DATASTREME OCEAN WEEK TWELVE: 18-22 April 2005

• Cruise ship damaged by giant wave -- The Norwegian Dawn, a 965-foot long cruise ship that was returning to New York from the Bahamas was battered by a seven-story wave that caused damage, flooded 62 cabins and injured four passengers late last week. The ship was diverted to Charleston, SC for repairs. [CNN]
• Hurricane evacuation plans overhauled -- Based upon experience gained from the traffic snarls in the New Orleans metropolitan area when Hurricane Ivan approached the Gulf coast last year, Louisiana and Mississippi state officials have recently unveiled a new plan that is designed to help residents evacuate coastal regions of the state more quickly and safely when a hurricane threatens. [USA Today]
• Whale kill plan protested -- New Zealand officials plan on protesting Japan's plan to double its killing of Antarctic whales at next month's meeting of the International Whaling Commission. [ENN]
• New marine pollution law sought for cruise ships -- Environmentalists and a variety of state and federal lawmakers are working on a Clean Cruise Ship Act designed to improve the treatment of wastewater on cruise ships operating off the US coasts, including banning of wastewater discharges within 12 miles of shore. [ENN]
• Spring salmon run is at record low level -- Scientists monitoring the annual spring run of chinook salmon in the Columbia River of Washington and Oregon have noted that fewest salmon in recent history have made their way upstream to the Bonneville Dam this spring. [ENN]
• Coral record suggests short-term sea level changes -- Scientists at Lamont-Doherty Earth Observatory report that their new method for isotopic dating fossil coral reefs would suggest that sea level may have changed more rapidly over shorter time periods than previously thought. [EurekAlert!]
• Study of tidal marshes meant to assess climatic change effects -- The Academy of Natural Sciences in Philadelphia has received funds to study the effects that changes in climate would have upon the ecosystems in the tidal marshes of the Delaware Estuary. [EurekAlert!]
• Ocean food chain could be disrupted by changes in currents -- A scientist from Oregon State University suggests that increased precipitation and sea surface temperatures could disrupt the Atlantic Conveyer current, which could result in a significant decrease in phytoplankton productivity and a major disruption in the ocean food chain in the Atlantic as well as the other oceans. [EurekAlert!]
• Carbon dioxide not oceans could have caused an earlier warm period -- After studying algae sediments to determine sea surface temperatures and running computer models, researchers with the British Antarctic Survey and the University of California, Santa Cruz have concluded that increased levels of carbon dioxide rather than ocean currents may have been responsible for the last large scale global warming approximately 3 million years ago. [EurekAlert!]
• Another factor discovered in coral reef decline -- Scientists from Spain and California's Scripps Institution of Oceanography have developed a model of a Caribbean marine ecosystem that involves a complex food web and they conclude that overfishing of sharks appears to be a key factor in the decline of coral reefs in the Caribbean. [Scripps Institution of Oceanography]
• 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 output and Earth-sun geometry (i.e., the Milankovitch cycles). Internal variables include properties of the Earth's surface (e.g., albedo, moisture), the concentration of key atmospheric components (e.g., greenhouse gases, sulfurous aerosols), and 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 lessen (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 ice cover in the Arctic greatly reduces the albedo of the Arctic Ocean causing higher sea surface temperatures 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 sea surface temperatures 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. Satellite measurements and numerical models indicate that cooling would dominate.

In general, negative feedback tends to dominate over positive feedback in Earth's climate system, 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 in Earth's climate system that amplifies climate change is described as [(positive)(negative)] feedback.
2. In general, [(negative)(positive)] feedback tends to prevail in Earth's climate system.

• 18 April 1848...U.S. Navy expedition to explore the Dead Sea and the River Jordan, commanded by LT William F. Lynch, reached the Dead Sea. (Naval Historical Center)
• 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 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 Álvares Cabral became the first known European to sight Brazil, claiming it for Portugal. (Wikipedia)
• 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)
• 24 April 1928...The fathometer was patented by Herbert Grove Dorsey (No. 1,667,540). The invention measured underwater depths by using a series of electrical sounds and light signals. (Today in Science)

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Prepared by AMS DS Ocean Central Staff and Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
ã Copyright, 2005, The American Meteorological Society.