ALBERT

Description: Here we present 230Th/U, 231Pa/U as well as 226Ra/230Th isotope ratios from five fossil reef corals of Last Interglacial origin from the Gulf of Aqaba, Northern Red Sea. The results show clear evidence for open-system behaviour with strongly elevated δ234U values and U concentrations indicating post-depositional U addition. The combined application of all isotope systems enables us to better constrain the nature and timing of the open-system processes than only based on the 230Th/U data. Quantitative modelling of the diagenetic processes allowed us to reproduce the trends in the isotope ratios. Two of the five corals were probably affected by two separate phases of U addition with different δ234U values. The trends observed for two other corals can be explained by U addition followed by U loss. The fifth coral shows signs of both U gain and loss at the same time in the more recent past. The timing of the diagenetic processes is remarkably similar for the five corals and can be constrained to approx. 1 and 6 thousand years (ka) and 100 and 102 ka after coral growth, respectively. Based on the modelling results, we suggest that conventional 231Pa/230Th ages provide the best estimate for the true age of four of the five corals, which range from 109.1 to 114.1 ka. This implies a late Last Interglacial time of deposition. For the fifth coral, the most reliable age estimate is the conventional 230Th/U age of one of the subsamples (117.3 ka), based on a concordia diagram for all subsamples. The timing of the modelled open-system processes suggests that the early event of U addition was associated with interaction of the corals with 234U-enriched seawater or saline groundwater. The later open-system event can be described as U redistribution within the coral reef, since some corals apparently lost U while others gained U. The timing of the second event is broadly consistent with the Bølling-Allerød interstadial, which was probably characterised by enhanced wetness in this typically hyper-arid region.

Description: We compared the suitability of two skeletal materials of the Atlantic brain coral Diploria strigosa for 230Th/U-dating: the commonly used bulk material comprising all skeletal elements and the denser theca wall material. Eight fossil corals of presumably Last Interglacial age from Bonaire, southern Caribbean Sea, were investigated, and several sub-samples were dated from each coral. For four corals, both the ages and the activity ratios of the bulk material and theca wall agree within uncertainty. Three corals show significantly older ages for their bulk material than for their theca wall material as well as substantially elevated 232Th content and (230Th/238U) ratios. The bulk material samples of another coral show younger ages and lower (230Th/238U) ratios than the corresponding theca wall samples. This coral also contains a considerable amount of 232Th. The application of the available open-system models developed to account for post-depositional diagenetic effects in corals shows that none of the models can successfully be applied to the Bonaire corals. The most likely explanation for this observation is that the assumptions of the models are not fulfilled by our data set. Comparison of the theca wall and bulk material data enables us to obtain information about the open-system processes that affected the corals. The corals showing apparently older ages for their bulk material were probably affected by contamination with a secondary (detrital) phase. The most likely source of the detrital material is carbonate sand. The higher (230Th/232Th) ratio of this material implies that detrital contamination would have a much stronger impact on the ages than a contaminant with a bulk Earth (230Th/232Th) ratio and that the threshold for the commonly applied 232Th reliability criterion would be much lower than the generally used value of 1 ng g^-1. The coral showing apparently younger ages for its bulk material was probably influenced by more than one diagenetic process. A potential scenario is a combination of detrital contamination and U addition by secondary pore infillings. Our results show that the dense theca wall material of D. strigosa is generally less affected by post-depositional open-system behaviour and better suited for 230Th/U-dating than the bulk material. This is also obvious from the fact that all ages of theca wall material reflect a Last Interglacial origin (~125 ka), whereas the bulk material samples are either substantially older or younger. However, for some corals, the 230Th/U-ages and activity ratios of the bulk material and the theca wall samples are similar. This shows that strictly reliable 230Th/U-ages can also be obtained from bulk material samples of exceptionally well-preserved corals. However, the bulk material samples more frequently show elevated activity ratios and ages than the corresponding theca wall samples. Our findings should be generally applicable to brain corals (Mussidae) that are found in tropical oceans worldwide and may enable reliable 230Th/U-dating of fossil corals with similar skeletal architecture, even if their bulk skeleton is altered by diagenesis. The 230Th/U-ages we consider reliable (120–130 ka), along with a recently published age of 118 ka, provide the first comprehensive dating of the elevated lower reef terrace at Bonaire (118–130 ka), which is in agreement in timing and duration with other Last Interglacial records.

Description: We present a new speleothem trace element and stable isotope record, which extends previous paleoclimate evidence from Cuban speleothems to the last 96 ka. Stable isotope samples were micromilled at a resolution of 0.10-0.33mm, and measured using an IRMS equipped with a Gasbench. Line scans of Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS and were reduced to the resolution of the stable isotope records.

Description: We present a new speleothem trace element and stable isotope record, which extends previous paleoclimate evidence from Cuban speleothems to the last 96 ka. Stable isotope samples were micromilled at a resolution of 0.10-0.33mm, and measured using an IRMS equipped with a Gasbench. Line scans of Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS and were reduced to the resolution of the stable isotope records.

Description: For trace element analyses, single specimens of C. wuellerstorfi have been analyzed using femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICP131 MS) at the Geochemistry Laboratory at the Max Planck Institute for Chemistry. Na, Mg, and Sr of 142 specimens of C. wuellerstorfi have been measured at high-resolution on (up to) each of the final five chambers to eliminate possible inaccuracies that are likely to be caused by varying sample size. The fs-LA-ICP-MS analyses were performed on 25-μm diameter spots on each chamber with a pulse repetition rate of 15 Hz at low fluence (0.1-0.3 J/cm2). Calibration was performed with the microanalytical synthetic reference material MACS‐3 for carbonate and NIST612 for silica. Average values of all chambers analyzed in the same specimen were used for further analyses. Since foraminifers from different regions show particular offsets in the Mg/Ca composition of their shell, depending on region specific temperature ranges of ambient seawater, region-specific formulas are used. We have applied the formula Mg/Ca=0.82e^0.19*BWT of Tisserand et al. (2013) from samples collected from similar geographic situations to avoid offsets. The formula has been applied to calculate temperature variability of each analyzed chamber. The average value obtained from chamber-to-chamber temperature variability of each specimen has been applied as average temperature data of the entire test.

Description: We present results of Th/U dating, stable isotope and trace element data from a speleothem from Puerto Rico. Th/U dating was performed using isotope dilution MC-ICPMS. Activity ratios were corrected for initial Th assuming an detrital weight ratio 232Th/238U = 0.154 ± 0.038 (corresponding to an activity ratio of the detritus in secular equilibrium of (230Th/232Th)detr = 19.79 ± 4.93), and secular equilibrium of the detritus. Ages are calculated using the decay constants by Cheng et al. (2000)). Uncertainties are given as 2σ- range, and do not include half-life uncertainties. Th/U dating shows that stalagmite PR-LA-1 covers the period from 15.4 to 46.2 ka with a growth interruption between 35.5 and 41.1 ka. Stable isotope samples were drilled with a spatial resolution of 1 mm and measured using an IRMS equipped with a Gasbench. Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS and were reduced to the resolution of the stable isotope records.