 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
| . |  |
. |
Marine Sediments Shed Light On 50,000 Years Of Climate Changes
For years, researchers have examined climate records indicating that millennial-scale climate cycles have linked the high latitudes of the Northern hemisphere and the subtropics of the North Pacific Ocean. What forces this linkage, however, has been a topic of considerable debate. Did the connection originate in the North Pacific with the sinking of oxygen-rich waters into the interior of the ocean during cool climate intervals, or did it originate in the subtropical Pacific with the transfer of heat between the ocean and the atmosphere? New research, led by scientists from the Lamont-Doherty Earth Observatory of Columbia University and publishing in the June issue of the journal Geology, shows that over the last 52 thousand years, these millennial-scale climate shifts linking the high latitudes of the Northern hemisphere with the subtropical Pacific have been associated with large variations in marine productivity off the coast of western North America. Changes in marine fertility in this area probably arose from local changes in subsurface nutrients concentrations that were driven remotely by wind patterns at low latitude. These millennial-scale climate cycles may have been driven by forces similar to El Nino-Southern Oscilations originating in the tropical Pacific on shorter time scales. "Such records provide an indication of the way climate has changed in the past and, therefore, hopefully also an indication of the way climate may change in the future," says Lex van Geen, Doherty Senior Research Scientist, Lamont-Doherty Earth Observatory, and Chief Scientist of the oceanographic expedition that collected the sediment cores used for this study. These findings overturn the previously held theory that bottom-water oxygen levels in Santa Barbara Basin off California were primarily linked to changes in ventilation of the North Pacific rather than changes in marine productivity. The evidence for the newly proposed theory was found in a 15-m-long sediment record, spanning the past 52 thousand years, collected off Baja California, Mexico in 1999. The core comes from a site with high sedimentation rates (30 cm/thousand years). The sediments indicate a remarkably consistent teleconnection between changes in marine productivity at this eastern Pacific location, as indicated by several independent proxies, with millennial-scale climate change over the North Atlantic, as recorded by the oxygen isotopic composition of Greenland ice. "The strength of the connection between the temperature record over Greenland and marine production off Baja California really challenges our understanding of the linkage between high and low latitude climate processes. Our results imply that variations in the workings of the equatorial heat engine may be as important as high latitude processes at millennial timescales," states Joseph Ortiz, Assistant Professor of Geology at Kent State University and first author of the Geology research paper. Dr. Ortiz began working on this research project as a Doherty Associate Research Scientist at the Lamont-Doherty Earth Observatory of The Earth Institute at Columbia University. A possible interpretation of the new data is that the current balance of El Nino conditions in the Pacific Ocean, which favor the supply of nutrients to the surface ocean and therefore high marine productivity today and during warm climate intervals of the past 52 thousand years, was altered towards El Nino-like conditions and a lower supply of nutrients during cool climate intervals. The same team of scientists is currently working on a sediment core collected during the same 1999 expedition from the Soledad Basin (25 N), an anoxic basin with many of the same desirable properties as the Santa Barbara Basin, but located closer to the tropics, a region that some scientists consider to be an important driver of climate change in the past. Sedimentation rates in this basin are 110 cm/thousand years. Related Links University of Columbia SpaceDaily Search SpaceDaily Subscribe To SpaceDaily Express 
Continents Played Key Role In Collapse And Regeneration Of Earth's Early Greenhouse
by Dawn LevyStanford CA (SPX) Jun 04, 2004 If a time machine could take us back 4.6 billion years to the Earth's birth, we'd see our sun shining 20 to 25 percent less brightly than today. Without an earthly greenhouse to trap the sun's energy and warm the atmosphere, our world would be a spinning ball of ice. Life may never have evolved.
|
|
| |||||||||
| The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service. |
