Static or dynamic: reconstructing past movement of the South Pacific Convergence Zone

Abstract

The largest climate system in the world exists over the Pacific Ocean. The behaviour of this system, which comprises El Nino/La Nina events and the South Pacific Convergence Zone (SPCZ), influences climate across the globe. Despite its importance, and because the region comprises archipelagos of sparsely populated islands, our understanding of the movement of the SPCZ is limited over the Holocene. This study addresses the lack of long, continuous records from this region to reconstruct movement of the SPCZ over millennial timescales.

Using a variety of geochemical proxies (compound-specific δ13C and δ2H analyses on nalkanoic acids, total organic carbon δ13C, C/N, Itrax and magnetic susceptibility) from two sites (Lake Teroto, Atiu, Cook Islands, and Lake Lanoto’o, Samoa) this study has developed two palaeoclimatic reconstructions from which clear changes in SPCZ movement have been identified. A clear expansion and/or migration southeast is determined in the mid-Holocene (ca. 5,600-2,700 cal yr BP). Using the known relationship between SPCZ movement and prevailing climate states in the Pacific, specifically ENSO and IPO, inferences have been made on changes in these climate phenomena over the Holocene. When using a network of ENSO records from the tropical Pacific it is apparent that there are three distinct periods where a flavour of El Niño dominates: an early Holocene (ca. 9,500-6,800 cal yr BP) dominated by east Pacific El Niños; a transition period from ca. 6,800-5,600 cal yr BP before central Pacific El Niños dominate from ca. 5,600-2,700 cal yr BP; and a dominance of east Pacific El Niños from 2,700 cal yr BP to present. The first evidence for the 8.2 ka event is presented from the southwest tropical Pacific.

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Identifiers

ORCID for David Sear: orcid.org/0000-0003-0191-6179

ORCID for Peter Langdon: orcid.org/0000-0003-2724-2643

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