"The initiation of the Holocene Great Barrier Reef coincided with rapid environmental change as sea level rose and inundated the shelf. Core data from One Tree Reef (southern Great Barrier Reef) shows coral growth started by ∼8.2 ka, but accretion between 8 and 7 ka was slower, occurred in deeper water, and comprised more sediment-tolerant coral communities compared to growth following sea-level stabilization. It has been postulated that environmental stressors (e.g. increased turbidity and nutrients) suppressed and delayed reef growth, however direct data supporting this hypothesis are scarce. Here we combine the isotopic composition of skeletal bound organic nitrogen (δ15N) and Ba/Ca ratios of coral skeletons with published geochemical proxies of terrestrial sediment discharge to constrain Holocene water conditions at One Tree Reef. Between 8 and 7 ka the skeletal δ15N values from multiple corals and genera were elevated (average of 8.45 ± 0.89‰) relative to the early transgression and following sea-level stabilization (average of 7.04 ± 0.82‰). We propose that elevated δ15N in corals reflects the discharge of deep terrestrial soil nitrogen resulting from high runoff. This is supported by Ba/Ca measurements and published rare earth element and yttrium (REE + Y) geochemical proxies in coral and reefal microbialites from the same cores. These data suggest that increased terrigenous discharge of sediment and nutrients did not inhibit reef growth, rather led to the establishment of slower-growing, deeper and more sediment-tolerant coral communities. Understanding the capacity for reef growth under adverse environmental conditions provides insight into thresholds and resilience of the GBR over centennial-millennial timescales."

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"The early Holocene initiation of the Great Barrier Reef (GBR) is an important case study to investigate the ability of coral reef systems to grow and withstand rapid environmental changes (Marshall and Davies, 1982; Dechnik et al., 2015; Sanborn et al., 2020). This time interval was marked by rapid relative sea-level (RSL) rise (∼6–7 m/ka; Sloss et al., 2007; Lewis et al., 2013), increasing sea surface temperatures (SST) (+4° mean annual water temperature anomaly between 8 and 6 ka; Gagan et al., 2004; Sadler et al., 2016; Leonard et al., 2018), a wetter climate contributing to increased terrestrial runoff (Hembrow et al., 2014), along with the reworking of terrestrial shelf sediments during the transgression of the GBR shelf (Davies and Kinesy, 1977; Hallock and Schlager, 1986). These factors are generally recognized as being detrimental to reef growth, particularly for present reef systems threatened by rising SSTs, declining water quality, and increased nutrient runoff (Hughes et al., 2003; Pandolfi et al., 2003; Brodie et al., 2012; Waterhouse et al., 2017). Despite these unfavorable environmental conditions, studies across the GBR show extensive early Holocene reef growth by ∼8 ka, following a lag of ∼1200–700 years between the flooding of the shelf and first coral growth (Dechnik et al., 2015; Sanborn et al., 2020). "