ENSO and internal sea surface temperature variability in the tropical Indian Ocean since the Maunder Minimum

Abstract. The dominant modes of climate variability on interannual timescales in the tropical Indian Ocean are the El Nino Southern Oscillation (ENSO) and the Indian Ocean Dipole. El Nino events have occurred more frequently during recent decades and it has been suggested that an asymmetric ENSO teleconnection (warming during El Nino events is stronger than cooling during La Nina events) caused the pronounced warming of the western Indian Ocean. In this study, we test this hypothesis using coral Sr / Ca records from the central Indian Ocean (Chagos Archipelago) to reconstruct past sea surface temperatures (SST) in time windows from the Maunder Minimum to the present. Three sub-fossil massive Porites corals were dated to the 17–18th century (one sample) and 19–20th century (two samples), and were compared with a published, modern coral Sr / Ca record from the same site. All corals were sub-sampled at a monthly resolution for Sr / Ca measurements, which were measured using a simultaneous ICP-OES. All four coral records show typical ENSO periodicities, suggesting that the ENSO-SST teleconnection in the central Indian Ocean was stationary since the 17th century. To determine the symmetry of ENSO events, we compiled composite records of positive and negative ENSO-driven SST anomaly events. We find similar magnitudes of warm and cold anomalies indicating a symmetric ENSO response in the tropical Indian Ocean. This suggests that ENSO is not the main driver of central Indian Ocean warming.