DATASTREME OCEAN WEEK FOUR: 22-26 February 2010

Ocean in the News

• Eye on the tropics ---
During the last week:
• Tropical Cyclone Gelane formed over the South Indian Ocean early in the week as the sixteenth tropical cyclone of the season in the basin. This cyclone intensified into a major category 4 cyclone on the Saffir-Simpson Wind Scale as it traveled southward passing near La Reunion Island. By the Sunday, this cyclone had weakened to a tropical storm. Satellite images and additional information on Tropical Cyclone Gelane can be found on the NASA Hurricane Page.
• Tropical Cyclone Rene, which had become a category-3 cyclone in the South Pacific basin, traveled southwestward across Tonga archipelago at the start of the week and finally dissipated before reaching New Zealand by midweek. For more information and satellite imagery on Tropical Cyclone Rene, consult the NASA Hurricane Page.
• New hurricane wind scale will be used --
Officials with NOAA's National Weather Service recently announced that beginning this upcoming hurricane season, the agency will use a new hurricane scale called the "Saffir-Simpson Hurricane Wind Scale," which differs slightly from the familiar Saffir-Simpson Scale used for more than 30 years. The new scale will keep the same wind speed ranges as the original scale for each of the five hurricane categories, but will no longer tie specific storm surge and flooding effects to each category. [NOAA News]
• Health of dolphins may be an indicator of ocean and human health --
A panel of governmental, academic and non-profit scientists attending the last week's annual meeting of the American Association for the Advancement of Science reported on research suggesting a similarity between diseases found in dolphins and those in humans, which could provide clues into how human health might be affected by exposure to contaminated coastal water or seafood. [NOAA News]
• Warmer oceans appear to speed Greenland glacier melt --
Researchers from NASA's Jet Propulsion Laboratory, the University of California-Irvine and the University of British Columbia who measured the submarine melting rates of four west Greenland glaciers from their network of oceanographic instruments in the glacier fjords claim the underwater edges of these west Greenland glaciers are melting nearly one hundred times faster than the their surfaces. They attribute this increased glacial melt to higher ocean temperatures. [NASA JPL]
• Subtropical waters flush through Greenland fjord--
Oceanographers from Woods Hole Oceanographic Institution, the University of Maine and colleagues from Canada and Greenland have found that recent changes in the ocean circulation in the North Atlantic have permitted subtropical waters to be flushed into several of Greenland's fjords. This intrusion of warm subtropical water appears to contribute to glacial melting, with the melt waters adding more fresh water into the ocean, which could disrupt the global system of currents known as the Ocean Conveyor. [Woods Hole Oceanographic Institution]
• Lack of "ice arches" contributed to recent Arctic ice loss --
Using high-resolution radar images collected from the Canadian RADARSAT and European Envisat satellites, researchers from NASA's Jet Propulsion Laboratory conclude that the record loss of Arctic sea ice during 2007 could be attributed in part to the lack of "ice arches", or curved ice structures that form naturally across openings between two land points. [NASA JPL]
• Fossil reefs help record past sea level changes --
An international team of researchers associated with the European Consortium for Ocean Research Drilling recently concluded an ocean research cruise in which they collected samples of fossilized coral from the Great Barrier Reef that will help in the reconstruction of the changes in sea level that have occurred over the last 20,000 years. Analysis of the coral seasonal growth rings could also help develop a chronology of past ocean temperatures and salinity. [BBC News]
• An All-Hazards Monitor --
This Web portal provides the user information from NOAA on current environmental events that may pose as hazards such as tropical weather, drought, floods, marine weather, tsunamis, rip currents, Harmful Algal Blooms (HABs) and coral bleaching. [NOAAWatch]
• Global and US Hazards/Climate Extremes --
A review and analysis of the global impacts of various weather-related events, to include drought, floods and storms during the current month. [NCDC]
• Earthweek --
Diary of the Planet [earthweek.com] Requires Adobe Acrobat Reader.

Concept of the Week: Variations in Marine Sediment Thickness

Sediments are particles of organic or inorganic origin that accumulate in loose form in depositional environments such as lake or ocean bottoms. Marine sediments, the central focus of this week's investigations, have a variety of sources and exhibit a wide range of composition, size, and shape. Marine sediments settle to the ocean floor as unconsolidated accumulations but ultimately may be converted to solid sedimentary rock via compaction and cementation. The pattern of variations in marine sediment thickness on the ocean floor confirms some basic understandings regarding marine geological processes.

Go to the DataStreme Ocean Website and under "Geological," click on "Sediment Thickness." This map of marine sediment thickness in the ocean basins was compiled by the National Geophysical Data Center (NGDC), Marine Geology and Geophysics Division primarily based on existing maps, ocean drilling, and seismic reflection profiles. Sediment thickness is color-coded in meters from violet (thinnest) to red (thickest). Many factors account for the variation in the thickness of marine sediment deposits including type and location of sediment sources, sediment transport mechanisms, and the age of the underlying crust.

According to the map, sediment thickness generally increases with distance from near the central portion of an ocean basin to the continental margin. This pattern may be explained by the principal sediment source and/or the age of the underlying crust. Rivers and streams that empty into the ocean slow and diverge, releasing the bulk of their suspended sediment load in coastal environments (e.g., bays, estuaries, deltas) and onto the continental shelf. Ocean currents transport sediment along the coast. In some areas of the continental shelf, massive amounts of sediment accumulate, become unstable, and flow down the continental slope to the base of the continental rise and beyond. However, only the finer fraction of river-borne sediment is swept into the deep ocean waters. Thickening of marine sediments in the direction of the continental margin may also reflect the aging of oceanic crust with distance away from divergent (spreading) plate boundaries where new oceanic crust forms. Th e older the crust the longer is the period that sediment rains down on the ocean bottom and the thicker is the blanket of accumulated sediment.

The map indicates that the thickness of marine sediment deposits is greater in the continental margin along the Atlantic coast of North America than along the Pacific coast. The Atlantic coast of North America is a passive margin; that is, the continental margin is not affected significantly by tectonic processes (no plate boundary) and the principal geological processes consist of sedimentation along with erosion by ocean waves and currents. In fact, passive margins and relatively thick marine sediment deposits occur on both sides of the Atlantic. (Passive margins also occur around the Arctic Ocean and surrounding Antarctica.) On the other hand, the Pacific coast of North America is an active margin; that is, the continental margin is associated with plate boundaries and is subject to deformation by tectonic stresses. Active continental margins are relatively narrow so that sediment delivered to the coast by rivers and streams flows directly into deeper water or trenches—preventing thick accumulations of marine sediments from building in the continental margin.

Concept of the Week: Questions

1. The thickness of marine sediment deposits is greater in the [(continental margins)(deep-ocean basins)].
2. The thickness of marine sediment deposits generally is greater in [(active)(passive)]continental margins.

Historical Events

• 22-26 February 1995...Cyclone Bobby slammed into the Western Australia coast causing widespread flooding. Some areas reported up to 12 in. of rain from the storm. (The Weather Doctor)
• 23 February 1802...A great snowstorm raged along the New England coast producing 48 inches of snow north of Boston and 54 inches of snow at Epping, NH. Three large (indiamen) ships from Salem were wrecked along Cape Cod by strong winds. (David Ludlum) (Intellicast)
• 24 February 1881...De Lesseps' Company began work on the Panamá Canal
• 25 February 1977...An oil tanker explosion west of Honolulu spilled 31 million gallons of oil into the Pacific Ocean.
• 26 February 1935...Robert Watson-Watt demonstrated RADAR (Radio Detection and Ranging) for the first time, using the BBC shortwave radio transmitter to successfully detect the distance and direction of a flying bomber during the so-called Daventry Experiment.
• 26 February 1938...The first passenger ship was equipped with radar.
• 27 February 1949...Aerial ice observation flights by long-range aircraft operated from Argentia, Newfoundland. An International Ice Patrol by vessels was neither required nor established during the 1949 season, and it was the first time that aircraft alone conducted the ice observation service. (USCG Historian's Office)
• 27 February 1988...A major rain event occurred across Saudi Arabia's Foroson Islands in the Red Sea and on the adjacent mainland around Jizon when 1.15 in. fell. The monthly average rainfall is only 0.02 in. On the following day, flash flooding south of Riyadh killed three children. (Accord's Weather Calendar)
• 28 February 1849...Regular steamboat service to California from the East Coast via Cape Horn arrived in San Francisco for the first time. The SS California had left New York Harbor on 6 October 1848 on a trip that took 4 months and 21 days. (Wikipedia)
• 28 February 1964...A world 12-hour rainfall record was set at Belouve, La Reunion Island in the western Indian Ocean when 52.76 inches of rain fell. World records for 9 hours and 18.5 hours were also set with 42.79 and 66.49 inches, respectively. (Accord's Weather Calendar) (The Weather Doctor)
• 29 February 1504...Christopher Columbus used his knowledge of a lunar eclipse that night to convince Native Americans to provide him with supplies. (Wikipedia)

Return to DataStreme Ocean Website

Prepared by DS Ocean Central Staff and Edward J. Hopkins, Ph.D.,
email hopkins@meteor.wisc.edu
© Copyright, 2010, The American Meteorological Society.