Early Oceanography: Edmond Halley and Magnetic Declination

 

This is Jim Fiorendino, your host for On the Ocean. “If I have seen further, it is by standing on the shoulders of giants.” This famous quote by Isaac Newton describes the process of investigation and discovery; any major scientific breakthrough has been the result of work by many individuals. Though oceanography is a relatively young field, the study of marine environments requires knowledge of several disciplines. Many early oceanographers were experts in other fields, applying their knowledge to investigations of the oceans. Their contributions laid the foundation for modern oceanography.

Oil painting of Edmond Halley (http://collections.rmg.co.uk/mediaLib/393/media-393720/large.jpg)

Much of the early scientific work that may be considered oceanography focused on solving problems of navigation on ships. Edmond Halley, best known for his discovery of the eponymous Halley’s Comet, conducted the first expedition in which the primary goal was furthering scientific knowledge. Halley was commissioned by the British government to study variations in Earth’s magnetic field. He was given command of the Paramore in 1698, and sailed the Atlantic Ocean between 52 degrees north and 52 degrees south.

Halley’s ship, the Paramore, from Thrower’s The Three Voyages of Edmund Halley (https://halleyslog.files.wordpress.com/2013/03/img_6898.jpg?w=425&h=352)

The Paramore expedition lasted two years. Unfortunately, insubordination forced Halley to cut his first voyage short, returning to England before setting sail again in September, 1699. Halley took daily measurements of the angle of his compass needle in relation to a true north and south line. The angle of the compass in relation to this line is known as the magnetic declination. Halley created a contour chart of the magnetic declination he observed in the Atlantic Ocean, in which continuous lines represent equal values of magnetic declination. Originally called Halleyan lines, they were later given the name isogonic lines.

Edmond Halleys' map of magnetic declination, recreated by Murray and Bellhouse (2016). Curved lines represent contours of constant magnetic declination.
Edmond Halleys’ map of magnetic declination, recreated by Murray and Bellhouse (2016). Curved lines represent contours of constant magnetic declination.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script Author: James M. Fiorendino

Featured image from: Pexels

Light in the Oceans Part 4: Bioluminescence

This is Jim Fiorendino, your host for On the Ocean. Fireflies are a common sight on a summer’s night, blinking softly as they fly through the air. Fireflies are able to produce light through a chemical reaction in their bodies, a process known as bioluminescence. Bioluminescence is common in marine organisms, as well, producing some spectacular effects!

Bioluminescence is the result of a chemical reaction between a pigment molecule, luciferin, and an enzyme, luciferase. Luciferase promotes the reaction of luciferin with oxygen, which releases light energy in the visible spectrum. The bioluminescence we see may come from the animal itself, or a symbiotic relationship in which an animal relies on bioluminescent bacteria to produce light. The deep-sea anglerfish has an appendage on its head called an esca which is home to bioluminescent bacteria. The anglerfish uses the esca and the light from the bacteria to attract prey.

In addition to hunting, bioluminescence can be used as a defense mechanism or warning to predators, or even as a means of communication. Species of squid are known to use bioluminescence to hide themselves against the illuminated background of surface waters using light-emitting bacteria on their lower side, making them difficult to spot when seen from below. Some dinoflagellates, a major group of phytoplankton, are known to produce light in response to predation. When disturbed, these phytoplankton light up, drawing attention to the location of the zooplankton, which may then be targeted by a higher predator following the light produced by the phytoplankton.

A japanese firefly squid bioluminescing. Image from : https://newsdeeply.imgix.net/20180712041025/nd_squid_7.png

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script author: James M. Fiorendino

Contributing Professor: Dr. Lisa Campbell

Featured Image from: http://unasd.org/climate-actions-oceans-literacy/ocean-underwater-light-wallpaper-3-1/

Light and the Oceans Part 3: Hiding in the Light

This is Jim Fiorendino, your host for On the Ocean. On average, the ocean is 12,000 feet deep; though light only reaches the first few hundred feet of water, it is an important factor in marine environments. Many marine organisms have developed specific adaptations over evolutionary time because of how light behaves in marine environments.

Herring, with shiny iridescent scales. Image from: https://www.aoseafood.co.uk/wp-content/uploads/2016/08/herring1.jpg

Scales cover the skin of most species of bony fish. In addition to protection, some fish have shiny, iridescent scales that help to hide them in plain sight, particularly those that live in the open ocean like tuna or herring. Light in the ocean is often polarized, which means it travels with a specific orientation. Fish scales reflect light in the ocean, bending or changing its polarization, which makes the fish difficult to see.

A great white shark exhibiting countershading. The dorsal (top) side of the shark is dark to blend in with the deep ocean, while the ventral (bottom) side is white to blend in with illuminated surface waters. Image from: https://upload.wikimedia.org/wikipedia/commons/3/31/Great_white_shark_south_africa.jpg

The coloration of marine animals, though striking in may cases, is about more than just looks; the pattern of colors on an organism’s body conveys some benefit for survival because of how light behaves in the ocean. For example, a shark’s skin is often dark on the upper, or dorsal, side and light on their bottom, or ventral, side. This type of coloration is called countershading and helps to camouflage the shark. Remember, light is absorbed rapidly in the ocean, so the deep ocean is dark while the surface is light. If a fish were to look at a shark swimming beneath it, the shark’s dark dorsal side would be hidden against the darkness of the ocean beneath it. If a fish were to look up at a shark swimming above it, the white ventral side would blend in with the illuminated surface waters. Additionally, patterns like stripes disrupt the outline of a fish, making them more difficult for a predator or prey to identify.

The vertical stripes on this fish break up its outline, making it more difficult to spot by predators. Photo credit: Tex Texin, from: https://c1.staticflickr.com/7/6009/5991975153_08980f66a8_b.jpg

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script Author: James M. Fiorendino

Contributing Professor: Dr. Lisa Campbell

Featured Image from: http://unasd.org/climate-actions-oceans-literacy/ocean-underwater-light-wallpaper-3-1/

Light in the Oceans Part 2: Reaching the Ocean

This is Jim Fiorendino, your host for On the Ocean. Only about half of the radiation reaching Earth from the Sun makes it through the atmosphere to the ocean; the rest is scattered or absorbed by particles and molecules in Earth’s atmosphere. What happens to the half that reaches the surface of the ocean?

The amount of light that strikes the surface of the ocean is affected by day length, the weather (because clouds will block incoming light), and the angle of the sun in relation to the surface of the ocean. At small angles, more light reflects off the surface of the ocean. The angle of the sun and the length of a day changes with the seasons; this means the amount of light that makes it into the ocean varies greatly at the poles, which experience the most extreme seasonal shifts. Light is more consistent at the equator, where there is little seasonality.

The mean insolation of Earth, from the tropics to the poles. The tropics receive the greatest, most direct irradiance while the poles are variable, with less direct light and greater seasonality. Image from: http://ftp.comet.ucar.edu/ootw/tropical/textbook_2nd_edition/media/graphics/insolation.jpg

As light passes through the ocean, it is scattered and absorbed. Light is absorbed differently, depending on its wavelength or energy level. Infrared radiation is absorbed as heat quickly in surface waters. Visible light is especially important, because this light is capable of driving photosynthesis, the process by which phytoplankton make food for themselves. The layer of ocean water where there is enough light within this spectrum to drive photosynthesis is called the euphotic zone.

Light zones in the ocean. Image from: https://aamboceanservice.blob.core.windows.net/oceanservice-prod/facts/lightinocean.jpg

Different wavelengths of light within the visible spectrum produce different colors; colors of light behave differently in water. Red light is absorbed very quickly, within 30 feet in clear open ocean water. Blue light will reach the greatest depths. In perfectly clear open ocean waters, only 1 percent of light at the surface of the ocean remains at a depth of 500 feet.

Penetration of different wavelengths of light in coastal and open ocean waters. Blue light penetrates deepest. In coastal waters, suspended particles and cells result in more rapid absorption of light. Image from: http://www.scienceline.ucsb.edu/images/light_depth.jpg

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script Author: James M. Fiorendino

Contributing Professor: Dr. Lisa Campbell

Featured Image from: http://unasd.org/climate-actions-oceans-literacy/ocean-underwater-light-wallpaper-3-1/