ALBERT

Description: Radiocarbon and uranium-thorium dating results are presented from a genus of calcitic Antarctic cold-water octocorals (family Coralliidae), which were collected from the Marie Byrd Seamounts in the Amundsen Sea (Pacific sector of the Southern Ocean) and which to date have not been investigated geochemically. The geochronological results are set in context with solution and laser ablation-based element/Ca ratios (Li, B, Mg, Mn, Sr, Ba, U, Th). Octocoral radiocarbon ages on living corals are in excellent agreement with modern ambient deep-water D14C, while multiple samples of individual fossil coral specimens yielded reproducible radiocarbon ages. Provided that local radiocarbon reservoir ages can be derived for a given time, fossil Amundsen Sea octocorals should be reliably dateable by means of radiocarbon. In contrast to the encouraging radiocarbon findings, the uranium-series data are more difficult to interpret. The uranium concentration of these calcitic octocorals is an order of magnitude lower than in the aragonitic hexacorals that are conventionally used for geochronological investigations. While modern and Late Holocene octocorals yield initial d234U in good agreement with modern seawater, our results reveal preferential inward diffusion of dissolved alpha-recoiled 234U and its impact on fossil coral d234U. Besides alpha-recoil related 234U diffusion, high-resolution sampling of two fossil octocorals further demonstrates that diagenetic uranium mobility has offset apparent coral U-series ages. Combined with the preferential alpha-recoil 234U diffusion, this process has prevented fossil octocorals from preserving a closed system U-series calendar age for longer than a few thousand years. Moreover, several corals investigated contain significant initial thorium, which cannot be adequately corrected for because of an apparently variable initial 232Th/230Th. Our results demonstrate that calcitic cold-water corals are unsuitable for reliable U-series dating. Mg/Ca ratios within single octocoral specimens are internally strikingly homogeneous, and appear promising in terms of their response to ambient temperature. Magnesium/lithium ratios are significantly higher than usually observed in other deep marine calcifiers and for many of our studied corals are remarkably close to seawater compositions. Although this family of octocorals is unsuitable for glacial deep-water D14C reconstructions, our findings highlight some important differences between hexacoral (aragonitic) and octocoral (calcitic) biomineralisation. Calcitic octocorals could still be useful for trace element and some isotopic studies, such as reconstruction of ambient deep water neodymium isotope composition or pH, via boron isotopic measurements.

Description: This dataset is presented in the article "Precessional cyclicity of seawater Pb isotopes in the late Miocene Mediterranean" (accepted, Paleoceanography and Paleoclimatology). Marginal Mediterranean marine sediments from three separate basins were sampled at sub-precessional resolution (~4-10 samples per precessional cycle). Authigenic Pb isotope compositions of the bulk sediment were extracted using acid reductive leaching and measured with MC-ICP-MS. In addition, strong leaching and total dissolution was applied to a subset of samples. This dataset includes the results of all of the measurements, plus an extensive set of secondary standard measurements performed at the same periods for quality control purposes, on two different MC-ICP-MS (Nu Plasma and Thermo Neptune Plus, GEOMAR Helmholtz Institute for Ocean Research, Kiel). Finally, there is a table of alternative sample ages based on different orbital tuning options (see manuscript text).

Description: Pb isotope results of secondary standards and calculation of external reproducibility for measurements performed on Nu Plasma MCICPMS and Neptune Plus MCICPMS, GEOMAR. Uncertainties in the table are internal measurement uncertainties reported in 2 SE format.

Description: Pb isotope results of acid-reductive leaching of bulk sediments from the Sorbas and Caltanissetta Basins and the Apennine Foredeep. Uncertainties in the table are internal measurement uncertainties reported to 2 SE. Some samples were repeated; if RPT# is noted, this is a repeated measurement of the same solution. Otherwise, the repeat measurement was performed with a separate leaching of a new portion of sediment. An average value of these measurements is provided where relevant. The analytical session in which the measurement was performed is explained in the table footnote.

Description: Pb isotope results from total dissolution of bulk sediment samples from the Sorbas Basin. Uncertainties in the table are internal measurement uncertainties and reported in 2 SE format.

Description: Pb isotope results of strong leachates performed on bulk sediments from the Sorbas Basin. Uncertainties in the table are internal measurement uncertainties, reported in 2SE format.

Description: In this dataset we present new high resolution Pb isotope data alongside elemental concentration and ARM (anhysteretic remanant magnetization) data for four core sites in the arctic Mackenzie Delta area as well as the Amundsen Gulf. Cores were recovered with a piston corer during USCGC Healy cruise HLY1302. Cores are characterized by high sedimentation rates of up to 1 m/ka and reach back until 15 ka and therefore the late Heinrich Stadial 1. We also provide radiocarbon ages for sediment cores JPC-19 and JPC-9. With these high resolution records of the deglacial period we are capable to trace meltwater drainage of the decaying Laurentide Ice Sheet with a more or less pronounced Lake Agassiz source. The isotopic compositions were measured with a Neptune Plus at GEOMAR, Kiel, Germany. Also at the GEOMAR, the elemental composition has been measured with an Agilent 7500 cx ICP-MS-Quadrupole. Radiocarbon ages were measured at the LARA laboratory at the University of Bern, Switzerland, with an MICADAS AMS. Dates given here are uncalibrated 14C ages.