Sea‐level fall implicated in profound societal change about 2570 cal yr bp (620 bc) in western Pacific island groups

Abstract

During the warmest time of the last 10 000 years (Holocene Thermal Maximum), approximately 6000-4000 cal yr BP in the western Pacific, sea level is known to have reached as much as 2.1 m above its present mean level before declining subsequently. Records throughout the region show that sea level fell an average 0.7 m in the period 3500-2000 cal yr BP during which the earliest (culturally distinct) period of human occupation occurred in five western Pacific island groups [Bismarck Archipelago (Papua New Guinea), Fiji, Mariana Islands, New Caledonia, Vanuatu]. In the interest of testing whether there is evidence for climate forcing of cultural change in this region, dates are presented for the archaeologically conspicuous termination of early-period settlement in these island groups which show that it ended in each around 2570 cal yr BP. From the contemporaneity of this, it is argued that sea-level fall was the principal driver of this cultural transformation, forcing coastal peoples who had previously depended (largely) on foraging from nearshore-marine ecosystems to reconfigure their subsistence economy, something that invariably involved moving their settlements to places where horticulture and agriculture could be practiced more successfully. This research provides an example of where insights into causation of cultural change can be gleaned from comparing precise chronologies of human occupation to equally precise palaeoclimate chronologies.

New Evidence for a Mid- to Late-Holocene Change in the Marine Reservoir Effect Across the South Pacific Gyre

“…Moreover, initial human colonization in West Polynesia followed close on the heels of falling sea-levels. To evaluate whether a regional forcing mechanism, independent of societal drivers, was primarily responsible for any societal changes (cf., Nunn and Carson 2015) it is necessary to obtain precise dates for these events. With the development of the first temporal model of changing ∆R, we are only now entering a phase where 14 C may be able to answer these questions.…”

Early settlement and subsistence on Tongatapu, Kingdom of Tonga: Insights from a 2700–2650 cal BP midden deposit

“…Data summarized by Woodroffe and Horton (2005) indicate a complicated post-highstand pattern in some parts of the Indo-Pacific with sea-level falling rapidly rather than gradually (see also Bird et al 2010). Nunn and Carson (2015) in a recent review suggest that reconfiguration of marine-focused subsistence economies in the western Pacific as a result of sea-level fall dates to 2570 cal BP. On Tongatapu, archaeological results and palynological analysis of mangrove sediments suggest that a critical threshold was reached with the closure of the Fanga 'Uta lagoon passage at the high-tide level by 2500 cal BP (Ellison, 1988;Spennemann, 1997).…”

“…Dickinson (2003) noted that Lapita settlement of Oceania occurred after a mid-Holocene hydro-isostatic highstand suggesting that colonization of Pacific Islands was aided by a sea-level fall of 1-2 m. A declining sea-level caused the emergence of coastal flats on high islands, protected lagoons and stable islets that were new and attractive environments for human settlement (Dickinson et al 1994;Dickinson, 2003:498;Nunn, 2007a;Nunn, 2007b:121). The transformation of near-shore environments facilitated human occupation of Pacific islands, yet sea-level fall over several centuries also had the potential to reduce the productivity of littoral marine zones that were heavily utilized by early prehistoric people for subsistence such as embayments, reef flats, estuaries and lagoons (Nunn and Carson, 2015). Lapita sites typically contain substantial quantities of shellfish and finfish, especially the remains of inshore reef and lagoon taxa (Kirch, 1997;Kirch, 2010;Szabó and Amesbury, 2011), and many sites are located on former shorelines that are now stranded by sea-level fall and coastal progradation (Best, 1984).…”

Multi-isotopic analysis of first Polynesian diet (Talasiu, Tongatapu, Kingdom of Tonga)

“…During the Lapita period in Tonga, the Talasiu site would have been an attractive location for human settlement as it overlooked an embayment holding large numbers of sessile and gregarious shellfish close to a fresh water solution channel, with gardening soils immediately inland. However, sea levels were declining from a mid-Holocene high stand in the western Pacific (Nunn and Carson, 2015) and, in Tongatapu, sea level fall led to the closure of the Fanga 'Uta Lagoon passage at the high-tide level by~2500 cal. BP (Ellison, 1988;Spennemann, 1997).…”