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Implications of anomalous relative sea-level rise for the peopling of Remote Oceania

Sefton, JP and Kemp, AC and Engelhart, SE and Ellison, JC and Karegar, MA and Charley, B and McCoy, MD (2022) 'Implications of anomalous relative sea-level rise for the peopling of Remote Oceania.', Proceedings of the National Academy of Sciences, 119 (52). e2210863119.


Beginning ~3,500 to 3,300 y B.P., humans voyaged into Remote Oceania. Radiocarbon-dated archaeological evidence coupled with cultural, linguistic, and genetic traits indicates two primary migration routes: a Southern Hemisphere and a Northern Hemisphere route. These routes are separated by low-lying, equatorial atolls that were settled during secondary migrations ~1,000 y later after their exposure by relative sea-level fall from a mid-Holocene highstand. High volcanic islands in the Federated States of Micronesia (Pohnpei and Kosrae) also lie between the migration routes and settlement is thought to have occurred during the secondary migrations despite having been above sea level during the initial settlement of Remote Oceania. We reconstruct relative sea level on Pohnpei and Kosrae using radiocarbon-dated mangrove sediment and show that, rather than falling, there was a ~4.3-m rise over the past ~5,700 y. This rise, likely driven by subsidence, implies that evidence for early settlement could lie undiscovered below present sea level. The potential for earlier settlement invites reinterpretation of migration pathways into Remote Oceania and monument building. The UNESCO World Heritage sites of Nan Madol (Pohnpei) and Leluh (Kosrae) were constructed when relative sea level was ~0.94 m (~770 to 750 y B.P.) and ~0.77 m (~640 to 560 y B.P.) lower than present, respectively. Therefore, it is unlikely that they were originally constructed as islets separated by canals filled with ocean water, which is their prevailing interpretation. Due to subsidence, we propose that these islands and monuments are more vulnerable to future relative sea-level rise than previously identified.

Item Type:Article
Full text:Publisher-imposed embargo until 19 June 2023.
(AM) Accepted Manuscript
File format - PDF
Publisher Web site:
Date accepted:31 October 2022
Date deposited:12 January 2023
Date of first online publication:19 December 2022
Date first made open access:19 June 2023

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