CoAuthors

P. Ted Strub (Oregon State University - College of Earth, Ocean, and Atmospheric Sciences, United States); Craig Risien (Oregon State University - College of Earth, Ocean, and Atmospheric Sciences, United States); Corinne James (Oregon State University - College of Earth, Ocean, and Atmospheric Sciences, United States); Carlos Moffat (University of Delaware - School of Marine Science and Policy, United States); Kevin S. Brown (Oregon State University - Department of Pharmaceutical Sciences and School of Chemical, Biological, and Environmental Engineering, United States)

The coastal ocean off southwest Africa experiences interannual warming events known as Benguela Niños (Shannon et al. 1986). These events have important ecological effects on the Benguela coastal upwelling system. However, a qualitatively different type of warm water anomaly occurred during the 2016 January-March upwelling season (Lübbecke et al., 2018). This warm event ended earlier in the year than typical Benguela Niños. Sea-surface temperature (SST) anomalies exceeded 3ºC. Here, we examine the sea-surface height (SSH) anomalies and atmospheric forcing during this and other warm water anomaly, or marine heat wave (MHW), events during 2000–present in the Benguela upwelling region. We compare the Benguela MHWs to MHW events observed in the California and Chile-Peru upwelling systems over the past 20 years.

Strong regional spatial variability is observed in MHWs in coastal areas worldwide, but is largely unexplained. Therefore, the scientific community presently has little to no ability to predict the timing or location of future MHWs that could have major economic and ecological impacts. Our previous work in the California Current upwelling system indicates that coastline shape, via its influence on the wind stress field, explains regional variability within MHWs in summer and could give predictability for the spatial pattern of future MHWs in that upwelling system. A direct relationship between wind stress and SST anomalies existed during a MHW off California in July 2015 because the net air-sea heat flux anomalies were small in the region of warm water anomaly. In a new project, we are working to determine whether the above relationships hold during other MHW events in the California and Chile-Peru upwelling systems. Here, we extend this analysis to the Benguela upwelling region, and also examine the role of along-coast advection of warm water during MHWs.

We include an overview of the statistics of MHW occurrences in the Benguela region during 2000–present. We present climatologies and anomalies of SST, satellite ocean vector wind stress from QuikSCAT and ASCAT, objectively analyzed air-sea fluxes from OAFlux, radiative fluxes from CERES, and sea level anomalies from satellite altimetry offshore of the Benguela upwelling region. Examining MHW and wind events on shorter time scales than the monthly anomalies used in most previous studies allows diagnosis of the relative importance of changes in ocean advective heat fluxes, air-sea fluxes, and wind stress in structuring MHW in the Benguela region during the summer upwelling season.