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Carbonate beach sand of Abaiang Atoll, Kiribati: geochemistry, biogenic sources, and properties

Citation

Ellison, JC and Han, P and Lewis, TW, Carbonate beach sand of Abaiang Atoll, Kiribati: geochemistry, biogenic sources, and properties, Atoll Research Bulletin, (621) pp. 1-21. ISSN 0077-5630 (2019) [Refereed Article]


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Abstract

Sandy beaches are critical resources for low-lying Pacific atoll communities, providing protection during storms, and land area for many coastal villages. Information on the nature of atoll beach sediment, its geochemistry and composition, can help to establish priorities to effectively protect the sources of Pacific island beach sediment. To understand sand sources, this study evaluated its physical characteristics including grain-size, geochemistry and composition, from windward and leeward beach profiles around Abaiang Atoll, Kiribati. Beach sand was >99% carbonate, averaging 37% coral fragments, 30% mollusc shells, 12% foraminifera, and 20% calcareous algae. Significant differences were found between reef and lagoonal sites in proportions of coral and mollusc fragments and foraminifera tests, with lagoon beaches having higher mollusc and coral proportions and lower foraminifera relative to reef beaches. This is attributed to high foraminiferal productivity offshore of reef beaches, and taphonomic durability of coral fragments in longshore drift into the lagoon. Mean sediment diameter increased from the upper to lower beaches at all sites, but fine sediment was lacking, attributed to its dissolution by rainfall and groundwater outflow. Geochemical analysis showed a mean of 84% Ca-Mg carbonates, of which 80% was calcium carbonate. There was no significant difference in the mean calcium percentage or calcium carbonate composition of the sediment between lagoon and reef beach sediment sources. Magnesium and magnesium carbonate content were significantly higher at reef sites relative to lagoon sites, attributed to higher proportions of foraminifera. Sediment-producing near shore habitats are critical to village protection through provision of beach sand, and this study shows the need to better conserve and manage coral reefs and habitats such as lagoon seagrass beds, to ensure continued atoll beach sand supply.

Item Details

Item Type:Refereed Article
Keywords:carbonate beach, foraminifera, molluscs, texture, geochemistry, Kiribati
Research Division:Earth Sciences
Research Group:Physical Geography and Environmental Geoscience
Research Field:Surface Processes
Objective Division:Environment
Objective Group:Land and Water Management
Objective Field:Coastal and Estuarine Land Management
UTAS Author:Ellison, JC (Associate Professor Joanna Ellison)
UTAS Author:Han, P (Mr Paul Han)
UTAS Author:Lewis, TW (Associate Professor Trevor Lewis)
ID Code:131518
Year Published:2019
Deposited By:Geography and Spatial Science
Deposited On:2019-03-21
Last Modified:2019-04-26
Downloads:7 View Download Statistics

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