Reef cores that have been radiometrically dated are increasingly used to examine Holocene reef geomorphology, accretion rates, and community changes. Further, these accretion rates can be compared to sea level change regimes to see if, and how coral reefs have been keeping up with sea level. As Sea level rise is expected to accelerate over the next 100 years, it is important to examine whether these reef complexes are able to “keep up” and avoid “drowning.” Coring has been conducted in many highly studied areas such as the Great Barrier Reef and the Caribbean. However, in the Indo-Pacific region, an area of the highest coral diversity, there have been only a handful of reef cores collected. Here, we present data of 16 cores from two islands of different reef zones from the Spermonde Archipelago, South Sulawesi, Indonesia. Cores were taken from the reef flat and slope, with recovered length varying from 0.41 to 3.53 m, providing a history of each reef after radiocarbon dating. From 7200 to 5500 YBP, sea level rise rapidly increased and these reef complexes accreted at rates able to match this. This is in part driven by a higher occurrence of massive and foliose corals. After this point and toward the present day, sea level declined, causing sub-aerial exposure of these sand cays and the slope now sustaining the growth. This shows that these reef complexes (some of which contain heavily populated islands) are able to keep growing in the face of sea level rise regimes.

Quaternary coral reef science has limited understanding of coral reef response to the Mid Pleistocene Climate Transition (MPT) (ca. 0.8–0.6 Ma) that triggered the Earth's transition into a dry, arid climate and eventually into a period of glacial-interglacial cycles. During this period many of the extant large reef systems initiated, for example barrier reefs around Pacific atolls and the Great Barrier Reef, however, data availability is low. North and South Scott reefs are isolated carbonate platforms on the North West Shelf of Australia that have outpaced subsidence and oceanographic stressors intermittently since the Miocene. The long-term carbonate platform evolution from ca. 20 Ma to present has been characterised using seismic stratigraphy and seismic geomorphology, integrated with industry well log data, but, high-resolution reconstructions of sedimentological and environmental processes controlling coral reef growth cycles have not been determined prior to the Holocene. Lithologic and chrono-stratigraphic interpretations of four fossil coral reef boreholes extending to 200 m below sea floor provide new insights into the sensitivities of coral reef response to regional (i.e., tectonics, oceanographic) and global (i.e., climate, eustacy) environmental forcing conditions at millennial scale resolution since the MPT. Depositional facies and paleoenvironmental reconstructions are based on; detailed logging and petrologic, mineralogic and sedimentary lithofacies analyses of four cores located on the windward and leeward reef crests of north and south Scott Reef. Coralgal assemblages and other reef biota (e.g., foraminifera) constrain paleowater depths and precise paleoenvironmental settings. New radiometric dating based on sample selection from hyperspectral and neutron scattering data are presented. We recognise distinct reef growth sequences within lithologic and chrono-stratigraphic units that correspond to global high sea levels within Marine Isotope Stages (MIS) 1 (Holocene), 5, 7, 8, 11, 13. Each reef growth sequences established on the drowned platforms during deglacial and interglacial sea levels. Hiatuses in reef growth represented by paleosol horizons in the core that signals subaerial exposure events during glacial (low sea level) periods. Significant variations in elevation, subsidence histories, paleo-coralgal communities and geomorphological features occur between the north and south reef, as well as spatially across each reef. Sequences of coral reef growth kept pace with deglacial sea level rise owing to favourable environmental and oceanographic conditions that allowed the cyclic re-establishment of shallow, moderate and deep-water coral reef development across both platforms since the MPT. A comprehensive review of comparable MPT-triggered coral reef sequences for Ribbon Reef 5 on the NE margin of Australia exposes some significant variations in reef response to eustatic (subsidence and sea level) and environmental controls, including: proximity to land, position along the continental shelf, terrigenous sediment influx, seabed geomorphology, ocean currents and nearby sites for coral larvae recruitment. Analysis of two newly acquired and two undescribed fossil coral reef cores provides a unique insight into the Quaternary history of a key site along the NWS, demonstrating how fossils can be used to reconstruct Earth history to answer broader questions in the bio and geological sciences with respect to coral reef ecological responses to climate change.

Coral reef hydrodynamics control the transport and distribution of sediments, nutrients, and coral larvae, consequently influencing all coral reef processes across broad spatio-temporal scales. Yet, in situ hydrodynamic data from the disparate morphological zones (e.g., forereef slope) are limited. Spurs and grooves (SaG) morphology, consisting of reef normal coral ridges alternating with grooves, has been documented globally across fringing reefs, barrier reefs and atoll reefs (da Silva et al. 2020). Here, we present field observations of wave and tidally driven flows through a forereef groove. Our data captures wave and current flow characteristics in shallow, highly turbulent SaG and provides insight into the geomorphic role and origin of SaG.

Key Messages: (1) Three phases of biogenic carbonate development occur on the North Queensland margin during the Quaternary with the central GBR finally forming in the last phase <800 ka. (2) Sea Surface Temperatures (SST) may not have directly influenced the initiation of the GBR. (3) The barrier reef phase began after a substantial decrease in the flux of siliciclastic sediment, suggesting a causal relationship.

Coral reefs provide substantial evidence of Quaternary sea-level positions because of their geological preservation and suitability for dating, using both radiocarbon and U-series techniques. Interpretation of this evidence requires an understanding of reef geomorphology, modern reef organism distributions, and the environmental factors influencing them. Fossil reef terraces, formed during the Last Interglacial, marine oxygen isotope (MIS) substage 5e (~128–116 ka), occur at elevations of at least 2 m above present sea level on many tropical shorelines. Along plate margins experiencing rapid tectonic uplift there are flights of reef terraces, and radiometric dating of corals within these provided some of the first evidence in support of the orbital fluctuations of sea level, related to Milankovitch cycles. Observations of corals at elevations up to 8–9 m above present on apparently stable shorelines continue to contribute to ongoing debate about the height reached by sea level during the Last Interglacial. Elsewhere Last Interglacial reefs are found below sea level. Oscillation of sea level during MIS 5e has been interpreted from several sites, with some studies inferring rapid rise of several meters during the interglacial. Older reef terraces are apparent on uplifted margins, but ages become increasingly unreliable before MIS7. Drilling of coral reefs, initially in Barbados and on the Huon Peninsula in Papua New Guinea, but augmented by more recent Integrated Ocean Drilling Program (IODP) expeditions to Tahiti, and the Great Barrier Reef, has provided insights into Last Glacial Maximum (LGM) and deglacial sea level changes. Dating of corals indicates a stepped fall to the LGM followed by several phases of rapid sea-level rise, attributed to pulses of meltwater input to the oceans, resulting in drowning and demise of the reefs. The magnitude and timing of these remains poorly resolved and is a function of the extent to which fossil corals may have been in growth position and the paleowater depth in which they grew. Studies of Holocene coral reefs have indicated three different modes of reef growth; some reefs kept up with sea level, others caught up when sea level decelerated, whereas some were drowned, or back-stepped with establishment of a new reef higher and landward of the former reef structures. Holocene sea level appears to have experienced a gradual rise up to present across the Caribbean, providing accommodation space for reefs to accrete vertically; whereas in the Indo-Pacific sea level has been near its present level for the past 6–7000 years, with many reef flats emergent following a slight fall of sea level caused by ocean siphoning. Microatolls, large flat-topped intertidal corals on reef flats, provide the clearest evidence of past sea-level position, but, in their absence, novel biological or other sea-level indicators, such as thick crusts of specific coralline algae and vermetids, are required to better constrain paleowater depths. The upper surface of living microatolls can preserve a subdued indication of water level changes that have occurred during the decades of its lifetime. The sensitivity of corals to exposure by the lowest tides means that long-lived intertidal microatolls can contain a filtered record of low water levels, with the prospect of extrapolating this across recent centuries to millennia using preserved fossil colonies. Some living intertidal corals show upward growth in response to the increased accommodation space as a result of ongoing sea-level rise.

Rapid, millennial-scale changes in sea level have been proposed for the beginning, middle, and/or end of the Last Interglacial (LIG) [~129 to 116 thousand years ago (ka)]. Each of these scenarios has different implications for polar ice sheet behavior in a warming world. Here, we present a suite of 230Th ages for fossil corals in the Seychelles within a detailed sedimentary and stratigraphic context to evaluate the evolution of sea level during this past warm period. The rise to peak sea level at ~122 to 123 ka was punctuated by two abrupt stratigraphic discontinuities, defining three distinct generations of reef growth. We attribute the evidence of episodic reef growth and ephemeral sea-level fall to the competing influence of Northern Hemisphere ice melt and Antarctic ice regrowth. Asynchronous ice sheet contributions would mask the full extent of retreat for individual ice sheets during the LIG and imply greater temperature sensitivity of ice sheets than previously inferred.

During the 2024 global mass bleaching event, a rapid bleaching assessment was conducted on two large benthic foraminifera populations on One Tree Reef, southern Great Barrier Reef. In tropical reef ecosystems, large benthic foraminifera are major carbonate sediment producers and function as important ecological engineers. We documented the thermal stress of Marginopora vertebralis and Baculogypsina sphaerulata from two high-density populations along the leeward and windward side of One Tree Reef in March 2024 following an 8-degree heating week with local on-reef temperatures exceeding 30 °C. Bleaching was more prevalent at the lower-energy leeward site (81.4

The timing, rate, and magnitude of rapid sea-level rise during Meltwater Pulse 1B (MWP-1B, ~11.45-11.1 ka) remain controversial. Robust constraints on past MWPs are crucial to future predictions of global ice sheet instability. Using 154 new and existing U/Th and calibrated 14C-AMS dates from coral, algae, and microbialites recovered during Integrated Ocean Drilling Program Expedition 325, this study reconstructs reef development and relative sea-level (RSL) rise on the Great Barrier Reef (GBR). We identify 107 in situ RSL index points while refining estimates of vertical accretion and paleowater depth. Results show RSL rise during MWP-1B did not exceed 10.2-7.7 m or rates of 30-23 mm/yr, and was likely less. The GBR did not drown, indicating resilience to MWP-1B. These findings are more consistent with Tahiti and other Pacific records and do not support the Barbados record of MWP-1B as an abrupt step in global sea level, with a magnitude > 11 m.

Morphology, internal structure, and in situ facies distribution of mesophotic Halimeda bioherms from the Queensland Plateau (NE Australia) are presented based on hydroacoustic and oceanographic data, seafloor observations, and discrete sediment sampling carried out during RV SONNE cruise SO292 in 2022. Halimeda buildups consist of cone-like mounds up to 500 m in diameter and 3–10 m high, with gentle slopes (2°–5° on the top of Tregrosse Bank). Bioherms occur in water depths of 10–70 m, with most bioherm between 50 and 65 m. Their internal structure consists of aggrading low-amplitude reflections at the core of the bioherm interfingering with high-amplitude reflections to the flanks. Surface facies distribution displays one to four facies belts, from distal to proximal: Halimeda rudstone, Halimeda rudstone with living plants, Halimeda rudstone with coralgal debris, and coralgal boundstone (when present, occupied the top of the bioherms). It is proposed that the alternation of two key processes contributes to the formation of these bioherms: (1) in situ accumulation of Halimeda debris and (2) episodic dismantling of the mesophotic coralgal boundstone at the centre of the bioherm by severe storms. These storms may dismantle the mesophotic reef and export coralgal rubble to the flanks. Flanks may be recolonized by Halimeda during fair-weather periods. Due to their different geomorphic expressions, complex internal structure, and surficial facies distribution, we suggest that the buildups of the Queensland Plateau represent a new Halimeda bioherm morphotype, distinct from previously described bioherms on the adjacent Great Barrier Reef and elsewhere globally.

Coral reefs are among the most biologically diverse and economically valuable ecosystems on Earth, but they are threatened by climate change. Understanding how reefs developed over geological timescales can provide important information about past environmental changes and their impacts on reef systems. Significant effort and capital have been invested in drilling and analyzing reef cores. Recognizing coral and sediment patterns visually from fossil reefs is a laborious task that demands domain expertise. In this paper, we present a machine learning-based framework that utilizes clustering and classification methods to fuse multiple sources of data for the segmentation and annotation of reef cores. The framework produces an annotated image of a reef core with six lithologies identified; massive corals, encrusted corals, coralline algae, microbialite, sand, and silt. We utilize reef cores recovered from Expedition 325 of the International Ocean Discovery Program (IODP) to the Great Barrier Reef. We use reef core image data and physical properties data to segment reef cores. We evaluate the framework using selected clustering and classification models. The results show that Gaussian mixture models can provide accurate segmentation of reef core image data, with a clear visual distinction between two major classes: massive corals and stromatolitic microbialites. Furthermore, we find that the random forest classifier provides the best annotations for the segmented reef core image data with an accuracy of 96%.

The steep slopes of carbonate platforms frequently display large-scale sediment destabilization features like rockfalls, mass transport complexes, and slope erosion. The processes and factors triggering such instabilities and how they interact are a matter of ongoing discussion. We use hydroacoustic, sedimentological, and seafloor imaging data to map and characterize slope instabilities and potential controlling factors at the flank of the isolated Tregrosse carbonate bank in the Coral Sea, northeast Australia. Erosion of gullies and submarine valleys is concentrated in slope segments with the platform rim at several 10s of meters of water depth, i.e. where there is potential for sediment transfer from the bank interior to the slope. Gravity core data indicate that most sediment export from the platform occurs during sea-level fall. The toe of slopes neighboring segments with a shallower platform rim are mostly characterized by mass-transport complexes of platform rim and upper slope rocks forming extended block fields. Distal slope areas are dismantled through submarine landslides resulting in scalloped head scarps. The basal detachment surface of these submarine landslides appears to be rooted in several 100 s of meters in the subsurface at a lithological heterogeneity, which is documented by a gamma-ray peak in the downhole logging data from Ocean Drilling Program Site 817. Our findings show that (1) canyon erosion, (2) platform rim and upper slope destabilization as well as (3) lower slope dismantling, largely act independently of each other to destabilize the flanks of the carbonate bank. The complexity of the carbonate platform dismantling processes and the corresponding controlling factors shown in this study should also be considered when interpreting seismic morphological data.

Reef cores are a powerful tool for investigating temporal changes in reef communities. Radiometric dating facilitates the determination of vertical accretion rates, which has allowed for examination of local-regional controlling factors, such as subsidence and sea level changes. Coral reefs must grow at sufficient rates to keep up with sea level rise, or risk ‘drowning.’ As sea level is expected to rise significantly in the next 100 years and beyond, it is important to understand whether reefs will be able to survive. Historical records of reef accretion rates extracted from cores provide valuable insights into extrinsic controlling factors of reef growth and are instrumental in helping predict if future reefs can accrete at rates needed to overcome predicted sea level changes. While extensive research exists at local and regional scales, limited attention has been given to identifying global patterns and drivers. To address this, we present “RADReef”: A global dataset of dated Holocene reef cores. RADReef serves as a foundation for further research on past, present and future reef accretion.

Tropical carbonate platforms are edifices built by shallow-water, carbonate-producing organisms. Prolonged suppression or shutdown of tropical shallow-water carbonate factories may result in partial or complete platform demise. Factors triggering the drowning process can relate to rates of accommodation increase exceeding carbonate accumulation and/or the establishment of ecological conditions not favorable for carbonate producers, with increasing water temperatures and high nutrient contents proposed as drivers. More recently, the intensification of ocean circulation and currents has been identified as a major factor in carbonate platform drowning. We tested the latter with seismic reflection and multibeam data collected with RV Sonne in 2022 on the Queensland Plateau (north-east Australia) and by correlating these data with ODP Leg 133 sedimentological and biostratigraphic results. The carbonate platforms of the Queensland Plateau underwent a partial drowning between 13.6 and 12.7 Ma. This partial drowning is coeval with the onset of current-driven sedimentation. Relict platforms, which form the core of the presently still active platforms, were established in two steps: After the demise of a spatially expanded platform, a system with smaller, low-relief banks and mounds established. At around 3.7 Ma, there was a turnover and higher relief, flat-topped platforms established. We propose that the geologic history of the Queensland Plateau represents another example of a carbonate platform evolution controlled by ocean currents.

Understanding and preserving the deep sea ecosystems is paramount for marine conservation efforts. Automated object (deep-sea biota) classification can enable the creation of detailed habitat maps that not only aid in biodiversity assessments but also provide essential data to evaluate ecosystem health and resilience. Having a significant source of labelled data helps prevent overfitting and enables training deep learning models with numerous parameters. In this paper, we contribute to the establishment of a significant deep-sea remotely operated vehicle (ROV) image classification dataset with 3994 images featuring deep-sea biota belonging to 33 classes. We manually label the images through rigorous quality control with human-in-the-loop image labelling. Leveraging data from ROV equipped with advanced imaging systems, our study provides results using novel deep-learning models for image classification. We use deep learning models including ResNet, DenseNet, Inception, and Inception-ResNet to benchmark the dataset that features class imbalance with many classes. Our results show that the Inception-ResNet model provides a mean classification accuracy of 65%, with AUC scores exceeding 0.8 for each class.

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 (815N) 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 815N values from multiple corals and genera were elevated (average of 8.45 +/- 0.89%o) relative to the early transgression and following sea-level stabilization (average of 7.04 +/- 0.82%o). We propose that elevated 815N 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.

The Great Barrier Reef (GBR), Australia, has a long history of palaeoenvironmental coral research. However, it can be logistically difficult to find the relevant research and records, which are often unpublished or exist as "grey literature". This hinders researchers' abilities to efficiently assess the current state of coral core studies on the GBR and thus identify any key knowledge gaps. This study presents the Great Barrier Reef Coral Skeletal Records Database (GBRCD), which compiles 208 records from coral skeletal research conducted since the early 1990s. The database includes records from the Holocene, from similar to 8000 years ago, to the present day; records are from the northern, central, and southern GBR from inshore and offshore locations. Massive Porites spp. coral records comprise the majority (92.5 %) of the database, and the remaining records are from Acropora, Isopora, or Cyphastrea spp. The database includes 78 variables, with Sr/Ca, U/Ca, and Ba/Ca being the most frequently measured. Most records measure data over 10 or more years and are at monthly or lower resolution. The GBRCD is machine readable and easily searchable so that users can find records relevant to their research, e.g. by filtering for site name, time period, or coral type. It is publicly available as comma-separated values (CSV) data and metadata files with entries linked by the unique record ID and as Linked Paleo Data (LiPD) files. The GBRCD is publicly available from the NOAA National Center for Environmental Information World Data Service for Paleoclimatology at 10.25921/hqxk-8h74 (Arzey et al., 2024). The intention is to update the GBRCD annually, depending on the availability of relevant new GBR records or submission of legacy records to the GBRCD for archiving. The collection and curation of existing GBR coral research data provide researchers with the ability to analyse common proxies such as Sr/Ca across multiple locations and/or examine regional to reef-scale trends. The database is also suitable for multi-proxy comparisons and combination or composite analyses to determine overarching changes recorded by the proxies. This database represents the first comprehensive compilation of coral records from the GBR. It enables the investigation of multiple environmental factors via various proxy systems for the GBR, northeastern Australia, and potentially the broader Indo-Pacific region.

Following the Last Glacial Maximum (LGM), the marine transgression experienced intermittent periods of accelerated sea-level rise related to melt water pulses (MWP) in polar regions, preceded by intervals of stillstands. Global stratigraphic and relict geomorphology studies have unveiled the impact of such sea-level rise variability on the formation and submergence of coastal and shallow shelf environments far from the melting source. Despite the opportunity to document these processes with reduced isostatic effects, there are still limited research focused on the South Atlantic continental margins. In this scenario, the present work contributes to investigating the possible repercussions of those eustatic events during the last deglaciation on the occurrence of drowned reefs on the eastern Brazilian margin. The analysis was based on comparing of sea-level curves with high-resolution depth signatures of different geomorphometric classes from a sector of the outer reef arc of the Abrolhos National Marine Park, known as California Reef. The frequency of occurrence of the bottom class identifying low-relief reef tops around -30 m water depth does not show a genetic relationship to some postLGM eustatic events already described in the literature. These structures are probably inherited from the MIS5a or MIS7c stillstands. The main concentration of the class related to reef pinnacles between 18 and 25 m water depth (median of 21 m), decreasing towards -10 m, indicates a drowning trend of these features. This drowning process probably correlates with the MWP-1C, triggered soon after the -8200 years B & sdot;P. cooling event. The extrapolation of the MWP-1C depth range on the regional morphological dataset reveals a potential simultaneous influence in the drowning of other coastal and reef areas along the western South Atlantic margin. Despite the consistent morphological evidence shown, it is essential to point out that the supposed impact of the eustatic phenomena discussed here, in establishing and drowning of reef features on the region, would still need to be confirmed by sampling and geochronological methods.

Context Increasing interest in mesophotic coral ecosystems has shown that reefs in deep water show considerable geomorphic and ecological variability among geographic regions. Aims We provide the first investigation of mesophotic reefs at the southern extremity of the Great Barrier Reef (GBR) to understand the biotic gradients and habitat niches in the lower mesophotic zone. Methods Multibeam data were used to target five benthic imagery transects collected in the lower mesophotic (80-130 m) zone from the shelf edge near One Tree Island (23(degrees)S, 152(degrees)E) by using a single HD-SDI subsea camera. Key results Transects supported similar benthic communities in depths of 80-110 m, with the abundance of sessile benthos declining below similar to 110 m where the shelf break grades into the upper continental slope. Conclusions The effect of the Capricorn Eddy may be promoting homogeneity of benthic assemblages, because it provides similar environmental conditions and potential for connectivity. Variation in benthic communities between hard and soft substrate and differing topographic relief within the study site are likely to be influenced by variation in sedimentation, including sensitivity to suspended particles.Implications This study highlighted that the lower mesophotic region on the One Tree shelf edge supports mesophotic coral ecosystems that vary depending on depth and substrate.