Marine Reservoir Age Research Articles

Radiocarbon Chronometry of Site QJ-280, Quebrada Jaguay, a Terminal Pleistocene to Early Holocene Fishing Site in Southern Peru

ABSTRACTExcavations in 1970, 1996, and 1999 at Site QJ-280, Quebrada Jaguay, in southern Peru, yielded enough dateable terrestrial plant material to establish an extensive radiocarbon chronology for the site. QJ-280 is one of oldest well-dated fishing sites in the Americas: it was occupied from the terminal Pleistocene to the mid-Holocene (about 13,000–8,300 calibrated years BP) based on 42 terrestrial radiocarbon dates, encompassing the Jaguay and Machas Phases of the local archaeological sequence. In addition to the terrestrial dates, radiocarbon measurements on valves of two marine surf clam (Mesodesma donacium) individuals from a single, well-dated mid-Holocene Manos Phase archaeological context have provided insight into marine upwelling conditions during the occupation of Quebrada Jaguay. The marine reservoir age varied between 130 and 730 14C years during the brief lives of the two clams (up to 5 years each), and varied by up to 530 14C years within an individual valve, suggesting strong and variable deep marine upwelling; conditions broadly similar to those that exist in coastal Peru today. These rapid variations in marine radiocarbon age suggest that marine radiocarbon dates from environments with variable upwelling could be skewed by up to hundreds of years.

The 3.6 ka Aniakchak tephra in the Arctic Ocean: a constraint on the Holocene radiocarbon reservoir age in the Chukchi Sea

Abstract. The caldera-forming eruption of the Aniakchak volcano in the Aleutian Range on the Alaskan Peninsula at 3.6 cal kyr BP was one of the largest Holocene eruptions worldwide. The resulting ash is found as a visible sediment layer in several Alaskan sites and as a cryptotephra on Newfoundland and Greenland. This large geographic distribution, combined with the fact that the eruption is relatively well constrained in time using radiocarbon dating of lake sediments and annual layer counts in ice cores, makes it an excellent stratigraphic marker for dating and correlating mid–late Holocene sediment and paleoclimate records. This study presents the outcome of a targeted search for the Aniakchak tephra in a marine sediment core from the Arctic Ocean, namely Core SWERUS-L2-2-PC1 (2PC), raised from 57 m water depth in Herald Canyon, western Chukchi Sea. High concentrations of tephra shards, with a geochemical signature matching that of Aniakchak ash, were observed across a more than 1.5 m long sediment sequence. Since the primary input of volcanic ash is through atmospheric transport, and assuming that bioturbation can account for mixing up to ca. 10 cm of the marine sediment deposited at the coring site, the broad signal is interpreted as sustained reworking at the sediment source input. The isochron is therefore placed at the base of the sudden increase in tephra concentrations rather than at the maximum concentration. This interpretation of major reworking is strengthened by analysis of grain size distribution which points to ice rafting as an important secondary transport mechanism of volcanic ash. Combined with radiocarbon dates on mollusks in the same sediment core, the volcanic marker is used to calculate a marine radiocarbon reservoir age offset ΔR = 477 ± 60 years. This relatively high value may be explained by the major influence of typically carbon-old Pacific waters, and it agrees well with recent estimates of ΔR along the northwest Alaskan coast, possibly indicating stable oceanographic conditions during the second half of the Holocene. Our use of a volcanic absolute age marker to obtain the marine reservoir age offset is the first of its kind in the Arctic Ocean and provides an important framework for improving chronologies and correlating marine sediment archives in this region. Core 2PC has a high sediment accumulation rate averaging 200 cm kyr−1 throughout the last 4000 years, and the chronology presented here provides a solid base for high-resolution reconstructions of late Holocene climate and ocean variability in the Chukchi Sea.

The Usiminas shellmound on the Cabo Frio Island: Marine reservoir effect in an upwelling region on the coast of Brazil

Abstract The mixture of different water masses can strongly influence the marine reservoir effect (MRE) in localities under the effect of coastal marine upwelling. The Cabo Frio region, on the southeastern Brazilian coast, is well known for its seasonal marine upwelling and for its rich landscape of Holocene shellmounds. In this kind of archaeological settlement, common on the southern and southeastern Brazilian coasts, marine mollusk shells are frequently used for radiocarbon dating and can represent a valuable tool in the study of MRE. On the other hand, terrestrial mollusks have proven to be an important alternative to represent the atmospheric carbon isotopic concentration. In this work we analysed the most frequent terrestrial and marine mollusk shells from the Usiminas shellmound, on Cabo Frio Island. The radiocarbon signal of marine shells from Pinctada imbricata (Roding, 1798), Ostreidae (Rafinesque, 1815), Cymathium parthenopeum (Von Salis, 1793), Leucozonia nassa (Gmelin, 1791), Lithopoma olfersii (Philippi, 1846), and that of terrestrial shells from Thaumastus achilles (Pfeiffer, 1852) and Megalobulimus terrestris (Spix, 1827), collected from the archaeological layers in the sequence, were measured and a value of 67 ± 33 14C yr was obtained for the local offset from the average global marine reservoir age. The effect of upwelling in this region and in its surrounding area is discussed.

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.

Variability of 14C reservoir age and air–sea flux of CO2 in the Peru–Chile upwelling region during the past 12,000 years

The variability of radiocarbon marine reservoir age through time and space limits the accuracy of chronologies in marine paleo-environmental archives. We report here new radiocarbon reservoir ages (ΔR) from the central coast of Chile (~32°S) for the Holocene period and compare these values to existing reservoir age reconstructions from southern Peru and northern Chile. Late Holocene ΔR values show little variability from central Chile to Peru. Prior to 6000calyr BP, however, ΔR values were markedly increased in southern Peru and northern Chile, while similar or slightly lower-than-modern ΔR values were observed in central Chile. This extended dataset suggests that the early Holocene was characterized by a substantial increase in the latitudinal gradient of marine reservoir age between central and northern Chile. This change in the marine reservoir ages indicates that the early Holocene air–sea flux of CO2 could have been up to five times more intense than in the late Holocene in the Peruvian upwelling, while slightly reduced in central Chile. Our results show that oceanic circulation changes in the Humboldt system during the Holocene have substantially modified the air–sea carbon flux in this region.

Solar forcing of Holocene summer sea-surface temperatures in the northern North Atlantic

Research Article| March 01, 2015 Solar forcing of Holocene summer sea-surface temperatures in the northern North Atlantic Hui Jiang; Hui Jiang * 1Key Laboratory of Geographic Information Science and State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 200062 Shanghai, People’s Republic of China *E-mails: hjiang@geo.ecnu.edu.cn; raimund.muscheler@geol.lu.se Search for other works by this author on: GSW Google Scholar Raimund Muscheler; Raimund Muscheler * 2Department of Geology, Quaternary Sciences, Lund University, Sölvegatan 12, 22362 Lund, Sweden *E-mails: hjiang@geo.ecnu.edu.cn; raimund.muscheler@geol.lu.se Search for other works by this author on: GSW Google Scholar Svante Björck; Svante Björck 2Department of Geology, Quaternary Sciences, Lund University, Sölvegatan 12, 22362 Lund, Sweden Search for other works by this author on: GSW Google Scholar Marit-Solveig Seidenkrantz; Marit-Solveig Seidenkrantz 3Centre for Past Climate Studies and Arctic Research Centre, Department of Geoscience, Aarhus University, DK-8000 Aarhus C, Denmark Search for other works by this author on: GSW Google Scholar Jesper Olsen; Jesper Olsen 4Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark Search for other works by this author on: GSW Google Scholar Longbin Sha; Longbin Sha 1Key Laboratory of Geographic Information Science and State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 200062 Shanghai, People’s Republic of China3Centre for Past Climate Studies and Arctic Research Centre, Department of Geoscience, Aarhus University, DK-8000 Aarhus C, Denmark Search for other works by this author on: GSW Google Scholar Jesper Sjolte; Jesper Sjolte 2Department of Geology, Quaternary Sciences, Lund University, Sölvegatan 12, 22362 Lund, Sweden Search for other works by this author on: GSW Google Scholar Jón Eiríksson; Jón Eiríksson 5Institute of Earth Science, University of Iceland, Askja, IS-101-Reykjavík, Iceland Search for other works by this author on: GSW Google Scholar Lihua Ran; Lihua Ran 6Second Institute of Oceanography, State Oceanic Administration, 310012 Hangzhou, People’s Republic of China Search for other works by this author on: GSW Google Scholar Karen-Luise Knudsen; Karen-Luise Knudsen 3Centre for Past Climate Studies and Arctic Research Centre, Department of Geoscience, Aarhus University, DK-8000 Aarhus C, Denmark Search for other works by this author on: GSW Google Scholar Mads F. Knudsen Mads F. Knudsen 3Centre for Past Climate Studies and Arctic Research Centre, Department of Geoscience, Aarhus University, DK-8000 Aarhus C, Denmark Search for other works by this author on: GSW Google Scholar Geology (2015) 43 (3): 203–206. https://doi.org/10.1130/G36377.1 Article history received: 21 Oct 2014 rev-recd: 09 Dec 2014 accepted: 10 Dec 2014 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Hui Jiang, Raimund Muscheler, Svante Björck, Marit-Solveig Seidenkrantz, Jesper Olsen, Longbin Sha, Jesper Sjolte, Jón Eiríksson, Lihua Ran, Karen-Luise Knudsen, Mads F. Knudsen; Solar forcing of Holocene summer sea-surface temperatures in the northern North Atlantic. Geology 2015;; 43 (3): 203–206. doi: https://doi.org/10.1130/G36377.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Mounting evidence from proxy records suggests that variations in solar activity have played a significant role in triggering past climate changes. However, the mechanisms for sun-climate links remain a topic of debate. Here we present a high-resolution summer sea-surface temperature (SST) record covering the past 9300 yr from a site located at the present-day boundary between polar and Atlantic surface-water masses. The record is age constrained via the identification of 15 independently dated tephra markers from terrestrial archives, circumventing marine reservoir age variability problems. Our results indicate a close link between solar activity and SSTs in the northern North Atlantic during the past 4000 yr; they suggest that the climate system in this area is more susceptible to the influence of solar variations during cool periods with less vigorous ocean circulation. Furthermore, the high-resolution SST record indicates that climate in the North Atlantic regions follows solar activity variations on multidecadal to centennial time scales. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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.

New Data on Marine Radiocarbon Reservoir Effect in the Eastern Adriatic Based on Pre-Bomb Marine Organisms from the Intertidal Zone and Shallow Sea

Radiocarbon analyses of 14 modern, pre-bomb marine organisms collected between AD 1836 and 1946 along the eastern Adriatic coast were performed. The14C ages of five algal and nine mollusk samples were measured by accelerator mass spectrometry (AMS). Marine14C reservoir ages (R) and regional offsets (ΔR) were calculated and compared. The marine reservoir ages of shells and algae significantly differ, even though both inhabit the hard substrate from the intertidal zone to shallow sea. Coralline algae had a considerably lower reservoir age (355 ± 3414C yr) and ΔR value (–9 ± 3414C yr) than mollusks (R 513 ± 5314C yr; ΔR 154 ± 5214C yr), though the variability of R was high in both groups. Although the microlocations of pre-bomb samples were not known and the studied mollusk species are able to inhabit marine or estuarine environments, it can be assumed that they were not significantly influenced by a freshwater admixture, due to their δ13C values being mostly in the marine range. However, as the entire eastern Adriatic is formed in carbonates, mollusk shells could be influenced by limestone-depleted14C. In examining new data together with previously published data, the marine reservoir effect (MRE) for the Adriatic area is estimated to be 424 ± 5714C yr (ΔR is 77 ± 5714C yr). Without mussel shells, the estimated MRE is 378 ± 4414C yr (ΔR is 28 ± 4514C yr). The presented values are comparable to the MREs and mean ΔRs obtained for the Mediterranean by other authors.

Evaluating marine diets through radiocarbon dating and stable isotope analysis of victims of the AD79 eruption of vesuvius

The stable carbon (δ(13) C) and nitrogen (δ(15) N) isotope values of bone collagen are frequently used in paleodietary studies to assess the marine contribution to an individual's diet. Surprisingly, the relationship between stable isotope these values characteristics and the percentage of marine foods in diet has never been effectively demonstrated. To clarify this relationship, the stable isotope values and radiocarbon dates of nine humans and one sheep from Herculaneum, all who perished simultaneously during the AD 79 eruption of Vesuvius, were determined. Significant differences were found in the radiocarbon dates which are attributable to the incorporation of "old" carbon from the marine reservoir. The magnitude of the observed differences was linearly correlated with both δ(13) C and δ(15) N values allowing the response of each isotope to increasing marine carbon in collagen to be independently verified. Regression analyses showed that for every 1‰ enrichment in δ(13) C and δ(15) N, 56 years and 34 years were added to the radiocarbon age, respectively. Predictions of the maximum marine reservoir age differed considerably depending on which stable isotope was considered. This discrepancy is attributed to some degree of macronutrient scrambling whereby nitrogen from marine protein is preferentially incorporated in collagen over marine carbon. It is suggested that the macronutrient scrambling explains the observed relationship between δ(13) C and δ(15) N from Roman coastal sites and should be considered when interpreting any diet which is not dominated by protein. Nevertheless, without knowing the degree of macronutrient scrambling in different dietary scenarios, the accuracy of dietary reconstructions is severely compromised.

Modern Tasman Sea surface reservoir ages from deep-sea black corals

Marine reservoir ages are a key element in calculating and constraining uncertainty in radiocarbon age estimates and are also essential to better understand regional ocean circulation. In this study, we present a new method to reconstruct long-term, high-resolution sea surface reservoir ages based on analysis of the organic skeleton of deep-sea (560m) black coral (Anthozoa, Antipatharia). Our results confirm that antipatharians are extremely slow growing (typical radial growth rate for a South Pacific specimen around 0.03mm/yr). Coupled uranium series and radiocarbon measurements were made on black coral collected live from the Norfolk Ridge (north Tasman Sea) to provide the first modern reservoir ages for this region. At the Norfolk Ridge, the average reservoir age between 1790 AD and 1900AD was ∼330 years. This was followed by a steep decrease over time of about 70 years to 1950 AD (our most modern value). This indicates an increase in surface ocean ventilation of water masses in this region. These results are consistent with observational studies for the early twentieth century, which suggest significant changes in regional circulation of the southwest pacific.

Marine radiocarbon reservoir age variation in Donax obesulus shells from northern Peru: Late Holocene evidence for extended El Nino

For at least 6 m.y., El Nino events have posed the greatest environmental risk on the Peruvian coast. A better understanding of El Nino is essential for predicting future risk and growth in this tropical desert. To achieve this we analyzed archaeological and modern pre-bomb shells from the surf clam Donax for the radiocarbon reservoir effect (ΔR) to characterize late Holocene coastal upwelling conditions in northern Peru (8°14′S). Mean ΔR values from these shells suggest that modern upwelling conditions in this region were likely established between A.D. 539 and A.D. 1578. Our radiocarbon data suggest that upwelling conditions ca. A.D. 539 were less intense than those in modern times. The observed coastal water enrichment in 14 C may be consequence of frequent strong El Nino events or extended El Nino–like conditions. These ΔR-inferred marine conditions are in agreement with proposed extended El Nino activity in proxy and archaeological records of ca. A.D. 475–530. Extended El Nino conditions have been linked to political destabilization, societal transformation, and collapse of the Moche civilization in northern Peru. A return to such conditions would have significant impacts on the dense population of this region today and in the near future.

A revised age for the Kawakawa/Oruanui tephra, a key marker for the Last Glacial Maximum in New Zealand

The Kawakawa/Oruanui tephra (KOT) is a key chronostratigraphic marker in terrestrial and marine deposits of the New Zealand (NZ) sector of the southwest Pacific. Erupted early during the Last Glacial Maximum (LGM), the wide distribution of the KOT enables inter-regional alignment of proxy records and facilitates comparison between NZ climatic variations and those from well-dated records elsewhere. We present 22 new radiocarbon ages for the KOT from sites and materials considered optimal for dating, and apply Bayesian statistical methods via OxCal4.1.7 that incorporate stratigraphic information to develop a new age probability model for KOT. The revised calibrated age, ±2 standard deviations, for the eruption of the KOT is 25,360 ± 160 cal yr BP. The age revision provides a basis for refining marine reservoir ages for the LGM in the southwest Pacific.

A Marine Reservoir Correction for the Houtman-Abrolhos Archipelago, East Indian Ocean, Western Australia

High-precision analysis using accelerator mass spectrometry (AMS) was performed upon known-age Holocene and modern, pre-bomb coral samples to generate a marine reservoir age correction value (ΔR) for the Houtman-Abrolhos Archipelago (28.7°S, 113.8°E) off the Western Australian coast. The mean ΔR value calculated for the Abrolhos Islands, 54 ± 30 yr (1 σ) agrees well with regional ΔR values for Leeuwin Current source waters (N-NW Australia-Java) of 60 ± 38 yr. The Abrolhos Islands show little variation with ΔR values of the northwestern and north Australian coast, underlining the dominance of the more equilibrated western Pacific-derived waters of the Leeuwin Current over local upwelling. The Abrolhos Islands ΔR values have remained stable over the last 2896 cal yr BP, being also attributed to the Leeuwin Current and the El Niño Southern Oscillation (ENSO) signal during this period. Expected future trends will be a strengthening of the teleconnection of the Abrolhos Islands to the climatic patterns of the equatorial Pacific via enhanced ENSO and global warming activity strengthening the Leeuwin Current. The possible effect upon the trend of future ΔR values may be to maintain similar values and an increase in stability. However, warming trends of global climate change may cause increasing dissimilarity of ΔR values due to the effects of increasing heat stress upon lower-latitude coral communities.

A Marine Reservoir Correction for the Houtman-Abrolhos Archipelago, East Indian Ocean, Western Australia

High-precision analysis using accelerator mass spectrometry (AMS) was performed upon known-age Holocene and modern, pre-bomb coral samples to generate a marine reservoir age correction value (ΔR) for the Houtman-Abrolhos Archipelago (28.7°S, 113.8°E) off the Western Australian coast. The mean ΔR value calculated for the Abrolhos Islands, 54 ± 30 yr (1 σ) agrees well with regional ΔR values for Leeuwin Current source waters (N-NW Australia-Java) of 60 ± 38 yr. The Abrolhos Islands show little variation with ΔR values of the northwestern and north Australian coast, underlining the dominance of the more equilibrated western Pacific-derived waters of the Leeuwin Current over local upwelling. The Abrolhos Islands ΔR values have remained stable over the last 2896 cal yr BP, being also attributed to the Leeuwin Current and the El Niño Southern Oscillation (ENSO) signal during this period. Expected future trends will be a strengthening of the teleconnection of the Abrolhos Islands to the climatic patterns of the equatorial Pacific via enhanced ENSO and global warming activity strengthening the Leeuwin Current. The possible effect upon the trend of future ΔR values may be to maintain similar values and an increase in stability. However, warming trends of global climate change may cause increasing dissimilarity of ΔR values due to the effects of increasing heat stress upon lower-latitude coral communities.

Holocene marine tephrochronology on the Icelandic shelf: An overview

Currently the Late-glacial and Holocene marine tephrochronology on the shelf around Iceland comprises 130 tephra layers from 30 sediment cores ranging in age from 15,000 years cal. BP to AD 1947. A vast majority of the cores and tephra layers are from the North Iceland shelf. Much fewer tephra layers have been found on the South and West Iceland shelf. The early Holocene Saksunarvatn ash and Vedde Ash are the only tephra layers identified on all investigated shelf areas. For the last 15,000 years correlated tephra layers from the shelf sediments around Iceland to their terrestrial counterparts both in Iceland and overseas are 40 of which 26 are terrestrially dated tephra markers. Thirty correlations are within the last 7050 years. The terrestrially dated tephra markers found on the shelf have been used to constrain past environmental variability in the region, as well as marine reservoir age. The marine tephra stratigraphy on the North Iceland shelf has revealed variations in volcanic activity in Iceland further back in time than terrestrial records in Iceland. The numerous tephra layers identified in the sediments on the shelf demonstrate the potential of marine tephrochronology for dating purposes, land-sea correlation, marine reservoir estimations and reconstruction of past volcanic activity of Icelandic volcanoes.

Using an independent geochronology based on palaeomagnetic secular variation (PSV) and atmospheric Pb deposition to date Baltic Sea sediments and infer 14C reservoir age

Dating of sediment cores from the Baltic Sea has proven to be difficult due to uncertainties surrounding the 14C reservoir age and a scarcity of macrofossils suitable for dating. Here we present the results of multiple dating methods carried out on cores in the Gotland Deep area of the Baltic Sea. Particular emphasis is placed on the Littorina stage (8 ka ago to the present) of the Baltic Sea and possible changes in the 14C reservoir age of our dated samples. Three geochronological methods are used. Firstly, palaeomagnetic secular variations (PSV) are reconstructed, whereby ages are transferred to PSV features through comparison with varved lake sediment based PSV records. Secondly, lead (Pb) content and stable isotope analysis are used to identify past peaks in anthropogenic atmospheric Pb pollution. Lastly, 14C determinations were carried out on benthic foraminifera (Elphidium spec.) samples from the brackish Littorina stage of the Baltic Sea. Determinations carried out on smaller samples (as low as 4 μg C) employed an experimental, state-of-the-art method involving the direct measurement of CO2 from samples by a gas ion source without the need for a graphitisation step – the first time this method has been performed on foraminifera in an applied study. The PSV chronology, based on the uppermost Littorina stage sediments, produced ten age constraints between 6.29 and 1.29 cal ka BP, and the Pb depositional analysis produced two age constraints associated with the Medieval pollution peak. Analysis of PSV data shows that adequate directional data can be derived from both the present Littorina saline phase muds and Baltic Ice Lake stage varved glacial sediments. Ferrimagnetic iron sulphides, most likely authigenic greigite (Fe3S4), present in the intermediate Ancylus Lake freshwater stage sediments acquire a gyroremanent magnetisation during static alternating field (AF) demagnetisation, preventing the identification of a primary natural remanent magnetisation for these sediments. An inferred marine reservoir age offset (ΔR) is calculated by comparing the foraminifera 14C determinations to a PSV & Pb age model. This ΔR is found to trend towards younger values upwards in the core, possibly due to a gradual change in hydrographic conditions brought about by a reduction in marine water exchange from the open sea due to continued isostatic rebound.

Early Holocene deglaciation of northern Hudson Bay and Foxe Channel constrained by new radiocarbon ages and marine reservoir correction

Radiocarbon ages from Southampton Island (Canada) provide new chronological control on the deglaciation of Foxe Channel and northern Hudson Bay, a strategic area for understanding the demise of a marine-based portion of the Laurentide Ice Sheet. A regional marine reservoir age of 630±45yr and a reservoir offset (ΔR) of 263±48yr were calculated from two early to mid-Holocene terrestrial/marine radiocarbon age pairs. These values are consistent with corrections based on early 20th century mollusks suggesting that following deglaciation the oceanic conditions controlling the regional reservoir effect rapidly became similar to those of modern times. However, our ΔR value is 352±52yr less than another correction from eastern Foxe Basin, which may be affected by 14C dilution from carbonate rocks. Our ΔR value is used to calibrate new marine radiocarbon ages which help further develop the deglaciation history of Southampton Island, especially along the north coast where deglaciation of Foxe Channel appears to have been completed by 8100–7800calyr BP (2σ). This provides key chronological constraints on the development of a long marine ice margin in southern Foxe Basin prior to the final breakup of the Foxe ice dome.

Preboreal onset of cold-water coral growth beyond the Arctic Circle revealed by coupled radiocarbon and U-series dating and neodymium isotopes

Cold-water coral mounds of Lophelia pertusa are widespread across the Scandinavian shelf, which was completely ice-covered during the Last Glacial Maximum between 22 to 18ka BP. Rapid deglacial meltdown of the Fennoscandian inland ice and the retreat of its ice-streams freed most of the shelf of ice by ∼15ka BP. However, cold-water coral growth commenced only after the Pleistocene–Holocene transition at 11.65ka BP, when modern-like climatic patterns and oceanographic conditions were established. A tight climatic coupling has been constrained with U-series ages. Coupled 14C ages provide local reservoir ages from various gravity cores in a fjord-setting in Stjernsund at 70°N and on the open shelf in Trænadjupet at 66°N. Reinvestigation of earlier 14C coral chronologies suggests that coral ecosystems widely established themselves across the entire 3000km long Scandinavian shelf prior to ∼10ka BP. The earliest occurrence of Madrepora oculata at ∼2.4ka BP suggests a late Holocene colonization of the Norwegian shelf, which is linked to a prominent mound growth hiatus in Trænadjupet (64°N). Mound growth rates near the northern biogeographic boundary of L. pertusa with up to ∼614cmka−1 during certain growth periods are much higher than the previously reported fastest rates of ∼220cmka−1 from the Irish margin. Contemporaneous rapid fjordbasin sedimentation is slower with ∼63cmka−1. Matrix 14C ages overlap with coral 14C ages from the same horizon. This indicates rapid framework construction and efficient trapping of background sediment. Hiatuses are frequent in on-mound sediments and only short periods of coral growth are recorded. Coupled Δ14C and εNd values indicate a persistent Holocene inflow of the North Atlantic Current in Stjernsund, but also deglacial meltwater mixing during the early Holocene prior to ∼9.5ka BP. Reservoir ages are overall close to the surface marine reservoir age, but ΔR is highly localized.

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‰.

Paleoceanographic control on a large marine reservoir effect offshore of Tokai, south of Japan, NW Pacific, during the last glacial maximum-deglaciation

Knowledge of the marine reservoir effect is important in calibrating radiocarbon ages to calendar ages, and in correlating geologic and paleoceanographic events among different sites, including global events. Large, explosive volcanic eruptions have yielded numerous volcanic ash layers (tephras) over geological time. Because tephra layers are deposited both on land and upon the seafloor, they represent a unique and important link between the geological records of terrestrial and marine areas. Comparison of the radiocarbon ages of a tephra layer deposited in marine (planktonic foraminifera) and terrestrial (peat) materials reveals a local marine reservoir age (600–700 years or more) during the early part of the last deglaciation off Tokai, south of Japan. This age is larger than that determined for the present-day Pacific coast of Japan (82 years) and similar to that of the present-day subarctic NW Pacific (350–580 years). This difference between modern-day and deglaciation marine reservoir values is thought to reflect the contrasting properties of surface water masses between the two periods.