Ancient polar bear remains explained by sea ice expansion and open water polynyas

Lay summary authored by Susan Crockford. Read the full paper here: http://doi.org/10.5334/oq.107

No Arctic animal is more iconic than its apex predator, the polar bear (Ursus maritimus). Ice-edge habitats are essential for the survival of polar bears today because that’s where they consistently find seals, their primary prey. What we know about where and when polar bears lived in the past is limited to reports of their skeletal remains recovered from archaeological and geological sites. However, the distribution across time and space of these records has not previously been reported.

In her article in Open Quaternary, archaeozoologist Dr. Susan Crockford (Pacific Identifications Inc.) presents the first historical compilation of known records of ancient polar bear remains from fossil and archaeological contexts before AD 1910. The study also presents the locations of known polynyas (recurring areas of thin ice or open water surrounded by sea ice) across the Arctic.

Left lower jaw of polar bear found at Kjul Å near Asdal in northern Jylland (Denmark). Photo credit: Photo by Geert Brovad, courtesy Natural History Museum of Denmark.

It turns out that natural death skeletal specimens of this species (‘fossils’) are rare but archaeological remains are much more common. Most polar bear remains date to the Holocene (the last 11,700 years) and come from human habitation sites within the modern range of the species. Specimens found outside the modern range of polar bears have been documented in the north Atlantic during the late Pleistocene (ca. 115,000- 11,700) and the southern Bering Sea during the middle Holocene (ca. 8,300-4,200 years ago), and are associated with natural expansions of sea ice during known cold periods.

Surprisingly, the single largest find is also the oldest archaeological site with polar bear skeletal remains. Zhokhov Island, Russia is one of the northern-most land forms in the East Siberia Sea and sits at the edge of the Great Siberian Polynya, which polar bears still use today. The site was occupied primarily for about one hundred years (ca. 8,000-7,900 years ago) near the beginning of the Holocene Climatic Optimum (about 9,000-5,500 years ago), when the Arctic was warmer than today. Almost 6,000 polar bear bones were recovered, some of them chewed by dogs.

Crockford, author of the report, also pointed out a little-known fact. ‘The Zhokhov Island assemblage is our first evidence of the return of polar bears to the western Arctic after extraordinarily thick sea ice during the Last Ice Age drove seals and bears into the north Pacific.’

The study shows that ancient polar bear remains, whether archaeological or fossil, are most often found in proximity to areas where polynyas are known today and which likely also occurred in the past. This includes the oldest known fossil (dated to about 130-115 years ago) and the oldest known archaeological specimens from Zhokhov Island. This pattern indicates that as they do today, polar bears may have been most commonly found near polynyas throughout their known historical past because of their need for ice-edge habitats.

Full paper: Crockford, S.J., 2022. Polar Bear Fossil and Archaeological Records from the Pleistocene and Holocene in Relation to Sea Ice Extent and Open Water Polynyas. Open Quaternary, 8(1), p.7. DOI: http://doi.org/10.5334/oq.107

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Left and right hands, brain and cognitive evolution – Exploring prehistoric handedness rates through hominins’ lithic production

Lay summary authored by Stefanos Ligkovanlis. Read the full paper here: http://doi.org/10.5334/oq.111

What do we know about the prehistory of handedness? Did our distant ancestors share similar rates of hand preference with us? And what does this ratio might reveal about prehistoric societies and their cognitive capabilities? Such questions are not new, but until know days they have not received a decisive answer.  Utilising, thus, preexisting knowledge and investigations, my research aimed to explore further the issue of prehistoric handedness with main emphasis given to Neanderthal populations.

Fig. 1: Digital measurements on experimentally produced lithic artifacts and snapshots of modern left and right-handed knappers’ flaking procedures (figure provided by S. Ligkovanlis).

For doing so, the current survey focused on lithic technology with the idea that chiropractic procedures of the stone artifacts’ construction can leave characteristic traces on them, reflecting the hand preference of their manufactures. The methodological protocol of the research included the conduction of an experiment series with the participation of modern right- and left-handed flintknappers and the multifactor evaluation of their results, using computerized techniques. These procedures showed, that the geometrics of a specific element created during lithic production flakes, the ‘cone of percussion’ of the flakes, are strongly and correspondingly related with the knappers’ hand-preference.

After these positive results, the research methodology for distinguishing handedness through lithic artifacts has been applied on the actual archaeological record: flint flakes, from Kalamakia cave-southern Greece. These artifacts have been constructed during the Middle Palaeolithic period by Neanderthals. The analyses conducted indicate that right-handed flintknappers on the site predominated over left-handed ones.

Fig. 2: Possible rates of left- and right-handed Neanderthal flintknappers among the occupational levels of Kalamakia cave-southern Greece. PLH: Possible left-hander. PLR: Possible right-hander (figure provided by S. Ligkovanlis).

Although more effort is needed in order the methods and results of the current study to be verified, I suggest that my research opens a new hopeful perspective for the exploration of the handedness phenomenon during human evolution. The proposed method could easily be applied to lithic artifacts constructed during different periods of the prehistory, by different types of hominins such as Homo erectus, Homo heildebelgensis etc., in order the evolutional trends of hand-preference to be investigated.

Although this is a next logical step to this research discipline the cognitive extensions and interpretations of handedness evolution through millennia (e.g. how exactly the formulation of hand-preference could be connected with the cerebral development and the neurophysiological prerequisites for speech pronunciation and comprehension) should also occupy future efforts. This ‘requests’ could only be fulfilled within an interdisciplinary framework, where collaborative research will be invited to interpret the behavioural and neuroscientific dimensions of what the evolution of handedness means even today, beyond a convenient arrangement at the dining table!

Full paper: Ligkovanlis, S., 2022. Hand-Preference and Lithic Production-Exploring Neanderthal Handedness Rates through the Study of Hertzian Fracture Features on Lithic Blanks. Open Quaternary, 8(1), p.4. DOI: http://doi.org/10.5334/oq.111

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Sparking a new open science direction for Phytolith Research

Lay summary written by Emma Karoune. Read the full paper here: http://doi.org/10.5334/oq.88

The movement to open science is currently happening in all academic disciplines. Open science aims to transform research by making it more reproducible, transparent, reusable, collaborative, accountable, and accessible to society. My paper about assessing open science practices in phytolith research was initiated after I read Lisa Lodwick’s paper ‘Sowing the Seeds of Future Research: data sharing, citation and reuse in archaeobotany’, also published in Open Quaternary. I had been thinking much the same things about my discipline, phytolith research – a sub-discipline of archaeobotany, and especially about the need to make research accessible and reproducible so that data, and research in general, is much more sustainable. So, I decided to undertake a similar study, as a comparison to Lisa’s work, and to start a conversation about open science in my community. 

Phytolith image (Image source: https://commons.wikimedia.org/wiki/File:Phytolithes_observ%C3%A9s_au_Microscope_Electronique_%C3%A0_Balayage_06.jpg)

The research for this article started as a solo effort that I undertook during the first covid pandemic lockdown in 2020. My planned fieldwork and lab work was on hold and so this seemed like a good use of my time while not able to do other research activities. But during the data collection phase I needed help from my colleagues to gain access to their articles and the associated data. This started to create awareness of the work I was undertaking.  Many colleagues replied to my article requests with great enthusiasm at what I was trying to achieve and wanted to get more involved. This led to the formation of a working group on phytolith open science with colleagues from Universitat Pompeu Fabra and the Spanish National Research Council. We decided to initiate a project to investigate data sharing and the potential implementation of the FAIR (Findable, Accessible, Interoperable, Reusable) data principles for phytolith data. This FAIR project is now underway – The FAIR Phytoliths project funded by EOSC-Life. We have conducted a community survey on data sharing and we are currently completing a FAIR assessment of phytolith data. We then intend to go on to draw up FAIR data guidelines with input from the wider community. 

FAIR principles. (Image created by Scriberia for The Turing Way community and is used under a CC-BY licence.  DOI 10.5281/zenodo.3332807)

We have also been keen to continue community building to further this direction of interest in open science. We sought to engage with the International Phytolith Society to form a new committee and we were successful in our efforts in September 2021. The work of the new International Committee on Open Phytolith Science has now begun with regular committee meetings, establishing more awareness of open science through social media, organisation of training events and discussions about open publishing guidelines. We hope that with the FAIR Phytoliths project and the work of the new committee, we can really move phytolith research into a new era of open science.

Read the full paper here: Karoune, E., 2022. Assessing Open Science Practices in Phytolith Research. Open Quaternary, 8(1), p.3. DOI: http://doi.org/10.5334/oq.88

Acknowledgements: Thank you to the members of the FAIR Phytolith Project – Carla Lancelotti, Javier Ruiz-Pérez, Juan José García-Granero, Marco Madella and Celine Kerfant for their great efforts in driving this work forward. And also thanks to the other members that make up the International Committee on Open Phytolith Science – Doris Barboni, Jennifer Bates, Abraham Dabengwa, Zach Dunseth and Maria Gabriela Musaubach. 

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Palaeoecological interpretation of a Late Holocene sediment sequence from the alpine belt of the southern Mongolian Altai Mountains

Lay summary authored by Sven Goenster-Jordan. Read the full paper here: http://doi.org/10.5334/oq.90.

Palaeoecology is a scientific discipline that contributes to a better understanding of interrelations between organisms and their environment during past geological times. The Altai Mountains, located in the center of the Asian continent and inhabited by nomads for thousands of years, are well suited for palaeoecological studies due to their location at the interface of two global climate systems, the North Atlantic climate system from the West and the Pacific climate system from the East. The dominance of one of these systems has varied over time, so that precipitation and temperature in the Altai have changed repeatedly over the millennia. Numerous studies on the Holocene climate history have been carried out in the Altai, most of them with a focus on the northern and southern Chinese part of the mountain range. With records on temperature and humidity variations derived from a soil-sediment profile in the alpine belt of the southern Mongolian Altai, our study complements the picture of the Altai’s climate and environmental history for the late Holocene. To detect such variations, fossil pollen grains in combination with age determinations of organic matter sampled from the soil-sediment profile provided information on regional vegetation changes during the last 2600 years. Pollen is very diverse in size, shape and surface structure and can be assigned to the respective plant species or at least genera based on these characteristics. Some plants and plant communities identified by pollen analyses have special climatic requirements, so that changes in pollen composition indicate changes in temperature and humidity conditions over time.

Overview of the summer pasture at Tsunkhul Lake in the southern Mongolian Altai Mountains. Photo credit: S. Goenster-Jordan.

The characteristics of the soil-sediment profile of the investigated site helped to make assumptions about previous climatic conditions. Based on the pollen data and soil-sediment characteristics, a warm and dry climate predominated between 2600 and 2250 years before present (i.e. 1950), followed by a cool and humid phase that lasted until about 130 years before present. Since then the climate is characterized again by warmer and drier conditions. Such an observation of the mode of climate variability together with its temporal sequence has not been observed in the Altai so far, with the exception of a study in the Chinese southern Altai 50 km away. Additionally, an influence of livestock grazing on the vegetation during the last 2600 years could be shown. This not only indicates a long-term human impact, but also that the climatic influence on the vegetation was predominant.

Full Paper: Goenster-Jordan, S., Urban, B. and Buerkert, A., 2022. Palaeoecological Interpretation of a Late Holocene Sediment Sequence from the Alpine Belt of the Southern Mongolian Altai Mountains. Open Quaternary, 8(1), p.2. DOI: http://doi.org/10.5334/oq.90

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The Occurrence of Lithic Raw Materials in the Western Part of Central Germany 

Lay summary authored by Thomas Hess. Link to full article: http://doi.org/10.5334/oq.108

The western part of Central Germany reveals an extensive archaeological record, including sites dating potentially as far back as the Lower Palaeolithic. Due to its geomorphological features, the region is extraordinarily diverse in terms of the occurrence of lithic raw materials that were used by prehistoric people for the production of tools and weapons. It is virtually impossible to distinguish the various rock types in the area based on macroscopic criteria alone. Nevertheless, only a few studies have addressed this topic so far. In the framework of a research project funded by the Swiss National Science Foundation (SNSF) in cooperation with the Department of Archaeology and Heritage Studies of the University of Aarhus, the use of lithic raw materials by Late Palaeolithic and Mesolithic groups in Central Germany was systematically analyzed. For this purpose, important raw material outcrops in the study area were sampled, in order to establish a reference collection. The latter comprises a broad range of specimens, including various types of silicified sandstone, siliceous shale, chalcedony, Cretaceous flint, jasper, Jurassic chert, and several variants of Triassic chert.

Colour spectrum of chalcedony occurring in the
western part of Central Germany. Photograph: T. Hess.

The rocks were subsequently described petrographically, using optical microscopy with reflected light. Additionally, selected materials were studied in thin-section. Our article presents a detailed description of lithic raw materials in the Federal State of Hesse and adjacent regions. Furthermore, it contains a diachronic overview of the importance of the respective rock types throughout history. The results of the study give interesting new insights into the formation and distribution of the mentioned raw materials. In combination with GIS-analyses, they contribute to a better understanding of subsistence strategies, mobility patterns, and social networks in the past.    

‘Macroscopic and microscopic view of
rock samples. Figure: T. Hess

Full paper: Hess, T. and Riede, F., 2022. The Occurrence of Lithic Raw Materials in the Western Part of Central Germany. Open Quaternary, 8(1), p.1. DOI: http://doi.org/10.5334/oq.108

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Ngalau Sampit cave site, Sumatra: in the footsteps of Dutch Palaeoanthropologist Eugène Dubois

Lay summary authored by Mathieu Duval and Julien Louys. Read the full paper here: http://doi.org/10.5334/oq.96

Our work results from a long-standing investigation initiated at the end of the XIX century by the Dutch Palaeoanthropologist M. Eugène F.T. Dubois. Before finding the famous fossil remains of Pithecanthropus (now Homo) erectus in Java, Dubois spent time on another Indonesian island, Sumatra, in the search of the missing link between apes and humans. His work led to the identification and excavation of several caves in the Padang Highlands.

More than 120 years later, the palaeontologist Julien Louys, working closely with Indonesian collaborators from the Institute of Technology in Bandung, and their team (co-authors of the present work) explored the highlands again, looking for the sites mentioned by Dubois in his field notes. This work, funded by the Australian Research Council, led to the (re-)discovery of the fossil deposits in Ngalau Sampit (“scary cave”), which was originally visited by Dubois in June 1888, and excavated about a year later.

(A) Northern cave entrance today (indicated by white arrow, picture credit: Gerrell Drawhorn); (B) Dubois’s notes: original sketch of Ngalau Sampit entrance likely made by Franke, one of Dubois’s engineer workmen (handwriting is Dubois’).

In the present work, we provide the results of a multidisciplinary investigation of the fossil deposits undertaken over the last few years. They include a general mapping of the cave and the fossil-bearing chambers and passages, the identification of the fossils exposed at the surface of the breccia deposits, and some numerical dating results. To place our finds in historical context, and likely of interest to those examining human evolution from an historical point of view, we also provide a copy and detailed English translation of Dubois’s original notes on Ngalau Sampit, written at the end of the XIX century. In our study, we applied different dating methods (namely U-series, Electron Spin Resonance and Luminescence) in order to determine the age of the sediment and associated fossils found in the cave.

Our results yield an age of about 100,000 years for Ngalau Sampit, which makes the site of great significance for two main reasons: (i) there is currently no other fossil site in Sumatra with this age, but it is coeval with the oldest rainforest site in Java (Punung); (ii) the site is older than Lida Ajer Cave, another Sumatran site excavated by Dubois that has provided the earliest evidence of modern human in south-east Asia.

Full paper: Duval, M., Westaway, K., Zaim, J., Rizal, Y., Aswan, Puspaningrum, M.R., Trihascaryo, A., Albers, P.C.H., Smith, H.E., Drawhorn, G.M., Price, G.J. and Louys, J., 2021. New Chronological Constraints for the Late Pleistocene Fossil Assemblage and Associated Breccia from Ngalau Sampit, Sumatra. Open Quaternary, 7(1), p.9. DOI: http://doi.org/10.5334/oq.96

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Paleo Mega Lake of Rey, the Largest Lake in world History

Lay summary authored by Hadi Jarahi. Read the full paper here: http://doi.org/10.5334/oq.94

I have done extensive research into the morphologic evidence of an ancient lake in Iran. The evidence was, in fact, the remains of the escarps located on the lake’s shore. The height of the escarps ranged from 1 m to 15 m and they were up to 45 km long. The common feature among all of them is that, along the stretches, they all follow specific topographic altitudes. As a result of the various cycles of transgression and regression of the lake, numerous escarps have been formed. In the satellite image, in particular, those dating back to 1970s, the escarps can be seen as white parallel narrow bands. My purpose is to discover the unknowns regarding this lake, and in doing so, I’d like to conduct more comprehensive research and focus on dating, to modeling the paleoclimatic and paleomorphologic conditions of the lake.

Figure 1: Kahrizak scarp in the southeast of Tehran; Corona satellite imagery (1968) of PS-A1; Aerial image of PS-A2 scarp; Worm tubes are abundant in the samples; Broken pieces of the ancient pottery can be seen abundantly on the top of the scarp. Photo credit: H. Jarahi.

In my research, different water levels were investigated, and the major and minor altitudes were determined based on the sediment remains. Additionally, the materials of the sediment were examined. Currently, I am working on my second study on the paleogeography and paleomorphology of the lake. My findings have revealed surprising evidence for the effect of water erosion on the highlands, which were in fact islands in the lake. The drainage basin’s conditions and the amount of water in the lake were also evaluated, and it became clear that the lake contained almost 1.7 times as much water as is found in the Caspian Sea today. The approximate age of the lake puts it in the Younger Dryas. Obtaining more detailed information requires more comprehensive field studies and dating for different altitudes, which could enable us to make comments on the lake with a higher degree of certainty.

Full paper: Jarahi, H., 2021. Paleo Mega Lake of Rey Identification and Reconstruction of Quaternary Lake in Central Iran. Open Quaternary, 7(1), p.7. DOI: http://doi.org/10.5334/oq.94

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A new survey model for the detection of archaeological sites in Argentina

Lay summary authored by Dan Rafuse. Read the full paper here: http://doi.org/10.5334/oq.97

The detection of archaeological sites in the southern Pampas region of Argentina offers significant challenges due to the extension of the landscape, and the natural and modern cultural processes. With thousands of shallow lakes, multiple levels of streams, and variable changes in elevations, the finding of archaeological material is difficult for archaeologists. Traditional survey strategies are usually guided by informants, such as local landowners or farmers, who come across isolated remains or sites. The riverbanks, streams, and shallow lakes are also useful starting points. During wet periods, the riverbanks and streams erosion expose older deposits, giving archaeologists a window into the buried record. In order to help aid in the discovery of more archaeological sites, a computer-generated predictive model may offer archaeologists an innovative method for the detection of new sites.

Archeological survey along the banks of a small river in the southeast Pampas region of Argentina. Photo credit: Dan Rafuse.

Among the available tools for archaeological predictive modelling, Maximum Entropy Modeling (Maxent) is one of the most widely used computer-based approaches. These models can help guide archaeological survey by identify the contributing environmental variables (land-use choices) used by hunter-gatherers, as well as provide insight into mobility and archaeological settlement patterns. Maxent has been broadly used by archaeologists to predict archaeological site locations in different environments and time-periods around the world. The model is a flexible cost-effective way to identify areas most likely to reveal the presence of archeological sites.

The Maxent predictive model for hunter-gatherer archaeology sites in the southern Pampas region of Argentina. Values closer to 1.00 are places with the highest probability of detecting new archaeology sites. Image credit: Dan Rafuse.

After controlling for bias and adjustment of several modifiable parameters, the Maxent software provided a potentially effective predictive model to direct archaeological survey and heritage management in the southern Pampas region. The results of this research suggest that environmental variables; in particular watercourses and slope, were some of the key environmental factors influencing the distribution of hunter-gatherer archaeological sites in the southern Pampas region. The results from this study also reinforced the need for using standardized protocols when working with computer generated distribution models. In order for our models to improve, we need to continue to use these protocols to enhance transparency, reproducibility, evaluation and reuse in the research.

Read the full paper here: Rafuse, D.J., 2021. A Maxent Predictive Model for Hunter-Gatherer Sites in the Southern Pampas, Argentina. Open Quaternary, 7(1), p.6. DOI: http://doi.org/10.5334/oq.97

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Developing new training sets of salt-marsh foraminifera for high-resolution relative sea-level reconstruction in southeastern Australia

Lay Summary authored by Sophie Williams. Read the full paper here: https://www.openquaternary.com/articles/10.5334/oq.93/

High-resolution relative sea-level records are important for understanding both the timings and causes of the onset of modern sea-level rise coming out of the late Holocene. These sea-level reconstructions are created using foraminifera preserved in salt-marsh sediment cores as indicators, taking advantage of the fact that assemblages of modern foraminifera live in distinct vertical niches relative to tide levels. Whilst there are now numerous late Holocene sea-level records for the Northern Hemisphere, there is a paucity of research conducted in the Southern Hemisphere where we would expect higher rates of sea-level rise as a consequence of melting Northern Hemisphere ice. The few high-resolution records from this area show an acceleration in sea-level rise during the early 20th century that is faster than the accelerations seen in both the global mean as well as Northern Hemisphere records. However, these proxy-based records do not agree with instrumental data recorded by tide gauges and so it is important to create new historical sea-level records to address this discrepancy.


The ecological zones of Lutregala salt marsh – the upland is dominated by regenerating grazing land and sclerophyll forest comprised of Eucalyptus forest with a grassy understorey. In the marsh, the flora is comprised of Juncus krausii (salt-marsh rush), Gahnia filum (chaffy saw sedge), Tecticornia arbuscula (shrubby glasswort) and Sarcocornia quinqueflora (beaded glasswort). We take transects of from upland to tidal flat and sample along the elevational gradient. Photo credit: Professor Roland Gehrels.

Two steps were involved in generating the three new training sets using salt-marsh foraminifera from sites in southeastern Australia. The first step was establishing transects crossing all ecological zones within a marsh, surveying the samples we collected relative to a height datum and then identifying the different species within the samples. From this, the distribution and variability of the modern foraminifera was assessed using statistical analyses that look for groups or “clusters” within the data. Many studies have now shown that foraminifera cluster by elevation, which is a proxy for tidal inundation or “hydroperiod”.


Surveying surface samples into the local height datum using a total station at Wapengo salt marsh. Photo credit: Professor Roland Gehrels.

The second step was the creation of transfer function models i.e. regression models that link foraminifera with their heights relative to sea level. These modelled relationships between elevation and modern foraminiferal distributions can be used to calculate past sea-level changes from fossil foraminifera in cores. Some studies find that creating transfer functions from just a local training set (i.e. samples taken within a few km) will provide sufficiently good modern analogues for fossil foraminifera, whereas other studies advocate combining training sets from a region (i.e. samples from several salt marshes within a few hundred kilometres of each other) to obtain a wider range of modern analogues. This latter notion was tested in this study by combining local training sets into a regional model for southeastern Australia. Results show that microtidal coastlines, such as those sampled in this study, yield models with low vertical uncertainty and can help to refine understanding of late Holocene sea-level change in Australia. This will shed light on the discrepancy in rates of sea-level rise observed in proxy and instrumental records in the western Pacific, as well as help to elucidate the causes of the early 20th century sea-level acceleration.   

Full paper: Williams, S., Garrett, E., Moss, P., Bartlett, R. and Gehrels, R., 2021. Development of a Training Set of Contemporary Salt-Marsh Foraminifera for Late Holocene Sea- Level Reconstructions in southeastern Australia. Open Quaternary, 7(1), p.4. DOI: http://doi.org/10.5334/oq.93

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Revised Postglacial Sea-Level Rise and Meltwater Pulses from Barbados

Lay Summary authored by Paul Blanchon. Read the full paper here: https://www.openquaternary.com/articles/10.5334/oq.87/

The precise timing and rate of postglacial sea-level (SL) rise not only provides key insight into the nature of ice sheet disintegration during the last deglacial warming ~15 thousand years ago, but also helps constrain the response to future warming. One of the most complete reconstructions of postglacial SL rise is from Barbados where thick, back-stepping, sequences of the reef-crest coral Acropora palmata have been recovered in cores from the shelf and slope off the south coast. As seen in the figure below, successive reconstructions of SL using the Barbados data show rapid accelerations in SL rise at ~14 and 11 thousand years ago, and these have been linked to pulses of ice and meltwater discharge during the most rapid phase of ice-sheet decay. Similar meltwater pulses have subsequently been found in other SL reconstructions, but their timing, depth and magnitudes show significant differences with those from Barbados.


Successive postglacial sea-level reconstructions from reef-crest drill-core sequences at Barbados. The first 3 reconstructions assume that all dated corals are in growth position and so only plot the age and uplift-corrected depth of individual colonies. They consequently show variations in the timing and magnitude of the meltwater pulses as new coral data are added. Our revised reconstruction, however, shows that many of these data points are from coral clasts. In addition to accounting for this bias, we also add key stratigraphic data, such as the depth of tops and bases of reef-crest units, which allow for a more accurate assessment of the timing and magnitude of meltwater pulses. Figure provided by P. Blanchon.

To help resolve these differences, we re-examine the stratigraphy and growth history of the reef-crest sequences at Barbados and find that rather than consisting only of in-place coral colonies (as previously claimed), they are in-fact composed of a mixture of in-place colonies and large clasts generated by skeletal fragmentation and transport during hurricanes. This finding is important because the downslope transport of clasts complicates the assumption that the reef-crest corals grew within a few metres of SL, and so necessitates a reappraisal of the SL reconstruction and how the depth and magnitude of melt-water pulses are defined.


Classic vista of a coral-reef crest composed of dense thickets of Acropora palmata with wave-oriented branches. Photo credit: P. Blanchon.

By accounting for the bias created by downslope clast transport, we provide a revised SL reconstruction and show that the deepest A. palmata units were deposited on a slope next to deep-water corals, not on a shallow elevated reef-crest structure as previously thought. As a consequence, the onset of the first meltwater pulse, MWP-1a, cannot be identified from Barbados, which explains it’s earlier timing in other SL reconstructions. We also show that the depth and magnitude of the second meltwater pulse, MWP-1b, is best defined from the difference in elevation between the top of the reef-crest that was drowned by the pulse, and the base of the reef-crest that back-stepped after the pulse ended. Using these elevations, with adjustments for water depth, we estimate that the second meltwater pulse was 5 m smaller, shallower, and occurred 150 years later than previously claimed. This smaller magnitude may explain why MWP-1b has not been recognized in the other major SL reconstruction at Tahiti: it may not have been large enough to shift the reef crest into waters with deeper corals, thereby allowing it to simply regrow and catch-up with sea level. So although these new findings help reconcile differences with other reconstructions, they also highlight the limitations and uncertainties in reconstructing SL from more complex reef sequences.


The aftermath of a hurricane, with the decimated reef crest being reduced to a field of rubble. Looking at the contrast to the picture above, it’s easy to understand how our fairweather perspective and limited lifespans bias the interpretation of fossil reef-crest sequences, like those found at Barbados. Photo credit: P. Blanchon.

Full paper: Blanchon, P., Medina-Valmaseda, A. and Hibbert, F.D., 2021. Revised Postglacial Sea-Level Rise and Meltwater Pulses from Barbados. Open Quaternary, 7(1), p.1. DOI: http://doi.org/10.5334/oq.87

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