DATASTREME OCEAN WEEK SEVEN: 18-22 October 2004

• Gulf fisheries threatened by wetland loss and runoff -- A researcher at Woods Hole Oceanic Institution recently reported that the loss of wetlands and the amount of agricultural runoff could be responsible for the development of a "dead zone" of oxygen-depleted water in the Gulf of Mexico, which would cause a decline in the fisheries. He recommended steps to avert additional expansion of the dead zone that would include wetland restoration and a marked reduction in the use of fertilizers on the Mississippi River watershed. [US Water News Online]
• Ivan continues to cause a problem on the Chesapeake -- All of the debris produced by remnants of former Hurricane Ivan as it crossed the Middle Atlantic States in September and that was accumulated along the beaches of Chesapeake Bay has yet to be removed. The torrential rains from Ivan also caused disastrous flooding, with a record amount of the freshwater entering the nation's largest estuary. [USA Today]
• Name that ship -- Officials with NOAA, in cooperation with Coastal America and the National Environmental Education and Training Foundation, announced a nationwide contest for students in grades 6 through 12 to name a newly acquired NOAA exploration ship and to develop an education project based on that proposed name. [NOAA News]
• Oil spill affecting Indonesian islands -- An oil leak that began over one week ago has developed into an oil spill that has spread across the Java Sea to a chain of Indonesian tourist islands called the Thousand Islands near Jakarta, adversely affecting the tourism and fishing industries. [ENN]
• Keeping Asian carp from the Great Lakes -- Within the next two weeks, the US Army Corps of Engineers will begin building a $9.1 million electric barrier on the Chicago Sanitary and Ship Canal that is intended to keep the invasive Asian carp from entering Lake Michigan from the Mississippi and Illinois river systems. [ENN]
• A new pricey fad -- At least one company on the Kona coast of the Big Island of Hawaii has been cashing in on the soaring Japanese demand for bottled water obtained from the bottom of the ocean. The desalinated water that has been extracted from an ocean depth of 2000 feet is marketed as being high-quality, natural and pure and sells for up to $6 for a 1.5-liter bottle. [US Water News Online]
• Global and US Hazards/Climate Extremes-- A review and analysis of the global impacts of various weather-related events, including drought, floods, and storms during the current month. [NCDC]
• Earthweek -- Diary of the Planet [earthweek.com] Requires Adobe Acrobat Reader.

Concept of the Week: Seiche Model

A seiche (pronounced "say-sh") is a rhythmic oscillation of water in an enclosed basin (e.g., bathtub, lake, or reservoir) or a partially enclosed coastal inlet (e.g., bay, harbor, or estuary). With this oscillation, the water level rises at one end of a basin while simultaneously dropping at the other end. A seiche episode may last from a few minutes to a few days. (Refer to pages 141-142 in your DataStreme Ocean textbook for more on seiches.)

With a typical seiche in an enclosed basin, the water level near the center does not change at all although that is where the water exhibits its greatest horizontal movement; this is the location of a node. At either end of an enclosed basin, vertical motion of the water surface is greatest (with minimal horizontal movement of water); these are locations of antinodes. The motion of the water surface during a seiche is somewhat like that of a seesaw: The balance point of the seesaw does not move up or down (analogous to a node) while people seated at either end of the seesaw move up and down (analogous to an antinode).

Go to the University of Delaware's Seiche Calculator at http://www.coastal.udel.edu/faculty/rad/seiche.html. Set the "Modal Number" to 1 and then press "Calculate" for a graphical simulation of a seiche in an enclosed basin.

Partially enclosed basins usually have a node located at the mouth (rather than near the center) and an antinode at the landward end. Go to the Seiche Calculator, set the "Modal Number" to 0.5 and then press "Calculate" for a simulation of a seiche in a basin open to the right. Furthermore, some basins are complex and have multiple nodes and antinodes; these can be simulated on the Seiche Calculator by selecting different values of "Modal Number" greater than one.

The natural period of a seiche depends on the length and depth of the basin and generally ranges from minutes to hours. The period is directly proportional to basin length. For example, the natural period of a seiche in a small pond is considerably less than its period in a large coastal inlet. Also, for the same basin, the natural period is inversely proportional to water depth; that is, the period shortens as water deepens. Using the Seiche Calculator, you may wish to experiment with different values of basin length and depth. Conversely, one can determine the average depth of a lake by determining the period of the seiche and the length of the lake.

Concept of the Week: Questions

1. In an enclosed basin the node of a seiche is located [(at either end) (near the center)] of the basin.
2. The natural period of a seiche [(depends on) (is independent of)] the size of an enclosed basin.

• 18 October 1910...Northeasterly winds as high as 70 mph (from a hurricane moving northward up the Florida peninsula) carried water out of Tampa Bay and the Hillsboro River. The water level lowered to nine feet below mean low water. Forty ships were grounded. (The Weather Channel)
• 19 October 1843...Captain Robert Stockton of the Princeton, the first screw propelled naval steamer, challenged the British merchant ship Great Western to a race off New York, which Princeton won easily. (Naval Historical Center)
• 20 October 1892...After ten years of difficult and costly construction, the St. George Reef Lighthouse, built on a rock lying six miles off the northern coast of California, midway between Capes Mendocino and Bianco, was first lighted. (USCG Historian's Office)
• 20 October 1956...A German physician, Dr. Hannes Lindemann, began a voyage on which he would become the first person to cross the Atlantic in the smallest craft. Using a double-seat folding kayak that was 17 feet in length and outfitted with an outrigger and sail, he made the 72 day trip from Las Palmas in the Canary Islands to St. Thomas in the US Virgin Islands in 72 days. He had made a prior crossing in a 23-foot African dugout canoe. He later wrote a book, Alone at Sea, describing his experiences. (Today in Science) 
• 20 October 1984...The Monterey Bay Aquarium opened on Cannery Row in Monterey, CA as the largest artificial environment for marine life, housing 500 marine animals from at least 525 species. The aquarium also supports active research and conservation programs. (Today in Science)
• 21 October 1797...The USS Constitution was launched at the Charlestown Navy Yard in Boston, MA. The ship, nicknamed "Old Ironsides," is now the oldest commissioned ship in the U.S. Navy. (Naval Historical Center)
• 21 October 1580...Portuguese navigator Ferdinand Magellan on his famous circumnavigation voyage of the globe reached Cape Virgenes and the strait at the tip of South America that now bears his name. Only three ships entered the 373-mile long passage separating Tierra del Fuego (land of fire) and the continental mainland. Navigating the treacherous strait in 38 days, the expedition entered the South Pacific Ocean, which Magellan named "Mar Pacifico" for the relatively tranquil seas that he found. However, one ship had been wrecked and another deserted. (The History Channel)
• 21-26 October 1998...Hurricane Mitch, a category 5 hurricane (on the Saffir-Simpson Scale), developed as a tropical depression over the southwestern Caribbean Sea about 360 mi south of Kingston, Jamaica on the 21^st. It would intensify over the next few days to become the second deadliest Atlantic hurricane on record, on the 24^th. By the 26^th, Mitch finally dissipated after remaining a category 5 hurricane for 33 hours. Estimated rainfall totals of up to 75 in. caused devastating flooding and mudslides in Honduras and Nicaragua for days. Estimated death toll from this hurricane was more than 11,000, the worst since 1780. ( The Weather Doctor) (Accord Weather Calendar)
• 22 October 1988...A "nor'easter" swept across the coast of New England. Winds gusted to 75 mph, and large waves and high tides caused extensive shoreline flooding. (The National Weather Summary) (Storm Data)
• 23-24 October 1918...The Canadian steamship Princess Sophia carrying miners from the Yukon and Alaska became stranded on Vanderbilt Reef along coastal British Columbia. A strong northerly gale hampered rescue attempts, and the next day, the ship sank with the loss of the 268 passengers and 75 crewmen on board. (The Weather Doctor)

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Prepared by AMS DSOcean Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 2004, The American Meteorological Society.