Influence of the canary upwelling system on SST during the unprecedented 2023 North Atlantic marine heatwave

Abstract

The heightened occurrence of marine heatwaves (MHWs) attributed to climate change has garnered significant attention, primarily due to its profound impacts on marine ecosystems. Eastern Boundary Upwelling Systems, recognized as high-productivity oceanic areas, have emerged as crucial thermal refuges mitigating the effects of global warming, thereby safeguarding marine fauna and flora. Acknowledging the synergies between MHWs and upwelling becomes pivotal in this context. The main objective of this study is to assess the unprecedented extreme SSTs observed in the North Atlantic Ocean throughout 2023 which represent a departure from the norms observed in the past 40 years of satellite data, resulting in quasi-permanent MHW conditions. Additionally, the investigation aims to delineate the influence of upwelling on the disparities between oceanic and coastal SST throughout the Canary Upwelling System. For this purpose, SST and wind data from OISST ¼ and ERA5 databases, respectively, have been used to calculate SST extremes and differences between coast and ocean as well as Upwelling Index (UI) values from 1982 to 2023.Despite the overall increase in oceanic and nearshore SST during 2023, substantial differences between coastal and oceanic temperatures were noted compared to the 1982–2023 period average. Moreover, distinct upwelling regimes along the Canary Upwelling System exhibited discernible variations in the impact of upwelling on coastal SST. Nonetheless, the influence of upwelling mitigated warming nearshore more effectively than offshore, underscoring its capacity to modulate climate change impacts, even under the extreme SST conditions arising from the unprecedented 2023.