Evidence of reduced mid-Holocene ENSO variance on the Great Barrier Reef, Australia

Globally, coral reefs are under increasing pressure both through direct anthropogenic influence and increases in climate extremes. Understanding past climate dynamics that negatively affected coral reef growth is imperative for both improving management strategies, and for modelling coral reef responses to a changing climate. The El Nino Southern Oscillation (ENSO) is the primary source of climate variability at inter-annual timescales on the Great Barrier Reef (GBR), north-eastern Australia. Applying continuous wavelet transforms to visually assessed coral luminescence intensity in massive Porites corals from the central GBR we demonstrate that these records reliably reproduce ENSO variance patterns for the period 1880 – 1985. We then applied this method to three sub-fossil corals from the same reef to reconstruct ENSO variance from ~5200 – 4300 years before present (yBP). We show that ENSO events were less extreme and less frequent after ~5200 yBP on the GBR compared to modern records. Growth characteristics of the corals are consistent with cooler sea surface temperatures (SST) between 5200 and 4300 yBP compared to both the millennia prior (~6000 yBP) and modern records. Understanding ENSO dynamics in response to SST variability at geological timescales will be important for improving predictions of future ENSO response to a rapidly warming climate.