Anthropogenic climate change and eutrophication increasingly result in large-scale ocean deoxygenation, with drastic impacts on marine life and biogeochemical cycles. Past deoxygenation events recorded in the sedimentary record can be used to unravel processes involved in anoxia, providing critical knowledge to accurately predict future marine anoxic events. For deoxygenation reconstructions, sedimentary trace metal concentrations are essential proxies. Novel developments in XRF-core-scanning now allow to measure such trace elements, offering a fast, non-destructive, low-cost way to study past ocean deoxygenation. In this talk I will focus on past episodes of widespread marine oxygen deficiency and associated organic-rich layers (sapropels) recorded in the eastern Mediterranean basin, which typically show rapid transitions within decades to centuries from oxic to anoxic conditions. These records contain eight past oxic-anoxic transitions in the eastern Mediterranean Sea, which deliver information on a key question: can fast transitions towards anoxia be predicted using so-called early-warning signals? In the end of this talk I will also shortly address other XRF-core-scanning applications, focusing on both sediments, corals, and future XRF-core-scanning developments that may stimulate exciting new research.