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  • 1
    Publication Date: 1978-09-01
    Description: The reef-crest coral Acropora palmata from late Pleistocene reefs on Barbados has recorded the same global variations in oxygen isotopes as planktonic and benthonic foraminifera. Although the record of oxygen isotopes in Acropora palmata is discontinuous, it offers several advantages over the isotope records from deep-sea sediments: (1) the coral grows at water depths of less than 5 m; (2) the samples are unmixed; (3) specimens may be sampled from various elevations of paleo-sea level; and (4) aragonitic corals are suitable for 230Th/234U and He/U dating techniques. The latter advantage means that direct dating of the marine oxygen isotope record is possible. Oxygen isotope stage 5e corresponds to Barbados III, dated at 125,000 ± 6000 yr BP. Petrographic and geochemical evidence from five boreholes drilled into the south coast of Barbados indicates a major eustatic lowering (greater than 100 m below present sea level) occurred between 180,000 and 125,000 yr BP. The age and isotopic data suggest correlation of this change in sea level to Emiliani's oxygen isotope stage 6. Acropora palmata deposited at various elevations of sea level during oxygen isotope stage 6 vary by 0.11 ‰ δ18O for each 10 m of change in sea level. We further hypothesize a minimum drop of 2°C in the average temperature occurred during the regressive phase of oxygen isotope stage 6. These data indicate that temperature lowering of surface water near Barbados lagged behind a major glacial buildup during this time period. Using the δ18O vs sea level calibration herein derived, we estimate the relative height of sea stands responsible for Barbados coral reef terraces in the time range 80,000 to 220,000 yr BP.
    Print ISSN: 0033-5894
    Electronic ISSN: 1096-0287
    Topics: Geography , Geosciences
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  • 2
    Publication Date: 2004-01-01
    Description: New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally ratified to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0–26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0–10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-resolution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5–26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 3
    Publication Date: 1993-01-01
    Description: In 1988, Fairbanks conducted a drilling expedition off the south coast of Barbados to recover submerged corals contemporaneous with the last deglaciation. Core recovery was excellent and 〉30 different samples were dated by conventional β-counting techniques (Fairbanks 1989). At about the same time, we developed, at Lamont, the thermal ionization mass spectrometry (TIMS) technique to obtain precise U-Th ages (Edwards 1988), and to compare them with the 14C estimates measured on the same samples. A surprising result was that the discrepancy between 14C and U-Th ages increased through time to ca. 3000–3500 yr at ca. 15,000 14C BP (Bard et al. 1990a). Because the three youngest samples yielded U-Th ages in agreement with their calibrated 14C ages, we concluded initially that the TIMS U-Th determinations were not only precise, but also accurate, and that the 14C vs. U-Th data set could be used for a first-order 14C calibration.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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