Interpreting volcanic ocean colour anomalies in a variable ocean

Submarine volcanic eruptions are one of the most common yet least observed forms of volcanic activity, as their unpredictability and remote locations limit opportunities for direct observation and monitoring. The observability of surface manifestations depends on vent depth and associated hydrostatic pressure, magma properties, eruptive intensity and surrounding oceanographic conditions that control plume ascent and dispersion.

In shallow water environments these events can have variable manifestations at the sea surface (mostly in the first 500mbsl), ranging from ejection of material and explosions to volcanic plumes and pumice rafts. Among these, discolouration plumes are one of the most frequently observed surface expressions, as the result of the interaction between hot volcanic fluids and cold seawater. Their colour can vary depending on the concentration of certain elements (such as Fe, Al and Si) in the volcanic fluids. Therefore, these plumes change the optical properties of the upper ocean and are often detected by satellite observations.

However, interpretation of these signals is challenged by natural ocean colour variability that can generate optically similar features. Additionally, data limitations related to sensor resolution, cloud contamination, and scarce in-situ observation used for validation, further aggravate these interpretations. This study explores how this type of activity manifests in satellite ocean colour time series across different regions and eruptive events, with the aim of distinguishing volcanic related signals from background variability. An updated global database of documented submarine eruptions was used to extract multi-sensor ocean colour observations and to examine their temporal and spectral behaviour before, during and post eruption. By analysing these changes in sea surface reflectance relative to non-eruptive conditions, we are able to investigate the characteristics and consistency of volcanic ocean colour anomalies and evaluate their detectability within different marine environments.

As a next step, this framework provides a basis for integrating physical oceanographic data, such as temperature and surface currents, to improve discrimination between volcanic discolouration plumes and optically similar features of different origin, including phytoplankton blooms, river discharge and sediment resuspension. This approach will support more robust interpretation of ocean colour anomalies and feed the development of future automated detection, classification and monitoring tools for submarine volcanic eruptions.