One Thousand Three Hundred Years of Variability in the Position of the South Pacific Convergence Zone

Abstract

The South Pacific Convergence Zone (SPCZ) is the largest rain belt in the Southern Hemisphere and a key driver of precipitation variability, impacting South Pacific island communities. Our millennial‐long reconstruction is based on a trans‐Pacific tree‐ring network, containing chronologies sensitive to changes in the SPCZ because of its pervasive nature, spatial extent, and link to the El Niño‐Southern Oscillation. The reconstruction explains 58% of variance in the instrumental SPCZ index from 1911–1998. El Niño‐Southern Oscillation cycles are identified throughout the reconstruction period. Multidecadal periodicities wax and wane, coinciding with a sustained eastward shift during the Medieval Climate Anomaly (~1,000–1,200 CE). We find large volcanic eruptions increased the tendency for the SPCZ to be displaced eastward. The reconstruction helps improve our understanding of past hydroclimatic behavior in the southwest Pacific and can be used to validate general circulation model projections for Pacific Island communities and the wider region in the 21st century.

Contrasting Common Era climate and hydrology sensitivities from paired lake sediment dinosterol hydrogen isotope records in the South Pacific Convergence Zone

“…A dry MCA at these locations could represent a reduction in rainfall intensity, a reduction in SPCZ extent, or a northeastward shift of the mean SPCZ position such that it collapsed towards the equator into a more zonal position. An equatorward-shifted SPCZ is an orientation supported by drought atlases based on tree-ring networks from an Australia-New Zealand-Indonesia cluster compared to a Mexico-southern United States-western Guatemala cluster (Higgins et al, 2020). While this drought atlas is based on sites far from the SPCZ regions and contains no tropical tree ring data, which brings into question the applicability of its conclusions to SPCZ sites, the two largest westward/equatorward shifts in the Higgins et al (2020) reconstructed SPCZ index occur during the MCA (gold sections in Fig.…”

“…An equatorward-shifted SPCZ is an orientation supported by drought atlases based on tree-ring networks from an Australia-New Zealand-Indonesia cluster compared to a Mexico-southern United States-western Guatemala cluster (Higgins et al, 2020). While this drought atlas is based on sites far from the SPCZ regions and contains no tropical tree ring data, which brings into question the applicability of its conclusions to SPCZ sites, the two largest westward/equatorward shifts in the Higgins et al (2020) reconstructed SPCZ index occur during the MCA (gold sections in Fig. 6A) and may reflect orientations similar to zonal SPCZ positions observed during some strong El Niño events (1982/83 and 1997/98), as well as the 1991/92 moderate event (Vincent et al, 2011).…”

“…Values at the top of each panel (more negative isotope values, higher magnetic susceptibility values, and natural logarithm ratios closer to zero) indicate periods of relatively higher precipitation. (A) A 50-year gaussian filter applied to the SPCZ index (dotted black line Salinger et al, 2014) and the SPCZ index reconstructed from tree rings (teal and gold segments, Higgins et al, 2020) reflects the relative position of the SPCZ (note inverted axis), (B) d 2 Hwax from C30 nalkanoic acid from terrestrial leaf wax inputs measured in marine sediments from the W. Sulawesi margin of Indonesia (Tierney et al, 2010), (C) d 2 Hwax from C28 n-alkanoic acid from terrestrial leaf wax inputs measured in Lake Lading sediment (Konecky et al, 2013), (E) XRF ln(Ti/Ca) runoff record (gold) with a 100-yr low pass filter (dark gold) from Apu Bay off the island of Tahaa in French Polynesia (Toomey et al, 2016), (D) d 2 Hwax from C26 n-alkanoic acid from terrestrial leaf wax inputs measured in Lake Te Roto sediment (Sear et al, 2020). (F) Lac Lanutavake UC1 and UC4 magnetic susceptibility (not available for the uppermost material sectioned in the field) and d 2 Hdinosterol (G) records from 'Uvea (this study), and d 2 Hdinosterol records from Samoa (Sear et al, 2020) (H), and Vanuatu (Sear et al, 2020) Year CE wetter drier supplied by the Southeastern Pacific's subtropical high contributes to the formation of the SPCZ (Lintner and Neelin, 2008;Battisti, 2007a, 2007b).…”

Literature survey of subseasonal‐to‐seasonal predictions in the southern hemisphere

“…Agricultural activities in the South Pacific region are heavily dependent on rainfall due to the absence of extensive irrigation (Beischer et al, 2021). South Pacific Convergence Zone (SPCZ) affects rainfall variability of the South Pacific region (e.g., Beischer et al, 2021; Higgins et al, 2020; Narsey et al, 2022). Variations in the SPCZ location, slope, and intensity affect water availability and as a result, productivity of subsistence crops is affected (Beischer et al, 2021).…”

Cross-continental hydroclimate proxies: Tree-rings in Central Chile reconstruct historical streamflow in Southeastern South American rivers

“…Tree-ring networks are used to reconstruct annual and seasonal hydroclimate variability in broad geographical regions (Coulthard et al, 2021; Higgins et al, 2020; Meko and Woodhouse, 2011; Sauchyn et al, 2011; Maxwell et al, 2017). While Southern Annular Mode (SAM) influences tree growth throughout the extra-tropical Southern Hemisphere (Villalba et al, 2012), El Niño Southern Oscillation (ENSO) plays a critical role for growth, precipitation and streamflow anomalies in tropical and subtropical latitudes (Garreaud, 2009).…”