Long-Term Trend of Equatorial Atlantic Zonal Sea Surface Temperature Gradient Linked to the Tropical Pacific Cold Tongue Mode Under Global Warming

The equatorial Atlantic zonal sea surface temperature (SST) gradient, which has significant climatic and biogeochemical effects, is closely associated with the equatorial Pacific zonal SST gradient through Walker circulation on seasonal and interannual time scales. However, discrepancies in current SST data sets mean that its long-term trend is not well understood. Here, using multiple data sets, we find a robust weakening long-term trend (i.e., greater warming in the east than west) in the equatorial Atlantic zonal SST gradient over the period 1900-2010 in all data sets. We also find that this weakening trend is closely linked to the tropical Pacific cold tongue mode (CTM), which corresponds to a strong increasing long-term trend of zonal SST gradient along the equatorial Pacific (i.e., warming in the west and cooling in the east). Specifically, the long-term cooling SST anomalies associated with the CTM modify the Walker circulation, and leads to weaker trade winds over the western equatorial Atlantic. These in turn deepen the thermocline in the eastern equatorial Atlantic, and cause the weakening long-term trend of SST gradient along the equatorial Atlantic. The long-term trend of the CTM is induced by ocean dynamical feedback in response to global warming, suggesting that global warming could affect the equatorial Atlantic zonal SST gradient via the CTM. Our results provide a novel explanation of the linkages between the long-term trend of equatorial Atlantic zonal SST gradient and the CTM under global warming, which carries important implications for the relationship between global warming and the equatorial Atlantic zonal SST gradient. Plain Language Summary The tropical Atlantic plays an important role in global climate change, with socioeconomic impacts that are felt worldwide. In the equatorial Atlantic, we find a robust weakening long-term trend (i.e., greater warming in the east than west) in the zonal sea surface temperature (SST) gradient over the period 1900-2010 in five data sets (HadISST1, ERSST5, COBE2, Kaplan2, and their ensemble mean). Interestingly, this weakening trend is closely linked to the tropical Pacific cold tongue mode (CTM), which represents an out-of-phase relationship of SST variability between the Pacific cold tongue region and elsewhere in the tropical Pacific. In particular, the CTM shows a strong increasing long-term trend that is induced by the response of ocean dynamical feedback to global warming. In addition to the impacts of anthropogenic aerosols on the equatorial Atlantic, our study provides a linkage between the weakening long-term trend of the equatorial Atlantic zonal SST gradient and global warming. Future changes in global warming may impact the Atlantic SST and have socioeconomic consequences for the Atlantic and surrounding continents.

Automated summary

Our research reveals a significant trend in the weakening of the zonal sea surface temperature gradient in the equatorial Atlantic from 1900 to 2010. This trend is closely linked to the tropical Pacific cold tongue mode, showing a clear pattern of warming in the west and cooling in the east. The weakening trend is induced by ocean dynamical feedback in response to global warming, highlighting the potential impact of global warming on the equatorial Atlantic zonal SST gradient.