NEXT WEEK Tuesday 29th April at 4pm, 312.207 at Curtin University

Dr Jens Zinke

UWA

UWA Oceans Institute & University of Western Australia, AIMS
What drives current marine heat waves and coral bleaching in Western Australia?

Sea surface temperatures (SST) along the western shelf of Australia are tightly connected to those of the Western Pacific Warm Pool (WPWP) and the magnitude of El Niño/ Southern Oscillation (ENSO) events. Recent El Niño and La Niña events have been associated with mass coral bleaching on both fringing and isolated atoll reefs along the west coast of Australia, including those along the edge of the northwest continental shelf. Long-term temperature records, with which to establish the occurrence of past ENSO events at these atoll reefs, are nonexistent. Here, we use the strontium/calcium and stable isotope sea surface temperature proxies from ten coral cores drilled from three reef complexes (17-28S, 113-119E) to reconstruct a robust 215 year (1795-2010) mean annual SST record for the western Australian shelf. The record suggests a close association between WPWP SST throughout the 215 years while ENSO event impacts varied. Here we show that after 1980, the strongest warming signals are associated with strong La Niña’s and Western Pacific (WP) SST gradient, with the most severe warm event on record in 1999/2000. Our reconstruction shows that the recent extreme events were exacerbated by a strong WP warming trend after 1980. These findings point to an uncertain future for the southeastern Indian Ocean coral atoll reefs, living close to their upper thermal threshold.