El Niño-Southern Oscillation Variability in the 14th Century

The centuries prior to the industrial Revolution provide important baseline information for understanding 20th century climate. Yet the El Niño-Southern Oscillation, the largest source of global interannual climate variation, is poorly characterised for this period. Whilst it is known that the Little Ice Age (1400-1750CE) (LIA) was characterised by cooling SSTs, there is still some contention surrounding ENSO behaviour; with some records suggesting greater ENSO variability while others indicate periods of ENSO inactivity. This is largely due to the availability and shortness of records, highlighting the need to continue to reconstruct and assess ENSO within this period. In this thesis, a ~50-year long Porites coral from Kiritimati Island in the central equatorial Pacific, U/Th dated to 1333-1383CE, is used to investigate past ENSO variability. Sr/Ca, an independent recorder of SST, was measured at a bi-monthly resolution. This record was used to indirectly reconstruct SST and ENSO variability for this period, with the average SST found to be 28.0 ±1.6°C (1σ), slightly warmer than the modern average. The reconstruction indicated that ENSO variability had a stronger magnitude compared to modern times, and showed a degree of multidecadal variation, with a reduction of ENSO from the 14th to 15th century at Kiritimati Island. Ultimately, the results from this study help to characterise the behaviour of ENSO during the 14th century, and, in combination with other records and further research, may provide insight into climate variation in the transition from the Medieval Climate Anomaly (MCA) to the LIA.