Northern Great Barrier Reef coral documents seasonal ocean temperature, salinity, productivity and runoff from the last 250 years

Abstract:

Climate variability on the northeast coast of Queensland, Australia, is highly seasonal and is modulated by large-scale ocean-atmosphere systems such as the Australian monsoon, El Niño/Southern Oscillation, and the Pacific Decadal Oscillation. In this region, modern seasonally-resolved records of ocean temperature and salinity are available from both instrumental sources and recent coral geochemical studies. However, nearly all such records are relatively short, recording, at most, the past 50-100 years of climate. Longer, high-resolution records of coastal ocean temperature, salinity, and river runoff in this region would improve characterization of changes in multi-decadal climate cycles, aid the development of accurate regional climate models and further guide understanding of potential future climate change in this region.

Multi-proxy records from the long coral cores allow for just such a rich picture of past climate change. Here we developed multiple geochemical and physical properties from a long coral core from the northern Great Barrier Reef, at the mouth of the Jeannie River. This record is continuous and seasonally resolved from roughly 1735-1985 CE, a 250-year span that overlaps with the instrumental era. We use coral carbonate trace elements (Sr/Ca, Ba/Ca), isotopes (δ¹⁸O), coral density, and coral luminescence to reconstruct approximately monthly estimates of ocean temperature, salinity, productivity, and terrestrial runoff. Summer ocean surface temperature peaks in January-February; peak precipitation and runoff lag behind and occur in February-March and March-April, respectively. Here we further link measured coral physical and geochemical parameters to climate variability in the modern instrumental era and extend the continuous monthly-resolution record of ocean temperature, salinity, productivity and terrestrial runoff to ~1735 CE. Initial results suggest that the Australian monsoon dominates annual variability in this region and that inter-annual variability is governed in large part by longer multi-decadal cycles such as the Pacific Decadal Oscillation.