ObsSea4Clim investigates extreme events in the ocean, such as marine heatwaves. For the purpose of this work, we have identified ocean indicators to study these extremes and published this list in a Milestone 5 report.

What are ocean indicators?

The Global Ocean Observing System (GOOS) currently defines ocean indicators as “measures based on scientifically verified approaches and data that allow for the identification of the state in ocean phenomena across a range of temporal and spatial scales that are accessible to inform decision makers and beyond” (von Schuckmann et al., in prep.).

An example of widely-used indicators can be found on Copernicus Marine Service, the Ocean Monitoring Indicators (OMIs), which are described as “free downloadable trends and datasets covering the past quarter of a century. These are key variables used to track the vital signs of the ocean and changes in line with climate change”.

What are extreme events?

An extreme event occurs when a physical or biogeochemical variable crosses into a threshold which has some tangible impact on physical processes, ecosystem health or the economy.

Extreme indicators

At ObsSea4Clim, we agreed on the definition of extremes of temperature, sea ice and sea level, and the metrics/characteristics used to describe these extremes.

Extreme indicator	EOVs
Extreme temperature (marine heatwaves)	SST, subsurface temperature, OHC
Extreme sea level	SSH
Extreme sea ice loss	Sea ice (SIC, SIE) Sea ice (SIT) Sea and sea-ice surface temperature* (*proposed EOV)

For more details (full descriptions and information on the temporal resolution, climatology frequency, climatology type, thresholds, and metrics) please refer to the MS5 report: https://zenodo.org/records/14623263