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The convergence analysis for least-squares finite element methods led to various adaptive mesh-refinement strategies: Collective marking algorithms driven by the built-in a posteriori error estimator or an alternative explicit residual-based error estimator as well as a separate marking strategy based on the alternative error estimator and an optimal data approximation algorithm. This paper reviews and discusses available convergence results. In addition, all three strategies are investigated empirically for a set of benchmarks examples of second-order elliptic partial differential equations in two spatial dimensions. Particular interest is on the choice of the marking and refinement parameters and the approximation of the given data. The numerical experiments are reproducible using the author's software package octAFEM available on the platform Code Ocean. [ABSTRACT FROM AUTHOR]

• Long-term dynamics of algal bloom patterns and their causative factors are assessed. • Time-series satellite data are analyzed and modelled using non-parametric methods. • Increased occurrence and reduction in the areal extent of algal blooms are observed. • The relative influence of ocean, atmosphere, and land parameters changes by regions. • Temporal prediction of blooms is possible with a time lag of 2 months. Algal blooms are global phenomena in marine and fresh waters. An understanding of the impacts of climate change and anthropogenic activities on marine algal blooms is essential for protecting marine ecosystems. We have studied the long-term changes in the spatial patterns of algal blooms over the northern Indian Ocean and assessed the influence of the ocean, atmosphere, and land-based processes on them. We have analyzed multi-source satellite data (2003 – 2020) of various parameters such as algal concentration, temperature, salinity, sea level, particulate organic carbon, precipitation, wind speed, and river discharge on an open-source cloud computing platform. The seasonality of variables is assessed using a harmonic model, and their spatial trend is estimated using the non-parametric Mann-Kendall test. The spatial relationship between various geophysical parameters and algal bloom concentration is assessed by the cross-correlation test, and the prediction is done using a multivariate autoregression model. Results suggest that each variable exhibits distinguishable seasonal patterns. Algal bloom duration showed a significant increase over time. However, algal bloom coverage showed a significant decline in the coastal waters in all seasons except post-monsoon. The cross-correlation test unveils that lower temperatures, salinity, and sea level promote algal bloom occurrences in coastal waters rather than open waters. Furthermore, the statistical model with a time lag of 2 months shows better performance for prediction of bloom intensity (r2 = 0.86). [ABSTRACT FROM AUTHOR]

A significant proportion of marine calcium carbonate sediments are comprised of metastable minerals that are susceptible to diagenetic alterations during burial. These reactions can reset the geochemical signature of sediments and pore fluids and influence elemental cycling in the ocean. However, the timing and mechanisms by which these reactions take place are poorly constrained. This study uses cores drilled on the slope of the Great Bahama Bank to provide quantitative constraints on important diagenetic reactions; namely respiration-driven dissolution, authigenic carbonate mineral formation, and conversion of aragonite to low Mg calcite (LMC). We perform detailed mineralogical characterization using newly acquired, high resolution X-ray diffraction (XRD) data and over 1000 reanalyzed XRD scans, characterize sediments texturally and elementally using electron microprobe data, calculate pore fluid saturation state with respect to aragonite using a Pitzer ion interaction approach, and use pore fluid chemistry and experimental distribution coefficients to predict authigenic carbonate compositions. These data suggest that aerobic organic matter oxidation, enabled by the advection of oxygenated seawater throughout the upper ∼ 30 m interval of sediment, causes undersaturation and thus dissolution of biogenic high Mg calcite (HMC) and aragonite. Deeper, anaerobic organic matter oxidation takes over and causes supersaturation, promoting authigenic precipitation in the form of HMC, which in turn decreases pore fluid Mg/Ca and promotes aragonite conversion to LMC. One novel aspect of this study is the identification of three types of calcites using the newly acquired XRD and electron microprobe data. Based on their unique crystallographic characteristics and chemical compositions, these types of calcites are interpreted to represent pelagic biogenic LMC, bank-derived biogenic HMC, and authigenic HMC precipitated from pore fluids. Notably, the composition of the authigenic calcite matches that predicted to precipitate from pore fluids using an empirical Mg partition coefficient in calcite. Calcites that form authigenically and from aragonite via replacement are suggested to recrystallize with burial as evidenced by the decrease in Mg content and micro-strain. This process-based geochemical framework assigns diagenetic processes to a specific depth window within the sediment column and paves the way for a mechanistic understanding of carbonate diagenesis, one that is rooted in thermodynamic and kinetic bases. [ABSTRACT FROM AUTHOR]

Chemosynthesis fixes carbon using energy acquired from reduced chemical compounds and is a primordial process that occurs ubiquitously throughout contemporary marine ecosystems. Diverse and abundant marine bacteria and archaea gain energy from inorganic compounds such as ammonia, nitrite, sulfide, hydrogen, carbon monoxide, and iron using specific enzymes. Chemosynthesis is enriched relative to photosynthesis in aphotic waters, including at increased ocean depths, and may show diel, seasonal, and latitudinal variations. Some regions of the ocean are primarily driven by chemosynthesis, ranging from highly productive geologically fuelled hydrothermal vents to oligotrophic below-shelf waters. Dark carbon fixation through chemosynthetic processes may play a quantitatively significant role in oceanic primary production, though carbon budgets remain poorly resolved. Chemosynthesis is a metabolic process that transfers carbon to the biosphere using reduced compounds. It is well recognised that chemosynthesis occurs in much of the ocean, but it is often thought to be a negligible process compared to photosynthesis. Here we propose that chemosynthesis is the underlying process governing primary production in much of the ocean and suggest that it extends to a much wider range of compounds, microorganisms, and ecosystems than previously thought. In turn, this process has had a central role in controlling marine biogeochemistry, ecology, and carbon budgets across the vast realms of the ocean, from the dawn of life to contemporary times. [ABSTRACT FROM AUTHOR]

• We study the chemistry of the core and ocean of Enceladus based on different core compositions. • We study the hydrothermal products from the ocean-core interaction in the context of the chemistry of the plume of Enceladus. • We evaluate the chemistry of the ocean based on its possible pH values and the saturation indices of mineral products. • We find that the actual composition of the core poses a somewhat wide range of possible compositional scenarios. Measurements made by the Cassini spacecraft instruments were able to reveal the composition of the geysers of the Saturn moon, Enceladus, among which salts (sodium chloride, sodium bicarbonate and/ or sodium carbonate) and traces of silica could be the result of hydrothermal processes from the interaction of an inner liquid ocean with the core of Enceladus. The chemistry of the ocean should be closely connected to the chemistry of the core. Even though. the actual composition of the core is unknown, Enceladus has been characterised as a moon with a silicate core and different authors have estimated the properties of the ocean. A core with a silicate composition alone, does not necessarily justify most of the observed species of the plume. Given the many uncertainties, in the current work, we study the possible chemistry of the core and the ocean in the context of a four-layered Enceladus (dry core, hydrated core, ocean and crust) with three different compositional scenarios for the core: primordial (represented by an ordinary chondrite), composite (represented by a carbonaceous chondrite with an igneous inclusion) and non primordial (epresented by a given peridotite). The scenarios comprise a set of minerals that interact with a primordial ocean (either pure or enriched water) at a given temperature and pressure, producing a series of secondary minerals and compounds, some of them, coincident with the chemical species observed in the geysers. Specifically, we make a chemical speciation for each proposed compositional scenario with the software PhreeqC, however our analysis is limited to the study of interactions that reach a given equilibrium. In particular, output values like the potential of hydrogen of the ocean or the saturation indices of mineral products may give us hints about the chemistry of the ocean and the core. We find that, based on the species observed in the plume, the actual composition of the core (and the ocean as well) poses a somewhat wide range of possible compositional scenarios and each of our proposed scenarios and their products justify, to some extent, the observations of the plume. [ABSTRACT FROM AUTHOR]

A conceptual framework is proposed for understanding the relationship between temperature and biological N 2 fixation (BNF) across levels of biological organization from enzymes to ecosystems on land and in the ocean. Global compilations of measured N 2 fixation rates reveal a temperature dependence that is broadly similar in marine and terrestrial systems, including a common thermal optimum at ~25°C, suggesting an overarching enzymatic constraint. Rate–temperature relationships also reveal features unique to marine and terrestrial domains, including greater heat tolerance of terrestrial BNF, suggesting the presence of, and adaptation to, distinct thermal and ecological niches. Climate warming is projected to reduce N 2 fixation in the tropics while increasing it in higher latitudes in terrestrial and marine ecosystems, a spatial shift that would impact productivity and N cycling, unless modulated by other environmental factors and physiological adaptations. Biological N 2 fixation sustains the global inventory of nitrogenous nutrients essential for the productivity of terrestrial and marine ecosystems. Like most metabolic processes, rates of biological N 2 fixation vary strongly with temperature, making it sensitive to climate change, but a global projection across land and ocean is lacking. Here we use compilations of field and laboratory measurements to reveal a relationship between N 2 fixation rates and temperature that is similar in both domains despite large taxonomic and environmental differences. Rates of N 2 fixation increase gradually to a thermal optimum around ~25°C, and decline more rapidly toward a thermal maximum, which is lower in the ocean than on land. In both realms, the observed temperature sensitivities imply that climate warming this century could decrease N 2 fixation rates by ~50% in the tropics while increasing rates by ~50% in higher latitudes. We propose a conceptual framework for understanding the physiological and ecological mechanisms that underpin and modulate the observed temperature dependence of global N 2 fixation rates, facilitating cross-fertilization of marine and terrestrial research to assess its response to climate change. [ABSTRACT FROM AUTHOR]

Trace metals (TMs) manganese (Mn), cobalt (Co), and aluminium (Al) have important geochemical and biological roles in the ocean. Here, we present full depth profiles of dissolved (d) and particulate Al, Mn, and Co along the latitude of 40 °S in the South Atlantic Ocean from the GEOTRACES GA10 cruises that operated in austral spring 2010 and summer 2011. The region is characterized by enhanced primary productivity and forms a key transition zone between the Southern Ocean and South Atlantic Subtropical Gyre. The mean concentrations of dAl, dCo, and dMn (±standard deviation) were 3.36 ± 2.65 nmol kg−1, 35.3 ± 17.6 pmol kg−1, and 0.624 ± 1.08 nmol kg−1, respectively. Their distributions in surface waters were determined by external sources and complex internal biogeochemical processes. Specifically, surface ocean dCo was controlled by the interplay between phytoplankton uptake, remineralization and external inputs; dMn was likely determined by the formation and photoreduction of Mn-oxides; and dAl was supplied by atmospheric deposition and removed by scavenging onto particles. Fluvial and sedimentary inputs near the Rio de La Plata estuary and benthic sources from the Agulhas Bank resulted in elevated dTM concentrations in near-shore surface waters. These externally sourced dTMs were effectively delivered to the open ocean by offshore diffusion and/or advection, and potentially facilitated enhanced primary productivity along the transect. The distributions of dTMs at depth were predominantly controlled by the mixing of North Atlantic Deep Water (NADW) and waters of Antarctic origin (e.g., Upper Circumpolar Water (UCDW) and Antarctic Bottom Water (AABW)). The calculated endmember concentrations of dAl and dCo in NADW showed minor decreases in the SASTG following north–south transport, suggesting removal rates of 0.064 nM/year and 0.035–0.075 pM/year, respectively. The endmember concentration of dCo in AABW was maintained at ∼30 pmol kg−1 without evidence for scavenging removal in the Southern Ocean and SASTG (time frame >400 years). The concentrations of dMn in NADW and AABW were between 0.1 and 0.16 nmol kg−1, and any elevated dMn concentrations were ascribed to local external inputs (e.g., from sediments in the Argentine Basin and hydrothermal activity near the Mid-Atlantic Ridge). Hence, four controlling factors (sources, internal cycling, water mass mixing and time) need to be considered when assessing TM distributions in the global ocean, even for TMs that are vulnerable to scavenging removal processes. Because the deep waters formed in high latitude oceans are crucial components of the global thermohaline overturning system, any processes (e.g., glacier melting, upwelling and sinking, and biological activity) that impact the preformed dTM concentrations in high latitude oceans will determine the downstream dTM distributions. Therefore, the sources and sinks of TMs and associated biological activity in high latitude oceans could engender basin to global scale impacts on seawater distributions of Al, Co, and Mn and their stoichiometric relationships with macronutrients, and the global biogeochemical cycles of these scavenged-type TMs. [ABSTRACT FROM AUTHOR]

Major geodynamic processes, including mantle convection and plate tectonics, govern the exchange of mass between Earth's interior and its surface. These processes drive mass-transfer mechanisms such as partial melting and crustal recycling, which have generated a lithologically and compositionally heterogeneous mantle over time. Ocean island basalts (OIB) directly sample these heterogeneities, making them excellent tools to constrain the mantle's dynamic geochemical evolution. In this study, we probe the connection between crustal recycling, mantle mineralogy, and partial melting using the stable Ca isotope compositions of OIB, ultimately contextualizing their Ca isotope variability using conventional mantle "endmember" components including DMM, HIMU, EM-1, and EM-2. Using the state-of-the-art Nu Sapphire collision cell MC-ICP-MS, we measured the Ca isotope compositions of 27 well-characterized OIB samples from 11 different ocean island groups. By supplementing our new data with additional high-precision Ca isotope measurements from the literature, we create an expanded dataset consisting of 15 ocean islands, facilitating a global-scale investigation of Ca isotope variability among hotspots. Our findings reveal that island-averaged Ca isotope compositions form two distinct groups on the basis of their radiogenic isotope compositions. The first group, consisting of OIB with un-enriched radiogenic isotope compositions (non-EM-type), exhibits robust negative correlations with both lithospheric thickness and primitive TiO 2 contents, providing compelling evidence that Ca isotopes are sensitive to the degree of partial melting (F) as well as to the effects of crustal recycling. This joint signal appears to trace the process of decompression melting beneath oceanic lithosphere of variable thickness, as recycled lithologies rich in garnet and pyroxene (i.e., pyroxenites)—which generate large solid-melt Ca isotope fractionations—disproportionally control the Ca isotope composition of the final aggregate melt when F is limited by thick overlying lithosphere. In contrast, the island-averaged Ca isotope compositions of OIB with enriched radiogenic isotope compositions (EM-type) form a distinctly light negative correlation with primitive TiO 2 contents without exhibiting a relationship with lithospheric thickness. In addition to lithology-dependent partial melting effects, the Ca isotope compositions of EM-type OIB appear to be sensitive to the compositional effects of crustal recycling, which may explain their decoupling from the physical controls of partial melting. Calcium isotopes show exceptional potential for elucidating the origin of both enriched and ultra-depleted mantle sources, emphasizing the need to prioritize localities with these signatures in future studies. [ABSTRACT FROM AUTHOR]

Basaltic volcanism on the Moon produced low- and high-Ti mare basalt suites that are also distinct with respect to their iron, titanium, and magnesium isotopic compositions. Here, the equilibrium fractionation of Fe and Ti isotopes between ilmenite and melt was experimentally investigated in order to evaluate the role of ilmenite in generating the isotopic compositional variability among the lunar mare basalts. Ilmenite crystallization experiments were conducted using two bulk compositions: an ilmenite-saturated basaltic andesite and an ilmenite-saturated Apollo 14 black glass, and the Fe and Ti isotopic compositions of the experimental ilmenites and glass (quenched melt) were analyzed using solution MC-ICPMS after hand-picking. Additionally, Nuclear Resonant Inelastic X-ray Scattering (NRIXS) measurements on synthetic ilmenite were conducted and compared to previous NRIXS measurements on synthetic lunar glasses in order to derive temperature-dependent equilibrium ilmenite-melt Fe isotopic fractionations. Experimentally determined ilmenite-melt fractionations were then incorporated into a lunar magma ocean crystallization model that tracks the major element and isotopic compositional evolution of lunar magma ocean cumulates and residual liquid. There is good agreement between the Fe equilibrium isotopic fractionation measured by NRIXS and the laboratory equilibration experiments, and we find that the isotopic fractionation is sensitive to ilmenite compositional differences (0 vs. 10% Fe3+). Further, the light Ti isotopic composition of ilmenite relative to the melt (Δ 49 Ti = ilmenite-melt − 0.09 ± 0.03 ‰ at 1100 ∘C) is consistent with the higher coordination of Ti in ilmenite relative to melts and results of previous studies. The modeled Ti isotopic compositions for lunar magma ocean cumulates display Ti isotopic variability sufficient to explain the low- and high-Ti mare basalt sources. However, the difference in Fe isotopic composition between the low- and high-Ti mare basalts cannot be attributed solely to ilmenite fractionation. Instead, Fe isotopic fractionation by additional products of lunar magma ocean crystallization, such as clinopyroxene, is required to generate the inferred Fe and Mg isotopic variability in the lunar mantle. Alternatively, the Fe and Mg isotopic compositions of the lunar mare basalts may indicate Fe-Mg interdiffusion has occurred in the Ti-rich component of the mare basalt source regions via reaction between ilmenite cumulates and the olivine- and pyroxene-rich lunar mantle. [ABSTRACT FROM AUTHOR]

Recently developed temperature proxies based on hydroxylated isoprenoid Glycerol Dialkyl Glycerol Tetraethers (OH-isoGDGTs), such as % O H , R I - O H , R I - O H ′ and O H C , have shown potential for reconstructing past temperature changes. However, progress has been limited by the lack of a global core-top calibration with ample geographical coverage. Here, we compile an extensive global surface sediment dataset of OH-isoGDGTs as well as regular isoprenoid GDGTs (isoGDGTs), with both data generated at NIOZ (n = 575) and previously published data from other laboratories (n = 297). We find interlaboratory differences for proxy indices that incorporate both OH-isoGDGTs and regular isoGDGTs, indicating that care must be taken in compiling large GDGT datasets from multiple laboratories. Our results confirm a strong temperature signal in the isoGDGT distribution, especially for OH-isoGDGT-0 and non-hydroxylated isoGDGTs, but also reveal that water depth might have an impact on the distribution of OH-isoGDGTs with 1 and 2 cyclopentane moieties. This will affect the R I - O H and R I - O H ′ indices, particularly in tropical regions, where OH-isoGDGT-0 occurs at low abundance. We explore new proxy indices that combine the temperature dependence of both isoGDGT and OH-isoGDGT distributions and propose the use of T E X 86 O H , which includes OH-isoGDGT-0 in the denominator of the T E X 86 index. This modification leads to a much higher temperature sensitivity of the index, especially in regions with annual mean sea surface temperatures between 5 and 15 °C. Application of this novel paleothermometer to a polar sediment core suggests that this proxy is likely to result in more reliable temperature reconstructions in polar regions where OH-isoGDGTs are abundant. [ABSTRACT FROM AUTHOR]

The ocean region along the latitude of 40°S in the South Atlantic, characterized by enhanced primary productivity, forms a transition zone between the nutrient replete but iron depleted Southern Ocean, and the nitrate and iron depleted Subtropical Gyre. Here, we present distributions of nutrient-type dissolved and particulate trace metals (dTMs and pTMs) including cadmium (Cd), nickel (Ni), copper (Cu), and zinc (Zn) in the South Atlantic from the GEOTRACES GA10 cruises. Phytoplankton uptake, riverine and atmospheric inputs shaped dTM and pTM concentrations in surface waters (dCd 27.8 ± 36.0 pmol kg−1, n = 222; dCu 0.732 ± 0.429 nmol kg−1, n = 222; dNi 3.38 ± 0.52 nmol kg−1, n = 219; dZn 0.332 ± 0.398 nmol kg−1, n = 214). Subsurface nutrients and dTMs (dCd 563 ± 184 pmol kg−1, n = 335; dCu 1.819 ± 0.773 nmol kg−1, n = 334; dNi 6.19 ± 1.06 nmol kg−1, n = 330; dZn 3.71 ± 2.10 nmol kg−1, n = 333) were controlled by the mixing of Antarctic origin waters and North Atlantic Deep Waters (NADW) with negligible contributions from local remineralization. Dissolved and particulate TMs in the Argentine Basin showed elevated concentrations towards the seafloor because of benthic inputs. Direct hydrothermal inputs of dTMs and pTMs to deep waters were not observed along the transect. The Cd-Cu-Zn-phosphate stoichiometries of Antarctic origin waters were set by a combination of dynamic physical circulation and preferential uptake of Cd, Cu, and Zn relative to phosphate in surface waters because of a dominance by diatoms in the Southern Ocean. Water mass mixing subsequently produced convoluted dCu-P and dZn-P relationships and apparent linear dCd-P and dNi-P relationships in the South Atlantic. More importantly, endmember characteristics of Antarctic waters and NADW are largely fixed in their formation regions in high latitude oceans. Therefore, the highly dynamic high latitude oceans are key regions that supply nutrients and TMs at specific ratios to low latitude oceans via the thermohaline circulation. Changes to processes in the high latitude oceans may have consequences for marine primary productivity downstream, and hence the global carbon cycle. [ABSTRACT FROM AUTHOR]

Ocean surface monitoring, detection of oil spills, and accurate maritime vehicle detection is an important set of problem statements associated with ocean pollution monitoring. This paper proposes a novel study on Pix2Pix or generative adversarial networks for the aforementioned task. A comparative analysis is presented on various convolutional network-based encoders for semantic segmentation. A publicly available Synthetic Aperture Radar (SAR) dataset from the Sentinel-1 C-band sensor is used, constituting a total of 1112 images for the task of multiclass segmentation. Each integrant image pixel is classified into five classes, Oil Spills, Ships, Look-Alikes, Land Surface, and Ocean Surface. Deep architectures like U-Nets, SegNets, LinkNets, and FCNs are thoroughly assessed to obtain a practical analysis of this approach. Through a systematic exploration of hyperparameters, we identified the best-performing encoder configuration, achieving impressive results with a weighted Mean IoU of 0.898 and an F1-score of 0.931. These findings hold great promise for the advancement of solutions in ocean pollution monitoring, contributing to more accurate and efficient detection and mitigation efforts. respectively. [ABSTRACT FROM AUTHOR]

• TCEP and TCPP were dominant in the seawater and atmosphere from the northwest Pacific to the Southern Ocean. • Dry and wet deposition were two main processes influenced the air-seawater transport of OPEs in the Ross Sea. • Ross Sea has played the role of a "sink" of OPEs in summer. Eleven organophosphate esters (OPEs) in the air and seawater were investigated from the northwestern Pacific Ocean to the Southern Ocean during the 2018 Chinese 34th Antarctic Scientific Expedition. The concentration of total OPEs ranged from 164.82 to 3501.79 pg/m3 in air and from 4.54 to 70.09 ng/L in seawater. Two halogenated OPEs, tri(chloropropyl) phosphate (TCPP) and tri (2-chloroethyl) phosphate (TCEP), were generally more abundant than the non-halogenated OPEs. A level III fugacity model was developed to simulate the transfer and fate of seven OPEs in the air and seawater regions of the central Ross Sea. The model results indicate that OPEs are transferred from the air to the seawater in the central Ross Sea in summer, during which the Ross Sea acts as a final OPE sink. Dry and wet deposition dominated the processes involving OPE transfer to seawater. The OPE degradation process was also found to be more pervasive in the atmosphere than in the seawater region. These findings highlights the importance of long-range transport of OPEs and their air–seawater interface behavior in the Antarctic. [ABSTRACT FROM AUTHOR]

Wildfire byproducts enter into the oceans via terrestrial and atmospheric routes. They pose a challenge to the sustainability of marine ecosystems, especially under the current increase in fire activity. Research is needed to unravel the dynamics between wildfires and marine life, and the oceans' potential to mitigate wildfire emissions. [ABSTRACT FROM AUTHOR]

Some of the most CO 2 -rich magmas on Earth are erupted by intraplate ocean island volcanoes. Here, we characterise olivine-hosted melt inclusions from recent (<10 ky) basanitic tephra erupted by Fogo, the only active volcano of the Cape Verde Archipelago in the eastern Atlantic Ocean. We determine H 2 O, S, Cl, F in glassy melt inclusions and recalculate the total (glass + shrinkage bubbles) CO 2 budget by three independent methodologies. We find that the Fogo parental basanite, entrapped as melt inclusion in forsterite-rich (Fo 80-85) olivines, contains up to ∼2.1 wt% CO 2 , 3–47 % of which is partitioned in the shrinkage bubbles. This CO 2 content is among the highest ever measured in melt inclusions in OIBs. In combination with ∼2 wt% H 2 O content, our data constrain an entrapment pressure range for the most CO 2 -rich melt inclusion of 648–1430 MPa, with a most conservative estimate at 773–1020 MPa. Our results therefore suggest the parental Fogo melt is stored in the lithospheric mantle at minimum depths of ∼27 to ∼36 km, and then injected into a vertically stacked magma ponding system. Overall, our results corroborate previous indications for a CO 2 -rich nature of alkaline ocean island volcanism. We propose that the Fogo basanitic melt forms by low degrees of melting (F = 0.06–0.07) of a carbon-enriched mantle source, containing up to 355–414 ppm C. If global OIB melts are dominantly as carbon-rich as our Fogo results suggest, then OIB volcanism may cumulatively outgas as high as ∼16–21 Tg of carbon yearly, hence substantially contributing to the global deep carbon cycle. [ABSTRACT FROM AUTHOR]

The TetraEther indeX of 86 carbon atoms (TEX 86) is widely used as a proxy to reconstruct past sea surface temperatures. Most current applications of TEX 86 are primarily based on analyzing the composition of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) that comprise TEX 86 in sediments, with the assumption that the sedimentary isoGDGTs are mainly derived from the surface mixed layer. Here we report on the variations in the isoGDGT distribution, archaeal abundance and community through the water column of the Western Pacific Ocean, directly testing the export depth of isoGDGTs and constraining the temperature records of TEX 86. Our data show that maximum isoGDGT concentrations occurred in subsurface waters (150–200 m) with maximum archaeal abundances. The ratio between isoGDGTs bearing 2 vs. 3 cyclopentane moieties, i.e. [2/3] ratio, increased with depth, which is likely related to the shift of the archaeal community from Ca. Nitrosopelagicus-dominance to norank_f__Nitrosopumilaceae -dominance. Models based on the [2/3] ratios in the water column predicted an average export depth of isoGDGTs to sediments of around 150–200 m, consistent with the robust relationship between the compiled sedimentary TEX 86 and the annual mean subsurface temperature. Taken together, our findings support that TEX 86 records subsurface rather than surface temperatures in the open ocean. [ABSTRACT FROM AUTHOR]

Aeolian transport of mineral dust is an important carrier of nutrients and trace metals to the surface ocean and, hence, affects the biogeochemical cycles of C and N therein. Studies focusing on the provenances of dust across the latitudinal gradients over the open ocean waters are essential for better constraining the biogeochemical effects of dust deposition. Here, we analyzed the radiogenic isotope composition of Sr (87Sr/86Sr) and Nd (ε Nd (0)) in the silicate fraction of mineral aerosols collected over the pelagic northern and southern Indian ocean waters during the GEOTRACES-India research expeditions (GI-01: March-April 2014 and GI-02: April-May 2014). Both tracers, 87Sr/86Sr and ε Nd (0), exhibited marked spatial variability for dust deposition to different basins, including the Bay of Bengal (BoB), Arabian Sea (AS), equatorial Indian Ocean (EIO), and the southern sector of the Indian Ocean (SIO). The dust deposited in the AS showed a narrow spread in both 87Sr/86Sr (0.71520–0.71642) and ε Nd (0) (−10.9 to −10.1), along with the air mass back trajectories, indicating transport from the Arabian Peninsula. Likewise, the dust collected over the BoB was mainly sourced from the Thar Desert (87Sr/86Sr > 0.72, −16 < ε Nd (0) 〈 −1 3), whereas the EIO received mineral dust from the Thar Desert and sand dunes in northern Australia (87Sr/86Sr: 0.72, ε Nd (0): −11) and Indonesian Archipelago. In contrast, the SIO appeared to receive dust deposition from three different source regions, including dust from Antarctica, western Australia (87Sr/86Sr: 0.712, −20 < ε Nd (0) <−16, and South Africa/South America (87Sr/86Sr: 0.708–0.710; −24.5 < ε Nd (0) >−8.4). These results have important implications for modelling the dust transport to pelagic Indian and southern Indian Ocean waters. [ABSTRACT FROM AUTHOR]

The sulfur content at sulfide saturation (SCSS) of a silicate melt can regulate the stability of sulfides and, therefore, chalcophile elements' behaviors in planetary magma oceans. Many studies have reported high-pressure experiments to determine SCSS using either linear or exponential regressions to parameterize the thermodynamics of the system. Although these empirical equations describe the effects of different parameters on SCSS, they perform poorly when predicting laboratory measurements. Here, we compiled 542 published analyses of experiments performed on a range of sulfide and silicate compositions at varying P - T conditions (<24 GPa, <2673 K). Using empirical equations, linear regression, Random Forest algorithms, and a hybrid algorithm employing empirical fits to P - T conditions and the Random Forest algorithm for compositions, we developed several SCSS models and compared them to laboratory measurements. The Random Forest and hybrid models (R 2 = 0.82–0.91, mean average error [MAE] < 746 ppmw S, residual mean standard error [RMSE] < 972 ppmw S), significantly outperform previous empirical models (R 2 = 0.28–0.69, MAE = 622–1,170 ppmw S, RMSE = 1,070–1,744 ppmw S), whereas linear regression performs moderately well, i.e., between the classic and machine learning models. We applied our hybrid model to predict SCSS during magma ocean solidification on Earth, Mars, and the Moon, and we compared our model results to expected S contents in the residual magma oceans calculated by mass balance. Our results confirm that during early accretion, sulfides precipitated from magma oceans and into the outer cores of Earth and Mars, but not the Moon. Subsequently, once the respective magma oceans began precipitating minerals with increasingly FeO-rich and SiO 2 -, Al 2 O 3 -, and MgO-depleted compositions, the increasing S concentration in the residual magma was offset by temperature and compositional effects on SCSS, preventing sulfide precipitation during intermediate stages of crystallization. Sulfides precipitated late during magma ocean crystallization, but failed to percolate through the underlying crystalline mantle, significantly contributing to the modern bulk-silicate sulfur abundances of Earth, Mars, and the Moon. Our calculations suggest that late-stage sulfide precipitation occurred at shallow depths of 120–220 km, 40–320 km, and < 10 km in the magma oceans of Earth, Mars, and the Moon, respectively. [ABSTRACT FROM AUTHOR]

Zirconium (Zr) stable isotopes recently emerged as potential tracers of magmatic processes and, as a result, their behavior in high-temperature environments have been the focus of extensive characterization. In contrast, few studies have focused on Zr behavior and isotopic fractionation in low temperature or aqueous environments. Here, we describe a new analytical routine for highly precise and accurate analysis of Zr isotopes of water samples, using a combination of double-spike and iron co-precipitation methods. To assess the impact of potential systematic biases a series of experiments were conducted on natural and synthetic water samples. Our results show that the spike-to-sample ratio, matrix composition, and high field-strength element (HFSE) concentration have negligible effects on measured seawater Zr isotopic compositions, and that the Fe co-precipitation method used yields accurate and precise Zr isotope data. We thus apply this method to natural seawater samples collected from a water column profile in the Pacific Ocean off the coast of California, with depths ranging from 5 to 711 m. We find that the natural seawater samples are highly fractionated relative to solid-Earth values and display marked variability in δ 94/90Zr as a function of depth, ranging from ∼ +0.650 ‰ near the surface, to + 1.530 ‰ near the profile bottom, with an analytical uncertainty of ± ∼0.045 ‰ (2 SE, external reproducibility). The δ 94/90Zr value of seawater is much higher than that of Earth's mantle and continental crust, which has a δ 94/90Zr value near zero, indicating the presence of processes in the hydrosphere capable of inducing large mass-dependent fractionation. Furthermore, the seawater δ 94/90Zr value exhibits systematic variations with respect to water depth and salinity, suggesting that Zr isotopic compositions may be sensitive to seawater chemical properties and source highlighting its potential utility as a tracer of biogeochemical processes within the ocean. [ABSTRACT FROM AUTHOR]

A common technique for determining the mass accumulation rates of marine sediments is through measurements of constant flux proxies. These proxies, like unsupported 230Th and extraterrestrial 3He, are buried at a known rate at the seafloor, and thus their concentration in sediments is inversely proportional to the vertical mass accumulation rate of ambient sediments. These two proxies have varied assumptions regarding their behavior that have been difficult to test, particularly in regions of very low sedimentation. We present new measurements of helium and thorium isotopes in coretop sediments from the South Pacific Gyre. Our main finding is that 230Th- and 3He-derived mass accumulation rates of these sediments differ by a factor of 2–10, with 230Th-based mass accumulation rates systematically higher than those derived from 3He. While the final cause of the discrepancy is difficult to elucidate, we suggest that up to a factor of 2 worth of the sedimentary 230Th deficit can be explained by lateral transport of 230Th, while the remainder must be explained by other processes, such as ancient coretops undercorrected for post-depositional 230Th decay. Regardless of the mechanism, our findings have critical implications for the application of constant flux proxies in the South Pacific Gyre, with one example being the calibration of dust deposition models in this region. Ultimately, additional testing is required to determine the accuracy of the 3He and 230Th techniques for estimating sediment accumulation rates in regions of the open ocean with extremely low sedimentation rates. [ABSTRACT FROM AUTHOR]

SARAL/AltiKa, the first microwave altimeter operating at Ka-band frequency, recently completed nine years of operations in orbit. During these years, it has catered to many applications related to operational oceanography, climate sciences, hydrology and cryosphere. More specifically, in oceanography, SARAL has contributed immensely to operational wave and circulation modelling, eddy detection/tracking, ocean current generation and many more. However, since Feb 2019, SARAL has moved from the drifting phase (DP) to the mispointing phase (MP) due to the malfunctioning of the star sensor of the spacecraft. In this study, we analyse the instrument's performance and its waveforms during its ongoing MP. We find out that during the MP, significant wave height (SWH) measurements are anomalously high between 18 and 24 m, and wind speed measurements are between 16 and 19 m/s. In sea surface height anomaly (SSHA), there is a steady rise in negative values during the MP. In the return waveform, ∼15% degradation in Brown-type waveforms in the open ocean region is noticed. These changes significantly impact the SARAL applications. Two important applications of wave forecast and eddy detection are discussed here as examples. Following this, we also recommend using provided quality flags so that the data can be further explored for various ocean applications. [ABSTRACT FROM AUTHOR]

A poorly diverse trilobite assemblage is described from the Tremadocian strata (Tangissart Member of the Mousty Formation; Chevlipont Formation) of the Brabant Massif. These specimens represent so far the oldest trilobite record from Belgium. The recorded taxa, identified as Platypeltoides cf. croftii , Macropyge ? sp., and Asaphidae indet., resemble contemporaneous trilobites from other parts of Avalonia (e.g., Wales, Shropshire) as well as some others from high-latitude Gondwana (Morocco). The nileid species P. cf. croftii suggests that the Tangissart Member of the Mousty Formation was likely deposited in deeper offshore environments on the open shelf of Avalonia. Morphological similarities between P. cf. croftii from the Brabant Massif, P. croftii from the UK, and P. magrebiensis from Morocco suggest close faunal interchange across the narrow Rheic Ocean. [ABSTRACT FROM AUTHOR]

Halogens are powerful tracers for the accretion of Earth's volatiles. Their sensitivity to Earth's differentiation, such as core formation, magma ocean crystallization, and planetary evaporation allows us to track such major events and the origin of Earth's building blocks. Here we examine the role of magma ocean crystallization in fractionating F/Cl ratio of the BSE by experimentally determining the partitioning behavior of F and Cl between silicate melt and crystallized minerals. Previous experimental data, due to technical challenges, are only available at pressures <25 GPa. To simulate relevant conditions for deep magma oceans, we perform laser-heated diamond anvil cell experiments to determine partition coefficients of F and Cl between bridgmanite and silicate melt at temperatures of ∼4000–4500 K and pressures of 33–55 GPa. Our data show that F and Cl are both strongly favored in silicate melt, with partition coefficients of F and Cl in the range of 0.12–0.16 and 0.007–0.017, respectively. Given plausible magma ocean scenarios, our results indicate that F and Cl are not significantly fractionated during crystallization of a deep magma ocean. Neglecting other potential processes that may fractionate F and Cl, the F/Cl ratio in the BSE should reflect that of Earth's building blocks. It indicates Earth's volatiles may be largely derived from inner solar system, in alignment with other isotopic systems such as nitrogen and hydrogen. [ABSTRACT FROM AUTHOR]

• Design and construction of single wheel test rig for Ocean World rover is presented. • Built using commercially available mechanical parts, motors, actuators, and sensors. • Test rig allows control of slip ratio, vertical load, slip angle, and camber angle. • Modular test-bed can simulate fine-grained ice, sharp ice, and ice boulder fields. Ocean Worlds such as Europa and Enceladus are known to harbor subsurface liquid water oceans under their icy crust and are high-priority targets for in situ exploration. Compared to the Moon and Mars, Ocean Worlds likely present a significantly more challenging environment for surface mobility systems due to the extremely cold temperature, high radiation dosage, and poorly constrained material properties under these conditions. Small-diameter wheels such as those used by Mars rovers are prone to slip-sinkage in loose soil and damage from sharp rock and ice formations. A 4-wheel rover with a simple drive system and large deployable compliant tires is proposed as a solution for extreme terrain mobility on Ocean World surfaces. The present work describes the design and construction of a single wheel test rig and a prototype large-diameter deployable wheel for Ocean World rovers and initial test results. The test rig allows independent control of the vertical load, slip ratio, slip angle, and camber angle, and accommodates large-diameter deployable wheels. The test rig features a modular test bed that can simulate varied surface features such as fine-grained ice, smooth hard ice, sharp ice formations, and large ice boulder fields. [ABSTRACT FROM AUTHOR]

The possibility of a collapse (or marked weakening) of the Atlantic Meridional Overturning Circulation (AMOC) within a few centuries boosted the interest of the scientific community on the responses of different compartments of the climate system to past AMOC collapses (or marked weakening). The most recent examples of such periods are Heinrich Stadial 1 (HS1,18-15 ka BP; near-collapsed AMOC) and the Younger Dryas (YD, 12.9-11.7 ka BP; markedly weakened AMOC). Here, we present data from elemental ratios, spectral reflectance, organic biomarkers, sea surface temperatures and planktonic foraminiferal assemblage from two marine sediment cores recovered from the western tropical South Atlantic Ocean spanning the last ca. 20 kyr. The recovered sediments record the responses of eastern tropical South American hydroclimate, western tropical South Atlantic productivity and sea surface temperatures to changes in AMOC strength associated with HS1 and the YD. Our data show that both periods were characterized by wetter conditions over eastern tropical South America associated with increased continental runoff compared to the Last Glacial Maximum. High sea surface temperatures during HS1 and the YD are in line with marked AMOC decreases that led to heat accumulation in the surface layer of the western South Atlantic Ocean, facilitating increased precipitation over eastern tropical South America. Our data demonstrate for the first time that intense runoff during HS1, and hence nutrient transfer to the ocean, affected the pelagic ecosystem, likely increasing primary productivity in the otherwise oligotrophic western tropical South Atlantic Ocean. Our study demonstrates a tight coupling between marine and terrestrial processes in the eastern South American realm during periods of strong climate instability. [ABSTRACT FROM AUTHOR]

Recent findings indicate that pelagic fungi should not be neglected as valuable members of oceanic pelagic ecosystems. However, research on the ecological role of pelagic fungi is the ocean is extremely limited. Recent technological advances allow the uncovering and characterization of the abundance, diversity, and functional roles played by pelagic fungal taxa/communities in the ocean. A new acknowledged role of fungi in the ecology and biogeochemistry of the oceanic water column provides a more complete picture of marine food webs and biogeochemical cycles. These findings also bridge terrestrial and freshwater with marine fungal ecology, expanding the global relevance of fungi in natural environments. Most investigations into ocean ecology and biogeochemistry have tended to focus on marine bacteria, archaea, and protists, while pelagic fungi (mycoplankton) have traditionally been neglected and considered to reside only in association with benthic solid substrates. Nevertheless, recent studies have revealed that pelagic fungi are distributed ubiquitously throughout the water column in every ocean basin and play an active role in the degradation of organic matter and the cycling of nutrients. We review the current status of knowledge on the ecology of mycoplankton and highlight knowledge gaps and challenges. These findings underscore the need to recognize this neglected kingdom as significant contributors to the organic matter cycling and ecology of the oceans. [ABSTRACT FROM AUTHOR]

Bacteria are key players in the marine sulfur cycle, from the sunlit ocean surface to the dark abyssal depths. Here, we provide a brief overview of the interlinked metabolic processes of organosulfur compounds, an elusive sulfur cycling process that exists in the dark ocean, and the current challenges that limit our understanding of this key nutrient cycle. [ABSTRACT FROM AUTHOR]

The aim of this work is to assess the influence of different degrees of adaptability of the power take-off (PTO) system on the power absorption of dense wave energy converter (WEC) arrays. The adaptability is included in simulations through a transmission ratio that scales the force actuating the PTO relative to the force generated by the motion of a floater. A numerical model is used in which hydrodynamic interactions between floaters and nonlinearities in the PTO are considered. The lower computational cost of this numerical model makes it possible to study the power extraction of a dense WEC array in irregular waves to easily create power matrices and other performance metrics. The methodology is applied to the case study of the Ocean Grazer WEC to showcase the potential performance improvements achieved through the inclusion of a transmission ratio. The analysis shows that including a high degree of adaptability and choosing WEC array configurations and PTO designs specific to potential deployment locations early in the design process can lead to an increase in extracted power. • The adaptability of a wave energy converter array needs to be defined at the design stage. • The range of adaptability of a design depends on the deployment location. • Increased adaptability results in increased power extraction. [ABSTRACT FROM AUTHOR]

The 2004 Indian Ocean tsunami caused 230,000 fatalities and massive physical damage along the shorelines of the Indian Ocean. Holocene sedimentary archives along the coastline of Sri Lanka can provide evidence for similar past events. The objective of our current study is to investigate the sedimentological and geochemical characteristics of Sri Lankan paleo-tsunami deposits, and their chronology. Sediment samples were collected down to 10 m depth using core drilling at a sheltered site (low-lying swale depression) in Koddiyar Bay (Trincomalee) on the east coast of Sri Lanka. Visual stratigraphic observations and grain size analyses were carried out to identify lithological changes. Bulk sediments, shells, and wood fragments were used for 14C age dating. Seven sand layers were identified throughout the core in this marshy wetland. Sedimentological observations and geomorphological features show that sheltered/protected swales of the inner bay have a high potential for preservation of paleo-tsunami sediments. Three possible paleo-tsunami deposits were identified earlier than 700 years, ca. 2000 years, and ca. 2700 years. These paleo-tsunami sand layers exhibited relatively high total organic carbon (TOC) contents due to admixture of continental shelf and lagoon sediments. Analysis of paleo-tsunami records suggests that the Andaman Sea is vulnerable to both 'low-risk and high-frequency' and 'high-risk and low-frequency' type tsunamis, whereas other areas in the Indian Ocean are more prone to destructive and low-frequency type tsunamis. This study contributes to improving tsunami risk assessment and mitigation strategies along the east coast of Sri Lanka. [ABSTRACT FROM AUTHOR]

The small temperature difference in ocean thermal energy conversion (OTEC) causes the high sensitivity of thermodynamic process to perturbations such as temperature and power load, which requires an efficient control strategy of thermodynamic process for OTEC. To this aim, an integral dynamic model is established to study the dynamic response of thermodynamic process in an OTEC system. To ensure the system efficiency and operating safety of power cycle, a multi-objective active-disturbance rejection control (ADRC) strategy is proposed and compared with corresponding single-objective ADRC and PI controller. Multi-objective ADRC includes a load-following control loop and two auxiliary control loops (evaporator control loop and condenser control loop). The results indicate that the multi-objective ADRC is most efficient to track the change of power load, in which the overshoot and integration absolute error (IAE) of load-following are reduced by 50% and 16% when compared with the single-objective ADRC. In addition, the multi-objective control strategy can maintain the stability of superheat degree and condensation pressure, and hence improves the system efficiency by 8.64% for the output power of 35 kW. Especially, the feedback-feedforward controller and feedback controller are attractive candidates to maintain the stable superheat degree and condensation pressure. [ABSTRACT FROM AUTHOR]

Radiocarbon ages from contemporaneous samples of varying types can show large age differences (Nakamura et al., 2016; Raymond and Bauer, 2001), and changes in offsets between these ages (δage) within a core have been scarcely examined. Changes in δage have previously suggested disturbances or shifts to the depositional setting (Nakamura et al., 2016; Ishiwa et al., 2021; Yokoyama et al., 2019). Radiocarbon dating of ocean sediment cores from near Ube City, Yamaguchi prefecture, Japan revealed periods of slower and rapid sedimentation which aligned with, respectively, post-Holocene High Stand (HHS, ∼7–4 cal ka BP (Yokoyama, 2021)) conditions and sea level fall, and pre-HHS conditions with rising sea levels. δage patterns implied that the reliability of sample types as depositional age indicators may depend on the depositional environment. Radiocarbon ages and relative sea level (RSL) curves suggested that local inundation may have occurred up to ∼ 200 years earlier than previously reported. In addition to constraining the relative timing of sea transgression and regression during the HHS, this study highlights the need to examine the depositional setting to accurately represent depositional ages. [ABSTRACT FROM AUTHOR]

The formation of green rust (GR; a mixed ferric/ferrous hydroxide) and vivianite (ferrous phosphate) are likely to have exerted a major control on phosphorus (P) cycling in ancient anoxic oceans. However, the factors that influence the formation of these minerals under different chemical conditions are poorly constrained, which limits understanding of the pathways that ultimately result in P drawdown and retention in anoxic sediments. This, in turn, limits understanding of P cycling in anoxic oceans and hence potential productivity feedbacks. Here we explore the effect of dissolved P concentration on the formation of sulfate GR (FeIII 2 FeII 3 (OH) 12 SO 4) versus vivianite (FeII 3 (PO 4) 2 ·8H 2 O) under anoxic conditions. Our results show that at low dissolved P concentrations and with P:Fe(II) molar ratios <1:30, P drawdown is effectively controlled by interlayer anion exchange and adsorption onto GR species, via the formation of amorphous Fe-P precursors. Such precursors may delay the precipitation of crystalline GR, but vivianite was not detected under these conditions. At higher dissolved P concentrations and P:Fe(II) ratios, GR also forms. However, the GR formed under these conditions rapidly dissolves, likely forming amorphous ferric hydroxides together with dissolved Fe(II) and phosphate, with the dissolved species subsequently reacting to form crystalline vivianite. Our observations agree with studies showing the water column formation of GR in modern oligotrophic, anoxic Fe-rich (ferruginous) settings, and provide support for a major role for GR in controlling P cycling in ancient oligotrophic ferruginous oceans. By contrast, in more productive ancient anoxic settings, enhanced redox-controlled P recycling and/or increased weathering inputs would have led to higher dissolved P concentrations in the water column and sediments. Our observations show that such conditions ultimately promote the formation of vivianite, which would have exerted a limiting control on the extent of P recycling in ancient, more productive settings, via the long-term fixation of P in the sediments. [ABSTRACT FROM AUTHOR]

The time-domain motion of a finite depth ocean subject to an arbitrary (in both time and space) imposed displacement of the bottom is studied under the assumption of linear theory. This solution provides results for this limiting case which may be helpful for benchmarking. The focus is on the numerical simulation of the near-field waves with application to the simulation of tsunami waves. The fluid domain is assumed two-dimensional, and the effect of compressibility is included. The time-domain solution is built from the frequency domain solution taking a Fourier series expansion of the bottom motion. This expansion allows complex displacements to be simulated. The solution in the frequency domain is expressed as a sum over modes. The time-domain solution is calculated by numerical evaluation of the Fourier transform in time, allowing arbitrary time-dependent motion. This code is extremely efficient and highly accurate, and there is no time–stepping so that errors do not accumulate in time. The eigenfunction expansion method to obtain the velocity potential for a flat ocean bottom case is independently derived. A shallow water limit for all the above cases is provided, giving a method to check the correctness of the numerical solution. Separate treatment for all the situations under the compressible assumption is also performed. The horizontal and vertical particle velocities are graphically presented for the time-harmonic oscillation. Time-dependent surface wave propagation is computed to show the initiation of tsunami waves in the deep ocean and their subsequent propagation. The calculations presented here allow for the simulation of tsunami wave generation and to investigate various effects, including the role of acoustic gravity waves. It is shown that the compressibility is not always significant, but that when the water is either sufficiently deep or the rise sufficiently rapid, acoustic gravity waves are produced. It is shown that, in this case, the ocean surface undergoes a rapid oscillation and that this may be a method to detect tsunamis. [ABSTRACT FROM AUTHOR]

In situ 14C surface exposure dating is a powerful tool for understanding the Earth's surface processes during the late Quaternary. This study developed an in situ 14C extraction system that heats samples to 1650 °C to extract in situ 14C from quartz. The initial experiments showed a high blank level (1.80 × 107 14C atoms) and low extraction efficiency (5.36%). Each procedural step required a blank test to understand the cause of the high background, and the results identified several components of the extraction system as sources of 14C contamination. After improving the apparatus design, the new system showed a sufficiently low blank level (5.32 × 104 14C atoms). The extraction efficiency ranged from 111% to 127% with this system. These results show that the system is capable of extracting in situ 14C from quartz for surface exposure dating. [ABSTRACT FROM AUTHOR]

The irregular ocean environment brings difficulties to observation and affects the movement state of underwater vehicles. Multisource information fusion can provide more reliable results on information-rich datasets. This paper proposes a multisource information fusion-based environment perception and dynamics model for underwater vehicles in irregular ocean environments. First, the multisource observation data is decomposed by the latent feature disentanglement learning model into the latent stable and dynamical features. The dynamical feature is predicted by the retrospect regression method and then integrated with the latent stable feature to predict the ocean field. After that, the environment-vehicle coupling effect is explored by thermodynamics and statics simulation. Then, a real-time dynamic model of the underwater vehicle is constructed by combining multisource information from physical principles, environmental perception, and sensor observations. Finally, extensive experiments are performed on a novel underwater glider and a publicly available South China Sea dataset to verify the proposed method. • An environment perception model is proposed for the underwater vehicle array. • A real-time dynamic model is proposed for the underwater vehicle. • Environment-vehicle coupling effect is explored. [ABSTRACT FROM AUTHOR]

With the rapid development of offshore exploration, autonomous underwater vehicles (AUVs) have come in great diversities depending on their particular specifications in civil and military practices. We focus on AUV swarms in the shallow ocean for their potentialities in economic and military uses as well as in scientific investigations. Nowadays, the advanced technologies of perception, communication, and control in underwater environment give the AUV abilities to perform certain tasks in the shallow ocean. Still, many missions require the large-scale AUV swarms due to the complexities of the tasks and the uncertainties of the environment. In this paper, we start with the introduction of underwater technologies in AUVs. Then we induce the AUV swarms and present several key methods to form swarms and to keep collaboration. Finally, we propose some necessitates technological advances that can facilitate the application of the AUV swarms in the shallow ocean. [ABSTRACT FROM AUTHOR]

Ocean microbes are fundamental for the functioning of the Earth system. Yet, our understanding of how they are reacting to global change in terms of evolution is limited. Microbes typically grow in large populations and reproduce quickly, which may allow them to rapidly adapt to environmental stressors compared to larger organisms. However, genetic evidence of contemporary evolution in wild microbes is scarce. We must begin coordinated efforts to establish new microbial time-series and explore novel tools, experiments, and data to fill this knowledge gap. The development of coordinated microbial 'genomic' observatories will provide the unprecedented opportunity to track contemporary microbial evolution in the ocean and explore the role of evolution in enabling wild microbes to respond to global change. Most of our knowledge about contemporary microbial evolution comes from laboratory experiments and microbial evolution studies of human infections, with few examples of this process measured directly in the wild. Marine microbes have enormous potential for rapid evolution over short timescales (months or years), due to their large population sizes and short generation times, yet we do not have a clear understanding of how fast marine microbial populations evolve in the wild. Long-term time-series of natural microbial populations and paleogenomics is crucial in enabling us to explore the role that contemporary evolution plays in wild microbes' survival and acclimation to environmental stressors, and how this acclimation affects future generations. Establishing genomic observatories will increase our understanding of the marine microbiome and provide genetic data of microbial evolution directly in the wild. Comprehending contemporary evolution of microbes will have implications for our understanding of ecosystems as well as the emergence of new pathogens or antimicrobial-resistant strains. [ABSTRACT FROM AUTHOR]

The Philippine coastal marine ecosystem provides many Ecosystem Services (ES) and is a region where coastal communities are closely dependent on the sea. Previous ES studies focus mainly on biophysical and economic assessments with limited studies about Cultural Ecosystem Services (CES), particularly in the Philippines. Here, we present the CES provided by Taytay Bay, Palawan through local knowledge. Using semi-structured interviews together with participatory mapping activities we quantified marine-related values and threats across Taytay Bay. Spatial mapping of CES, including sense of place, heritage, identity, spiritual, inspiration, knowledge, education, aesthetics, recreation, and intergenerational showed benefits occurring in particular spatial patterns, suggesting that services are provided and contribute to human wellbeing at a community level. Respondents highly valued benefits to their livelihoods but also identified many distinct values beyond income generation, including sense of place, spiritual, aesthetics, and recreational values. The connection between some cultural services e.g., source of ecological knowledge, and provisioning services e.g., seafood, was also recognized. Destructive fishing practices, agrochemicals from pearl and seaweed farms, and privatization of islands were perceived to introduce the highest threats. This has management implications since threats to CES also threaten other ES. The co-occurrence of CES values with provisioning values suggests a holistic approach to ecosystem valuation is needed. The loss of one ES is likely to represent a loss in multiple other services and protecting key service-providing habitats leads to multiple benefits. The study results demonstrate the importance of integrating cultural and non-monetary environmental values into ecosystem valuation and practical on-the-ground policies. • First study on cultural services from coastal marine areas in Palawan, Philippines. • Cultural ecosystem services valuation based on local perception. • Interlinking ecosystem services. • Low values on cultural services within formal education system. • Anthropogenic factors threatening the capacity of the coastal marine environment to provide ecosystem services. [ABSTRACT FROM AUTHOR]

As the largest iodine reservoir on the Earth's surface, the ocean plays a vital role in global iodine cycling. Here, we present results on concentrations of stable- and radio-iodine (127I and 129I) of total iodine (TI), iodide (I–), and iodate (IO 3 –) in seawater samples collected in the top 800 m of the subarctic Pacific Ocean. The speciation distributions of both 127I and 129I showed large variations in depth and geographical location. The T127I concentrations ranged from 321 to 484 nM, were lower at the surface, and increased with depth. In all depth profiles of T129I, the maximum concentrations occurred in the subsurface layer, below which, the T129I concentrations decreased with depth and ranged from 0.2 to 2.1 × 107 atoms/L. Besides, the 129I/127I atom ratios in iodide were significantly higher than those in iodate. It can be inferred from existing research that anthropogenic 129I from atmospheric deposition is the overwhelming source of 129I in the subarctic Pacific Ocean. On this basis, we successfully simulated the 129I vertical dispersion using a one-dimensional vertical diffusion model. The unbalanced distribution of 129I among different iodine species provided useful information for demonstrating the inevitability of the oxidation process of iodide in nature, although whether this oxidation occurred in the ocean remains to be further explored, and the indispensable contribution of iodate to the iodine removal processes in the upper ocean. Our study suggests that anthropogenic 129I can be used as an effective intrinsic tracer for the study of iodine cycling. [ABSTRACT FROM AUTHOR]

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Silicon (Si) isotopic compositions of marine authigenic and biogenic silica deposits are valuable proxies for reconstructing Si cycling in the Earth's oceans. Recent studies predict that pre-diatom-controlled oceans would have Si isotopic compositions of dissolved silicic acid (δ30Si DSi) that were enriched in heavier isotopes, ranging from +1.9‰ to +4.6‰, relative to NBS28 silica. This predicted range is based on calculations that assume a fractionation factor between sponges and silicic acid (Δ30Si s) in ancient (or modern) ocean waters of −3.8‰. Recently published data on sponge silicon isotopic compositions (δ30Si) and Δ30Si s , indicate that a Δ30Si s value for ancient sponges is more accurately calculated by applying corrections based on Michaelis–Menten enzyme kinetics. Predicted Δ30Si s values for pre-diatom sponges using the Michaelis–Menten enzyme kinetics corrections are −4.6 ± 0.1‰, roughly 0.9‰ lower than previous predictions. The new Δ30Si s value, applied to silicon isotopic compositions of silicified mid-Paleozoic and mid-Cenozoic coral fossils, allows for the calculation of δ30Si DSi between +2.0‰ and +2.3‰ for a Paleozoic open shelf environment. Applying the model to silicified mid-Cenozoic coral fossils, using Δ30Si values based on diatoms (−1.1‰) and sponges (−3.0 to −3.5, corresponding to DSi of 10 to 20 µM), resulted in an estimation of ocean's δ30Si DSi of +0.8 to +2.9‰. The mid-Cenozoic samples highlight the strong control of Δ30Si on the calculated values for δ30Si DSi. The results show the promise of these approaches in understanding the ocean water δ30Si DSi from Si isotope abundances measured in abiotic precipitates where DSi and Δ30Si are accurately known. [ABSTRACT FROM AUTHOR]

Enhanced silicate weathering induced by the uplift of the Himalayan-Tibetan Plateau (HTP) has been considered as the major cause of p CO 2 decline and Cenozoic cooling. However, this hypothesis remains to be validated, largely due to the lack of a reliable reconstruction of the HTP weathering flux. Here, we present a 37-million-year record of the difference in the seawater radiogenic neodymium isotopic composition (Δ ε Nd) of Ocean Drilling Program (ODP) sites and Fe-Mn crusts between the northern and central Indian Ocean, which indicates the contribution of regional weathering input from the South Asian continent to the Indian Ocean. The results show a long-term increase in Δ ε Nd and thus provide the first critical evidence of enhanced South Asian weathering input since the late Eocene. The evolution coincided well with major pulses of surface uplift in the HTP and global climatic transitions. Our foraminiferal ε Nd record suggests that tectonic uplift and silicate weathering in South Asia, especially in the Himalayas, might have played a significant role in the late Cenozoic cooling. [ABSTRACT FROM AUTHOR]

Special attention has been given to chromium (Cr) as a paleoproxy tracing redox cycling throughout Earth's history, due to differences in the solubility of its primary redox species at Earth's surface (Cr(III) and Cr(VI)) and isotope fractionation associated with their interconversion. In turn, chromium's paleoproxy potential has motivated studies of the modern ocean to better understand which processes drive its cycling and to constrain their impact on the Cr isotope composition (δ53Cr) of seawater. Here, we present total dissolved seawater Cr concentrations and δ53Cr along the GEOTRACES GP13 section. This section is a zonal transect extending from Australia in the subtropical southwest Pacific Ocean. Surface signals of local biological Cr cycling are minimal, in agreement with distributions of dissolved major nutrients as well as biologically-controlled trace metals in this low productivity, oligotrophic environment. Depth profiles have Cr concentration minima in surface waters and maxima at depth, and are largely shaped by the advection of nutrient- and Cr-rich subsurface waters rather than vertically-driven processes. Samples close to the sediment–water interface indicate important benthic Cr fluxes across the section. The GP13 transect crosses the hydrothermally-active Kermadec Arc. Hydrothermal fluids (consisting of <15% background seawater) were collected from three venting sites at the Brothers Volcano (along the Kermadec Arc). These fluids yielded near-crustal δ53Cr values (−0.17 to +0.08‰) and elevated [Cr] (7.5–23 nmol kg−1, hydrothermal endmember [Cr] ≈ 8–27 nmol kg−1), indicating that the Kermadec Arc may be an isotopically light Cr source. Dissolved [Fe] enrichments have been reported previously in deep waters (∼1600–3000 m) along the GP13 transect, east of the Kermadec Arc. These same waters show elevated [Cr] compared to Circumpolar Deep Water ([Cr] = 3.88 ± 0.11, δ53Cr = 0.89 ± 0.08, n = 32), with an average [Cr] accumulation of 0.71 ± 0.11 nmol kg−1 (1 SD), and an estimated δ53Cr of +0.46 ± 0.30‰ (2 SD, n = 9) for the accumulated Cr. Comparing high-temperature vent and neutrally buoyant plume data, hydrothermal-sourced Cr is likely negligable compared to Cr contributions from other processes (benthic fluxes, release from particles), and the advection of more Cr-rich Pacific Deep Water. It is unlikely that hydrothermal vents would be a major contributor within the regional or global biogeochemical Cr cycle, even if hydrothermal fluxes change by orders of magnitude, and therefore δ53Cr trends in the paleorecord may be attributable, at least in part, to major changes in other controls on Cr (e.g. widespread anoxia). [ABSTRACT FROM AUTHOR]

Beryllium-10 (10Be) has proven to be an essential tool for building chronology and understanding millennial-scale surface processes. Measurements in both the water column and authigenic fractions from various archives (such as surface sediments and Fe-Mn crusts) have provided valuable information on processes regulating Be isotopic distribution in the global oceans. Unlike the Pacific and the Atlantic Oceans, Be isotopic measurements in the Indian Ocean are sparse. Here, based on Be isotopic measurements on surface sediments from the central and northern Indian Ocean, an attempt is made to understand the processes controlling spatial Be isotopic distribution. Our data from the northern Indian Ocean suggests that terrestrial input is one of the primary contributors of 9Be. Owing to higher terrestrial flux, the sediment samples from the Bay of Bengal show higher 9Be concentrations and lower 10Be/9Be ratios. Our study suggests that scavenging by sediment particles plays a vital role in the distribution of Be isotopes in well-mixed open ocean water. Between carbonates and clay particles, carbonates are less efficient in scavenging Be from the water column. [ABSTRACT FROM AUTHOR]

• Helical organization of TC emerges self-sustaining when primary tangential and secondary overturning circulation starts intensifying mutually. • The Okubo-Weiss parameter demonstrates the similar qualitative behavior of deep convection as total helicity. • The local maximas in helicity time series commensurate with the changes in tropical cyclones' stages. Tropical cyclones (TCs) are violent multiscale convections occurring in the atmosphere. The destructive impact of the TCs is commensurate to the helicity associated with their evolution. The evolution of helicity of three TCs viz. Fani, Luban, and Ockhi formed over the north Indian ocean have been analyzed in this study. The analysis of kinetic energy density of primary (EP), secondary (ES) circulation and total helicity has shown that TCs showed helical features when the secondary overturning circulation knotted with primary tangential circulation in a moist convective situation. This condition can be considered a starting of the self-sustained helical feedback process. At this time, the core region became a rotation-dominated region that suppressed strain-dominated surroundings. The Okubo-Weiss parameter demonstrates the similar qualitative behavior of deep convection as total helicity. The local maximas in helicity time series are related with the changes in tropical cyclones' stages (intensification/dissipation). Therefore, consideration of helicity analysis is essential to analyze the TC intensification and dissipation. [ABSTRACT FROM AUTHOR]

Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em−2day−1; and a mean net bias of 2.917 Em−2day−1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions. [ABSTRACT FROM AUTHOR]

A Tremadocian (Early Ordovician, base Stairsian North American Stage) mass extinction event is recorded globally in rocks from several ancient continents and is accompanied by a globally correlated positive carbon isotope excursion (CIE; the largest during the Early Ordovician). In this study, elemental concentrations and uranium isotope compositions (δ238U) were measured for carbonate samples from three sections (along a proximal-to-distal transect: Ibex area, Shingle Pass, Meiklejohn Peak, respectively) in the Great Basin to test the role of ocean anoxia/euxinia on the base Stairsian mass extinction event. Dysoxic/suboxic to oxic water columns and non-sulfidic porewaters are inferred for these sections based on multiple local redox proxies (e.g., Mo/Al, U/Al, Mo and U concentrations, Mo/U ratios). Carbonate δ238U data exhibit different δ238U trends in the three sections. The proximal Ibex area exhibits a small negative δ238U excursion (a magnitude of 0.2–0.3‰) and the Shingle Pass section has one sample with unusually low δ238U, in both cases within the middle of the CIE. Samples with the lowest δ238U in each section also have the highest Mn/Sr ratios, suggesting diagenetic alteration associated with adsorption of isotopically light U onto Mn oxides, followed by dissolution of Mn oxides by reducing porewaters and capture of the isotopically light U by sediments. The distal Shingle Pass and Meiklejohn Peak sections better preserve global ocean signals and the limited δ238U variations in these sections imply no significant changes in global seawater δ238U and thus no significant changes in the extent of global ocean euxinia. Given the non-sulfidic porewaters inferred for these carbonates, we apply a sediment–seawater δ238U offset of 0–0.27‰ (the 0.27 ± 0.14‰ isotopic offset observed for modern Bahamas carbonates with sulfidic porewaters is used as a maximum constraint) to the average carbonate δ238U from the two distal sections (−0.48 ± 0.09‰) to derive a coeval seawater δ238U of between −0.75 ± 0.09‰ and −0.48 ± 0.09‰. A three-sink U isotope mass balance model suggests 0.2–15.8% global euxinic seafloor area existed during deposition of these Tremadocian carbonates. Our study implies that a small biotic crisis during a small CIE was not associated with an expansion of global ocean euxinia, in contrast to major Phanerozoic mass extinctions that were commonly associated with significant expansion of ocean euxinia during large carbon perturbations (e.g., the Late Devonian). In addition, we propose that the post-SPICE Cambrian and Early Ordovician oceans were characterized by limited changes in ocean euxinia and only a few episodes of expanded ocean suboxia-anoxia during carbon perturbations. The "biomere" events within this period, including the base Stairsian event, were probably related to these episodes of expanded suboxic-anoxic oceans and/or other ecological stresses. [ABSTRACT FROM AUTHOR]

Paleoproductivity, calcification and preservation patterns are presented from calcareous nannoplankton paleo-assemblages records covering the last ∼25 kyr retrieved from Integrated Ocean Drilling Program Sites U1385 (37°34.285′N; 10°7.562′W) and U1313 (41°0.0′N; 32°57.4′W), located respectively along the Western Iberian Margin and in the North Atlantic Ocean. The main aim of the study is to provide paleoceanographic and paleoclimatic analyses together with an investigation of changes in coccolithophore calcification processes occurring in response to climate variability from the Last Glacial Maximum up to the Holocene. Coccolithophore calcification was investigated by comparing variations in coccolith thickness and total coccolith calcite; at the same time dissolution/preservation indices were used to better understand the response of coccolithophores to changes in environmental parameters. In general, the increasing CO 2 recorded during the last 25 kyr has a negative effect on calcification, resulting in a reduction of the different species size-normalized thicknesses at both sites. However, differences between the responses at the two latitudes studied are identified, in particular during the Heinrich Stadials; in contrast, during both Younger Dryas and Holocene intervals, the different size-normalized species thicknesses show consistent patterns at the two sites. During the Last Glacial Maximum the influence of subtropical waters due to Azores Current recirculation leads to a moderate productivity, initially at Site U1385 and later at Site U1313. At the same time, temperature influences the calcification at both sites. At Site U1385, the temperature is the main parameter affecting the paleoproductivity during Heinrich Stadial events; in addition, during Heinrich Stadial 1 alone, it also affects the calcification. At Site U1313 the calcification processes during Heinrich Stadial events are apparently hampered by an increasing water turbidity, caused by icebergs acting as ice rafted debris transporters, which affects light filtration in the water column. Light availability is an important calcification-influencing factor. At Site U1313 during Heinrich Stadial 1 and at the Last Glacial Maximum inception, dissolution, a consequence of increased CO 2 solubility in the colder ice-age ocean, has a negative influence on calcification. Furthermore, at Site U1313, in contrast to Site U1385, the continually increasing CO 2 concentration recorded during the Bølling-Allerød hampers both calcification and preservation. [ABSTRACT FROM AUTHOR]

Aiming at the high-efficiency OTEC application, a 30 kW radial-inflow turbine using ammonia was constructed via the one-dimensional design. In addition, a 3D CFD simulation was carried out to research the turbine performance. Furthermore, the effects of blade tip clearance on the flow characteristic in turbine were elucidated and the turbine performance under the off-design conditions was examined. It is indicated that the performance of the designed turbine is satisfactory with a theoretical isentropic efficiency of 85.2% under the design condition. The leakage flow encounters the scraping flow after leaving the tip clearance, forming the vortexes in the cross-section of the flow passage, which decreases the turbine efficiency, and the best ratio of blade tip clearance to inlet blade height is suggested to be 0.04–0.06. When the rotational speeds deviated from the design value, the vortexes appear in the flow passage of the turbine, resulting in non-negligible impact loss of blade and the consequent efficiency reduction. At the design rotational speed, the turbine shows a good adaptability to the inlet temperature variations with the inlet temperature varying from T 0 = 296K to T 0 = 304K. When the inlet pressure increases, the rotational speed corresponding to the maximum efficiency is also increased. [ABSTRACT FROM AUTHOR]