Dense Water Research Articles

Analytical Model of Thermohaline Circulation in Land-Locked Basins: Analyzing the Impact of Friction on Circulation Reversal

Abstract The paper investigates switches of circulation orientation in inland basins, either at the surface or near the bottom. The study is based on an analytical 2D model used to simulate thermohaline circulation in lakes and inland seas. The model allows different density profiles varying in both horizontal and vertical directions. By assuming some simplifications (such as steady state, vanishing of an alongshore variability, and flat bottom), we are able to obtain an explicit expression of the circulation in the central transverse section of an elongated basin. Starting from three typical density profiles (bottom dense water, surface light water, and a combination of the two), the model reveals different circulation types (cyclonic and anticyclonic surface circulation, either prevailing along the whole vertical column or accompanied by an opposite circulation in the bottom layer). In addition, we analyze the impact of friction coefficients and basin dimensions on the switch from one circulation type to another. The simplified assumptions turn out not to be limiting, as other studies have shown that they do not change the main flow characteristics. More importantly, the results obtained are in keeping with empirical findings, numerical simulations, and physical experiments studied elsewhere.

Ocean Variability Beneath the Filchner‐Ronne Ice Shelf Inferred From Basal Melt Rate Time Series

AbstractFourteen phase‐sensitive radars (ApRES) were deployed on the Filchner‐Ronne Ice Shelf (FRIS) to measure variability in its basal melt rate. Melt rates from sites along the Ronne Depression vary seasonally, consistent with the dynamics of the propagation of seasonal dense water from the western ice front into the cavity. Several sites at the back of the FRIS cavity feature a signal with two seasonal maxima. Sub‐ice shelf oceanographic data available from one of the sites indicate that this signal is caused by two different pathways followed by the same source water. Inter‐annual variability is strongest along a direct flow pathway between western Ronne Ice Front and western Berkner Island. Highest melting occurred in 1999 and 2018, following anomalously low summer sea‐ice concentrations in front of the ice shelf. Inter‐annual melt rate variability at the back of the FRIS cavity is limited. If present, it is expressed as a suppression or delay in the arrival of the seasonal melt rate minimum, which can be understood in terms of inter‐annual stratification changes and variable inflow pathways toward the sites. Long term mean ApRES melt rates agree with estimates from satellite data over eastern FRIS. However, the satellite estimates overstate the area of active basal freezing in the western part of the ice shelf. Furthermore, the temporal melt rate variability from the satellite estimates exaggerates the range of variability at both seasonal and inter‐annual time scales with any correspondence between the in‐situ and remotely derived inter‐annual variability being limited to a single site.

Impact of Graphene Oxide on Properties and Structure of Thin-Film Composite Forward Osmosis Membranes.

Forward osmosis (FO) membranes have the advantages of low energy consumption, high water recovery rate, and low membrane pollution trend, and they have been widely studied in many fields. However, the internal concentration polarization (ICP) caused by the accumulation of solutes in the porous support layer will reduce permeation efficiency, which is currently unavoidable. In this paper, we doped Graphene oxide (GO) nanoparticles (50~150 nm) to a polyamide (PA) active layer and/or polysulfone (PSF) support layer, investigating the influence of GO on the morphology and properties of thin-film composite forward osmosis (TFC-FO) membranes. The results show that under the optimal doping amount, doping GO to the PA active layer and PSF support layer, respectively, is conducive to the formation of dense and uniform nano-scale water channels perpendicular to the membrane surface possessing a high salt rejection rate and low reverse solute flux without sacrificing high water flux. Moreover, the water channels formed by doping GO to the active layer possess preferable properties, which significantly improves the salt rejection and water permeability of the membrane, with a salt rejection rate higher than 99% and a water flux of 54.85 L·m−2·h−1 while the pure PSF-PA membrane water flux is 12.94 L·m−2·h−1. GO-doping modification is promising for improving the performance and structure of TFC-FO membranes.

Spatio-Temporal Classification and Prediction of Land Use and Land Cover Change in Finima Nature Park Bonny Island, Nigeria

Land Use Land Cover (LULC) is naturally dynamic, thus change is inevitable. However, its changes have greatly increased to a frightening proportion as a result of high rate of anthropogenic and natural processes. Consequently, land use and land cover classes of Finima Nature Park were classified and changes were observed within the last 33 years (1987 - 2021) and predicted for the next 33 years (2021 – 2054).
 Remote sensing and Geographic Information System (GIS) were used to achieve the goal. Coordinate points were collected from the various land use and land cover classes as a reference data for accuracy assessment of the classification. Landsat imageries of 1987, 1999, 2010 and 2021 were acquired from The United States Geological Survey (USGS). The imageries were pre-processed, processed and classified into various LULC classes using Maximum Likelihood Classification in Idrisi and ArcGis10.5. Confusion matrix and Cellular Automata (CA) Markov Chain algorithm were used for accuracy assessment and prediction of LULC respectively.
 Results showed that dense vegetation, sparse vegetation, bare land, and water body were the main LULC class in 1987 and 1999, while dense vegetation, sparse vegetation, bare land, water body and built up were observed in the years 2010, 2021 and 2054. The Kappa Coefficient values were 93%, 81%, 83% and 90% for 1987, 1999, 2010 and 2021 respectively; an indication of strong accuracy of the classification. Generally, there were changes in land use and land cover within the study periods. However, changes were mostly observed in the areas of water body and bare lands closer to the sea coast. Hence, the sea was implicated as the major driver of land use and land cover change in the park. The slight decrease in dense vegetation and sparse vegetation from 1999 to 2021, and 2021 to 2054 underscores the importance and benefit of conservation.

Pleistocene oceanographic variability in the Ross Sea: A multiproxy approach to age model development and paleoenvironmental analyses

Understanding how ocean circulation has varied around Antarctica in the past is vital because significant volumes of ice are grounded below sea level, and therefore ice sheet variations are strongly coupled with oceanographic variability at the continental shelf margin. This study investigates the 11.75 m sediment core RS15-LC42, retrieved from the Central Basin of the Ross Sea. A magneto-biostratigraphic age model was constructed from a magnetic reversal stratigraphy, diatom biostratigraphy, and the relative paleointensity of the geomagnetic field. The core spans the last 1.34 Myr with a mean sedimentation rate of 0.88 cm/kyr, providing insights into paleoceanographic variability in the Ross Sea throughout the Pleistocene. Winnowed deposits enriched in iceberg rafted debris were formed due to a combination of enhanced glacial calving during glacial retreats, and export of Dense Shelf Water during interglacial and weak glacial periods when the ice-sheet was not grounded in the outer Joides Trough. During periods where the ice sheet grounded on the outer Ross Sea continental shelf, laminated sediments rich in reworked diatoms are interpreted to have formed due to glacial scouring and transport of shelf sediments to the mouth of the Joides Trough, where slope failures and meltwater pulses remobilized this material downslope to the Central Basin. Dense shelf water formation is inferred to be most intense during interglacial periods, with reduced export from the Joides Trough during ice sheet advances. The study does not find any evidence for prolonged ice-sheet grounding in the outer Ross Sea since ~0.3 Ma, however, we conclude that the grounding line reached the outer shelf frequently between 0.3 and 1.2 Ma, supporting higher Antarctic ice volumes during glacial periods in this interval. • High-resolution sediment age modelling of Pleistocene Antarctic sediments • The WAIS has likely not been grounded in the outer Ross Sea since MIS 10. • Bottom water export from the Ross Sea is strongest during interglacial periods.

Changes in Arctic Halocline Waters Along the East Siberian Slope and in the Makarov Basin From 2007 to 2020

AbstractThe evolution of halocline waters in the Makarov Basin and along the East Siberian continental slope is examined by combining drifting platform observations, shipborne hydrographic data, and simulations from a global operational physical model from 2007 to 2020. From 2012 onwards, relatively shallow and cold Atlantic‐derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian continental slope. Their eastward extent abruptly shifted from 155°E to 170°E in early 2012, stabilized at 170°E until the end of 2015, then gradually advanced to reach the western Chukchi Sea in 2017. Such eastward progression led to a strengthening of the associated boundary current and to the shedding of mesoscale eddies of cold Atlantic‐derived waters into the lower halocline of the Makarov Basin in September 2015 and near the East Siberian continental slope in November 2017. Additionally, active mixing between upwelled Atlantic Water and shelf water formed dense warm water supplying the Makarov Basin lower halocline. The increasing contribution from Atlantic‐derived waters into the lower halocline along the East Siberian continental slope and in the Makarov Basin led to a weakening of the halocline, which is characteristic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime may now extend toward the Amerasian Basin.

Physical and biological controls on anthropogenic CO2 sink of the Ross Sea

The Antarctic continental shelf is known as a critical anthropogenic CO2 (Cant) sink due to its cold waters, high primary productivity, and unique circulation, which allow it to sequester large amounts of organic and inorganic carbon into the deep ocean. However, climate change is currently causing significant alteration to the Antarctic marine carbon cycle, with unknown consequences on the Cant uptake capacity, making model-based estimates of future ocean acidification of polar regions highly uncertain. Here, we investigated the marine carbonate system in the Ross Sea in order to assess the current anthropogenic carbon content and how physical–biological processes can control the Cant sequestration along the shelf-slope continuum. The Winter Water mass generated from convective events was characterized by high Cant level (28 µmol kg−1) as a consequence of the mixed layer break-up during the cold season, whereas old and less-ventilated Circumpolar Deep Water entering the Ross Sea revealed a very scarce contribution of anthropogenic carbon (7 µmol kg−1). The Cant concentration was also different between polynya areas and the shelf break, as a result of their specific hydrographic characteristics and biological processes: surface waters of the Ross Sea and Terra Nova Bay polynyas served as strong CO2 sink (up to −185 mmol m−2), due to the remarkable net community production, estimated from the summertime surface-dissolved inorganic carbon deficit. However, a large amount of the generated particulate organic carbon was promptly consumed by intense microbial activity, giving back carbon dioxide into the intermediate and deep layers of the continental shelf zone. Further Cant also derived from High-Salinity Shelf Water produced during winter sea ice formation (25 µmol kg−1), fueling dense shelf waters with additional input of Cant, which was finally stored into the abyssal sink through continental slope outflow (19 µmol kg−1). Our results suggest that summer biological activity over the Ross Sea shelf is pivotal for the shunt of anthropogenic CO2 between the organic and inorganic carbon pools, enhancing the ocean acidification of the upper mesopelagic zone and the long-term Cant sequestration into the deep ocean.

ПАДЕНИЕ ПЯТЕН СОЛЕНОЙ ВОДЫ НА НАКЛОННОЕ ДНО В ОКРУЖЕНИИ ПРЕСНОЙ: ДИНАМИКА И СТРУКТУРНЫЕ ОСОБЕННОСТИ РАСПРОСТРАНЕНИЯ ПЛОТНОСТНОГО ФРОНТА ВВЕРХ ПО СКЛОНУ

The study of the dynamics of two small volumes of water with negative buoyancy (patches of salt water), imitated a sinking of dense water into an underlying water, was carried out. These volumes usually appear in the process of surface water cooling during seasonal convection in the coastal zone of the sea. The main tools of investigation were laboratory and numerical experiments. The main stages of motion of patches were identified: sinking, contact, and spreading along a bottom slope. The process of interaction of the water patches during their movement up the bottom slope was detailed in laboratory experiments. Patches of salt water retained unmixed long time, that confirm the laminar character of the appearing flows. Distributions of tracers obtained in the calculations was analyzed with the aim to identify the characteristic stages of the flow of patches up the slope. Three stages were suggested: initial contact, diving, wrapping and breaking. For the first time dense water flow up the slope, which occur as a result of sinking of small volumes of salt water, was described. The results allow us to notice the intensification of mixing of water dense than underlying waters in the process of surface water cooling in coastal zone of the sea.

Slowdown and Recovery of the Atlantic Meridional Overturning Circulation and a Persistent North Atlantic Warming Hole Induced by Arctic Sea Ice Decline

AbstractWe investigate the impact of Arctic sea ice loss on the Atlantic meridional overturning circulation (AMOC) and North Atlantic climate in a coupled general circulation model (IPSL‐CM5A2) perturbation experiment, wherein Arctic sea ice is reduced until reaching an equilibrium of an ice‐free summer. After several decades we observe AMOC weakening caused by reduced dense water formation in the Iceland basin due to the warming of surface waters, and later compensated by intensification of dense water formation in the Western Subpolar North Atlantic. Consequently, AMOC slightly weakens in deep, dense waters but recovers through shallower, less dense waters overturning. In parallel, wind‐driven intensification and southeastward expansion of the subpolar gyre cause a depth‐extended cold anomaly ∼2°C around 50°N that resembles the North Atlantic “warming hole.” We conclude that compensating dense water formations drive AMOC changes following sea ice retreat and that a warming hole can develop independently of the AMOC modulation.

The Mediterranean Sea overturning circulation: A hindcast simulation (1958–2015) with an eddy-resolving (1/36°) model

The interannual variability of the Mediterranean overturning circulation is investigated using a high-resolution (1/36°) ocean model. As the overturning circulation regulates the replenishment and ventilation of the deep layers, we study the spatiotemporal scales of the maximum value of the overturning streamfunction over three main sub-basins of dense water formation (Aegean Sea, Adriatic, and the northwestern Mediterranean). The variability of the zonal overturning is also discussed. The spectrum analysis shows that the overturning variability has its largest signal on annual timescales in all sub-basins, explained by perpetual winter formation. On shorter frequencies (decadal) there are marked differences observed, due to regional processes of the overturning cells, led by buoyancy flux long-term variability in each sub-basin. The decomposition of the total overturning circulation into barotropic, geostrophic shear, and Ekman components revealed weakening and strengthening for the Aegean and Adriatic Sea total overturning, respectively, with opposite trends for the barotropic and geostrophic shear components. The simultaneous contribution of the Ekman and geostrophic component to the total overturning differentiates the variability of zonal overturning circulation from the local meridional overturning circulation of the three sub-basins. The cross spectra between the maximum overturning value and the buoyancy fluxes also revealed that the system keeps the “memory” of this forcing and shows annual variability.

Comprehensive effects of integrated management on reducing nitrogen and phosphorus loss under legume-rice rotations

Paddy fields-based cropping systems are usually located in areas with dense water networks, so nitrogen (N) and phosphorus (P) losses from rice paddy fields caused by runoff might pose a serious pollution risk to their surrounding water bodies. However, current research over establishing a low fertilizer input paddy-based cropping system with comprehensive management for reducing runoff losses of N and P is insufficient. A five-year field trial was carried out with a rice-fava planting system in the Erhai Lake watershed from 2015 to 2019. Three treatments were designed namely chemical fertilizer plus manure (CMF), reduced chemical fertilizer combined with manure at the same application rate under CMF treatment (RF), and returning straw plus chemical and organic fertilizers at the same rate with RF treatment (RFS). The mean annual runoff losses of total N (TN) and total P (TP) range from 0.99 to 1.39 kg ha −1 yr −1 and 0.09–0.12 kg ha −1 yr −1 . Compared with CMF treatment, RF had lower runoff losses of TN and TP by 20.86% and 23.05%, respectively, but the yields and soil fertility were also reduced. After returning straw, soil organic carbon (SOC), TN, and crop yields were maintained or even increased, and runoff losses of TN and TP were further reduced by 9.48% and 7.41%, respectively, compared with RF. Therefore, the runoff losses of N and P decreased by selecting the rice-fava rotation system and reducing chemical fertilizer input through manure application and straw returning, which greatly reduced the surplus N and P in this system. Moreover, the temporal variation in the concentration of TN and TP, along with the N:P ratio approved the existence of potential risk caused by TN and TP losses to the watershed in the early stage of rice growth. Overall, in addition to taking field measures to reduce the N and P runoff losses from paddy fields, the runoff water with high N and P concentrations in early rice growth stage cannot be ignored. • Rice-fava system with low fertilizer maintained yield and had low environment risk. • Straw returning ensured crop yields under substituting chemical fertilizer by manure. • Combined of straw returning and manure substitution reduced nutrient runoff loss. • Runoff N/P concentration and N:P ratio in early stage of rice may need interception.

Topographic effects on buoyancy driven flows along the slope

The flow and descent of dense water masses formed in shallow regions of the ocean is an important leg in the global overturning circulation. The dense overflow waters tend to flow along the continental slopes as geostrophically balanced gravity plumes, but may be steered downslope by canyons and ridges cross-cutting the slopes. In that process, entrainment and mixing will be greatly enhanced. Ilicak et al. (Ocean Model 38:71–84, 2011) propose a parameterization to include the effects of corrugations in large scale models by increasing the vertical mixing locally. We re-visit the problem using the terrain-following Bergen Ocean Model and a DOME-inspired idealized topography. It is shown that the applied corrugations can move the core of the plume 800 m down the slope, while enhanced mixing raises the center of gravity by only 1–200 m. The overall effect of a corrugation is hence to lower the center of gravity, suggesting that the parameterization proposed by Ilicak et al. (Ocean Model 38:71–84) will act in the wrong vertical direction, if used on its own. A comparison of two bottom drag parameterizations, show that a parameterization consistent with a no-slip boundary condition is needed to correctly represent Ekman drainage, and that the Ekman drainage contribution to plume descent is comparable to that of the corrugation. Ridges are more effective in steering dense water downward than canyons, and we compare the dynamics between the two settings to explain the difference.

Coastal oceanographic conditions during a cold front passage over a fish spawning aggregation site located in the Mesoamerican Reef

In this study, an observational campaign that included measurements of coastal currents and thermohaline structure on a fish aggregation reef site during 11–17 March 2017 is analyzed. For the period of the present study, we observed the response of the coastal oceanographic conditions to meteorological forcing. In particular, we described the effects of the cold front passage (locally called a “Norte”) on the water column over a fish aggregation reef site. Before the passage of the Norte, the site was exposed to NE - SE Trade winds, stratification of the water column and sea surface currents moved mainly northward in the alongshore component and offshore in the cross-shore component. However, during the passage of the cold front or Norte, there were changes in the wind field, temperature and atmospheric pressure. Norte conditions were associated with strong northerly winds and with a continuous drop in air temperature. This atmospheric forcing resulted in an evolution of the oceanographic conditions at the reef site from that observed during Trade winds. It changed from stratified to a well-mixed water column, and then dense water on the shallow reef area resulted by cooling and evaporation due to the extreme weather condition during Nortes. This dense water descends down the inner-shelf with density contrast of 0.52 kg/m3 producing a near bottom offshore flow (below 15 m depth). Thus, weather conditions have a determinant role in coastal currents and in the thermohaline structure in the fish aggregation reef site.

Tracing Water Particles Back in Time

Every summer, a low-oxygen pool settles off Canada’s western coast. A new study uses robust modeling to track the origins of the dense water.

Impact of the Novaya Zemlya Bora on the Ocean-Atmosphere Heat Exchange and Ocean Circulation: A Case-Study with the Coupled Model

Novaya Zemlya bora is a strong downslope windstorm in the east of the Barents Sea. This paper considers the influence of the Novaya Zemlya bora on the turbulent heat exchange between the atmosphere and the ocean and on processes in the ocean. Another goal of this study is to demonstrate the sensitivity of simulated turbulent fluxes during bora to model coupling between atmosphere, ocean and sea waves. In this regard, a high-resolution numerical simulation of one winter bora episode was carried out using the COAWST (Coupled-Ocean-Atmosphere-Wave-Sediment Transport) modeling system, which includes the atmospheric (WRF-ARW model), oceanic (ROMS model), and sea waves (SWAN model) components. As shown by the simulation results, in the fully coupled experiment, turbulent heat exchange is enhanced in comparison with the uncoupled experiment (by 3% on average over the region). This is due to the atmosphere-sea-waves interaction, and the results are highly sensitive to the choice of roughness parameterization. The influence of the interaction of the atmospheric and oceanic components on turbulent fluxes in this episode is small on average. Bora has a significant impact on the processes in the ocean directly near the coast, forming a strong coastal current and making a decisive contribution to the formation of dense waters. In the open sea, the bora, or rather, the redistribution of the wind and temperature fields caused by the orography of Novaya Zemlya, leads to a decrease in ocean heat content losses due to a decrease in turbulent heat exchange in comparison with the experiment with flat topography.

Land cover change across 45 years in the world’s largest mangrove forest (Sundarbans): the contribution of remote sensing in forest monitoring

ABSTRACT This study explored the land use land cover (LULC) change over 45 years (1975 -2020) in the world’s largest mangrove forest, Sundarbansusing Landsat imagery. LULC maps were created with same-season imagery with the lowest cloud cover at four intervals: 1975, 1990, 2005, and 2020. Maximum likelihood classification (MLC) was applied to assign five classes: dense forest, moderate forest, sparse forest, barren land, and water body. Accuracy assessment was carried out with 250 control points for each year resulting in overall accuracy and kappa coefficient ranging from 84.8% to 90.0% and 0.81 to 0.87, respectively. Results show dense forest at its highest cover in 1975 and then decreasing by an estimated annual rate of 1.3% from 1975 to 2020, but not consistently. Dense forest class mostly turned moderate and sparse; most of the sparse forest class turned to barren land. Most of the barren lands were located near the boundary between forest and human settlement, and these two classes were more frequent in the Indian part of Sundarbans than in the Bangladesh part. The conclusion is that the time-series of remote sensing data can validly support effective forest management by identifying space and time changes in the biodiversity of Sundarbans.

Open-Ocean Polynyas in the Cooperation Sea, Antarctica

Abstract Extensive studies have addressed the characteristics and mechanisms of open-ocean polynyas in the Weddell and Cosmonaut Seas. Here, we show that more persistent open-ocean polynyas occur in the Cooperation Sea (CS) (60°–90°E), a sector of the Southern Ocean off the Prydz Bay continental shelf, between 2002 and 2019. Polynyas are formed annually mainly within the 62°–65°S band, as identified by sea ice concentrations less than 0.7. The polynyas usually began to emerge in April and expanded to large sizes during July–October, with sizes often larger than those of the Maud Rise polynya in 2017. The annual maximum size of polynyas ranged from 115.3 × 103 km2 in 2013 to 312.4 × 103 km2 in 2010, with an average value of 188.9 × 103 km2. The Antarctic Circumpolar Current (ACC) travels closer to the continental shelf and brings the upper circumpolar deep water to much higher latitudes in the CS than in most other sectors; cyclonic ocean circulations often develop between the ACC and the Antarctic Slope Current, with many of them being associated with local topographic features and dense water cascading. These oceanic preconditions, along with cyclonic wind forcing in the Antarctic Divergence zone, generated polynyas in the CS. These findings offer a more complete circumpolar view of open-ocean polynyas in the Southern Ocean and have implications for physical, biological, and biogeochemical studies of the Southern Ocean. Future efforts should be particularly devoted to more extensively observing the ocean circulation to understand the variability of open-ocean polynyas in the CS. Significance Statement An open-ocean polynya is an offshore area of open water or low sea ice cover surrounded by pack ice. Open-ocean polynyas are important for driving the physical, biogeochemical, and biological processes in the Southern Ocean. Extensive studies have addressed the characteristics and mechanisms of open-ocean polynyas in the Weddell and Cosmonaut Seas. The purpose of this study is to document the existence of more persistent open-ocean polynyas in the Cooperation Sea (60°–90°E) and explore the atmospheric and oceanic forcing mechanisms responsible for the formation of the open-ocean polynyas. Our results would offer a more complete circumpolar view of open-ocean polynyas in the Southern Ocean and have implications for physical, biological, and biogeochemical studies of the Southern Ocean.

Warm surface waters increase Antarctic ice shelf melt and delay dense water formation

Melting ice shelves around Antarctica control the massive input of freshwater into the ocean and play an intricate role in global heat redistribution. The Amery Ice Shelf regulates wintertime sea-ice growth and dense shelf water formation. We investigated the role of warm Antarctic Surface Water in ice shelf melting and its impact on dense shelf water. Here we show that the coastal ocean in summer 2016/17 was almost sea-ice free, leading to higher surface water temperatures. The glacial meltwater fraction in surface water was the highest on record, hypothesised to be attributable to anomalous ice shelf melting. The excess heat and freshwater in early 2017 delayed the seasonal evolution of dense shelf water. Focused on ice shelf melting at depth, the importance and impacts of warming surface waters has been overlooked. In a warming climate, increased surface water heating will reduce coastal sea-ice production and potentially Antarctic Bottom Water formation.

Stability of high-temperature salty ice suggests electrolyte permeability in water-rich exoplanet icy mantles

Electrolytes play an important role in the internal structure and dynamics of water-rich satellites and potentially water-rich exoplanets. However, in planets, the presence of a large high-pressure ice mantle is thought to hinder the exchange and transport of electrolytes between various liquid and solid deep layers. Here we show, using first-principles simulations, that up to 2.5 wt% NaCl can be dissolved in dense water ice at interior conditions of water-rich super-Earths and mini-Neptunes. The salt impurities enhance the diffusion of H atoms, extending the stability field of recently discovered superionic ice, and push towards higher pressures the transition to the stiffer ice X phase. Scaling laws for thermo-compositional convection show that salts entering the high pressure ice layer can be readily transported across. These findings suggest that the high-pressure ice mantle of water-rich exoplanets is permeable to the convective transport of electrolytes between the inner rocky core and the outer liquid layer.

A Cycle of Wind-Driven Canyon Upwelling and Downwelling at Wilmington Canyon and the Evolution of Canyon-Upwelled Dense Water on the MAB Shelf

Submarine canyons provide a conduit for shelf-slope exchange via topographically induced processes such as upwelling and downwelling. These processes in the Wilmington Canyon, located along the shelf-break of the Mid-Atlantic Bight (MAB), have not been previously studied, and the associated hydrographic variability inside the canyon and on the adjacent shelf are largely unknown. Observations from an underwater glider deployed in Wilmington Canyon (February 27 - March 8, 2016), along with wind and satellite altimetry data, showed evidence for a wind-driven canyon upwelling event followed by a subsequent downwelling event. Next, a numerical model of the MAB was developed to more fully represent these two events. Modeled results showed that under upwelling-favorable winds during February 25 - March 3, sea level increased seaward, shelf currents flowed northeastward, and canyon upwelling developed. Then under downwelling-favorable winds during March 4-7, sea level increased landward, shelf currents flowed southwestward, and canyon downwelling developed. Modeling experiments showed that canyon upwelling and downwelling were sub-tidal processes driven by winds and pressure gradients (associated with SSH gradients), and they would occur with or without tidal forcing. During the upwelling period, slope water originating from 150-215 m depths within the canyon (75 m below the canyon rim), was advected onto the shelf, forming a cold and dense canyon-upwelled slope-originated overflow water at the bottom of the outer shelf (75-150 m isobaths). The dense overflow current flowed was directed northeastward and expanded in the cross-shelf direction. It was 5-20 km wide and 10-30 m thick. The estimated volume of the plume overflow water exceeded 6×109 m3 at peak. The density front at the shoreward side of the dense overflow water caused a subsurface baroclinic frontal jet, which flowed northeastward and along-shelf with maximum speed exceeding 0.5 m/s. In the ensuing downwelling event, a portion of the previously upwelled dense water was advected back to the canyon, and then flowed down-slope in the upper canyon in ~0.3 m/s bottom-intensified currents. Dynamical investigation of the overflow current showed that its evolution was governed by unbalanced horizontal pressure gradient force in the cross-shelf direction and that the current was geostrophic.