Central Pacific El Niño and decadal climate change in the North Pacific Ocean

Decadal fluctuations of the ocean and atmosphere over the North Pacific Ocean significantly affect the weather and climate of North America and Eurasia. They also cause transitions between different states of marine ecosystems across the Pacific Ocean1–3. An important fraction of North Pacific low-frequency variability is linked to the North Pacific Gyre Oscillation4, a climate pattern associated with decadal fluctuations of the ocean circulation. Decadal variations in the North Pacific Gyre Oscillation are characterized by a pattern of sea surface temperature anomalies that resemble the central Pacific El Niño, a dominant mode of interannual variability with far-reaching effects on global climate patterns5–7. Here we use an ensemble of simulations with a coupled ocean– atmosphere model to show that the sea surface temperature anomalies associated with central Pacific El Niño force changes in the extra-tropical atmospheric circulation. These changes in turn drive the decadal fluctuations of the North Pacific Gyre Oscillation. Given that central Pacific El Niño events could become more frequent with increasing levels of greenhouse gases in the atmosphere8, we infer that the North Pacific Gyre Oscillation may play an increasingly important role in shaping Pacific climate and marine ecosystems in the twenty-first century. Previous studies document the wide-ranging impacts of North Pacific decadal-scale climate variability associated with the Pacific Decadal Oscillation1,2 (PDO) and the North Pacific Gyre Oscillation4,9–11 (NPGO). The PDO closely tracks the first mode of North Pacific sea surface temperature (SST) variability, and is connected to atmospheric circulation anomalies associated with the El Niño Southern Oscillation12–14 (ENSO). The NPGO, defined as the second dominant mode of sea surface height anomalies in the central and easternNorth Pacific4 (see theMethods section), closely tracks the second dominant mode of North Pacific SST anomalies, and is associated with decadal-scale variations in the ocean gyres circulation4,11. The NPGO explains prominent low-frequency fluctuations of upper ocean salinity and nutrients observed in long-term records in the central and eastern North Pacific9, as well as a variety of other ecosystem indicators15. However, the origin of the NPGO low-frequency variability remains unknown, as does its sensitivity to greenhouse climate forcing. Analysis of Pacific basin SST fields show that the SST signature of the decadal-scale NPGO shares important common features with the Central Pacific warming (CPW) El Niño pattern (Fig. 1; see the Methods section). The CPW, also referred to as the Date Line El Niño5, El Niño Modoki6 or warm-pool El Niño7, emerges as