Coral records of reef-water pH across the central Great Barrier Reef, Australia: assessing the influence of river runoff on inshore reefs

The boron isotopic (δ11Bcarb) compositions of long-lived Porites coral are used to reconstruct reef-water pH across the central Great Barrier Reef (GBR) and assess the impact of river runoff on inshore reefs. For the period from 1940 to 2009, corals fro

Intraspecific variation in recent populations of Globigerinoides ruber from the eastern Indian Ocean: evidence from test morphology and geochemistry

Abstrac

Controls on boron incorporation in cultured tests of the planktic foraminifer Orbulina universa

Culture experiments with living planktic foraminifers reveal that the ratio of boron to calcium (B/Ca) in Orbulina universa increases from 56 to 92 μmol mol−1 when pH is raised from 7.61+/–0.02 to 8.67+/–0.03 (total scale). Across this pH range, the abundances of carbonate, bicarbonate, and borate ions also change (+530, −500, and +170 μmol kg−1, respectively). Thus specific carbonate system control(s) on B/Ca remain unclear, complicating interpretation of paleorecords. B/Ca in cultured O. universa also increases with salinity (55–72 μmol mol−1 from 29.9–35.4‰) and seawater boron concentration (62–899 μmol mol−1 from 4–40 ppm B), suggesting that these parameters may need to be taken into account for paleorecords spanning large salinity changes (~ 2‰) and for samples grown in seawater whose boron concentration ([B]SW) differs from modern by more than 0.25 ppm. While our results are consistent with the predominant incorporation of the charged borate species B(OH)4−into foraminiferal calcite, the behavior of the partition coefficient KD (defined as [B/Ca]calcite/[B(OH)4−/HCO3−]seawater) cannot be explained by borate incorporation alone, and suggests the involvement of other pH-sensitive ions such as CO3 2− For a given increase in seawater B(OH)4−, the corresponding increase in B/Ca is stronger when B(OH)4− is raised by increasing [B]SW than when it is raised by increasing pH. These results suggest that B incorporation controls should be reconsidered. Additional insight is gained from laser-ablation ICP-MS profiles, which reveal variable B/Ca distributions within individual shells

Micron-scale intrashell oxygen isotope variation in cultured planktic foraminifers

In this study, we show that the rate of shell precipitation in the extant planktic foraminifer Orbulina universa is sufficiently rapid that 12 h calcification periods in 18O-labeled seawater can be resolved and accurately measured using secondary ion mass spectrometry (SIMS) for in situ δ18O analyses. Calcifying O. universa held at constant temperature (22 °C) were transferred every 12 h between ambient seawater (δ18Ow = −0.4‰ VSMOW) and seawater with enriched barium and δ18Ow = +18.6‰ VSMOW, to produce geochemically distinct layers of calcite, separated by calcite precipitated with an ambient geochemical signature. We quantify the position of the Ba-labeled calcite in the shell wall of O. universa via laser ablation ICP-MS depth profiling of trace element ratios, and then measure intrashell δ18Ocalcite in the same shells using SIMS with a 3 μm spot and an average precision of 0.6‰ (±2 SD). Measured δ18Ocalcite values in O. universa shell layers are within ±1.1‰ of predicted δ18Ocalcite values. Elemental and oxygen isotope data show that LA-ICP-MS and SIMS measurements can be cross-correlated within the spatial resolution of the two analytical techniques, and that δ18Ocalcite and elemental tracers appear to be precipitated synchronously with no measurable spatial offsets. These results demonstrate the capability of SIMS to resolve daily growth increments in foraminifer shells, and highlight its potential for paleoceanographic and biomineralization applications on microfossils

Sequential changes in ocean circulation and biological export productivity during the last glacial-interglacial cycle: a model-data study

We conduct a model-data analysis of the marine carbon cycle to understand and quantify the drivers of atmospheric CO2 concentration during the last glacial-interglacial cycle. We use a carbon cycle box model, "SCP-M", combined with multiple proxy data for the atmosphere and ocean, to test for variations in ocean circulation and Southern Ocean biological export productivity across marine isotope stages spanning 130 000 years ago to the present. The model is constrained by proxy data associated with a range of environmental conditions including sea surface temperature, salinity, ocean volume, sea-ice cover and shallow-water carbonate production. Model parameters for global ocean circulation, Atlantic meridional overturning circulation and Southern Ocean biological export productivity are optimized in each marine isotope stage against proxy data for atmospheric CO2, delta C-13 and Delta C-14 and deep-ocean delta C-13, Delta C-14 and CO32-. Our model-data results suggest that global overturning circulation weakened during Marine Isotope Stage 5d, coincident with a similar to 25 ppm fall in atmospheric CO2 from the last interglacial period. There was a transient slowdown in Atlantic meridional overturning circulation during Marine Isotope Stage 5b, followed by a more pronounced slowdown and enhanced Southern Ocean biological export productivity during Marine Isotope Stage 4 (similar to -30 ppm). In this model, the Last Glacial Maximum was characterized by relatively weak global ocean and Atlantic meridional overturning circulation and increased Southern Ocean biological export productivity (similar to -20 ppm during MIS 3 and MIS 2). Ocean circulation and Southern Ocean biological export productivity returned to modern values by the Holocene period. The terrestrial biosphere decreased by 385 Pg C in the lead-up to the Last Glacial Maximum, followed by a period of intense regrowth during the last glacial termination and the Holocene (similar to 600 Pg C). Slowing ocean circulation, a colder ocean and to a lesser extent shallow carbonate dissolution contributed similar to -70 ppm to atmospheric CO2 in the similar to 100 000-year leadup to the Last Glacial Maximum, with a further similar to -15 ppm contributed during the glacial maximum. Our model results also suggest that an increase in Southern Ocean biological export productivity was one of the ingredients required to achieve the Last Glacial Maximum atmospheric CO2 level. We find that the incorporation of glacial-interglacial proxy data into a simple quantitative ocean transport model provides useful insights into the timing of past changes in ocean processes, enhancing our understanding of the carbon cycle during the last glacial-interglacial period

Mapping of bioavailable strontium isotope ratios in France for archaeological provenance studies

Strontium isotope ratios (⁸⁷Sr/⁸⁶Sr) of archaeological samples (teeth and bones) can be used to track mobility and migration across geologically distinct landscapes. However, traditional interpolation algorithms and classification approaches used to generate Sr isoscapes are often limited in predicting multiscale ⁸⁷Sr/⁸⁶Sr patterning. Here we investigate the suitability of plant samples and soil leachates from the IRHUM database (www.irhumdatabase.com) to create a bioavailable ⁸⁷Sr/⁸⁶Sr map using a novel geostatistical framework. First, we generated an ⁸⁷Sr/⁸⁶Sr map by classifying ⁸⁷Sr/⁸⁶Sr values into five geologically-representative isotope groups using cluster analysis. The isotope groups were then used as a covariate in kriging to integrate prior geological knowledge of Sr cycling with the information contained in the bioavailable dataset and enhance ⁸⁷Sr/⁸⁶Sr predictions. Our approach couples the strengths of classification and geostatistical methods to generate more accurate ⁸⁷Sr/⁸⁶Sr predictions (Root Mean Squared Error = 0.0029) with an estimate of spatial uncertainty based on lithology and sample density. This bioavailable Sr isoscape is applicable for provenance studies in France, and the method is transferable to other areas with high sampling density. While our method is a step forward in generating accurate ⁸⁷Sr/⁸⁶Sr isoscapes, the remaining uncertainty also demonstrates that fine-modelling of ⁸⁷Sr/⁸⁶Sr variability is challenging and requires more than geological maps for accurately predicting ⁸⁷Sr/⁸⁶Sr variations across the landscape. Future efforts should focus on increasing sampling density and developing predictive models to further quantify and predict the processes that lead to ⁸⁷Sr/⁸⁶Sr variability.Funding was provided by ARC DP110101415 (Grün, Spriggs, Armstrong, Maureille and Falguères) Understanding the migrations of prehistoric populations through direct dating and isotopic tracking of their mobility patterns. Part of this research was supported by the Australian French Association for Science & Technology through the ACT Science Fellowship program (2013) to M. Willme

Last interglacial (MIS 5e) sea-level determined from a tectonically stable, far-field location, Eyre Peninsula, southern Australia

The last interglacial maximum (Marine Isotope Substage 5e [MIS 5e], 128¿116 ka) is a distinctive event in recent Earth history. Shoreline successions of this age are important for calibrating climate models and defining the overall behaviour of the crust¿mantle system to fluctuating ice and ocean-water volumes. In a global context, the recently intensified interest in last interglacial shoreline successions has revealed considerable variability in the magnitude of sea-level rise during this time interval and highlighted the need to examine paleosea-level evidence from tectonically stable, far-field settings. Situated in the far-field of continental ice sheets and on the tectonically stable Gawler Craton, the 300 km coastal sector of western Eyre Peninsula between Fowlers Bay and Lake Newland in southern Australia represents an important region for defining the glacio-eustatic (ice-equivalent) sea-level attained during the last interglacial maximum based on the relative sea-level observations from this region. Low-energy, shoaling upward, peritidal bioclastic carbonate successions of the last interglacial (locally termed Glanville Formation) formed within back-barrier, estuarine¿lagoonal environments in the lee of eolianite barrier complexes (locally termed Bridgewater Formation) along this coastline. The well-preserved shelly successions (coquinas) contain diverse molluscan fossil assemblages including species no longer living in the coastal waters of South Australia (e.g. the Sydney cockle Anadara trapezia and the benthic foraminifer Marginopora vertebralis). The extent of amino acid racemisation (a measure of fossil age based on increasing d/l value) in a range of species, and in particular A. trapezia and Katelysia sp., confirms the time equivalence of the isolated embayment-fill successions, correlated with the informal type section of the Glanville Formation at Dry Creek, north of Adelaide. Preliminary U-series analyses on A. trapezia also suggest a correlation with the last interglacial maximum, but further highlight the complexity in dating fossil molluscs by the U-series method in view of their open-system behaviour. The shelly successions of the Glanville Formation occur at elevations higher than attained by sea-level in the current, Holocene interglacial. A higher sea-level of between 2.1 ± 0.5 and 4 ± 0.5 m above present sea-level is inferred for the last interglacial maximum (MIS 5e) along this coastline based on the elevation of sedimentary successions host to the shallow subtidal¿intertidal fossil molluscs Katelysia sp., and Anadara trapezia. The paleosea-level observations place a lower limit on the sea-level attained during the last interglacial maximum and suggest that caution be exercised in the definition of the upper limit of sea-level during this interglacial

Timing and mechanism for intratest Mg/Ca variability in a living planktic foraminifer

Geochemical observations indicate that planktic foraminifer test Mg/Ca is heterogeneous in many species, thereby challenging its use as a paleotemperature proxy for paleoceanographic reconstructions. We present Mg/Ca and Ba/Ca data collected by laser ablation ICP-MS from the shells of Orbulina universa cultured in controlled laboratory experiments. Test calcite was labeled with Ba-spiked seawater for 12 h day or night calcification periods to quantify the timing of intratest Mg-banding across multiple diurnal cycles. Results demonstrate that high Mg bands are precipitated during the night whereas low Mg bands are precipitated during the day. Data obtained from specimens growing at 20 °C and 25 °C show that Mg/Ca ratios in both high and low Mg bands increase with temperature, and average test Mg/Ca ratios are in excellent agreement with previously published empirical calibrations based on bulk solution ICP-MS analyses. In general, Mg band concentrations decrease with increasing pH and/or [CO2−3] but this effect decreases as experimental temperatures increase from 20 °C to 25 °C. We suggest that mitochondrial uptake of Mg2+ from the thin calcifying fluid beneath streaming rhizopodial filaments may provide the primary locus for Mg2+ removal during test calcification, and that diurnal variations in either mitochondrial density or activity produce Mg banding. These results demonstrate that Mg banding is an inherent component of test biomineralization in O. universa and show that the Mg/Ca paleothermometer remains a fundamental tool for reconstructing past ocean temperatures from fossil foraminifers

Mapping of bioavailable strontium isotope ratios in France for archaeological provenance studies

© 2017 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license: http://creativecommons.org/licenses/by-nc-nd/4.0/ This author accepted manuscript is made available following 24 month embargo from date of publication (Dec 2017) in accordance with the publisher’s archiving policyStrontium isotope ratios (87Sr/86Sr) of archaeological samples (teeth and bones) can be used to track mobility and migration across geologically distinct landscapes. However, traditional interpolation algorithms and classification approaches used to generate Sr isoscapes are often limited in predicting multiscale 87Sr/86Sr patterning. Here we investigate the suitability of plant samples and soil leachates from the IRHUM database (www.irhumdatabase.com) to create a bioavailable 87Sr/86Sr map using a novel geostatistical framework. First, we generated an 87Sr/86Sr map by classifying 87Sr/86Sr values into five geologically-representative isotope groups using cluster analysis. The isotope groups were then used as a covariate in kriging to integrate prior geological knowledge of Sr cycling with the information contained in the bioavailable dataset and enhance 87Sr/86Sr predictions. Our approach couples the strengths of classification and geostatistical methods to generate more accurate 87Sr/86Sr predictions (Root Mean Squared Error = 0.0029) with an estimate of spatial uncertainty based on lithology and sample density. This bioavailable Sr isoscape is applicable for provenance studies in France, and the method is transferable to other areas with high sampling density. While our method is a step forward in generating accurate 87Sr/86Sr isoscapes, the remaining uncertainty also demonstrates that fine-modelling of 87Sr/86Sr variability is challenging and requires more than geological maps for accurately predicting 87Sr/86Sr variations across the landscape. Future efforts should focus on increasing sampling density and developing predictive models to further quantify and predict the processes that lead to 87Sr/86Sr variability