Ratio Of Seawater Research Articles

Do adult eelgrass shoots rule seedling fate in a large seagrass meadow in a eutrophic bay in northern China?

We conducted field sampling over 19 months to investigate eelgrass population reproduction status and ecological interactions in a large seagrass meadow in a eutrophic bay in northern China. The results showed asexual growth played an important role in the maintenance of existing meadows, and sexual reproduction played a critical role in the colonization of new areas. We conclude that adult eelgrass shoots do rule the fate of seedlings in the large seagrass meadow. Additionally, nutrient resources (N and P) at this location were found to meet eelgrass growth demand. The N/P ratios of seawater and seagrass indicated N limitation relative to P in the eutrophic bay based on the seagrass Redfield ratio (25–30). Nutrient uptake by seagrass might be an important factor in reducing the probability of a red tide in the study area. The results of this study provide fundamental information for eelgrass restoration and conservation.

Factors controlling the transfer of biogenic organic species from seawater to sea spray aerosol

Ocean waves transfer sea spray aerosol (SSA) to the atmosphere, and these SSA particles can be enriched in organic matter relative to salts compared to seawater ratios. A fundamental understanding of the factors controlling the transfer of biogenic organic matter from the ocean to the atmosphere remains elusive. Field studies that focus on understanding the connection between organic species in seawater and SSA are complicated by the numerous processes and sources affecting the composition of aerosols in the marine environment. Here, an isolated ocean–atmosphere system enables direct measurements of the sea–air transfer of different classes of biogenic organic matter over the course of two phytoplankton blooms. By measuring excitation–emission matrices of bulk seawater, the sea surface microlayer, and SSA, we investigate time series of the transfer of fluorescent species including chlorophyll-a, protein-like substances, and humic-like substances. Herein, we show the emergence of different molecular classes in SSA at specific times over the course of a phytoplankton bloom, suggesting that SSA chemical composition changes over time in response to changing ocean biological conditions. We compare the temporal behaviors for the transfer of each component, and discuss the factors contributing to differences in transfer between phases.

Shipborne variable-FOV, dual-wavelength, polarized ocean lidar: design and measurements in the Western Pacific.

For the requirement of high-precision vertical profile of the polarization and optical properties of natural seawater, a ship-borne variable-FOV, dual-wavelength, polarized ocean lidar system is designed to obtain the volume linear depolarization ratio (VDR), color ratio and optical parameter profiles of seawater. With the high signal-to-noise ratio, which benefits from the high power (355 nm with 120 mJ, 532 nm with 200 mJ) solid-state laser and a photon counting recorder with a sampling rate of 1 GHz, the attenuated backscattered signal of seawater in the western Pacific campaign reaches to the depth of 50 m, where a plankton layer presents. The receiver of lidar is capable of switching to wide and narrow field of view (FOV), respectively, to obtain the lidar attenuation coefficient Klidar, which is in good agreement with the beam attenuation coefficient of seawater c with a narrow FOV and diffuse attenuation coefficient Kd with a wide FOV. Besides, the Klidar, and the VDR, at two wavelengths of 355 nm and 532 nm are compared to explore the possibility of multi-wavelength of laser application in the ocean lidar. The VDR and the color ratio profiles have a desirable correlation with the in-situ measurement of chlorophyll a (Chla) and chromophoric dissolved organic matter (CDOM) profiles, respectively. With the combination of the Klidar, the VDR and the color ratio profiles, measured in different regions and time periods during the campaign, the multi-wavelength and polarization lidar shows its potential to explore various ocean compositions, such as the ocean particles size shape, the species and vertical migration characteristics of planktons, and the profile distribution of the ocean compositions.

Fractionation of germanium and silicon during scavenging from seawater by marine Fe (oxy)hydroxides: Evidence from hydrogenetic ferromanganese crusts and nodules

Germanium (Ge) and silicon (Si) are an element pair which shows rather coherent behaviour in many geochemical systems. In aqueous systems and in the critical zone, however, Ge and Si may fractionate from each other, leading to slight differences between the Ge/Si ratios of continental crust, river water and seawater. We here show that even stronger fractionation of the GeSi couple occurs within seawater during the formation of hydrogenetic ferromanganese (FeMn) crusts and nodules. We determined Ge/Si ratios of hydrogenetic FeMn crusts from the Pacific Ocean following a new analytical approach using laser-ablation ICP-MS on nano-particulate tablets prepared from the FeMn crust material. Data quality was monitored and demonstrated by repetitive measurements of FeMn nodule reference material (RM) NOD-P1 from the Pacific Ocean (Ge/Siwt: 16.8 × 10−6 g/g; Ge/Simol: 6.47 × 10−6 mol/mol), which is the only RM for which high-quality GeSi reference data are available. We also report Ge/Si ratios for FeMn nodule RMs NOD-A1 from the Atlantic Ocean (Ge/Siwt: 24.9 × 10−6; Ge/Simol: 9.6 × 10−6) and for JMn-1 from the Pacific Ocean (Ge/Siwt: 17.9 × 10−6; Ge/Simol: 6.9 × 10−6). The Ge/Siwt ratios of the hydrogenetic FeMn crusts from the Pacific Ocean range from 13.2 × 10−6 to 33.5 × 10−6 (Ge/Simol: 5.1 × 10−6 to 13 × 10−6). The Ge/Si ratios of both FeMn crusts and nodules are significantly higher than those of ambient seawater (ca. Ge/Siwt: 1.7 × 10−6; Ge/Simol: 0.7 × 10−6). Their Ge/Si ratios are also well-above those of potential (alumino)silicate detritus. Hence, these high Ge/Si ratios reveal fractionation of Ge and Si during scavenging from seawater by the iron (oxy)hydroxide component in FeMn crusts, and do not result from the presence of detrital material in the chemical precipitate. Their high Ge/Si ratios relative to seawater also suggest that despite higher complexation constants with organic ligands for Ge than Si, dissolved organic ligands do not control marine GeSi fractionation via preferential retention of Ge in seawater.

Speciation analysis of both inorganic and organic 129I in seawater and its application in the study of the marine iodine cycle.

A complete protocol is presented for the speciation analysis of 129I for both inorganic and organic iodine in seawater using coprecipitation and solid-phase extraction (SPE) combined with accelerator mass spectrometry (AMS). By modifying the iodide separation process and adding a crossover removal step, the improved coprecipitation method significantly reduces the cross-contamination of iodide and iodate to less than 0.05% in the speciation analysis of inorganic 129I, with the separation efficiencies of about 95% and 93% for iodide and iodate, respectively. The SPE-DOI method for the dissolved organic 129I (DO129I) analysis was developed, whereby we report the first direct observation of DO129I/DO127I atom ratios in seawater in this paper. 129I species in seawater from Tokyo Bay were analysed. The 129I results demonstrated that our protocol for speciation analysis of 129I is reliable and provided new insights into understanding the iodine cycle.

Responses of Biogenic Sulfur Compound Concentrations to Dust Aerosol Enrichment and Ocean Acidification in the Western Pacific Ocean

AbstractDeck incubation experiments were conducted to investigate how the addition of atmospheric dust aerosols and ocean acidification (OA) affects phytoplankton growth and the production of dimethylsulfide (DMS), its precursor dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO) in the oligotrophic western Pacific Ocean. The incubation experiment showed that the deposition of simulated dust aerosols greatly influenced phytoplankton growth and the release of biogenic sulfur compounds (BSCs). Furthermore, it altered the N:P ratios in seawater and phytoplankton community composition, elevating the proportions of strong DMSP and DMSO producers (mainly haptophytes). The average Chl‐a and DMS/P/O concentrations in the acidified treatment (pH 7.9) were 86.76%, 82.53%, 84.17%, and 231.06% higher than in the control. The results indicated that lower pH promoted the growth of diatoms and to a certain extent, the release of the three BSCs.

The Steptoean Positive Carbon Isotope Excursion (SPICE), inorganic aragonite precipitation and sea water chemistry: Insights from the Middle–Late Cambrian Port au Port Group, Newfoundland

AbstractThe Late Cambrian Steptoean Positive Carbon Isotope Excursion marks a time of significant change in ocean chemistry and trilobite faunas. On the lead up to the carbon isotope excursion and at the excursion itself, there is global evidence from Laurentia and Gondwana of cementation by primary aragonite in shallow subtidal environments accompanied by deposition of aragonitic ooids. However, this occurred at a time widely considered to have been characterised by ‘calcite seas’ when the primary inorganic phases (marine cements and ooids) are normally presumed calcitic. This study has investigated the chemostratigraphy of the Middle–Late Cambrian Port au Port Group, Newfoundland, including the early marine cements. Here, the marine cements contain increasing concentrations of strontium towards the peak carbon isotope excursion (up to 5500 ppm at the peak excursion) before dropping off post‐peak excursion, consistent with the original cements having been aragonitic. This trend is accompanied by relict oomouldic porosity, again suggesting an aragonitic precursor. Primary inorganic mineralogy is largely controlled by the Mg/Ca ratio of sea water but estimates of the Mg/Ca ratio of Late Cambrian oceans are variable (0.8–2). At this level, other factors such as water temperature and pCO2 have been shown to affect mineralogy with warm waters and high levels of CO2 favouring aragonite. It is possible that the warm waters and anoxia that caused the carbon isotope excursion created conditions favourable for the precipitation of aragonite at the same time as major trilobite faunal turnover.

Lithium elemental and isotope systematics of modern and cultured brachiopods: Implications for seawater evolution

Lithium has proven a powerful tracer of weathering processes and chemical evolution of seawater. Skeletal components of marine calcifying organisms, and in particular brachiopods, present promising archives of Li signatures. However, Li incorporation mechanisms and potential influence from biological processes or environmental conditions require a careful assessment. In order to constrain Li systematics in brachiopod shells, we present Li concentrations and isotope compositions for 11 calcitic brachiopod species collected from six different geographic regions, paralleled with data from culturing experiments where brachiopods were grown under varying environmental conditions and seawater chemistry (pH–pCO2, temperature, Mg/Ca ratio). The recent brachiopod specimens collected across different temperate and polar environments showed broadly consistent δ7Li values ranging from 25.2 to 28.1‰ (with mean δ7Li of 26.9 ± 1.5‰), irrespective of taxonomic rank, indicating that incorporation of Li isotopes into brachiopod shells is not strongly affected by vital effects related to differences among species. This results in Δ7Licalcite–seawater values (per mil difference in 7Li/6Li between brachiopod calcite shell and seawater) from −2.9‰ to −5.8‰ (with mean Δ7Licalcite–seawater value of −3.6‰), which is larger than the Δ7Licalcite–seawater values calculated based on data from planktonic foraminifera (~0‰ to ~−4‰). This range of values is further supported by results from brachiopods cultured experimentally. Under controlled culturing conditions simulating the natural marine environment, the Δ7Licalcite–seawater for Magellania venosa was −2.5‰ and not affected by an increase in temperature from 10 to 16 °C. In contrast, a decrease in Mg/Ca (or Li/Ca) ratio of seawater by addition of CaCl2 as well as elevated pCO2, and hence low-pH conditions, resulted in an increased Δ7Licalcite-seawater up to −4.6‰. Collectively, our results indicate that brachiopods represent valuable archives and provide an envelope for robust Li-based reconstruction of seawater evolution over the Phanerozoic.

Distributions of 239Pu and 240Pu Concentrations and 240Pu/239Pu Atom Ratios and 239+240Pu Inventories in a Water Column in the Eastern Indian Ocean: Transport of Pacific Proving Grounds-Derived Pu via the Indonesian Throughflow

The 239+240Pu concentrations and 240Pu/239Pu atom ratios in seawater from the eastern Indian Ocean were determined to identify their Pu sources and to propose the transport pathway of Pacific Proving Grounds (PPG)-derived Pu into the studied area. This is the first study by anyone on these Pu atom ratios in the Indian Ocean. In the West Australia Basin, the 239+240Pu concentration was 2.89 mBq m-3 in the surface water and increased with depth; a subsurface maximum was identified at 200 m depth and then decreased gradually with depth; its water column inventory was 32.8 Bq m-2. The inventory-weighted mean 240Pu/239Pu atom ratios were 0.208 in the South Australia Basin, 0.226 in the Perth Basin, 0.242 in the West Australia Basin, 0.232 in the Bay of Bengal, and 0.225 in the Andaman Sea. The obtained 240Pu/239Pu ratios were clearly greater than the mean global fallout ratio of 0.18. These high atom ratios proved the presence of close-in fallout Pu from PPG nuclear tests. The relative contribution of global and PPG fallouts was evaluated using the two-end-member mixing model. The 239+240Pu inventories originating from the PPG fallout were calculated as 2.9-14.9 Bq m-2, which corresponded to 20-46% of the total 239+240Pu inventory. A significant amount of the PPG-derived Pu has been transported to the eastern Indian Ocean. The proposed transport pathway accounting for the high 240Pu/239Pu ratio is the transportation of PPG-derived Pu by the North Equatorial Current followed by the Mindanao Current, Indonesian Throughflow, and then spreading over the Indian Ocean by its surface circulation system.

Seawater chemistry of a modern subtropical ‘epeiric’ sea: Spatial variability and effects of organic decomposition

Direct studies of recent epeiric seawater chemistry and their geological significance are relatively few compared to the far more abundant studies from ancient epeiric marine carbonates. Acknowledging the limitations of analogue studies in the modern glaciated world, we propose that the recent Abu Dhabi offshore and lagoonal areas share important attributes with the shallow-marine coastal zones of a subtropical epeiric carbonate sea. The study area in Abu Dhabi is dwarfed by the vast epeiric seas of the geological past, but its seawater properties and related geochemistry have relevance for paleoenvironmental interpretations for similar ancient systems. This study documents the geochemical properties of seawater along the Abu Dhabi coast, and discusses their trends within a spatial context. Results show a positive correlation between salinity, temperature, elemental concentrations, and oxygen isotopic composition of seawater, indicating a significant influence of evaporation on seawater chemistry. A distal-to-proximal negative correlation between seawater Mg/Ca and Sr/Ca ratios may be related to a landward increase in abundance of high-Mg calcite foraminifera. After normalization to chloride, seawater elemental (Ca2+, Mg2+, Sr2+) concentrations and alkalinity show decreasing trends in a landward direction, consistent with seawater aging from the open marine to restricted lagoonal settings. Lower ΔAlk (alkalinity change) : ΔCa2+ (Ca2+ change) ratios in seawater compared with the theoretical value, and more negative δ13CDIC values relative to typical (sub)tropical oceans in the study area indicate an influence of factors apart from CaCO3 precipitation on properties of aged seawater. An input of alkalinity and 12C-enriched carbon by organic carbon decomposition (via sulfate reduction) during early diagenesis is proposed to account for these deviations from typical values. The input of alkalinity and 12C-enriched carbon by organic carbon decomposition may be further related to reduced seawater pCO2 and early-marine cementation. Findings discussed here suggest that organic carbon decomposition during early-marine diagenesis may influence the geochemical properties of the coastal areas of shallow epeiric seas, and thus assumedly produce significant differences in proxy data compared with those from carbonates deposited in open oceans.

Pennsylvanian paleoclimatic record in rhythmites developed on an oceanic island of low-latitude Panthalassa

Terrestrial carbonate deposits associated with exposed limestone are potential recorders of paleoclimates and karst paleohydrology. Here we examine the depositional process of the Omi rhythmite layers, which filled karstic cavities in the Pennsylvanian (middle Kasimovian) section of the Omi Limestone, a seamount-type limestone in central Japan. The laminated rhythmite layers accompanied signatures of subaerial exposure, including Microcodium, which indicates a seasonally dry climate in the late Kasimovian. The rhythmite layers are calcareous, low in siliciclastic content, and composed of millimeter-scale laminae. In each lamina, the grain size decreases and the δ18O value increases upwards. We inferred that each lamina corresponds to a single cave flood event followed by a dry and evaporative interval. 87Sr/86Sr ratios of the rhythmites are almost identical to the ratio of the surrounding limestone, but clearly lower than the Kasimovian seawater ratio. This indicates that the rhythmites and the surrounding limestone were subjected to the same post-depositional alteration, before the subduction of the seamount in the Guadalupian (middle Permian). The sedimentary and isotopic features of the Omi rhythmite and occurrence of Microcodium support repetition of wetting and drying on an equatorial Panthalassan island during the Pennsylvanian (late Carboniferous).

Sodium incorporation into inorganic CaCO3 and implications for biogenic carbonates

The sodium content of biogenic carbonates shows potential as a palaeoceanographic proxy for salinity and/or calcium concentration but the incorporation of Na+ into inorganic and biogenic calcite is poorly understood. Taxonomic and conspecific variations in the sensitivity of carbonate Na/Ca to seawater Na+/Ca2+ and salinity point to a biological influence on Na+ partitioning and/or covariations with other environmental parameters. One major unknown of the biological control during calcification is the rate of mineral precipitation, which has a strong control on trace-element partitioning in inorganic carbonate systems. We conducted inorganic CaCO3 precipitation experiments where the effect of solution composition and crystal growth rate on Na+ uptake by carbonate crystals are independently assessed. Calcite crystals were precipitated at rates varying from 10−6.5 to 10−4.5 mol/m2/s, while faster growth rate than 10−4.5 mol/m2/s resulted in the coprecipitation of aragonite and vaterite. For a given crystal growth rate, calcite Na/Ca increases by 0.22% per % increase in solution (Na+)2/Ca2+ activity ratio. However, calcite Na/Ca increases up to fivefold per order of magnitude increase in crystal growth rate, suggesting crystal growth rate and precursor phases are likely dominant controls on marine carbonate Na/Ca. We use these results in the framework of the DePaolo (2011) model for trace element uptake by calcite to assess the origin of variable (Na/Ca)foraminifer sensitivities to [Ca2+]seawater and salinity. Last, maximum mineral growth rates are estimated for a range of marine carbonates based on known carbonate Na/Ca and the (Na+)2/Ca2+ activity ratio of seawater. Estimated rates vary from 10−5.6 (planktic foraminifers) to above 10−4 (sea urchins) mol/m2/s. Such high mineral growth rates imply high degrees of oversaturation with respect to calcite (10 to >100), supporting the idea that elemental partitioning and isotopic fractionation recorded in marine biogenic carbonates are controlled by kinetic rather than equilibrium exchanges.

Coupled Mg/Ca and Clumped Isotope Measurements Indicate Lack of Substantial Mixed Layer Cooling in the Western Pacific Warm Pool During the Last ∼5 Million Years

AbstractThe Indo‐Pacific Warm Pool (IPWP) plays a crucial role in influencing climate dynamics both in the tropics and globally. Yet, there is an ongoing controversy concerning the evolution of surface temperatures in the IPWP since the Pliocene, which is fueled by contradictory proxy evidence. Temperature reconstructions using TEX86 indicate a gradual cooling by ∼2°C from the Pliocene to today while Mg/Ca‐based studies using planktonic foraminifera do not report any long‐term trends. A bias in Mg/Ca records due to seawater chemistry changes has been suggested as an explanation for this proxy mismatch. Here, we present data from two independent foraminifera‐based temperature proxies, Mg/Ca and clumped isotopes (Δ47), measured on the same samples from IODP Site U1488 in the IPWP. We reconstructed mixed layer and subsurface temperatures and find very good agreement among Mg/Ca and Δ47 when applying a minor correction for changing Mg/Ca ratios of seawater. Diagenetic effects could influence Δ47 but the evaluation of foraminifera preservation at Site U1488 suggests that this effect is unlikely to have masked a long‐term trend in the data. While remaining uncertainties prevent us from fully ruling out particular hypotheses, our study adds evidence that mixed layer temperatures likely did not cool substantially, while subsurface temperatures cooled more strongly since the Pliocene. The substantial Pleistocene cooling previously observed in TEX86 data is consistent with this finding when interpreting it as a combined surface and subsurface signal.

Study of a compact falling film evaporation/condensation alternate-arrayed desalination system

This work presents a highly integrated humidification-dehumidification desalination approach that is implemented by compact falling film evaporation/condensation. The featured structure is hot seawater, and cold freshwater is uniformly distributed by a compact membrane array with a hot–cold alternate method. Vapor generated from hot seawater films can directly transfer to cold freshwater films and condense. Thus, the mass transfer resistance is reduced considerably. A typical structure with a membrane size of 60 mm × 700 mm is designed, containing 6 cold membranes and 5 hot membranes. The heat and mass transfer characteristics are discussed theoretically and experimentally. The inlet seawater temperature is proven to be the most crucial factor affecting water productivity. In contrast, the mass flow ratio of freshwater and seawater has a weak influence on water productivity. The maximum water productivity is approximately 1344.8 g/h with a corresponding gained-output-ratio of 0.804 when the inlet temperatures of freshwater and seawater are 18.5 ℃ and 80 ℃, respectively, and the mass flow rate of seawater is 90 kg/h. Due to the compact structure, its unit volume water productivity is approximately 90.88 kg/(h·m3), which is much higher than that of other devices. This research may help improve the application of small-scale desalination systems.

Mantle-derived helium released through the Japan trench bend-faults

Plate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.

Sources and transport of plutonium in the Indo-Pacific Intersection: Implications for South China Sea freshwater transport into Indonesian Seas

The Indo-Pacific Intersection (IPI), centered in the Indonesian Seas (IS) and South China Sea (SCS), is a convergence zone of both hydrological and atmospheric circulations and plays an important role in the water cycle and global climatic system. This study presents a unique dataset of both 239+240Pu activities and 240Pu/239Pu atom ratios to trace Plutonium (Pu) source terms and their transport in the IPI, to examine constituent water masses, notably freshwater fluxes. The 240Pu/239Pu atom ratios in surface IPI seawater ranged from 0.194 to 0.258 with an average of 0.223 ± 0.021, values that were consistently higher than global fallout (~0.18). 239+240Pu activities ranged widely from 0.55 to 2.8 mBqm−3 with a generally accumulating trend from the western Pacific Ocean (WP) to the IPI as previously observed. We further reveal, using a two end-member mixing model between global fallout and Pacific Proving Grounds (PPG), that the PPG source contributes 34 ± 8% of the Pu to the IS. In the IS, both 239+240Pu activities and 240Pu/239Pu atom ratios further show values between those in the WP and SCS, indicating a two-endmember mixing scheme between the SCS (characteristically lower-salinity but higher PPG Pu-fraction) and the WP (higher-salinity and higher PPG Pu-fraction). We estimate the fractional contribution of the SCS water mass as 35 ± 16% in the surface mixed layer and 49 ± 14% in the IS 50–235 m depth interval. This water mass transport is equivalent to a freshwater influx of 80 ± 47 mSv from the SCS to the IS (known as the South China Sea Throughflow (SCSTF), a branch of the Indonesian Throughflow (ITF)). It accounts for over half (53 ± 31%) of the total freshwater flux transported by the ITF into the Indian Ocean and supplies ~24% the freshwater net evaporation in the Indian Ocean over the 8°N – 32°S latitudinal range, and it is thus crucial in maintaining the fresh water balance therein. This freshwater influx to the IS from the SCS also leads to a ~ 0.2 kg m−3 decrease in the mean density of the upper 235 m water layer, which serves to inhibit the transport of upper layer warm water from the western tropical Pacific warm pool into the Indian Ocean. Therefore, the SCS, together with the SCSTF, play a critical role in regulating freshwater and heat balance in the IPI and Indian Ocean. These findings have strong implications for the integrative role of the SCS and SCSTF on the Indo-Pacific climate and water cycle.

Carbon, oxygen and strontium isotope geochemistry of the late Neoproterozoic carbonate platform deposit Hyangsanni Dolomite of the Okcheon metamorphic belt, Korea

The age-unknown Hyangsanni Dolomite is distributed in the northeastern part of the Okcheon metamorphic belt in central South Korea. It has been claimed as Early to Middle Cambrian because of the misidentified Archaeocyatha fossil in the past, but the time of sedimentation has not yet been confirmed. We performed elemental and isotopic analyses for the Hyangsanni Dolomite. The REE + Y patterns of the samples of the Hyangsanni Dolomite are generally flat and Ce negative anomaly is generally negligible to the extent that it appears only weakly in some samples. Y/Ho values are in the range of 29–43, which is fairly lower than typical Y/Ho ratio of seawater, indicating the influence of terrigenous materials. REE and trace element geochemical discrimination diagrams indicate that the Hyangsanni Dolomite was deposited in a continental margin environment rather than an open ocean. We suggest that the Hyangsanni Dolomite was deposited in a rift basin connected to the ocean rather than in the passive continental margin, considering occurrence of magmatism related to continental rifting within the Okcheon metamorphic belt. Carbon and oxygen isotope analysis was performed on dolomite powders scraped off from polished surfaces unstained with Alizarin-Red-S in order to avoid the recrystallized calcite. The Hyangsanni Dolomite has δ13C(V-PDB) values between +2.9‰ and + 6.2‰, and δ18O(V-SMOW) values between +11.3‰ and + 24.5‰. These δ13C values are markedly higher than the Cambro-Ordovician values, and are consistent with the Neoproterozoic values. The minimum value of 87Sr/86Sr ratio obtained from the Hyangsanni Dolomite also refers to Neoproterozoic, not Phanerozoic. We suggest that the Hyangsanni Dolomite belongs to the sedimentary sequence of the Neoproterozoic, along with other sediments of the northeastern Okcheon metamorphic belt.

An ICP‐AES method for routine high‐precision measurement of seawater Sr/Ca ratios to validate coral paleothermometry calibrations

AbstractA new inductively coupled plasma atomic emission spectrometry (ICP‐AES) method is presented for rapid and routine analysis of Sr/Ca molar ratios in seawater, with a long‐term precision of < 0.2%. It is an adaptation of a method widely employed for the analysis of coral aragonite Sr/Ca ratios in marine paleothermometry studies, which are based on the assumption that the seawater Sr/Ca ratio is constant in space and time. While prior studies have shown variations of up to 1% with depth, smaller variations at the ocean surface are generally accounted for via empirical, species‐specific calibrations of coral Sr/Ca vs. temperature. We found Sr/Ca variations in some coastal waters to be even larger, with distinct periodicity, complicating this approach. Although the high precision necessary for measurements of seawater Sr/Ca has previously relied on advanced mass spectrometry, long analysis times, and expensive isotopic spikes, our method uses more accessible instrumentation and is both time‐ and cost‐saving. The intricate composition of seawater, relative to coral aragonite solutions, requires an intensity ratio calibration technique combined with rigorous normalization to a suitable seawater standard. Key aspects of our method are discussed, including the choice of wavelengths, instrument parameters, accuracy, precision, and matrix effects. Special attention is given to the need for a certified seawater Sr/Ca reference standard, which does not presently exist. Analytical validation is provided by concurrent sharp gradients in Sr/Ca and δ18O, coinciding with the Florida landfall of hurricane Irma, as recorded at near‐daily resolution in a continuous seawater sample collected with an osmotic pump.

Influence of high marine Ca/SO4 ratio on alteration of submarine basalts at 2.41 Ga documented by triple O and Sr isotopes of epidote

Over the course of Earth’s history, marine sulfate concentrations have been increasing in response to long-term atmospheric oxygenation. In contrast to modern oceans, where abundant sulfate precipitates in hot oceanic crust as anhydrite, Precambrian oceans contained much less (~0–10 mM) sulfate, so that submarine hydrothermal systems were comparatively poor in anhydrite. As a step towards exploring the role of chemical evolution of seawater solutes, we investigate the reaction between basalt and seawater that took place at the ca. 2.43–2.41 Ga Vetreny Belt (Karelia craton, NW Russia) using fluid inclusion and multi-isotope measurements complemented by reactive transport and static aqueous-mineral equilibrium calculations. Using fluid inclusion measurements by LA-ICP-MS, we constrain the Sr concentration in the least modified seawater-derived fluids and address the effect of phase separation. Then, we complement the previous δ18O – Δ′17O datasets with new 87Sr/86Sr measurements performed on 2.41 Ga epidote from the Vetreny Belt, and recent (0–6 Ma) oceanic epidote from Reykjanes, Iceland and the drilling site 504B in the eastern Pacific Ocean. The 2.41 Ga epidote with 87Sr/86Srinitial of 0.7029–0.7042 and Δ′17O of –0.06 to 0.00‰ is best explained by a relatively high fraction (~90%) of marine Sr that was delivered from contemporaneous seawater with 87Sr/86Sr ≈ 0.7045, and without significant removal by early anhydrite. Using Monte-Carlo simulation of a dual-porosity model, we constrain the range of possible exchange trajectories based on the variability of physical parameters (porosity, fluid flow velocity, fracture spacing, recrystallization rates). Further, we use a series of static equilibrium seawater-basalt reaction calculations with emphasis on the possible range of marine Ca/SO4 values at 2.41 Ga. Our calculations demonstrate that co-existing quartz and epidote in absence of feldspars represent equilibrium with less-evolved hydrothermal fluids. Consequently, equilibrium assemblage of quartz and epidote provide an insightful archive for marine Sr. Based on our modeling and assumptions about marine 87Sr/86Sr and Sr/Ca ratios, the 2.41 Ga epidotes document a seawater-basalt reaction where the initial fluid contained between 30 and 40 mM of Ca and 0–10 mM SO4, representing a high marine input and the possible effect of phase separation. Based on our data, we suggest that high Ca/SO4 ratio of seawater (≫1) and low concentration of anhydrite in submarine systems of the contemporaneous oceans promote a higher fraction of seawater Sr to be permanently stored in silicates of altered oceanic crust. In contrast, modern altered oceanic crust is depleted in radiogenic Sr due to partitioning into anhydrite, which partly returns into the ocean upon cooling.

Technical note: Excess alkalinity in carbonate system reference materials

Certified reference materials (CRMs) for oceanic carbonate system measurements are critical for verifying the accuracy of laboratory protocols and the reliability of field sensors. CRMs are certified for total alkalinity and dissolved inorganic carbon, parameters that are (1) stable for a long period of time when a sample is properly stored and (2) not affected by changes in temperature and pressure. In experimentation initially designed to measure the total boron to salinity ratio of seawater, an interesting result has emerged regarding CRMs. A unique acidimetric titration method has indicated that three different batches of CRM contain excess alkalinity (i.e., alkalinity that is not attributable to inorganic bases included in the traditional definition of seawater total alkalinity) that is statistically greater than the excess alkalinity measured in open-ocean water from the Gulf of Mexico. Further, the amount of excess alkalinity appears to differ in certain CRM batches. Excess alkalinity in CRMs is likely caused by organic proton acceptors that are not completely oxidized by the ultraviolet sterilization procedure that CRMs undergo. The primary use of CRMs — to maintain the accuracy and consistency of carbonate system measurements — may be inhibited by excess alkalinity, which can cause differences in total alkalinity values determined by different titration methods. Excess alkalinity also invalidates the assumptions applied to marine CO2 system calculations, and so would produce incorrect values of CO2 system parameters calculated from certified total alkalinity and dissolved inorganic carbon values of CRMs. Finally, excess alkalinity analyses highlight the urgent need for the marine chemistry community to establish a universally agreed upon total boron to salinity ratio.