Marine 14C Research Articles

Seasonal radiocarbon reservoir ages for the 17th century James River, Virginia estuary

This study utilizes a combined stable isotope and 14C dating approach to determine the radiocarbon reservoir age correction, ΔR, for the James River, Virginia estuary from 17th century Crassostrea virginica shells of known collection dates. ΔR, which can vary spatially and temporally, is a locality-specific adjustment applied to the global ocean reservoir, R, to further account for the offset between the atmospheric and marine 14C calibration curves. To assess the temporal variability in ΔR, continuous δ18O sampling along the oyster shell hinge provides a seasonal record throughout the oyster's life. This is then used to identify sampling locations for 14C measurements based on calcite precipitated during the Summer (>19 °C) and Fall through Spring (F-Sp, <15 °C) months. The resulting seasonal ΔR values range from −151 ± 46 to +109 ± 55 14C years (260 years) due to changes in the contribution and age of dissolved inorganic carbon (DIC) from marine and freshwater sources in the James River estuary. The F-Sp samples display a larger ΔR range than the Summer samples, as do the shells precipitated during drought conditions (1606–1612) when compared to shells from the remainder of the 17th century. The largest intrashell ΔR variability, 195 14C years, is similarly found in a drought shell and is attributed to variability caused by the extreme regional 1606–1612 drought. Early land use changes related to European development and farming practices also altered the age of DIC in the James River estuary. We estimate that the soil inorganic carbon (SIC) contributing to freshwater DIC ranged from 0 to ∼1800 years old and reflected both the drought and land use changes that occurred during the 17th century. Using only the Summer samples, which represent the majority of shell calcite, we obtain a mean ΔR = −32 ± 11 14C years (1σ) for 17th century James River estuary ΔR at the very onset of European colonization. Employing a seasonally resolved sampling method will provide the greatest constraint on 14C measurements in an estuarine environment where multiple carbon sources can fluctuate on seasonal timescales and as a result of large scale environmental change.

An Online Application for ΔR Calculation

AbstractA regional offset (ΔR) from the marine radiocarbon calibration curve is widely used in calibration software (e.g. CALIB, OxCal) but often is not calculated correctly. While relatively straightforward for known-age samples, such as mollusks from museum collections or annually banded corals, it is more difficult to calculate ΔR and the uncertainty in ΔR for 14C dates on paired marine and terrestrial samples. Previous researchers have often utilized classical intercept methods that do not account for the full calibrated probability distribution function (pdf). Recently, Soulet (2015) provided R code for calculating reservoir ages using the pdfs, but did not address ΔR and the uncertainty in ΔR. We have developed an online application for performing these calculations for known-age, paired marine and terrestrial 14C dates and U-Th dated corals. This article briefly discusses methods that have been used for calculating ΔR and the uncertainty and describes the online program deltar, which is available free of charge.

A radiocarbon investigation of Moriori forest use on Rēkohu (Chatham Island), southwestern Polynesia

The first colonists of temperate climate, southwestern Polynesia settled an archipelago unsuited generally to the cultivation of several tropical homeland crops, including fruiting trees. On the Chatham Islands, these colonists achieved settlement permanency after the thirteenth century AD to become the indigenous Moriori in the absence of all Polynesian domesticates. We test the thesis that edible and storable seeds of introduced New Zealand karaka or (in Moriori) kōpi trees (Corynocarpus laevigatus J.R. Forst. & G. Forst.) replaced tropical crops in the Moriori economy. Archaeological midden sites associated with kōpi are dated by radiocarbon (14C) from Rēkohu (Chatham Island), the largest island of the Chathams group. We examine new accelerator mass spectrometry ages for individual kōpi seeds and twigs <10years old and review extant standard ages. A local marine 14C value is determined to improve confidence in mollusc dates. Our results include the earliest reliable 14C age on a kōpi seed from Rēkohu (calyrAD 1450–1620, 95% probability). Strategic tree plantings in sheltered locations and initial if not ongoing forest management are indicated. Archaeological evidence of comparable, later, leeward and windward island Corynocarpus use suggests that kōpi production supported the permanent Moriori settlement of Rēkohu.

Marine Radiocarbon Reservoir Effect in Late Pleistocene and Early Holocene Coastal Waters off Northern Iberia

AbstractRadiocarbon dating of closely associated marine mollusk shells and terrestrial material (mammal bones or charred wood) collected from archaeological contexts in northern Atlantic Iberian coastal areas is used to quantify the marine14C reservoir effect (ΔR) for the coastal waters off the Cantabrian coast of northern Iberia. For the first time, ΔR values were reliably determined for these coastal waters and, also for the first time, a ΔR was calculated for the Late Pleistocene in Atlantic Iberia. Pairs of coeval samples of different carbon reservoirs selected from Upper Paleolithic (Late Pleistocene) and Mesolithic (Early Holocene) contexts yielded ΔR weighted mean values of –117±7014C yr and –105±2114C yr, respectively. These values show oceanographic conditions characterized by a reduced offset between atmospheric and surface water14C contents, suggesting a nonexistent or very weak upwelling and some stratification of the water column. Similar oceanographic conditions have been recorded in other areas of Atlantic Iberia during the Holocene, such as off Andalusian and northwestern Galician coasts. Results not only provide useful information on environmental conditions but also a framework to obtain more precise and reliable absolute chronologies for the Late Pleistocene and Early Holocene in northern Iberia.

Punctuated Shutdown of Atlantic Meridional Overturning Circulation during Greenland Stadial 1.

The Greenland Stadial 1 (GS-1; ~12.9 to 11.65 kyr cal BP) was a period of North Atlantic cooling, thought to have been initiated by North America fresh water runoff that caused a sustained reduction of North Atlantic Meridional Overturning Circulation (AMOC), resulting in an antiphase temperature response between the hemispheres (the ‘bipolar seesaw’). Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon (14C) record spanning GS-1. By precisely aligning Southern and Northern Hemisphere tree-ring 14C records with marine 14C sequences we document two relatively short periods of AMOC collapse during the stadial, at ~12,920-12,640 cal BP and 12,050-11,900 cal BP. In addition, our data show that the interhemispheric atmospheric 14C offset was close to zero prior to GS-1, before reaching ‘near-modern’ values at ~12,660 cal BP, consistent with synchronous recovery of overturning in both hemispheres and increased Southern Ocean ventilation. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our findings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes.

High-precision dating and correlation of ice, marine and terrestrial sequences spanning Heinrich Event 3: Testing mechanisms of interhemispheric change using New Zealand ancient kauri (Agathis australis)

Robustly testing hypotheses of geographic synchroneity of abrupt and extreme change during the late Pleistocene (60,000 to 11,650 years ago) requires a level of chronological precision often lacking in ice, marine and terrestrial sequences. Here we report a bidecadally-resolved New Zealand kauri (Agathis australis) tree-ring sequence spanning two millennia that preserves a record of atmospheric radiocarbon (14C) during ice-rafted debris event Heinrich Event 3 (HE3) in the North Atlantic and Antarctic Isotope Maximum 4 (AIM4) in the Southern Hemisphere. Using 14C in the marine Cariaco Basin and 10Be preserved in Greenland ice, the kauri 14C sequence allows us to precisely align sequences across this period. We observe no significant difference between atmospheric and marine 14C records during HE3, suggesting no stratification of surface waters and collapse in Atlantic Meridional Overturning Circulation (AMOC). Instead our results support recent evidence for a weakened AMOC across at least two millennia of the glacial period. Our work adds to a growing body of literature confirming that Heinrich events are not the cause of stadial cooling and suggests changes in the AMOC were not the primary driver of antiphase temperature trends between the hemispheres. Decadally-resolved 14C in ancient kauri offers a powerful new (and complementary) approach to polar ice core CH4 alignment for testing hypotheses of abrupt and extreme climate change.

A Revised Radiocarbon Chronology of the Aceramic Shell Midden of Ra’s Al-Hamra 6 (Muscat, Sultanate of Oman): Implication For Occupational Sequence, Marine Reservoir Age, and Human Mobility

AbstractRa’s al-Hamra 6 (RH-6) is one of the earliest stratified archaeological sites along the eastern littoral of the Arabian Peninsula. This shell midden was radiocarbon dated to the 6th–5th millennium cal BC, but the majority of the dates were obtained before the advent of accelerator mass spectrometry (AMS) 14C dating and suffer from large uncertainties. In addition, most of these dates were obtained on marine and mangrove shells and required correction for local variations from the global average marine 14C reservoir age (MRA). This proved difficult because no consensus value exists for this period in the area. Recent excavations at RH-6 offered the opportunity to redate this important site in order to precisely determine its occupation history and later use as a graveyard, and establish the marine reservoir effect for this time period. Thirty-eight samples of charcoal, shells, and human bone apatite were selected for 14C dating. Bayesian modeling of the 14C dates suggests that the formation of the shell midden spanned ~1 millennium, between the mid-6th and the mid-5th millennium cal BC. Positive and consistent ΔR values were calculated throughout the entire sequence, ranging from 99±27 to 207±43 14C yr. At the beginning of the 4th millennium cal BC, RH-6 was used as a graveyard, as suggested by the 14C dating of a shell in strict association with an individual buried at the surface of the site. 14C dating of human bone apatite allowed us to calculate that 89% of this individual’s diet derived from marine resources. This finding confirms previous observations showing the overwhelming presence of marine and mangrove-dwelling species in the faunal and charcoal assemblage, and implies a low mobility, or mobility restricted to the coast for this population during the 4th millennium cal BC.

On the age of the Khvalynian deposits of the Caspian Sea coasts according to 14C and 230Th/234U methods

During the second half of the late Pleistocene, the Caspian experienced repeated transgressions (Early and Late Khvalynian) and regressions (Enotaevsk and Mangyshlak) with an oscillation amplitude of 120–150 m. The question about the age of the Khvalynian deposits is controversial. The investigation presents the age chronology of the Khvalynian deposits of the Caspian coasts on the basis of marine terrace stratigraphy and 14C and 230Th/234U dating conducted in the Laboratory of the Saint-Petersburg State University. Forty samples of mollusc material from Khvalynian deposits were dated. For dating, the shells of index-genus Didacna from the deposits of marine terraces with different elevations were sampled. Besides shells, a fragment of bone from Equus sp. was dated. The analysis of dating showed that during the maximum of the Late Valdai (Wurm) glaciation the Khvalynian basin was in a regressive situation. The maximum stage (+48 to +50 m) of the Early Khvalynian transgression was not dated. Transgressive stages of the Early Khvalynian basin with sea levels of +35 and +22 m occurred during the period of deglaciation approximately 16 ka cal BP and 14 ka cal BP. The transgressive stages of the Late Khvalynian basin with sea level at about 0 m and −12 m occurred 14–12 ka cal BP. Probably, the age of deposits of Makhachkala stage with level about 0 m reflected an Allerod warming, and the age of deposits of Sartassy stage with level about −12 is associated with warming at the end of Younger Dryas. Under cold climate conditions of Younger Dryas the level of the Late Khvalynian basin fell. Increasingly continental climatic conditions during the Boreal period of the Holocene resulted in the Mangyshlak regression.

Large variations in the Holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes

Accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect. This effect for a particular site/region is generally assumed constant through time when calibrating marine 14C ages. However, recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late Quaternary and Holocene. Here we report marine radiocarbon reservoir correction (ΔR) for Heron Reef and Moreton Bay in southwestern (SW) Pacific for the last 8 ka derived from 14C analysis of 230Th-dated corals. Most of our ΔR for the last ∼5.4 ka agree well with their modern value, but large ΔR variability of ∼410 yr (from trough to peak) with possible decadal/centennial fluctuations is evident for the period ∼5.4–8 ka. The latter time interval also has significant variations with similar features in previously published ΔR values for other sites in the Pacific, including southern Peru–northern Chile in southeastern (SE) Pacific, the South China Sea, Vanuatu and Papua New Guinea, with the largest magnitude of ∼920 yr from SE Pacific. The mechanisms for these large ΔR variations across the Pacific during the mid-Holocene are complex processes involving (1) changes in the quantity and 14C content of upwelled waters in tropical east Pacific (TEP) (frequency and intensity of ocean upwelling in the TEP, and contribution of Subantarctic Mode Water to the upwelled waters, which is influenced by the intensity and position of southern westerly winds), and (2) variations in ocean circulation associated with climate change (La Niña/El Niño conditions, intensity of easterly trade winds, positions of the Intertropical Convergence Zone and the South Pacific Convergence Zone), which control the spreading of the older upwelled surface waters in the TEP to the western sites. Our results imply the need for employing temporal changes in ΔR values, instead of constant (modern) values, for age calibration of Holocene marine samples not only for the SW Pacific sites but also for other tropical and subtropical sites in the Pacific.

Marine Radiocarbon Reservoir Values in Southern California Estuaries: Interspecies, Latitudinal, and Interannual Variability

Many studies use radiocarbon dates on estuarine shell material to build age-depth models of sediment accumulation in estuaries in California, USA. Marine 14C ages are typically older than dates from contemporaneous terrestrial carbon and local offsets (ΔR) from the global average marine offset need to be calculated to ensure the accuracy of calibrated dates. We used accelerator mass spectrometry (AMS) 14C dating on 40 pre-1950 salt marsh snail and clam shells previously collected from four California estuaries. The average ΔR and standard deviation of 217 ± 129 14C yr is consistent with previous calculations using mixed estuarine and marine samples, although the standard deviation and resulting age uncertainty was higher for our estuarine calculations than previous studies. There was a slight but significant difference (p = 0.024) in ΔR between epifaunal snails (ΔR = 171 ± 154 14C yr) and infaunal clams (ΔR = 263 ± 77 14C yr), as well as between samples from individual estuaries. However, a closer examination of the data shows that even for the same species, at the same estuary, ΔR can vary as much as ∼500 14C yr. In some cases, the bulk of this variation occurs between samples collected by different collectors at different times, potentially indicating time dependence in carbon sources and ΔR variation. These variations could also be attributed to differences in collection location within a single estuary and resulting spatial differences in carbon sources. Intertidal specimens located in the high marsh may have lower ΔR than fully marine counterparts because of increased terrestrial 14C input. The large variations in ΔR here highlight the need for conservative chronological interpretations, as well as the assumption of wide uncertainties, when dating samples from estuarine sources.

Slipstream: an early Holocene slump and turbidite record from the frontal ridge of the Cascadia accretionary wedge off western Canada and paleoseismic implications

Slipstream Slump, a well-preserved 3 km wide sedimentary failure from the frontal ridge of the Cascadia accretionary wedge 85 km off Vancouver Island, Canada, was sampled during Canadian Coast Guard Ship (CCGS) John P. Tully cruise 2008007PGC along a transect of five piston cores. Shipboard sediment analysis and physical property logging revealed 12 turbidites interbedded with thick hemipelagic sediments overlying the slumped glacial diamict. Despite the different sedimentary setting, atop the abyssal plain fan, this record is similar in number and age to the sequence of turbidites sampled farther to the south from channel systems along the Cascadia Subduction Zone, with no extra turbidites present in this local record. Given the regional physiographic and tectonic setting, megathrust earthquake shaking is the most likely trigger for both the initial slumping and subsequent turbidity currents, with sediments sourced exclusively from the exposed slump face of the frontal ridge. Planktonic foraminifera picked from the resedimented diamict of the underlying main slump have a disordered cluster of 14C ages between 12.8 and 14.5 ka BP. For the post-slump stratigraphy, an event-free depth scale is defined by removing the turbidite sediment intervals and using the hemipelagic sediments. Nine 14C dates from the most foraminifera-rich intervals define a nearly constant hemipelagic sedimentation rate of 0.021 cm/year. The combined age model is defined using only planktonic foraminiferal dates and Bayesian analysis with a Poisson-process sedimentation model. The age model of ongoing hemipelagic sedimentation is strengthened by physical property correlations from Slipstream events to the turbidites for the Barkley Canyon site 40 km south. Additional modelling addressed the possibilities of seabed erosion or loss and basal erosion beneath turbidites. Neither of these approaches achieves a modern seabed age when applying the commonly used regional marine 14C reservoir age of 800 years (marine reservoir correction ΔR = 400 years). Rather, the top of the core appears to be 400 years in the future. A younger marine reservoir age of 400 years (ΔR = 0 years) brings the top to the present and produces better correlations with the nearby Effingham Inlet paleo-earthquake chronology based only on terrestrial carbon requiring no reservoir correction. The high-resolution dating and facies analysis of Slipstream Slump in this isolated slope basin setting demonstrates that this is also a useful type of sedimentary target for sampling the paleoseismic record in addition to the more studied turbidites from submarine canyon and channel systems. The first 10 turbidites at Slipstream Slump were deposited between 10.8 and 6.6 ka BP, after which the system became sediment starved and only two more turbidites were deposited. The recurrence interval for the inferred frequent early Holocene megathrust earthquakes is 460 ± 140 years, compatible with other estimates of paleoseismic megathrust earthquake occurrence rates along the subduction zone.

Larger CO₂ source at the equatorial Pacific during the last deglaciation.

While biogeochemical and physical processes in the Southern Ocean are thought to be central to atmospheric CO2 rise during the last deglaciation, the role of the equatorial Pacific, where the largest CO2 source exists at present, remains largely unconstrained. Here we present seawater pH and pCO2 variations from fossil Porites corals in the mid equatorial Pacific offshore Tahiti based on a newly calibrated boron isotope paleo-pH proxy. Our new data, together with recalibrated existing data, indicate that a significant pCO2 increase (pH decrease), accompanied by anomalously large marine 14C reservoir ages, occurred following not only the Younger Dryas, but also Heinrich Stadial 1. These findings indicate an expanded zone of equatorial upwelling and resultant CO2 emission, which may be derived from higher subsurface dissolved inorganic carbon concentration.

North Atlantic marine radiocarbon reservoir ages through Heinrich event H4: a new method for marine age model construction

Abstract Cooling and sinking of dense saline water in the Norwegian–Greenland Sea is essential for the formation of North Atlantic Deep Water. The convection in the Norwegian–Greenland Sea allows for a northward flow of warm surface water and southward transport of cold saline water. This circulation system is highly sensitive to climate change and has been shown to operate in different modes. In ice cores the last glacial period is characterized by millennial-scale Dansgaard–Oeschger (D–O) events of warm interstadials and cold stadials. Similar millennial-scale variability (linked to D–O events) is evident from oceanic cores, suggesting a strong coupling of the atmospheric and oceanic circulations system. Particularly long-lasting cold stadials correlate with North Atlantic Heinrich events, where icebergs released from the continents caused a spread of meltwater over the northern North Atlantic and Nordic seas. The meltwater layer is believed to have caused a stop or near-stop in the deep convection, leading to cold climate. The spreading of meltwater and changes in oceanic circulation have a large influence on the carbon exchange between atmosphere and the deep ocean and lead to profound changes in the 14 C activity of the surface ocean. Here we demonstrate marine 14 C reservoir ages ( R ) of up to c. 2000 years for Heinrich event H4. Our R estimates are based on a new method for age model construction using identified tephra layers and tie-points based on abrupt interstadial warmings.

Application of 34S analysis for elucidating terrestrial, marine and freshwater ecosystems: Evidence of animal movement/husbandry practices in an early Viking community around Lake Mývatn, Iceland

Carbon and nitrogen stable isotope ratios (δ13C and δ15N) have been used widely in archaeology to investigate palaeodiet. Sulphur stable isotope ratios (δ34S) have shown great promise in this regard but the potential of this technique within archaeological science has yet to be fully explored. Here we report δ34S, δ13C and δ15N values for 129 samples of animal bone collagen from Skútustaðir, an early Viking age (landnám) settlement in north-east Iceland. This dataset represents the most comprehensive study to date of its kind on archaeological material and the results show a clear offset in δ34S values between animals deriving their dietary resources from terrestrial (mean=+5.6±2.8‰), freshwater (mean=−2.7±1.4‰) or marine (mean=+15.9±1.5‰) reservoirs (with the three food groups being significantly different at 2σ). This offset allows reconstruction of the dietary history of domesticated herbivores and demonstrates differences in husbandry practices and animal movement/trade, which would be otherwise impossible using only δ13C and δ15N values. For example, several terrestrial herbivores displayed enriched bone collagen δ34S values compared to the geology of the Lake Mývatn region, indicating they may have been affected by sea-spray whilst being pastured closer to the coast, before being traded inland. Additionally, the combination of heavy δ15N values coupled with light δ34S values within pig bone collagen suggests that these omnivores were consuming freshwater fish as a significant portion of their diet. Arctic foxes were also found to be consuming large quantities of freshwater resources and radiocarbon dating of both the pigs and foxes confirmed previous studies showing that a large freshwater radiocarbon (14C) reservoir effect exists within the lake. Overall, these stable isotope and 14C data have important implications for obtaining a fuller reconstruction of the diets of the early Viking settlers in Iceland, and may allow a clearer identification of the marine and/or freshwater 14C reservoir effects that are known to exist in human bone collagen.

Early Holocene M~6 explosive eruption from Plosky volcanic massif (Kamchatka) and its tephra as a link between terrestrial and marine paleoenvironmental records

We report tephrochronological and geochemical data on early Holocene activity from Plosky volcanic massif in the Kliuchevskoi volcanic group, Kamchatka Peninsula. Explosive activity of this volcano lasted for ~1.5 kyr, produced a series of widely dispersed tephra layers, and was followed by profuse low-viscosity lava flows. This eruptive episode started a major reorganization of the volcanic structures in the western part of the Kliuchevskoi volcanic group. An explosive eruption from Plosky (M~6), previously unstudied, produced tephra (coded PL2) of a volume of 10–12 km3 (11–13 Gt), being one of the largest Holocene explosive eruptions in Kamchatka. Characteristic diagnostic features of the PL2 tephra are predominantly vitric sponge-shaped fragments with rare phenocrysts and microlites of plagioclase, olivine and pyroxenes, medium- to high-K basaltic andesitic bulk composition, high-K, high-Al and high-P trachyandesitic glass composition with SiO2 = 57.5–59.5 wt%, K2O = 2.3–2.7 wt%, Al2O3 = 15.8–16.5 wt%, and P2O5 = 0.5–0.7 wt%. Other diagnostic features include a typical subduction-related pattern of incompatible elements, high concentrations of all REE (>10× mantle values), moderate enrichment in LREE (La/Yb ~ 5.3), and non-fractionated mantle-like pattern of LILE. Geochemical fingerprinting of the PL2 tephra with the help of EMP and LA-ICP-MS analyses allowed us to map its occurrence in terrestrial sections across Kamchatka and to identify this layer in Bering Sea sediment cores at a distance of >600 km from the source. New high-precision 14C dates suggest that the PL2 eruption occurred ~10,200 cal BP, which makes it a valuable isochrone for early Holocene climate fluctuations and permits direct links between terrestrial and marine paleoenvironmental records. The terrestrial and marine 14C dates related to the PL2 tephra have allowed us to estimate an early Holocene reservoir age for the western Bering Sea at 1,410 ± 64 14C years. Another important tephra from the early Holocene eruptive episode of Plosky volcano, coded PL1, was dated at 11,650 cal BP. This marker is the oldest geochemically characterized and dated tephra marker layer in Kamchatka to date and is an important local marker for the Younger Dryas—early Holocene transition. One more tephra from Plosky, coded PL3, can be used as a marker northeast of the source at a distance of ~110 km.

Planktic Foram Dates from the Indonesian Arc: Marine 14C Reservoir Ages and a Mythical AD 535 Volcanic Eruption

The Indonesian Arc represents the subduction of the Indian-Australian plate beneath Asia. It has been the scene of catastrophic tectonic activity, including the recent 2004 M=9.1 Aceh earthquake and resulting Indian Ocean tsunami. We have dated planktonic forams associated with historic tephras (Tambora, 1815 and Krakatau, 1883) in marine sediment cores to determine radiocarbon reservoir ages for 2 locations along the arc. Our best estimates for 19th century regional reservoir corrections (ΔR) are +90 ± 40 yr for surface-dwelling species and +220 ± 40 yr for mixed planktic assemblages containing some upper thermocline species, but scatter in the data suggests that past surface reservoir ages may have varied by about ±100 yr. We used the results of this study to investigate a proposed very large AD 535 eruption at or near Krakatau. We find no evidence for ash from such an eruption, and although this is negative evidence, we consider it sufficiently strong to rule out any possibility that one took place.

High-resolution radiocarbon dating of marine materials in archaeological contexts: radiocarbon marine reservoir variability between Anadara, Gafrarium, Batissa, Polymesoda spp. and Echinoidea at Caution Bay, Southern Coastal Papua New Guinea

The remains of shellfish dominate many coastal archaeological sites in the Pacific and provide a wealth of information about economy, culture, environment and climate. Shells are therefore the logical sample type to develop local and regional radiocarbon chronologies. The calibration of radiocarbon (14C) dates on marine animals is not straightforward, however, requiring an understanding of habitat and dietary preferences as well as detailed knowledge of local ocean conditions. The most complex situations occur where terrestrial influences impinge on the marine environment resulting in both the enrichment and depletion of 14C (Ulm Geoarchaeology 17(4):319–348, 2002; Petchey and Clark Quat Geochronol 6:539–549, 2011). A sampling protocol that combines a high-resolution excavation methodology, selection of short-lived samples identified to species level, and a tri-isotope approach using 14C, δ13C and δ18O, has given us the ability to identify 14C source variation that would otherwise have been obscured. Here, we present new research that details high-resolution mapping of marine 14C reservoir variation between Gafrarium tumidum, Gafrarium pectinatum, Anadara granosa, Anadara antiquata, Batissa violacea, Polymesoda erosa and Echinoidea from the Bogi 1 archaeological site, Caution Bay, southern coastal Papua New Guinea. These isotopes highlight specific dietary, habitat and behavioural variations that are key to obtaining chronological information from shell radiocarbon determinations.

The complexity of marine 14C chronologies in Arctic Canada: variable ΔR values, enhanced deep water reservoirs, and the Portlandia effect

The complexity of marine 14C chronologies in Arctic Canada: variable ΔR values, enhanced deep water reservoirs, and the Portlandia effect

Precisely dated AMS 14C marine cores reveal the complexity of millennial-scale Asian monsoon variability in the northern South China Sea (MD972146, MD972148)

High sedimentation rate (SR) cores retrieved from the South China Sea (SCS) form the basis for studying the marine components of millennial-scale Asian monsoon (AM) variability and for comparison with the AM reconstructions from cave records on land (e.g. Dongge and Hulu). However, carefully correlating the SCS sedimentary records to the cave records that are precisely dated by U/Th methods with resolution of decadal-scale, has not been completed. Such a correlation is essential when comparing AM influences expressed over land and sea, but requires a construction of marine AMS 14C age models that are precise enough to be compared to the cave U/Th age models. For the purpose of establishing such a correlation, this study presents new data from intensive AMS 14C dated marine cores retrieved from the northern SCS (MD972146, MD972148). The discrepancy of marine and cave δ18O record for the interval of ∼18–30ka might be due to the change of marine 14C reservoir age in SCS surface water during the glacial period, and to the change in interhemispheric dominance of the AM systems. With the new AMS 14C dating on MD972146 and MD972148, we examined the millennial-scale records of planktonic foraminifer δ18O and carbonate contents of MD972146, MD97248, and SONNE 17940-2 and compared those records with Dongge–Hulu δ18O record of the past 30ka. Our results show that in the intervals corresponding to the high-latitude Northern Hemisphere (NH) Younger Dryas (YD) and Heinrich I event (H1), the AMS 14C dated millennial-scale oscillations show relatively heavy δ18O and low carbonate contents, but H2 and H3 are in the opposite direction. Our results indicate the complexity for the marine cores which were used in interpreting the millennial-scale AM variability.

Late-Holocene marine radiocarbon reservoir correction (ΔR) for the west coast of South Africa

In order to calibrate radiocarbon ages based on samples with a marine carbon component it is important to know the marine carbon reservoir correction or ΔR value. This study measured the ΔR on both known-age pre-bomb marine shells and paired marine and terrestrial samples from two regions on the west coast of South Africa: the southwestern Cape and Namaqualand. Pooling the data by region produces ΔR values that are similar enough to use a west coast weighted mean ΔR of 146 ± 85 14C years to correctly calibrate marine shell or mixed marine and terrestrial 14C ages. There are however temporal differences in ΔR throughout the Holocene, which we compare with proxy data for upwelling and sea surface temperatures.