EVIDENCE OF RESILIENCE IN REEF ISLANDS IN RESPONSE TO RISING SEA LEVEL ON HUVADHOO ATOLL, MALDIVES

Christine Yiqing Liang,Holly K East,Paul S Kench,Murray R Ford

doi:10.9753/icce.v36v.papers.43

Abstract

Reef islands are at the forefront of concern for future accelerating sea-level rise since their low-lying and isolated nature puts them at higher risk of marine inundation compared to continental coastlines. However, the perceived threat of complete submersion as implied by projected future sea-level rise and current island elevations do not consider the morphologically resilient nature of reef island systems. In particular, the role of sediment supply in the resilience of these islands is still relatively poorly studied. This study presents detailed descriptions of the sedimentary characteristics and stratigraphy of two lagoonal platform islands in Huvadhoo Atoll, Maldives, that formed during periods of Holocene sea-level rise. Island subsurface stratigraphy was reconstructed by analysing the skeletal composition and textural properties of 306 sediment samples from 37 cores extracted across the islands. Island sediments were dominated by coral sands with varied proportions of secondary constituents (molluscs, Halimeda, foraminifera, and crustose coralline algae). Downcore variations in composition show that the proportion of coral sands decrease with depth and the proportion of molluscs and Halimeda increase with depth (with the exception of cores that terminated on lagoon infill). The increased proportion of Halimeda and molluscs in these early island deposits may have resulted from the catch-up growth strategy of the reef during the mid-Holocene highstand as both organisms have high turnover rates and directly contribute to sediment production after death. The sedimentological response of increased Halimeda and molluscs highlights the resilient and dynamic nature of reef islands and the ability of reefs to adjust ecologically to changing sea levels.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/gy3zhqocMGw

Highlights

Reef islands are at the forefront of concern for future accelerating sea-level rise since their lowlying and isolated nature puts them at higher risk of marine inundation compared to continental coastlines
Previous studies of medium-term morphological change have found that some reef islands have been morphologically stable or have accreted over timescales of decades to centuries over periods of contemporary sea-level rise (Dawson and Smithers, 2010; Ford and Kench, 2014; Kench et al, 2015; Webb and Kench, 2010)
Island subsurface stratigraphy was reconstructed by analyzing the skeletal composition and textural properties of 306 sediment samples from 37 cores extracted across the islands

Summary

Introduction

Reef islands are at the forefront of concern for future accelerating sea-level rise since their lowlying and isolated nature puts them at higher risk of marine inundation compared to continental coastlines. Previous studies of medium-term morphological change have found that some reef islands have been morphologically stable or have accreted over timescales of decades to centuries over periods of contemporary sea-level rise (Dawson and Smithers, 2010; Ford and Kench, 2014; Kench et al, 2015; Webb and Kench, 2010). These studies question assertions of island vulnerability, though they only represent case studies from the Pacific and the northern Maldives archipelago. The existence of islands in the region that have persisted during these periods of sea-level change infer that other factors aside from sea-level history are involved in island formation and building, including sediment supply

Methods

Results

Discussion

Conclusion