{"179651":{"#nid":"179651","#data":{"type":"news","title":"Coral Records Suggest that Recent El Nino Activity Rises Above Noisy Background","body":[{"value":"\u003Cp\u003EBy examining a set of fossil corals that are as much as 7,000 years old, scientists have dramatically expanded the amount of information available on the El Nino-Southern Oscillation, a Pacific Ocean climate cycle that affects climate worldwide. The new information will help assess the accuracy of climate model projections for 21st century climate change in the tropical Pacific.\u003C\/p\u003E\u003Cp\u003EThe new coral data show that 20th century El Nino Southern Oscillation (ENSO) climate cycles are significantly stronger than ENSO variations captured in the fossil corals. But the data also reveal large natural variations in past ENSO strength, making it difficult to attribute the 20th century intensification of ENSO to rising carbon dioxide levels. Such large natural fluctuations in ENSO activity are also apparent in multi-century climate model simulations.\u003C\/p\u003E\u003Cp\u003E\u201cWe looked at the long-term variability of ENSO in the climate models and asked how it compares to the long-term variability of ENSO in the real world,\u201d said Kim Cobb, an associate professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. \u201cWe show that they actually match fairly well. This project sets the stage for conducting more detailed data-model comparisons from specific time intervals to test the accuracy of ENSO characteristics in the various models.\u201d\u003C\/p\u003E\u003Cp\u003EThe research, sponsored by the National Science Foundation (NSF), was reported January 3 in the journal \u003Cem\u003EScience\u003C\/em\u003E. Researchers from the Scripps Institution of Oceanography and the University of Minnesota also contributed to the work.\u003C\/p\u003E\u003Cp\u003EEl Nino Southern Oscillation extremes drive changes in global temperature and precipitation patterns every two to seven years. The variations are particularly pronounced in the central tropical Pacific, where Cobb and her team collected the fossil corals used in this study. By analyzing the ratio of specific oxygen isotopes in the coral skeletons, the scientists obtained information about ENSO-related temperature and rainfall variations during the periods of time in which the corals grew.\u003C\/p\u003E\u003Cp\u003E\u201cFossil corals are the kings of El Nino reconstruction,\u201d said Cobb. \u201cCorals grow in the heart of the El Nino region, and with monthly-resolved records, they provide a very high level of detail.\u201d\u003C\/p\u003E\u003Cp\u003EThe researchers collected the coral samples by drilling into massive coral \u201crocks\u201d rolled onto Pacific island beaches by the action of strong storms or tsunamis. Cobb and her team studied 17 such cores of varying lengths and ages recovered from beaches on Christmas and Fanning Islands, which are part of the Line Island chain located in the mid-Pacific.\u003C\/p\u003E\u003Cp\u003EThe islands are ideal places for obtaining records of past ENSO activity because they are close enough to the source region for ENSO to be affected by its temperature and precipitation variations, but not so close that the islands\u2019 corals are bleached by large temperature increases during strong El Nino warm events.\u003C\/p\u003E\u003Cp\u003EThe study of each core began with careful dating, done by analyzing the ratio of uranium to thorium. That work was performed by co-authors Larry Edwards and Hai Cheng at the University of Minnesota. Once the age of each core was determined, Cobb and her team chose a subset of the collection to be studied in detail.\u003C\/p\u003E\u003Cp\u003EThey sawed each core in half, then X-rayed the cross-sections to reveal the growth direction of each coral. The researchers then drilled out small samples of coral powder every millimeter down the core and analyzed them with mass spectrometers at Georgia Tech and the Scripps Institution of Oceanography to determine the ratio of oxygen isotopes.\u003C\/p\u003E\u003Cp\u003EThe isotope ratio of the coral skeleton changes with the temperature and amount of rainfall, providing detailed information about environmental conditions during each period of the coral\u2019s growth. As many as 20 samples are analyzed for each year of the coral\u2019s lifetime.\u003C\/p\u003E\u003Cp\u003E\u201cWe are able to count back in time, following the seasonal cycles locked in the coral skeleton, as long as the core will allow us,\u201d Cobb explained.\u003C\/p\u003E\u003Cp\u003EIn all, Cobb\u2019s team added 650 years of monthly-resolved information about ENSO variations across nearly 7,000 years. That required analyzing approximately 15,000 samples over the course of the study, which began in 2005.\u003C\/p\u003E\u003Cp\u003EUsing the new sequences to quantify the range of natural variability in ENSO strength, the researchers have detected a modest, but statistically-significant increase in 20th century ENSO strength that may be related to anthropogenic climate change. However, the coral reconstruction shows an even higher level of ENSO strength 400 years ago, though its duration was shorter.\u003C\/p\u003E\u003Cp\u003E\u201cThe level of ENSO variability we see in the 20th century is not unprecedented,\u201d Cobb said. \u201cBut the 20th century does stand out, statistically, as being higher than the fossil coral baseline.\u201d\u003C\/p\u003E\u003Cp\u003EInformation about the El Nino-Southern Oscillation is important for climate scientists because the cycle helps drive other aspects of global climate change.\u003C\/p\u003E\u003Cp\u003E\u201cEl Nino is something that people want to know about when they reconstruct past climate changes at a specific site,\u201d Cobb said. \u201cOur data will provide a reference for the magnitude of ENSO-related changes that may have occurred, and allow researchers to probe the causes of past climate changes evident in other paleoclimate records and in model simulations of past climates.\u201d\u003C\/p\u003E\u003Cp\u003EThe work has already called into question a long-held belief that ENSO was reduced some 6,000 years ago. Certain climate models support that picture, but Cobb said that fossil coral data from that period doesn\u2019t support a reduction in ENSO strength.\u003C\/p\u003E\u003Cp\u003ELooking to future research, Cobb believes the work will be useful in helping scientists assess the accuracy of climate models.\u003C\/p\u003E\u003Cp\u003E\u201cPrior to this publication, we had a smattering of coral records from this period of interest,\u201d she said. \u201cWe now have tripled the amount of fossil coral data available to investigate these important questions. We have been able to provide a comprehensive view of recent variations in ENSO.\u201d\u003C\/p\u003E\u003Cp\u003EBeyond the researchers already mentioned, the paper\u2019s co-authors include Hussein R. Sayani and Emanuele Di Lorenzo from Georgia Tech and Christopher Charles, Niko Westphal and Jordan Watson from the Scripps Institution of Oceanography. In addition to the National Science Foundation, the project received assistance from Norwegian Cruise Lines, the National Geographic WAITT program, and the Palmyra Atoll Research Consortium.\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThe bulk of the research reported here was supported by the National Science Foundation (NSF) under Grant OCE-0752091. The content of this article is solely the responsibility of the authors and does not necessarily represent the official views of the NSF.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Cobb, Kim M., et al. \u201cHighly variable El Nino-Southern Oscillation throughout the Holocene,\u201d Science (2013). \u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E171 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia\u0026nbsp; 30332-0181\u0026nbsp; USA\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cbr \/\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986)(\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EBy examining a set of fossil corals that are as much as 7,000 years old, scientists have dramatically expanded the amount of information available on the El Nino-Southern Oscillation, a Pacific Ocean climate cycle that affects climate worldwide. The new information will help assess the accuracy of climate model projections for 21st century climate change in the tropical Pacific.\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"Scientists have dramatically expanded the amount of information available on the El Nino-Southern Oscillation, a Pacific Ocean climate cycle that affects climate worldwide."}],"uid":"27303","created_gmt":"2013-01-02 18:00:52","changed_gmt":"2016-10-08 03:13:26","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2013-01-03T00:00:00-05:00","iso_date":"2013-01-03T00:00:00-05:00","tz":"America\/New_York"},"extras":[],"hg_media":{"179611":{"id":"179611","type":"image","title":"Removing Coral Fossil Cores","body":null,"created":"1449179039","gmt_created":"2015-12-03 21:43:59","changed":"1475894825","gmt_changed":"2016-10-08 02:47:05","alt":"Removing Coral Fossil 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