Interannual variability (2014-2016) of coastal mesoscale activity at the entrance of the Gulf of California as determined by remote sensing

Abstract

Early in 2014, the waters at the entrance of the Gulf of California experienced exceptionally high sea surface temperature (2–4 °C above normal) and coincided with a period of unusually weak winds. The warm anomalies continued after March with the arrival of the Warm Blob (2014) and subsequent 2014–2015 El Niño. Our objective was to investigate how the combination of atypical winter winds and unusual heat advection patterns affected regional upwelling by evaluating the variability in coastal sea level and remotely sensed chlorophyll (CHL). The sea level anomaly (SLA) time series for 2014 contained a weak winter minimum and two successive SLA peaks instead of a single summer maximum. The first peak was due to anomalously weak winds. Another double peak was recorded the following summer. The consequences of such anomalous patterns on the productivity of the region were severe. Large oceanic regions at the entrance to the Gulf of California maintained very low CHL concentrations for three consecutive years. Notably, coastal CHL reached record-low values from 2003 to 2016. At two upwelling sites, we found a remarkable association between the CHL mean and CHL variance. High/low variance corresponded to high/low monthly mean CHL. We attributed this to the excess/lack of mesoscale variability associated with upwelling zones, which affected offshore filaments. The low CHL variance at the coast confirms what is apparent from the CHL fields of the southern Gulf of California and its entrance. Not only was coastal productivity low, but weak coastal upwelling led to fewer offshore filaments, effectively inhibiting the transport of the limited amount of coastal primary production to the oceanic domain.