Intense tropical cyclone activity over the past 2000 years at Bay of Islands, Fiji

Tropical cyclones (TCs) are among the most devastating hazards, causing damage and fatalities in coastal communities. Our understanding of the climatic factors that modulate tropical cyclone activity is impeded by the short historical records and the scarcity of paleoclimatic reconstructions, with a notable dearth of data in the Southern Pacific region. In this paper, we present a sedimentary record from a coastal karst basin in Bay of Islands, Vanua Balavu, Fiji to provide insight into the regional intense TC activity over the past two millennia. A total of 53 intense storm events captured by this site are identified using coarse fraction (>63 μm) anomalies in sediment core retrieved from the basin, yielding an overall average event frequency of 2.6 events/century. Multiple centennial-scale quiescent periods (from 200 to 300 CE and 1000 to 1150 CE) and active periods (namely from 350 to 750 CE, 900 to 1000 CE, 1150 to 1250 CE, 1400 to 1500 CE, and 1650 to 2017 CE) are found in the reconstruction, and the most active interval spans from 1650 to 1800 CE at 4.5 events/century.

A comparison between existing paleostorm records and climate forcing indices suggests that the southward displacement of the South Pacific Convergence Zone (SPCZ) during the Little Ice Age with more La Niña events is responsible for the basin-wide increasing of tropical cyclone activity in the South Pacific. Decline of TC occurrence in the western SP during the Medieval Climate Anomaly is attributed to the northward movement of SPCZ. However, event frequency peaks of the latitudinally aligned sites in the South Pacific exhibit a certain degree of asynchrony, necessitating the acquisition of more detailed high-resolution paleostorm reconstructions within these basins and corroborative evidence from global climate models.