The Indian Ocean Dipole (IOD) is an ocean-atmosphere climate oscillation within the Indian Ocean basin and one of Australasia’s key climate drivers that influences the distribution of rainfall across the region. Future projections of IOD activity suggests that extreme positive IOD events may become more frequent with greenhouse warming leading to an increase in occurrence of extreme climate and weather events in regions influenced by the IOD. However, the short duration of instrumental records and biases in model representations of the IOD make it difficult to confidently separate anthropogenic-related trends from natural variability. To better understand natural IOD variability, high-resolution reconstructions of the Indian Ocean sea surface temperature (SST) are needed to provide a comprehensive view of IOD upwelling activity prior to the Industrial Revolution.
In this research, a fossil Porites coral has been used reconstruct past SST from the Sunda Strait, Indonesia. The southern Sunda Strait (6.5ºS, 105.5ºE) region is a key area for measuring IOD activity, as the cold upwelling waters in the eastern Indian Ocean, associated with a positive IOD event have a clear signature here that is captured by geochemical changes in coral skeletal material. The focus of this project is on a 205 year, ~monthly resolution d18O record from a coral tsunami block that spans the interval 1668 to 1872. The coral temperature record has been combined with historical ship log book records from the region to create a 350-year record of tropical Indian Ocean SSTs. This extended SST reconstruction reveals insights into the frequency and intensity of positive IOD events prior to anthropogenic climate change.