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The Holocene epoch offers a potential analogue for understanding future sea-level variability as both SST's and Global Mean Sea Levels (GMSL) were at times higher than observed today. However, GMSL can differ significantly from Relative Sea Level (RSL), even at far-field sites remote from margins of former ice sheets. Much of this spatial variability has been shown to be consistent with the predictions of glacial isostatic adjustment (GIA) models. Whilst it is generally accepted that RSL at far-field sites reached its maximum during the mid-Holocene, there have been many interpretations of sea level fall following the highstand from ∼6 ka. Here, we present a RSL history from several tectonically stable, far-field sites in eastern Brazil, derived from 17 microatoll and 45 fossil reef flat ages. Our results show evidence for two periods of RSL instability during the Holocene which differ from GIA predictions, including a hiatus in reef growth ∼3.7–2.5 ka. These results are broadly synchronous with several other locations in the Southern Hemisphere suggesting global rather than regional climatic forcing mechanisms are responsible. Variations in SST and southern hemisphere ice sheet dynamics are proposed as possible controlling mechanisms for the observed RSL oscillations beginning at ∼3.7 ka and 2 ka respectively. We suggest that these global processes combined with increased precipitation (and higher sediment flux) from several regional climatic forces created inhospitable conditions for reef growth, contributing to the observed hiatus and reduced reef flat accretion during the late Holocene (∼2 ka to present).

The hydromagnesite–magnesite playas near Atlin, British Columba, Canada are unique Mg-carbonate depositional environments that have formed at Earth’s surface since the end of the last deglaciation. This study elucidates the mechanisms, pathways, and rates of magnesite (MgCO3) formation in these near-surface environments, which are challenging to study in short-duration laboratory experiments because magnesite precipitation is extremely slow at low temperature. The Atlin playas, having formed over millennia, contain abundant magnesite as well as a suite of other Mg- and Ca-carbonate minerals. Mineralogical and textural evidence demonstrate that hydromagnesite [Mg5(CO3)4(OH)2·4H2O] forms at least in part through transformation of more hydrated phases, e.g., lansfordite (MgCO3·5H2O). Deposition of these hydrated Mg-carbonate minerals is limited by the evaporative flux, and thus, is effectively transport-controlled at the scale of the playas. Magnesite is a spatially distinct phase from hydromagnesite and its crystal morphology varies with depth indicating variable crystal growth mechanisms and precipitation rates. Particle size distributions and mineral abundance data indicate that magnesite formation is nucleation-limited. Furthermore, mineralogical data as well as stable and radiogenic isotope data support magnesite formation starting after the majority of hydromagnesite had been deposited likely resulting from long induction times and slow precipitation rates. Hydrated Mg-carbonate minerals precipitate relatively rapidly and control pore water chemistry while magnesite remains highly supersaturated, and thus, is reaction-controlled. This difference in controlling regime allows for magnesite abundance to increase over time without the loss of hydromagnesite such as through its transformation, which the data also does not support. We estimate rates of magnesite formation (nucleation + crystal growth) in the range of 10−17 to 10−16 mol/cm2/s over approximately 8000 yea

Native fish populations have been strongly impacted by fishing, habitat alteration and the introduction of invasive species. Understanding the dynamics of native fish populations prior to commercial fishing can be problematic, but provides critical baseline data for fish conservation, rehabilitation and management. We combined fish size, age and growth data, as well as month of catch data, from archaeological fish otoliths (1670–1308 cal BP to 409–1 cal BP), historical anecdotes (CE 1871–1999), and contemporary data sources (CE 1984–2014) to examine changes to mulloway, Argyrosomus japonicus, populations in the waters of eastern South Australia. We found that the data from the three different sources – archaeological, historical and contemporary – corroborate each other in many aspects. The time of catch for all three datasets was seasonal, with increases evident during the summer months. No significant changes in fish length over time were evident over the time span of the three data sources. Given the impact that fishing in the region is regarded to have had, this may imply that while the maximum recorded sizes of the species have remained stable, the abundance of these large specimens may have declined.

We investigate the ability of coralline red algae to record historical nickel mining activity that occurred between the early 1960s and 1981 in the Coulée River watershed, southwest New Caledonia. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was used to determine high-resolution (sub-annual) variations of trace metal ratios (Mn/Ca, Fe/Ca, Ni/Ca and Co/Ca) in three ~45 years old, free-living forms of the rhodolith coralline red alga Sporolithon durum from Ricaudy Reef in the inner lagoon of New Caledonia, 15 km from the Coulée River mouth. We find increased Mn/Ca and Fe/Ca ratio values track the intensity of mining in the Coulée River catchment whereas Ni/Ca ratio values appear more sensitive to the ore type (saprolite versus laterite) that were targeted during two separate stages of mining activity. Mn/Ca, Fe/Ca and Ni/Ca decrease following the cessation of mining in 1981, but did not reach current values until >10 years after that date. Surprisingly, Co/Ca variations do not correlate with mining activity but rather increase steadily through the record period. We argue this relates to nickel refining and smelting activity over the past half century. Our results further suggest that the local, inter-annual rainfall variability may influence the metal concentrations recorded in the rhodoliths during the period of intense mining activity, but the link between metal uptake and rainfall is not entirely clear for the entire growth period of the rhodoliths.

A slice from a Porites Lutea coral core collected inside the Enewetak Atoll lagoon, within 15 km of all major nuclear tests conducted at the atoll, was analysed for 236U, 239Pu and 240Pu over the time interval 1952-1964 using a higher time resolution than previously reported for a parallel slice from the same core. In addition two sediment samples from the Koa and Oak craters were analysed. The strong peaks in the concentrations of 236U and 239Pu in the testing years are confirmed to be considerably wider than the flushing time of the lagoon. This is likely due to the growth mechanism of the coral. Following the last test in 1958 atom concentrations of both 236U and 239Pu decreased from their peak values by more than 95% and showed a seasonal signal thereafter. Between 1959 and 1964 the weighted average of the 240Pu/239Pu atom ratio is 0.124 ± 0.008 which is similar to that in the lagoon sediments (0.129 ± 0.006) but quite distinct from the global fallout value of ∼0.18. This, and the high 239,240Pu and 236U concentrations in the sediments, provides clear evidence that the post-testing signal in the coral is dominated by remobilisation of the isotopes from the lagoon sediments rather than from global fallout

Unambiguous identification of biosignatures on Mars requires access to well-characterized, long-lasting geochemical standards at the planet’s surface that can be modified by theoretical martian life. Ordinary chondrites, which are ancient meteorites that commonly fall to the surface of Mars and Earth, have well-characterized, narrow ranges in trace element and isotope geochemistry compared to martian rocks. Given that their mineralogy is more attractive to known chemolithotrophic life than the basaltic rocks that dominate the martian surface, exogenic rocks (e.g., chondritic meteorites) may be good places to look for signs of prior life endemic to Mars. In this study, we show that ordinary chondrites, collected from the arid Australian Nullarbor Plain, are commonly colonized and inhabited by terrestrial microorganisms that are endemic to this Mars analogue site. These terrestrial endolithic and chasmolithic microbial contaminants are commonly found in close association with hygroscopic veins of gypsum and Mg-calcite, which have formed within cracks penetrating deep into the meteorites. Terrestrial bacteria are observed within corrosion cavities, where troilite (FeS) oxidation has produced jarosite [KFe3(SO4)2 (OH)6]. Where terrestrial microorganisms have colonized primary silicate minerals and secondary calcite, these mineral surfaces are heavily etched. Our results show that inhabitation of meteorites by terrestrial microorganisms in arid environments relies upon humidity and pH regulation by minerals. Furthermore, microbial colonization affects the weathering of meteorites and production of sulfate, carbonate, Fe-oxide and smectite minerals that can preserve chemical and isotopic biosignatures for thousands to millions of years on Earth. Meteorites are thus habitable by terrestrial microorganisms, even under highly desiccating environmental conditions of relevance to Mars. They may therefore be useful as chemical and isotopic ‘‘standards” that preserve evidence of

The eastern side of Hawaii Island is a rapidly subsiding margin dominated by drowned carbonate platforms. We present detailed bathymetric and backscatter data, remotely operated vehicle and submersible observations, sedimentological and 14C accelerator mass spectrometry and U/Th age data from seven submerged terraces (H7, H2a-d, H1a-b) in water depths between 1100 and 25m off Hilo, north-eastern Hawaii. The main carbonate deposits on these terraces are coral deposits, rhodolith beds, coralline algal mounds, crusts, pavements and tabular sheets. We identified five previously described sedimentary shallow- to deep-water facies and one new facies type that are consistent with reef drowning on a rapidly subsiding margin. We used palaeobathymetric data derived from the sedimentary facies, age versus depth relationships, and published sea-level curves, to estimate a uniform long-term subsidence rate of 2.80±0.36m/ky for the eastern side of Hawaii over the last 150ky. Terrace H7 developed about 380ka based on data from the western side of the island. Active coral growth on terrace H2d occurred during the Marine Isotope Stage (MIS) 6 to 5 transition, and the terrace drowned during the peak of MIS 5e when sea level rose faster than reefs could grow. Favoured by the gentle platform gradient, reefs established progressively landwards with a backstepping pattern during MIS 5e to form the terraces H2c and H2b 122ka. Final turn-off of shallow water carbonate production on terraces H2b-d coincided with the relative sea-level rise of the interstadial MIS 5a. Bathymetry and submersible data suggest that carbonate sediments on terraces H2a and H1b were deposited over an antecedent topography of local lava deltas emplaced during rising sea levels at ca. 85 and 65ka, while terrace H1a established on lava delta substrates of the Mauna Loa volcano ca. 11ka. We conclude that the initiation, growth and drowning of coral-reef terraces off Hilo differ in some ways from the pattern observed i

It has been proposed that the ventilation of the deep Pacific carbon pool was not significantly reduced during the last glacial period, posing a problem for canonical theories of glacial-interglacial CO2 change. However, using radiocarbon dates of marine

Sample preparation protocols for concentrating organic material from sediments for radiocarbon dating often include a large number of steps and the use of hazardous chemicals. Thus, these protocols are often problematic for pollen-poor sediments as material can get lost or may become degraded. Pyrite in samples for radiocarbon dating hinders an effective graphitisation process and thus needs to be removed during sample preparation. Standard protocols require the use of nitric acid, a strong oxidant that corrodes organic material. Therefore, the use of nitric acid needs to be avoided when preparing pollen-poor but pyrite-rich sediments.We present a method that minimises the sample preparation steps by replacing acid treatment with heavy liquid separation. Using non-toxic LST at a density of 2.0gcm-3 is shown to be effective for separating the organic fraction from sulphides, silicates and carbonates. We applied this method to pyrite-rich and pollen-poor sediments from Western Australia that had previously been problematic to date. The successful AMS radiocarbon dating of all samples pre-treated with LST demonstrates the effectiveness of this method.

Two-component models are often used to determine the contributions made by fossil fuel and natural sources of carbon in airborne particulate matter (PM). The models reduce thousands of actual sources to two end members based on isotopic signature. Combustion of fossil fuels produces PM free of carbon-14 (14C). Wood or charcoal smoke, restaurant fryer emissions, and natural emissions from plants produce PM with the contemporary concentration of 14C approximately 1.2 × 10-1214C/C. Such data can be used to estimate the relative contributions of fossil fuels and biogenic aerosols to the total aerosol loading and radiocarbon analysis is becoming a popular source apportionment method. Emissions from incinerators combusting medical or biological wastes containing tracer 14C can skew the 14C/C ratio of PM, however, so critical analysis of sampling sites for possible sources of elevated PM needs to be completed prior to embarking on sampling campaigns. Results are presented for two ambient monitoring sites in different areas of the United States where 14C contamination is apparent. Our experience suggests that such contamination is uncommon but is also not rare (∼10%) for PM sampling sites.

We report the first uranium-series age estimates for rock art in China. Calcite bracketing a paint layer was used to constrain the age of a naturalistic outline hunter-gatherer painting in the Jinsha River area of northwest Yunnan Province (southwest China). The rock paintings in this region are unique in style and content compared with other bodies of rock art in China, which are dominated by Neolithic subject matter. The minimum and maximum ages were determined using isochron techniques on multiple samples of calcite from above and beneath the paint layer. A large painted deer head was dated to between 5738 and 2050 years. This painting and underlying flowstone are superimposed on older paintings that suggest the older paintings are at least 3400 years old, if not older than 5738 years. The results indicate for the first time that Jinsha River rock art is older than other forms of rock art in the region and show that rock art likely extends back to at least the transition from the Palaeolithic to Neolithic in this part of China.

In February 2007, a single stage AMS from the National Electrostatics Corporation (NEC) was installed at the Research School of Earth Sciences at the Australian National University. This instrument is equipped with a gas/graphite hybrid ion source allowing direct analysis of CO2 as well as traditional graphite targets. The instrument was funded by an Australian Research Council grant and by a consortium of eight universities plus the CSIRO Division of Land and Water. Its purpose is to support integrated environmental and archaeological research and access is open to the wider research community. In the first year ∼1500 samples have been analysed. A precision of ∼3‰ is routinely observed. The background for processed graphite (coal, calcite, Carrera marble) is better than 45,000 years. This paper summarizes the first year of measurements.

The ability to reliably age siliceous sponges is explored using radiocarbon dating of several hexactinellid sponge specimens including Rossella racovitzae racovitzae Topsent, 1901 (C. Hexactinellida: O. Lyssacinosida: F. Rossellidae), collected from the Ross Sea, Antarctica. The optimal pretreatment was found to consist of both sequential acid digestion and pre-roasting at temperatures >400 °C. Subsequent combustion at 900 °C liberated the proteinaceous material within the spicule matrix and once the reservoir age of the surrounding water was accounted for, a linear extension rate was calculated to be around 2.9 mm yr-1, aging the sponge at ∼440 years old.

We use a combination of nanometer-resolution secondary ion mass spectrometry (NanoSIMS) and analytical transmission electron microscopy (ATEM) for chemical imaging of material transformed in a laser-heated diamond anvil cell (LH-DAC), in the pressure and

The Center for AMS, Lawrence Livermore National Laboratory (CAMS) modified high-intensity Cs+ sputter source has several key characteristics, including very high ion current output, that make it useful for AMS applications. Within the AMS community there

Coralline sponges (sclerosponges) have been proposed as a new source for paleo subsurface temperature reconstructions by utilizing methods developed for reef-building corals. However unlike corals, they do not have density variations, making age determination difficult. In this study, we examined multiple elemental ratios (B / Ca, Mg / Ca, Sr / Ca, Ba / Ca, U / Ca) in the coralline sponge Astrosclera willeyana. We also measured skeletal density profiles along the outer "living" edge of the sponges and these data indicate significant thickening of skeletal material over intervals of 2-3 mm which corresponds to 2-3 years. This suggests that any skeletal recovered environmental record from A. willeyana is an integration of signals over a ∼2-3 year period. Sponge Sr / Ca seemed to hold the most promise as a recorder of water temperature and we compared Sr / Ca from 2 sponges in the Great Barrier Reef and one from Truk in Micronesia to their respective sea surface temperature record. The correlations were not strong (∼r = - 0.5) but were significant. It appears that the signal smoothing due to thickening or perhaps even some other control (biologic, biomineralization) on Sr skeletal partitioning limits the use of Sr / Ca as an indicator of water temperature in A. willeyana. Variations of B / Ca, Mg / Ca, Ba / Ca and U / Ca only have moderate to poor correlations to Sr / Ca and are not consistent between samples. They also do not show correlations with water temperature and may be more heavily influenced by the biomineralization occurring in the secondary thickening.

The rapid analytical technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to measure the trace elements B, Mg, Sr, Ba and U in a high-latitude coral colony (Porites lobata) taken from Shirigai Bay, Japan (32°N). A