Natural Convection, Solute Trapping, and Channel Formation during Solidification of Saltwater

Worster, M. Grae; Wettlaufer, J. S.

doi:10.1021/jp9632448

Cited by 102 publications

(87 citation statements)

References 14 publications

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“…From day 1 to day 2, the homogeneous bulk salinity throughout the ice indicates that convection had occurred. However, sea ice has to reach a thickness of about 5 cm for gravity drainage to occur (Worster and Wettlaufer, 1997). Our samples were all thinner than 5 cm.…”

Section: Physical Imprints On Nutrient Incorporationmentioning

confidence: 73%

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

et al. 2014

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a b s t r a c t a r t i c l e i n f oWe investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14°C for 14 days after which ice decay was induced by increasing the air temperature to −1°C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.

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Section: Physical Imprints On Nutrient Incorporationmentioning

confidence: 73%

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

et al. 2014

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“…Another mechanism that could affect the dissolution/precipitation dynamics of trapped ikaite crystals involves convective solutes (Worster and Wettlaufer, 1997) ensuring contact between the interior brine system and the underlying water column. CO 2 -enriched brine can exchange with seawater via gravity drainage (Notz and Worster, 2009) if the brine volume is above 5 % to allow vertical ice permeability (Cox and Weeks, 1975;Notz and Worster, 2009).…”

Section: Spatial and Temporal Variability Of Ikaite Occurrence And Comentioning

confidence: 99%

Ikaite crystal distribution in winter sea ice and implications for CO<sub>2</sub> system dynamics

et al. 2013

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Abstract. The precipitation of ikaite (CaCO 3 ·6H 2 O) in polar sea ice is critical to the efficiency of the sea ice-driven carbon pump and potentially important to the global carbon cycle, yet the spatial and temporal occurrence of ikaite within the ice is poorly known. We report unique observations of ikaite in unmelted ice and vertical profiles of ikaite abundance and concentration in sea ice for the crucial season of winter. Ice was examined from two locations: a 1 m thick land-fast ice site and a 0.3 m thick polynya site, both in the Young Sound area (74 • N, 20 • W) of NE Greenland. Ikaite crystals, ranging in size from a few µm to 700 µm, were observed to concentrate in the interstices between the ice platelets in both granular and columnar sea ice. In vertical sea ice profiles from both locations, ikaite concentration determined from image analysis, decreased with depth from surface-ice values of 700-900 µmol kg −1 ice (∼25 × 10 6 crystals kg −1 ) to values of 100-200 µmol kg −1 ice (1-7 × 10 6 crystals kg −1 ) near the sea ice-water interface, all of which are much higher (4-10 times) than those reported in the few previous studies. Direct measurements of total alkalinity (TA) in surface layers fell within the same range as ikaite concentration, whereas TA concentrations in the lower half of the sea ice were twice as high. This depth-related discrepancy suggests interior ice processes where ikaite crystals form in surface sea ice layers and partly dissolve in layers below. Melting of sea ice and dissolution of observed concentrations of ikaite would result in meltwater with a pCO 2 of <15 µatm. This value is far below atmospheric values of 390 µatm and surface water concentrations of 315 µatm. Hence, the meltwater increases the potential for seawater uptake of CO 2 .

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“…The phase evolution of sea ice is largely characterized by the spacetime variation in , which determines the internal release of latent heat within the system and thereby influences the overall growth rate of the layer and its long time microstructural evolution and desalination [Wettlaufer et al, 1997a, b;Worster and Wettlaufer, 1997]. If we assume that the local solid-liquid coexistence is determined by (1), then the "lever rule" [e.g., Kurz and Fisher, 1984] can be used to infer if the local temperature and the bulk composition are known.…”

Section: Solid Fraction and Brine Volumementioning

confidence: 99%

“…Hence its permeability is lower, and therefore its resistance to flow is greater. Finally, the return flow driven by the abrupt onset of salinity flux penetrates deep within the mushy layer [Worster, 1997;Worster and Wettlaufer, 1997] and gives rise to local solidification and melting, creating "brine channels" which are the principal path for brine drainage from the mushy layer. These mechanisms are basic to the heat and mass transfer in two-phase, twocomponent regions and have been confirmed by the theoretical description that brine expulsion is initially determined by a critical Rayleigh number for the mushy layer:…”

Section: Salinity Fluxesmentioning

confidence: 99%

Solidification of leads: Theory, experiment, and field observations

Wettlaufer¹,

Worster²,

Huppert³

2000

J. Geophys. Res.

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Abstract. Thin sea ice plays a central role in the surface heat and mass balance of the Arctic Ocean. In order to develop understanding of these balances we describe and analyze highly resolved temperature data taken through the air/sea/ice interface during the transition from an ice-free to an ice-covered Arctic Ocean surface. The data were taken to observe the thermodynamic evolution of a lead, a process that has previously only been accessible to measurement techniques confined to the lead edge. Our detailed analysis of the field data is guided by recent theoretical and experimental advances in understanding the phase dynamics of directionally solidified alloys. Because of the dearth of direct observations we also present time series of the relevant heat fluxes inferred from our data and demonstrate the controlling influence that the internal phase evolution has on these quantities. We have previously examined the stability of the brine trapped in a growing sea ice matrix both theoretically and experimentally and now find that haline convection, driven from within the growing layer, is consistent with this previous work and with the nature of direct turbulence measurements. The importance of this process is that although ice growth is continuous, the local brine flux commences abruptly, only after some time, in contrast to what had previously been supposed. Hence the ice growth process itself is a source of intermittency in oceanic boundary layer turbulence. Furthermore, we find that in this particular situation the sea ice growth is not simply a square root function of time, in contrast to the model typically used in numerical simulations. By far the most practical methods of studying lead convection are numerical simulations and laboratory models, and a strong conclusion of this study is the importance of the proper treatment of the boundary conditions describing the buoyancy flux.

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Natural Convection, Solute Trapping, and Channel Formation during Solidification of Saltwater

Cited by 102 publications

References 14 publications

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

Ikaite crystal distribution in winter sea ice and implications for CO<sub>2</sub> system dynamics

Solidification of leads: Theory, experiment, and field observations

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Natural Convection, Solute Trapping, and Channel Formation during Solidification of Saltwater

Cited by 102 publications

References 14 publications

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

Ikaite crystal distribution in winter sea ice and implications for CO&lt;sub&gt;2&lt;/sub&gt; system dynamics

Solidification of leads: Theory, experiment, and field observations

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Ikaite crystal distribution in winter sea ice and implications for CO<sub>2</sub> system dynamics