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

Abstract

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 modeling coral reef responses to a changing climate. The El Niño–Southern Oscillation (ENSO) is the primary source of climate variability at interannual timescales on the Great Barrier Reef (GBR), northeastern 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 subfossil corals from the same reef to reconstruct ENSO variance from ~5200 to 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 (SSTs) 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.

ENSO Weather and Coral Bleaching on the Great Barrier Reef, Australia

“…incl. GBR (inshore reefs mostly affected; central reef) (AIMS, ; Berkelmans et al, ; Leonard et al, )…”

“…1 January to 30 April Worldwide (Baker et al, 2008;Reaser et al, 2000) incl. GBR (inshore reefs mostly affected; central reef) (AIMS, 2016;Berkelmans et al, 2004;Leonard et al, 2016Leonard et al, ) 2010 1 January to 31 March GBR (AIMS, 2016) 2016…”

“…Previous studies have established that reef growth and decline across the Pacific has been driven by El Niño–Southern Oscillation (ENSO) variability as far back as the Mid‐Holocene (~6,000 years B.P.) (Leonard et al, ; Toth et al, ). Mass coral bleaching events have occurred with increasing frequency since the early 1980s and often coincide with El Niño events (Baker et al, ; Glynn et al, ; Kleypas et al, ).…”

The 4.2 ka event, ENSO, and coral reef development

“…There is now broad consensus across both climate models and paleoclimate reconstructions that the middle Holocene was a period of relatively low ENSO variability (Sandweiss et al, 2001;Tudhope et al, 2001;Rein et al, 2005;Koutavas et al, 2006;Zheng et al, 2008;Cobb et al, 2013;Carré et al, 2014;Liu et al, 2014;Leonard et al, 2016b;Thompson et al, 2017). In particular, the interval 5-3 ka stands out as a period when paleoclimate records from throughout the tropical Pacific show a significant reduction in ENSO activity .…”

“…Whereas El Niño events are typically associated with a weaker monsoon and resultant drought conditions, the monsoon is stronger during La Niña events (Liu et al, 2000;Wang et al, 2003). The similarity in the climatic changes associated with ENSO and the 4.2 ka event, coupled with the evidence for increasing ENSO variability around 4.2 ka (Conroy et al, 2008;Koutavas and Joanides, 2012;Carré et al, 2014), has led a number of researchers to suggest that ENSO may have played a salient role in the 4.2 ka event (e.g., Marchant and Hooghiemstra, 2004;Booth et al, 2005;Walker et al, 2012;Li et al, 2018). It is not yet clear, however, whether changing ENSO variability around 4.2 ka is likely to have been an ultimate driver of broadscale climatic changes around this time or whether ENSO was a proximal response to other climatic forcing.…”