EVIDENCE FOR A BYZANTINE-ERA HYDROTHERMAL EVENT IN SANTORINI’S CALDERA FROM Hg IN IODP EXPEDITION 398 SEDIMENTS

Santorini is a mature volcanic system located in the South Aegean volcanic arc. Its history of large explosive eruptions, which culminated in a caldera-forming eruption 3600 years ago, has been well studied. However, the post-caldera evolution of the volcanic and hydrothermal systems remains poorly understood. Our objective is to better understand of the relationship between volcanic eruptions and the activity of hydrothermal fields within the caldera, by analysing intra-caldera sediments.

This study focuses on the lithological and chemical analysis of samples from seafloor sediment cores collected from the Santorini caldera during International Ocean Discovery Program (IODP) Expedition 398 in 2023. Samples from six holes, which penetrated between depths 45 and 130 mbsf, were selected to obtain a comprehensive record of volcanic and sedimentary activity since the last caldera forming eruption in the Late Bronze Age ca.1650 BCE. The sediment record is hypothesized to include both subaerial and submarine eruptive products from the young edifice that has progressively grown within the caldera over the past 3600 years, now forming the Kameni islands.

The main aim of our study is to determine if we can detect past episodes of heightened hydrothermal activity within Santorini’s flooded caldera by examining trace metal enrichment patterns in the accumulating sediments. Our hypothesis is that sedimentary units show enrichments in elements that are typically elevated in hydrothermal fluids, indicating periods of heightened hydrothermal activity at Santorini. We will present preliminary results for down-core concentrations of elements that are strongly enriched in hydrothermal fluids, in particular mercury (Hg). We have identified a key horizon between 55 and 60 mbsf where Hg concentrations are particularly elevated, and where we have other lines of evidence that are consistent with a period of strong hydrothermal activity prior to 726 CE. We draw comparisons with the present-day hydrothermal fields on the caldera floor, and explore ways that we may constrain the extent and significance of this ancient hydrothermal event.