Brine Formation and Mobilization in Submarine Hydrothermal Systems: Insights from a Novel Multiphase Hydrothermal Flow Model in the System H2O–NaCl

Numerical models have become indispensable tools for investigating submarine hydrothermal systems and for relating seafloor observations to physicochemical processes at depth. Particularly useful are multiphase models that account for phase separation phenomena, so that model predictions can be compared to observed variations in vent fluid salinity. Yet, the numerics of multiphase flow remain a challenge. Here we present a novel hydrothermal flow model for the system H2O–NaCl able to resolve multiphase flow over the full range of pressure, temperature, and salinity variations that are relevant to submarine hydrothermal systems. The method is based on a 2-D finite volume scheme that uses a Newton–Raphson algorithm to couple the governing conservation equations and to treat the non-linearity of the fluid properties. The method uses pressure, specific fluid enthalpy, and bulk fluid salt content as primary variables, is not bounded to the Courant time step size, and allows for a direct control of how accurately mass and energy conservation is ensured. In a first application of this new model, we investigate brine formation and mobilization in hydrothermal systems driven by a transient basal temperature boundary condition—analogue to seawater circulation systems found at mid-ocean ridges. We find that basal heating results in the rapid formation of a stable brine layer that thermally insulates the driving heat source. While this brine layer is stable under steady-state conditions, it can be mobilized as a consequence of variations in heat input leading to brine entrainment and the venting of highly saline fluids.

A thermodynamic description for the hygroscopic growth of atmospheric aerosol particles

The phase state of atmospheric particulate is important to atmospheric processes, and aerosol radiative forcing remains a large uncertainty in climate predictions. That said, precise atmospheric phase behavior is difficult to quantify and observations have shown that “precondensation” of water below predicted saturation values can occur. We propose a revised approach to understanding the transition from solid soluble particles to liquid droplets, typically described as cloud condensation nucleation – a process that is traditionally captured by Köhler theory, which describes a modified equilibrium saturation vapor pressure due to (i) mixing entropy (Raoult's law) and (ii) droplet geometry (Kelvin effect). Given that observations of precondensation are not predicted by Köhler theory, we devise a more complete model that includes interfacial forces giving rise to predeliquescence, i.e., the formation of a brine layer wetting a salt particle at relative humidities well below the deliquescence point.

Hydrochemistry Research of Intercrystalline with Pore Brine and Pre-3D Modelling of Heibeiwadi Brine Deposit

Intercrystalline and pore brine develop extensively in the Heibewadi research area which is located at south foot of Altun mountain of Qaidam basin. In central area, intercrystalline brine’s depths range from 5m to 90m. In northwest, south area and central deeper area, pore brine develops under intercrystalline brine layer. The 2 types of aquifers have strong yield property, TDS is 200-350g/l with average of 276g/l. Main salt compound can be mined out economically. According to analysis result of intercrystalline brine, TDS, Cl-, Na+, K+, Mg2+, Li+ irons’ grades are very steady. That mean intercrystalline brine exist in the water-salt system under balance. Only the stability of Ca2+ and SO42- are slightly poor. According the Kurtosis characteristics analysis, Ca2+, SO42- are no-normal positively platykurtic distribution, K+, Cl- and PH are normal positively platykurtic distribution. These 2 groups fall into a sub-class. And the combined with normal negatively platykurtic distribution-TDS and fall into platykurtic distribution group. Mg2+, Li+ are normal positively peaked distribution; Na+ is normal negatively peaked distribution. They all belong to peaked distribution group. According to Na+, K+, Mg2+//Cl-H2O quarternary phase diagram and Na+, K+, Mg2+//Cl-SO42-H2O pentabasic phase diagram, the chlorite and magnesium sulfate subtype have different hydro chemical characteristics and salting-in and salting-out rules.

A thermodynamic description for the hygroscopic growth of atmospheric aerosol particles

The phase state of atmospheric particulate is important to atmospheric processes and aerosol radiative forcing remains a large uncertainty in climate predictions. That said, precise atmospheric phase behavior is difficult to quantify and observations have shown that precondensation of water below predicted saturation values can occur. We propose a revised approach to understanding the transition from solid soluble particles to liquid droplets, typically described as cloud condensation nucleation – a process that is traditionally captured by Köhler theory, which describes a modified equilibrium saturation vapor pressure due to I. mixing entropy (Raoult's law) and II. droplet geometry (Kelvin effect). Given that observations of precondensation are not predicted by Köhler theory, we devise a more complete model which includes interfacial forces giving rise to predeliquescence, i.e., the formation of a brine layer wetting a salt particle at relative humidities well below the deliquescence point.

Numerical Solution of Rapid Freezing of Sea Water on Cold Substrates

Rapid freezing of sea water on a cold substrate of spongy ice is investigated. The mechanism of transient ice accretion on cold substrates is different than slow freezing of salt water. An investigation of rapid freezing in this paper fills a gap of knowledge related to periodic icing of salt water on marine and offshore structures. The equation of transient heat conduction through brine-spongy ice is analyzed. Rapid freezing causes complete salt trapping, which makes the salinity constant and stable at the phase interface during the solidification. A thin layer of salt water is considered in contact with a spongy substrate. A finite difference method is employed to calculate the rate of solidification of the brine layer and consequently the thickness of ice accumulated. The discretization is based on the Method of Lines (MOL) which is a useful numerical-iterative method for boundary moving problems. Numerical results show that colder substrates and brine layers have the potential to create a thicker layer of new ice.

Detecting the Depth of a Subsurface Brine Layer in Lop Nur Lake Basin Using Polarimetric L-Band SAR

Lop Nur once was a huge lake located in northwestern China. At present, there is no surface water in Lop Nur Lake basin and on SAR images it looks like an “Ear.” The objective of this paper is to retrieve the depth of subsurface brine layer in Lop Nur by copolarized phase difference of surface scattering. Based on field investigation and analysis of sample properties, a two-layer scattering structure was proposed with detailed explanations of scattering mechanisms. The relationship between copolarized phase difference and the brine layer depth in the region of Lop Nur were studied. The copolarized phase difference of surface scattering was extracted by model-based polarimetric decomposition method. A good linear correlation between measured subsurface brine layer depth and copolarized phase difference with R2 reaching 0.82 was found. Furthermore, the subsurface brine layer depth of the entire lake area was analyzed. According to the retrieved maps, some interesting phenomena were found, and several hypotheses about the past water withdrawal process and the environmental evolution had been proposed to theoretically explain these phenomena. Based on the penetration capability of SAR the reconstruction of historical evolution process of Lop Nur will be an interesting topic for future research.

Liquid-like layers on ice in the environment: bridging the quasi-liquid and brine layer paradigms

Liquid-like layers on ice significantly influence atmospheric chemistry in polar regions. In the absence of impurities a nanoscale region of surface disorder known as the "quasi-liquid layer" (QLL) may exist below the bulk melting point (down to ~−30 °C). Surface and bulk impurities are known to modulate the QLL thickness. In aqueous systems containing ionic solutes, a liquid brine layer (BL) may form upon freezing due to the exclusion of impurities from the ice crystal lattice coupled with freezing point depression in the concentrated surface layer. Brine layers are conceptually distinct from the QLL, which can exist in the absence of impurities. We have developed a unified model for liquid-like layers in environmental ice systems that is valid over a wide range of temperatures and solute concentrations, spanning the QLL and BL regimes. The model consists of two coupled modules describing the thickness of the BL and the QLL. The BL module is derived from fundamental equlibrium thermodynamics, whereas the QLL formulation is derived semi-empirically based on statistical mechanical principles and previously published QLL thickness data. The resulting unified model has been tested against experimental data from literature and applied to several environmentally important systems, such as HCl(g)-ice, HNO3(g)-ice, and frozen sea ice. This model can be used to improve the representation of air-ice chemical interactions in polar atmospheric chemistry models.