Mapping coral calcification strategies from in situ boron isotope and trace element measurements of the tropical coral Siderastrea siderea

Boron isotopic and elemental analysis of coral aragonite can give important insights into the calcification strategies employed in coral skeletal construction. Traditional methods of analysis have limited spatial (and thus temporal) resolution, hindering attempts to unravel skeletal heterogeneity. Laser ablation mass spectrometry allows a much more refined view, and here we employ these techniques to explore boron isotope and co-varying elemental ratios in the tropical coral Siderastrea siderea. We generate two-dimensional maps of the carbonate parameters within the calcification medium that deposited the skeleton, which reveal large heterogeneities in carbonate chemistry across the macro-structure of a coral polyp. These differences have the potential to bias proxy interpretations, and indicate that different processes facilitated precipitation of different parts of the coral skeleton: the low-density columella being precipitated from a fluid with a carbonate composition closer to seawater, compared to the high-density inter-polyp walls where aragonite saturation was ~ 5 times that of external seawater. Therefore, the skeleton does not precipitate from a spatially homogeneous fluid and its different parts may thus have varying sensitivity to environmental stress. This offers new insights into the mechanisms behind the response of the S. siderea skeletal phenotype to ocean acidification

The genesis of gold mineralisation hosted by orogenic belts: A lead isotope investigation of Irish gold deposits

Lead isotope analyses have been performed on 109 gold and 23 sulphide samples from 34 Irish gold occurrences, including 27 placers, and used to shed light on the sources of mineralising fluids and metals associated with gold mineralisation hosted by orogenic belts. The Pb isotope ratios of lode and placer gold range from 206Pb/204Pb=17.287-18.679, 207Pb/204Pb=15.382-15.661, and 208Pb/204Pb=37.517-38.635, consistent with the Pb isotopic data on previously reported Irish sulphide mineralisation. There is no evidence that gold mineralisation is associated with distinctive source regions, and it appears to have been derived from similar sources to those responsible for the widespread sulphide mineralisation in Ireland. It is inferred that the principal controls on the Au mineralisation are structural and not related to the distribution of Au in their source rocks. The range of Pb isotope ratios favours the interaction of multiple source reservoirs predominantly during the Caledonian Orogeny (c. 475-380Ma). Underlying basement was the primary control on two key sources of Pb. Gold occurrences located to the south-east of the Iapetus Suture are characterised by Pb compositions that derive predominantly from the Late Proterozoic crustal basement or overlying Lower Palaeozoic sediments, whilst those located north-west of the Iapetus Suture are characterised by less radiogenic Pb signatures derived predominantly from Late Proterozoic or older crustal basement. A third source, relatively enriched in radiogenic Pb, also played a role in the formation of a number of Irish gold occurrences, and may have been associated with syn- to post-orogenic intrusives. Magmatic processes may therefore have played an important role in the formation of some orogenic gold occurrences

Mobility and migration in late Iron Age and early Medieval Ireland

Strontium and oxygen isotope analysis has been performed on a selection of human teeth dating from late Iron Age and early Medieval Ireland to test the hypothesis that the appearance of new burial rites was associated with phases of migration from, and contact with, the Roman and Late Antique world. In particular, the appearance of crouched inhumations from the beginning of the 1st century CE, and the appearance of extended supine inhumations alongside the reappearance of crouched burials after the c. 4th century CE are investigated. Isotopic data favours the presence of non-local individuals during both periods. As parallels for virtually all of these new burial practices can be found elsewhere, for example throughout Iron Age and Roman Britain, the data are seen to support previously proposed theories that such burial practices were intrusive and reflected new rites associated with migrant peoples. This adds to the increasing body of evidence demonstrating that rather than being isolated, Ireland was very much part of a connected Europe throughout the entire period of Roman administration in the western provinces, and in the centuries after its demise

A non-local source of Irish Chalcolithic and Early Bronze Age gold

Lead isotope analyses of 50 Irish Chalcolithic and Early Bronze Age gold artefacts favour a gold source in southern Ireland. However when combined with major element analysis, the artefacts are not consistent with any Irish gold deposit analysed to date. Understanding the lead isotope signatures of ore deposits within a study region allows informed inferences to be drawn regarding the likelihood that an unanalysed ore deposit was exploited in the past. If an Irish gold source is assumed, then the gold is most likely to have originated from deposits hosted by Old Red Sandstone in the Variscan ore field of south-west Ireland. However, based on our current understanding of mineralisation in the region, this scenario is considered unlikely. A non-Irish source for the gold is therefore preferred – a scenario that may favour cosmologically-driven acquisition, ie, the deliberate procurement of a material from distant or esoteric sources. Available geochemical data, combined with current archaeological evidence, favour the alluvial deposits of south-west Britain as the most likely source of the gol

The influence of geochemical variation among Globigerinoides ruber individuals on paleoceanographic reconstructions

Variation among individuals within species is a biological precondition for co-existence. Traditional geochemical analysis based on bulk averages from multiple planktic foraminifera individuals facilitates rapid data gathering but necessarily means the loss of large amounts of potentially crucial information into variability within a given sample. As the sensitivity of geochemical analysis improves, it is now feasible to build sufficiently powerful datasets to investigate paleoclimatic variation at the level of individual specimens. Here, we investigate geochemical and morphological variation among the sensu stricto, sensu lato and sensu lato extreme subspecies of the workhorse extant planktic foraminifera Globigerinoides ruber. Our experimental design distinguishes between subspecies and intraspecific variability as well as the repeatability of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We show that geochemical variability in Mg/Ca ratios is driven by differences in subspecies depth habitat and that ontogenetic trends in Mg/Ca ratios are evident in the final whorl, with the final chamber consistently showing depleted Mg/Ca. These ontogenetic trends are not driven by individual chamber or test size. The Mg/Ca value variance among individuals is ~100 times higher than the variance among repeated laser spot analyses of a signal chambers, directing laboratory protocols towards the need to sample ecologically and environmentally homogeneous samples. Our results emphasize that we can use LA-ICP-MS to quantify how individual variability aggregates to bulk results, and highlights that, with sufficient sample sizes, it is possible to reveal how intraspecific variability alters geochemical inference

Imaging of boron in altered mantle rocks illuminates progressive serpentinisation episodes

Serpentinised mantle rocks reflect the cumulative sum of multiple alteration events, but to date, identifying distinct serpentinisation episodes has remained challenging due to limited knowledge of the spatial distribution of tracers of fluid-rock exchange. Here we present novel high spatial resolution (∼10 μm) boron, nickel, calcium, and lithium concentration maps combined with in situ boron isotope analyses of strongly serpentinised mantle peridotites from the Troodos ophiolite, Cyprus. Our maps indicate strongly heterogenous boron concentrations with high boron concentrations in early formed serpentine replacing olivine but much lower boron contents in mesh-textured serpentine and bastitic pyroxene. Late stage crosscutting serpentine veins have very low boron concentrations. In contrast, boron isotope measurements, made at coarser scales, are remarkably uniform (mean value +11.9 ± 3.2 %, 1σ, n = 49). We interpret the high boron serpentine as reflecting the partial preservation of an early pervasive serpentinisation episode by fluids with high boron concentrations sourced from the dehydration of the subducting Cyprus slab. Subsequent serpentine phases with moderate to low boron reflect progressive recrystallisation and leaching by low boron concentration meteoric waters.</p

Reconstructing high-resolution climate using CT scanning of unsectioned stalagmites: A case study identifying the mid-Holocene onset of the Mediterranean climate in southern Iberia.

The forcing mechanisms responsible for the mid-Holocene onset of the Mediterranean-type climate in south-western Europe are currently unclear, but understanding these is critical for accurate climate projections under future greenhouse gas warming. Additionally, regional studies that present conflicting patterns for the onset and advancement of Mediterranean climatic conditions complicate definitively ascribing causality. Here, we use a new high resolution stalagmite density record obtained non-destructively using Computed Tomography (CT scanning) to reconstruct southern Iberian climate between 9.3 and 2.9 ka BP. We suggest that stalagmite density can be used as a water-excess proxy, with lower densities associated with more variable drip rates, possibly reflecting increased seasonality consistent with expectations from previous studies of speleothem textures and crystal fabrics. Our results reveal an early Holocene humid interval and mid-Holocene year-round aridity that preceded the onset of Mediterranean climate at 5.3 ka BP in southern Iberia. Using this new dataset combined with previously published results, we link the gradual advancement of the Mediterranean climate to the southward migration of the North Atlantic Subtropical High induced by an orbitally driven decrease in Northern Hemisphere insolation. Future anthropogenic warming could result in a reversal of this trend, a northward migration of the North Atlantic Subtropical High, and a return to year-round aridity in south-western Europe