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Response of the Great Barrier Reef to sea-level and environmental changes over the past 30,000 years

DOI:10.1038/s41561-018-0127-3
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Jody M. Webster at The University of Sydney
Jody M. Webster
Juan C. Braga at University of Granada
Juan C. Braga
Marc Humblet at Nagoya University
Marc Humblet
Donald Cameron Potts at University of California, Santa Cruz
Donald Cameron Potts
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Abstract and Figures

Previous drilling through submerged fossil coral reefs has greatly improved our understanding of the general pattern of sea-level change since the Last Glacial Maximum, however, how reefs responded to these changes remains uncertain. Here we document the evolution of the Great Barrier Reef (GBR), the world's largest reef system, to major, abrupt environmental changes over the past 30 thousand years based on comprehensive sedimentological, biological and geochronological records from fossil reef cores. We show that reefs migrated seaward as sea level fell to its lowest level during the most recent glaciation (∼20.5-20.7 thousand years ago (ka)), then landward as the shelf flooded and ocean temperatures increased during the subsequent deglacial period (∼20-10 ka). Growth was interrupted by five reef-death events caused by subaerial exposure or sea-level rise outpacing reef growth. Around 10 ka, the reef drowned as the sea level continued to rise, flooding more of the shelf and causing a higher sediment flux. The GBR's capacity for rapid lateral migration at rates of 0.2-1.5 m yr⁻¹ (and the ability to recruit locally) suggest that, as an ecosystem, the GBR has been more resilient to past sea-level and temperature fluctuations than previously thought, but it has been highly sensitive to increased sediment input over centennial-millennial timescales. © 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
| Geomorphic, chronostratigraphic and biological development of the Hydrographer's Passage drill transect (HYD-01C) off Mackay. a, A highresolution multibeam image shows the surface geomorphic context 16,38 of HYD-01C and the drill-hole locations (red lines represent the penetration depths). b, A simplified stratigraphic section that shows the distribution of recovered core intervals, coral assemblages and their interpreted palaeowater depths, and selected U-Th and 14 C AMS ages. Chronostratigraphic boundaries of the four main shallow reef sequences (Reefs 1-4) are represented by solid coloured lines and long dashes; short dashes show their corresponding deep-water fore-reef slope deposits (Methods, Supplementary Notes 1-3 and Supplementary Fig. 1). Reef 5 represents the modern Holocene reef and is characterized by deep-water fore-reef slope deposits on the shelf edge. The x axis represents the distance across the shelf and is schematic (a gives the actual core locations).
| Geomorphic, chronostratigraphic and biological development of the Hydrographer's Passage drill transect (HYD-01C) off Mackay. a, A highresolution multibeam image shows the surface geomorphic context 16,38 of HYD-01C and the drill-hole locations (red lines represent the penetration depths). b, A simplified stratigraphic section that shows the distribution of recovered core intervals, coral assemblages and their interpreted palaeowater depths, and selected U-Th and 14 C AMS ages. Chronostratigraphic boundaries of the four main shallow reef sequences (Reefs 1-4) are represented by solid coloured lines and long dashes; short dashes show their corresponding deep-water fore-reef slope deposits (Methods, Supplementary Notes 1-3 and Supplementary Fig. 1). Reef 5 represents the modern Holocene reef and is characterized by deep-water fore-reef slope deposits on the shelf edge. The x axis represents the distance across the shelf and is schematic (a gives the actual core locations).
… 
| Geomorphic, chronostratigraphic and biological development of the Noggin Pass drill transect (NOG-01B) off Cairns. a, The high-resolution multibeam image shows the surface geomorphic context 16,38 of NOG-01B and the drill-hole locations (red lines represent penetration depths). b, A simplified stratigraphic section that shows the distribution of recovered core intervals, coral assemblages and their interpreted palaeowater depths, and selected U-Th and 14 C AMS ages. Chronostratigraphic boundaries of the four main shallow reef sequences (Reefs 1-4) are represented by solid coloured lines and long dashes; short dashes show their corresponding deep-water fore-reef slope deposits (Methods and Supplementary Notes 1-3 and Supplementary Fig. 1). Reef 5 represents the modern Holocene reef and is characterized by deep-water fore-reef slope deposits on the shelf edge. The x axis represents the distance across the shelf and is schematic (a gives the actual core locations).
| Geomorphic, chronostratigraphic and biological development of the Noggin Pass drill transect (NOG-01B) off Cairns. a, The high-resolution multibeam image shows the surface geomorphic context 16,38 of NOG-01B and the drill-hole locations (red lines represent penetration depths). b, A simplified stratigraphic section that shows the distribution of recovered core intervals, coral assemblages and their interpreted palaeowater depths, and selected U-Th and 14 C AMS ages. Chronostratigraphic boundaries of the four main shallow reef sequences (Reefs 1-4) are represented by solid coloured lines and long dashes; short dashes show their corresponding deep-water fore-reef slope deposits (Methods and Supplementary Notes 1-3 and Supplementary Fig. 1). Reef 5 represents the modern Holocene reef and is characterized by deep-water fore-reef slope deposits on the shelf edge. The x axis represents the distance across the shelf and is schematic (a gives the actual core locations).
… 
| Evolution of the GBR over the past 30 kyr in relation to major sealevel and environmental changes. a, North Greenland Ice Core Project (NGRIP ice-core δ 18 O record, with timing and duration of MWPs 1A0 (19 ka), MWP 1A and MWP 1B and other global climate events (LGM and YD) as vertical grey shaded bars 1,2, 29,30. The brown bar shows a massive flux of fine sediment to the slope at ~10 ka (ref. 18 ) when > 60-75% of the GBR shelf area was flooded (Supplementary Note 4). The orange line shows the western Pacific warm pool (WPWP) SST anomalies (reconstructed from planktonic foraminifera Mg/Ca (ref. 22 )). Points and regression lines are regional SST anomalies (Expedition 325 coral Sr/Ca (ref. 17 )) from Noggin Pass (red) and Hydrographer's Passage (blue). b, VA history for HYD-01C with the GBR maximum RSL curves (Y. Yokoyama et al., manuscript in preparation) (blue line) and percentage of shelf flooded (brown lines, not scaled to depth). Stepped plots are calculated VA rates, binned at 0.5 kyr intervals. c, Summary of spatial and temporal patterns of reef evolution (Reefs 1-5) at HYD-01C that encompass the outer-, mid-and inner-reef terraces, the inner-and outer-reef barriers and the modern Holocene reef. Periods of major reef turn-on, reef turn-off or reef death events caused by RD, RE and hiatus events are shown along with the distribution of coral assemblages (same colours as in Figs. 1, 2 and 4). The grey dashed boxes represent the timing and duration of the deep-water (> 10 m) fore-reef slope deposits, which are sometimes coeval with shallow-water (< 10 m) reef deposits upslope. d, VA history for NOG-01B (colours and plots as for b). e, Summary of spatial and temporal patterns of reef evolution (Reefs 1-5) at NOG-01B that encompass the outer-, mid-and inner-reef terraces, the inner-and outer-reef barriers and the modern Holocene reef. Periods of major reef turn-on, reef turn-off or reef death events caused by RD, RE and hiatus events are shown along with the distribution of coral assemblages (same colours as in Figs. 1, 2 and 4). The grey dashed boxes represent the timing and duration of the deep-water (> 10 m) fore-reef slope deposits, which are sometimes coeval with shallow-water ( < 10 m) reef deposits upslope.
| Evolution of the GBR over the past 30 kyr in relation to major sealevel and environmental changes. a, North Greenland Ice Core Project (NGRIP ice-core δ 18 O record, with timing and duration of MWPs 1A0 (19 ka), MWP 1A and MWP 1B and other global climate events (LGM and YD) as vertical grey shaded bars 1,2, 29,30. The brown bar shows a massive flux of fine sediment to the slope at ~10 ka (ref. 18 ) when > 60-75% of the GBR shelf area was flooded (Supplementary Note 4). The orange line shows the western Pacific warm pool (WPWP) SST anomalies (reconstructed from planktonic foraminifera Mg/Ca (ref. 22 )). Points and regression lines are regional SST anomalies (Expedition 325 coral Sr/Ca (ref. 17 )) from Noggin Pass (red) and Hydrographer's Passage (blue). b, VA history for HYD-01C with the GBR maximum RSL curves (Y. Yokoyama et al., manuscript in preparation) (blue line) and percentage of shelf flooded (brown lines, not scaled to depth). Stepped plots are calculated VA rates, binned at 0.5 kyr intervals. c, Summary of spatial and temporal patterns of reef evolution (Reefs 1-5) at HYD-01C that encompass the outer-, mid-and inner-reef terraces, the inner-and outer-reef barriers and the modern Holocene reef. Periods of major reef turn-on, reef turn-off or reef death events caused by RD, RE and hiatus events are shown along with the distribution of coral assemblages (same colours as in Figs. 1, 2 and 4). The grey dashed boxes represent the timing and duration of the deep-water (> 10 m) fore-reef slope deposits, which are sometimes coeval with shallow-water (< 10 m) reef deposits upslope. d, VA history for NOG-01B (colours and plots as for b). e, Summary of spatial and temporal patterns of reef evolution (Reefs 1-5) at NOG-01B that encompass the outer-, mid-and inner-reef terraces, the inner-and outer-reef barriers and the modern Holocene reef. Periods of major reef turn-on, reef turn-off or reef death events caused by RD, RE and hiatus events are shown along with the distribution of coral assemblages (same colours as in Figs. 1, 2 and 4). The grey dashed boxes represent the timing and duration of the deep-water (> 10 m) fore-reef slope deposits, which are sometimes coeval with shallow-water ( < 10 m) reef deposits upslope.
… 
| Simplified model that shows the evolution of the GBR over the past 30 kyr. a, Basic chronostratigraphy, facies relationships and key stages during the development of the shelf-edge reefs. Darker shading indicates the distribution of shallower (< 10 m) reef facies and paler shading that of deeper (> 10 m) reef facies. The basement substrate (orange line) is composed of MIS 3 or older deposits that range from shallow reef (Reef 1) to deep lower shelf/slope settings. b, Key reef events (turn-on and reef death) and associated palaeoenvironmental changes, which include the rate of RSL change (Y. Yokoyama et al., manuscript in preparation), mean SST relative to the modern SST 17,22 and sediment flux 18,24,25,31 (Supplementary Table 6).
| Simplified model that shows the evolution of the GBR over the past 30 kyr. a, Basic chronostratigraphy, facies relationships and key stages during the development of the shelf-edge reefs. Darker shading indicates the distribution of shallower (< 10 m) reef facies and paler shading that of deeper (> 10 m) reef facies. The basement substrate (orange line) is composed of MIS 3 or older deposits that range from shallow reef (Reef 1) to deep lower shelf/slope settings. b, Key reef events (turn-on and reef death) and associated palaeoenvironmental changes, which include the rate of RSL change (Y. Yokoyama et al., manuscript in preparation), mean SST relative to the modern SST 17,22 and sediment flux 18,24,25,31 (Supplementary Table 6).
… 
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Articles
https://doi.org/10.1038/s41561-018-0127-3
1Geocoastal Research Group, School of Geosciences, The University of Sydney, Sydney, Australia. 2Departamento de Estratigrafía y Paleontología,
Universidad de Granada, Granada, Spain. 3Department of Earth and Planetary Sciences, Nagoya University, Nagoya, Japan. 4Department of Ecology &
Evolutionary Biology, University of California, Santa Cruz, CA, USA. 5Institute of Geology and Paleontology, Graduate School of Science, Tohoku University,
Sendai, Japan. 6Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan. 7Department of Earth and Planetary Science, Graduate
School of Science, University of Tokyo, Tokyo, Japan. 8Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan. 9Department of Physics
and Earth Sciences, University of the Ryukyus, Okinawa, Japan. 10EA 4592G&E, ENSEGID, Bordeaux INP, Pessac Cedex, France. 11Research School of Earth
Sciences, Australian National University, Canberra, Australia. 12Research School of Physics and Engineering, Australian National University, Canberra,
Australia. 13Department of Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA. 14School of GeoSciences, University
of Edinburgh, Edinburgh, UK. 15Graduate School of Integrated Sciences for Global Society Kyushu University, Fukuoka, Japan. 16School of Earth and
Environmental Sciences, University of Wollongong, Wollongong, Australia. 17Graduate School of International Resource Science, Akita University, Akita,
Japan. 18LSCE/IPSL, Laboratoire CNRS-CEA-UVSQ, Gif-sur-Yvette, France. *e-mail: jody.webster@sydney.edu.au
The Last Glacial Maximum (LGM) and subsequent deglacia-
tion represents a major reorganization of the global climate
system, with rapid sea-level rises (for example, meltwater
pulses (MWPs) 1A0, 1A, 1B and 1C)1–4 linked to ice-sheet collapse,
changes in global ocean circulation and temperatures5, and periods
of divergent atmospheric CO2 concentrations and ocean aragonite/
calcite saturation states6. Although to understand the responses of
coral reef systems to these major, abrupt environmental changes is
crucial to place possible reef futures into an appropriate time frame
within the context of global processes7,8, few fossil reef records (for
example, Barbados, Huon Peninsula, Vanuatu and Tahiti)1,2,9–11 fully
span this ~30–10 thousand years (kyr) period. Thus, questions
remain about the critical environmental thresholds that led to reef
demise9,12 in the past and how reefs recover after disturbances on
different spatiotemporal scales13–15.
In this study, we present a synthesis of all the available geomor-
phic, sedimentological, biological and dating information from
fossil reef cores recovered from the Great Barrier Reef (GBR)
shelf-edge reefs during Integrated Ocean Drilling Program (IODP)
Expedition 32516. Radiometric and geochemical investigations of
these cores, combined with sediment cores from the adjacent basin,
have yielded precise constraints on variations in the relative sea level
(RSL) (Y. Yokoyama et al., manuscript in preparation), sea-surface
temperature (SST)17 and sediment flux18 over this period. We now
document how the GBR responded to these major environmental
variations, which includes the corresponding changes to reef mor-
phologies, communities and growth rates. We also confirm the
existence and location of reef refugia19,20 during the LGM sea level
and establish the critical environmental conditions at which the reef
died and re-established on centennial–millennial timescales8 over
the past 30 kyr.
Shelf-edge reef structure, composition and sequences
Transects of reef cores were recovered off Mackay (Hydrographer’s
Passage at 19.7 °S, HYD-01C, Sites M0030–M0039) and Cairns
(Noggin Pass at 17.1 °S, NOG-01B, Sites M0053–M0057), and
consisted of 20 holes drilled at 16 different sites (Figs. 1 and 2 and
Supplementary Notes 1 and 2), and were used to investigate the
evolution of the GBR. U–Th and 14C accelerator mass spectrometry
(AMS) dating16,17,21(Y. Yokoyama et al., manuscript in preparation)
Response of the Great Barrier Reef to sea-level
and environmental changes over the past
30,000 years
Jody M. Webster1*, Juan Carlos Braga 2, Marc Humblet3, Donald C. Potts 4, Yasufumi Iryu 5,
Yusuke Yokoyama 6,7,8, Kazuhiko Fujita 9, Raphael Bourillot10, Tezer M. Esat11,12, Stewart Fallon11,
William G. Thompson13, Alexander L. Thomas14, Hironobu Kan15, Helen V. McGregor 16,
Gustavo Hinestrosa 1, Stephen P. Obrochta17 and Bryan C. Lougheed18
Previous drilling through submerged fossil coral reefs has greatly improved our understanding of the general pattern of sea-
level change since the Last Glacial Maximum, however, how reefs responded to these changes remains uncertain. Here we docu-
ment the evolution of the Great Barrier Reef (GBR), the world’s largest reef system, to major, abrupt environmental changes
over the past 30 thousand years based on comprehensive sedimentological, biological and geochronological records from fossil
reef cores. We show that reefs migrated seaward as sea level fell to its lowest level during the most recent glaciation (~20.5–
20.7 thousand years ago (ka)), then landward as the shelf flooded and ocean temperatures increased during the subsequent
deglacial period (~20–10 ka). Growth was interrupted by five reef-death events caused by subaerial exposure or sea-level rise
outpacing reef growth. Around 10 ka, the reef drowned as the sea level continued to rise, flooding more of the shelf and causing
a higher sediment flux. The GBR’s capacity for rapid lateral migration at rates of 0.2–1.5 m yr−1 (and the ability to recruit locally)
suggest that, as an ecosystem, the GBR has been more resilient to past sea-level and temperature fluctuations than previously
thought, but it has been highly sensitive to increased sediment input over centennial–millennial timescales.
© 2018 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
NATURE GEOSCIENCE | VOL 11 | JUNE 2018 | 426–432 | www.nature.com/naturegeoscience
426
The Nature trademark is a registered trademark of Springer Nature Limited.
... However, recent coral reef records from Noggin Pass (NOG) and Hydrographer's Passage (HYD), two shelf edge sites with similar shelf morphology located 500 km apart from each other, show a consistent RSL offset (reconstructed RSL at NOG is several metres higher at HYD) during the last deglaciation Webster et al., 2018) which cannot be explained by a GIA model. To understand this discrepancy, an additional physical process that is able to generate metre scale regional RSL variation within a 10 3 -10 5 year timescale is required. ...
... We use a version of the ANU ice model (denoted as ANU_LGM; Lin, 2019) that has been updated to reflect the early rapid global mean sea-level (GMSL) fall to the LGM lowstand, as revealed by sea-level index points (SLIPs) from NOG and HYD Webster et al., 2018). We assume that the majority (90%) of this GMSL fall was caused by rapid growth of the North American and Eurasian Ice Sheets (Fig. 2), possibly due to the saddle merger mechanism (Ji et al., 2021). ...
... During early MIS 2 (28-22 ka BP; Fig. 2), RSL was 90-105 m below present with only part of the shelf edge submerged near the south-eastern Capricorn Channel. The growth of reef stage 2 here (Supplementary Figure 1; Webster et al., 2018) contributed 10% to overall sediment accumulation for this period (Fig. 6). Comparatively, 19.1 Gt/ka (14.7-23.5 Gt/ka) of siliciclastic sediment was deposited at the continental slope and shelf edge during this period, which dominated the sediment budget (contributing ∼90% of total loading). ...
Relative sea level response to mixed carbonate-siliciclastic sediment loading along the Great Barrier Reef margin
Article
Full-text available
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 (18.4-21.6S). 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.
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... As RSL falls, shallow-reef habitats such as mangroves, lagoons, patch reefs, barrier reefs, spur and groove habitats, and shallow fore-reefs (among others) disappear from oceanic atolls and islands with steep bathymetry (Wise and Schopf 1981, Kosaki et al. 1991, Valentine and Jablonski 1991, Nunn 1998, Camoin et al. 2001, Dickinson 2004, Lisiecki and Raymo 2005, Norris and Hull 2011, Woodroofe and Webster, 2014, Camoin and Webster 2015, Ludt and Rocha 2015. Conversely, such shallow-reef habitats are more likely to shift along bathymetric contours (and thereby persist across glacial cycles) in regions with sloped bathymetry (Abbey et al. 2011, Webster et al. 2018see Fig. 2a-c). ...
... Although examples of both sloped and steep bathymetry can be found within many archipelagos and other similarly-sized geographic regions (e.g., Toomey et al. 2013), the important factor for the purposes of the HPH is the presence of substantial sloped bathymetry within a relatively small (~10's -100's of km) geographic scale; such that shallowreef habitats persist within the geographic range of reef-dwelling populations. Several studies have also explored the influence of varying substrate slopes on coral reef development on both oceanic islands (Webster et al. 2007) and continental margins (Webster et al. 2018, Esat et al. 2022. In both cases, reef development in response to sea level fall and rise on steep bathymetry leads to narrower reefs (and likely compressed associated habitats) compared with sloped bathymetry. ...
... In such cases, the resulting submerged reef ("drowned atoll") will also lack the suite of shallow-reef habitats as described above. Conversely, a fall in RSL can lead to restoration of shallow-reef habitat in areas with submerged reefs and seamounts (Pinheiro et al. 2017, Webster et al. 2018). However, these examples are not as likely to have as broad-scale impact on species distribution as RSL drops that reduce the availability of shallow-reef habitats throughout regions with steep bathymetry. ...
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... Even within localities, coral depth ranges might change depending on geomorphology, energy and sediment input (Done, 1982;Braithwaite, 2016). On the other hand, this knowledge on the environmental distribution of reef builders, including their depth ranges, is crucial to reconstruct the response of reef ecosystems to spatio-temporal variations in global to local environmental parameters, such as climate, sea-level, water quality, and turbidity in the past (Blanchon et al., 2009;Camoin et al., 2012;Woodroffe & Webster, 2014;Camoin & Webster, 2015;Toth et al., 2015;Webster et al., 2018). ...
... The accuracy and usefulness of coral RSL indicators can be improved by adding depthrelated information about co-existing coralline algae (CAA) and vermetid gastropods. Palaeodepth interpretations based on CAA and vermetids, which are common encrusters contributing to reef growth, have been used to reconstruct RSL from fossil reefs (Davies & Montaggioni, 1985;Pirazzoli & Montaggioni, 1988;Bard et al., 1996;Camoin et al., 2001;Cabioch et al., 2003;Abbey et al., 2011;Deschamps et al., 2012;Dechnik et al., 2015;Gischler et al., 2016;Dechnik et al., 2017;Gischler et al., 2018b;Webster et al., 2018;Yokoyama et al., 2018;Humblet et al., 2019). The living and fossil representatives of these two groups have received less attention than corals and the available literature on the depth ranges of the reef-related species is relatively scarce and concentrated in a few geographic areas (Adey, 1986;Dechnik et al., 2017;Humblet et al., 2019 and references therein). ...
... With slight variations in their palaeodepth meaning, the coral assemblages proposed by Montaggioni and co-authors in the 90s and 2000s have been used as palaeo-RSL indicators in reconstructions of reef development and RSL curves based on reef cores or samples collected from the sea floor in diverse localities across the Indo-Pacific. In particular the occurrence of the robustbranching coral assemblage has been considered indicative of palaeodepths varying from 0-5 m to 0-10 m (Bard et al., 1996;Galewsky et al., 1996;Camoin et al., 2001;Cabioch et al., 2003;Webster & Davies, 2003;Camoin et al., 2004;Webster et al., 2004b;Frank et al., 2006;Andersen et al., 2008;Thomas et al., 2009;Andersen et al., 2010;Bard et al., 2010;Shen et al., 2010;Abbey et al., 2011;Deschamps et al., 2012;Dechnik et al., 2015;Gischler et al., 2016;Dechnik et al., 2017;Gischler et al., 2018a;Webster et al., 2018;Yokoyama et al., 2018;Humblet et al., 2019;Webster et al., this volume). In addition to the depth distribution proposed by Montaggioni's group, these papers refer to other works on Indo-Pacific coral ecology (see references in Supplementary table). ...
Quaternary coral, coralline algal and vermetid assemblages as sea-level indicators: a review
Article
  • Dec 2022
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 and vermetid in modern coral reefs from a variety of oceans and reef settings.
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... Yellow rectangles highlight the periods of Guyanese beachrock cementation, green rectangle signal oolite neoformation age; b the last 35 ka of detailed sea level reconstructions using data obtained from Northeastern and Northwestern Australia. Rapid rises and falls of sea level can be identified during LGM-a and LGM-b Webster et al. 2018;Ishiwa et al. 2019) fragments ( The North and East Brazilian outer shelves, covered by carbonate sediments, are bound between a well-defined shelf break at 75-m water depth and a beachrock ridge at 25 m (Gomes et al. 2020). Patch reefs scattered over the terraces rise in average to 3 m in height. ...
... Still on the dive 11 site, the cement of a nearby beachrock indicates a much more recent age (16,170 yr BP, that is 19,535 yr median cal age). This chronology is reminiscent of that observed at the shelf edge of the Great Barrier Reef, where the sea level dropped by around 20 m between 21,900 and 20,500 yr BP, to − 118 m relative to the modern level Webster et al. 2018;Ishiwa et al. 2019). Subsequently, the relative sea level rose at a rate of about 3.5 mm per year for around 4000 years. ...
Beachrocks of the last low sea level, substrate of the Great Amazon Reef system along the outer Guiana shelf
Article
Full-text available
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.
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... Fluctuations of sea level of ~100-120 m resulted in reefs being displaced as sea level lowered, and reef limestones became emergent and were karstified. Corals were able to re-establish as the sea rose again, but if the rate of sea-level rise exceeded the capacity for vertical reef accretion the reef terraces were drowned (Woodroffe and Webster, 2014;Webster et al., 2018). ...
... Although reef 4, described by Webster et al. (2018) was also formed in about 50 m water depth, it appears that shelf-edge reefs on the Great Barrier Reef terminated accretion slightly earlier than those at Lord Howe Island and Balls Pyramid. We attribute this to the differences in topography in the hinterland, with the shelf behind the outer reefs providing a range of topographic features on which platform reefs could establish, in contrast to the limited accommodation space into which reefs could backstep at Lord Howe Island, and its absence in the case of Balls Pyramid. ...
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... Complex depositional histories developed in response to Quaternary sea-level change have also been described from other areas including the Pacific reefs of Polynesia (Blanchon et al., 2009;Blanchon, 2011) and the Great Barrier Reef of Australia (Webster et al., 2018), where the role of karstification and aquifer control on wetland development in the Great Barrier Reef was briefly discussed by Stieglitz (2005). Table 1 provides a fuller list of modern analogues for palustrine carbonate deposition from locations around the world. ...
... Carbonate catchment area Although palustrine dolomites are described from the early Carboniferous ice-house ramp cyclothems of the eastern USA, they are conspicuously absent from flat-topped platforms of the same age (Wright et al., 1997;Barnett et al., 2013), suggesting that drainage from extensive areas of subaerially exposed carbonate pediment may be required for these systems to develop. In modern carbonate settings with mixed catchment area geology, such as the Queensland coast to the west of the Great Barrier Reef in Australia (Webster et al., 2018), higher clastic supply may also limit the potential for freshwater carbonate factories to form. ...
Flooding of a carbonate platform: The Sian Kaʼan Wetlands, Yucatán, Mexico—A model for the formation and evolution of palustrine carbonate factories around the modern Caribbean Sea and in the depositional record
Article
Full-text available
  • Feb 2023
The dynamic inter‐relationships between marine and freshwater carbonate depositional environments are illustrated in the Sian Ka’an Wetlands, a 5,280 km2 complex of groundwater‐fed freshwater marshes, lakes and brackish coastal lagoons in the South East Yucatán Peninsula (Mexico). The Yucatán Platform was subaerially emergent and extensively karstified during the last glacial maximum at 18,000 yr BP. The Late Holocene transgression has caused progressive reflooding of the continental margin, backstepping of the MesoAmerican Reef and encroachment of coastal environments into the platform interior as rising groundwaters flood an interconnected cave and sinkhole system and feed seasonal marshes above. The Sian Ka’an Wetlands form a vast palustrine carbonate factory which is directly juxtaposed and dynamically linked with the marine carbonate factory to seaward. Continuing sea‐level rise has caused synchronous landward migration of marginal marine and freshwater environments as beach barriers were breached and palustrine sloughs flooded to form marginal marine seagrass lagoons. The Rio Hondo Fault conditions fluid inflow while the sub‐environments of the Sian Ka’an Wetlands reflect tectonic controls on microtopography and hydroperiod. Modern analogues for the Sian Ka’an Wetlands include the Florida Everglades, formed during transgression of the Florida Platform, and relict marsh environments preserved on leeward shores of Andros, Abaco and other Bahama islands. A wide range of ancient examples deposited in coastal and continental interior settings similarly reflect seasonal aquifer rise in response to marine transgression and/or onlap of late‐stage basin fill onto a karstified pediment. Freshwater palustrine carbonate factories on carbonate platforms are transient deposystems, controlled by subtle water depth, climate, vegetation and hydrological factors while being critically sensitive to sea‐level changes. The preservation potential of palustrine carbonates may be relatively low in coastal settings due to erosion or shallow marine overprinting, while greater further inland where marine flooding is rarer and in tectonically subsident continental interior basins where accommodation space is continuously created.
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... Drowned reefal ridges described in the literature tend to be only a few 100's metres or a few kilometres long (e.g., Jorry et al., 2016;Khanna et al., 2017;Mallarino et al., 2021;Rovere et al., 2018) or to be composed of joint and isolated pinnacles (Abbey et al., 2011), and as such are dissimilar to Ridge 1. Finally, lithological data do not fully support a reefal origin, as no bioconstructed crust, lithified coral conglomerate or other indicators of reefal bioconstruction were observed along the time-equivalent outcrops (Riera et al., 2021) or from well data. Those elements are known not only from modern reefs James et al., 1976;Webster et al., 2018) but also from fossil ones (James & Jones, 2015). ...
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... According to Kandziora [13], it is estimated that 80% of marine environmental pollution is caused by activities carried out on land. Coupled with the increasing use of fossil fuels, it causes drastic climate change, so it impacts increasing sea level and increasing sea temperature [14]. According to Diez [15], this disturbs the marine ecosystem and disrupts the availability of marine natural resources. ...
Implementing Artificial Intelligence to Reduce Marine Ecosystem Pollution
Article
Full-text available
  • Feb 2023
Industrial growth has a positive impact because it brings prosperity to humans. But on the other hand, it also has a negative effect, mainly due to industrial pollution produced. The pollution impacts environmental damage, one of which is the marine environment. This damage can be reduced by increasing understanding of the marine environment by monitoring it using technology. Although efforts have been made to monitor the marine environment, there are difficulties interpreting the large amount of data collected. To overcome these obstacles, we need technology that can process big data. One of the technologies that can be used is Artificial Intelligence which will be discussed in this study. This study aims to provide further understanding regarding the application of Artificial Intelligence to monitor the marine environment. This study uses a literature review method from several studies related to Artificial Intelligence. The final result of this study explains the potential and impact of applying Artificial Intelligence in reducing pollution of the marine environment sustainably. Although there have been many efforts to monitor the ocean for pollutants remotely, classifying the data is challenging because of the high volume of data. Therefore, the novelty of this research is to discuss a use case of a new approach to monitoring the ocean with the help of Artificial Intelligence. This research is expected to be motivated to develop better solutions in overcoming marine environment pollution using Artificial Intelligence technology.
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Chronological implications of changes in the accumulation rate of long marine cores from the continental shelf, southeastern Korea
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Three long marine cores collected from the southwestern part of the Ulleung Basin in the East Sea were investigated in terms of chronology, from the middle Pleistocene to Holocene. We propose an age–depth model in cores 19ESDP-101, 19ESDP-103, and 19ESDP-104 obtained through precise age data using a suitable statistical method and classified in chronological units according to their accumulation rates. Changes in accumulation rate in cores 19ESDP-103 and 19ESDP-104, located at the entrance to the contact of the Korean Strait and the Ulleung Basin, showed good agreement with glacial and interglacial cycles. Relatively increased accumulation rates are related to ocean currents flowing through the Korea Strait during interglacial periods of Marine Isotope Stage (MIS) 5 and 7. However, core 19ESDP-101 obtained from the Hupo Basin, located in the northern site, showed a high accumulation rate in the glacial periods of MIS 6 and 8. It is interpreted as an increase in the sediment input from the exposed shallow shelf and inland fluvial, despite the fact that ocean currents from the Korea Strait are blocked by the exposed shelf platform as the sea-level falling down. These results show that the continental shelf on the western East Sea has been deposited from various factors related to several sea-level fluctuations from the glacial-interglacial cycle during the middle to late Quaternary. This study contributes to stratigraphic study in the Korean continental shelf environment of the East Sea from the middle Pleistocene to Holocene.
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Factors controlling coral P/Ca nutrient proxy: Insights from Porites culture experiments and synchrotron‐based X-ray spectroscopy
Article
Abstracts Coral skeletal P/Ca ratio has been developed as an indicator of temporal seawater dissolved inorganic phosphorus (DIP). The use of coral P/Ca proxy helps to assess oceanographic and climatic impacts such as upwelling, circulation, and continent runoffs on marine biogeochemical cycles. However, factors controlling skeletal P incorporation and elemental partitioning between seawater and coral skeletons remain elusive. We conducted temperature-controlled (~21 to 29 ⁰C) aquaria culture experiments using two colonies of Porites australiensis corals (here refer to B and C) with the only difference in zooxanthellae density (B>C). The coral growth rate ranges from 9.4 to 19.4 mg/day (B) and 0.7 to 14.1 mg/day (C). Only the growth rate of colony C significantly correlates to temperature, potentially reflecting physiological controls on the two colonies given the difference in the zooxanthellae density. We measured coral P/Ca ratios by Inductively coupled plasma mass spectrometry and determined skeletal P speciation through a synchrotron-based spectroscopic approach. Coral P/Ca ratio ranges from 6.5 to 18.6 μmol/mol (B) and 7.2 to 19.8 μmol/mol (C). The dominance of organic-P is confirmed, and the presence of inorganic-P cannot be excluded. Only colony C has a strong P/Ca dependence on temperature and both colonies show strong correlations between P/Ca and growth rate. Although growth rate and temperature are intercorrelated, the growth rate is more likely the direct controlling factor on coral P/Ca in our experiments. Combined laboratory data with field observations, we suggest that the validity of the Porites P/Ca proxy may be influenced by seawater DIP, coral species, and growth rate.
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Instability and breakdown of the coral–algae symbiosis upon exceedence of the interglacial pCO2 threshold (>260 ppmv): the ‘‘missing’’ Earth-System feedback mechanism
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Changes in the atmospheric partial pressure of CO2 (pCO2) leads to predictable impacts on the surface ocean carbonate system. Here, the importance of atmospheric pCO2 <260 ppmv is established for the optimum performance (and stability) of the algal endosymbiosis employed by a key suite of tropical reef-building coral species. Violation of this symbiotic threshold is revealed as a prerequisite for major historical reef extinction events, glacial-interglacial feedback climate cycles, and the modern decline of coral reef ecosystems. Indeed, it is concluded that this symbiotic threshold enacts a fundamental feedback mechanism needed to explain the characteristic dynamics (and drivers) of the coupled land-ocean-atmosphere carbon cycle of the Earth System since the mid-Miocene, some 25 million years ago.
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MatCal: Open Source Bayesian 14C Age Calibration in Matlab
Article
Full-text available
  • Nov 2016
The matcal function provides radiocarbon (14C) age calibration in Matlab using the Bayesian highest posterior density (HPD). The function produces a probability distribution function (PDF) of calibrated ages, as well as 1 sigma (68.27%) and 2 sigma (95.45%) probability calibrated age credible intervals, calculated using HPD. Publication ready calibration plots are also produced, with the option to save to disk. Calibration output can be in either Cal BP or BCE/CE (BC/AD), and a reservoir age can be specified if necessary. The user can choose from a number of calibration curves, including the latest version of IntCal.
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Global warming and recurrent mass bleaching of corals
Article
  • Mar 2017
During 2015-2016, record temperatures triggered a pan-tropical episode of coral bleaching, the third global-scale event since mass bleaching was first documented in the 1980s. Here we examine how and why the severity of recurrent major bleaching events has varied at multiple scales, using aerial and underwater surveys of Australian reefs combined with satellite-derived sea surface temperatures. The distinctive geographic footprints of recurrent bleaching on the Great Barrier Reef in 1998, 2002 and 2016 were determined by the spatial pattern of sea temperatures in each year. Water quality and fishing pressure had minimal effect on the unprecedented bleaching in 2016, suggesting that local protection of reefs affords little or no resistance to extreme heat. Similarly, past exposure to bleaching in 1998 and 2002 did not lessen the severity of bleaching in 2016. Consequently, immediate global action to curb future warming is essential to secure a future for coral reefs.
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Coral community changes in the Great Barrier Reef in response to major environmental changes over glacial-interglacial timescales
Article
The Ribbon Reef 5 borehole offers a unique record of reef growth spanning the entire history of the northern Great Barrier Reef (GBR). Previous studies have reported the main stratigraphical, lithological and chronological patterns, as well as basic descriptions of the coralgal assemblages, but no detailed coral community analysis was undertaken. We present a quantitative analysis of the nature and distribution of Pleistocene coral communities and apply several statistical tools to define recurrent coral associations and compare the eight reef-building cycles recognized throughout the evolution of the GBR. The start of significant reef building occurs at 137 m based on a major change in coral community structure and the inception of the reef cycles (Cy1–8). This revision, along with available stratigraphical and chronological data, suggests that barrier reef initiation may have occurred prior to MIS 11, earlier than previous reports. The coral assemblages at 137 m reflect the transition from lower mesophotic (60–100 m) to upper mesophotic (30–60 m) settings, while the eight reef cycles above are characterized by three recurrent shallow-water reef-coral associations: Porites-Montipora-faviids (Po-Mo-Fa), pocilloporids (Poc), and Acropora-Isopora (Acro-Iso). Typically, these cycles begin with the Po-Mo-Fa association and end with the Acro-Iso association, reflecting shallowing and a catch-up growth mode. However, the first two cycles are characterized by a transitional phase dominated by the Poc association. The dominance of pocilloporids during the early stages of the GBR's history and the long-term shift to an Acropora-Isopora-dominated community may reflect an increase in competitive pressure of acroporids over pocilloporids. Our findings are consistent with the view that reef coral community structure is predictable over 100-kyr time scale. However, variations within reef cycles highlight the importance of environmental changes operating at millennial time scales. Further studies are needed to better refine the reef chronology and clarify the influence of environmental variables (i.e. sea surface temperature, turbidity) on reef coral community structure.
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The undatables: Quantifying uncertainty in a highly expanded Late Glacial‐Holocene sediment sequence recovered from the deepest Baltic Sea basin: IODP Site M0063
Article
Laminated, organic-rich silts and clays with high dissolved gas content characterize sediments at IODP Site M0063 in the Landsort Deep, which at 459 m is the deepest basin in the Baltic Sea. Cores recovered from Hole M0063A experienced significant expansion as gas was released during the recovery process, resulting in high sediment loss. Therefore during operations at subsequent holes, penetration was reduced to 2 m per 3.3 m core, permitting expansion into 1.3 m of initially empty liner. Fully filled liners were recovered from Holes B through E, indicating that the length of recovered intervals exceeded the penetrated distance by a factor of >1.5. A typical down-core logarithmic trend in gamma density profiles, with anomalously low density values within the upper ∼1 m of each core, suggests that expansion primarily occurred in this upper interval. Thus, we suggest that a simple linear correction is inappropriate. This interpretation is supported by anisotropy of magnetic susceptibility data that indicate vertical stretching in the upper ∼1.5 m of expanded cores. Based on the mean gamma density profiles of cores from Holes M0063C and D, we obtain an expansion function that is used to adjust the depth of each core to conform to its known penetration. The variance in these profiles allows for quantification of uncertainty in the adjusted depth scale. Using a number of bulk 14C dates, we explore how the presence of multiple carbon source pathways leads to poorly constrained radiocarbon reservoir age variability that significantly affects age and sedimentation rate calculations. This article is protected by copyright. All rights reserved.
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Bulk sediment 14 C dating in an estuarine environment - How accurate can it be?: Estuarine bulk sediment 14 C dating
Article
  • Feb 2017
Due to a lack of marine macrofossils in many sediment cores from the estuarine Baltic Sea, researchers are often forced to carry out ¹⁴C determinations on bulk sediment samples. However, ambiguity surrounding the carbon source pathways that contribute to bulk sediment formation introduces a large uncertainty into ¹⁴C geochronologies based on such samples, and such uncertainty may not have been fully considered in previous Baltic Sea studies. We quantify this uncertainty by analyzing bulk sediment ¹⁴C determinations carried out on densely spaced intervals in independently dated late-Holocene sediment sequences from two central Baltic Sea cores. Our results show a difference of ~600¹⁴Cyr in median bulk sediment reservoir age, or R(t)bulk, between the two core locations (~1200¹⁴Cyr for one core, ~620¹⁴Cyr for the other), indicating large spatial variation. Furthermore, we also find large downcore (i.e., temporal) R(t)bulk variation of at least ~200¹⁴Cyr for both cores. We also find a difference of 585¹⁴Cyr between two samples taken from the same core depth. We propose that studies using bulk sediment ¹⁴C dating in large brackish water bodies should take such spatiotemporal variation in R(t)bulk into account when assessing uncertainties, thus leading to a larger, but more accurate, calibrated age range.
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Contribution of Antarctica to past and future sea-level rise
Article
  • Mar 2016
Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6-9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics - including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs - that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.
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Younger Dryas Sea-Level and Meltwater Pulse 1B Recorded in Barbados Reef-Crest Coral Acropora palmata
Article
  • Feb 2016
The Younger Dryas climate event occurred during the middle of the last deglacial cycle and is marked by an abrupt shift in the North Atlantic polar front almost to its former glacial position, trending east to west. Using high-precision and high-accuracy U-Th-dated Barbados reef crest coral, Acropora palmata, we generate a detailed sea level record from 13.9 to 9000 years before present (kyr B.P.) and reconstruct the ice volume response to the Younger Dryas cooling. From the mid-Allerød (13.9 kyr B.P.) to the end of the Younger Dryas (11.65 kyr B.P.), rates of sea level rise decreased smoothly from 20 mm yr-1 to 4 mm yr-1, culminating in a 400 year "slow stand" before accelerating into meltwater pulse 1B (MWP-1B). The MWP-1B event at Barbados is better constrained as beginning by 11.45 kyr B.P. and ending at 11.1 kyr B.P. during which time sea level rose 14 ± 2 m and rates of sea level rise reached 40 mm yr-1. We propose that MWP-1B is the direct albeit lagged response of the Northern Hemisphere ice sheets to the rapid warming marking the end of the Younger Dryas coinciding with rapid warming in the circum-North Atlantic region and the polar front shift from its zonal to meridional position 11.65 kyr B.P. As predicted by glaciological models, the ice sheet response to rapid North Atlantic warming was lagged by 400 years due to the thermal inertia of large ice sheets. The regional circum-North Atlantic Younger Dryas climate event is elevated to a global response through sea level changes, starting with the global slowdown in sea level rise during the Younger Dryas and culminating with MWP-1B. No meltwater pulses are evident at the initiation of the Younger Dryas climate event as is often speculated.
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