Holocene Reef Research Articles

A mathematical model for wound healing in the reef-building coral Pocillopora damicornis

Coral reefs, among the most diverse ecosystems on Earth, currently face major threats from pollution, unsustainable fishing practices , and perturbations in environmental parameters brought on by climate change. Corals also sustain regular wounding from other sea life and human activity. Recent reef restoration practices have even involved intentional wounding by systematically breaking coral fragments and relocating them to revitalize damaged reefs, a practice known as microfragmentation. Despite its importance, very little research has explored the inner mechanisms of wound healing in corals. Some reef-building corals have been observed to initiate an immunological response to wounding similar to that observed in mammalian species. Utilizing prior models of wound healing in mammalian species as the mathematical basis, we formulated a mechanistic model of wound healing, including observations of the immune response and tissue repair in scleractinian corals for the species Pocillopora damicornis. The model consists of four differential equations which track changes in remaining wound debris, number of cells involved in inflammation, number of cells involved in proliferation, and amount of wound closure through re-epithelialization. The model is fit to experimental wound size data from linear and circular shaped wounds on a live coral fragment. Mathematical methods, including numerical simulations and local sensitivity analysis, were used to analyze the resulting model. The parameter space was also explored to investigate drivers of other possible wound outcomes. This model serves as a first step in generating mathematical models for wound healing in corals that will not only aid in the understanding of wound healing as a whole, but also help optimize reef restoration practices and predict recovery behavior after major wounding events.

RADReef: A global Holocene Reef Rate of Accretion Dataset

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.

Strontium Isotopic, Ostracod fauna, and Paleoenvironmental Features of the Late Miocene Sequence in Mut/Dağpazarı Region (Southern Turkey)

The primary focus of this study was the Dağpazarı village in the Mut region of Mersin, southern Turkey. In this research area, two stratigraphic sections were meticulously measured. The study conducted a comprehensive examination of the Middle-Late Miocene period in the Dağpazarı, Ballı, and Mut Formations by analyzing the ostracod fauna and utilizing strontium isotope chemostratigraphic dating. This research determined that the upper levels of the Mut/Köselerli formations, specifically from the Burdigalian to Serravallian, signify the commencement of the Miocene succession in the study area.The Dağpazarı Formation, characterized by abundant silty-clay, Ostrea fossils, and lignite layers, is deposited unconformably just above these levels.This formation contains the following ostracod taxa; Bairdia subdeltoidea, C. glypta, Cytheridea acuminata acuminata, Acanthocythereis hystrix, Krithe monosteracensis, Neomonoceratina mouliana, Hemicyprideis sp., Cistacythereis caelatura, Cyherella terguemi, T. prava, K. langhiana, A. ulicznyi, Pokornyella deformis minor, Loxoconcha alata, Tenedocythere salebrosa. Furthermore, the planktonic foraminifera species are; O. universa, Globigerinoides trilobus, Glb. ruber, Orbulina bilobata, Glb. sacculifer, O. suturalis, and the formation includes abundant bryozoa, echinoid spines, gastropods such as Terebralia at distinct levels, and fish otolith. The formation, dating from the late Serravallian to the early Tortonian, exhibits the shallow reef characteristics that continued to develop in the late Miocene.The formation consists of dark green, bulbous weathered claystone, Bairdia subdeltoidea and Ostrea which are reduced in size at the levels that pass into hard clayey sandstone, abundant benthic foraminifera with abundant echinoid spines. The formation consists of benthic foraminifera, hard clayey sandstone, and weathered dark green claystone, which contains numerous echinoid spines.Ostrea and Bairdia subdeltoidea are also present. The upper section of the analyzed succession concludes with silty, compact, clayey limestone layers and light-colored limestone bands. The Tırtar Ballı Formation, which conformably overlays the Dağpazarı Formation, signifies the culmination of a relatively recent reef formation during the Tortonian period.Ostracod species such as Aurila pigadiana, Thalmannia hodgii, Buntonia sublatissima dertonensis, Bairdia subdeltoidea, Aurila sp. Bassiouni have been defined. The limestones also contain abundant benthic foraminifera and echinoid spines. The 87Sr/86Sr ratio analyzed from the carbonate sample obtained from the Dağpazarı formation is 0.708920. Based on these isotope data, the age of the Dağpazarı formation was calculated to be 8.7 million years (Ma).

Dolphin-shaped island: Exploring the natural resources and radiological hazards of Wadi El Gemal Island

The objective of this study is to assess the natural resources and radiological risks of Wadi El Gemal Island by examining its topography, mineralogy, geochemistry, and radioactive distributions. This island, which is situated at the outlet of Wadi El Gemal in Egypt's southeastern Desert, has a unique shape resembling a dolphin based on Landsat imagery. It's a part of the Wadi El Gemal-Hamata Protectorate and is notable for its diverse environmental, geological, economic, and archeological features, including recent reefs, sandy deposits, Quaternary carbonate sediments, and mangroves. The main natural resources on the island are fauna, mangrove forests, and flora. Samples collected from the island were analyzed using a NaI detector to measure the concentrations of radionuclides such as 238U, 232Th, 226Ra, and 40K, which were found to be within acceptable levels according to UNSCAR guidelines. The radionuclide 238U, 232Th, 226Ra, and 40K activity concentrations of the collected samples were 32.55 ± 9, 12.63 ± 4, 12.49 ± 4, and 325 ± 34 Bq/kg, respectively. Regarding radiological hazard indices, the values of absorbed gamma dose rate (36.06 ± 5.42 nGy/h), radium equivalent activity (73.88 ± 14.4 Bq/kg), annual effective dose indoor (0.18 ± 0.03 mSv/y) and outdoor (0.04 ± 0.01 mSv/y), internal (0.29 ± 0.05) and external (0.2 ± 0.03) indices, and excess lifetime cancer index (0.15 ± 0.05 × 10−3).This is suggest that there is no significant risk associated with these sediments.

Beachrocks of the last low sea level, substrate of the Great Amazon Reef system along the outer Guiana shelf

The Great Amazon Reef System is a living biogenic mesophotic reef ecosystem that has been recently described along the shelf break of Brazil. An oceanographic cruise was carried out in 2019 along the outer edge of the French Guiana Shelf. A side-scan sonar survey was conducted to locate reef outcrops and allowed twelve in situ 80- to 120-m depth dives and sampling of the reef rocks and peripheral sands. The majority of the hard rocks are composed of biological concretions. However, several fragments revealed the inside presence of sandstone clasts. These clasts, more or less enveloped by biogenic coatings, probably represent destroyed clasts of underlying or neighboring beachrock banks. Their dominant cement is micritic (high-magnesian calcite); the intergranular or extragranular porous field was later filled with low-magnesian sparry calcite. The sand or gravel that accumulated near the barrier mainly consists of the blunt debris of coastal fauna and flora associated with different carbonate or ferruginous neoformed ooids. At 104-m depth, ooids extracted from dive 11 samples dated from the start of MIS2 (27,370 cal yr BP) and attest to the presence of a significant coastal accumulation. At this same site, cementing did not take place until about 3500 years later (23,990 cal yr BP). The cement of a nearby beachrock indicates a much more recent age (16,170 cal yr BP). Lastly, the age of 4100 yr BP measured on the barnacles attached to the top of the reef attests to the late Holocene reef's biological activity.

Relative sea level response to mixed carbonate-siliciclastic sediment loading along the Great Barrier Reef margin

The continental shelf along northeastern Australia is the world's largest mixed carbonate-siliciclastic passive margin and the location of the Great Barrier Reef (GBR). Following sea-level transgression during the last deglaciation, extensive sediment was deposited along the GBR due to neritic carbonate deposition (including shelf edge reefs, Holocene reefs and Halimeda bioherms) and fluvial discharge of terrigenous siliciclastic sediments. Such sediment loading can alter local relative sea level (RSL) by several metres through the sediment isostatic adjustment (SIA) process, a signal that is poorly constrained at the GBR. In this study, we used a glacial isostatic adjustment (GIA) model to develop an ensemble-based sediment loading history for the GBR since Marine Isotope Stage 2 (MIS 2). A Bayesian style framework is adopted to calibrate the sediment history ensemble and GIA model parameters using a sea-level database. According to our results, 1853.7 Gt (1613.1-2078.7 Gt, 95% confidence interval) of sediment have been deposited across the GBR since MIS 2 (28 ka BP), causing spatially variable relative sea-level change with the highest magnitude (0.9-1.1 m) found in the outer shelf of the southern central GBR (18.4-21.6∘ S). Because the SIA-induced RSL rise is unrelated to ice mass loss, failing to correct for this signal will lead to systematic overestimation of grounded ice volume by up to ∼4.3 × 105 km3 during the Last Glacial Maximum. Additionally, we found that spatial variation in sediment loading and coastal environment may explain the different RSL history documented by published fossil coral reef records from Noggin Pass and Hydrographer's Passage. These results highlight the importance of considering SIA for any postglacial sea-level studies adjacent to large sediment systems. Lastly, by quantifying both the GIA and SIA signals, we provide a spatially and temporally complete RSL reconstruction that is well-suited to be used as a boundary condition to study the evolution of the GBR shelf and slope sedimentary system.

Herbicide Fate and Transport in the Great Barrier Reef: A Review of Critical Parameters

Herbicides used for weed management on agricultural land in Australia’s Great Barrier Reef catchments are a key concern for its ecosystem, including the lagoon’s marine plants and corals, whose productivity has been found to decline. The most reliable way to assess herbicide risk is by monitoring a site regularly, but this is costly and time-consuming, so numerical simulations and computer models are an alternative method. Despite the availability of low-cost and less labor-intensive modelling methods, they have been limited in their effectiveness due to a lack of specific herbicide usage data and an inadequate understanding of the breakdown and transport processes of herbicides after application. This paper reviews current findings regarding herbicide risk in all Great Barrier Reef catchments according to their agricultural land use, and the most recent Reef Water Quality Protection Plan recommendations. The various pathways for fate and transport of the herbicides were also examined, and a list of critical parameters was developed to help with computer simulations. The accuracy and reliability of modelling can be improved by including aerial drifts, interceptions by crop residues, mechanisms within the root zone, and subsurface and groundwater contributions to the herbicide load in the GBR lagoon. Moreover, the findings will provide new directions for management practices adoption data with the fate and transport model from paddock to reef and improve the reliability of model results.

Are the coral mounds of the Kushimoto area, Wakayama Prefecture, Japan, submerged Holocene reefs?

We investigated coral mounds at 10–15 m water depth in the Kushimoto area of Wakayama Prefecture, Japan. These mounds may be submerged Holocene reefs, but no evidence has yet been presented to support this hypothesis. We collected two cores and three dead corals from one of the mounds. Our results show that Miocene bedrock lies only 0.1 m below the surface of the mound, and in situ corals form a thin veneer above the antecedent substrate. Radiocarbon dating of four coral samples yielded ages of 112 cal. yr BP to modern. These findings indicate that the mounds are not submerged Holocene reefs. The sea-surface temperatures in February are <18°C in the study area and would be insufficient for rapid precipitation of calcium carbonate by coral species. Given that the study area faces the open ocean, it is probable that the corals are frequently dislodged by high wave forces during intense tropical cyclones and/or tsunamis. Consequently, the study area appears to lie beyond the distributional limit of coral reefs during the Holocene.

Climate-modulated range expansion of reef-building coral communities off southeast Florida during the late Holocene

The Holocene reefs off southeast Florida provide unique insights into the biogeographical and ecological response of western Atlantic coral reefs to past climate change that can be used to evaluate future climate impacts. However, previous studies have focused on millennial-scale change during the stable mid-Holocene, making it difficult to make inferences about the impact of shorter-term variability that is relevant to modern climate warming. Using uranium-series dating of newly discovered subfossil coral rubble deposits, we establish a new high-resolution record of coral community development off southeast Florida during a period of variable climate in the late Holocene. Our results indicate that coral communities dominated by reef-building Acropora palmata and Orbicella spp. persisted in the nearshore environments off southeast Florida ~75 km north of their primary historical ranges between ~3500 and 1800 years before present. This timing coincides with regional warming at the northern extent of the Atlantic Warm Pool, suggesting a likely link between regional oceanographic climate and the expansion of cold-sensitive reef-building coral communities to the high-latitude reefs off southeast Florida. These findings not only extend the record of coral-reef development in southeast Florida into the late Holocene, but they also have important implications for future range expansions of reef-building coral communities in response to modern climate change.

Neogene and Quaternary reef terraces of Mangaia, Rarotonga and Aitutaki (southern Cook Islands, South Pacific) revisited: gauges of sea-level change and island uplift?

New sedimentological data of facies and diagenesis as well as chronological data including strontium (87Sr/86Sr)-isotope ratios and uranium (U)-series dating, radiocarbon (14C) accelerator mass spectrometry (AMS) dating and biostratigraphy from elevated reef terraces (makatea) in the southern Cook Islands of Mangaia, Rarotonga and Aitutaki contribute to controversial discussions regarding age and sea-level relationships of these occurrences during the Neogene and Quaternary. The oldest limestones of the uplifted makatea island of Mangaia include reef-related facies which are mid-Miocene in age, based on new Sr-isotope and biostratigraphical data. In between these older deposits and the lowest coastal reef terrace of marine isotope stage (MIS) 5e, various older Pleistocene reef-related facies were identified. Based on Sr-isotope ratios, these were deposited during earlier Pleistocene highstands (as old as 2.28 Ma). Rare reef terraces on Rarotonga belong to the Plio-Pleistocene and the late Miocene, according to 87Sr/86Sr ratios. The late Miocene age is enigmatic as it exceeds the age of subaerially exposed volcanic rocks of Rarotonga island. The fossil reef could have formed on an older submarine volcanic high that was later displaced by younger volcanism to its present position, or the Sr-age could be too old due to diagenetic resetting. The Plio-Pleistocene Rarotonga reef terraces are overlain irregularly by Holocene reef deposits that are interpreted as storm rubble. Reef terraces on Aitutaki represent evidence of a higher-than-present (up to 1 m) sea-level during the late Holocene, based on 14C AMS age data. They are very similar to elevated late Holocene reefs of adjacent French Polynesia with regard to composition, elevation and age.

New insights on the Late Quaternary evolution of Abrolhos reefs, Eastern Brazilian Shelf

The Abrolhos shelf, in the eastern Brazilian margin, encompasses the largest reef province in the South Atlantic, characterised by low coral diversity and a high level of endemism. Knowledge gaps about how the Abrolhos coastal reefs evolved, during the post LGM and MIS 6/MIS 5, favoured a paradigm that is revisited in the light of new data. Here, new data from two new, long boreholes (20 and 50 m-long) are presented in order to investigate and provide new insights into the evolution of two shallow reefs on the Abrolhos Shelf during the late Pleistocene and Holocene epochs. Results show that Holocene and Pleistocene reefs grew on highly turbid waters with a significant terrigenous sediment input. Corals and CCA assemblages were identified as main framework builders of Abrolhos inner-shelf reefs since the Pleistocene. No clear shallowing upward sequence of reef builders was observed, which differs from other reef sequences all over the world. In terms of Holocene reef growth, Pedra Grande and Coroa Vermelha reefs turned on roughly coevally at different depths and with different coral assemblages. Pedra Grande reef started growing circa 6.8 kyr BP in a water depth approximately 10 m deeper than Coroa Vermelha, which started growing around 6.4 kyr BP, but Coroa Vermelha turned off at around 4 kyr BP, while Pedra Grande kept growing until around 1.2 kyr BP. This novel reef stratigraphy data provided a new insight on the evolution of the Abrolhos coastal reefs, showing that different environmental and topographic controls could have acted spatially in different ways. Coroa Vermelha reef seems to have started its growth as a result of a topographic high control. Pedra Grande reef seems to be connected to a broader submerged reef setting and started to grow in deeper water depths. The presence of three reef arcs in Abrolhos is proposed, including a submerged reef arc.

Microscale evolution of reefal microbialites

Reefal microbialites are crusts and infills of microbialites developed within primary cavities of late Quaternary coralgal reef frameworks. In spite of many previous studies, factors controlling mesofabric transitions, particularly from laminated to digitate microbialites but as well as the microscale formation process in relation to microbial communities, have not yet been fully understood. Furthermore, there are still controversies regarding age differences between reef framework growth and microbialite formation. The authors have discussed the macroscale evolution of primary cavities as well as the microscale evolution of reefal microbialites obtained in a middle Holocene reef core drilled off Okinawa Island, south-west Japan, based on petrographic observations using light and scanning electron microscopy with energy dispersive X-ray spectroscopy and radiocarbon (14C) ages of corals and reefal microbialites. The authors’ petrographic observations show that coralgal reef framework growth was followed by encrusting foraminifers and metazoans, coevally with macro-bioerosion and microbioerosion of coralgal frameworks, then finally infilled with an intraskeletal and boring-filling microbialite (IBFM) and encrusted by reefal microbial crusts (RMCs), including structureless and digitate microbialites. The observed macroscale evolution was probably driven in response to progressive changes to reduced light and water circulation in the primary cavities associated with middle Holocene transgression and reef formation. The microfabric of reefal microbialites consists of primary in situ precipitated peloids (spherical micritic clots), voids (primary pores) and allochthonous detrital grains (bioclastic and siliciclastic) fallen from upper reef surfaces. IBFM geopetally infilled inside bioeroded cavities soon after the bioerosion of coralgal frameworks. RMCs have a two-layered microfabric succession, which is composed of the alternation of dense peloidal aggregates and laterally aligned voids in the lower part and the mixing of peloidal aggregates and irregularly and vertically developed voids in the upper part. The authors speculate that the repeated occurrences of laterally aligned voids in the lower part may imply the intermittent pauses of peloidal formation, while peloids accumulated on the irregular outer surfaces may result in the formation of vertically developed voids and digitate surfaces in the upper part. These peloids are probably formed by coccoid sulfate-reducing bacteria in anoxic environments developed by the degradation of bacterial biofilms and organic matters, allowing sulfate reduction and increasing alkalinity, therefore carbonate precipitation. The two-layered microfabric succession generally observed in RMCs may reflect spatial-temporal oxic/anoxic variations in interstitial water and the degree of sulfate ion supply by the gradual closing of primary cavities.

Multiple severe storms revealed by coral boulders at Pasuquin, northwestern Luzon, Philippines

Over 30 meter-sized coral boulders are scattered 45–140 m away from the edge and above high tide on a Holocene reef flat at Pasuquin, northwestern Luzon, Philippines. The boulders are overturned or tilted as indicated by the framework fossil corals in them, but have the same lithology as those along the reef edge and thus were likely broken off from there. The dimensions of boulders larger than 3 m were calculated from 3D models constructed by photogrammetry. Their volumes range from 10 to 53 m3. Assuming 2.1 g/cm3 for wet density, weights of boulders would range from 21 to 110 metric tons. Boulders of such size and weight can't be moved by normal waves, and thus must have been dislodged by extreme wave events (EWEs). Small and well-preserved corals found on the surface of seven boulders were collected for 230Th dating to reconstruct the timing of displacement. The ages of corals are 1781.6 ± 1.9, 1903.4 ± 2.7, 1945.8 ± 1.2, 1956.9 ± 1.2, 1956.75 ± 0.99, 1978.1 ± 1.5 and 2002.78 ± 0.88 CE, respectively. These ages are considered to constrain the timing of boulder displacement from the reef edge. We propose that typhoon-induced EWEs were responsible for the displacement of these boulders at Pasuquin.

Unraveling Moreton Bay reef history: An urban high-latitude setting for coral development

High-latitude habitats have become increasingly recognized as a potential climate refuge for coral communities, supporting both tropical and sub-tropical corals. Despite the increasing interest in the ecology of high-latitude corals, our current knowledge of their temporal dynamics is limited, especially within urbanized settings. Here, we examined the entire history of a high-latitude coral reef ecosystem in an urbanized setting. We surveyed Holocene fossil and modern coral communities along a water quality gradient in Moreton Bay, southeast Queensland, Australia, representing near-river (Wellington Point), intermediate (Peel Island) and near-oceanic (Myora Reef) environmental conditions. Reef accretion occurred during three discrete episodes from 7,400 to 5,800, 4,900 to 3,000, and 2,100 to 300 years BP, each separated by roughly 1,000-year hiatuses, where conditions were probably not favorable enough for reef accretion to occur. Episodic reef initiation and termination suggests strong environmental controls over reef development. Eastern Australian Holocene reef growth and cessation has been linked previously to sea level fluctuations and climatic regimes (e.g., ENSO). Within each reef building episode, there were few changes in coral assemblages over time. The fast growing and branching Acropora had a relative abundance greater than 90% in ten of the 13 sediment cores and all the submerged terrace excavations. However, substantial modification of adjacent coastal catchments from European colonization in the mid 1800’s resulted in increased sediment and nutrient discharge into the bay. This perturbation coincided with a greater abundance of stress-tolerant coral species (e.g., Dipsastraea, Goniastrea, and Goniopora) and the near extirpation of Acropora in the modern coral communities of near-river and intermediate sites due to poor water quality. In contrast, the modern coral assemblage at the near-oceanic site (Myora Reef) continues to be dominated by Acropora, likely due to the consistent oceanic input, resulting in lower sediment loading and higher water quality. In order for conditions for reef growth to improve, especially within the near-river portions of the bay, further sediment and nutrient runoff from anthropogenic land-use changes need to be mitigated. Given the historical abundance of Acropora, we recommend this genus be used as an indicator of natural resource management success in the bay.

Heightened storm activity drives late Holocene reef island formation in the central Pacific Ocean

The impact of global environmental change on coral reef islands is uncertain, with few studies having resolved the critical controls on island formation and change. Based on detailed, topographic surveys, sediment analysis and radiometric dating, we present a multi-phase model of the formation of two reef islands in Jaluit atoll, Republic of the Marshall Islands. The initial phase of island building occurred 1300 years ago, later than elsewhere in the Marshall Islands and during a period of relative sea level fall from the mid-Holocene sea level highstand . Initial accumulation occurred as a consequence of relative emergence of the reef flat that forced a transition in reef flat ecology and dominant foraminifera sediment producers that contributed to island building. Distinctive sets of progradational ridges and their coarse sediment character provide evidence for the importance of extreme wave events in island expansion from an initial core. Expansion occurred in two principle phases, 650–350 years ago and 200 years ago to the present, each coincident with known phases of increased storminess in the central Pacific. Results highlight the complexity of island formation and show that future change will depend not only on sea level but storm processes that have been a major influence on island development over the past 650 years. Anticipated reduction in cyclogenesis in the southern Marshall Islands region suggests a near-future period of geomorphic stasis of the islands of Jaluit. An increase in cyclogenesis in the central Pacific and higher latitudes may enhance opportunities for storm-driven island accumulation events over the next century where coral growth is able to be maintained. • Island formation in Jaluit atoll occurred over the past 1300 years, during relative sea level fall and subsequent stability. • Cyclonic events were critical in the episodic expansion of islands over the past 700 years. • Relative sea-level fall forced changes in reef ecology and sediment production and transport regimes for island accumulation. • Formation of islands in Jaluit atoll lagged other parts of the archipelago and post-date habitation of the Marshall Islands. • Reduced storm dynamics in the tropical western north Pacific suggests a future period of island geomorphic stasis.

Coral community of Holocene coral reef in the southern South China Sea and its significance for reef growth

Ancient coral reefs are rich archives of historical process and vital baselines for future development. Coring gives a window into the growth of ancient coral reefs and the fossil coral community's response to paleoenvironment. Well NK-1 drilled from Meiji Reef is the longest scientific core with the highest recovery in the South China Sea. This study focused on the upper section of the Well NK-1 accumulated during the Holocene. From 8200 yr BP, Holocene reef initiated on the substrates of Pleistocene limestone and stopped accreting vertically at 4800 yr BP. It consisted of an initiation and fast reef growth (5.6 mm yr−1) from 8200 yr BP to 7300 yr BP, a shift to slow reef growth (2.0 mm yr−1) between 7300 yr BP and 5400 yr BP, a return to a rapid reef growth (8.8 mm yr−1) from 5400 yr BP to 4800 yr BP, and finally a cessation of upward accretion and a reinforced lateral progradation since 4800 yr BP. A total of 11 coral genera and 16 Acropora species were identified from the Holocene segment of the core. The diversity of coral communities had an impact on reef growth. Coral communities with less genera and absolute predominance of branching Acropora were corresponded with a rapid vertical accumulation of reef framework with higher accretion rate. Acropora corals with rapid growth and dispersion by fragmentation were principal reef-builders during the Holocene, with A.valida being the most prevalent coral species. The highest Acropora species richness occurred at the geological era of 5400–5300 yr BP when reef accumulated with the fastest upward accretion rate of 23.1 mm yr−1. This intricate and detailed pattern presented a new and novel model for the development of Holocene reef, indicating that the coral community and key reef builders were crucial to reef growth. These findings are extremely helpful for understanding the current ecological state of modern coral reefs as well as their potential response to global climate change.

Antecedent topography and active tectonic controls on Holocene reef geomorphology in the Great Barrier Reef

The Great Barrier Reef is generally considered a passive tectonic setting, however the effect of antecedent topography and local geological structures on Holocene reef development is poorly understood. Offshore reefs along the central shelf were recently hypothesized to have grown continuously through a possible small Holocene sea level fall, in response to greater local subsidence, in contrast to reefs immediately to the north and south, which experienced synchronous turnoff phases. We tested this hypothesis by isolating four map zones along the GBR shelf and using: (1) a geomorphic reef type classification applying perceived evolutionary “age” as juvenile, mature, and senile domains based on geomorphology; (2) analysis of bathymetry data to understand the role of antecedent topography on the spatial distribution of reef type domains and general sea floor depths; and (3) the distribution of earthquake epicentres as an indication of possible active geological structures (i.e., faults). The results reveal that juvenile reefs (42.25 %) are more abundant in the central shelf, whereas mature-2 (40 %) and senile (31 %) reefs are more abundant in the northern zone. In the south-central zone, mature-2 reefs are prevalent, while the southern zone includes a mixture of juvenile and mature to senile domains with a sharp internal boundary. These results support the hypothesis that the central zone may have experienced greater active subsidence during the Holocene. Bathymetric data support greater regional subsidence in both central and south-central zones, but reefs are less abundant and cover a lesser percentage area of their antecedent platforms in the central zone, consistent with greater subsidence there. The boundaries between the central zone and adjacent zones are the sites of clusters of recent earthquakes, consistent with the occurrence of active geological faults bounding the zone of greater Holocene subsidence. Combined, our data support the occurrence of a tectonically defined region of active greater subsidence in the central GBR shelf that has affected the geomorphology and growth history of reefs through the Holocene. Knowledge of such spatial partitioning of reef behaviour may allow reef managers to better suite their efforts to local conditions, especially in regard to predicted sea level rise, while highlighting potential seismic risks over longer time frames.

New constraints on the postglacial shallow-water carbonate accumulation in the Great Barrier Reef

More accurate global volumetric estimations of shallow-water reef deposits are needed to better inform climate and carbon cycle models. Using recently acquired datasets and International Ocean Discovery Program (IODP) Expedition 325 cores, we calculated shallow-water CaCO3 volumetrics and mass for the Great Barrier Reef region and extrapolated these results globally. In our estimates, we include deposits that have been neglected in global carbonate budgets: Holocene Halimeda bioherms located on the shelf, and postglacial pre-Holocene (now) drowned coral reefs located on the shelf edge. Our results show that in the Great Barrier Reef alone, these drowned reef deposits represent ca. 135 Gt CaCO3, comparatively representing 16–20% of the younger Holocene reef deposits. Globally, under plausible assumptions, we estimate the presence of ca. 8100 Gt CaCO3 of Holocene reef deposits, ca. 1500 Gt CaCO3 of drowned reef deposits and ca. 590 Gt CaCO3 of Halimeda shelf bioherms. Significantly, we found that in our scenarios the periods of pronounced reefal mass accumulation broadly encompass the occurrence of the Younger Dryas and periods of CO2 surge (14.9–14.4 ka, 13.0–11.5 ka) observed in Antarctic ice cores. Our estimations are consistent with reef accretion episodes inferred from previous global carbon cycle models and with the chronology from reef cores from the shelf edge of the Great Barrier Reef.

Clustered, Stacked and Imbricated Large Coastal Rock Clasts on Ludao Island, Southeast Taiwan, and Their Application to Palaeotyphoon Intensity Assessment

This work investigated the characteristics of a boulder field on the exposed south east coast of Ludao Island (Green Island) in southern Taiwan. Although the region regularly experiences seasonal Pacific typhoons, fieldwork on Ludao was prompted following the double-strike of Typhoon Tembin in August 2012, which followed an unusual looping track and was one of the strongest storms to affect the island in recent decades. In Wen Cuen Bay, large limestone and volcanic clasts (103–105 kg) occur both as isolated individuals and also grouped into distinct clusters across the gently-sloping emerged reef platform of Holocene age. Some individuals reach megaclast proportions. Observations revealed limited evidence for the production of new coastal boulders by Typhoon Tembin. However, clustering, stacking and notable imbrication of old large clasts provide evidence for multiple high-energy palaeoevents. Stacking and imbrication are significant depositional features, implying that (partial) lifting by wave transport was responsible. Boulders deposited by Typhoon Tembin suggest that storm produced minimum flow velocities of 3.2–5.1 m/s. This range of minimum flow velocity (MFV) values is lower than the 4.3–13.8 m/s range inferred from the pre-Tembin boulders, which indicates that older storm washovers must have been stronger, judging from their ability to stack and imbricate large clasts. One explanation for high upper values of palaeoevent MFVs is that localized funnelling of water flow through narrow relict channels (inherited spur-and-groove morphology, oriented perpendicular to the modern reef edge) concentrates onshore flow energy into powerful confined jets. Support for this hypothesis is the positioning and train-of-direction of the main imbricated boulder cluster at the landward head of one such feature. Geomorphic controls amplifying wave-driven flow velocities across the emerged Holocene reef mean that a palaeotyphoon origin is sufficient for explaining large clast stacking and imbrication, without the need to invoke a tsunami hypothesis.

Environmental controls on holocene reef development along the eastern brazilian margin

Environmental controls on holocene reef development along the eastern brazilian margin