The Tropical Pacific: A changeable communicator or Holocene solar forcing

Small variations in radiation emitted from the sun are correlated with some of the largest climate fluctuations that occurred globally during the Holocene. Still, debate persists about how these variations in solar irradiance were communicated to the climate system. We present data-based evidence demonstrating that solar irradiance variations forced changes in the coupled ocean-atmosphere system of the Tropical Pacific throughout the Mid-Late Holocene. By applying novel statistical analyses to multiple proxy reconstructions we show that the Tropical Pacific warmed in response to solar irradiance increases during the Mid Holocene but cooled under increased solar irradiance in the Late Holocene. This opposite response was caused by orbital trends strengthening solar forcing of the ocean-atmosphere system in the Tropical Pacific during the Late Holocene. Our analysis indicates that El Niño was subdued during solar maxima; a finding that has important implications for understanding how ENSO responds during globally warmer periods. In a paleoclimate context, our finding of a changeable response of the Tropical Pacific to solar forcing has important implications for the interpretation of paleoclimate reconstructions in regions teleconnected with the Tropical Pacific. Total solar irradiance [Steinhilber et al., 2009, 2012] cross-correlated with (a) the surface temperature of the Indo Pacific Warm Pool [Stott et al., 2004] and (b) red colour intensity measurements which are an indication of SST off the coast of Ecuador [Moy et al., 2002]. Correlations within the bold black outlines are significant at 95% confidence interval. X's indicate when a statistically significant (95% CI) change in correlation occurred. In the Mid Holocene solar irradiance maxima were associated with warmer surface temperatures of the Tropical Pacific. However, after ~5000 yr BP the surface temperature of the Tropical Pacific cooled during globally warmer solar maxima.