Oxygen isotope record for 1520 to 2011 from a coral colony in American Samoa. The gray line shows the data resampled at monthly intervals, then smoothed with an 8 year (red) and 25 year (blue) Hann filter. More negative δ18O values correspond to warmer and/or fresher conditions. Credit: Tangri et al., 2018, Figure 2
Source: Paleoceanography and Paleoclimatology

The intensity and frequency of events in the Pacific Ocean called El Niño and La Niña or El Niño-Southern Oscillation (ENSO) influence weather patterns globally, and temporarily intensify or temporarily counteract anthropogenic global warming. Tangri et al. [2018] present an almost 500 year long, continuous time series from a massive Porites coral colony from American Samoa, which records contrasting responses to different types of ENSO in a mixed sea surface temperature (SST) and salinity signal.

Over the course of the twentieth century, the records changed and underwent a polarity shift in response to conventional ENSO: A warm and fresh response to El Niño combined with a cool and salty response to La Niña were replaced by the opposite pattern. The authors interpret this as evidence for the movement of the Eastern Pacific ENSO null zone, the narrow band of the surface ocean where SST variability is on average not correlated with ENSO. This movement appears to be related to overall shrinking of the ENSO footprint over the twentieth century at one location, but not at another.

The new record may have recorded changes in the strength of ENSO or in its spatial footprint. The latter manifests as a changing sensitivity to ENSO at any given location, presenting challenges to established methods of ENSO reconstruction.

Citation: Tangri, N., Dunbar, R. B., Linsley, B. K. and Mucciarone, D. M. [2018], ENSO’s Shrinking Twentieth‐Century Footprint Revealed in a Half‐Millennium Coral Core From the South Pacific Convergence Zone. Paleoceanography and Paleoclimatology. https://doi.org/10.1029/2017PA003310

—Ellen Thomas, Editor-in-Chief, Paleoceanography and Paleoclimatology

Correction, 27 November 2018: The title of this article has been updated to specify that the corals used in the study were from American Samoa.

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