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Testing the utility of geochemical proxies to reconstruct Holocene coastal environments and relative sea level: a case study from Hungry Bay, Bermuda

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posted on 2023-05-20, 00:30 authored by Kemp, AC, Vane, CH, Khan, NS, Joanna EllisonJoanna Ellison, Engelhart, SE, Horton, BP, Nikitina, D, Smith, SR, Rodrigues, LJ, Moyer, RP
On low-lying, tropical and sub-tropical coastlines freshwater marshes may be replaced by salt‑tolerant mangroves in response to relative sea-level rise. Pollen analysis of radiocarbon‑dated sediment cores showed that such a change occurred in Hungry Bay, Bermuda during the late Holocene. This well-established paleoenvironmental trajectory provides an opportunity to explore if geochemical proxies (bulk-sediment δ13C and Rock-Eval pyrolysis) can reconstruct known environmental changes and relative sea level. We characterized surface sediment from depositional environments in Bermuda (freshwater wetlands, saline mangroves, and wrack composed of Sargassum natans macroalgae) using geochemical measurements and demonstrate that a multi-proxy approach can objectively distinguish among these environments. However, application of these techniques to the transgressive sediment succession beneath Hungry Bay suggests that freshwater peat and mangrove peat cannot be reliably distinguished in the sedimentary record, possibly because of post‑depositional convergence of geochemical characteristics on decadal to multi‑century timescales and/or the relatively small number of modern samples analyzed. Sediment that includes substantial contributions from Sargassum is readily identified by geochemistry, but has a limited spatial extent. Radiocarbon dating indicates that beginning at -700 CE, episodic marine incursions into Hungry Bay (e.g., during storms) carried Sargassum that accumulated as wrack and thickened through repeated depositional events until ∼300 CE. It took a further ∼550 years for a peat‑forming mangrove community to colonize Hungry Bay, which then accumulated sediment rapidly, but likely out of equilibrium with regional relative sea-level rise.

History

Publication title

Open Quaternary

Volume

5

Pagination

1-17

ISSN

2055-298X

Department/School

School of Geography, Planning and Spatial Sciences

Publisher

Ubiquity Press Ltd

Place of publication

United Kingdom

Rights statement

Copyright 2019 The Authors. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/

Repository Status

  • Open

Socio-economic Objectives

Assessment and management of terrestrial ecosystems; Expanding knowledge in the earth sciences

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