Climate changes the oceans testify it.
Extreme phenomena, for biodiversity, consequences are innumerable.The oceans also send us of signs perhaps less spectacular, but more obvious, of actual climatic change.
Never the oceans had been watched of also near. Permanently, a multitude of data is gathered in effect thanks to oceanographic campaigns, satellites, networks of water wings or core sampling of sediments. They are then archived then synthetized by more and more realistic simulation. Why all these efforts ? Simply because the oceans are one of our best tools to understand(consist of) actual climate and its announced changes, but also past climates and their changeability. In effect, they react finely to the impairments of the atmosphere, to the changes of temperature, of pH or saltiness, and print their mark in return on the climate of the planet. Of their side, the scientists are today able of noticing(observing) the first effects of total warming on the ocean. To them to interpret these signs and to envisage , globalwarming awareness2007 could arrive at us in the course of this century.
Storm of 1999, particularly intense events El Niño, devastation of News-Orléans by the hurricane Katrina : here are indeed the most remarkable signs of a possible ongoing climatic change,globalwarming awareness2007. Besides, for public opinion, these extreme phenomena are often proof which the fault of climate already hits(strikes) us. To the scientists to modify these purpose(comments). And thanks to the battery of campaigns of observation which they set up, thanks to the gathered data in situ which feed their models then, the oceans are them for it of a big help(assistance).
Let us take the case of El Niño, an anomaly of climate which happens every three-seven years and that draws away an inversion of winds and currents of surface in Pacific. Her(its) appearance of 1997, one of the strongest ever recording, was a cataclysm : uncontrollable fires of forest in Indonesia, bloody rains in Central America and from the South of globalwarming awareness2007, dryness on Nordeste in Brazil, etc. However, for Pascale Delecluse, seeker in LSCE, « it is obvious in no way that climatic warming has an effect on El Niño. They cannot say if the force of events of 1982-83 and 1997 overlaps in total warming or if this one is the representative ». On the side of modelling, which take into account numerous oceanic data, no real tendency frees from different simulation. The mechanisms which trigger off El Niño are too badly known and still avoid our capacity of modelling.
On the other hand, on the side of Atlantic tropical and from Caribbean, a recent result comes to counter the idea of a multiplication of cyclones. « We made simulation by taking into account the total warming envisaged for the xxie century, and we do not see from increase of their frequency, asserts(affirms) Jean-François Royer, researcher with Weather forecast France and globalwarming awareness2007. The birth of cyclones depends on the difference of temperatures between the low and the high atmosphere. Future warming should not change the vertical gradient of temperatures a lot. » Nevertheless, this simulation envisages that these destructive whirls could be more powerful 1. Terrible(awful) Katrina, Emily and Rita of last cyclonic season are they already signs of this strengthening ? An article appeared in Science in September, 2005 maintained that the number of cyclones of category 4 and 5 had augmented by 57 % between 1970 and 2004. « For my part, I think that series taken into account by this study are still too short to draw » globalwarming awareness2007 is final conclusions from it, modifies Jean-François Royer.
The inexorable rise(climb) of waters
The oceans also send us of signs(signals) perhaps less spectacular, but more obvious, of actual climatic change. Among them, the rise(climb) of waters. So, the inhabitants of islands Tuvalu are anxious : they think that their archipelago is not going to defer being gulped down.globalwarming awareness2007 For Anny Cazenave, additional head of the Laboratory of space studies in geophysics and oceanography (Legos) 2), reality is more complex, but less worrying, for these atolls just above water. « The rise(climb) of the medium level of the ocean around this archipelago is only some millimetres a year. On the other hand, certain phenomena as El Niño can make vary 20-centimetre level shortly. I think that eventually, these islands will not be able to be any more lived. »
For fifty years, the medium level of the sea takes up 1,8 mm a year, but this elevation accelerated to attain(affect) 3 mm a year since a dozen years. According to the researchers, about 60 % of this elevation am owed to the thermal widening of the ocean which, as the atmosphere, warms itself up. The rest explains by the cast iron of the glaciers of mountain (0,8 mm a year) and the cast iron of the ice of Greenland and, in a lesser measure, from the Antarctic (0,2 - 0,4 mm a year). « This elevation is not homogeneous across the globe because warming is not uniform. This one is function(office) of the transport of warmth performed by the oceanic circulation », explains Anny Cazenavefrom globalwarming awareness2007. The data which allowed to arrive at these results are first measurements(measures) by satellite (among whom Jason-1, Envisat and soon Jason-2), a true revolution for the study of the oceans and climates.
Their altimeters allow very definite mapping of the level of the oceans. The researchers also have marégraphiques measurements(measures) (height of tides) dependable(reliable) over last fifty yearsafter globalwarming awareness2007, but they limit themselves to harbours and to some coastal zones.
If it makes no doubt that the increase of greenhouse effect contributes to this acceleration of the rise(climb) of waters, it is always very difficult to know what is the part of natural changeability. And the detachment which give measurements(measures) altimétriques is not still sufficient to appreciate evolutions well on long term.
Fresh water in the attack of salt water andglobalwarming awareness2007 Other sign of visible(obvious) climatic warming in the oceans : the cast iron of the polar ice. If, of the side the Antarctic, the skull cap and see ice well seem to resist, the detachment of the Arctic see ice (to see p. 19) am already apparently observable. « We are also rather anxious for the ice of Greenland, alert Frederica Rémy, seeker in Legos. While the coat of ice dwindles on the edges of this island, it thickens in the central regions because of an increase of rainfall. And if the slope augments, the speed of flow also augments. Many researchers think that the detachment of this ice could get carried away. »
A destabilization of the Arctic system would have of strong consequences to the saltiness of waters of surface of north Atlantic. « At the moment, the cast iron of the ice of Greenland does not represent a big provision of fresh water in comparison with the Siberian rivers », modifies Gil Reverdin, researcher in Locean. The saltiness of waters of surface is a parameter very studied by the oceanographers. This one depends on rainfall, on currents of surface and on exchanges with the deep coats of water. And, « on long term, an important variation of saltiness in north Atlantic could have a negative impact on the whole circulation thermohaline, as the slowing down of the Gulf Stream », follows(continues) the researcher. In effect, who says fall of saltiness says loss of specific gravity. And, it is precisely a benefit of specific gravity that allows waters of the Gulf Stream to dive(flounder) in high degrees of latitude.
Since the seventies, the researchers measured a reduction of saltiness in Atlantic above the 45 degrees of north degree of latitude. However, this one seems to go back up for five or ten years. Natural changeability or first observations of a climatic fault ? In a system which fluctuates, at all times difficult to cut. The positive point is that, thanks to a huge international effort, the tools of measure are in the point consequently. Networks of water wings as Pirates off Brazil allows to collect(store) series of notings down of temperatures and saltiness since 1997. From 2001, Argo network fanned out with even more sophisticated(mannered) instruments : prospinners floating in 1 000 or 2 000 metres deep and which go back up every ten days to the surface to measure various physical parameters throughout the column of water. A true happiness for the oceanographers and modélisateurs ! They do not have more than to wait that series of data are rather long to measure consequences of human activities.
A more and more corrosive ocean
Other phenomenon noticed(observed) by the researchers in the ocean : the acidification, direct consequence of the program(issue) of CO2 owed in frenetic human activity. If the influence of this gas on climate is still difficult to estimate, the acidification of the sea leaves hardly place in doubt. It obeys chemical basic equations in effect. In 2005, an international team "globalwarming awareness2007" simulated fall of pH of the ocean in the course of this century according to the scenarioes of program(issue) of carbon dioxide. Results are oppressive : before fifty-one hundred years, the ocean will have become corrosive for numerous organisms. The aragonite, a form of limestone, will be soluble(solvable) in the seawater, drawing away the disappearing of animals as ptéropodes, a group of molluscs planctoniques the envelope of which is made of this material. « The increase of the atmospheric content of CO2 has already caused(provoked) a fall of 0,1 point of pH. In 2100, it will have lowered 0,4 point », asserts(affirms) James Orr, researcher in LSCE.
For biodiversity, consequences are innumerable. So, ptéropodes is a fundamental(basic) element of numerous food chains in high degrees of latitude. Whales, cods and young salmons ingest huge quantities. « With the increase of CO2 in water, the carbonates which are of use for the training(forming) of limestone will be less available. Even if they do not attain(affect) the threshold of dissolution of limestone, organisms will have to invest much more energy to fabricate the exoskeleton and will be more fragile. The tropical corals are very threatened, and with them, a comparable biodiversity in that of the equatorial forests. For the corals of cold waters, situation is even more serious : in less than hundred years, the two thirds of these reefs will bath in corrosive waters », deplores James Orr. Is damage already observable ? « They are not sure(reliable) there. They have only little data and they are especially qualitative, but some researchers think that corals are already more fragile than before. »
The witnesses an past
The rings of the Austral pétoncle allow to know temperatures with an annual resolution. © E. Amice / Photographic collection national centre for scientific research Hurricanes, rise(climb) of waters, cast iron of ice, acidification : if the ocean informs us directly on ongoing climatic changes, it is also a very good tool to know what took place before. « And, in the polemic to know which is the part of the man in climatic warming and which will be consequences, they absolutely need to know the past », assert(affirm) Edward Bard, paléoclimatologue in the European Centre of research and education of géosciences of environment (Cerege) 3). Witnesses of these past epochs, corals, shellfishes, diatomées and coccolithophoridés tell big climatic shake-ups an past. But interpretation is not simple : the information which they give is always often fragmented, sometimes ambiguous and extremely costly to extract. But they are the long-term only memory of the ocean. The reconstructions of paleoclimates which they allow serve then for testing climatic models, thanks to that they try to reproduce(copy) in a realistic manner the confusion which the world knew. A technology with the wind in poop is the extraction of carrots in marine sediments. Thanks to carrots taken in the Indian ocean and from Pacific Edward Bard is, and her(its) team can so show that when the deep Atlantic circulation was weak(slow), there happened major changes of the saltiness of waters of surface and rate of oxygenation with medium depth in the tropical oceans. During these periods, major disturbances of rainfall level were felt in Central America and in the south of Asia, with notably a complete drainage of the Indian subcontinent.
With another 40-metre carrot, harvested in 2003 during a campaign in the Austral seas, Xavier Crosta, researcher of the laboratory of Bordeaux « Environments and oceanic paléoenvironnements » (Epoc) 4), studies particularly the siliceous skeletons of diatomées, very abounding unicellular seaweeds in the cold seas. « Different kinds of diatomées have marked environmental priorities, what by way of very good indicators for temperatures, expanse(span) of floe and content of nutriments of waters of surface. »
The isotopic analyses of organic matter preserved in sediments provide other information : for instance, the report between carbon 13 and carbon informs 12 us about the content of water of dissolved CO2 and about primary production. « Eventually, with this carrot, we shall acquire climate on ten thousand years with a lower precision in decade. For most important and best preserved periods, we shall arrive even at a practically seasonal ladder », asserts(affirms) Xavier Crosta.
Among other studied organisms, corals are a wonderful tool for the researchers : they can point out the evolution of marine level and their bands of growth provide data on temperatures in the annual ladder. Coccolithophoridés, another group of unicellular seaweeds, are poor markers of temperature, but point out very well the intensity of primary production in the ocean.globalwarming awareness2007« This group interests us in comparison with the carbon cycle. If there is more primary production, the ocean becomes a well of carbon and brings down the rate of CO2 of the atmosphere », explains Luke Beaufort, researcher in Cerege.
The coccolithophoridés of Pacific showed that primary production was strong during glacial periods, when the content of CO2 of the atmosphere was weak(slow).
To supplement the picture of the past climates, the scientists are always in search of new markers paléoclimatiques. They are also in search of models allowing to understand(consist of) how the characteristics of environment record themselves in the limestone produced by organisms. In The Laboratory of the sciences of the marine environment (Lemar) 5) of Brest, the researchers so succeeded in deciphering the message contained in shells of bivalve as the famous scallop. « It is an extraordinary(exceptional) tool : it bivalve marks streaks of growth every day. Thanks to the report between the concentration of oxygen 18 and oxygen 16 of its shell, they can acquire 300 measurements(measures) of temperature more a year for, to the half degree near, gets enthusiastic Yves-Marie Paulet, teacher-researcher in Lemar. Thanks to scallops discovered in “poubelles ” prehistoric, we could rebuild temperature charts day after day of a distant period of several millenniums ! » In brief, with still many other kinds in their fishnets, as the Austral pétoncle, who saw(lived) on the coastal region the Antarctic, our researchers do not lack marine means to understand(consist of) the starts of our climate.
To study the oceans under all angles, oceanographic programs increase in the world. Coordinated in France by the national Institute of the sciences of the World (Insu), they require series of campaigns in open sea from which the bet there œuvre returns to Ifremer or to the Institute Paul-Émile Victor. It was the case of Program multiple-subject ocean méso-ladder (Apple), campaigns of which took place between 2000 and 2001. He allowed to understand(consist of) better how oceanic winter waters of surface bury themselves in intermediate depths and to study the mechanisms of the stocking of carbon in the ocean. Currently, it is Egee program globalwarming awareness2007, oceanographic shutter of Analyses multiladders of the Africain monsoon (Amma) which gathers an important part of the oceanographic community. Egee, whose third campaign ends these days, will allow to know the oceanic circulation better in the gulf of Guinea, as well as her relations with climate and with Africain monsoon. Also let us name Damocles, for the study of see ice in Arctic as well as big international Integrated Ocean Drilling Program (IODP) program, in which participle the NATIONAL CENTRE FOR SCIENTIFIC RESEARCH globalwarming awareness2007, which, thanks to boring in marine sediments, notably allows to study hydroxides of gas, just like the campaign finished(ended) in October, 2005 1.
A thing is sure(reliable) : the punctual(prompt) campaigns are not enough. « We need long series of measurements(measures) » : here is the refrain of all researchers and globalwarming awareness2007 who study oceans and climate. It is for it that services of observation in ocean, atmosphere and climate were set up. Dependent on several research establishments, they are the French contribution with big international networks of instrumentation. Among them, let us name Ovide, who allows to have measurements(measures) definite and repeated (temperatures, saltiness, etc) in north Atlantic, Oiso / Caraus for the rate of CO2 in the Indian ocean, Dyfamed for different measurements(measures) in Mediterranean Sea or else Somlit for the observation of hydroclimatic, chemical and biological parameters on the French coastal region.
S. E.