Modelling the effect of submarine iceberg melting on glacier-adjacent water properties

The rate of ocean-driven retreat of Greenland’s tidewater glaciers remains highly uncertain in predictions of future sea level rise, in part due to poorly constrained glacier-adjacent water properties. Icebergs and their meltwater contributions are likely important modifiers of fjord water properties, yet their effect is poorly understood. Here, we use a 3-D ocean circulation model, coupled to a submarine iceberg melt module, to investigate the effect of submarine iceberg melting on glacier-adjacent water properties in a range of idealised settings. Submarine iceberg melting can modify glacier-adjacent water properties in three principle ways: (1) substantial cooling and modest freshening in the upper ~50 m of the water column; (2) warming of Polar Water at intermediate depths due to iceberg melt-induced upwelling of warm Atlantic Water, and; (3) warming of the deeper Atlantic Water layer when vertical temperature gradients through this layer are steep (due to vertical mixing of warm water at depth), but cooling of the Atlantic Water layer when vertical temperature gradients are shallow. The overall effect of iceberg melt is to make glacier-adjacent water properties more uniform with depth. When icebergs extend to, or below, the depth of a sill at the fjord mouth, they can cause cooling throughout the entire water column. All of these effects are more pronounced in fjords with higher iceberg concentrations and deeper iceberg keel depths. These iceberg melt-induced changes to glacier-adjacent water properties will reduce rates of glacier submarine melting near the surface, but increase them in the Polar Water layer, and cause typically modest impacts in the Atlantic Water layer. These results characterise the important role of submarine iceberg melting in modifying ice sheet-ocean interaction, and highlight the need to improve representations of fjord processes in ice sheet-scale models.

Distribution and Abundances of Planktic Foraminifera and Shelled Pteropods During the Polar Night in the Sea-Ice Covered Northern Barents Sea

Planktic foraminfera and shelled pteropods are important calcifying groups of zooplankton in all oceans. Their calcium carbonate shells are sensitive to changes in ocean carbonate chemistry predisposing them as an important indicator of ocean acidification. Moreover, planktic foraminfera and shelled pteropods contribute significantly to food webs and vertical flux of calcium carbonate in polar pelagic ecosystems. Here we provide, for the first time, information on the under-ice planktic foraminifera and shelled pteropod abundance, species composition and vertical distribution along a transect (82°–76°N) covering the Nansen Basin and the northern Barents Sea during the polar night in December 2019. The two groups of calcifiers were examined in different environments in the context of water masses, sea ice cover, and ocean chemistry (nutrients and carbonate system). The average abundance of planktic foraminifera under the sea-ice was low with the highest average abundance (2 ind. m–3) close to the sea-ice margin. The maximum abundances of planktic foraminifera were concentrated at 20–50 m depth (4 and 7 ind. m–3) in the Nansen Basin and at 80–100 m depth (13 ind. m–3) close to the sea-ice margin. The highest average abundance (13 ind. m–3) and the maximum abundance of pteropods (40 ind. m–3) were found in the surface Polar Water at 0–20 m depth with very low temperatures (–1.9 to –1°C), low salinity (<34.4) and relatively low aragonite saturation of 1.43–1.68. The lowest aragonite saturation (<1.3) was observed in the bottom water in the northern Barents Sea. The species distribution of these calcifiers reflected the water mass distribution with subpolar species at locations and depths influenced by warm and saline Atlantic Water, and polar species in very cold and less saline Polar Water. The population of planktic foraminifera was represented by adults and juveniles of the polar species Neogloboquadrina pachyderma and the subpolar species Turborotalita quinqueloba. The dominating polar pteropod species Limacina helicina was represented by the juvenile and veliger stages. This winter study offers a unique contribution to our understanding of the inter-seasonal variability of planktic foraminfera and shelled pteropods abundance, distribution and population size structure in the Arctic Ocean.

Substantial Sub-Surface Chlorophyll Patch Sustained by Vertical Nutrient Fluxes in Fram Strait Observed With an Autonomous Underwater Vehicle

We present results from a coordinated frontal survey in Fram Strait in summer 2016 using an autonomous underwater vehicle (AUV) combined with shipboard and zodiac-based hydrographic measurements. Based on satellite information, we identified a front between warm Atlantic Water and cold Polar Water. The AUV, equipped with oceanographic and biogeochemical sensors, profiled the upper 50 m along a 10 km-long cross-front oriented transect resulting in a high-resolution snapshot of the upper ocean. The transect was dominated by a 6 km-wide, 10 m-thick subsurface patch of high chlorophyll, located near the euphotic depth within a band of cold water. Nitrate was depleted in the surface, but abundant below the pycnocline. Potential vorticity and Richardson number estimates indicate conditions favorable for vertical mixing, which indicates that the high chlorophyll patch may have been sustained by upward nitrate fluxes. Our observations underline the complex hydrographic and biogeochemical structure in a region featuring fronts and meanders, and further underline the patchy and small-scale nature of subsurface phytoplankton blooms potentially fueled by submesoscale dynamics, which are easily missed by traditional surveys and satellite missions.

Influence of additives on rheological and textural properties of cellulose based fat mimetic

Cellulose based fat mimetics play important role in substitution of fat in reduced fat food products. Production of food often includes application of additives. This work examines the influence of additives on the obtaining stable fat mimetic based on fibers of microcrystalline cellulose. Applied additives affect to the durability of food products and increase their shelf life. The influence of added additives was observed trough the rheological and textural properties of MCG fat mimetic, thus its further functional characteristics. Increasing concentration of fibers positively influenced to crosslinking during hydration and increased strength and consistency of obtained gel. But, application of small hydrophilic molecules of additives disturbed rheological and textural properties of fat mimetics. Obtained gels were still with the thixotropic behavior, but with significantly reduced viscoelastic properties, consistency, firmness and cohesiveness. Based on results, in the aim to ensure obtaining of stable, cross–linked gel of fat mimetic with adequate rheological, textural and functional properties, the mixture of additives is added after the hydration of fat mimetic gels, because of competition for polar water molecules between small additives molecules and available hydroxyl groups of cellulose chains.

Holocene paleoceanography of the Northeast Greenland shelf

The Northeast Greenland shelf is highly sensitive to climate and ocean variability because it is swept by the East Greenland Current, which, through the western Fram Strait, forms the main pathway of export of sea ice and cold water masses from the Arctic Ocean into the North Atlantic Ocean. We carried out benthic foraminiferal assemblage, stable isotope- and sedimentological analyses of a marine sediment core retrieved from the Northeast Greenland shelf (core DA17-NG-ST7-73), which provided a multiproxy reconstruction of Holocene paleoceanographic conditions. The results reveal significant variations in the water masses and thus, in the strength of the East Greenland Current over the last ca. 9.4 ka BP. Between 9.4 and 8.2 ka BP the water column off Northeast Greenland was highly stratified, with cold, sea ice-loaded surface waters and strong influx of warm Atlantic Water in the subsurface. At ~8.4 ka BP a short-lived peak in terrestrial elements may be linked to influx of ice-berg transported sediments and thus, to the so-called 8.2 ka event. Holocene Thermal Maximum like conditions prevailed from 8.2 to 6.2 ka BP, with a strong influence of the Return Atlantic Current and a weakened transport of Polar Water in the upper East Greenland Current. After 6.2 ka BP we recorded a return to a more stratified water column with sea-ice loaded surface waters and still Atlantic-sourced subsurface waters. After 4.2 ka BP increased Polar Water at the surface of the East Greenland Current and reduction of the Return Atlantic Water at subsurface levels led to freshening and reduced stratification of the water column and (near) perennial sea-ice cover. The Neoglaciation started at 3.2 ka BP at our location, characterized by a strengthened East Greenland Current. Cold subsurface water conditions with possible sea-ice cover and minimum surface water productivity persisted here throughout the last ~3 kyr.

Synthesis and Solvatochromic Behavior of Zwitterionic Donor–Bridge–Acceptor Systems with Oligo(p-phenylene) Spacers

Oligo(p-phenylene)s with a donor phenol group and an acceptor pyridinium moiety separated by one and two p-phenylene units were synthesized by the linear iterative Suzuki–Miyaura coupling method using aryl nonaflates as effective coupling reagents. Zwitterionic forms of these push–pull molecules were generated upon deprotonation of the phenol leading to large redshifts in absorbance maxima. UV-vis absorbance studies also revealed strong dependence of the band position on solvent polarity: a smooth bathochromic shift can be observed with the decrease of the solvent polarity. The molecule with one p-phenylene bridging unit showed the strongest solvatochromic characteristics in the series, spanning the range of 167 nm while moving from polar water to less polar N,N-dimethylformamide. The magnitude of this shift was close to Reichardt's dye — one of the most solvatochromic organic dyes known.

Н-комплексы 1,2-нафтохинона с молекулами воды в водном растворе и их влияние на сдвиги полос поглощения

Optical absorption spectra of 1,2-naphthoquinone in non-polar (n-hexane) and polar (water) solvents were obtained. It is shown that the use of quantum chemical calculations based on time-dependent density functional theory (TDDFT B3LYP/6-311+G(d, p)) with the polarizable continuum model (PCM) for calculating 1,2-naphthoquinone in a solution of n-hexane and hydrogen complex of 1,2-naphthoquinone with two water molecules in an aqueous medium describes well the shifts of the absorption bands of 1,2-naphthoquinone in a water solution compared to a solution in n-hexane. Based on the analysis of deviations of the calculated band shifts from the experimental ones, the question of the formation of 1,2-naphthoquinone hydrogen complexes with n water molecules (n = 1-4) in an aqueous solution is considered.

Energy of adsorption of polar molecules on NaLSX zeolite

The article presents precision data of isotherms and total thermodynamic characteristics, i.e. ΔH, ΔF and ΔS of H2O adsorption on NaLSX zeolite. The stepwise nature of the change in the heat of adsorption on the studied systems with surface filling is revealed, and the molecular mechanism of water adsorption on NaLSX zeolite in the entire filling area is revealed. It was found that the polar water molecule is adsorbed in the NaLSX zeolite in an amount of 31.8 H2O/1/8 e.u., of which 25.3 are in super cavities, and 6.5 are in β-cavities.