Coral Reefs and Sea-Level Change: Quaternary Records and Modelling最新文献

{"title":"Microscale evolution of reefal microbialites","authors":"Shōgo Koyano, F. Shiraishi, Y. Yokoyama, K. Fujita","doi":"10.54780/iassp49/02","DOIUrl":"https://doi.org/10.54780/iassp49/02","url":null,"abstract":"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.","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"424 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122884051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coral reef development and sea-level changes over the past 50,000 years: new evidence from the north-west shelf of Australia","authors":"J. Webster, B. Dechnik, K. Sanborn, Y. Yokoyama, J. Braga, W. Renema, M. Humblet, Robin J. Beamani, L. Nothdurft, G. Webb, Jian-xin Zhao, R. Murphy, S. Gallagher, M. O’Leary, V. Paumard","doi":"10.54780/iassp49/08","DOIUrl":"https://doi.org/10.54780/iassp49/08","url":null,"abstract":"Understanding of global sea-level changes and coral reef development is poorly constrained during Marine Isotope Stage 3 (MIS 3; ~ 60 to 30 ka). Australia’s North West Shelf (NWS), at depths of ~ 50 to 120 m below present sea-level (mbsl), represents an ideal natural laboratory to address these knowledge gaps. In this study, the authors investigate a unique suite of sea-bed rock drill (PROD) cores recovered as part of a geotechnical survey from the NWS ~ 150 km south-east of Ashmore Reef. Twenty cores, penetrating to 28 m below sea floor, were collected from the top of the now drowned platform complex in similar water depths (74.8 to 81.6 mbsl), forming two transects ~ 17 km apart. High-resolution 3D seismic and multibeam bathymetry data reveal three distinct, multigenerational platforms that are rimmed by smaller reef terraces and bisected by deeper channels, placing the core transects into a robust, regional geomorphic context that includes a succession of linear palaeo-shorelines and tidal-estuarine channel systems on the adjacent shelf between ~ 90 to 110 mbsl. The authors have completed detailed logging, high-spatial resolution hyperspectral scanning, petrologic, mineralogic and sedimentary facies analysis of these cores, including a precise palaeoenvironmental reconstruction based on coral, algal and larger benthic foraminifera assemblages; and extensive radiometric dating. The authors have observed a complex suite of lithologies including in situ coralgal reef frameworks, well-lithified to friable grainstones, packstones and coralline algal floatstone facies separated by at least two major palaeosol horizons. Together with thirty 14C-AMS and closed-system U/Th ages spanning 10.7 to > 50 ka, the authors define a complex but consistent record of four distinct chrono-stratigraphic units (Units 1 to 4), representing a repeated succession of shallow reef to deep reef-slope depositional settings as the platforms experienced repeated sea-level oscillations (interstadial/stadial to glacial/deglacial) over the last 75,000 yr. Two distinct phases of shallow-water, high-energy reef development are defined. The age of the older, diagenetically distinct reef unit (Unit 3) is unknown but interpreted to have developed before the MIS 4 lowstand (~ 65 ka). However, firm chronological constraints on the MIS 3 development of the younger reef unit (Unit 2), place the position of relative sea-level (RSL) between ~ 63 to 75 + 1.8 mbsl by 45.95 to 39.23 + 0.2 ka, consistent with other predictions and observations for the region. Following its exposure and demise due to sea-level fall to the Last Glacial Maximum (LGM), the platform system was unable to re-establish fully as it was reflooded during the subsequent deglacial sea-level rise. Deeper reef slope (Unit 1) facies dominate the core tops between ~ 13.2 to 10.7 ka, representing a major hiatus in shallow-water reef development on the platforms. Deglacial sea-level rise was either too fast and/or other environ","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124505721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Neogene and Quaternary reef terraces of Mangaia, Rarotonga and Aitutaki (southern Cook Islands, South Pacific) revisited: gauges of sea-level change and island uplift?","authors":"E. Gischler, Gabriela Meyer, J. Braga, S. Riechelmann, A. Immenhauser, A. Eisenhauer","doi":"10.54780/iassp49/09","DOIUrl":"https://doi.org/10.54780/iassp49/09","url":null,"abstract":"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.","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"90 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121925691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shelf-edge deglacial reef establishment and subsequent partial demise: Response to distinct pulses of sea-level rise associated with environmental changes","authors":"B. Harper, A. Droxler, J. Webster, P. Montagna, Y. Yokoyama, M. Humblet, S. Jorry, L. Beaufort, K. Tachikawa, E. Bard, E. Pons‐Branchu","doi":"10.54780/iassp49/05","DOIUrl":"https://doi.org/10.54780/iassp49/05","url":null,"abstract":"The partial melting of Earth’s bi-polar ice sheets since the Last Glacial Maximum (LGM) has translated into a ~ 120 m amplitude stepwise sea-level rise punctuated by three major meltwater pulses that were tracked and recorded with some of the best accuracy by coral reefs. However, the initial meltwater pulse marking the end of the LGM, at 19 ka, is anchored in only two palaeo reefs (Barbados, Great Barrier Reef). Here, the authors present the analysis of a coralgal reef that thrived along the south-east Papua New Guinea Peninsula outer shelf during this initial pulse. In the cone of a piston core, a shallow Goniastrea retiformis coral colony was retrieved at 111 m below present sea-level and uranium/thorium dated to 19.4 ka BP. This colony had been buried beneath the debris of a proximal coralgal reef before its partial drowning at 14.5 ka BP. Seismic survey data suggest that the reef edifice was established directly on the eroded top of a lowstand shelf-edge delta, partially drowned and then back-stepped towards the south-east in response to three distinct deglacial sea-level pulses and stepwise increases of water column turbidity.","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"35 1-2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132728477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late Pleistocene-Holocene Evolution of Malé Island (North Malé Atoll Rim, Republic of Maldives)","authors":"T. Yildirim, A. Droxler, Eberhard Gishler, D. Naar, Y. Yokoyama, P. Montagna, E. Pons‐Branchu","doi":"10.54780/iassp49/04","DOIUrl":"https://doi.org/10.54780/iassp49/04","url":null,"abstract":"Malé, the capital of the Republic of Maldives, is established on an island of about 6.8 square kilometres, with a maximum relief of 2.7 m and a population of 236,000 inhabitants. It is amongst the most densely populated areas on Earth and located virtually at sea-level. This study focuses on the late Pleistocene-Holocene evolution of Malé island that recently formed as part of the discontinuous North Malé Atoll rim. Understanding the formation of Malé Island is relevant in predicting its future in the context of accelerating rates of sea-level rise in the next centuries due to anthropogenic global warming. Analyses of two boreholes up to 35 m-long, published information from additional boreholes drilled on Malé Island and a high-resolution multi-beam bathymetric survey acquired along its upper slopes and deep surroundings were available for this study. Two distinct sedimentary units were recovered from the boreholes. Facies analyses of the lower unit reveal an overall deepening coralgal reef that accumulated probably during the previous interglacial (Marine Isotope Stage = MIS 5e) and which was subsequently altered by meteoric diagenesis during a 100 kyr-long time of exposure. The upper unit consists of Holocene unconsolidated coralgal accumulation, unconformably overlying the lower karstified coralgal MIS 5e unit. The upper unit, protected behind a karstified late Pleistocene reef, was initiated at ~8200 yr BP and vertically grew 25 m-high until 6510 yr BP in the northern part of the Malé Island area, which at the time was a karstified limestone island with a central geomorphological depression. The narrow, 30 to 35 m-deep, newly formed central faro lagoon started to fill ~ 5500 yr BP, when a reef initiated on top of the southern highest Pleistocene karstified reef and sea-level rise stalled. The infilling of the faro lagoon was completed ~ 4500 yr BP. An island formed that was flanked on its south side by a shallow lagoon and surrounded by a reef flat. Through several phases of land reclamation since the 1950s, the shallow lagoon was infilled and the reef flat buried with sand and rubble to form Malé Island as it is known today.","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130909529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New insights on the Late Quaternary evolution of Abrolhos reefs, Eastern Brazilian Shelf","authors":"L. S. Vieira, A. Bastos, B. Dechnik, J. Braga, R. Moura, D. D'Agostini, F.C. Morales, J. Webster","doi":"10.54780/iassp49/03","DOIUrl":"https://doi.org/10.54780/iassp49/03","url":null,"abstract":"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.","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"90 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125995858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling. A Window Into the Future","authors":"G. Camoin, N. Hallmann","doi":"10.54780/iassp49/00","DOIUrl":"https://doi.org/10.54780/iassp49/00","url":null,"abstract":"Introduction to: Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117327966","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quaternary coral, coralline algal and vermetid assemblages as sea-level indicators: a review","authors":"J. Braga, M. Humblet, Dino A. Ramos, B. Dechnik, J. Webster","doi":"10.54780/iassp49/01","DOIUrl":"https://doi.org/10.54780/iassp49/01","url":null,"abstract":"Corals, coralline algae and vermetid gastropods are indirect (marine limiting) relative sea-level (RSL) indicators. The precision in sea-level reconstruction based on fossils of those organisms depends on the probable palaeodepth in which they grew. Constraining such palaeodepth depends, in turn, on the available information about the habitats of their living counterparts. Diverse genera, species and species assemblages of corals, coralline algae and vermetid gastropods have historically been proposed as reliable indicators of narrow, shallow depth ranges. However, the increased information on depth distribution of marine benthos in the last two decades has challenged some early assumptions about depth ranges of taxa considered diagnostic of precise palaeodepths. Here, the authors test the reliability of coral, coralline algal and vermetid assemblages that have been extensively used in RSL reconstructions in the light of data from Ocean Biogeographical Information System (OBIS) and other recently published data. In the Indo-Pacific province, these data support the use of the robust-branching and the shallow, high-energy encrusting coral assemblages with a 0 to 10 m uncertainty. In both cases many component species have unimodal distributions and both median and average water depths are shallower than 10 m. The reliability of these coral assemblages as indicative of shallow water depths is strengthened when corals are encrusted by thick plants of the coralline alga Porolithon gr. onkodes. According to OBIS data, coralline algae of this species group in the Indo-Pacific are restricted to very shallow waters (95% probability of occurrence shallower than 0.2 m and in 99.6% of records shallower than 6 m). However, such a narrow depth range and the overall scarce data on coralline algal species in the OBIS database are questionable due to difficulties of coralline algal species identification with the naked eye. A comprehensive survey of the modern distribution of coralline algae at One Tree Reef (southern Great Barrier Reef) indicates that P. gr. onkodes has a log-normal distribution with median depth of less than 5 m and 95% of occurrence probability of thick crusts (> 0.2 mm) shallower than 8.8 m. Data on modern distribution of vermetids are scarce. In the OBIS database, vermetid species are reported from relatively wide depth ranges. However, relatively high densities (> 10 individuals per m2) on coral and coralline algal surfaces only occur from above mean low tide to some 6 m depth. In the Western Atlantic-Caribbean province Acropora palmata is the most precise RSL marker and no additional components of fossil assemblages improve its palaeodepth information. The confident use of coralgal and vermetid assemblages as RSL indicators relies on the identification of fossil corals and coralline algae at the species or species-group level. The scarcity of available data highlights the need for further studies on distribution of coralline algal species a","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125201977","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"How reefs drown: A case study from the Northwest Hawaiian Islands","authors":"M. Toomey, M. Sandstrom, E. Magette, T. Cronin","doi":"10.54780/iassp49/06","DOIUrl":"https://doi.org/10.54780/iassp49/06","url":null,"abstract":"Thousands of deeply submerged seamounts are scattered across ocean basins, many capped by thick successions of reef carbonates accumulated over millions of years prior to island drowning. How conditions sustaining shallow-water reef development at these sites deteriorated is often unclear but could lend insights into the processes that put stress on modern reef communities. Here the authors examine reef drowning in the Northwest Hawaiian Islands, brought on by low rates of carbonate accretion that often occur at mid-latitude (> 30) locations. New strontium-isotope stratigraphy from shallow water carbonates sampled from a 499 m-long boring through Midway Atoll suggest limited accumulation has occurred at the site since the early-Miocene (~ 16 Ma). The offshore morphology of Midway indicates carbonate production has often been outpaced by wave erosion during the Pleistocene, shifting the island’s centre ~ 3 km to the south-east in the prevailing wave direction and increasing its circularity. Strong wave action and slow reef accretion may also explain development of extensive reef flats on Midway and nearby islands. Similar features are shared with some other carbonate islands at mid-latitudes but are not typical of Central Pacific atolls, more generally, or guyots. Abrupt sea-level rise may therefore provide a more plausible mechanism for atoll/guyot drowning in the geologic past than poor environmental conditions for carbonate accretion as has previously been invoked.","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117172449","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reef growth history at intermediate to mesophotic depths since the end of the Last Glacial period along the Great Barrier Reef shelf edge","authors":"M. Humblet, J. Webster, Y. Yokoyama, J. Braga, K. Fujita, Y. Iryu, S. Fallon, W. Thompson","doi":"10.54780/iassp49/07","DOIUrl":"https://doi.org/10.54780/iassp49/07","url":null,"abstract":"Reef communities at intermediate (10 to 30 m) and mesophotic (~ 30 to 150 m) depths occupy large areas of sea floor but little is known about their potential to accrete vertically, their response to sea-level change and other environmental perturbations. In this study, the authors have examined cores from two holes, M0040A and M0041A, drilled by the International Ocean Drilling Program Expedition 325 along the shelf edge of the modern GBR at 131 m water depth. The objective was to investigate reef growth history at palaeo-water depths > 20 m over a time period spanning 30,000 years, from the end of the Last Glacial period through the last deglaciation. Based on changes in lithologies and biotic components, and a robust chronostratigraphic framework supported by 47 radiometric ages, the authors have identified two episodes of reef growth, one during Marine Isotope Stage (MIS) 2 and the other at the onset of the deglaciation, both characterised by abundant microbialite crusts and distinct coral assemblages. Palaeo-water depths range from 30 to 60 m and from 20 to 30 m for the MIS 2 and early deglacial reef sections, respectively. The first episode of reef growth documented in the cores initiated at 27 to 25 ka, possibly in response to increased light availability and change in sedimentation resulting from falling sea-level between 32 and 29 ka from MIS 3 and also to low atmospheric pCO2 at the end of the Last Glacial period. Reef accretion was reduced or ceased sometime between 24 and 19 ka, coinciding with the rapid 20 m sea-level fall of the peak Last Glacial Maximum and minima of SSTs. Reef growth resumed at 19.5 to 18.5 ka, influenced by a period of moderate sea-level rise and increasing sea surface temperatures at the onset of the deglaciation. Reef growth termination at ca. 17 ka correlates with a major episode of reef demise previously identified in adjacent mid and outer terrace cores and linked to reduced water quality combined with rapid deglacial sea-level rise. Vertical accretion (VA) rates were calculated based on two methods: linear visual fitting and Bayesian modelling. The findings show that the highest VA rates are associated with microbialite boundstone. Reef ecosystems dominated by microbialite and corals developed at intermediate and mesophotic depths, and grew vertically at maximum rates of 2 to 5 mm yr-1 depending on the method used, over a period of rapid environmental change during the transition from MIS 3 to MIS 1. Further study needs to explore the potential of modern-type deep coralgal communities to cope with higher rates of sea-level rise predicted this century.","PeriodicalId":297740,"journal":{"name":"Coral Reefs and Sea-Level Change: Quaternary Records and Modelling","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130551336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}