A Century of Reduced ENSO Variability During the Medieval Climate Anomaly.

Autor: Lawman, Allison E., Quinn, Terrence M., Partin, Judson W., Thirumalai, Kaustubh, Taylor, Frederick W., Wu, Chung‐Che, Yu, Tsai‐Luen, Gorman, Meaghan K., Shen, Chuan‐Chou
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Zdroj: Paleoceanography & Paleoclimatology; Apr2020, Vol. 35 Issue 4, p1-17, 17p
Abstrakt: Climate model simulations of El Niño–Southern Oscillation (ENSO) behavior for the last millennium demonstrate interdecadal to centennial changes in ENSO variability that can arise purely from stochastic processes internal to the climate system. That said, the instrumental record of ENSO does not have the temporal coverage needed to capture the full range of natural ENSO variability observed in long, unforced climate model simulations. Here we demonstrate a probabilistic framework to quantify changes in ENSO variability via histograms and probability density functions using monthly instrumental and coral‐based sea surface temperature (SST) anomalies from 1900–2005 and 1051–1150 CE. We find that reconstructed SST anomalies from modern corals from the southwest Pacific capture changes in ENSO variability that are consistent with instrumental SST data from the central equatorial Pacific. Fossil coral records indicate 100 years of relatively lower ENSO variability during part of the Medieval Climate Anomaly. Our results demonstrate that periods of reduced ENSO variability can last a century, far longer in duration than modern observations in the instrumental record of ENSO, but consistent with results from unforced climate model simulations. Plain Language Summary: The chemistry of coral skeletal material is a passive recorder of environmental conditions, like the temperature of the water in which the coral lives. For example, the ratio of the element strontium (Sr) to the element calcium (Ca) in the coral skeleton will vary in response to changes in sea surface temperature (SST). Paleoclimatologists measure coral Sr/Ca to determine how SSTs vary in the past. In this study, we use corals from the southwest Pacific to understand how SSTs in the tropical Pacific Ocean varied during the twentieth century and ~900 years ago during a time interval called the Medieval Climate Anomaly. We focus on SST variability related to the El Niño–Southern Oscillation, a climate phenomenon that operates on year‐to‐year timescales and impacts global temperature and rainfall patterns. Here we use temperature estimates inferred from corals and find that past changes in El Niño–Southern Oscillation variability during part of the Medieval Climate Anomaly is similar to the early part of the twentieth century. Key Points: Vanuatu coral Sr/Ca‐SST variations are a proxy of El Niño–Southern Oscillation (ENSO) variabilityVanuatu fossil coral Sr/Ca‐SST variations indicate 100 years of lower ENSO variability during part of the Medieval Climate AnomalyPeriods of reduced ENSO variability can last a century, far longer than modern observations in the instrumental record of ENSO [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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