Marine Radiocarbon Reservoir Correction Research Articles

Ocean circulation and climate variability in the northern South China Sea during the Greek Minimum derived from coral Δ14C and Sr/Ca records

Ocean circulation transports heat, salt and nutrients, and has profound impacts on the marine environment and climate change. However, the seasonal to centennial variations of the paleocirculation of the South China Sea (SCS) and their driving forces are still unclear due to limited records. Here we reconstructed a high-resolution Δ14C record of a coral from Sanya to investigate the seasonal variations of the SCS ocean circulation around 2300 cal yr BP during a grand solar minimum (GSM) period. The seasonal Δ14C variability shows the influence of coastal upwelling caused by the East Asian Summer Monsoon (EASM) in summer and the effect of water intrusion from the western Pacific Ocean driven by the Kuroshio Intrusion (KI) in winter. We compiled the marine radiocarbon reservoir correction (ΔR) records since 2500 cal yr BP, which indicate a gradual decrease of upwelling significantly correlated with the EASM. Comparisons with other climate records suggest that both the EASM and KI may regulate the ocean circulation variability on centennial time scales. As a good index of the sea surface temperature (SST), our Sr/Ca record and spectral analysis results show a low temperature and a low frequency of El Niño-Southern Oscillation (ENSO) events around 2300 cal yr BP. Moreover, the composite coral Sr/Ca-SST and ENSO index records since 2500 cal yr BP show relatively low SST and weak ENSO during GSMs, supporting the modulation of tropical SST and ENSO by solar activity. Our study has provided high-resolution proxy data and revealed the driving forces of ocean circulation and climate change in the SCS at multiple time scales, which should be considered in further modeling work.

Late Holocene Marine Radiocarbon Reservoir Correction for the Southern and Eastern Coasts of South Africa

AbstractThe marine reservoir effect is the difference in radiocarbon (14C) between the atmosphere and the marine surface ocean. To overcome the dating errors induced, it is necessary to correct marine 14C ages for this effect. ΔR is the difference between the marine 14C age and the marine calibration curve based on an ocean-atmosphere box diffusion model, which accounts for the time delay in diffusion of carbon into the ocean from the atmosphere and biosphere. This global assessment, however, requires computation of a regional ∆R value for calibration to cater for studies based on a local scale. In this paper the marine reservoir effect is assessed for the southern and eastern coasts of South Africa using 14C dating on pre-1950 marine shells of known age. The resultant ∆R values enable a more complete understanding of the marine reservoir effect along the southern and eastern coastal zone of South Africa. 14C age determinations were conducted on 15 shell samples of known age and the results, combined with previously published values, were used to calculate regional marine reservoir correction values. The east coast has a weighted mean ∆R of 121±16 14C yr, while the south coast has a weighted mean ∆R of 187±18 14C yr.

Holocene marine radiocarbon reservoir correction delta R for the west coast of South Africa

Holocene marine radiocarbon reservoir correction delta R for the west coast of South Africa

Radiocarbon reservoir corrections on the Brazilian coast from pre-bomb marine shells

Despite the great extent of the Brazilian coast, there are very few studies on the marine radiocarbon reservoir correction local offset (ΔR) for this region.In the present study, we used marine shells from the malacological collection of the National Museum of Brazil to obtain values of ΔR for different locations on the Brazilian coast. According to the museum records, the mollusks were collected alive from the coasts of Rio de Janeiro, Rio Grande do Sul, São Paulo and Bahia, prior to the 14C bomb-peak. The exact year of collection for each shell is known.The samples were chemically prepared and measured at the Radiocarbon Laboratory of the Universidade Federal Fluminense (LAC-UFF) in Brazil. The conventional ages were calibrated using the Marine13 curve and the ΔR values were calculated using the OxCal software. The values range from 17 ± 56 14C yr in São José do Norte, Rio Grande do Sul to 96 ± 48 14C yr in Cabo Frio, Rio de Janeiro.

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.

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.

Marine radiocarbon reservoir corrections (∆R) for Chesapeake Bay and the Middle Atlantic Coast of North America

Radiocarbon dates from known age, pre-bomb eastern oyster (Crassostrea virginica) shells provide local marine reservoir corrections (∆R) for Chesapeake Bay and the Middle Atlantic coastal area of eastern North America. These data suggest subregional variability in ∆R, ranging from 148±46 14Cyr on the Potomac River to −109±38 14Cyr at Swan Point, Maryland. The ∆R weighted mean for the Chesapeake's Western Shore (129±22 14Cyr) is substantially higher than the Eastern Shore (−88±23 14Cyr), with outer Atlantic Coast samples falling between these values (106±46 and 2±46 14Cyr). These differences may result from a combination of factors, including 14C-depleted freshwater that enters the bay from some if its drainages, 14C-depleted seawater that enters the bay at its mouth, and/or biological carbon recycling. We advocate using different subregional ∆R corrections when calibrating 14C dates on aquatic specimens from the Chesapeake Bay and coastal Middle Atlantic region of North America.

Continuous marine radiocarbon reservoir calibration and the 13C Suess effect in the Irish Sea: Results from the first multi-centennial shell-based marine master chronology

The identification in various proxy records of periods of rapid (decadal scale) climate change over recent millennia, together with the possibility that feedback mechanisms may amplify climate system responses to increasing atmospheric CO 2, highlights the importance of a detailed understanding, at high spatial and temporal resolutions, of forcings and feedbacks within the system. Such an understanding has hitherto been limited because the temperate marine environment has lacked an absolute timescale of the kind provided by tree-rings for the terrestrial environment and by corals for the tropical marine environment. Here we present the first annually resolved, multi-centennial (489-year), absolutely dated, shell-based marine master chronology. The chronology has been constructed by detrending and averaging annual growth increment widths in the shells of multiple specimens of the very long-lived bivalve mollusc Arctica islandica, collected from sites to the south and west of the Isle of Man in the Irish Sea. The strength of the common environmental signal expressed in the chronology is fully comparable with equivalent statistics for tree-ring chronologies. Analysis of the 14C signal in the shells shows no trend in the marine radiocarbon reservoir correction (Δ R), although it may be more variable before ∼ 1750. The δ 13C signal shows a very significant ( R 2 = 0.456, p < 0.0001) trend due to the 13C Suess effect.

Building Confidence in Shell: Variations in the Marine Radiocarbon Reservoir Correction for the Northwest Coast Over the Past 3,000 Years

In many regions, fluctuations have occurred through time in the local 14C activity of seawater. Evaluating these shifts and their effects on 14C age estimates is difficult, and, as a result, archaeologists working in coastal settings tend to preferentially date charcoal samples over shell. Our research on 18 charcoal–shell pairs from Puget Sound and Gulf of Georgia archaeological sites helps elucidate the spatial and temporal dynamics associated with marine reservoir effects in the Pacific Northwest. This analysis suggests that between 0 and 500 B.P. the regional correction value (ΔR) is 400 years, which agrees with the modern value determined by Stuiver and others. Between 500 and 1200 B.P., however, ΔR dips close to zero, possibly reflecting a decrease in offshore upwelling. From 1200 to 3000 B.P., ΔR returns to 400 years. These data are presented as a Puget Sound/Gulf of Georgia regional correction curve for the late Holocene, which local researchers may use to calibrate dates of marine shell. In addition, we detail our methods for constructing calibration curves and present guidelines for archaeologists working in other coastal settings to develop calibration curves for their regions.

Marine radiocarbon reservoir corrections for the midto late Holocene in the eastern subpolar North Atlantic

The time dependency of the regional difference ΔR in the marine radiocarbon reservoir correction is an important issue for the calibration of marine radiocarbon ages and also provides information about past ocean circulation changes. Few measurements of Holocene reservoir corrections are available for the climatically important North Atlantic. We determined ΔR for intervals during the past 6100 years before present (BP) by comparing radiocarbon ages of 31 marine and terrestrial sample pairs from 14 archaeological sites from the coast of Ireland, Scotland and the Orkney Islands. We find that, while a time dependency in ΔR for this region cannot be ruled out, within the error of the determinations, the ΔR appears to have been constant for at least the last 2000 and possibly the last 6000 years. This work results in a recommendation for ΔR of 33 +93 for the region.

Marine Radiocarbon Reservoir Corrections for the Mediterranean and Aegean Seas

Radiocarbon measurements of nine known age shells from the Mediterranean and the Aegean Seas combined with previous measurements provide an updated value for δR, the local variation in the reservoir correction for marine samples. Comparison of pre-1950s samples from the Algerian coast, with one collected in 1954, indicates early incorporation of nuclear weapons testing 14C into the shallow surface waters of the Mediterranean. Comparisons between different basins indicate the surface waters of the Mediterranean are relatively homogenous. The recommended δR for calibration of the Mediterranean marine samples with the 1998 marine calibration dataset is 58 ± 85 14C yr, but variations in the reservoir age beyond 6000 cal BP should be considered.