Characteristics of oceanic gyres

Table of contents Page no:

1. Oceanic gyres 022. Five major oceanic gyres 03

I. Indian Ocean gyre 03II. North Atlantic gyre 04III. North Pacific gyre 05IV. South Atlantic gyre 06V. South Pacific gyre 07

3. References 08

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Bahria University Islamabad

Department: Earth and environmental sciences

Submission date: 10 Dec 2014

Submitted by Khurram Shahzad

Submitted to Saima Akbar

1) Oceanic gyre: A gyre is another name for a swirling vortex. Ocean gyres are large swirling bodies of water that are often on the scale of a whole ocean basin or 1000’s of kilometers across (hundreds to thousands of miles across). Ocean gyres dominate the open ocean and represent the long-term average pattern of ocean surface currents. Ocean gyres in the Northern hemisphere rotate clockwise and gyres in the Southern hemisphere rotate counter-clockwise due to the Coriolis Effect. The major gyres of the ocean include: North Atlantic, South Atlantic, North Pacific, South Pacific and Indian Ocean gyres. A simplistic drawing of those can be seen on this page. Many other smaller gyres exist in the ocean too.

One such smaller gyre is the Beaufort gyre found in the Arctic Ocean. The Beaufort gyre is a huge vortex of water being driven by strong winds that force currents in a clockwise direction. This gyre is full of relatively fresh water as Siberian and Canadian rivers drain into the Beaufort gyre. Scientists have been keeping a close eye on the Beaufort gyre because of the relatively fresh water it holds. When winds slack off and the gyre weakens, fresh water leaks out of the gyre and into the North Atlantic Ocean. The addition of fresh water from the Beaufort gyre along with fresh water from melting sea ice could be contributing to the disruption of the global ocean current system known as the ocean conveyor. This slowing or halting of the ocean conveyor system will have impacts on the climate in the North Atlantic and surrounding areas. One of the largest ocean gyres, the North Pacific gyre, is home to an area called the Great Pacific Garbage Patch. This area contains a lot of litter! It is estimated to cover an area roughly twice the size of Texas and contains approximately 3 million tons of plastic litter, though much of this plastic is broken up into pieces too small to see with the naked eye.

Figure 01: Oceanic gyres and 5 major oceanic gyres.

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2) Five major oceanic gyres: I. Indian Ocean Gyre:

The Indian Ocean Gyre, located in the Indian Ocean, is one of the five major oceanic gyres, large systems of rotating ocean currents, which together form the backbone of the global conveyer belt. The Indian Ocean Gyre is composed of two major currents: the South Equatorial Current, and the West Australian Current. Normally moving counter-clockwise, in the winter the Indian Ocean gyre reverses direction due to the seasonal winds of the South Asian Monsoon. In the summer, the land is warmer than the ocean, so surface winds blow from the ocean to the land. However, during the winter, these temperatures reverse, making the winds blow from the land to the ocean. Because most of the air pressure gradient is retained behind the Tibetan plateau, air pressure gradients over the Indian Ocean and the gyre are small. This results in winds of moderate strength, due to the protection from the full force winds blowing off the Mongolian high pressure region. Because of these moderate, dry winds, the Winter Monsoon season in the Indian Ocean region is the dry season for most of Southern Asia. Due to this seasonal wind cycle, the currents of the Indian Ocean, which make up the Indian Ocean gyre, are directly affected, causing reversal.

In the Indian Ocean Gyre, the garbage patch has been more of a mystery. Having just been discovered in 2010, it is still under researched. It is known, however, that like most garbage patches, it is very fluid, and changes with the seasons, making its location difficult to pinpoint. It seems to circulate with the Indian Ocean Gyre, from the Australian side to the African side, down the African coast, and then back to Australia.

Figure 02: The Indian Ocean Gyre.

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II. North Atlantic Gyre: The North Atlantic Gyre, located in the Atlantic Ocean, is one of the five major oceanic gyres. It is a circular system of ocean currents that stretches across the North Atlantic from near the equator almost to Iceland, and from the east coast of North America to the west coasts of Europe and Africa. The currents that compose the North Atlantic Gyre include the Gulf Stream in the west, the North Atlantic Current in the north, the Canary Current in the east, and the Atlantic North Equatorial Current in the south. This gyre is particularly important for the central role it plays in the thermohaline circulation, bringing salty water west from the Mediterranean Sea and then north to form the North Atlantic Deep Water.

This gyre is similar to the North Pacific Gyre in the way it traps man-made marine debris in the North Atlantic Garbage Patch, similar to the Great Pacific Garbage Patch in the North Pacific. The North Atlantic Gyre forms the Sargasso Sea, noted for its still waters and dense seaweed accumulations.

Figure 03: The north Atlantic gyre.

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III. North Pacific Gyre: The North Pacific Gyre, located in the northern Pacific Ocean, is one of the five major oceanic gyres. This gyre covers most of the northern Pacific Ocean. It is the largest ecosystem on Earth, located between the equator and 50° N latitude, and comprising 20 million square kilometers.[1] The gyre has a clockwise circular pattern and is formed by four prevailing ocean currents: the North Pacific Current to the north, the California Current to the east, the North Equatorial Current to the south, and the Kuroshio Current to the west. It is the site of an unusually intense collection of man-made marine debris, known as the Great Pacific Garbage Patch.

Figure 04: The north Pacific gyre.

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IV. South Atlantic Gyre: The South Atlantic Gyre is the subtropical gyre in the South Atlantic Ocean. In the southern portion of the gyre, northwesterly (or southeastward-flowing) winds drive eastward-flowing currents that are difficult to distinguish from the northern boundary of the Antarctic Circumpolar Current. Like other oceanic gyres, it collects vast amounts of floating debris. South of this gyre is the Antarctic Circumpolar Current. This current flows from West to East around Antarctica. Another name for this current is the West Wind Drift. This current allows Antarctica to maintain its huge ice sheet by keeping warm ocean waters away. The Brazil Current is the western boundary current of the gyre. It flows south along the Brazilian coast to the Rio de la Plata. The current is considerably weaker than its North Atlantic counterpart, the Gulf Stream.

The Brazil current is the South Atlantic Gyre's western boundary current and brings warm equatorial water to the pole. The Benguela current is the eastern boundary current, bringing cold Antarctic water towards the equator. The South Atlantic's northern boundary is the South Equatorial Current and it is bordered on the south by the Antarctic Circumpolar Current. The South Atlantic Gyre is one of 5 major gyres, the others being the North Atlantic Gyre, The Indian Ocean Gyre, the North Pacific Gyre, and the South Pacific Gyre.

Figure 05: The south Atlantic gyre.

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V. South Pacific Gyre: The Southern Pacific Gyre is part of the Earth’s system of rotating ocean currents, bounded by equator to the north, Australia to the west, the Antarctic Circumpolar Current to the south, and South America to the east. The center of the South Pacific Gyre is the site on Earth farthest from any continents and productive ocean regions and is regarded as Earth’s largest oceanic desert.

Figure 06: The south pacific circulation gyre.

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3) References: http://iodp.tamu.edu/scienceops/expeditions/south_pacific_gyre_microbio.html

http://education.nationalgeographic.com/education/encyclopedia/ocean-gyre/?ar_a

http://www.whoi.edu/main/topic/currents--gyres-eddies

http://en.wikipedia.org/wiki/South_Pacific_Gyre

http://www.gyrecleanup.org/what-is-the-gyre/

http://en.wikipedia.org/wiki/South_Atlantic_Gyre

http://www.oneworldoneocean.com/blog/entry/south_pacific_plastic_gyre_discovered

http://oceanmotion.org/html/background/wind-driven-surface.htm

http://en.wikipedia.org/wiki/North_Atlantic_Gyre

http://www.thefreedictionary.com/North+Atlantic+Gyre

http://science.howstuffworks.com/environmental/earth/oceanography/great-pacific-garbage-patch.htm

http://en.wikipedia.org/wiki/Indian_Ocean_Gyre

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