Milwaukee Deep and Deep Diving Animals

     The deepest part of the Atlantic Ocean is not where you would probably think it is. It's not in the middle of the Atlantic somewhere. The Milwaukee Deep, also known as the Milwaukee Depth, is part of the Puerto Rico Trench. 

     Together with the surrounding area, known as Brownson Deep, the Milwaukee Deep forms an elongated depression that constitutes the floor of the trench. The floor of the trench constitutes the deepest point in the Atlantic Ocean. 

     It is named for the USS Milwaukee, US Navy light cruiser (the third of five Navy ships with that name) which was itself named for the city of Milwaukee. While steaming north of Hispaniola and Puerto Rico on February 14, 1939, Milwaukee discovered the deepest place in the Atlantic Ocean. The spot is now known as the Milwaukee Deep. 

     The Milwaukee's depth reading was 28,680 feet, but on August 19, 1952, a US.Fish and Wildlife vessel obtained a reading of 28,560 feet. One of the area's earliest soundings was obtained June 12, 1852 by Lieutenant S. P. Lee with a reading of 22,950 feet. 

     In 1964, a French submersible explored the Puerto Rico Trench to a depth of approximately 27,200 ft but did not reach its deepest point. On December 21, 2018 Victor Vescovo made the first manned descent to the deepest point of the trench and measured a depth of 27,480 feet. 

     The Deep itself is a spot 100 miles northwest off the coast of Puerto Rico and is a low spot where two tectonic plates meet along the boundary between the Caribbean Sea and the Atlantic Ocean. 

 

     The suspense of what's down there is probably killing you, so just what IS down there? The bottom is covered with mud, sand, rock and shells. But, the Deep is also home to a host to several new species discoveries, like the sei, fin, and minke whales; it is also the well-known humpback whales' breeding ground.

     Speaking of whales, how do sea creatures survive at great depths, far beyond what man can survive? The physiological challenges in adapting to pressure faced by creatures that routinely travel from the surface to great depths is nothing short of amazing. 

     The sperm whale and the bottlenose whale are known as exceptional divers. Dating back to whaling days they have been known to have made dives lasting as long as two hours after they were harpooned. Today, sonar tracking and attached recorders reveals them making dives as deep as 6,000 feet although routine dive depths are usually in the 1,500- to 3,000-foot range, and dives can last between 20 minutes and an hour. 

     Diving to those depths can result in distortion and tissue compression, especially in gas-filled spaces in the body such as the middle ear, sinuses in the head and the lungs. In human beings these distortions are known as the squeeze.

     In some species of whales, dolphins and porpoises, the middle ear cavity is lined with an extensive blood vessels which it is believed become engorged at depth and thus reduce or eliminate the air space. 

     These animals also have large Eustachian tubes between their ears and the large sinuses of the head. These sinuses also have a lot of blood vessels which are thought to function in a similar manner. 

     Another organ susceptible to compression are the lungs. In deep-diving whales and seals, the peripheral airways are reinforced and it is believed this allows the lungs to collapse during deep dives. 

     Collapse of the lungs forces air away from the alveoli, where gas exchange between the lungs and blood occurs. This is important in deep dives because it prevents the absorption of nitrogen into the blood. In humans high blood nitrogen pressure can exert a narcotic effect (so-called nitrogen narcosis) on the diver. It may also lead to nitrogen bubble formation during ascent which is known as decompression sickness or the bends. 

     Collapse of the lungs in deep diving animals avoids these two problems. In animals making deep dives the lungs cannot serve as a source of oxygen during the dive. Instead deep-diving whales and seals rely on large oxygen stores in their blood and muscle. 

     First, these animals have mass specific blood volumes that are three to four times those found in land mammals. Second, the concentration of hemoglobin (the blood's oxygen-transporter) is also elevated to a level about twice that found in humans. Third, the concentration of the oxygen storage protein in muscles (myoglobin) is about 10 times that in human muscle. 

     So, deep-diving mammals such as the sperm whale have air cavities that are lined with blood vessels which are thought to fill at depth, obliterate the air space, and prevent the squeeze. 

    The lungs collapse, which prevents lung rupture and blocks gas exchange in the lungs. Lack of nitrogen absorption at depth prevents the development of nitrogen narcosis and decompression sickness. 

     In addition, because the lungs do not serve as a source of oxygen at depth, deep divers rely on enhanced oxygen stores in their blood and muscles.