South Pacific hydrologic and cyclone variability during the last 3000 years

Abstract

Major excursions in the position of the South Pacific Convergence Zone (SPCZ) and/or changes in its intensity are thought to drive tropical cyclone (TC) and precipitation variability across much of the central South Pacific. A lack of conventional sites typically used for multimillennial proxy reconstructions has limited efforts to extend observational rainfall/TC data sets and our ability to fully assess the risks posed to central Pacific islands by future changes in fresh water availability or the frequency of storm landfalls. Here we use the sedimentary record of Apu Bay, offshore the island of Tahaa, French Polynesia, to explore the relationship between SPCZ position/intensity and tropical cyclone overwash, resolved at decadal time scales, since 3200 years B.P. Changes in orbital precession and Pacific sea surface temperatures best explain evidence for a coordinated pattern of rainfall variability at Tahaa and across the Pacific over the late Holocene. Our companion record of tropical cyclone activity from Tahaa suggests major storm activity was higher between 2600-1500 years B.P., when decadal scale SPCZ variability may also have been stronger. A transition to lower storm frequency and a shift or expansion of the SPCZ toward French Polynesia around 1000 years B.P. may have prompted Polynesian migration into the central Pacific.

Human settlement of East Polynesia earlier, incremental, and coincident with prolonged South Pacific drought

“…In the Atiu sediment record (Fig. 3D) and also in the Society Islands (27) (Fig. 3C), this is evidenced by concomitant precipitation increases.…”

Using seafaring simulations and shortest-hop trajectories to model the prehistoric colonization of Remote Oceania

“…The Mobile Founding Migrant models (5) that proposed a rapid movement into Remote Oceania also seems reasonable given the timing of dispersal and supporting genetic data (29), though it seems clear that the late expansion into East Polynesia was also the result of factors such as land distribution, technological advances in seafaring, and climate (12). There are indications that post-AD 1000, more favorable winds (22) and changes to long-term mean precipitation, with drier conditions in the west in the increase rainfall over East Polynesia (30) could have promoted eastward colonization. It has also been suggested that the punctuated temporal pattern of Pacific colonization could be associated to millennial variability of ENSO frequency and intensity and the changes to ease of eastward movement these generate (24).…”

Wave-driven geomorphology of Pacific carbonate coastlines: from landscape to wavelength scale

“…However, the lack of inter-model agreement in the equatorial region for GPI and its individual components suggests that the anomalies there may not be a robust response to consistent forcing. South China Sea (Yu et al, 2009), Jaluit Atoll (this study), Tahaa, French Polynesia (Toomey et al, 2013(Toomey et al, , 2016b, and cave KNI-51, northwestern Australia (Denniston et al, 2015(Denniston et al, , 2016.…”

“…Recently, records of TC landfall have been constructed with high temporal resolution from speleothem proxies of cave flooding (Denniston et al, 2015) and proxies of sediment transport over coastal barriers, over fringing reefs, or into coastal karst basins Toomey et al, 2016b;Donnelly et al, 2015;van Hengstum et al, 2016van Hengstum et al, , 2014Lane et al, 2011;Gischler et al, 2008;Donnelly et al, 2001). These reconstructions extend the observational record by several millennia and reveal large centennial variability in TC activity.…”

“…5-3c,d). A sedimentary reconstruction of TC landfall on Tahaa, French Polynesia recorded few storms over the past 1000 years (Toomey et al, 2016b), but reef-top storm deposits collected from across the central South Pacific basin suggest higher TC activity during the MCA than the LIA (Toomey et al, 2013;Kench et al, 2018b) (Fig. 5-3a,b).…”