Tropical Eastern Pacific SST Variability Over the Last 2 Millennia, Possible Links with Global Climate and the Response of the Peruvian Upwelling

Tropical Pacific sea surface temperature (SST) is viewed as a key driver for large scale climate variability on interannual, decadal and longer timescales. Yet, global compilations highlight a critical lack of proxy SST data in this oceanic realm, and especiallly in its eastern part. Well-preserved, high-resolution laminated sediments from the Peruvian upwelling system allow for reconstructing past oceanic changes in the Eastern Tropical Pacific over the last 2000 years, and for assessing relevant changes in the biogeochemical functionning of the system. The alkenone-SST record in the study area does not show significant contrast between the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) periods, unlike the records from the Western Pacific. Our proxy data clearly demonstrate different SST zonal gradients, while our model experiments show corresponding anomalies in the tropical Pacific thermocline depth. For the last 150 years, SSTs show an overall decreasing trend with short-term positive excursions that correspond to strong El Nino events. The signature of IPO is identified in our record indicating large-scale modulation of SSTs. Changes in the tropical Pacific ocean-atmosphere system are shown to have a fundamental impact on the biogeochemistry of the Peruvian upwelling system, as well as on the S. America hydroclimate on decadal time scales. Possible forcings for tropical SST changes and underlying causal mechanisms are investigated through comparing proxy data with climate modeling.