Sedimentary porewaters record regional tectonic and climate events that perturbed a deep-sea brine pool in the Gulf of Aqaba, Red Sea.

Brine pools in deep-sea environments provide unique perspectives into planetary and geological processes, extremophile microbial communities, and sedimentary records. The NEOM Brine Pool Complex was the first deep-sea brine pool system found in the Gulf of Aqaba, representing a significant extension of the geographical range and depositional setting of Red Sea brine pools. Here, we use a combination of brine pool samples collected via cast using a conductivity, temperature, depth instrument (CTD), as well as interstitial porewaters extracted from a sediment core collected in the NEOM Brine Pool to characterize the chemical composition and subsurface evolution of the brine. New results indicate that the NEOM brines and the subsurface porewaters may originate from different sources. Elemental concentrations suggest the brines in the NEOM pool are likely derived from dissolution of sub-seabed evaporites. In contrast, the sedimentary porewaters appear to have been influenced by periodic turbidite flows, generated either by earthquakes, submarine landslides, or flash floods, in which normal marine waters from the overlying Red Sea became entrained, periodically disturbing the chemistry of the brine pool. Thus, sediment porewaters beneath brine pools may record transient and dynamic changes in these deep marine depositional environments, reflecting the interplay between climate, tectonics, and sedimentation patterns along a rapidly urbanizing coastline. In concert, new results from NEOM extend the range and chemical constraints on Red Sea Brine Pools and highlight the dynamic interplay between Red Sea Deep water, dissolving evaporites, turbidites, and subsurface fluids that produce these unique depositional environments which host microbial life at the edge of habitability. In concert with sedimentological indicators, the chemistry of porewaters beneath deep-sea brine pools may present detailed records of natural hazards arising from interactions between the atmosphere, lithosphere, hydrosphere, and anthroposphere.

Assessing quality and beneficial uses of Sargassum compost.

Sargassum spp. (specifically Sargassum fluitans and S. natans), one of the dominant forms of marine macroalgae (seaweed) found on the beaches of Florida, is washing up on the shores throughout the Caribbean in record quantities. Currently, a common management option is to haul and dispose of beached Sargassum in local landfills, potentially wasting a valuable renewable resource. The objective of this study was to determine whether composting represents a feasible alternative to managing Sargassum inundations through measurements and comparisons to eleven guidelines. Specifically, we assessed the characteristics of the compost [physical-chemical parameters (temperature, moisture content, pH, and conductivity), nutrient ratios (C:N), elemental composition, bacteria levels, and ability to sustain plant growth] in both small- and large scale experiments. Results show that although nutrient concentration ratios were not within the standards outlined by the U.S. Composting Council (USCC), the Sargassum compost was able to sustain the growth of radishes (Raphanus sativus L., var. Champion). Trace metal concentrations in the compost product were within five regulatory guidelines evaluated, except for arsenic (As) (6.64-26.5 mg/kg), which exceeded one of the five (the Florida Soil Cleanup Target Level for residential use). Bacteria levels were consistent with regulatory guidelines for compost produced in large-scale outdoor experiments but not for the small-scale set conducted in enclosed tumblers. Overall results support that Sargassum compost can be beneficially used for fill and some farming applications.

Coevolution of diagenetic fronts and fluid-fracture pathways.

Diagenetic boundaries are paleo-reaction fronts, which have the potential to archive the termination of metasomatic processes in sedimentary rocks. They have not been extensively studied, perhaps because they appear simple in outcrop. Recent work has demonstrated the significance of paleo-reaction fronts to decipher multiphase recrystallization processes and provide high porosity zones. This paper provides a detailed documentation of reaction front evolution in a tectonically active salt basin and reveals a high level of complexity, associated with multiple fluid flow and tectonic events. Here, consistent patterns of increasing dolomite stoichiometry and ordering, along with a change from seawater-derived, fabric-retentive dolomite to fracture-controlled, fabric-destructive hydrothermal dolomite are observed vertically across the stratabound dolomite bodies. These patterns, coupled with a decrease in porosity, increase in ∆47 temperature and δ18Owater values indicate multiphase recrystallization and stabilization by warm, Mg-rich fluids. The stratabound dolomite bodies apparently terminated at a fracture-bound contact, but the presence of dolomite fragments within the fracture corridor suggests that fracturing post-dated the first dolomitization event. The termination of dolomite formation is therefore interpreted to be associated with a decrease in the capacity of the magnesium-rich fluids to dolomitize the rock, as indicated by the presence of non-stoichiometric and poorly ordered dolomite at the reaction fronts. The fracture corridors are interpreted to exploit dolostone-limestone boundaries, forming prior to a later, higher temperature, hydrothermal dolomitization event, which coincided with the formation and growth of the anticline. Karstification subsequently exploited these fracture corridors, widening fractures and leading to localized collapse and brecciation. The results demonstrate that an apparently simple reaction front can have a complex history, governed by the inheritance of prior diagenetic events. These events modified rock properties in such a way that fluid flow was repeatedly focused along the original dolomite-limestone boundary, overprinting much of its original signature. These findings have implications to the prediction of structurally controlled diagenetic processes and the exploration of naturally fractured carbonate reservoirs for energy exploration globally.

A calibration equation between Δ48 values of carbonate and temperature.

RATIONALE: Information on the temperature of formation or alteration of carbonate minerals can be obtained by measuring the abundance of the isotopologues 47 and 48 (Δ47 and Δ48 values) of CO2 released during acid dissolution. The combination of these two proxies can potentially provide a greater insight into the temperature of formation, particularly if the carbonate minerals form by non-equilibrium processes. METHODS: We have precipitated calcium carbonates at seven temperatures between 5 and 65°C and measured their δ48 values using a Thermo-253 plus isotope ratio mass spectrometer. The values were transformed to Δ48 values in the conventional manner and then converted to the carbon dioxide equilibrium scale. RESULTS: Using the Δ48 values, we have established an empirical calibration between temperature and Δ48 values: [Formula: see text] CONCLUSIONS: The calibration line produced allows the determination of the temperature of natural carbonates using the Δ48 values and agrees with the measurements of the Δ47 and Δ48 values of some carbonates assumed to have formed under equilibrium conditions.

Dataset of characteristic remanent magnetization and magnetic properties of early Pliocene sediments from IODP Site U1467 (Maldives platform).

This data article describes data of magnetic stratigraphy and anisotropy of isothermal remanent magnetization (AIRM) from "Magnetic properties of early Pliocene sediments from IODP Site U1467 (Maldives platform) reveal changes in the monsoon system" [1]. Acquisition of isothermal magnetization on pilot samples and anisotropy of isothermal remanent magnetization are reported as raw data; magnetostratigraphic data are reported as characteristic magnetization (ChRM).

Boiled or roasted? Bivalve cooking methods of early Puerto Ricans elucidated using clumped isotopes.

Cooking technique reflects a combination of cultural and technological factors; here, we attempt to constrain bivalve cooking temperatures for a pre-Columbian Puerto Rican native population using carbonate clumped isotopes. Analyses of 24 bivalve specimens (Phacoides pectinatus) from a shell midden in Cabo Rojo, Puerto Rico, suggest that samples were heated up to 200°C, indicating that roasting rather than boiling may have been the preferred cooking technique. More than half of analyzed samples exhibited a distinct change from modern uncooked shells, possibly reflecting different cooking techniques or the use of a single method wherein shells are unevenly heated, such as when placed on a heated surface. Roasting bivalves would not necessitate the use of ceramic technologies, an observation concurrent with the absence of such artifacts at this site.

Prehistoric cooking versus accurate palaeotemperature records in shell midden constituents.

The reconstruction of pre-depositional cooking treatments used by prehistoric coastal populations for processing aquatic faunal resources is often difficult in archaeological shell midden assemblages. Besides limiting our knowledge of various social, cultural, economic and technological aspects of shell midden formation, unknown pre-depositional cooking techniques can also introduce large errors in palaeoclimate reconstructions as they can considerably alter the geochemical proxy signatures in calcareous skeletal structures such as bivalve shells or fish otoliths. Based on experimental and archaeological data, we show that carbonate clumped-isotope thermometry can be used to detect and reconstruct prehistoric processing methods in skeletal aragonite from archaeological shell midden assemblages. Given the temperature-dependent re-equilibration of clumped isotopes in aragonitic carbonates, this allows specific processing, cooking or trash dispersal strategies such as boiling, roasting, or burning to be differentiated. Besides permitting the detailed reconstruction of cultural or technological aspects of shell midden formation, this also allows erroneous palaeoclimate reconstructions to be avoided as all aragonitic shells subjected to pre-historic cooking methods show a clear alteration of their initial oxygen isotopic composition.

Species-specific responses to climate change and community composition determine future calcification rates of Florida Keys reefs.

Anthropogenic climate change compromises reef growth as a result of increasing temperatures and ocean acidification. Scleractinian corals vary in their sensitivity to these variables, suggesting species composition will influence how reef communities respond to future climate change. Because data are lacking for many species, most studies that model future reef growth rely on uniform scleractinian calcification sensitivities to temperature and ocean acidification. To address this knowledge gap, calcification of twelve common and understudied Caribbean coral species was measured for two months under crossed temperatures (27, 30.3 °C) and CO2 partial pressures (pCO2 ) (400, 900, 1300 µatm). Mixed-effects models of calcification for each species were then used to project community-level scleractinian calcification using Florida Keys reef composition data and IPCC AR5 ensemble climate model data. Three of the four most abundant species, Orbicella faveolata, Montastraea cavernosa, and Porites astreoides, had negative calcification responses to both elevated temperature and pCO2 . In the business-as-usual CO2 emissions scenario, reefs with high abundances of these species had projected end-of-century declines in scleractinian calcification of >50% relative to present-day rates. Siderastrea siderea, the other most common species, was insensitive to both temperature and pCO2 within the levels tested here. Reefs dominated by this species had the most stable end-of-century growth. Under more optimistic scenarios of reduced CO2 emissions, calcification rates throughout the Florida Keys declined <20% by 2100. Under the most extreme emissions scenario, projected declines were highly variable among reefs, ranging 10-100%. Without considering bleaching, reef growth will likely decline on most reefs, especially where resistant species like S. siderea are not already dominant. This study demonstrates how species composition influences reef community responses to climate change and how reduced CO2 emissions can limit future declines in reef calcification.

The abrupt onset of the modern South Asian Monsoon winds.

The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

The inversion of aragonite to calcite during the sampling of skeletal archives: implications for proxy interpretation.

RATIONALE: Understanding changes in Earth's oceans and climate requires the reliable application of paleo-proxies. However, inconsistencies between individual δ(18) O records within biogenic specimens commonly have significant impacts on environmental reconstructions. This study addresses the stable isotope variability associated with sample milling from aragonitic organisms commonly used for paleoclimate studies. METHODS: Aragonite samples were hand-ground and milled from sclerosponge, coral, and mollusc specimens using a computerized micromill. An X-ray diffractometer was used to analyze sample mineralogy prior to measurement of δ(18) O and δ(13) C values via isotope ratio mass spectrometry of CO2 gases provided from the samples by a Kiel III device. Possible influences on the Sr/Ca ratios were assessed on a sclerosponge through paired elemental analysis by inductively coupled plasma optical emission spectrometry. RESULTS: Analyses revealed up to 36% inversion to calcite in milled samples that correlated with a decrease in the δ(18) O value of 0.02 ‰ per 1% inversion. Replicate sclerosponge transects yielded similar trends in δ(13) C values and Sr/Ca ratios, although the δ(18) O values showed irregular variations consistent with those measured for the inversion of individual organisms during milling. CONCLUSIONS: While the δ(13) C values and Sr/Ca ratios of milled samples were largely consistent, the δ(18) O values co-varied with the inversion of aragonite to calcite suggesting significant implications for the resulting temperature and salinity reconstructions from aragonitic archives. The effect appears to be density-driven and, given that the skeletal density tends to vary seasonally in organisms such as corals, would subsequently mask temperature-induced changes in skeletal δ(18) O values.

Interpreting carbonate and organic carbon isotope covariance in the sedimentary record.

Many negative δ(13)C excursions in marine carbonates from the geological record are interpreted to record significant biogeochemical events in early Earth history. The assumption that no post-depositional processes can simultaneously alter carbonate and organic δ(13)C values towards more negative values is the cornerstone of this approach. However, the effects of post-depositional alteration on the relationship between carbonate and organic δ(13)C values have not been directly evaluated. Here we present paired carbonate and organic δ(13)C records that exhibit a coupled negative excursion resulting from multiple periods of meteoric alteration of the carbonate δ(13)C record, and consequent contributions of isotopically negative terrestrial organic matter to the sedimentary record. The possibility that carbonate and organic δ(13)C records can be simultaneously shifted towards lower δ(13)C values during periods of subaerial exposure may necessitate the reappraisal of some of the δ(13)C anomalies associated with noteworthy biogeochemical events throughout Earth history.

Measurement of δ18O and δ2H values of fluid inclusion water in speleothems using cavity ring-down spectroscopy compared with isotope ratio mass spectrometry.

RATIONALE: The hydrogen and oxygen isotopic analyses (δ(2)H and δ(18)O values) of water trapped within speleothem carbonate (fluid inclusions) have traditionally been conducted utilizing dual-inlet isotope ratio mass spectrometry (IRMS) or continuous-flow (CF)-IRMS methods. The application of cavity ring-down spectroscopy (CRDS) to the δ(2)H and δ(18)O analysis of water in fluid inclusions has been investigated at the University of Miami as an alternative method to CF-IRMS. METHODS: An extraction line was developed to recover water from the fluid inclusions consisting of a crusher, sample injection port and an expansion volume (either 100 or 50 cm(3)) directly connected to the CRDS instrument. Tests were conducted to determine the reproducibility of standard water injections and crushes. In order to compare results with conventional analytical methods, samples were analyzed both at the University of Miami (CRDS method) and at the Vrije Universiteit Amsterdam (CF-IRMS method). RESULTS: The analytical reproducibility of speleothem samples crushed on the Miami Device demonstrates an average external standard deviation of 0.5 and 2.0 ‰ for δ(18)O and δ(2)H values, respectively. Sample data are shown to fall near the global meteoric water line, supporting the validity of the method. Three different samples were analyzed at Vrije Universiteit Amsterdam and the University of Miami in order to compare the performance of each laboratory. The average offset between the two laboratories is 0.7 ‰ for δ(18)O and 2.5 ‰ for δ(2)H. CONCLUSIONS: The advantage of CRDS is that the system is a low-cost alternative to CF-IRMS for fluid inclusion isotope analysis. The CRDS method demonstrates acceptable precision and good agreement with results from the CF-IRMS method. These are promising results for the future application of CRDS to fluid inclusion isotope analysis.

New insights to the use of ethanol in automotive fuels: a stable isotopic tracer for fossil- and bio-fuel combustion inputs to the atmosphere.

Ethanol is currently receiving increased attention because of its use as a biofuel or fuel additive and because of its influence on air quality. We used stable isotopic ratio measurements of (13)C/(12)C in ethanol emitted from vehicles and a small group of tropical plants to establish ethanol's δ(13)C end-member signatures. Ethanol emitted in exhaust is distinctly different from that emitted by tropical plants and can serve as a unique stable isotopic tracer for transportation-related inputs to the atmosphere. Ethanol's unique isotopic signature in fuel is related to corn, a C4 plant and the primary source of ethanol in the U.S. We estimated a kinetic isotope effect (KIE) for ethanol's oxidative loss in the atmosphere and used previous assumptions with respect to the fractionation that may occur during wet and dry deposition. A small number of interpretive model calculations were used for source apportionment of ethanol and to understand the associated effects resulting from atmospheric removal. The models incorporated our end-member signatures and ambient measurements of ethanol, known or estimated source strengths and removal magnitudes, and estimated KIEs associated with atmospheric removal processes for ethanol. We compared transportation-related ethanol signatures to those from biogenic sources and used a set of ambient measurements to apportion each source contribution in Miami, Florida-a moderately polluted, but well ventilated urban location.

Leaf and root pectin methylesterase activity and 13C/12C stable isotopic ratio measurements of methanol emissions give insight into methanol production in Lycopersicon esculentum.

Plant production of methanol (MeOH) is a poorly understood aspect of metabolism, and understanding MeOH production in plants is crucial for modeling MeOH emissions. Here, we have examined the source of MeOH emissions from mature and immature leaves and whether pectin methylesterase (PME) activity is a good predictor of MeOH emission. We also investigated the significance of below-ground MeOH production for mature leaf emissions. We present measurements of MeOH emission, PME activity, and MeOH concentration in mature and immature tissues of tomato (Lycopersicon esculentum). We also present stable carbon isotopic signatures of MeOH emission and the pectin methoxyl pool. Our results suggest that below-ground MeOH production was not the dominant contributor to daytime MeOH emissions from mature and immature leaves. Stable carbon isotopic signatures of mature and immature leaf MeOH were similar, suggesting that they were derived from the same pathway. Foliar PME activity was related to MeOH flux, but unexplained variance suggested PME activity could not predict emissions. The data show that MeOH production and emission are complex and cannot be predicted using PME activity alone. We hypothesize that substrate limitation of MeOH synthesis and MeOH catabolism may be important regulators of MeOH emission.

Growth rates of Florida corals from 1937 to 1996 and their response to climate change.

Ocean acidification causes declines in calcification rates of corals because of decreasing aragonite saturation states (Ω(arag)). Recent evidence also indicates that increasing sea surface temperatures may have already reduced growth and calcification rates because of the stenothermic threshold of localized coral populations. Density banding in coral skeletons provides a record of growth over the coral's lifespan. Here we present coral extension, bulk density and calcification master chronologies from seven subtropical corals (Montastraea faveolata) located in the Florida Keys, USA with a 60-year common period, 1937-1996. Linear trends indicate that extension increased, density decreased and calcification remained stable while the most recent decade was not significantly different than decadal averages over the preceding 50 years for extension and calcification. The results suggest that growth rates in this species of subtropical coral have been tolerant to recent climatic changes up to the time of collection (1996).

Delta13C stable isotope analysis of atmospheric oxygenated volatile organic compounds by gas chromatography-isotope ratio mass spectrometry.

We present a new method for analyzing the delta(13)C isotopic composition of several oxygenated volatile organic compounds (OVOCs) from direct sources and ambient atmospheric samples. Guided by the requirements for analysis of trace components in air, a gas chromatograph isotope ratio mass spectrometer (GC-IRMS) system was developed with the goal of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the isotope ratio mass spectrometer (IRMS). The technique relies on a two-stage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. The instrument's measurement precision is 0.6 to 2.9 per thousand (1sigma), and results indicate that negligible sample fractionation occurs during gas sampling. Measured delta(13)C values have a minor dependence on sample size; linearity for acetone was 0.06 per thousand ng C(-1) and was best over 1-10 ng C. Sensitivity is approximately 10 times greater than similar instrumentation designs, incorporates the use of a diluted working reference gas (0.1% CO(2)), and requires collection of >0.7 ng C to produce accurate and precise results. With this detection limit, a 1.0 L sample of ambient air provides sufficient carbon for isotopic analysis. Emissions from vegetation and vehicle exhaust are compared and show clear differences in isotopic signatures. Ambient samples collected in metropolitan Miami and the Everglades National Park can be differentiated and reflect multiple sources and sinks affecting a single sampling location. Vehicle exhaust emissions of ethanol, and those collected in metropolitan Miami, have anomalously enriched delta(13)C values ranging from -5.0 to -17.2 per thousand; we attribute this result to ethanol's origin from corn and use as an additive in automotive fuels.

Global synchronous changes in the carbon isotopic composition of carbonate sediments unrelated to changes in the global carbon cycle.

The carbon isotopic (delta(13)C) composition of bulk carbonate sediments deposited off the margins of four carbonate platforms/ramp systems (Bahamas, Maldives, Queensland Plateau, and Great Australian Bight) show synchronous changes over the past 0 to 10 million years. However, these variations are different from the established global pattern in the delta(13)C measured in the open oceans over the same time period. For example, from 10 Ma to the present, the delta(13)C of open oceanic carbonate has decreased, whereas platform margin sediments analyzed here show an increase. It is suggested that the delta(13)C patterns in the marginal platform deposits are produced through admixing of aragonite-rich sediments, which have relatively positive delta(13)C values, with pelagic materials, which have lower delta(13)C values. As the more isotopically positive shallow-water carbonate sediments are only produced when the platforms are flooded, there is a connection between changes in global sea level and the delta(13)C of sediments in marginal settings. These data indicate that globally synchronous changes in delta(13)C can take place that are completely unrelated to variations in the global carbon cycle. Fluctuations in the delta(13)C of carbonate sediments measured during previous geological periods may also be subject to similar processes, and global synchroniety of delta(13)C can no longer necessarily be considered an indicator that such changes are related to, or caused by, variations in the burial of organic carbon. Inferences regarding the interpretation of changes in the cycling of organic carbon derived from delta(13)C records should be reconsidered in light of the findings presented here.