http___matrixworldhr.wordpress.com_2012_05_04_konacno-dokaz-mi-nismo-krivci-za-globalne-klimatske-promjene__1.xml
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JournalOfSciences (Mar. 21, 2012) The first day of spring brought record high temperatures across the northern part of the United States, while much of the Southwest was digging out from a record-breaking spring snowstorm. The weather, it seems, has gone topsy-turvy. Are the phenomena related? Are climate changes in one part of the world felt half a world away? To understand the present, scientists look for ways to unlock information about past climate hidden in the fossil record. A team of scientists led by Syracuse University geochemist Zunli Lu has found a new key in the form of ikaite, a rare mineral that forms in cold waters. Composed of calcium carbonate and water, ikaite crystals can be found off the coasts of Antarctica and Greenland. "Ikaite is an icy version of limestone," say Lu, assistant professor of earth sciences in SU's College of Arts and Sciences. "The crystals are only stable under cold conditions and actually melt at room temperature." It turns out the water that holds the crystal structure together (called the hydration water) traps information about temperatures present when the crystals formed. This finding by Lu's research team establishes, for the first time, ikaite as a reliable proxy for studying past climate conditions. The research was recently published online in the journal Earth and Planetary Science Letters and will appear in print on April 1. Lu conducted most of the experimental work for the study while a post-doctoral researcher at Oxford University. Data interpretation was done after he arrived at SU. The scientists studied ikaite crystals from sediment cores drilled off the coast of Antarctica. The sediment layers were deposited over 2,000 years. The scientists were particularly interested in crystals found in layers deposited during the "Little Ice Age," approximately 300 to 500 years ago, and during the "Medieval Warm Period," approximately 500 to 1,000 years ago. Both climate events have been documented in Northern Europe, but studies have been inconclusive as to whether the conditions in Northern Europe extended to Antarctica. Ikaite crystals incorporate ocean bottom water into their structure as they form. During cooling periods, when ice sheets are expanding, ocean bottom water accumulates heavy oxygen isotopes (oxygen 18). When glaciers melt, fresh water, enriched in light oxygen isotopes (oxygen 16), mixes with the bottom water. The scientists analyzed the ratio of the oxygen isotopes in the hydration water and in the calcium carbonate. They compared the results with climate conditions established in Northern Europe across a 2,000-year time frame. They found a direct correlation between the rise and fall of oxygen 18 in the crystals and the documented warming and cooling periods. "We showed that the Northern European climate events influenced climate conditions in Antarctica," Lu says. "More importantly, we are extremely happy to figure out how to get a climate signal out of this peculiar mineral. A new proxy is always welcome when studying past climate changes." Other social bookmarking and sharing tools: Story Source: The above story is reprinted from materials provided by Syracuse University. Note: Materials may be edited for content and length. For further information, please contact the source cited above. Journal Reference: - Zunli Lu, Rosalind E.M. Rickaby, Hilary Kennedy, Paul Kennedy, Richard D. Pancost, Samuel Shaw, Alistair Lennie, Julia Wellner, John B. Anderson. An ikaite record of late Holocene climate at the Antarctic Peninsula. Earth and Planetary Science Letters, 2012; 325-326: 108 DOI: 10.1016/j.epsl.2012.01.036 Note: If no author is given, the source is cited instead. Disclaimer: Views expressed in this article do not necessarily reflect those of JournalOfSciences or its staff.
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Prevela i uredila: Ljubica Šaran Matrix World Pronađeni su dokazi u rijetkim mineralima koji su zabilježili globalne temperature, s njima se otkrilo planetarno zagrijavanje iz daleke prošlosti, svi ti nalasci potpuno bacaju u sumnju općeprihvaćenu ortodoksnu teoriju o „globalnom zagrijavanju.“ Trenutačne teorije krive djelovanje ljudi i našeg društva na klimatske promjene, poglavito na globalno zagrijavanje, no takve teorije su potpuno dovedene u pitanje s novim nalascima i studijama koje dokazuju da se za vrijeme srednjeg vijeka Europa i Antartika zagrijala. Nakon toga oba područja su se „ohladila“ i nastalo je mini ledeno doba. (Poznato pod nazivom „Marauderov minimum.“ Op. Tim znanstvenika predvođenog geokemičarom Zunli Luom sa Sveučilišta Syracuse u New Yorku, je otkrio da je zatopljenje za vrijeme srednjeg vijeka prije 1000-500 godina obuhvatilo Europu i druge dijelove svijeta. U stvari to zatopljenje je bilo toliko veliko da je obuhvatilo i Antarktik. Do sada je Internacionalni Međuvladin Odbor o Klimatskim Promjenama – Intergovernmental Panel on Climate Change (IPCC) tvrdio da se srednjevjekovno zatopljenje dogodilo samo u Europi. Čudnovati mineral ikait. Pa ipak profesor Lu je pronašao dokaze koji pokazuju da se to srednjevjekovno zatopljenje dogodilo na puno širem i većem području – dokazi leže u mineralu koji se naziva ikait, koji se formira u hladnoj vodi. „Iakait je vrsta vapnenca,“ rekao je Lu. „Njegovi kristali su stabilni samo u hladnim uvjetima i klimi, i u stvari se otapaju na sobnoj temperaturi.“ Ikait u potpunosti zavisi od hladne vode, koja ga drži na okupu – taj proces se zove hidracija vode – uz pomoć takvih nalaza dobivamo informacije o temperaturama, kada su se stvorili kristali. Istraživanja Luovog tima su po prvi put doveli ikait u direktnu vezu s temperaturnim razlikama, točnije ustanovili su da je ovaj mineral pouzdan izvor u otkrivanju klimatskih promjena u prošlosti. Ikait je dokazao da se Antarktik zagrijavao u prošlosti. Lu je izjavio da njegova istraživanja nisu ispitivale trenutačne poveznice s klimom i da su njegova istraživanja fokusirana na područje Antarktika, također dodaje da to još uvijek nije dokaz da se tada zagrijala cijela Zemlja. Znanstvenici su izučavali kristale ikaita koje su izvadili zajedno s ledenom jezgrom duboko ispod površine leda Antarktika. Sedimenti leda koje su ispitivali dosežu 2000 godina u prošlost. Znanstvenici su najviše bili zainteresirani za kristale pronađene u slojevima naslaga koje su nastale za vrijeme malog ledenog doba prije otprilike 300-500 godina, te za kristale koji su nastali za vrijeme srednjevjekovnog zagrijavanja koje se zabilježilo neposredno prije Marauderovog minimuma. Oba dva klimatska događaja su dokumentirana u Sjevernoj Europi, no prijašnje studije nisu mogle dokučiti jesu li se događaji odvijali izvan Europe. Točnije jesu li se posljedice osjećale i na Antarktiku? Luov tim je potvrdio da je Antarktik sinkrono događajima u Europi prošao kroz zagrijavanje i hlađenje. Oni su otkrili ove nalaze zahvaljujući količini izotopa teškog kisika koji se mogao pronaći u kristalima ikaita. Za vrijeme hladnih perioda njih je bilo puno, dok ih je za vrijeme toplih perioda bilo malo. „Mi smo dokazali da su klimatski događaji u Sjevernoj Europi utjecali na klimatske događaje na Antarktiku,“ rekao je Lu. „Što više, zaista smo zadovoljni jer smo shvatili kako možemo otkriti klimatske uzorke zapisane u čudnovatom mineralu ikaitu. Novi načini istraživanja su uvijek dobrodošli naročito ako se istražuju klimatske promjene.“ Ova studija je nedavno publicirana u žurnalu Earth and Planetary Science Letters.