Oceanic Temperatures and Climate Effects
The study of ancient climates and oceanic temperatures can lend clues as to how future climate changes might happen. An international team of researchers, led by the members of the Institut de Ciència i Tecnologia Ambientals (ICTA) at the Universitat Autònoma de Barcelona (UAB), has published studies of the evolution of Northern Pacific and Southern Atlantic sea surface temperatures, dating from the Pliocene Era; some 3.65 million years ago. The data obtained in the reconstruction indicate that the regions closer to the poles of both oceans have played a fundamental role in climate evolution in the tropics.
During the Pliocene epoch, the global average temperature was 5-7°F higher than today with global sea levels being about 80 feet higher and with a reduced northern hemisphere ice sheet. Towards he end of the era global cooling occurred.
The formation of an Arctic ice cap was started as indicated by an abrupt shift in oxygen isotope ratios in the North Atlantic and North Pacific ocean beds. Mid-latitude glaciation was probably underway before the end of the epoch. The global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas.
The study of Pliocene climate has now been the object of intense research for several years, as this era represents (in the Earth's history) the most recent climatic period in which, over a sustained period of time, average temperatures on the planet were significantly higher than those of the present. As a result, the Pliocene is thought of as a climatic period that might be representative of the Earth's climate in future conditions of global warming.
A permanent El Niño state existed in the early mid Pliocene, warmer temperature in the eastern equatorial Pacific increased a water vapor greenhouse effect and reduced the area covered by highly reflective stratus clouds thus decreasing the albedo of the planet.
In the new study, the researchers analyzed marine sediment collected by the Integrated Ocean Drilling Program (an international initiative), and measured its composition of organic compounds termed alkenones. Alkenones are highly resistant organic compounds produced by phytoplankton. Some are known to respond to changes in water temperature by altering the production of long chain unsaturated alkenones. At higher temperatures, more of the di-unsaturated molecules are produced than tri-unsaturated. The molecules are resistant to degradation, and can be recovered from sediments up to 110 million years old. Hence they can be used as an indicator of climatic temperatures.
The ambient water temperature in which the organisms dwelt can be estimated from ratio of their unsaturated alkenones (C37-C39).
Reconstruction of the surface temperature in the Northern Pacific and Southern Atlantic has enabled a simultaneous sea surface cooling to be identified in the subpolar regions of the two hemispheres in the period between 1.8 and 1.2 million years ago. This finding coincides in time with the formation of the equatorial Pacific cold tongue which currently almost disappears during the "El Niño" phenomenon.
Previous studies have shown that, during the warm conditions of the Pliocene, this cold tongue was not present; thus, conditions in the equatorial Pacific were similar to those of a permanent "El Niño" episode. Data obtained in this study indicate that the cooling and expansion of polar waters towards the tropics intensified atmospheric circulation.
The research undertaken provides empirical evidence, previously suggested by studies using climatic models, that the oceans in high latitudes may play a key role in the control of tropical climate and, most especially, in the thermocline depth in the equatorial Pacific. In a sense the north Pacific and the South Atlantic act somewhat as a thermostat control for global climate changes.
The study contributes to the debate on which regions on the planet are those that, when their local climates change, give rise to processes of global change. It is often indicated that these regions are found in the tropics, since, when phenomena such as "El Niño" occur, they have global repercussions. This study provides evidence for the key role that may be played by the polar regions of the planet.
Currently, high latitudes are the ones that appear to be responding in the clearest way to global warming. Given the direct relationship established in this study between high latitude climate variation and thermocline depth in the equatorial Pacific, it appears possible that the equatorial Pacific cold tongue will eventually respond to the current warming, giving rise to a climatic scenario similar to that of the Pliocene.
For further information: http://www.eurekalert.org/pub_releases/2010-06/uadb-tkr061810.php