Seasonal, Interannual and Long-Term Variability of Sea Surface Temperature in the NW Iberian Upwelling, 1982-2020

Here the seasonal, inter-annual and long-term variability of satellite-derived sea surface temperature (SST) was analyzed in the NW Iberian margin from 1982 to 2020 to explore spatial differences at high (5-km) resolution. In-situ temperature measurements from five coastal buoys were used to validate the satellite-derived SST data, discarding pixels from areas close to the shoreline. Regional SST increased significantly from 0.07 to 0.25 degrees C per decade, with the lowest rates in shelf waters directly affected by seasonal coastal upwelling. Upwelling filaments also contributed to dampen the temperature increase in the adjacent slope and ocean waters. The spatial variability observed in the amplitude and timing of the seasonal cycle of SST is directly related to hydrography and circulation patterns of the region such as upwelling events during summer and the development of the river's buoyant plume and the warm Iberian Poleward Current during winter. Monitoring primary climate variables such as sea surface temperature (SST) is crucial to assess the sensitivity of the highly productive coastal upwelling systems to global warming and their associated socioeconomic consequences. Here we explore 39-year of daily satellite SST data in the NW Iberian upwelling system. We aim at gaining knowledge on the high resolution (5 km) spatial differences in the seasonal, interannual and long-term variability of this ocean climate variable. Our analysis reveals a significant overall long-term sea surface warming, showcasing marked spatial differences, mainly associated with the interaction of coastal upwelling and topography. Coastal upwelling buffers the temperature rise due to global warming by replacing the warm coastal surface water with cold deep water from the adjacent ocean. Hence, coastal upwelling regions provide a mechanism to counteract global warming. Forecasted increase of upwelling intensity at high latitudes in coastal upwelling systems, as the NW Iberian margin, would guarantee the functioning of this buffering mechanism in the forthcoming decades. Long-term sea surface temperature (SST) rise ranged from 0.07 to 0.25 degrees C per decade in the NW Iberian margin Seasonal coastal upwelling substantially buffers the long-term SST increase in shelf and slope waters Large uncertainty in nearshore satellite-derived SST data indicates the need for in situ data