Over the last 25 years considerable information on the geomorphological evolution of the world's largest coral reef system, the Great Barrier Reef, has become available. This book reviews the history of geomorphological studies of the Great Barrier Reef and assesses the influences of sea-level change and oceanographic processes on the development of reefs over the last 10,000 years. It presents analyses of recently attained data from the Great Barrier Reef and reconstructions of the sequence of events which have led to its current geomorphology. The authors emphasise the importance of the geomorphological time span and its applications for present management applications. This is a valuable reference for academic researchers in geomorphology and oceanography, and will also appeal to graduate students in related fields.

The Geomorphology of the Great Barrier Reef: Development, Diversity and Change

Coral reefs and sea-level change

https://www.deepreef.org/images/stories/publications/peer-reviewed-literature/DrownedReefsGBR2008.pdf

New evidence for drowned shelf edge reefs in the Great Barrier Reef, Australia

There is considerable uncertainty about future sea-level projections due to the current poor understanding of the vulnerability and sensitivity of ice sheets to global warming. Fossil coral reefs represent a unique archive of sea-level and associated environmental changes that extend far beyond instrumental records. Here, recent advances in this field are summarized, focusing on periods of Earth history typified by rapid sea-level rise and short-term climate excursions. Sea-level and reef response records from the Last Deglaciation, and periods characterized by higher sea-level stands and short-term and low-magnitude sea-level oscillations such as the Mid to Late Holocene and the Last Interglacial are synthesised. Special emphasis is given to understanding how coral reefs have responded to these changes in terms of reef development, architecture and composition. Finally, seven major challenges and future research directions are identified.

Coral reef response to Quaternary sea‐level and environmental changes: State of the science

Macroalgae is a collective term used for seaweeds and other benthic marine algae that are generally visible to the naked eye. Larger macroalgae are also referred to as seaweeds. The macroalgae of the Great Barrier Reef (GBR) are a very diverse and complex assemblage of species and forms. They occupy a wide variety of habitats, including shallow and deep coral reefs, deep inter-reef areas, sandy bottoms, seagrass beds, mangroves roots, and rocky intertidal zones. Macroalgae broadly comprise species from three different phyla: Rhodophyta (red algae), Heterokontophyta (predominantly Phaeophyceae, the brown algae), and Chlorophyta (the green algae) (Table 7.1). Macroalgae are clearly distinguished from microalgae, which require a microscope to be observed (eg phytoplankton, benthic and pelagic diatoms, free-living dinoflagellates, cyanobacteria (blue-green algae) and the symbiotic zooxanthellae that live within coral tissue). In some cases, benthic microalgae, such as some cyanobacteria and Chrysophyta, form large colonies that resemble thalli of macroalgae. Such colony-forming cyanobacteria are often common components of turf algal assemblages and, in this context, will be included in this chapter.

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Vulnerability of macroalgae of the Great Barrier Reef to climate change

A new borehole, 210 mbsf (meters below sea floor) deep, drilled in Ribbon Reef 5 on the Great Barrier Reef off Cooktown, NE Australia, reveals a shallowing-upwards succession, the younger part of which is punctuated by a series of erosion surfaces. Nine depositional units have been defined by lithological changes and are numbered sequentially from the base of the hole upwards. Aminostratigraphy, magnetostratigraphy, radiocarbon dating, uranium series dating, and modeling together with strontium ratios have been applied in an attempt to establish a chronology of accumulation. Carbonate deposition began about 770 ka ago in a relatively deep-water slope environment and is represented by a series of debris flows. Lithoclasts within these rocks, indicate that older limestones already existed in the area. Subsequent accretion involved the downslope accumulation of grainstones and wackestones, sometimes cross-laminated, characterized by intervals with abundant rhodoliths and scattered, probably reworked, corals. Four units at the base of the hole reflect deposition that probably began during isotope stage 16 and continued through stage 15 from about 770 to about 564 ka. Unit 5 probably extended to stage 11 (about 400 ka), and unit 6 to stage 9 ( 330 ka). Typical reefal associations of corals and calcareous algae were established in this area only above depths of about 100 m in the borehole, units 5-4. The succession is apparently unbroken to an erosion surface at 36 mbsf indicating subaerial emergence. The lack of evidence of emergence below this surface reflects progressive accretion or progradation or both. Two younger erosion surfaces define further periods of lowered sea level. Unit 7 is attributed to deposition during isotope stage 7, but erosion during stage 8 resulted in the preservation of only 8 m of unit 7 limestones. Unit 8 is correlated with stage 5 (125 ka), and unit 9 is interpreted as Holocene (post 7,700 ka). The limited thicknesses of units 7, 8, and 9 are considered to reflect erosion. The progressive shallowing brought the depositional surface within the zone exposed during lowstands, and there is no sedimentological evidence that aggradation was restricted by a lack of accommodation.

Douglas D. Harkness

Papers

The Great Barrier Reef: The Chronological Record from a New Borehole