Browsing by Author "Dawson, JL"

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    Benthic foraminifera: their importance to future reef island resilience
    (International Coral Reef Society, 2012-07-19) Dawson, JL; Hua, Q; Smithers, SG
    The provenance, age and redistribution of sediments across Raine Reef (11°35’28”S 144°02’17”E), northern Great Barrier Reef (GBR) are described. Sediments of both the reef flat and sand cay beaches are composed predominantly of benthic foraminifera (35.2% and 41.5% respectively), which is a common occurrence throughout the Pacific region. The major contemporary sediment supply to the island was identified as Baculogypsina sphaerulata, a relatively large (1-2 mm exclusive of spines) benthic foraminifera living on the turf algae close to the reef periphery, and responsible for beach sand nourishment. Radiometric ages of foraminiferal tests of ranging taphonomic preservation (pristine to severely abraded) included in surficial sediments collected across the reef flat were remarkably young (typically <60 years). Results indicate rapid transport and/or breakdown of sand with a minimal storage time on the reef (likely <102 years), inferring a tight temporal link between the reef island and sediment production on the surrounding reef. This study demonstrates the critical need for further research on the precise residence times of the major reef sediment components and transport pathways, which are fundamental to predicting future island resilience. © Copyright belongs to the authors.
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    The importance of large benthic foraminifera to reef island sediment budget and dynamics at Raine Island, northern Great Barrier Reef
    (Elsevier, 2014-10-01) Dawson, JL; Smithers, SG; Hua, Q
    Low-lying reef islands are among the most vulnerable environments on earth to anthropogenic-induced climate change and sea-level rise over the next century because they are low, composed of unconsolidated sediment that is able to be mobilised by waves and currents, and depend on sediments supplied by reef organisms that are particularly sensitive to environmental changes (e.g. ocean temperatures and chemistry). Therefore, the spatial and temporal links between active carbonate production and island formation and dynamics are fundamental to predicting future island resilience, yet remain poorly quantified. In this paper we present results of a detailed geomorphological and sedimentological study of a reef and sand cay on the northern Great Barrier Reef. We provide an empirical investigation of the temporal linkages between sediment production and reef island development using a large collection of single grain AMS 14C dates. Large benthic foraminifera (LBF) are the single most important contributor to contemporary island sand mass (47%; ranging from 36% to 63%) at Raine Island, reflecting rapid rates of sediment production and delivery. Standing stock data reveal extremely high production rates on the reef (1.8 kg m− 2 yr− 1), while AMS 14C dates of single LBF tests indicate rapid rates of sediment transferral across the reef. We also demonstrate that age is statistically related to preservation and taphonomic grade (severely abraded tests > moderately abraded tests > pristine tests). We construct a contemporary reef and island sediment budget model for Raine Island that shows that LBF (Baculogypsina, Marginopora and Amphistegina) contribute 55% of the sediment produced on the reef annually, of which a large proportion (54%) contribute to the net annual accretion of the island. The tight temporal coupling between LBF growth and island sediment supply combined with the sensitivity of LBF to bleaching and ocean acidification suggests that islands dominated by LBF are likely to be very sensitive to short and long term climate change projections. Potential outcomes of this work relate to improving the understanding of the future change dynamics of reef islands in response to climate change. © 2014, Elsevier B.V.
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    The potential application of taphonomy-AMS 14C analysis in modelling reef island geomorphic response to climate change
    (18th INQUA Congress, 2011-07-21) Dawson, JL; Hu, Q; Smithers, SG
    The Great Barrier Reef (GBR) is the largest known reef system in the world with more than 2900 individual reefs and over 900 reef islands. As climate change progresses reef islands become increasingly vulnerable to sea-level rise, increased SST’s and ocean acidity, and more frequent tropical storms, through alterations to sediment production, transport and deposition. We focus on large benthic foraminifera, an important sediment component of reefs and reef islands globally. Using taphonomy coupled with more than 35 AMS 14C ages of individual foraminifera tests, we develop a novel approach to understanding the spatial and temporal patterns and rates of sediment production and delivery across a reef flat and how this relates to island formation and future change. Our study site was a platform reef and vegetated sand cay in the northern GBR (Raine Island, 11°35’28”S 144°02’17”E). Only four reef flat samples predate 1950 AD while all beach sediments are younger than ~1970 AD, indicating a remarkably short residence time for sediment on the reef flat. Calibrated 14C ages increase from the outer reef flat to the island consistent with the main transport pathways. At all sample sites, percent modern carbon (pMC) decreases as shell degradation increases (poorly abraded tests are ca. 10-20 yrs older than pristine tests). While the maximum residence time for foraminiferal sediment on the reef flat is in the order of 100-200 yrs, the bulk of sediment reaches the island within 10-15 yrs. These findings are of significant importance to the future stability and sustainable management of reef islands because such rapid exchange of sediment from the reef flat to the island would suggest a high degree of sensitivity to environmental change and an immediate island geomorphic response to any alteration to the reefs ability to produce sediment. Copyright (c) 2011 INQUA 18