Holocene “turn-on” and evolution of the Southern Great Barrier Reef: Revisiting reef cores from the Capricorn Bunker Group

Extensive drilling of the Great Barrier Reef (GBR) in the 70s and 80s illuminated the main factors controlling reef growth during the Holocene. However, questions remain about: (1) the precise nature and timing of reef "turnon" or initiation, (2) whether consistent spatio-temporal patterns occur in the bio-sedimentologic response of the reef to Holocene sea-level rise then stability, and (3) how these factors are expressed in the context of the different evolutionary states (juvenile-mature-senile reefs). Combining 21 new C14-AMS and 146 existing recalibrated radiocarbon and U/Th ages, we investigated the detailed spatial and temporal variations in sedimentary facies and coralgal assemblages in fifteen cores across four reefs (Wreck, Fairfax, One Tree and Fitzroy) from the Southern GBR. Our newly defined facies and assemblages record distinct chronostratigraphic patterns in the cores, displaying both lateral zonation across the different reefs and shallowing upwards sequences, characterised by a transition from deep (Porites/faviids) to shallow (Acropora/Isopora) coral types. The revised reef accretion curves show a significant lag period, ranging from 0.7-2 ka, between flooding of the antecedent Pleistocene substrate and Holocene reef turn-on. This lag period and dominance of more environmentally tolerant early colonizers (e.g., domal Porites and faviids), suggests initial conditions that were unfavourable for coral growth. We contend that higher input of fine siliciclastic material from regional terrigenous sources, exposure to hydrodynamic forces and colonisation in deeper waters are the main factors influencing initially reduced growth and development. All four reefs record a time lag and we argue that the size and shape of the antecedent platform is most important in determining the duration between flooding and recolonisation of the Holocene reef. Finally, our study of Capricorn Bunker Group Holocene reefs suggests that the size and shape of the antecedent substrate has a greater impact on reef evolution and final evolutionary state (mature vs. senile), than substrate depth alone. 

A revised age of AD 667-699 for the latest major eruption at Rabaul

The most recent major eruption at Rabaul was one of the largest known events at this complex system, having a VEI rating of 6. The eruption generated widespread airfall pumice lapilli and ash deposits and ignimbrites of different types. The total volume of pyroclastic material produced in the eruption exceeded 11 km3 and led to a new phase of collapse within Rabaul Caldera. Initial 14C dating of the eruptive products yielded an age of about 1400 yrs BP, and the eruption became known as the "1400 BP" eruption. Previous analyses of the timing of the eruption have linked it to events in AD 536 and AD 639. However, we have re-evaluated the age of the eruption using the Bayesian wiggle-match radiocarbon dating method, and the eruption is now thought to
have occurred in the interval AD 667-699. The only significant equatorial eruptions recorded in both Greenland and Antarctic ice during this interval are at AD 681 and AD 684, dates that coincide with frost rings in bristlecone pines of western USA in the same years. Definitively linking the Rabaul eruption to this narrow age range will require identification of Rabaul tephra in the ice records. However, it is proposed that a new working hypothesis for the timing of the most recent major eruption at Rabaul is that it occurred in the interval AD 681-684.

A multi-proxy chronological reconstruction of palaeosalinity in the eastern Limfjord, Denmark

The Jutland peninsula in northern Denmark is home to the Limfjord, one of the largest estuarine bodies of water in the region. Human inhabitance of the Limfjord’s surrounding coastlines stretches back further than 7,800 cal BP, with anthropogenic influence on the landscape beginning approximately 6,000 cal BP. Understanding how the Limfjord as a system has changed throughout time is useful in comprehending subsistence patterns and anthropogenic influence. This research is part of a larger project aimed at discerning subsistence patterns and environmental change in the region. Following the Younger Dryas, as the Fennoscandian ice sheet began to melt, Denmark experienced isostatic rebound, which contributed to the complex sea level history in the region. Between ice melt and isostatic rebound, the Jutland peninsula experienced many transgression and regression events. Connections to surrounding seas have shifted throughout time, with most attention focused on the western connection of the Limfjord with the North Sea, which has experienced numerous closures and subsequent re-openings throughout the Holocene. Furthermore, the Limfjord-North Sea connection has been the focal point of research because of the west to east water flow in the system, and the present day higher salinity in the west compared to the east. Little to no consideration has been paid to the influence of the Kattegat and Baltic on the Limfjord until now. A 10m sediment core was taken from Sebbersund (near Nibe, Limfjord), along the connection between the Limfjord and the Kattegat in the east to understand how the eastern part of the system has changed and differed from changes observed in the west. The Sebbersund sequence spans a majority of the Holocene, from 9600 cal BP to 1030 cal BP, determined via radiocarbon dating of terrestrial macrofossils and bulk sediment. Over this time period palaeoenvironmental conditions were reconstructed through the use of geochemical analyses (13C, 15N, C:N), physical sediment analyses, dinoflagellate cyst abundances and molluscan analyses. apart from two instances of low salinity, one at the top and one at the bottom of the core, the sequence has a strong marine signal for a majority of the Holocene. Radiocarbon dating of bulk sediment samples showed the presence of old carbon in the system, creating an age offset between 1,300 ± 200 and 2,800 ± 200 calibrated 14C years compared to the age-depth curve based on the terrestrial macrofossils. This finding, along with the strong marine influence in the system, discerned through geochemical data, dinoflagellate cyst and mollusc counts, is important for obtaining accurate radiocarbon ages in the region and stresses the importance of understanding both the marine and freshwater reservoir effects. The marine dominance in the eastern Limfjord differs from the west, which is characterized by a number of freshwater events when the North Sea connection was closed off during the Holocene. The eastern connection was open to the Kattegat throughout a large portion of the Holocene, with influx of open ocean water entering the system during periods of higher sea level.

Land use history of Village Bay, Hirta, St Kilda World Heritage Site:A palynological investigation of plaggen soils

This paper presents findings based on a palynological investigation of artificially accreting (plaggen) soils from the settlement of Village Bay, Hirta, in the St Kilda archipelago, which was perhaps the most distant and inhospitable outpost of sustained human habitation in the British Isles. The soils were developed principally through the addition of turf ash and seabird waste, although some ash may have been derived from upland peats. It is assumed that the woodland pollen signal (much lower in the soils than in an upland peat site nearby) represents off-island sources. Corylus avellana-type pollen (frequent in upland sites), along with Potentilla-type, may provide markers in the Village Bay profiles for the addition of ashed hillside turf, and possibly peat, to the plaggen soils. Cereal-type pollen is well represented through the profiles and is often strongly associated with the record for Chrysanthemum segetum (corn marigold), a frequent indicator of arable land. The Brassicaceae signal may partly reflect the cultivation of cabbages; Chelidonium majus (greater celandine) may have been grown for medicinal use. Soil mixing has rendered radiocarbon dating meaningless at this site, but the establishment of a change in cultivation regime before AD 1830 may have been identified from the patterns of pollen concentration and preservation in the profiles. © 2008 Elsevier B.V. All rights reserved.

Chronology of the site of Grotte du Renne, Arcy-sur-Cure, France: implications for Neanderthal symbolic behaviour

Higham et al (2010) published a large series of new dates from the key French Palaeolithic site of the Grotte du Renne at Arcy-sur-Cure. The site is important because it is one of only two sites in Europe in which Châtelperronian lithic remains co-occur with Neanderthal human remains. A large series of dates from the Mousterian, Châtelperronian, Aurignacian and Gravettian levels of the site was obtained. The 14C results showed great variability, which Higham et al (2010) interpreted as most likely to be due to mixing of archaeological material in the site. In contrast, Caron et al (2011) suggested that the site stratigraphy is well preserved and that the problem with the variability in the radiocarbon ages was due to unremoved contamination in the dated bone. In this paper we address their critique of the original Higham et al (2010) paper

Settlement Duration and Materiality:Formal Chronological Models for the Development of Barnhouse, a Grooved Ware Settlement in Orkney

Radiocarbon dating and Bayesian chronological modelling, undertaken as part of the investigation by the Times of Their Lives project into the development of Late Neolithic settlement and pottery in Orkney, has provided precise new dating for the Grooved Ware settlement of Barnhouse, excavated in 1985–91. Previous understandings of the site and its pottery are presented. A Bayesian model based on 70 measurements on 62 samples (of which 50 samples are thought to date accurately the deposits from which they were recovered) suggests that the settlement probably began in the later 32nd century cal bc (with Houses 2, 9, 3 and perhaps 5a), possibly as a planned foundation. Structure 8 – a large, monumental structure that differs in character from the houses – was probably built just after the turn of the millennium. Varied house durations and replacements are estimated. House 2 went out of use before the end of the settlement, and Structure 8 was probably the last element to be abandoned, probably during the earlier 29th century cal bc. The Grooved Ware pottery from the site is characterised by small, medium-sized, and large vessels with incised and impressed decoration, including a distinctive, false-relief, wavy-line cordon motif. A considerable degree of consistency is apparent in many aspects of ceramic design and manufacture over the use-life of the settlement, the principal change being the appearance, from c. 3025–2975 cal bc, of large coarse ware vessels with uneven surfaces and thick applied cordons, and of the use of applied dimpled circular pellets. The circumstances of new foundation of settlement in the western part of Mainland are discussed, as well as the maintenance and character of the site. The pottery from the site is among the earliest Grooved Ware so far dated. Its wider connections are noted, as well as the significant implications for our understanding of the timing and circumstances of the emergence of Grooved Ware, and the role of material culture in social strategies.

Radiocarbon wiggle-match dating of proglacial lake sediments - Implications for the 8.2 ka event

The problem of insufficient age-control limits the utilisation of the 8.2 ka BP event for modelling freshwater forcing in climate change studies. High-resolution radiocarbon dates, magnetic susceptibility and lithostratigraphic evidence from a lake sediment core from Nedre Hervavatnet located at Sygnefjell in western Norway provide a record of the early Holocene. We use the method of radiocarbon wiggle-match dating of the lake sediments using the non-linear relationship between the C-14 calibration curve and the consecutive accumulation order of the sample series in order to build a high-resolution age-model. The timing and duration of Holocene environmental changes is estimated using 38 AMS radiocarbon dates on terrestrial macrofossils, insects and chironomids covering the time period from 9750 to 1180 cal BP. Chironomids, Salix and Betula leaves produce the most consistent results. Sedimentological and physical properties of the core suggest that three meltwater events with high sedimentation rates are superimposed on a long-term trend with glacier retreat between 9750 and 8000 cal BP. The lake sediment sequence of Nedre Hervavatnet demonstrates the following: only a reliable high-resolution geochronology based on carefully selected terrestrial macrofossils allows the reconstruction of a more refined and complex environmental change history before and during the 8.2 ka event. (C) 2009 Elsevier Ltd. All rights reserved.

Precision dating of the Palaeolithic: A new radiocarbon chronology for the Abri Pataud (France), a key Aurignacian sequence

This paper presents a new series of AMS dates on ultrafiltered bone gelatin extracted from identified cutmarked or humanly-modified bones and teeth from the site of Abri Pataud, in the French Dordogne. The sequence of 32 new determinations provides a coherent and reliable chronology from the site's early Upper Palaeolithic levels 5-14, excavated by Hallam Movius. The results show that there were some problems with the previous series of dates, with many underestimating the real age. The new results, when calibrated and modelled using a Bayesian statistical method, allow detailed understanding of the pace of cultural changes within the Aurignacian I and II levels of the site, something not achievable before. In the future, the sequence of dates will allow wider comparison to similarly dated contexts elsewhere in Europe. High precision dating is only possible by using large suites of AMS dates from humanly-modified material within well understood archaeological sequences modelled using a Bayesian statistical method. © 2011.

THE MARINE RADIOCARBON BOMB PULSE ACROSS THE TEMPERATE NORTH ATLANTIC: A COMPILATION OF Delta C-14 TIME HISTORIES FROM ARCTICA ISLANDICA GROWTH INCREMENTS

Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Delta C-14 excess from known-age annual increments of the long-lived bivalve mollusk Arctica islandica from 4 sites across the coastal North Atlantic (German Bight, North Sea; Tromso, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of C-14 at the air-sea boundary, C-14 content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Delta C-14 excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic air-sea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration series for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.

A Bayesian framework for age modeling of radiocarbon-dated peat deposits: Case studies from the Netherlands

Recently, Bayesian statistical software has been developed for age-depth modeling (wiggle-match dating) of sequences of densely spaced radiocarbon dates from peat cores. The method is described in non-statistical terms, and is compared with an alternative method of chronological ordering of 14C dates. Case studies include the dating of the start of agriculture in the northeastern part of the Netherlands, and of a possible Hekla-3 tephra layer in the same country. We discuss future enhancements in Bayesian age modeling.

Asynchrony between the Greenland ice core chronology and the radiocarbon calibration curve? Evidence from Irish bogs

A significant cold event, deduced from the Greenland ice cores, took place between 8200 and 8000 cal. BP. Modeling of the event suggests that higher northern latitudes would have also experienced considerable decreases in precipitation and that Ireland would have witnessed one of the greatest depressions. However, no well-dated proxy record exists from the British Isles to test the model results. Here we present independent evidence for a phase of major pine recruitment on Irish bogs at around 8150 cal. BP. Dendrochronological dating of subfossil trees from three sites reveal synchronicity in germination across the region, indicative of a regional forcing, and allows for high-precision radiocarbon based dating. The inner-rings of 40% of all samples from the north of Ireland dating to the period 8500-7500 cal. BP fall within a 25-yr window. The concurrent colonization of pine on peatland is interpreted as drier conditions in the region and provides the first substantive proxy data in support of a significant hydrological change in the north of Ireland accompanying the 8.2 ka event. The dating uncertainties associated with the Irish pine record and the Greenland Ice Core Chronology 2005 (GICC05) do not allow for any overlap between the two. Our results indicate that the discrepancy could be an artifact of dating inaccuracy, and support a similar claim by Lohne et al. (2013) for the Younger Dryas boundaries. If real, this asynchrony will most likely have affected interpretations of previous proxy alignments.

Freshwater reservoir effect (FRE) on re-dating of the prehistoric Eurasian Steppe cultures

There is a major problem with dating human skeletal material in Eurasian
steppe, possibly due to the freshwater reservoir effects (FRE). The goal of the
project is to examine the extent of the FRE in key areas of Siberia and
Kazakhstan through AMS 14C dating and stable isotope (δ13C, δ15N, δ34S)
analysis of c. 150 archaeological and modern samples. Here, we present the
very first results of the tests. We hope that within next years the study will
provide advanced knowledge of FRE across the region; improved 14C sampling
protocols for 14C and isotopic studies; new data on the chronology, diet and
isotopic ecology of particular archaeological sites, and a database on the
extent and variability of the FRE in the region

Using radiocarbon and stable isotopes to identify sediment carbon sources in an alkaline, humic lake.

We present a pilot study that uses the radiocarbon (∆14C) method to determine the source of carbon buried in the surface sediment of Lough Erne, a humic, alkaline lake in northwest Ireland. ∆14C, δ13C and δ15N values were measured from phytoplankton, dissolved inorganic, dissolved organic and particulate organic carbon. A novel radiocarbon method, Stepped Combustion1 was used to estimate the degree of the burial of terrestrial carbon in surface sediment. The ∆14C values of the low temperature fractions were comparable to algal ∆14C, while the high temperature fractions were 14C-depleted (older than bulk sediment). The ∆14C end-member model indicated that ~64% of carbon in surface sediment was derived from detrital terrestrial carbon. The use of ∆14C in conjunction with stepped combustion allows the quantification of the pathways of terrestrial carbon in the system, which has implications for regional and global carbon burial.
1McGeehin, J., Burr, G.S., Jull, A.J.T., Reines, D., Gosse, J., Davis, P.T., Muhs, D., and Southon, J.R., 2001, Stepped-combustion C-14 dating of sediment: A comparison with established techniques: Radiocarbon, v. 43, p. 255-261.

Palynostratigraphic alignment chronology versus independent dating methods. 14C, OSL and tephra: an example from Lake Fimon, northern Italy

New independent dating evidence is presented for a lacustrine record for which an age-depth model had already been derived through the interpretation of the pollen signal. Quartz OSL ages support radiocarbon ages that were previously considered to suffer an underestimation due to contamination, and imply a younger chronology for the core. The successful identification of the Campanian Ignimbrite as a cryptotephra within the core also validates this younger chronology, as well as extending the known geographical range of this tephra layer within Italy. These new results suggest that care should always be taken when building chronologies from proxy records that are correlated to the tuned records from which the global signal is often derived (i.e. double tuning). We do not offer this as the definitive chronology for Lake Fimon, but multiple lines of dating evidence show that there is sufficient reason to seriously consider it. The Quaternary dating community should always have all age information available, even when significant temporal offsets are apparent between various lines of evidence to be: 1) better informed when they face similar dilemmas in the future and 2) allow multiple working hypotheses to be considered.