Seawater Alkalinity Research Articles

Marine Ooid Sizes Record Phanerozoic Seawater Carbonate Chemistry

AbstractSeawater carbonate chemistry links Earth's climate and carbon cycle through the production and preservation of carbonate sediments. Models and carbonate facies abundance records have generated hypotheses about trajectories of seawater carbonate chemistry, including responses to key events in the evolutionary history of carbonate biomineralizers. However, tests of these hypotheses have remained elusive. We applied a novel proxy for the carbonate mineral saturation state (Ω) of seawater based on the diameters of ooids—concentrically‐coated carbonate sand grains—to estimate Ω, dissolved inorganic carbon, alkalinity, and pH of seawater spanning Phanerozoic time. Reconstructed Ω values decreased sharply around ∼120 Ma, which we interpret as the fingerprint of the Mid‐Mesozoic Revolution of planktic calcifiers. Shifts in Ω across Ordovician time also suggest a possible causal relationship with the Great Ordovician Biodiversification Event. Our results demonstrate that ooid sizes are a useful tool for reconstructing Earth's ancient carbon cycle.

Mimicking the cementation mechanism of ancient Roman seawater concrete using calcined clays

The negative environmental impacts of Ordinary Portland Cement (OPC)-based materials, including high carbon emission, energy-intensive manufacturing process, and freshwater consumption, can be minimized by capitalizing on the concepts of ancient Roman concrete. Accordingly, this study presents a pathway of producing durable and sustainable seawater concrete by mimicking the cementation of ancient Roman concrete. Calcined clays with blended minerals (kaolinite and montmorillonite), portlandite, and seawater were used to produce these binder mixtures. The evolutions of the reaction products of the seawater-cured paste samples were monitored for up to 56 days using Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Nuclear Magnetic Resonance (NMR), and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS). Because of the high alkalinity (pH 8.2) of seawater, it acts as an activator for the calcined clay-portlandite mixtures eliminating the need for additional alkali activators. Accordingly, in the presence of seawater, the reaction between calcined clay and portlandite happens relatively rapidly, and compressive strengths of around 17 MPa can be achieved within 7 days. The early age strengths of these samples were primarily attributed to the formation of hydrocalumite. With increasing curing duration, geopolymer gel, C-A-S-H, ettringite, and phillipsite were formed. Both C-A-S-H and phillipsite showed binding of chlorides. Only phillipsite showed sequestration of sulfates in the matrix. The calcined clay blends containing 50 to 75% kaolinite performed better than the samples containing 100% kaolinite in terms of reaction rate and compressive strengths.

Ocean Deacidification Technologies for Marine Aquaculture

The increase in partial pressure of CO2 in the oceans directly affects the productivity and survival of coastal industries and ecosystems. For marine aquaculture, the decreased alkalinity of seawater results in reduced availability of carbonates for marine organisms to build their shells, leading to decreased aquaculture quality and productivity. The industry has been implementing recirculating aquaculture systems (RASs) to reduce CO2 in feedwaters, but recent interest in ocean-based CO2 capture has led to additional strategies that may be relevant. The new methods in addition to CO2 removal offer capture options for enhanced aquaculture sustainability. Here, we review and compare early-stage and commercially available technologies for deacidification of seawater and their suitability for aquaculture. Most methods considered rely on a voltage-induced pH swing to shift the carbonate/bicarbonate equilibrium toward the release of CO2, with subsequent capture of the released CO2 as a gas or as solid mineral carbonates. The modular design and distributed deployment potential of these systems offers promise, but current demonstrations are limited to bench scale, highlighting the need for sustained research and development before they can be implemented for marine aquaculture.

New and updated global empirical seawater property estimation routines

AbstractWe introduce three new Empirical Seawater Property Estimation Routines (ESPERs) capable of predicting seawater phosphate, nitrate, silicate, oxygen, total titration seawater alkalinity, total hydrogen scale pH (pHT), and total dissolved inorganic carbon (DIC) from up to 16 combinations of seawater property measurements. The routines generate estimates from neural networks (ESPER_NN), locally interpolated regressions (ESPER_LIR), or both (ESPER_Mixed). They require a salinity value and coordinate information, and benefit from additional seawater measurements if available. These routines are intended for seawater property measurement quality control and quality assessment, generating estimates for calculations that require approximate values, original science, and producing biogeochemical property context from a data set. Relative to earlier LIR routines, the updates expand their functionality, including new estimated properties and combinations of predictors, a larger training data product including new cruises from the 2020 Global Data Analysis Project data product release, and the implementation of a first‐principles approach for quantifying the impacts of anthropogenic carbon on DIC and pHT. We show that the new routines perform at least as well as existing routines, and, in some cases, outperform existing approaches, even when limited to the same training data. Given that additional training data has been incorporated into these updated routines, these updates should be considered an improvement over earlier versions. The routines are intended for all ocean depths for the interval from 1980 to ~2030 c.e., and we caution against using the routines to directly quantify surface ocean seasonality or make more distant predictions of DIC or pHT.

The Possible Effect of Seawater Total Alkalinity on Lightning Flash Intensity—An Experimental Approach

AbstractAtmospheric lightning has been the focus of many studies in atmospheric physics and chemistry. In previous studies we have shown that the intensity of electrical sparks discharged into natural and artificial saline solutions are strongly influenced by their salinity and pH. In this study we tested the effect of changes in the total alkalinity (TA) of Mediterranean seawater on its lightning flash intensity (LFI) by addition of concentrated HCl and NaOH. These experiments showed that the LFI was positively correlated with TA and varied by 40% between the lower and upper limit of our experimental range. These results imply that TA together with salinity and pH of natural waters, may also be a significant predictor of LFI, especially in oceanic regions where TA diverges positively from its conservation with salinity because of external inputs such as rivers and groundwater or upwelling of TA and CO2 enriched (low pH) deep waters.

Alkalinity of diverse water samples can be altered by mercury preservation and borosilicate vial storage

We compared the effects of preservation and storage methods on total alkalinity (AT) of seawater, estuarine water, freshwater, and groundwater samples stored for 0–6 months. Water samples, untreated or treated with HgCl2, 0.45 µm filtration, or filtration plus HgCl2, were stored in polypropylene or borosilicate glass vials for 0, 1, or 6 months. Mean AT of samples treated with HgCl2 was reduced by as much as 49.1 µmol kg−1 (1.3%). Borosilicate glass elevated AT, possibly due to dissolving silicates. There was little change in AT of control and filtered samples stored in polypropylene, except for untreated groundwater (~ 4.1% reduction at 6 months). HgCl2 concentrations of 0.02–0.05% reduced the AT of fresh, estuarine, and ground water samples by as much as 35.5 µmol kg−1 after 1 month, but had little effect on the AT of seawater. Adding glucose as a carbon source for microbial growth resulted in no AT changes in 0.45 µm-filtered samples. We suggest water samples intended for AT analyses can be filtered to 0.45 µm, and stored in polypropylene vials at 4 °C for at least 6 months. Borosilicate glassware and HgCl2 can be avoided to prevent analytical uncertainties and reduce risks related to use of Hg2+.

Photochemically generated nitric oxide in seawater: The peroxynitrite sink and its implications for daytime air quality

In this study, we experimentally investigated the magnitude of the peroxynitrite sink: a radical–radical consumption mechanism for photochemically generated nitric oxide (NO) in surface seawater that describes NO reactions with co-generated superoxide (O2−) to yield peroxynitrite (ONOO−). Measurements of photochemically generated NO, O2− and ONOO− were conducted on seawater samples obtained from the Seto Inland Sea, Japan. Nitrite, dissolved organic carbon, chromophoric dissolved organic matter and pH were also measured in the same samples using standard analytical methods. The average photoformation rates of NO, O2− and ONOO− were: 1.78 × 10−12 M s−1, 7.19 × 10−10 M s−1 and 9.0 × 10−10 M s−1, respectively, and the average steady-state concentrations were: 67.28 × 10−12 M, 2.69 × 10−12 M and 2.26 × 10−11 M, respectively. Further evaluation of the experimental data indicated that the existence of ONOO− in seawater strongly depends on, and is limited by, photoformed NO. Seawater alkalinity favored the consumption of photoformed NO· via the peroxynitrite sink. The magnitude of average sinks (%) calculated from kinetic estimates and experimental data were: 0.17% and 0.11%, respectively. These results show that the consumption of photochemically generated NO· via the peroxynitrite sink is not significant in surface seawater. Therefore, we propose that sea–to–air efflux across the marine boundary layer is the major sink of photochemical NO· and can be regarded as a non-anthropogenic contributor to daytime atmospheric NOx concentrations.

Effects of salinity, pH and alkalinity on hatching rate of fertilized eggs of Penaeus monodon

The fertilized eggs of “Nanhai 2” Penaeus monodon bred by our research group were incubated at the same temperature (30℃), different salinity (20, 25, 30, 35, 40), different pH (7.0, 7.5, 8.0, 8.5, 9.0) and different alkalinity (2.0 mmol/L, 2.5 mmol/L, 3.0 mmol/L, 3.5 mmol/L, 4.0 mmol/L) to explore the effects of salinity, pH and alkalinity on hatching rate of fertilized eggs of P. monodon. The results showed that the hatching rate of fertilization rate of P. monodon was closely related to salinity, and the best hatching rate was obtained when the seawater salinity was 30 with the average hatching rate was 82.60%. The hatching rate was very low when the salinity was as low as 20 or as high as 40, which was significantly lower than that of other treatments (P<0.05). The hatching effect of the fertilized eggs of P. monodon was closely related to the pH value of seawater, and the slightly alkaline seawater was conducive to the normal development of the fertilized eggs. Among them, the hatching effect of the seawater pH value of 8.0 was the best, and the average hatching rate of the fertilized eggs was 80.62%. Too low or too high pH value of the seawater was not conducive to the development of the embryo, and the hatching rate of the fertilized eggs decreased in varying degrees. There was no significant correlation between the hatching effect of fertilized eggs and the change of seawater alkalinity. The average hatching rate of fertilized eggs ranged from 78.65% to 83.12% in the alkalinity range of 2.0-4.0 mmol/L.

ASPEN PLUS desulfurization simulations for the scrubber of a large-scale marine diesel engine: main scrubbing section's desulfurization share optimization and superiority confirmation for the seawater/seawater cascade-scrubbing solution.

Aiming at perfecting the proposed three-stage cascade-scrubbing desulfurization technology, ASPEN PLUS simulations of seawater/seawater cascade-scrubbing desulfurization for an exhaust gas scrubber designed for a 10-MW large-scale marine diesel engine were performed to fix a reasonable desulfurization share for the main scrubbing section. Accordingly, three typical desulfurization share setups of 80%, 85%, and 90% were compared under various operational conditions by varying the fuel-sulfur content, liquid/gas ratio, and seawater alkalinity. In complying with the desulfurization requirements of emission control areas, 85% was obtained as the optimal desulfurization share among the three setups. Again, under the selected 85% setup, the cascade-scrubbing desulfurization was numerically compared with the conventional once-through open-loop solution, so as to confirm the seawater-saving advantage of the cascade-scrubbing desulfurization technology used for the exhaust gas of large-scale marine diesels. At relatively higher sulfur content above 3.5%, the open-loop solution solely achieved the desulfurization requirements of non-emission control areas by using higher liquid/gas ratio levels of 6.5-8.0L/Nm3, while fully failed to meet the much stricter requirements of emission control areas except the lowest 1.5% fuel-sulfur conditions. On the contrary, the cascade-scrubbing solution could meet the requirements of emission control areas under various fuel-sulfur content conditions and reduced the liquid/gas ratio by about 45%, in comparison to the open-loop solution.

Effect of seawater alkalinity on the performances of a marine diesel engine desulphurization scrubber

Since the last fifteen years, Flue Gas Desulphurization (FGD) plants based on seawater scrubbing found an interesting application in the maritime transportation, as an answer to the stringent regulations imposed by International Maritime Organization (IMO) on sulphur emissions. This work reports the experimental results on desulphurization in a pilot seawater scrubber (DN 400) from a marine Diesel engine (80 kW) operated under different loads (10, 25 and 50%). The pilot scrubber was fed with a gas velocity 0.15 m/s and a liquid to gas mass ratio 1-3 kg/kg. The scrubbing liquid was available at different alkalinity and salinity levels representing the ion speciation of marine water in different geographic areas. The experiments evaluate the SO2 removal efficiency of the scrubber as a function of seawater alkalinity and pH. Finally, the paper reports a correlation to assess the seawater flow rate required to comply with the current IMO restrictions. This correlation allows tuning the seawater flow rate during the ship navigation based on the registered marine alkalinities and to the operating conditions of the engine. The model can be integrated in the scrubber control system to identify optimal operating conditions and reduce pumping costs, helping to reduce the EEDI and the SEEMP ships energy indexes.

The Crystal Chemistry of Francolite in Akashat Phosphorites (Middle Paleocene), Iraqi Western Desert

تفرز الدراسة الجيوكيميائية للحبيبات الفوسفاتية المركزة، مجموعة العناصر التي ترتبط بمعدن الفرانكولايت (مثل: الكالسيوم (Ca) والصوديوم (Na) والسترونتيوم (Sr) والفوسفور (P) والكربون (C) والكبريت (S) والفلور (F) والكلور (Cl)) التي تدخل في حساب الصيغة الكيميائية للوحدة البنائية. أما العناصر الأثرية المرتبطة بالفرانكولايت (مثل: اليورانيوم (U) واليتريوم (Y) والكروميوم (Cr) والمنغنيز (Mn) والفناديوم (V))، ومجموعة عناصر السليكون (Si) والألمنيوم (Al) والحديد (Fe) والمغنيسيوم (Mg) والبوتاسيوم (K) والتيتانيوم (Ti) والعناصر الأثرية المرتبطة بها التي تمثل المعادن الطينية (ويعتقد إنها معادن الباليكورسكايت والسيبيولايت والمونتموريللونايت) فلا تدخل في حساب الصيغة الكيميائية بسبب تراكيزها الأثرية. وتوجد هذه المعادن ضمن الحبيبات الفوسفاتية بين التكسرات والأغلفة المحيطة بالحبيبة الفوسفاتية والتي تتكون بفعل نشاط المادة العضوية في التقاط دقائق الطين حول الحبيبات الفوسفاتية. وتقترح الدراسة عدم حصول إحلال في مواقع الكالسيوم والفوسفور والفلور بشكل إحلال مزدوج بأيونات موجبة وسالبة محددة، وإنما يكون الإحلال بشكل إحلال مفتوح لكثير من الأيونات ذات أعداد تناسقية متوافقة مع المواقع التي تحل فيها، وفي نفس الوقت فان هذا الإحلال يكون مركبا لاشتراك أكثر من ايون موجب وأيون سالب في إشغال هذه المواقع. إن انخفاض النسب المولية للـصوديوم والكبريت والكلور في الصيغة الكيميائية تشير إلى ملوحة المياه وقلويتها أكثر من الاعتيادي بشكل ضئيل، ويعكس وجود السترونتيوم تأثير المياه البينية في المناطق العميقة على تكوين الفرانكولايت. وتعكس النسبة المولية للكربون (الذي يمثل CO3) تأثير العمليات التحويرية في تكوين الفرانكولايت ونموه. كما تبين النسبة المولية المنخفضة للمغنيسيوم استهلاكه في أطوار أخرى مثل المعادن الطينية والدولومايت، مما يسـاعد على حصول النمو المتزايد للحبيبات الفوسفاتية.

Development of an automated transportable continuous system to measure the total alkalinity of seawater

Anthropogenic CO2 emissions are contributing to global warming and ocean acidification. Rapid and accurate measurements of seawater carbonate chemistry are critical to understand current changes in the ocean and to predict future effects of such changes on marine organisms and ecosystems. Total alkalinity (AT) measurements can be used to directly determine the calcification rate, but they are time-consuming and require large sample volumes. Herein, we describe an automated and transportable flow-through system that can conduct continuous AT measurement using an ion sensitive field effect transistor (ISFET) – Ag/AgCl sensor and three different reference materials. The response time, stability, and uncertainty of our system were evaluated by comparing AT values of calibrated reference materials to those calculated by our system. Our system requires only small amounts of seawater (<10 mL) and a short time per sample (<5 min) to produce results with a relative uncertainty of less than 0.1% (approx. 2.2 μmol kg−1). This system is expected to facilitate easy and rapid in-situ measurement of AT. Continuous AT measurements would enable us to determine short-term calcification responses to changes in light or temperature and improve our understanding of the metabolic mechanisms of creatures such as corals.

MICROBIALITE OCCURRENCE AND PATTERNS IN HOLOCENE REEFS OF BORA BORA, SOCIETY ISLANDS

ABSTRACT The thickness of microbialite crusts in Holocene barrier and fringing reefs of Bora Bora was quantified in drill cores from windward and leeward settings to decipher possible spatial and temporal patterns as well as controlling environmental factors. Based on the analysis of 145 occurrences in nine rotary cores, microbialite thickness ranges from 0.1–11.0 cm with an average value of 1.97 cm (SD = 2.47). Microbialites occur only from 9.5–5.6 ka corresponding to a period of rapid sea-level rise and reef accretion in the early Holocene. However, there is no statistically significant correlation between microbialite thickness and reef accretion rate. Also, there is no correlation between microbialite abundance and age. The upcore increase in microbialite abundance, however, suggests that time available for carbonate accretion in shallow water plays a role in microbialite formation. Crust thickness is greater on windward as compared to leeward fringing reef settings indicating that flushing of pore space is a likely factor controlling microbialite accretion. Other environmental factors potentially being responsible for the Holocene decrease in microbialite abundance include climate, i.e., decreasing temperatures and precipitation (supporting nutrient input by runoff) as well as decreasing seawater alkalinity. At the mesoscale, structureless and laminated microbialites are by far the most common types. Coated debris, boring infill, and digitate types are less common. Textures at the microscale, including laminated, clotted, and peloidal, do not necessarily match mesoscale textures. The Bora Bora microbialites consist in more or less equal parts of high-magnesium calcite and aragonite. The δ13C values range from +3.0 to +4.1‰ and the δ18O from -0.8 to +0.1‰. The contents of easy soluble sulfate (ESS) and carbonate associated sulfate (CAS) are relatively high. The δ18OCAS (+11.0 to +12.7‰) and δ34SCAS values (+21.9 to +23.6‰) exceed the seawater sulfate standard NBS-127 value and are in the same range as observed in other cryptic, Holocene reefal microbialites. The Bora Bora microbialites contain lipid biomarkers derived from sulfate-reducing bacteria (2–8 wt%), marine plankton, land plants, and unspecified bacteria. The former include branched, short-chain fatty acids and terminally branched fatty acids, whereby iso-fatty acids are more abundant than anteiso-fatty acids. Other compounds with terminally branched alkyl chains include iso- and anteiso-C15 and -C17 alcohols, which are interpreted as degradation products of monoalkyl glycerol ethers (MAGE). Collectively, the organic and inorganic geochemical data together with the sedimentological and mineralogical data suggest that sulfate-reducing bacteria were involved in microbialite development. The temporal and spatial distribution patterns suggest that factors such as exposure to waves and currents, time, nutrient availability, alkalinity, and climate play important roles, however, more quantitative data from other occurrences are needed to be able to better discriminate among them.

Chemical archeoceanography

Elemental fluxes to the ocean are expected to increase with the surface area of continental exposure to weathering and atmospheric PCO2. The record of phosphorus in sediments, which has no notable source within the ocean, and the radiogenic strontium isotopes in Archean carbonates indicate that, prior to the Great Oxidation Event (GOE), subaerial expanses represented only about 20% of the modern continental surface area, i.e. 7% of the surface of the Earth. Because these simple first-order observations, in contrast to the low oxygen content of the pre-GOE atmosphere, have so far received only little attention in the appraisal of the marine chemistry of the early Earth, a reassessment of the chemistry of the pre-GOE ocean is warranted. Here we discuss some of the geochemical cycles of the Archean world, including protons, alkalinity, electrons, and other electrolytes, and attempt to build a first conceptual framework for Chemical Archeoceanography. The smaller subaerial exposures characterizing the Archean and the low abundance of Archean carbonates and mudstones imply that the flux of alkalinity to the ocean was much weaker than today and therefore that the capacity of the runoff to neutralize the high-temperature hydrothermal fluids was less important. Such a reduced flux in turn entails lower seawater pH and higher chlorinity. The lack of atmospheric O2 allowed iron to be in its soluble Fe(II) form and to reduce HCO3− to CH4 while liberating large amounts of protons. The low pH of the pre-GOE ocean and the reduced alkalinity input, reinforced by scant P supply, account for reduced carbonate precipitation. Ocean chemistry evolved under the control of two changing factors: (i) the balance between chemical weathering and hydrothermal fluxes and (ii) the oxygen pressure in the ocean and the atmosphere. Seawater iron concentration was controlled by high [Fe2+]/[H+]2 ratios. With the temperature of hydrothermal fluids at mid-ocean ridges and other active volcanic edifices being determined by the expansion properties of seawater, the chemistry of hydrothermal fluids is controlled by the chlorinity of the ocean. Of all the major element cycles in seawater, those of Na, Mg, and P seem to be unbalanced when runoff falls below the modern value. The very low P content of banded iron formations is inconsistent with a major role of biological activity in the oxidation of Fe2+ dissolved in the Archean ocean. Prior to the GOE, banded iron formations were the major sedimentary sink of seawater cations, a role now played by carbonates. The controls of seawater alkalinity, which today are exerted by the Ca2+–CaCO3 couple, was exerted by dissolved Fe2+-magnetite or Fe2+-ferrihydrite. Plain language summaryWe here evaluate the constraints on seawater chemistry before free oxygen was introduced into the atmosphere some 2.4 billion years ago. We suggest a simple conceptual framework which we validated on modern seawater and which is based on two so-far largely overlooked observations, namely that the phosphorus concentration and strontium isotopic records in ancient sediments require that emerged continental land masses were covering only ~7% of Earth's surface at the time of the Great Oxidation Event instead of 30% today. Atmospheric and seawater chemistry critically depend on this proportion as well as on the chlorinity of the ocean. The oxygen-free atmosphere allowed iron to remain in solution and to reduce atmospheric carbon dioxide to methane. The pH of the ancient oceans must have been lower because less river water was available to neutralize the acidic submarine high-temperature hydrothermal fluids emitted at mid-ocean ridges. Limited continental surface starved the sedimentary column for clays. The low pH and scant phosphorus drainage led to rare carbonate deposition. We conclude by proposing a new scheme for Archean marine chemistry and geochemical cycles that can explain the chemical and geological observations from the Archean and early Proterozoic rock record.

The Enigma of Neoproterozoic Giant Ooids—Fingerprints of Extreme Climate?

AbstractGeologists have documented at least 14 occurrences of “giant ooids,” a geologically rare type of carbonate allochem, in Neoproterozoic successions at low paleolatitudes. Recent experiments and modeling demonstrated that ooid size reflects an equilibrium between precipitation and abrasion rates, such that ooid size could be used as a geological proxy for CaCO3 mineral saturation state (Ω). Here, the documented sizes of Neoproterozoic giant ooids were applied to estimate seawater Ω, which provided a novel approach to constraining temperature, partial pressure of CO2, and alkalinity preceding Neoproterozoic glaciations. The results suggest that giant ooid formation was most plausible with seawater alkalinity elevated over its present value by at least a factor of 2, and either much warmer (40 °C) or much colder (0 °C) climate than modern tropical carbonate platforms, which have important and divergent implications for climate states and ecosystem responses prior to the initiation of each Neoproterozoic glaciation.

An Estimate of Possible Impacts of Superoxide Chemistry on Seawater pH: A Mapping Exercise

Superoxide, produced photochemically as well as microbially, is an important reactant present in seawater and a major source of hydrogen peroxide. Superoxide decay may occur through catalyzed or uncatalyzed dismutation forming H2O2 and O2, through oxidation to O2, or through reduction into H2O2. Under definite circumstances, the redox processes that are different from dismutation could produce or consume H+, thereby altering the pH of seawater. In order to alter the pH, these processes have to involve, together with O2•, redox couples that exchange e and H+ in a ratio other than 1:1. This potential pH modification is dependent on several factors, including the extent of H+ imbalance, the rate of formation/transformation of superoxide (which reaches a steady-state concentration in seawater), and the alkalinity of seawater (which varies globally from 2.10 to 2.45 mmol L1 and buffers the pH variations). In the present study, an estimate of the possible pH changes associated with photochemically-produced superoxide in the global ocean has been provided. Among the important approximations that were required to perform the calculations, one was that it was not possible to include the microbially generated O2•, as a geographic distribution of microbial processes is not available. Unfortunately, the microbial production of O2• is comparable to or at certain times even higher than its photochemical production. Despite the above-stated and certain other limitations, it may be inferred that the tropical and equatorial oceans, because of the high O2• photoproduction rates, would be having the highest potential of undergoing pH variations (up to 0.005 pH units in ten years). Along the tropical/equatorial latitude belt, at comparable sunlight irradiance, such variations are expected to be the largest (0.005 pH units) in the Indian Ocean due to a relatively low alkalinity, in the range of 2.2–2.3 mmol L1. The lowest variations (0.003–0.004 pH units) are expected in the Atlantic Ocean, because of a relatively high alkalinity in the range of 2.3–2.4 mmol L1. The main requirement for the O2• chemistry to impact the pH of seawater significantly is that the H+-imbalance reactions should be maintained for a sufficiently long period of time. The pH effect is most probably to be operational in the river-impacted coastal areas (potential candidates are the areas affected by the following rivers: Ganges, Mekong, Irrawaddy, Zambezi, Amazon River, Orinoco, Mississippi, and Rio Grande), which are characterized by a continuous flow of redox-active organic compounds into the seawater.

Rare earth elements in the terminal Ediacaran Bambuí Group carbonate rocks (Brazil): evidence for high seawater alkalinity during rise of early animals

Rare earth elements plus yttrium (REY) mass fractions of ancient carbonate rocks are used to track changes in chemistry of past seawater. Here we investigate REY patterns in two carbonate sections from the Ediacaran Bambuí Group, São Francisco Basin (Brazil), which comprise its two lowermost transgressive-regressive second-order sedimentary sequences. Shale normalised distributions vary with the sequence stratigraphy framework. In the basal 2nd-order sequence, carbonate samples from the basal sequence transgressive systems tract display light REY (LREY) distributions slightly depleted to enriched that reflect input of freshwater, possibly in a post glacial episode. Upwards, carbonate rocks from the early highstand systems tract (EHST) yielded LREY enriched distributions, which progressively turns into LREY shale normalized depleted distributions on samples from the late highstand systems tract (LHST). This portion of the sequence also displays Y positive anomaly in some cases. Carbonate samples from the upper second-order sequence do not display coherent patterns. Ce/Ce* values > 1 in most samples throughout the two sections suggest permanent anoxia of seawater. The REY change from the EHST to LHST in the basal sequence marks an important paleoenvironmental overturn in the basin, with increasing alkalinity in seawater driving REY fractionation and LREY depletion. Confinement of the basin in the inner areas of West Gondwana due the uplift of marginal neoproterozoic orogens probably changed the weathering style of source areas to more congruent, thus delivering a higher ionic influx to a restricted setting, increasing alkalinity during LHST. Cloudina sp. fragments were reported in this stage of the Bambuí Group and in carbonate rocks with high Sr mass fractions in other West Gondwana basins, supporting the hypothesis that the high alkalinity of seawater during late Ediacaran may have driven the appearance of the first biomineralizing organisms.

Seawater/alkaline liquid cascade‐scrubbing desulfurization performance for the exhaust gas of a 162‐kW marine diesel engine

AbstractA cascade‐scrubbing technology was developed for marine diesel engines to improve the current once‐through desulfurization solutions. To confirm the seawater/alkaline liquid cascade‐scrubbing advantages of higher efficiencies and lower lye consumption compared with current solutions, desulfurization experiments with different scrubbing models were performed for a 162‐kW marine diesel engine. In the open‐loop model with SO2 of 1,000–2,860 mg/Nm3, desulfurization with the allowed liquid–gas ratios ≤8 L/Nm3 for the packing tower failed to fully meet the ECA's requirements, despite the efficiency increasing with liquid–gas ratio, seawater alkalinity, and packing height and decreasing with SO2 concentration. In the closed‐loop solution, to obligate the ECA's requirements with SO2 of 2,860 mg/Nm3, a high liquid–gas ratio of 4.8 L/Nm3 was necessitated at Na/S=2. In contrast, in the seawater/alkaline liquid cascade‐scrubbing model under high‐sulfur and low‐alkalinity conditions (2,860 mg/Nm3 and 0.84 mmol/L), the solution utilized 5–6 L/Nm3 seawater in the main scrubbing section to scrub 80–90% SO2 and an extremely low alkaline‐liquid dose below 1 L/Nm3 in the auxiliary scrubbing section to remove the residual SO2, finally allowing a high efficiency ahead of the open‐loop model and meanwhile cutting down an 80–90% lye consumption compared with the closed‐loop model.

Characterization of a novel autonomous analyzer for seawater total alkalinity: Results from laboratory and field tests

AbstractHigh‐quality seawater total alkalinity (AT) measurements are essential for reliable ocean carbon and acidification observations. Well‐established manual multipoint potentiometric titration methods already fulfill these requirements. The next step in the improvement of these observations is the increase of the spatial and temporal measuring resolution with minimal personnel and instrumental effort. For this, a rapid, automated underway analyzer meeting the same high requirements as the traditional method is necessary. In this study, we carried out a comprehensive characterization of the flow‐through analyzer CONTROS HydroFIA® TA (Kongsberg Maritime Contros GmbH, Kiel, Germany) for automated seawater AT measurements in the laboratory and in field with overall more than 5000 measurements. Under laboratory conditions, the analyzer featured a precision of ± 1.5 μmol kg−1 and an accuracy of ± 1.0 μmol kg−1, combined in an uncertainty of 1.6 – 2.0 μmol kg−1. High precision (± 1.1 μmol kg−1) and accuracy (−0.3 ± 2.8 μmol kg−1), and low uncertainty (2.0 – 2.5 μmol kg−1) were also achieved during field trials of 4 and 6 weeks duration. Although a linear drift appears to be the typical behavior of the system, this can be corrected for by regular reference measurements giving consistent measurement results. Another advantage of regular reference measurements is the early detection of any kind of malfunction due to its direct impact on the measurement performance. Based on the present study, recommendations for automated long‐term deployments are provided in order to gain optimal performance characteristics, aiming at the requirements for AT measurements.

Sedimentology and chemostratigraphy of the terminal Ediacaran Dengying Formation at the Gaojiashan section, South China.

The late Ediacaran Dengying Formation (ca. 551.1-538.8 Ma) in South China is one of two successions where Ediacara-type macrofossils are preserved in carbonate facies along with skeletal fossils and bilaterian animal traces. Given the remarkable thickness of carbonate-bearing strata deposited in less than 12.3 million years, the Dengying Formation holds the potential for a relatively continuous chemostratigraphic profile for the terminal Ediacaran stage. In this study, a detailed sedimentological and chemostratigraphic (δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyrite, and 87Sr/86Sr) investigation was conducted on the Dengying Formation at the Gaojiashan section, Ningqiang County of the southern Shaanxi Province, South China. Sedimentological results reveal an overall shallow marine depositional environment. Carbonate breccia, void-filling botryoidal precipitates, and aragonite crystal fans are common in the Algal Dolomite Member of the Dengying Formation, suggesting that peritidal facies were repeatedly karstified. The timing of karstification was likely early, probably soon after the deposition of the dolomite sediments. The presence of authigenic aragonite cements suggests high alkalinity in the terminal Ediacaran ocean. Geochemical analysis of micro-drilled samples shows that distinct compositions are registered in different carbonate phases, which should be considered when constructing chemostratigraphic profiles representative of true temporal variations in seawater chemistry. Integrated chemostratigraphic data suggest enhanced burial of organic carbon and pyrite, and the occurrence of extensive marine anoxia (at least in the Gaojiashan Member). Rapid basinal subsidence and carbonate accumulation during a time of elevated seawater alkalinity and increased rates of pyrite burial may have facilitated the evolutionary innovation of early biomineralizing metazoans.