DATASTREME OCEAN WEEK TWELVE: 19-23 April 2004

• A milestone reached-- DSV Alvin, the nation's only deep-sea submersible research vessel, made its 4000^th dive off the Mexican coast last week. [Woods Hole Oceanographic Institution]
• Iron supplies in the Southern Ocean may have been a key to Ice Age Climate -- A group of scientists reported on the results of a field experiment called SOFeX (Southern Ocean Iron Enrichment Experiments) that involved fertilization of two areas in the Southern Ocean with trace amounts of iron to monitor the growth of phytoplankton under iron-enriched conditions similar to those thought to have occurred during the Pleistocene ice ages. Three robotic Carbon Explorer floats were used by the Lawrence Berkeley National Laboratory to track the iron-fertilized plankton. [Berkley Lab] Preliminary results of this experiment indicate that addition of iron appeared to have initiated massive phytoplankton blooms that would have consumed significant amounts of atmospheric CO₂. [Moss Landing Marine Laboratories] In related research to the experiment, an oceanographer from Oregon State University indicates that phytoplankton may be one of the main historic controls on global warming. [EurekAlert!]
• Weakened North Atlantic current monitored from space -- A researcher with the Goddard Space Flight Center and an oceanographer at the University of Washington reported that their study of sea height data from satellites along with data from buoys, ships and robotic submersibles indicate that the oceanic circulation regime in the North Atlantic has weakened considerably in the last decade as compared with the previous two decades. The change in the circulation could have a dramatic effect upon the climate in the subpolar North Atlantic basin. [NASA/GSFC]
• Saharan dust could affect hurricanes --Using satellite technology to track the spread of dust from Africa's Sahara Desert, a NOAA researcher recently reported that the dust laden Saharan Air Layer could affect the development and intensity of hurricanes in the North Atlantic basin. [NOAA News]
• A return visit to the Titanic planned -- Marine explorer Robert Ballard is planning to return with remotely operated submersibles to the site of the RMS Titanic in June nearly 20 years after first finding sunken remains of this ocean liner in an effort to help NOAA study the ship's rapid deterioration. [EurekAlert!]
• Detailed monitoring of sea surface temperatures could reveal global temperature changes -- In an effort to determine the extent of global warming, the European Space Agency is funding an office in the United Kingdom that will coordinate efforts to map global sea surface temperatures in unprecedented detail with a spatial resolution of 10 km every 6 hours using satellite data along data from ships and buoys.[ESA News]
• Cruise ships asked to cleanup dumping practices-- Environmentalists have been pressuring several of the large cruise lines to cleanup sewage and wastewater dumped by their cruise liners in an effort to protect marine habitats and human health. [US Water News Online]
• More desalination plants could pose a problem--Environmentalists are concerned that plans for the construction of more desalination plants near Boston, MA could result in damage to delicate aquatic ecosystems, especially along tidal estuaries. [Yahoo! News]
• On ocean policy --
• US approval of ocean treaty uncertain -- The Bush Administration appears to be backing away from approval of The Law of the Sea Convention, an international treaty governing uses of the world's oceans. [Monterey Herald]
• US ocean policy recommended -- Following a three-year study, the Pew Oceans Commission is recommending five major reforms of US ocean policy. [Sun Herald]
• 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: Climate Feedback Processes

Earth's climate system includes many interacting variables. Some variables are external to the Earth-atmosphere system and some are internal. External variables include solar energy input and Earth-sun geometry (i.e., the Milankovitch cycles). Internal variables include properties of Earth's surface (e.g., albedo, moisture supply), the concentration of key atmospheric components (e.g., greenhouse gases, sulfurous aerosols, cloud cover and thickness.)

An important consideration in understanding how Earth's climate system responds to some perturbation is feedback. Feedback is defined as a sequence of interactions among variables in a system that determines how the system responds to some initial perturbation in one or more of the variables. Variables in Earth's climate system may interact in such a way as to either amplify (positive feedback) or reduce (negative feedback) a change in climate. An example of positive feedback is the ice-albedo effect described in Chapter 12 of the DataStreme Ocean textbook. Less extensive sea ice cover in the Arctic greatly reduces the albedo of the Arctic Ocean causing higher sea surface temperatures (SST) and accelerated melting of the multiyear pack ice.

Consider an example of negative feedback. Increasing concentrations of atmospheric carbon dioxide enhances the greenhouse effect causing global warming. Global warming, in turn, raises SST and increases the rate of evaporation. A more humid atmosphere means more persistent and thicker cloud cover but clouds have both a cooling and warming effect on the lower atmosphere. The relatively high albedo of cloud tops causes cooling whereas absorption and emission of infrared radiation by clouds causes warming by contributing to the greenhouse effect. Measurements by satellite sensors and simulations by numerical models indicate that the cooling effect of clouds would dominate.

Within Earth's climate system, negative feedback tends to dominate over positive feedback, thereby limiting the magnitude of climate change. The great thermal inertia of the ocean is the principal reason for dampening the planetary temperature response.

Concept of the Week: Questions

1. Feedback within Earth's climate system that amplifies climate change is described as [(positive)(negative)]feedback.

2. In general, [(negative)(positive)]feedback processes tend to prevail in Earth's climate system.

• 19 April 1770...Captain James Cook discovered New South Wales, Australia. Cook originally named the land Point Hicks.
• 20 April 1534...Jacques Cartier, a French explorer, set sail from St. Malo, France with two ships to explore the North American coastline in an attempt to find a passage to China. In this first voyage, he explored the Gulf of St. Lawrence.
• 20 April 1952...The tankers Esso Suez and Esso Greensboro crashed in a thick fog off the coast of Morgan City, LA. Only five of the Greensboro's crew survived after the ship burst into flame. (David Ludlum)
• 21 April 1910...The U.S. Government took over sealing operation of Pribilof Islands in the Bering Sea from private lessees. (USCG Historian's Office)
• 21 April 1906...Commander Robert Peary, USN, discovered that the supposed Arctic Continent did not exist. (Naval Historical Center)
• 22 April 1500...Portuguese navigator Pedro Alvares Cabral sighted Brazil and claimed it for Portugal.
• 23 April 1924...A tube transmitter for radio fog-signal stations, developed to take the place of the spark transmitters in use, was placed in service on the Ambrose Channel Lightship and proved successful. (USCG Historian's Office)
• 24 April 1884...USS Thetis, Bear, and Alert sailed from New York to search for Greeley expedition lost in the Arctic. (Naval Historical Center)
• 25 April 1859...Ground was broken at Port Said, Egypt for the Suez Canal, an artificial waterway that was to cross the isthmus of Suez to connect the Mediterranean and the Red seas. (The History Channel)
• 25 April 1959...With the first ocean-going ships passing through locks along the St. Lawrence River, the St. Lawrence Seaway was officially opened to shipping, serving as the international waterway connecting the Great Lakes with the Atlantic Ocean. The official dedication of the Seaway was on 26 June 1959.

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