Climate change, in particular the rise in tropical sea surface temperature, is the greatest threat to coral reef ecosystems today with associated climatic extremes affecting the livelihood of tropical societies. The interaction between the tropical ocean basins plays a key role in modulating climate variability on interannual to decadal timescales. These timescales are of strong relevance to societies and ecosystems, because they control the time interval for recovery between extreme events. Throughout the tropical oceans, a key archive for reconstructions of temperature and hydrology are massive shallow-water corals. Annually to monthly resolved coral proxy records are critical for our understanding of tropical ocean-atmosphere interactions. The DFG Priority Programme “Tropical Climate Variability and Coral Reefs” (SPP 2299) aims to enhance our understanding of tropical marine climate variability and its impact on coral reef ecosystems in a warming world, by quantifying climatic and environmental changes during both the ongoing warming and past warm periods on timescales relevant for society. Ultra-high resolution (monthly to weekly) geochemistry of the coral skeleton is a tool to understand the temporal response of corals to ongoing climate change. Developing reconstructions of past tropical climate and environmental variability, in conjunction with advanced statistical methods, earth system modelling and observed ecosystem responses allows improved projections of future changes in tropical climate and coral reef ecosystems. We present examples (1) for new reconstructions of tropical sea surface temperature and hydrology over the last two millennia using paired measurements of Sr/Ca and oxygen isotopes at monthly resolution, (2) for modes of tropical climate variability affecting coral reef ecosystems (IOD, ENSO), (3) for thermal stress signatures in coral geochemical and isotopic records, and (4) highlight knowledge gaps and future directions in this field, contributing to a better understanding of the response of coral reef ecosystems and tropical climate variability to ongoing and future climate change.

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