Dear Readers,
I am not a scientist -- my bad!!!!
UPDATE: Dear Readers,
I just located the abstract in Nature related to the Science Daily article below, and basically the Science Daily article draws out the wrong info. Please read the abstract in the post above this one.
Dear Readers,
This article focuses on the transfer of water vapor over the Atlantic from the equator during colder climes. Try to read the article from the perspective of hotter climes, thinking of what happens on the Pacific side of Central America. Also note that, this year, the Intertropical Convergence Zone decided not to go north as usual with the solar equator, thus dumping continuous and enormous quantities of rain on northern and northeastern Brazil, flooding some 500,000 people out of their homes. Next, have a look at the water vapor circulation animations at the links below and tell me where the water vapor from the equator is going now. Looks to be leaving the eastern Pacific south of Baja, Mexico, circles over the Midwest, then back down to the equator on the Atlantic side -- not much like the old days, is it?
http://weather.unisys.com/satellite/sat_wv_hem_loop-12.html
http://www.ssec.wisc.edu/data/east/animation/goeseastwv.html
A climate-change amplifying mechanism
ScienceDaily, March 8, 2007 — During the past 90,000 years, there were alternating hot and cold periods lasting several thousand years each which resulted in a modification of global oceanic circulation. With the help of paleoclimatic and paleo-oceanographic indicators, scientists at CEREGE1 have highlighted a feedback mechanism of ocean circulation on the climate which reinforces this heating or cooling. This mechanism relies on a close link between the circulation of the North Atlantic and the tropical hydrology of Central America. This study, published in the February 22, 2007, review edition of Nature, should allow us to better understand and therefore better predict the effects of climate change on oceanic circulation.In the past, major and rapid climatic variations which took place notably during the last glacial period (Heinrich period) disturbed ocean circulation. Climatic archives (marine and lake sediment, polar ice, stalagmites) show the close relationship existing between climatic variations and oceanic circulation. Changes in oceanic circulation in the North Atlantic have influence on a planetary level by affecting, in particular, the water cycle. These changes are accompanied by a shift in the climatic equator which separates the trade wind systems of the two hemispheres: southwards during cold events and northwards during hot ones.Central America, a narrow continental strip which separates the Atlantic and Pacific oceans, plays a key role in this system. On the Atlantic side surface waters evaporate, which increases salinity. The water vapour is transferred by the trade winds to the Pacific where it is deposited as rain, thus lowering salinity there. This enormous transfer of water (several hundred thousand cubic meters per second) maintains a contrast in salinity between the two oceans. The surface waters of the tropical Atlantic are then transported, via the Gulf Stream, towards the high latitudes where they warm the atmosphere before plunging into the abysses in the convection zones situated in the seas of Norway, Greenland and Labrador. The deep waters formed by this process then flow into the world ocean, purging the North Atlantic of part of its excess salt.
The scientists at CEREGE1 reconstituted the variations in surface water salinity in the area where the water vapour coming from the Atlantic is deposited. To do this they worked on the measurements taken in marine sediments collected in 2002 west of the Isthmus of Panama by the French oceanographic ship, the Marion Dufresne. This study shows that the cold Heinrich periods correspond to increases in salinity in the east Pacific. This is synonymous to a decrease in the transfer of water vapour. By comparing their results to other studies done in the Atlantic sector and in South America, the scientists were able to describe a feedback mechanism which amplified the climatic disturbance. During cold periods the trade winds, loaded with humidity, migrated southwards. Unable to cross the Andes part of the rain, which would normally have lowered the salinity of the East Pacific, fell in the Amazon basin. This feedback had the effect of re-injecting rainwater into the Atlantic, thereby decreasing the ocean's salinity. This water was then transported to the higher latitudes, contributing to the weakening of deep oceanic circulation, thereby reinforcing the cooling above and around the North Atlantic.
Today, the fact that global warming could disturb the water cycle and lead to a slowing down of the North Atlantic circulation is a real subject of concern. Oceanographic data from the last 50 years suggest that hydrographic changes (temperature and salinity), as well as a lessening of the flow of water transported by certain surface and deep-sea marine currents, have already occurred in the North Atlantic. The risk of an even greater variation of oceanic circulation by the end of this century or the beginning of the next needs to be taken seriously and actively studied.
Link to article: http://www.sciencedaily.com/releases/2007/02/070226131713.htm
Posts
Dear Cassandra,
I think you misunderstood the point of the Nature paper and of the Sciencedaily report, that indeed properly and fairly relates the essential of the original article.
Guillaume
Yeah, I think I did misunderstand it -- sorry.
Tenney
btw -- that darned Cassandra name has followed me around via yahoo for more than 10 years -- it has nothing to do with this blog but rather with a family financial matter in 1998.