Ice Brine Research Articles

Profiling The Growth Conditions and Persistent Organic Pollutants (POPS) Tolerance of Phenoliferia glacialis USM-PSY62

Antarctica is characterized by extreme cold, isolated, and unique ecosystems. Nevertheless, Antarctica harbors diverse species of microorganisms, particularly in its ice-covered lakes and subglacial environments. These microorganisms have special adaptations to extreme cold and low-nutrient conditions. Some extremophiles, like psychrophiles can thrive in these harsh environments. Phenoliferia glacialis USM-PSY62, previously identified as Rhodotorula sp. USM-PSY62 is a psychrophilic yeast isolated from the ice brine of Antarctica. However, there is very little information on this psychrophilic yeast. This study aims to characterize the P. glacialis USM-PSY62 through the identification of the optimum growth parameters in different media (Yeast Peptone Dextrose, YPD & Yeast Malt, YM), temperature (4°C, 15°C, 20°C) and pH (6, 7, 8, 9) as well as their ability in carbon assimilation and extracellular enzyme production. It has an optimal growth in YPD compared to YM broth media. P. glacialis USM-PSY62 grows optimally at 15°C and pH 7.0. This Antarctic yeast enters the stationary phase on day six of incubation under optimum conditions. It appeared mainly as elongated-shape and oval-shaped with budding formation and was found to produce extracellular enzymes such as protease and amylase in the presence of 2% glucose concentration in YM media. P. glacialis USM-PSY62 also can assimilate various types of carbon sources including raffinose, arabinose, and maltose. Interestingly, the psychrophilic yeast presented growth in media supplemented with Persistent Organic Pollutants (POPs) such as dichlorophenyldichloroethylene (DDE) and polychlorinated biphenyl (PCB). These preliminary findings suggest that P. glacialis USM-PSY62 has tremendous potential for bioremediation application in polluted cold regions, as well as deepening our knowledge of its optimal growth conditions.

Boron to salinity ratios in the Fram Strait entering the Central Arctic: The role of sea ice formation and future predictions

The Arctic Ocean's sea ice loss dynamically impacts carbon uptake potential, as assessed through measured carbonate parameters, such as total alkalinity. In the open ocean, boron (B) is the third largest contributor to alkalinity via borate and is usually accounted for through the conservative boron to salinity ratio (B/S), and not directly measured. Here, we present findings on non-conservative boron dynamics, that results in significant B/S deviations, observed in ice melt zone waters, snow, slush, brine, and annual sea ice (n = 169) in the Fram Strait entering the Central Arctic. These samples were collected during the onset of the melt season on the 2023 ARTofMELT expedition, covering a wide practical salinity range (2–59). Barring snow, the average B/S ratio across the study was 0.1321 ± 0.0032 mg kg−1 ‰−1, similar to the mean B/S ratio measured amongst several polar water masses near Iceland, as well as the accepted B/S for other ocean regions. Results indicate minor deviations from accepted B/S ratios (indicating conservative behavior) across the sample practical salinity range and reflect an uncertainty in the borate contribution to total alkalinity of less than 2.9 μmol kg−1 at in-situ temperatures. B fractionation appears to occur during sea ice formation, causing greater B in the sea ice reservoir whereas brine, slush, lead, and under-ice water reservoirs are depleted in B. As such, under-ice and lead, brine, and slush samples all had measured B/S ratios (0.1305 ± 0.0011, 0.1305 ± 0.0018, and 0.1304 ± 0.0017 mg kg−1 ‰−1, respectively) lower than the established ratio whereas the average sea ice B/S ratio (0.1331 ± 0.0035 mg kg−1 ‰−1) was closest to accepted values (0.1336 ± 0.0005 mg kg−1 ‰−1). Arctic open ocean samples also had a lower B/S ratio (0.1304 ± 0.0014 mg kg−1 ‰−1). Our findings, together with a previous Arctic B ice study, suggest that B (probably in the form of B(OH)4−) is incorporated into authigenic CaCO3 minerals, replacing CO32− within the mineral lattice during sea ice formation. This process consequentially lowers the B/S ratio in the open Arctic Ocean, compared to the established global ocean ratio. Nevertheless, the incorporation of B into the sea ice reservoir does not fully account for the deficit of B in the Arctic Ocean samples, suggesting further accounting of B Arctic pathways is necessary. In future climate scenarios involving increased sea ice melt, the transition from multiyear to annual sea ice, permafrost thaw, and increased riverine discharge, the behavior of B in the Arctic Ocean is expected to become more dynamic.

Freezing-induced acidification of sea ice brine

The acidity of sea ice and snow plays a key role in the chemistry of the cryosphere; an important example lies in the photochemical catalytic release of reactive bromine in polar regions, facilitated at pHs below 6.5. We apply in-situ acid-base indicators to probe the microscopic acidity of the brine within the ice matrix in artificial sea water at a range of concentrations (0.35–70 PPT) and initial pHs (6–9). The results are supported by analogous measurements of the most abundant salts in seawater: NaCl, Na2SO4, and CaCO3. In the research herein, the acidity is expressed in terms of the Hammett acidity function, H2−. The obtained results show a pronounced acidity increase in sea water after freezing at −15 °C and during the subsequent cooling down to −50 °C. Importantly, we did not observe any significant hysteresis; the values of acidity upon warming markedly resembled those at the corresponding temperatures at cooling. The acidity increase is attributed to the minerals' crystallization, which is accompanied by a loss of the buffering capacity. Our observations show that lower salinity sea water samples (≤ 3.5 PPT) reach pH values below 6.5 at the temperature of −15 °C, whereas higher salinity ices attain such values only at −30 °C. The ensuing implications for polar chemistry and the relevance to the field measurements are discussed.

Lipid composition, caloric content, and novel oxidation products from microbial communities within seasonal pack ice cores

Sea ice is a critical feature of polar environments with importance for coastal ecosystems. Along the West Antarctic Peninsula (WAP), climate change is causing decreases in seasonal sea ice duration and extent. Organic carbon within sea ice is an important aspect of southern ocean carbon cycling but less studied than water column or sedimentary carbon reservoirs. Though conditions within sea ice can be extreme, phytoplankton are able to flourish and serve as a key food source for higher trophic levels, especially in the spring and fall. A portion of this sea ice phytoplankton biomass is composed of lipids, which are both calorically dense and useful as tracers of biological processes within the sea ice. To better understand both the trophic value and the diversity of lipids present within sea ice we employed high-resolution accurate-mass mass spectrometry to analyze ice core samples from six sites collected along the peninsula in November 2018. Using untargeted methods we annotated 1,173 intact lipid species across 14 classes of intact polar lipids, triacylglycerols, and pigments. We compared lipids’ physical distribution within sea ice cores and found they are highly geographically and physically heterogenous within sites. Ratios between intact polar lipid classes show little signs of phytoplankton nutrient stress; a finding consistent with internally nutrient replete sea ice brines. We found key differences in the composition between pack ice versus fast ice and observed chlorophyll a to be inconsistently correlated with triacylglycerol content. We determined the mean caloric content of lipids within pack ice (4.45 ± 3.47 kJ m−2) and found that caloric densities from the lipids alone were in the range of total water column energy content. Lastly, we show evidence of fatty acid hydroxy fatty acid triacylglycerols within the ice matrix and discuss possible biochemical sources of these novel biomarkers in an ocean system. These results shed light on the chemical diversity of a dynamic and ecosystem relevant carbon pool.

Effect of cooling medium on the κ carbide precipitation behavior, microstructure and impact properties of FeMnAlC low-density steel

The effect of four different cooling mediums, namely ice brine, water, oil, and air on the κ carbide precipitation behavior, microstructure, and impact properties of FeMnAlC low-density steel is thoroughly investigated by using OM (Optical Microscope), SEM (Scanning Electron Microscope), TEM (Transmission Electron Microscope), XRD (X-Ray Diffraction), VSM (Vibrating Sample Magnetometer), Rockwell hardness tester and in conjunction with low-temperature impact experiments. The results indicate that after cooling with different mediums, the austenite structure exhibits a mixed crystalline phenomenon and has a significant presence of twins. The average grain size of austenite increases as the cooling rate decreases, with the largest size observed in air-cooled conditions. Concurrently, the volume fraction and size of intragranular κ carbides gradually increase with a decreasing cooling rate. This phenomenon contributes to an increase in Rockwell hardness, with the highest value recorded in the air-cooled state at 36.8 HRC. Furthermore, the impact toughness initially increases and then decreases as the cooling rate decreases. Notably, water cooling demonstrates the highest impact energy at 68 J. The formation of intergranular κ carbides in oil and air-cooled conditions is identified as the primary reason for the decline in impact toughness.

Lower viral evolutionary pressure under stable versus fluctuating conditions in subzero Arctic brines

BackgroundClimate change threatens Earth’s ice-based ecosystems which currently offer archives and eco-evolutionary experiments in the extreme. Arctic cryopeg brine (marine-derived, within permafrost) and sea ice brine, similar in subzero temperature and high salinity but different in temporal stability, are inhabited by microbes adapted to these extreme conditions. However, little is known about their viruses (community composition, diversity, interaction with hosts, or evolution) or how they might respond to geologically stable cryopeg versus fluctuating sea ice conditions.ResultsWe used long- and short-read viromics and metatranscriptomics to study viruses in Arctic cryopeg brine, sea ice brine, and underlying seawater, recovering 11,088 vOTUs (~species-level taxonomic unit), a 4.4-fold increase of known viruses in these brines. More specifically, the long-read-powered viromes doubled the number of longer (≥25 kb) vOTUs generated and recovered more hypervariable regions by >5-fold compared to short-read viromes. Distribution assessment, by comparing to known viruses in public databases, supported that cryopeg brine viruses were of marine origin yet distinct from either sea ice brine or seawater viruses, while 94% of sea ice brine viruses were also present in seawater. A virus-encoded, ecologically important exopolysaccharide biosynthesis gene was identified, and many viruses (~half of metatranscriptome-inferred “active” vOTUs) were predicted as actively infecting the dominant microbial genera Marinobacter and Polaribacter in cryopeg and sea ice brines, respectively. Evolutionarily, microdiversity (intra-species genetic variations) analyses suggested that viruses within the stable cryopeg brine were under significantly lower evolutionary pressures than those in the fluctuating sea ice environment, while many sea ice brine virus-tail genes were under positive selection, indicating virus-host co-evolutionary arms races.ConclusionsOur results confirmed the benefits of long-read-powered viromics in understanding the environmental virosphere through significantly improved genomic recovery, expanding viral discovery and the potential for biological inference. Evidence of viruses actively infecting the dominant microbes in subzero brines and modulating host metabolism underscored the potential impact of viruses on these remote and underexplored extreme ecosystems. Microdiversity results shed light on different strategies viruses use to evolve and adapt when extreme conditions are stable versus fluctuating. Together, these findings verify the value of long-read-powered viromics and provide foundational data on viral evolution and virus-microbe interactions in Earth’s destabilized and rapidly disappearing cryosphere.B3KUN5MJ8EAz4vqucsgZtLVideo

Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities.

Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities.

Improvement of tensile properties of low-carbon steels via short-time intercritical annealing

The effect of low volume fraction formation of martensite on the tensile properties of low carbon steel was evaluated. First, steel samples with ferrite-cementite microstructure were produced. The thermomechanical treatment used included austenitizing at 1000 °C and then quenching in ice brine solution, tempering the obtained martensitic structure for 1 h at 650 °C, 80% cold rolling, and re-tempering for 2 h at 650 °C. In order to form a low volume fraction of martensite, steel samples with ferrite-cementite microstructure were intercritically annealed for 30 seconds at 740 °C. As a result of intercritical annealing treatment, 6.2% martensite was formed. The results of tensile test showed that the formation of 6.2% martensite led to the elimination of yield point phenomenon and Lüders banding, decrease of yield stress and increase of true stress at maximum load, while true uniform strain did not change significantly. The work hardening rate also increased significantly. Based on the results of modeling of the flow behavior with the Holloman equation, the work hardening capability of the steel sample including ferrite-cementite decreased after a certain plastic strain, while the work hardening capacity remained constant with the formation of a low volume fraction of martensite in the microstructure.

Non-conservative nature of boron in Arctic marginal ice zones

The Arctic Ocean is experiencing a net loss of sea ice. Ice-free Septembers are predicted by 2050 with intensified seasonal melt and freshening. Accurate carbon dioxide uptake estimates rely on meticulous assessments of carbonate parameters including total alkalinity. The third largest contributor to oceanic alkalinity is boron (as borate ions). Boron has been shown to be conservative in open ocean systems, and the boron to salinity ratio (boron/salinity) is therefore used to account for boron alkalinity in lieu of in situ boron measurements. Here we report this ratio in the marginal ice zone of the Bering and Chukchi seas during late spring of 2021. We find considerable variation in born/salinity values in ice cores and brine, representing either excesses or deficits of boron relative to salinity. This variability should be considered when accounting for borate contributions to total alkalinity (up to 10 µmol kg−1) in low salinity melt regions.

Deciphering the Properties of Different Arctic Ice Types During the Growth Phase of MOSAiC: Implications for Future Studies on Gas Pathways

The increased fraction of first year ice (FYI) at the expense of old ice (second-year ice (SYI) and multi-year ice (MYI)) likely affects the permeability of the Arctic ice cover. This in turn influences the pathways of gases circulating therein and the exchange at interfaces with the atmosphere and ocean. We present sea ice temperature and salinity time series from different ice types relevant to temporal development of sea ice permeability and brine drainage efficiency from freeze-up in October to the onset of spring warming in May. Our study is based on a dataset collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) Expedition in 2019 and 2020. These physical properties were used to derive sea ice permeability and Rayleigh numbers. The main sites included FYI and SYI. The latter was composed of an upper layer of residual ice that had desalinated but survived the previous summer melt and became SYI. Below this ice a layer of new first-year ice formed. As the layer of new first-year ice has no direct contact with the atmosphere, we call it insulated first-year ice (IFYI). The residual/SYI-layer also contained refrozen melt ponds in some areas. During the freezing season, the residual/SYI-layer was consistently impermeable, acting as barrier for gas exchange between the atmosphere and ocean. While both FYI and SYI temperatures responded similarly to atmospheric warming events, SYI was more resilient to brine volume fraction changes because of its low salinity (<2). Furthermore, later bottom ice growth during spring warming was observed for SYI in comparison to FYI. The projected increase in the fraction of more permeable FYI in autumn and spring in the coming decades may favor gas exchange at the atmosphere-ice interface when sea ice acts as a source relative to the atmosphere. While the areal extent of old ice is decreasing, so is its thickness at the onset of freeze-up. Our study sets the foundation for studies on gas dynamics within the ice column and the gas exchange at both ice interfaces, i.e. with the atmosphere and the ocean.

Methane release from open leads and new ice following an Arctic winter storm event

We examine an Arctic winter storm event, which led to ice break–up, the formation of open leads, and the subsequent freezing of these leads. The methane (CH4) concentration in under–ice surface water before and during the storm event was 8–12 nmol L−1, which resulted in a potential sea–to–air CH4 flux ranging from +0.2 to +2.1 mg CH4 m−2 d−1 in open leads. CH4 ventilation between seawater and atmosphere occurred when both open water fraction and wind speed increased. Over the nine days after the storm, sea ice grew 27 cm thick. Initially, CH4 concentrations in the sea ice brine were above the equilibrium with the atmosphere. As the ice grew thicker, most of the CH4 was lost from upper layers of sea ice into the atmosphere, implying continued CH4 evasion after the leads were ice–covered. This suggests that wintertime CH4 emissions need to be better constrained.

Bacterial Community in Cold Surge-Caused Sea Ice Differs From Seawater in Mid-Latitude Region: A Case Study in Aoshan Bay, Southern Yellow Sea

Cold surges result in a rapid drop in air temperature and freezing of seawater, which was likely to impact bacterial communities. We examined the differences in bacteria abundance and bacterial community composition in the sea ice and seawater during a cold surge along Aoshan Bay, southern Yellow Sea in January 2021. Results showed that the differences in bacteria abundance between sea ice and seawater likely resulted from the physical impact of ice formation. The parent water played a key role in bacterial community composition in the early phase of ice formation, in which bacterial community compositions at class level were similar, but the relative abundances were different between sea ice and seawater. The Gammaproteobacteria dominated in sea ice, and the relative abundances of Verrucomicrobiae were also significantly higher, possibly due to the high concentration of algal-derived DOM in coastal areas. The predicted functional profiles suggested the lower abundance of functional genes related to ATP-binding cassette transporters in sea ice than in seawater, which might be due to the bacteria not requiring varieties of functional genes of ATP-binding cassette transporters in restricted sea ice brine.

Persistent Ross Sea Freshening From Imbalance West Antarctic Ice Shelf Melting

AbstractA 63‐year observational record in the southwest Ross Sea shows a continuing, near‐linear salinity decrease of 0.170 and slight warming of 0.013°C through 2020. That freshening exceeded any increase in sea ice production and brine release from stronger southerly winds, while melting and freezing at the Ross Ice Shelf base contributed little to the salinity change. The parallel seawater density decline appears not to have enhanced warm deep water intrusions onto the continental shelf (CS). Confirming prior inferences, the salinity change has been mainly caused by a growing imbalance in the meltwater available from thinning ice shelves and increased iceberg calving in the upstream Amundsen and Bellingshausen Seas. Shorter‐term salinity variability has tracked winds near the Amundsen Sea CS break, in turn coherent with a broader Pacific climate variability index, and with salinity reversals on and seaward of the Ross CS. The melt driven freshening is positively correlated with global atmospheric CO2 and temperature increases, and adds to the rise in sea level from increased glacier flow into weakened ice shelves. Continued erosion of those ice shelves could end the production of high salinity shelf and bottom waters, as defined in the Ross Sea, by the 2050s.

Inhibition effect of adsorption on brine pockets formation during seawater freeze desalination

High concentration of brine pockets formed during seawater freeze crystallisation reduces the freeze desalination efficiency. In this study, the inhibitory effect of salt-adsorption on brine pockets formation was investigated by simulation and experimental methods. A phase-field model coupled with the adsorption kinetic equation was established. The experiments on oriented growth of sea ice assisted with adsorption were conducted. In addition, the effects of adsorption on the morphology of ice crystals and brine pockets were studied. The results show that under the effect of adsorption, the planar crystal layer became thicker, the columnar crystals had a lower aspect ratio, the growth of brine pockets was inhibited, and the brine channels between adjacent ice crystals were reduced significantly. Stronger adsorption effect leads to less brine pockets. The area of ice crystals is increased by 6.08% in simulation and 11.79% in experiments, respectively. Moreover, the ice crystal growth rate and Peclet number were consistent between the simulation and experiment. The tip solute migration rate under adsorption increased by 17.69% compared with that without adsorption. This indicates that adsorption inhibits brine pockets formation in seawater freeze desalination and is favourable for improving the desalination rate.

Seasonal Transformation and Spatial Variability of Water Masses Within MacKenzie Polynya, Prydz Bay

AbstractWe provide a detailed description of the spatial distribution, seasonality and transformation of the main water masses within MacKenzie Polynya (MP) in Prydz Bay, East Antarctica, using data from instrumented southern elephant seals. Dense Shelf Water (DSW) formation in MP shows large spatial variability that is related to the (a) local bathymetry, (b) water column preconditioning from the presence/absence of different water masses, and (c) proximity to the Amery Ice Shelf meltwater outflow. MP exhibits sustained sea ice production and brine rejection (thus, salinity increase) from April to October. However, new DSW is only formed from June onward, when the mixed layer deepens and convection is strong enough to break the stratification set by Antarctic Surface Water above and Ice Shelf Water below. We found no evidence of DSW export from MP to Darnley polynya, as previously suggested. Rather, our observations suggest some DSW formed in Darnley Polynya may drain toward the western Prydz Bay. Then, DSW is exported offshore from Prydz Bay through the Prydz Channel. The interplay between sea ice formation, meltwater input, and sea floor topography is likely to explain why some coastal polynyas form more DSW than others, as well as the temporal variability in DSW formation within a particular polynya.

Studies of periodic seawater spray icing with unilateral NMR

Sea water ice has a complicated pore structure consisting of brine-filled pockets within a solid ice matrix. In this work, an unilateral Nuclear Magnetic Resonance instrument was used to characterize the evolution of sea-ice brine inclusions in two types of ice: stationary seawater ice and seawater spray ice formed by periodic spraying on horizontal and vertical surfaces. The portable unilateral NMR was capable of measuring very low amounts of brine (<10% of the water-filled volume). CPMG experiments were performed to extract the information on brine content and T2 distribution at temperatures between −6 °C and −16 °C. 1D imaging was used to spatially resolve the ice brine accumulation. The results show that the seawater spray ice growth, brine content (greater for the horizontal orientation than for the vertical one), and T2 distribution (unimodal for stationary ice and bimodal for spray ice) depend on temperature and surface orientation.

Landfast sea ice in the Bothnian Bay (Baltic Sea) as a temporary storage compartment for greenhouse gases

Although studies of biogeochemical processes in polar sea ice have been increasing, similar research on relatively warm low-salinity sea ice remains sparse. In this study, we investigated biogeochemical properties of the landfast sea ice cover in the brackish Bothnian Bay (Northern Baltic Sea) and the possible role of this sea ice in mediating the exchange of greenhouse gases, including carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) across the water column–sea ice–atmosphere interface. Observations of total alkalinity and dissolved inorganic carbon in both landfast sea ice and the water column suggest that the carbonate system is mainly driven by salinity. While high CH4 and N2O concentrations were observed in both the water column (up to 14.3 and 17.5 nmol L–1, respectively) and the sea ice (up to 143.6 and 22.4 nmol L–1, respectively), these gases appear to be enriched in sea ice compared to the water column. This enrichment may be attributable to the sea ice formation process, which concentrates impurities within brine. As sea ice temperature and brine volume decrease, gas solubility decreases as well, promoting the formation of bubbles. Gas bubbles originating from underlying sediments may also be incorporated within the ice cover and contribute to the enrichment in sea ice. The fate of these greenhouse gases within the ice merits further research, as storage in this low-salinity seasonal sea ice is temporary.

Local environment shapes adaptation of Phaeocystis antarctica to salinity perturbations: Evidence for physiological resilience

The Southern Ocean (SO) is a fragile ecosystem as judged by changes in the timing of the advance and retreat of its ice cover. In the SO, the Antarctic Circumpolar Current (ACC) and the near shore gyres (Weddell Sea and Ross Sea) provide local environments with distinct temperature and salinity attributes associated with varying sea ice history. Phaeocystis antarctica is a prymnesiophyte often dominating polar phytoplankton blooms in the (SO) and is a keystone species there because its abundance can have negative effects on higher trophic levels and it can influence air/sea gas exchange involved in DMSP production, Thus, its ability to survive in response to perturbations in the environments may be linked to its genetic diversity within its populations as they move around the SO. Here we apply increased (70 PSU) and decreased (18 PSU) salinity treatments to five genetically different P. antarctica strains isolated from three different water masses to test whether genetic similarity or water mass physical features were more important in determining responses to salinity changes, such as those encountered by inclusion into sea ice brine channels and/or its subsequent melt water in those water masses that have annual ice cover. Strains that were geographically close (isolated from the same water mass), but genetically distinct (ca. 30% similar and from different gene pools as judged by microsatellite (MS) and amplified fragment linked polymorphisms (AFLP) analyses responded similarly to higher and lower salinity regimes, whereas genetically close strains (ca. 95% identical or from the same gene pool) that originated from different water masses and hence different environmental conditions responded differently. Dimethylsulphoniopropionate (DMSP) production in response to these salinity changes were not significantly different between any of the strains/treatments. Considering the presence of highly similar genotypes in ice-free as well as seasonally ice covered sampling sites, the observed phenotypic differences most likely result from rapid local adaptation between both habitat types or a hybridization of isolates from the two gene pools with the resultant genotype for salinity tolerance being that from which the isolate originated, suggesting that the selective effect of seasonal presence or year-round absence of sea ice overrides gene flow between these habitats to adapt the physiology of cells to the environment in a relatively short period of time.

Effect of cooling rate on microstructure and mechanical properties of a low-carbon low-alloy steel

The advanced electron backscatter diffraction (EBSD) technique was used to examine the microstructure of a widely used A517GrQ low-carbon low-alloy steel after different heat treatments. Three distinguishable microstructures were studied. Slow cooling in the furnace after austenitization led to the formation of a granular structure that consisted of massive ferrite and randomly distributed M–A constituents. Medium rate cooling in air produced granular bainite that was composed of lath ferrite, and M–A constituents were distributed between the laths. Lath martensite was formed by fast cooling into ice brine. EBSD analysis revealed that, in one austenite grain, the massive ferrite in the granular structure and the lath ferrite in the granular bainite were predominately separated by high-angle boundaries, whilst the ferrite laths in the martensite were separated by low-angle boundaries. The specimens with granular bainite formed by medium rate cooling had higher strength (both yield strength and tensile strength), and also almost 5 times higher Charpy impact energy than that of the specimens containing granular structure obtained at the slow cooling. The strength of the specimens with lath martensite after quenching into ice brine was slightly higher than the granular bainite but were associated with much lower Charpy impact energy. The present work indicates that it is critical to control the cooling rate after austenitization in order to simultaneously achieve high strength and high toughness of low-carbon low-alloy steels.

A protocol for quantifying mono- and polysaccharides in seawater and related saline matrices by electro-dialysis (ED) – combined with HPAEC-PAD

Abstract. An optimized method is presented to determine dissolved free (DFCHO) and dissolved combined carbohydrates (DCCHO) in saline matrices, such as oceanic seawater, Arctic ice core samples or brine using a combination of a desalination with electro-dialysis (ED) and high-performance anion exchange chromatography coupled to pulsed amperometric detection (HPAEC-PAD). Free neutral sugars, such as glucose and galactose, were found with 95 %–98 % recovery rates. Free amino sugars and free uronic acids were strongly depleted during ED at pH=8, but an adjustment of the pH could result in higher recoveries (58 %–59 % for amino sugars at pH=11; 45 %–49 % for uronic acids at pH=1.5). The applicability of this method for the analysis of DCCHO was evaluated with standard solutions and seawater samples compared with another established desalination method using membrane dialysis. DFCHO in field samples from different regions on Earth ranged between 11 and 118 nM and DCCHO between 260 and 1410 nM. This novel method has the potential to contribute to a better understanding of biogeochemical processes in the oceans and sea–air transfer processes of organic matter into the atmosphere in future studies.