Calibrated density profiles of Caribbean mangrove peat sequences from computed tomography for assessment of peat preservation, compaction, and impacts on sea-level reconstructions

Oceanic mangroves accumulate peat with sea-level rise without terrestrial sediment inputs, but fossil peat’s elevation as a tide-range limited sea-level indicator is assumed to be affected by compaction. Despite assumption of decomposition, compression, and dewatering, pure Rhizophora mangle peat ap...

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Bibliographic Details
Published in:Quaternary research 2018-01, Vol.89 (1), p.201-222
Main Authors: Toscano, Marguerite A., Gonzalez, Juan L., Whelan, Kevin R.T.
Format: Article
Language:English
Subjects:
Aquatic plants
Compaction
Computed tomography
Coral reefs
Dewatering
Mangroves
Peat
Sea level
Sediments
Soil erosion
Studies
Tomography
Water content
Water depth
Wetlands
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Summary:Oceanic mangroves accumulate peat with sea-level rise without terrestrial sediment inputs, but fossil peat’s elevation as a tide-range limited sea-level indicator is assumed to be affected by compaction. Despite assumption of decomposition, compression, and dewatering, pure Rhizophora mangle peat appears coarse, water-saturated, and loose even at depth. Calibrated peat densities from computed tomography (CT) and petrologic analysis allow quantitative assessment of compaction in continuous peats from Florida (6 m thick), Belize (12 m thick), and Panama (3.5 m thick). Pure peat exhibits voids at all depths and >80% water contents. CT density does not increase with depth; bulk densities are low, minimally variable, and trend-free. Higher CT-density intervals coincide with compositional changes (sediment, coral). CT of peat buried under sediment shows a shift to higher densities. CT of air-dried continuous peat shows uncompressed fine and coarse roots and voids, with negative densities indicative of air in place of interstitial water. Peat’s high water content and hydraulic conductivity prevent dewatering and compaction, hypothetically maintaining original sea-level indicative elevations at intermediate depths. Non-compacted, sediment-free, offshore peats can provide a continuous proxy for reconstructing the record of sea-level rise at any site, if depositional, disturbance, and geochemical and biotic processes affecting 14C ages are also assessed.
ISSN:0033-5894
1096-0287
DOI:10.1017/qua.2017.101