From Marine Heat Waves Drivers to Impact Use Cases: Challenges and Opportunities

Marine heatwaves (MHWs) are prolonged periods of anomalously warm ocean temperatures, usually detected through Sea Surface Temperature (SST). Deeply connected to climate change, these extreme events signal how global warming affects the Earth’s subsystems, driving an uptick in the corresponding impacts. Key aspects related to MHWs are (i) the understanding of the MHWs drivers, (ii) the establishment of standard and (ii) the estimation of expected impacts. Through a multi-project journey, +ATLANTIC has been investigating these topics, to contribute to filling the existing knowledge gaps and to promote the societal uptake of satellite-based MHWs geospatial information.

Regarding (i) in the scope of the Horizon Europe ObsSea4Clim project, which aims to support the GCOS with novel indicators, we have been investigating the relationship between MHWs and the large-scale climate modes that modulate the North Atlantic basin climate. In addition to SST, several ocean variables, including mixed-layer depth and ocean currents, are combined with atmospheric drivers such as air-sea heat fluxes, wind speed, and sea level pressure to describe the most severe MHWs events, recognizing how pressure systems. Preliminary results indicated the importance of stable high-pressure systems in driving air-sea heat flux anomalies, particularly net, latent and sensible heat exchanges, which lead to lower wind speeds and increased energy absorption by the ocean, modulating the intensity and persistence of MHWs over the mid-latitude regions; specifically, the Portuguese EEZ.

Regarding (ii) we propose to evolve from a pixel-wise detection to an events-based labelling algorithm that allows to distinguish noisy pixel patches from meso-scale impactful events. Within the framework of XHEAT, an ESA-funded project, we are exploring the usage of ML/AI in post-processing the traditional MHWs methods to establish a novel mechanism that allows to study of specific events as a continuous element. Furthermore, it allows us to better investigate how large-scale MHWs over the North Atlantic can lead to certain continental extremes over Europe, particularly Compound Drought-Heatwaves (CDHW). Results already suggest that by adopting such techniques, more meaningful relationship patterns emerge, paving the way for probabilistic seasonal outlook predictions.

Regarding (iii) within the ESA-funded CAREHeat, the Impact Use Cases have allowed working alongside aquaculture producers to evaluate the MHW impacts in their activities. From the conducted work, several findings can be highlighted: (1) from the consulted users, all show an interest and willingness to adopt climate data on their operations, especially where local-specific indicators may impact their decision-making on short or long-term activities; nonetheless, few are capable to using geospatial products routinely; (2) the dialogue with the Early Adopters must be kept regularly, to ensure that the objective formulation of the use cases problem is scientifically sound but resonates with their needs; and (iii) biological data available is too limited to establish statistically significant relationships that span decadal time series, which hinders our capacity to measure impacts effectively, which indicates that further effort should be employed in biological data acquisition.