日本研究人員通過(guò)對(duì)珊瑚化石的分析發(fā)現(xiàn)，厄爾尼諾現(xiàn)象在約350萬(wàn)年前就已經(jīng)出現(xiàn),，這是目前發(fā)現(xiàn)的全球最古老的證明厄爾尼諾現(xiàn)象的化石,。
日本北海道大學(xué)與國(guó)立科學(xué)博物館和產(chǎn)業(yè)技術(shù)綜合研究所的聯(lián)合研究小組,，對(duì)在菲律賓呂宋島的上新世溫暖期（約460萬(wàn)年前至約300萬(wàn)年前）地層中發(fā)現(xiàn)的一種微孔珊瑚化石進(jìn)行了分析,。研究小組根據(jù)同一地層出現(xiàn)的浮游植物化石,，斷定珊瑚化石的年代在約350萬(wàn)年前。
珊瑚在生長(zhǎng)過(guò)程中,，會(huì)如同樹(shù)木的年輪一樣,，每年都會(huì)產(chǎn)生一道橫線,，而作為珊瑚主要成分的碳酸鈣中碳同位素的比例會(huì)隨著海水溫度和鹽分的變化而變化。研究小組以此為線索,，根據(jù)化石上的橫線數(shù)目,，分析了約70年間海水水溫的變化,，結(jié)果發(fā)現(xiàn)每隔三,、四年會(huì)出現(xiàn)水溫大幅下降和降水減少的現(xiàn)象。
化石顯示的水溫變化與現(xiàn)在出現(xiàn)厄爾尼諾現(xiàn)象時(shí)菲律賓附近的氣候很相似,。研究人員說(shuō),，化石表明當(dāng)時(shí)的厄爾尼諾現(xiàn)象是持續(xù)發(fā)生的，并且周期比現(xiàn)在的要短,。有關(guān)論文發(fā)表在3月9日的英國(guó)《自然》雜志網(wǎng)絡(luò)版上,。
厄爾尼諾現(xiàn)象指南美秘魯近海的海水溫度升高,，導(dǎo)致全球氣象異常的現(xiàn)象,。研究小組認(rèn)為，當(dāng)時(shí)的氣溫比現(xiàn)在高2至3攝氏度,，如果當(dāng)前全球變暖的趨勢(shì)持續(xù)下去,，厄爾尼諾現(xiàn)象很可能周期出現(xiàn)。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature doi:10.1038/nature09777
Permanent El Niño during the Pliocene warm period not supported by coral evidence
Tsuyoshi Watanabe,1 Atsushi Suzuki,2 Shoshiro Minobe,1 Tatsunori Kawashima,1 Koji Kameo,3 Kayo Minoshima,2 Yolanda M. Aguilar,4 Ryoji Wani,5 Hodaka Kawahata,6 Kohki Sowa,1 Takaya Nagai1 & Tomoki Kase7
The El Ni?o/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3–5 million years ago) may have existed in a permanent El Ni?o state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean1. This suggests that during the PWP, when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change2, ENSO variability—and related global climate teleconnections—could have been radically different from that today. Yet, owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites, this fundamental climate characteristic of the PWP remains controversial1, 3, 4, 5, 6, 7, 8, 9, 10. Here we show that permanent El Ni?o conditions did not exist during the PWP. Our spectral analysis of the δ18O SST and salinity proxy, extracted from two 35-year, monthly resolved PWP Porites corals in the Philippines, reveals variability that is similar to present ENSO variation. Although our fossil corals cannot be directly compared with modern ENSO records, two lines of evidence suggest that Philippine corals are appropriate ENSO proxies. First, δ18O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-δ18O events in the fossil corals closely resemble the decreases in δ18O seen in the live coral during El Ni?o events. Prior research advocating a permanent El Ni?o state may have been limited by the coarse resolution of many SST proxies, whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly.
