the next dives. They are also critical to all of the visual experiments that will be performed on board ship.
Once the water is characterized, it's time to locate the animals. The ship's bottom profiling sonar has revealed a very distinct scattering layer between about 1200 and 1800 feet. This is a thick layer of organisms that is scattering the sound and reflecting a reading back to the ship.
The sub's lights are turned on and it ascends through the layer of animals until no more are visible. Tammy and Edie then start doing horizontal transects starting at the top and then at 100 foot intervals to the bottom of the layer, counting and identifying larger animals like fish, shrimp and jellies, and capturing smaller animals for quantifying later.
July 11, 2:30 PM -- The sub is back on the surface. It's been a good dive, except Edie has to determine some calibration adjustments for the LoLAR. It's reporting slightly different depths than the submersible's depth gauge which has been recently calibrated. They've brought back some data and a few sample organisms: two species of krill, an orange jellyfish with a tangle of thin tentacles called Phacellophora and an as yet unidentified fish.
Sonke Johnsen takes the fish and looks at it using an ultra-violet video system to see how it would look to an animal that can see UV light. There is nothing out of the ordinary, except that the fish reflects most of the UV range. After the tanning session, Uli Siebeck takes the fish to determine if it can see UV light. It's a rough day for the fish, brought to the brightness at the surface from its home 2,000 feet below the waves.
July 11, 6:00 PM -- The sub dives again, this time with Tammy up front in the sphere and Edie in the aft compartment. They're going to plant themselves about 300 feet above where they found the top of the layer of animals in the previous dive - and wait. As millions of organisms begin their vertical migration upwards to feed in shallower depths, Tammy and Edie will run horizontal transects to monitor the animals that pass by.
Migrating organisms may be following an isolume, a secifically characterized band of irradiance and wavelength, in which they are able to hide from predators. Towards night, the isolume moves upward, into shallower depths where these organisms feed. The animals follow, and are able to eat in the same quality of light they hide from predators in during the day, and so remain relatively safe. In the open ocean, dim light or darkness can be an effective hiding place.
In the past, Tammy and Edie have observed the animals migration staggered by species. Could the reason be their degree of sensitivity to the isolume they follow?
July 11, 10:30 PM -- Before settling into entering data from the submersible dives, Tammy Frank and her crew prepare the Tucker trawl for deployment over the stern of the EDWIN LINK. It's a fairly large configuration with weight bar to hold the opening open and about 40 feet of net that end at a Cod end - a special container that can be closed at depth and is insulated to maintain the near-freezing temperatures of deep ocean water.
Not everything goes without a hitch. Both the depth wheel and meter wheel are not functioning, so the only way to estimate the depth the trawl will be deployed to is to count turns of the winch that is paying out the cable. Four hundred turns to be exact - or about 2,400 feet. Repairs to the meter wheel and depth wheel are planned. The trawl will remain at depth for over two hours. When it returns, Dr. Frank will hope to retrieve euphausiids, a species of krill, and sergestids, another crustacean. These will be the animals she uses to conduct visual receptor studies, and that her graduate student Trevor Myslinski will use to study behavioral responses to light stimulation.
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