Marine 14C Reservoir Research Articles

Evidence of temporal changes in the marine 14C reservoir in the South Pacific and implications for improved dating resolution across a radiocarbon plateau (2600-2350 cal BP)

The settlement of the Pacific is an important chapter in human dispersal for which radiocarbon (14C) dates provide chronological control. At some point during the last 3000 years, Polynesian culture developed within Tonga and Samoa out of earlier ancestral populations. Unfortunately, between ∼2650 and 2350 cal BP, the terrestrial 14C calibration curve used to convert 14C ages into calendar dates is relatively flat, resulting in low precision date interpretations. At this time, the South Pacific marine 14C reservoir appears to have diverged from the terrestrial reservoir for reasons that are not yet understood. This divergence may be key to refining the chronology of coastal sites dating to this broad 14C plateau. We investigate this at the site of Talasiu in Tongatapu – a site with evidence of both late Lapita and early Polynesian ceramics. Moreover, we show how careful evaluation of δ13C and δ18O, in combination with shell taxa diet and habitat, enables shell 14C dates impacted by hard water to contribute and refine chronologies blurred by this 2650-2350 cal BP plateau. Our finding has significant global implications for understanding the relationship between the marine and terrestrial 14C reservoirs and is of interest to those interested in refining dates from this time.

Vital evidence: Change in the marine 14C reservoir around New Zealand (Aotearoa) and implications for the timing of Polynesian settlement

Precise and accurate radiocarbon chronologies are essential to achieve tight chronological control for the ~ 750-years since Polynesian settlement of New Zealand. This goal has, however, been elusive. While radiocarbon datasets in the region are typically dominated by marine and estuarine shell dates, such chronological information has been ignored by those interpreting the timing of key events because a detailed regional calibration methodology for marine shell, comparable to the highly precise Southern Hemisphere calibration curve, is lacking. In this paper, we present the first temporal 14C marine offset (ΔR) model for New Zealand based on paired estuarine/marine and terrestrial radiocarbon dates from 52 archaeological contexts. Our dataset displays significant offsets between the measured New Zealand data and the modelled global marine radiocarbon curve. These shifts are associated with oceanographic fluctuation at the onset of the Little Ice Age ~ AD 1350–1450 (650–500 BP). The application of a regional and temporal correction to archaeological shell dates provides complimentary information to terrestrial radiocarbon production and has the potential to add structure to the blurred chronology that has plagued archaeological theories about the colonization of New Zealand, and other Pacific islands, for decades.

Variability of marine 14C reservoir ages in the Southern Ocean highlighting circulation changes between 1910 and 1950

Recent changes in the Southern Ocean overturning circulation have been attributed either to natural variability or to anthropogenic forcing. The 14C analyses of mollusk shells from Kerguelen Islands evidence a high decadal variability of the sea surface radiocarbon reservoir ages in the southern South Indian ranging from 832 to 1005 (±30) years between 1910 and 1930. Such high variability is common to the different sectors of the Southern Ocean (southern South Pacific and Atlantic), at inter-annual and decadal timescales between 1901 and 1950. Notably, a decrease of Δ14C of ∼40‰ (increased R of ∼290 years) occurred between 1901 and 1940, followed by an increase of ∼30‰ between 1940 and 1958. Using a simple box model of ocean–atmosphere 14CO2 exchange, this aging is attributed to increased upwelling of cold and 14C-depleted subsurface seawaters due to intensified poleward Southern Westerlies. The sea surface 14C aging is indeed well correlated to a positive phase of the Southern Hemisphere Annular Mode and to a cooling of the sea surface temperatures in the Southern Ocean between 1901 and 1940. These pre-1950 sea surface 14C changes highlight the importance of natural changes in wind intensities and ocean dynamics.

Forgotten news: Shellfish isotopic insight into changing sea-level and associated impact on the first settlers of the Mariana Archipelago

Abstract The colonisation of the Pacific is an important chapter in human dispersal for which chronological control is primarily provided by radiocarbon (14C) dates. In this context, the ability to reliably date shellfish is important because alternative dating materials, such as charcoal and bone, are typically highly degraded. However, the interpretation of shell 14C results is not always black and white because 14C is not evenly distributed throughout the marine environment, with estuarine taxa more likely to incorporate terrestrial sources of carbon. Regions where water has percolated through limestone bedrock provide an additional problem since ancient carbon is introduced into the estuarine waters. This “hardwater” has been put forward to explain old 3500 cal. BP results from culturally significant shells recovered from the site of Unai Bapot (Bapot-1) on the island of Saipan (Petchey et al., 2017). While arguments for (Carson and Hung, 2017) and against (Rieth and Athens, 2017) early settlement dates remain polarised, little attention has been given to the idea of change in the marine 14C reservoir over time, or to possible species-specific offsets in shell 14C. In this paper, we further develop a tri-isotope approach using 14C, δ13C, δ18O to identify carbon source. To investigate which shellfish are more prone to erroneous ages we have selected shell taxa that cover a range of nearshore environments commonly found in Pacific archaeological sites; including Anadara antiquata, Gafrarium pectinatum (both estuarine) and Tridacna (marine/reef). To test the possibility of change over time we extend the dating of the site beyond the earliest occupation layers to deposits considered to post-date the end of the mid-Holocene drawdown in sea-level.

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.

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.

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.

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.

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.

Radiocarbon reservoir effects in human bone collagen from northern Iceland

Human bone collagen from a series of Icelandic human pagan graves was radiocarbon (14C) dated to aid understanding of early settlement (landnám) chronologies in northern Iceland. These individuals potentially consumed marine protein. The 14C age of samples containing marine carbon requires a correction for the marine 14C reservoir effect. The proportion of non-terrestrial sample carbon was quantified via measurement of carbon stable isotopes (δ13C) using a simple mixing model, based on δ13C measurements of archaeofaunal samples. Non-terrestrial carbon was also quantified in six pig bones from the archaeofaunal dataset. Assuming all non-terrestrial carbon in human and pig bone collagen was marine-derived, calibrated age ranges calculated using a mixed IntCal09/Marine09 calibration curve were consistent with an early settlement date close to landnám, but several samples returned pre-landnám age ranges. Measurements of nitrogen stable isotopes (δ15N) strongly suggest that many of the human bone collagen samples contain freshwater diet-derived carbon. Icelandic freshwater systems frequently display large freshwater 14C reservoir effects, of the order of 10,000 14C years, and we suggest that the presence of freshwater carbon is responsible for the anomalously early ages within our dataset. In pig samples, the majority of non-terrestrial carbon is freshwater in origin, but in human samples the proportion of freshwater carbon is within the error of the marine component (±10%). This presents a major obstacle to assessing temporal patterns in the ages of human remains from sampled graves, although the majority of grave ages are within the same, broad, calibrated range.

Variability in the marine radiocarbon reservoir effect in Muscat (Sultanate of Oman) during the 4th millennium BC: reflection of taphonomy or environment?

Radiocarbon (14C) dating of archaeological coastal sites in arid areas is challenging because of the relative rarity of datable terrestrial artefacts. Marine artefacts provide an abundant source of carbon, which is technically easy to date but radiocarbon dates need to be corrected for local variations from the global average marine 14C reservoir age (ΔR). In archaeological sites, this is usually done by the comparison of the 14C age measured between coeval pairs of terrestrial and marine samples that have no inbuilt age. Here, we present the results of a study that aims to determine the local 14C marine reservoir effect (MRE) along the Eastern coast of the Arabic Peninsula during the 4th millennium BC, a period of important cultural, demographic and social changes in this region. Previous estimates of the MRE based on associated shells and charcoal vary by about 400 14C yr and this is a serious limitation to the establishment of a precise chronology in the area based on marine material. In order to maximize the chances to obtain contemporaneous terrestrial–marine pairs for a new assessment of the MRE in this region we dated charcoal, shells, fish and turtle bones as well as human bones found in three recently and carefully excavated graves from Ra’s al-Hamra RH5. A large variability was found between charcoals (up to 240 14C yr) and marine specimens (up to 785 14C yr) present in the same grave. This variability was attributed to inbuilt ages, diagenesis and possibly environmental factors although taphonomic processes cannot be excluded. We discarded the oldest charcoals and used the 14C ages obtained on human apatite as a cut-off value to remove the marine outliers. Two out of the three graves provided terrestrial and marine assemblages which did not differ statistically and were used to calculate an average MRE of 645 ± 40 14C yr (ΔR = 255 ± 55 14C yr). This value is consistent with previous estimates based on the 14C dating of marine sediments off Pakistan and suggests stability of the MRE in the Arabian Sea since the 4th millennium BC.

Improving the 14C Dating of Marine Shells from the Canary Islands for Constructing More Reliable and Accurate Chronologies

Radiocarbon dating of closely associated marine mollusk shells and terrestrial material (charred wood or bone) collected from archaeological contexts on Tenerife and Fuerteventura islands allowed us to quantify the marine 14C reservoir effect (ΔR) around the Canary Archipelago. Coastal Fuerteventura has a positive weighted mean ΔR value of +185 ± 30 14C yr, while for Tenerife a range of negative and positive values was obtained, resulting in a ΔR weighted mean value of 0 ± 35 14C yr. These values are in accordance with the hydrodynamic system present off the Canary Islands characterized by a coastal upwelling regime that affects the eastern islands (Fuerteventura and Lanzarote) but not the other islands of the archipelago, namely Tenerife. Because of this oceanographic pattern, we recommend the extrapolation of these results to the remaining islands of the archipelago, i.e. the first value must be used for the eastern islands, while for the central and western islands the acceptable ΔR value is 0 ± 35 14C yr.

Readjustment of glacial radiocarbon chronologies by self-consistent three-dimensional ocean circulation modeling

A critical problem in radiocarbon dating is the spatial and temporal variability of marine 14C reservoir ages. This is particularly true for the time scale beyond the tree-ring calibration range. Here, we propose a method to assess the evolution of marine reservoir ages during the last deglaciation by numerical modeling. We apply a self-consistent iteration scheme in which existing radiocarbon chronologies can be readjusted by transient, three-dimensional simulations of marine and atmospheric Δ14C. To estimate the uncertainties regarding the ocean ventilation during the last deglaciation, we consider various ocean overturning scenarios which are based on different climatic background states. An example readjusting 14C data from the Caribbean points to marine reservoir ages varying between 200 and 900 a during the last deglaciation. Correspondingly, the readjustment leads to enhanced variability of atmospheric Δ14C by ±30‰, and increases the mysterious drop of atmospheric Δ14C between 17.5 and 14.5calka BP by about 20‰.

Tongatapu hardwater: Investigation into the 14C marine reservoir offset in lagoon, reef and open ocean environments of a limestone island

Although significant advances in our understanding of variation in the Pacific marine 14C reservoir have been made over the last ten years, our ability to obtain accurate calibrated ages for shellfish recovered from archaeological sites on Tongatapu remains problematic because of the influence of hardwaters on the central lagoon. Ultimately, this has implications for documenting the chronology of human movement and adaptation in this region. In this paper, we compare marine reservoir (∆R) data obtained from archaeological sites located along the lagoon and open coastline of Tongatapu, and use a combination of ∆R, δ 18O and δ 13C information to confirm a hardwater or open marine 14C signal in the shellfish. Despite documented changes to the lagoon as sea levels fell post-3000 years ago, these results indicate that there has been no noticeable change over time in the inner lagoon reservoir 14C value. Instead, variability in shellfish habitat and feeding modes is of greater concern to researchers using shell for dating, and requires further research.

Marine Radiocarbon Reservoir Effect of Coastal Waters Off Cape Verde Archipelago

Quantification of the marine radiocarbon reservoir effect (ΔR) is essential in order to calibrate conventional 14C dates from marine shell samples with reliability. ΔR also provides information concerning the intensity of coastal upwelling in marine regions influenced by this phenomenon. 14C ages of closely associated marine samples (mollusk shells) and terrestrial samples (goat bones) from São Vicente Island, Cape Verde Archipelago, permitted the first calculation of the marine 14C reservoir effect in this region. A ΔR weighted mean value of 70 ± 70 14C yr was obtained. This value is in accordance with the previously published oceanographic conditions of the region indicating the existence of a seasonal active upwelling regime.

Comment on “Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model” by A. Rodríguez-Ramírez and C.M. Yáñez-Camacho [Marine Geology 254 (2008) 187–196

The application of the regional marine 14C reservoir effect (Δ R) to obtain an accurate calibration of conventional marine shell 14C dates requires prior research concerning the oceanographic conditions and the Δ R of that region. Rodríguez-Ramírez and Yánez-Camacho [A. Rodríguez-Ramírez, C.M. Yánez-Camacho, Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model, Marine Geology 254 (2008) 187–196] and afterwards A. Rodríguez-Ramírez, J.A. Morales, J. Borrego and E.G. San Miguel in a reply [A. Rodríguez-Ramírez, J.A. Morales, J. Borrego, E.G. San Miguel, Reply to the comment on “Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model” by A. Rodríguez-Ramírez and C.M. Yáñez-Camacho [Marine Geology 254 (2008) 187–196], Marine Geology 263 (2009) 123–125] to the comment by J. Rodríguez-Vidal, F. Ruiz and L.M. Cáceres on the paper mentioned above [J. Rodríguez-Vidal, F. Ruiz, L. M. Cáceres, Comment on “Formation of chenier plain of the Doñana marshland (SW Spain): Observations and geomorphic model” by A. Rodríguez-Ramírez, C.M. Yáñez-Camacho [Marine Geology 254 (2008) 187–196], Marine Geology 263 (2009) 120–122] use, in both cases, not only incorrect Δ R values for the calibration of 14C dates obtained from shell samples collected from the east coast of the Gulf of Cádiz, but they also confuse the Δ R concept with that of R( t), the 14C reservoir age. Because the misunderstanding of these concepts by these authors and, in the first case, also their failure to take into account the Δ R values obtained by us (and already published) from the east coast of Gulf of Cádiz, all the calibrated dates presented either in the first paper or in the reply cannot be accepted. Here I present a new calibrated dataset using accurate Δ R values and I recommend that the conclusions obtained by Rodríguez-Ramírez and their collaborators be revised, as J. Rodríguez-Vidal, F. Ruiz and L.M. Cáceres proposed in their comment.