Friday, May 18, 2012

Erin Hunter's Internship, Spring 2012 - Part 3

Week 2.5: Seafloor Features


Erin Hunter in the Okeanos Explorer control room.
We have made a long track mapping around the Northwest Florida Escarpment and following it down to the Keys. After reaching southern Florida a couple days ago, heading into the Dry Tortuga shoals for dive operations, we had to turn away due to rough sea conditions near shore for our small boat. The next day we stopped near Key Largo for a dive instead. During our first night in the Atlantic we watched a starlight movie on the fantail. It was great being out on deck at night.

During the Gulf of Mexico part of our trip we have picked up many features on the seafloor that I want to share with you. The multibeam has picked up numerous salt domes, seeps and sediment driven channel formations that look similar to rivers on land and other unusual seafloor characteristics. Some of these, Green Canyon (salt dome city), Mississippi Canyon and Desoto Canyon are all situated around the Mississipi delta and Northwest Florida Escarpment. These canyon areas are characterized by a sloping topography, rather than a sudden and continual drop off as with an escarpment.

Images that have been mapped on the NOAA Okeanos Explorer.
From mutlibeam soundings, water column data and previous remote operated vehicle (ROV) dives, seeps from salt domes found in these canyons can be seen as areas that either rise or remain flat, and where gas escapes the seafloor in a vertical fashion. Often masses of mussels, corals, and tube worms adorn this calcareous limestone bedding where the salt domes have risen. Salt domes have formed from ancient salt deposits originating from evaporated seas. Layers of depositional strata were later formed over the salt beds and under the salt layer gas and oil may reside. When the seafloor strata shifts or weakens the pressure change may allow this gas or oil to leak out of the areas where the salt domes have formed by building pressure. At right are some images that have been mapped on the NOAA Okeanos Explorer. Also their website has the ROV footage and track lines.

Two more features that intrigued me are a very long and winding sediment driven channel formation and two unusual semicircle formations on the West Florida Escarpment. The sediment river, or subterranean channel, originates around the Mississipi Delta southwest of Desoto Canyon and runs southeast for 164 km (or more-entire are not mapped yet). In the lower southern region, approximately 20m high ridge walls span 300m to over 700m across the channel. This entire snakelike formation lies at a seafloor depth of 2,954m. This is deep! The Northwest Florida Escarpment, situated directly to the northeast of the subterranean channel, rises 1,885m above the seafloor and presents a scene of an alien landscape.
The Northwest Florida Escarpment, situated directly to the northeast of the subterranean channel, rises 1,885m above the seafloor and presents a scene of an alien landscape.

Another more mysterious formation was read on the multibeam in the lower region of the escarpment west of the Florida Everglades. For now, since we only have half the picture, it looks like two large semicircles They are large in diameter with the southern formation stretching 8,247m but shallow in height with ridges of about 35m or less. We will have to wait for the next Gulf of Mexico cruise to fill in the blanks on these features.

Well if you are following along, I hope you are enjoying riding along the mapping adventures of the Okeanos Explorer. I will send another entry before we wrap things up in Norfolk next week. Cheers, Erin

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Erin Hunter

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