Significant Intensification of Eastern Pacific ENSO reflected in Gal pagos Corals since the Pre-Industrial Era: A Synthesis of New and Published Fossil Coral Cores from the Tropical Eastern and Central Pacific Ocean

Abstract

El Ni o Southern Oscillation (ENSO), and its potential response to anthropogenic climate change, has recently become a topic of great interest following the anomalously strong El Ni o events of the late 20th-early 21st centuries. Strong events such as these are associated with drought, flooding, and damages to ecosystems, human health, agriculture, and infrastructure in many parts of the world. Long-lived corals in the equatorial Pacific Ocean track ENSO-related sea surface temperature (SST) over time in the Sr/Ca and oxygen isotopic ratios (d18O) of their skeletons, and these multi-decadal to multi-century histories can be accessed at monthly resolution. SST anomalies can be reconstructed from well-dated subfossil corals, providing “windows” into past ENSO activity. Current ENSO trends can be assessed by comparing past (pre-industrial) and modern windows of variability. The 17th-18th centuries, within a period of cooler temperatures in the northern hemisphere (the so-called “Little Ice Age”), provide a climatologically interesting window, as previously published records from the central Pacific suggest high ENSO variability at this time. Here, we investigate central Pacific (CP) and eastern Pacific (EP) ENSO variability using new and published subfossil coral records from the 17th-18th centuries, and compare them to the 20th century, as well as to the “recent modern” interval of 1990-2010 CE. We find that in the EP, El Ni o variability has increased substantially since the 1600’s, particularly in the recent modern interval. This result contrasts with CP variability, which we find does not change substantially over the past 400 years. Our new Gal pagos coral records demonstrate that ENSO in the EP is intensifying, in line with model projections under anthropogenic forcing and with the limited instrumental record. Such amplification will likely intensify the global impacts of the ENSO system in a warming world.