Late glacial to deglacial variation of coralgal assemblages in the Great Barrier Reef, Australia

Abstract

Integrated Ocean Drilling Program (IODP) Expedition 325 cored submerged reefs along the shelf edge of the Great Barrier Reef (GBR) to study sea-level and environmental changes and their impacts on reef communities and reef growth since the Last Glacial Maximum (LGM). Previous work defined five reef sequences (Reef 1

Reef-flat and back-reef development in the Great Barrier Reef caused by rapid sea-level fall during the Last Glacial Maximum (30–17 ka)

“…27-25 ka (reef 2 in Figs. 1 and 2) for HYD-01C, and 22-19 ka (reef 3a) for HYD-02A, based on our foraminiferal production ages and other published data (Webster et al, 2018;Humblet et al, 2019). The timing of reef-flat and back-reef formation is consistent with the two stepwise falls in sea level during the LGM (Yokoyama et al, 2018; Fig.…”

“…Last Glacial Maximum (LGM) reefs have been observed at Mayotte (Indian Ocean), Vanuatu, Solomon Islands, Marquesas Islands (Pacific Ocean) (reviewed by Montaggioni, 2005), and Ryukyu Islands (Japan) (Sasaki et al, 2006) as thin veneers or coral communities 2-3 m thick, at depths of mostly 100-150 m below sea level (mbsl). More recently, sediment cores recovered from the shelf edge of the Great Barrier Reef during Integrated Ocean Drilling Project (IODP) Expedition 325 revealed that drowned shelf-edge reefs composed of in situ coralgal frameworks and associated microbialites developed during the LGM and the subsequent last deglaciation (Webster et al, 2018;Braga et al, 2019;Humblet et al, 2019). In addition, combined paleo-water depths and >580 radiometric ages of the coralgal assemblages revealed a two-step sea-level plunge, each of several tens of meters in magnitude and a change rate of 15-20 mm yr -1 , into the LGM (Yokoyama et al, 2018).…”

Coral Record of Younger Dryas Chronozone Warmth on the Great Barrier Reef

“…The reef sequences described in section 6.1 were distinguished based on lithologic, chronostratigraphic, and biologic criteria (Webster et al, 2018). The RSL envelopes for NOG and HYD were constructed based on U‐Th coral ages and 14 C AMS (radiocarbon) coral and coralline algal ages with paleo‐water depth established via a multiproxy approach including corals, coralline algae, algal crust thickness, and vermetid gastropod presence (Humblet et al, 2019; Webster et al, 2018; Yokoyama et al, 2018).…”

“…This allows us to explore how changing SSTs may have impacted or interacted with other environmental variables to influence the development of the GBR since the LGM. Each of these reefs is associated with unique changes in relative sea level (RSL) as well as coralgal assemblage shifts (Humblet et al, 2019;Webster et al, 2018;Yokoyama et al, 2018), discussed in detail in section 6.2, and considering the Figure 1. Map of study sites, Noggin Pass (17°S, NOG) and Hydrographer's Passage (20°S, HYD) in the GBR off the northeast coast of Australia in the Coral Sea with mean annual SST contours (reference period: 1955, World Ocean Atlas 2009Locarnini et al, 2010).…”

“…This allows us to explore how changing SSTs may have impacted or interacted with other environmental variables to influence the development of the GBR since the LGM. Each of these reefs is associated with unique changes in relative sea level (RSL) as well as coralgal assemblage shifts (Humblet et al, 2019; Webster et al, 2018; Yokoyama et al, 2018), discussed in detail in section 6.2, and considering the corresponding SSTAs provide a thorough understanding of the GBR. However, important questions remain regarding the relative importance of sedimentation, temperature rise, and rising sea level in controlling reef demise.…”