Ocean Chemistry Research Articles

Dissimilar Sensitivities of Ocean Acidification Metrics to Anthropogenic Carbon Accumulation in the Central North Pacific Ocean and California Current Large Marine Ecosystem

AbstractWe analyze and compare changes in ocean acidification metrics caused by anthropogenic carbon (Canth) accumulation in the North Pacific Ocean and California Current Large Marine Ecosystem (CCLME). The greatest declines in pH and carbonate mineral saturation state occur near the surface, coincident with the highest Canth concentrations. However, maximal increases in the partial pressure of carbon dioxide (pCO2) and hydrogen ion concentration occur subsurface where Canth values are lower. We attribute dissimilar sensitivities of these metrics to background ocean chemistry, which has naturally high pCO2 and low buffering capacity in subsurface waters due to accumulated byproducts of organic matter respiration, which interacts with Canth. In the CCLME, rising subsurface pCO2 has increased the frequency, duration, and intensity of hypercapnia (pCO2 ≥ 1,000 μatm) on the continental shelf. Our findings suggest that hypercapnia induced by Canth accumulation can co‐occur with hypoxia in the CCLME and is an additional modern stressor for marine organisms.

Exoskeletal predator defenses of juvenile California spiny lobsters (Panulirus interruptus) are affected by fluctuating ocean acidification-like conditions

Spiny lobsters rely on multiple biomineralized exoskeletal predator defenses that may be sensitive to ocean acidification (OA). Compromised mechanical integrity of these defensive structures may tilt predator-prey outcomes, leading to increased mortality in the lobsters’ environment. Here, we tested the effects of OA-like conditions on the mechanical integrity of selected exoskeletal defenses of juvenile California spiny lobster, Panulirus interruptus. Young spiny lobsters reside in kelp forests with dynamic carbonate chemistry due to local metabolism and photosynthesis as well as seasonal upwelling, yielding daily and seasonal fluctuations in pH. Lobsters were exposed to a series of stable and diurnally fluctuating reduced pH conditions for three months (ambient pH/stable, 7.97; reduced pH/stable 7.67; reduced pH with low fluctuations, 7.67 ± 0.05; reduced pH with high fluctuations, 7.67 ± 0.10), after which we examined the intermolt composition (Ca and Mg content), ultrastructure (cuticle and layer thickness), and mechanical properties (hardness and stiffness) of selected exoskeletal predator defenses. Cuticle ultrastructure was consistently robust to pH conditions, while mineralization and mechanical properties were variable. Notably, the carapace was less mineralized under both reduced pH treatments with fluctuations, but with no effect on material properties, and the rostral horn had lower hardness in reduced/high fluctuating conditions without a corresponding difference in mineralization. Antennal flexural stiffness was lower in reduced, stable pH conditions compared to the reduced pH treatment with high fluctuations and not correlated with changes in cuticle structure or mineralization. These results demonstrate a complex relationship between mineralization and mechanical properties of the exoskeleton under changing ocean chemistry, and that fluctuating reduced pH conditions can induce responses not observed under the stable reduced pH conditions often used in OA research. Furthermore, this study shows that some juvenile California spiny lobster exoskeletal defenses are responsive to changes in ocean carbonate chemistry, even during the intermolt period, in ways that can potentially increase susceptibility to predation among this critical life stage.

Extensive Early Marine Seafloor Cementation in a Modern Epeiric Sea Induced by Seawater Properties and a Shallow Redox Boundary Below the Seafloor

Extensive Early Marine Seafloor Cementation in a Modern Epeiric Sea Induced by Seawater Properties and a Shallow Redox Boundary Below the Seafloor

Protecting Coastal Environment in India: Reading Laws in the Context of Climate Change

The oceans’ role in maintaining the climate of this planet is unquestionably vital. But today, the fine balance in ocean chemistry is dangerously upset by the global warming, leading to more warmer oceans and a continuous rise in sea level across the globe. With that comes the threat to marine lives and ecosystems. India has a 7,516.6 km long coastline which is the home to many marginal poor communities who mainly survive on the ocean resources. Alongside, the adjacent marine environment contains an astounding array of biodiversity, harbouring innumerable species with ecological and commercial significance. However, Indian coastal regions are also not spared from the ill effects of climate change. The condition is frightening enough as the lives of hundreds and thousands of people living at the coast are at critical risk, along with the possibility of irreparable loss of biodiversity. India, thus far, has offered a fragmented conservation methodology for its coastal regions. The laws, regulations and policies that matter most in their current forms lack synergy and clear insight. This article tracks those ambiguities and advances a central argument that India needs to put in place an inclusive climate strategy without further eroding environmental laws that play a key role in conserving its coastal and marine environment.

Mercury anomalies across the Cryogenian-Ediacaran boundary in South China

The Cryogenian-Ediacaran transition represents a pivotal geological period in the evolution of global climate, ocean chemistry, and early organisms. The transition is concurrent with the change from Marinoan glacial deposits to overlying cap carbonate/dolomite, which is followed by the appearance of novel animal and algae fossils. Unusual carbon cycling during the deposition of cap carbonate/dolomite is recorded by prominent negative carbonate carbon isotope (δ13Ccarb) anomalies. The mechanisms which drove melting of the Marinoan icesheets remain uncertain. To explore the cause of this dramatic climate warming and its effect on oceanic biogeochemical cycles, we measured Hg concentrations and isotopes, along with major and trace elements, of the sedimentary succession across the Cryogenian-Ediacaran boundary at the Jiulongwan and Huajipo sections, South China. Hg concentrations show spikes with a ∼ 2 times increase at the top of the Marinoan Nantuo Formation at both sections, which are likely associated with organic matter drawdown rather than enhanced volcanism as indicated by increased TOC contents and similar Hg isotopic signature as those of background Hg deposition. A conspicuous negative shift in δ202Hg along with a positive shift in Δ199Hg are observed in the cap dolomite of the Doushantuo Formation at both sections, which are ascribed to contribution of Hg from anoxic deep water and Hg associated with dissolved organic carbon (Hg-DOC), due to upwelling and oceanic oxygenation after deglaciation. Our Hg data argue against a sudden large igneous province (LIP) event causing Marinoan deglaciation. Results also indicate enhanced upwelling and oceanic oxygenation event during the Cryogenian to Ediacaran transition.

Global Quaternary Carbonate Burial: Proxy- and Model-Based Reconstructions and Persisting Uncertainties.

Constraining rates of marine carbonate burial through geologic time is critical for interpreting reconstructed changes in ocean chemistry and understanding feedbacks and interactions between Earth's carbon cycle and climate. The Quaternary Period (the past 2.6 million years) is of particular interest due to dramatic variations in sea level that periodically exposed and flooded areas of carbonate accumulation on the continental shelf, likely impacting the global carbonate budget and atmospheric carbon dioxide. These important effects remain poorly quantified. Here, we summarize the importance of carbonate burial in the ocean-climate system, review methods for quantifying carbonate burial across depositional environments, discuss advances in reconstructing Quaternary carbonate burial over the past three decades, and identify gaps and challenges in reconciling the existing records. Emerging paleoceanographic proxies such as the stable strontium and calcium isotope systems, as well as innovative modeling approaches, are highlighted as new opportunities to produce continuous records of global carbonate burial.

Anthropogenic Carbon Increase has Caused Critical Shifts in Aragonite Saturation Across a Sensitive Coastal System

AbstractEstuarine systems host a rich diversity of marine life that is vulnerable to changes in ocean chemistry due to addition of anthropogenic carbon. However, the detection and impact of secular carbon trends in these systems is complicated by heightened natural variability as compared to open‐ocean regimes. We investigate biogeochemical changes between the pre‐industrial (PI) and modern periods using a high‐resolution, three‐dimensional, biophysical model of the Salish Sea, a representative Northeast Pacific coastal system. While the seasonal amplitude of the air‐sea difference in pCO2 has increased on average since pre‐industrial times, the net CO2 source has changed little. Our simulations show that inorganic carbon has increased throughout the model domain by 29–39 mmol m−3 (28–38 µmol kg−1) from the pre‐industrial to present. While this increase is modest in a global context, the region's naturally high inorganic carbon content and the low buffering capacity of the local carbonate system amplify the resultant effects. Notably, this increased carbon drives the estuary toward system‐wide undersaturation of aragonite, negatively impacting shell‐forming organisms. Undersaturation events were rare during the pre‐industrial experiment, with 10%–25% of the domain undersaturated by volume throughout the year, while under present‐day conditions, the majority (55%–75%) of the system experiences corrosive, undersaturated conditions year‐round. These results are extended using recent global coastal observations to show that estuaries throughout the Pacific Rim have already undergone a similar saturation state regime shift.

Geochemical Negative Emissions Technologies: Part I. Review

Over the previous two decades, a diverse array of geochemical negative emissions technologies (NETs) have been proposed, which use alkaline minerals for removing and permanently storing atmospheric carbon dioxide (CO2). Geochemical NETs include CO2 mineralization (methods which react alkaline minerals with CO2, producing solid carbonate minerals), enhanced weathering (dispersing alkaline minerals in the environment for CO2 drawdown) and ocean alkalinity enhancement (manipulation of ocean chemistry to remove CO2 from air as dissolved inorganic carbon). CO2 mineralization approaches include in situ (CO2 reacts with alkaline minerals in the Earth's subsurface), surficial (high surface area alkaline minerals found at the Earth's surface are reacted with air or CO2-bearing fluids), and ex situ (high surface area alkaline minerals are transported to sites of concentrated CO2 production). Geochemical NETS may also include an approach to direct air capture (DAC) that harnesses surficial mineralization reactions to remove CO2 from air, and produce concentrated CO2. Overall, these technologies are at an early stage of development with just a few subjected to field trials. In Part I of this work we have reviewed the current state of geochemical NETs, highlighting key features (mineral resources; processes; kinetics; storage durability; synergies with other NETs such as DAC, risks; limitations; co-benefits, environmental impacts and life-cycle assessment). The role of organisms and biological mechanisms in enhancing geochemical NETs is also explored. In Part II, a roadmap is presented to help catalyze the research, development, and deployment of geochemical NETs at the gigaton scale over the coming decades.

Sedimentary environment and relative sea level changes revealed by marine biological membrane

Marine pollution has a deleterious impact, both on the conditions of the ecosystem and the biodiversity of the ocean. Researchers in the field of marine chemistry have been putting effort into the creation of efficient catalysts for the purification of seawater. There has been extensive research done on membrane technology for the activation of peroxymonosulfate, which is an extremely effective therapy for saltwater. The sediment of QX03, which was obtained from the western coast of Bohai, is located very close to the modern coastline. The uppermost 15 m of this sector were thoroughly analyzed in sedimentary petrology, grain size, shell, and sediment chroma dating to reconstruct the sedimentary environment and relative sea-level during the time period of 44.80 ka cal BP. This indicates that a sea-retreating and retreating process has taken place; VI (5.2–0 m), Terrestrial deposition, is separated into swamp wetlands (VI-1) and flood plain (VI-2). The changes in sedimentary levels had a fairly strong correlation with the changes in sea level. Within the scope of this study, we conducted an in-depth investigation of the innovative membrane technology for the treatment of seawater by means of aqueous phase advanced oxidation close to the Bohai. The results of this study present a prospective technique that could make it possible to use membrane technology in the process of environmental restoration in marine settings.

TAPHONOMIC CONTROLS ON MICROBIALITE TEXTURES FROM THE STEAMBOAT POINT MEMBER, UPPER ORDOVICIAN BIGHORN DOLOMITE, WESTERN TETON MOUNTAINS, USA

ABSTRACT The Bighorn Dolomite is a massive, cliff-forming dolostone unit found across the state of Wyoming and adjacent areas that records the transition from greenhouse to icehouse conditions during the Late Ordovician. The basal Steamboat Point Member of the Bighorn Dolomite contains cm-scale mottled fabrics often attributed to the ichnogenus Thalassinoides, but their origin remains enigmatic in Upper Ordovician strata. The development of mottled fabrics may have significant implications for marine chemistry and paleoecology. We analyzed cm-scale mottled fabrics from the basal Steamboat Point Member of the western Teton Mountains to determine their origin and develop criteria for identification of similar mottled fabrics found in other Upper Ordovician strata. In vertical cross-section, massive, m-scale exposures display vertical columns (approximately 1 cm in diameter) that anastomose and maintain decimeter-scale vertical continuity. Microscopically, the columns are composed of micro-peloidal micritic textures surrounded by spar and microspar, whereas the intercolumnar matrix is composed of dolomicrite grains, skeletal clasts, and intraclasts. We interpret the microscopic peloidal texture as a product of benthic microbial calcification that coalesced to form mesoclots—diagnostic features of thrombolitic microbialites. Paragenetic analyses reveal evidence for early lithified microbial biofilms despite dolomite replacement and aggrading neomorphism. These observations indicate the Steamboat Point Member of the Bighorn Dolomite was deposited in seawater that was highly supersaturated with respect to carbonate, consistent with other studies that suggest deposition during greenhouse conditions prior to the end-Ordovician glaciation. We present a novel ternary diagram that contains criteria to help differentiate between burrows, microbialite textures, or physical processes that may result in mottled fabrics in the rock record.

Quantitative evaluation of the roles of ocean chemistry and climate on ooid size across the Phanerozoic: Global versus local controls

AbstractOoid size in natural systems can be predicted based on the expected equilibrium between precipitation and abrasion rates. Therefore, ooid size distributions may enable quantitative inferences about past ocean and climate conditions from sedimentology that complement insights from geochemistry. A few previous attempts have been made to compile information on ooid sizes across the Phanerozoic, but no systematic ooid size dataset is available and equilibrium models of ooid growth have not been explored comprehensively. In this study, convolutional neural network‐based segmentation was used to automate ooid size measurement and provide a systematic sampling of ooid sizes spanning the Phanerozoic. This data set is coupled with Monte Carlo simulations to quantitatively explore the interplay between three testable physicochemical parameters (long‐term average carbonate saturation state, bed shear velocity and intermittency of transport) in determining equilibrium ooid size. The numerical model shows that a typical‐sized ooid (≤1000 µm) can grow under a wide range of parameter combinations whereas giant ooids (>2000 µm) can only form under a more restricted set of circumstances. Furthermore, the model predicts that the formation of giant ooids is common when conditions favourable for rapid CaCO3 precipitation are achieved. This finding is consistent with the naturally rare occurrences of giant ooids, which developed under exceptional environmental conditions and are primarily associated with intervals of bimineralic seas and elevated sea‐surface temperature (greenhouse or transitional climate). Whereas global controls could help explain secular trends in ooid size, significant spatial variability of ooid size in several time intervals further demonstrates the importance of local environmental parameters in the growth of ooids. Together, spatial and temporal variation in ooid size distributions can complement geochemical proxies in quantitatively reconstructing ancient tropical marine environments.

Controls on marine primary productivity variation and organic matter accumulation during the Late Ordovician－Early Silurian transition

The Late Ordovician−Early Silurian is a convergence period of multiple events in geological history, including dramatic variations of biology, environment, and geology. Extensive research has demonstrated remarkable fluctuations in ocean chemistry, microbial ecosystems, and biogeochemical elemental cycles experienced. However, the spatial-temporal evaluation of marine primary productivity and its links to organic matter accumulation during this key period remain elusive. Here, we present high-resolution marine primary productivity proxy (organic carbon accumulation rates: OCAR) and geochemical data from the Fengtonggang and Qiliao sections deposited in South China and adopted numerous other coeval sections of geochemical data globally, to improve the understanding of these fundamental scientific questions. The results show that all statistical profiles presented broadly high marine primary productivity before and after the Hirnantian glaciation maximum and low values during the glaciation, and a maximum marine primary productivity typically recorded at the uppermost part of the P.pacificus Zone. The Corg/Ptotal ratios indicate that oceanic anoxia was ubiquitous during the Late Katian to Early Rhuddanian, but strong spatial heterogeneous during the Hirnantian glaciation maximum. The volcanism and nitrogen availability may have played an important role in regulating the variations of marine primary productivity globally. Besides, redox-controlled phosphorus cycling may have also exerted a remarkable influence on marine primary productivity. The high Corg/Ptotal ratios (exceed the Redfield ratio of 106/1) observed in the Wufeng and Longmaxi formations indicate that phosphorus was recycled effectively back to the water column, promoting a positive productivity feedback. By contrast, the low Corg/Ptotal ratios found in the Guanyinqiao Bed reflect phosphorus retention in the sediment, limiting phosphorus recycling back to the water column, consequently restricting the primary production. The enhanced marine primary productivity resulted from nutrient regeneration, ocean anoxia, and high sea level may have led to high organic carbon export and preservation. The consistency between the highest marine primary productivity and the first pulse of mass extinction suggests that eutrophication-induced marine anoxia may have played an essential killing mechanism during the first Late Ordovician mass extinction.

Vanadium isotope fractionation during hydrothermal sedimentation: Implications for the vanadium cycle in the oceans

Variations of V isotope ratios (δ51V) in sedimentary rocks have been proposed as a potential proxy for paleo-oceanic redox conditions, although the marine δ51V system is not fully constrained. Hydrothermal sediments are known to be a significant sink of V from the ocean. However, the V isotope fractionation associated with the accumulation into hydrothermal sediments from seawater and its influence on the marine isotopic budget of V are still unexplored. This work presents the first V isotope study of hydrothermal sediments specifically samples from the Trans-Atlantic Geotraverse (TAG) hydrothermal field and Pacific Ocean under influence of the hydrothermal plume arising from the southern East Pacific Rise (SEPR). The studied sediments show authigenic δ51V values ranging from −0.4 to −0.1‰, which is remarkably different from that of non-hydrothermal oxic sediments (−1.2 to −0.7‰) as well as open ocean seawater (+0.2‰). The V isotope composition of these hydrothermal sediments at TAG is likely controlled by the isotope fractionation during the rapid initial uptake of V from seawater into hydrothermal Fe oxyhydroxide particulates that precipitate when reducing hydrothermal fluids mix with oxic seawater. The sediments collected from the deep south Pacific Ocean west of SEPR show authigenic δ51V values overlapping with the range observed within the TAG field, despite their distal location extending to more than 4000 km from the buoyant portion of the SEPR hydrothermal plume. As has also been observed for Fe in particulates west of the SEPR, our results indicate the persistence of V within hydrothermal particulates (likely in the form of V-rich Fe oxyhydroxides) that settle to the sediments after long-range transport, while still preserving the original V isotope signature. Combination of this work with previous studies, allows us to establish a more robust mass balance model that assesses the effect of V removal by hydrothermal precipitation on the marine elemental and isotopic budget of V. Our new results suggest that the flux of V into the hydrothermal sink accounts for ∼13% of the global marine V input. This model also indicates that the V isotope composition of seawater could potentially be altered with variations in hydrothermal activity which is in addition to changes in the global marine redox conditions but likely on very different time scales. Thus, V isotope ratios have the potential to provide new insights into ancient ocean chemistry.

Volatile-bearing Partial Melts in the Lithospheric and Sub-Lithospheric Mantle on Earth and Other Rocky Planets

Research Article| May 01, 2022 Volatile-bearing Partial Melts in the Lithospheric and Sub-Lithospheric Mantle on Earth and Other Rocky Planets Rajdeep Dasgupta; Rajdeep Dasgupta Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USA rajdeep.dasgupta@rice.edu Search for other works by this author on: GSW Google Scholar Proteek Chowdhury; Proteek Chowdhury Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USACurrent address: Department of Earth and Planetary Sciences, University of California at Riverside, 900 University Avenue, Riverside, CA 92521, USA proteekc@ucr.edu Search for other works by this author on: GSW Google Scholar James Eguchi; James Eguchi Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USACurrent address: Department of Earth and Planetary Sciences, University of California at Riverside, 900 University Avenue, Riverside, CA 92521, USA james.eguchi@ucr.edu Search for other works by this author on: GSW Google Scholar Chenguang Sun; Chenguang Sun Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USADepartment of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78712, USA csun@jsg.utexas.edu Search for other works by this author on: GSW Google Scholar Sriparna Saha Sriparna Saha Department of Earth, Environmental and Planetary Sciences, Rice University, 6100 Main Street, MS 126, Houston, TX 77005, USACurrent address: School of Teacher Education and School of Earth and Environment, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand sriparna.saha@pg.canterbury.ac.nz Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2022) 87 (1): 575–606. https://doi.org/10.2138/rmg.2022.87.12 Article history first online: 01 May 2022 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Rajdeep Dasgupta, Proteek Chowdhury, James Eguchi, Chenguang Sun, Sriparna Saha; Volatile-bearing Partial Melts in the Lithospheric and Sub-Lithospheric Mantle on Earth and Other Rocky Planets. Reviews in Mineralogy and Geochemistry 2022;; 87 (1): 575–606. doi: https://doi.org/10.2138/rmg.2022.87.12 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Generation and extraction of partial melts from the interior of rocky planets are essential steps for supplying heat and life-essential nutrients to the surface environments. Mantle-derived partial melts dissolve key volatile elements such as carbon, hydrogen, and sulfur and when brought to the surface or near-surface conditions, liberate them as gases such as carbon dioxide (CO2), water vapor (H2O), and sulfur dioxide (SO2) or hydrogen sulfide (H2S). These gases influence the composition of the atmosphere–ocean systems, silicate-weathering feedback, (Walker et al. 1981) and/or ocean chemistry, thereby affecting the climate on... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Aromatic carotenoids: Biological sources and geological implications

• Aromatic carotenoids are robust biomarkers in reconstructing environments. • Aromatic carotenoids decipher the evolution of microorganisms and ocean chemistry. • Aromatic carotenoids are valid in interpreting on-going diagenetic processes. Aromatic carotenoids have been discovered in geological sections recording mass extinction events, oceanic anoxic events, and other geological abnormalities. Given their conventional biological source attribution to phototrophic sulfur bacteria, aromatic carotenoids have been adopted in interpreting photic zone euxinia (PZE), and encode significant paleoecological and paleoenvironmental information. Nevertheless, the recent detection of aromatic carotenoids in cyanobacteria challenges former assertions. Building on previous studies, this review summarizes the most recent progress on biological sources of aromatic carotenoids and details possible diagenetic processes and how these processes may bias or facilitate our understanding of aromatic carotenoids. This review further expands on typical instrumental and chemical preparative procedures in analyzing aromatic carotenoids. Finally, we illustrate the unique contribution of aromatic carotenoids in characterizing modern and ancient aquatic environments, unrevealing the evolution of microorganisms, and understanding on-going diagenetic processes.

Middle to Late Jurassic stable isotopes and element ratios of fossils from western India: Developing a reference temperature curve for northeastern Gondwana

The stable isotope (δ13C, δ18O) and element (Mg/Ca, Sr/Ca) composition of 374 well-preserved belemnites, bivalves, and brachiopods of the Kachchh and Jaisalmer basins in western India were used to reconstruct climatic changes in the Middle and Late Jurassic time interval. Absolute water temperatures reconstructed from δ18Oshell values depend on the used δ18Osea value and equation, but indicate a long-term temperature decrease of around 8–9 °C in the study area from the Bajocian to the Tithonian. Measured Mg/Ca ratios also point to decreasing temperatures, but additionally reflect species-specific factors and a lower Mg/Ca ratio of Jurassic seawater compared to today. The recorded cooling in western India agrees with previous results from neighbouring Madagascar and the Indian Himalayas and can be connected to a drift of Eastern Gondwana into higher latitudes. This palaeogeographic shift is accompanied by changes in sedimentation indicating an increasingly humid climate and in the composition of ecosystems reflecting increasingly cooler water temperatures. High-resolution stable oxygen isotope analyses of three oyster shells point to seasonal temperature changes of 4–5 °C in the Kimmeridgian. The recorded δ13C values reflect sea-level changes with a positive excursion in the Oxfordian connected to a major transgressive event. Sr/Ca ratios are observed to follow changes in global ocean chemistry.

The winter estuarine geochemistry of platinum in the Estuary and Gulf of St. Lawrence

The marine chemistry of platinum is poorly understood, and its oceanic budget remains unconstrained, mainly because of severe analytical artifacts and the paucity of studies on this element of increasing technological interest. Here, we report dissolved and acid-leachable Pt concentrations in the Estuary and Gulf of St. Lawrence (EGSL) under winter conditions, and relate its estuarine geochemical behaviour to that of Cd, an element with similar characteristics and for which we have a more comprehensive knowledge. In contrast to Cd and to most pristine river systems, dissolved Pt concentrations in the EGSL in the winter (0.46 ± 0.09 pM) are significantly higher than the marine endmember (0.26 ± 0.06 pM). This discrepancy could be ascribed to the geology of the EGSL's drainage basins as well as the wet deposition of atmospheric Pt. This observation draws attention to the impacts of anthropogenic Pt emissions on its environmental dispersion, background estuarine concentrations and processes, especially in high-latitude regions. Unlike the results of most studies carried out in estuarine systems under ice-free conditions, we observed a near-conservative mixing behaviour of Pt and Cd in the surface waters of the EGSL during the winter, as is the case for dissolved Mn, Fe and rare earth elements. This observation could be explained by a decreased delivery of colloidal and organic materials to the estuary under ice-covered conditions. We also observed that dissolved Pt and Cd concentrations increase in the bottom waters of the EGSL, where the waters are more saline and oxygen-depleted. These higher concentrations may originate from aerobic mineralization of Pt-bearing organic matter, a decrease of Pt-reactive surface sites on suspended particles, and a change in redox speciation of PtII into PtIV. Overall, these results highlight that winter and oxygen-depleted conditions can amplify continental Pt fluxes to the oceans and thus should be considered in future Pt oceanic budget calculations.

Characteristics of Desalination Brine and Its Impacts on Marine Chemistry and Health, With Emphasis on the Persian/Arabian Gulf: A Review

At a time when worldwide water shortage is increasing, seawater is being viewed as an inexhaustible supply of freshwater via the process of seawater desalination. As a result, seawater desalination is becoming more popular, especially in areas where freshwater is scarce, such as the Middle East and North Africa (MENA), which accounts for half of all global saltwater desalination activities. To enhance the efficiency of saltwater desalination, thermal and membrane-based desalination technologies are continually being developed and hybridized systems established. Brine is an unavoidable product of seawater desalination and is commonly disposed of in oceans and seas, where it has negative effects on the surrounding marine environment and its biodiversity due to the resultant increased salinity and temperature, as well as the presence of chemicals. Furthermore, the quality and amount of brine are influenced by several parameters, including the input quality and quantity, the desalination process, and the discharge method. The intensity of brine’s influence on the marine biota is determined by a number of factors; nevertheless, marine species differ in their tolerance to brine’s effects. Desalination technology is improving to maximize water recovery and reduce the volume of brine produced, with the objective of eventually reaching zero liquid discharge and limiting harmful effects on the marine environment. Meanwhile, proper systems for analyzing the effects of seawater desalination facilities on the marine ecology must be implemented. This review study will look at all of the factors that determine the physicochemical features of desalination brine, with a focus on its impact on marine chemistry and biodiversity. More crucially, the most cutting-edge brine management methods will be investigated for long-term desalination and a healthy marine ecosystem.

Palaeoenvironments and elemental geochemistry across the Permian–Triassic boundary at Ursula Creek, British Columbia, Canada, and a comparison with some other deep‐water Permian–Triassic boundary shelf/slope sections in western North America

The Permian–Triassic boundary sediments at Ursula Creek accumulated in a continental shelf basin, or on the continental slope of the western Canadian passive margin, at 30°N palaeolatitude along the eastern Panthalassic Ocean margin. The area lay within the cold northerly ocean currents at the junction of westerly and north-easterly trade wind belts, the latter causing summer coastal upwelling. The shift from uppermost Permian grey radiolarian cherts and grey shales to lowermost Triassic grey and black shales and fine-grained dolomites is typical of deep-water Panthalassic sediments. The palaeogeographical situation and palaeoenvironments are comparable to those of the present Canadian north-western Pacific margin. The Ursula Creek section reveals the progressive decline of seafloor oxygen values in the Changhsingian Stage), followed by the persistent development of euxinic conditions in the latest Changhsingian and throughout the Early Triassic; a transition that coincides with the disappearance of a siliceous sponge fauna and the loss of diverse radiolarian populations. Much of the detrital sediment was supplied by summer north-east Trade winds from the deserts of western North America, although variable amounts may have come across the Panthalassic Ocean as dust from contemporary volcanic eruptions. Relative palaeoproductivity changes show no consistent change in productivity across the Permian–Triassic boundary producing results that are comparable with those from the similar Opal Creek section to the south-east. The Ni/Co, Cu/Zn, U/Al and Th/U ratios indicate variable redox conditions in all sections, but with a tendency for oxic conditions to change to dysoxic across the Permian–Triassic boundary. The lack of consistent element geochemical changes across the boundary accompanied by significant isotopic changes, here and elsewhere, suggests that atmospheric and oceanic chemistry rather than physical changes, like provenance and sea-level changes, drove Permian–Triassic environmental changes and extinctions.

Tectonic controls on the isotopic juvenility of mid-Cretaceous continental arcs: Global compilations and implications for chemical weathering

Continental arcs influence the global carbon cycle via degassing and chemical weathering. Several studies also suggested that the isotopic composition of continental arcs plays an important role in controlling the strontium (Sr) isotopic composition of seawater through chemical weathering. Yet, geological or tectonic drivers of isotopic variations of continental arcs on a global scale are missing in previous studies. Here, we compiled two independent global databases for mid-Cretaceous (125-85 Ma) continental arcs. The first database maps the location, geometry, and tectonic nature of the basements upon which the arcs were built. The second compiles Sr-Nd-Hf isotopes data for these continental arcs. We find that isotopically-juvenile arcs form when their basements are generated by tectonic processes such as oceanic terrane accretion, upper plate extension, slab breakoff, and ridge subduction. During the mid-Cretaceous, most continental arcs were fully or partially built on juvenile basements and yielded juvenile isotopes on a global scale. Our compilation reinforces the importance of isotopically-juvenile continental arcs observed in the global Hf isotopes in detrital zircon for the mid-Cretaceous, but also provides the geological context for these trends. Since many of these isotopically-juvenile arcs were located in tropical or warm-temperate regions during the mid-Cretaceous, these uplifted rocks were preferentially eroded and weathered providing juvenile Sr isotopes to the oceans. This study highlights the importance of tectonic processes in controlling isotopic compositions of continental arc, which has implications for ocean chemistry, global chemical weathering feedback, and the long-term carbon cycle.