Reef islands have continually adjusted to environmental change over the past two millennia

Abstract

Global environmental change is identified as a driver of physical transformation of coral reef islands over the past half-century, and next 100 years, posing major adaptation challenges to island nations. Here we resolve whether these recent documented changes in islands are unprecedented compared with the pre-industrial era. We utilise radiometric dating, geological, and remote sensing techniques to document the dynamics of a Maldivian reef island at millennial to decadal timescales. Results show the magnitude of island change over the past half-century (±40 m movement) is not unprecedented compared with paleo-dynamic evidence that reveals large-scale changes in island dimension, shape, beach levels, as well as positional changes of ±200 m since island formation ~1,500 years ago. Results highlight the value of a multi-temporal methodological approach to gain a deeper understanding of the dynamic trajectories of reef islands, to support development of adaptation strategies at timeframes relevant to human security.

Coastal Morphodynamics and Climate Change: A Review of Recent Advances

“…Further understanding of the geological and geographical variability of reef systems will assist in deciphering how coral reefs will respond to future SLR. Several recent studies based on morphodynamic principles and observations have challenged the assumption that increased flooding due to SLR will automatically render reef islands uninhabitable within decades [110,112]. For instance, results have shown that the magnitude of island change from a range of locations over the past 50 years is not unprecedented compared with paleo-dynamic evidence that has defined large-scale changes in island dimension, shape, and beach levels since island formation c. 1500 years ago.…”

Honduran Reef Island Shoreline Change and Planform Evolution over the Last 15 Years: Implications for Reef Island Monitoring and Futures

“…Analysis of non-vegetated island shorelines from satellite imagery is typically impossible due to the low contrast between beach sediments and reef flat, and difficulty in accurately identifying the toe of the beach at different tidal stages [27,59]. However, these reef island beaches are just as, if not more, dynamic than the vegetated island cores [29,71,73,81,82]. Excluding non-vegetated areas thus prevents important island evolutionary behaviour from being documented.…”

Holocene Depositional History of Low-Lying Reef-Rim Carbonate Islets of Fakarava Atoll, Northwest Tuamotu, Central South Pacific

“…A number of atoll islet formation models have been previously established from reef sites in the Indo-Pacific domain, assuming that the long-term coral reef islet stability is mainly controlled by sea level changes [19,36,[46][47][48][49]52,55,91,92,[105][106][107][108]. The elevation of the antecedent substrates-e.g., reef flats, conglomerate platforms, lagoonal hard to soft surfaces-close to or at sea level at the time of motu initiation appears to be critical to motu initiation and expansion.…”