Onset Of Ice Formation Research Articles

Xylem embolism and bubble formation during freezing suggest complex dynamics of pressure in Betula pendula stems.

Freeze-thaw-induced embolism is a key limiting factor for perennial plants in frost-exposed environments. Gas bubbles are formed during freezing and expand during thawing resulting in xylem embolism. However, when water freezes, its volume increases by 9%, generating local pressures, which can affect the formation of bubbles. To characterize local dynamic of pressure-tension and physical state of the sap during freeze-thaw cycles, we simultaneously used ultrasonic acoustic emissions analysis and synchrotron-based high resolution computed tomography on the diffuse-porous species Betula pendula. Visualization of individual air-filled vessels was performed to measure freeze-thaw induced embolism after successive freeze-thaw cycles down to -10°C or -20°C during the leafy and the leafless periods. We also measured the distribution of gas bubbles in frozen xylem of Betula pendula, and made additional continuous monitoring of embolism spreading during one freeze-thaw cycle using a dedicated cooling system that allowed X-ray scanning during freezing and thawing. Experiments confirmed that ultrasonic emissions occurred after the onset of ice formation, together with bubble formation, whereas the development of embolism took place after thawing in all cases. The pictures of frozen tissues indicated that the positive pressure induced by the volumetric increase of ice can provoke inward flow from the cell wall toward the lumen of the vessels. We found no evidence that wider vessels within a tissue were more prone to embolism although the occurrence of gas bubbles in larger conduits would make them prone to earlier embolism. These results highlight the need to monitor local pressure as well as ice and air distribution during xylem freezing to understand the mechanism leading to frost-induced embolism.

Effect of Gravity on Ice-Layer Growth in a Freezable Heat Exchanger

The effect of gravity on the onset of nucleation and growth rate of the ice layer within a water/ice-phase-change heat exchanger has been experimentally investigated. A compressible bladder within the tube-in-tube heat exchanger provided the room needed for volumetric expansion during the freeze of water to ice without causing structural damage. The pressure drop, water inlet and outlet temperatures, and tube outer wall temperatures were measured, from which the heat transfer rate and onset of ice formation could be determined. By altering the orientation of the water/ice heat exchanger in , it is shown that the onset of freeze is delayed when the water flow is directed downward relative to horizontal and upward flow conditions, thus giving initial insight into the role of gravity in the ice formation process. Characterizing this behavior is important to the development of freeze-tolerant heat exchangers for use in spacecraft thermal control systems.

Results from the University of Toronto continuous flow diffusion chamber at ICIS 2007: instrument intercomparison and ice onsets for different aerosol types

Abstract. The University of Toronto continuous flow diffusion chamber (UT-CFDC) was used to study heterogeneous ice nucleation at the International Workshop on Comparing Ice Nucleation Measuring Systems (ICIS 2007) which also represented the 4-th ice nucleation workshop, on 14–28 September 2007. One goal of the workshop was to inter-compare different ice nucleation measurement techniques using the same aerosol sample source and preparation method. The aerosol samples included four types of desert mineral dust, graphite soot particles, and live and dead bacterial cells (Snomax®). This paper focuses on the UT-CFDC results, with a comparison to techniques of established heritage including the Colorado State CFDC and the AIDA expansion chamber. Good agreement was found between the different instruments with a few specific differences, especially at low temperatures, perhaps due to the variation in how onset of ice formation is defined between the instruments and the different inherent residence times. It was found that when efficiency of ice formation is based on the lowest onset relative humidity, Snomax® particles were most efficient followed by the desert dusts and then soot. For all aerosols, deposition mode freezing was only observed for T<45 K except for the dead bacteria where freezing occurred below water saturation as warm as 263 K.

On the spatiotemporal behavior of sea ice concentration anomalies in the Northern Hemisphere

Reduction in the aerial extent and thickness of sea ice in the Northern Hemisphere is an important element in understanding how the arctic responds to global‐scale climate variability and change. Previous studies have demonstrated a significant reduction in minimum sea ice extent [Serreze et al., 2003] with record reduction in 2005. Observational studies attribute this phenomenon to variations in sea level pressure and large‐scale atmospheric teleconnection patterns such as the Northern Annular Mode (NAM) [Deser et al., 2000; Serreze et al., 2003]. In this study we examine variations in sea ice in the context of spatiotemporal variability of sea ice concentration (SIC) anomalies in the Northern Hemisphere during the onset of ice formation. Examined in particular are timescales associated with coherent regions of persistence in an e‐folding time spatial distribution (EFSD). Annual variations of weekly SIC anomalies are studied and spatial relations between positive and negative SIC anomalies are explored on a hemispheric scale. The results from this investigation demonstrate coherent SIC persistence patterns throughout the Northern Hemisphere, with timescales ranging from 3 to 7 weeks. Spatial correspondence between negative trends in SIC anomalies and the EFSD suggests that the same mechanism may be responsible for both increased ice reduction and persistence in this region. Examination of spatial coherence in SIC anomalies indicates that maximum SIC anomalies prevail near the Kara Sea, Beaufort Sea, and Chukchi Sea regions during late summer/early fall from 1979 to 2004. A latitudinal assessment at 80°, 70°, and 60°N indicates a poleward shift and retreat in SIC anomalies, while also underlining the decadal shift in variability often attributed to the NAM.

Interannual Variability of Sea Ice Area in the Sea of Okhotsk: Importance of Surface Heat Flux in Fall

We examine the interannual variability of the sea ice area in the Sea of Okhotsk in terms of surface heat flux, using highly resolved flux data with the ice concentration taken into account. On the northwest and east Sakhalin shelves, where the initial ice formation occurs, the onset of ice formation is simply determined by the local heat flux in fall (October-November); the degree to which the ocean is cooled by the atmosphere. Consequently, this heat flux mostly determines the interannual variability of sea ice area in the Okhotsk Sea in the initial stage. The air temperature anomaly is the main cause of the heat flux anomaly in fall. The fall heat flux has persistently affected the ice area anomaly, particularly until mid-January. In the later sea ice season, the relationship between the ice area and heat flux is obscured, particularly after mid-January, by the heat insulating effect of sea ice. The ice area variabilities in the southern and northeast regions are correlated with the local heat flux in the months preceding ice appearance, but not strongly. Our analysis suggests that the heat flux does not determine to what extent the ice advances finally in the Okhotsk Sea. Typical heat flux distributions in heavy and light ice years are also presented from our heat flux data: the heat loss center is located in the central Okhotsk Sea in light ice years, and moves to the eastern Okhotsk Sea near the Kuril Straits in heavy ice years.

Heat transfer and power consumption in a scraped-surface heat exchanger while freezing aqueous solutions

Abstract The heat transfer coefficient and the power consumption of a laboratory scraped-surface heat exchanger (SSHE) were measured when it was used for freezing a 10 wt.% sugar solution. Experimental results show that the heat transfer coefficient with phase change (ice formation) was about three to five times greater than that without phase change. Once onset of ice-growth occurred, the torque for driving the scraper started to increase gradually until the scraper was ‘frozen’. The power consumption of SSHE with phase change was modelled in this work, which was influenced considerably by the ice content in the ice slurry. The initial power consumption at the onset of ice formation was however independent of the cooling surface temperature.

Ciliated epibionts on the Arctic sympagic amphipod Gammarus wilkitzkii as indicators for sympago–benthic coupling

In September 2003 specimens of the sympagic amphipod Gammarus wilkitzkii were sampled in drifting pack ice above 50 m water depth and in the pelagic/benthic environment beneath in the coastal waters off Svalbard (Norway). Abundance values ranged between 1.5 and 8 individuals m−2 for the pelagic/benthic and the sympagic environments, respectively, and showed corresponding sex ratios of 1:1.4, favoring males. In the ice a significantly higher number of juveniles prevailed. In contrast, ovigerous females were more abundant among pelagic/benthic living specimens. Approximately 25% of the individuals hosted ciliated epibionts of the genera Ephelota, Cryptacineta, Acineta, Podophrya (all suctoria), and Epistylis (peritrichia). Cryptacineta and Ephelota were the most abundant epibionts on this amphipod species. Female specimens of G. wilkitzkii showed the highest degree of infestation (>2,100 individual epibionts per amphipod specimen: indE/A) followed by juveniles (>1,200 indE/A) and males (>220 indE/A). Highest densities of epibionts were found on anterior body parts with the antennae bearing up to 130 individuals. This is the first sighting of epibionts on crustacea from the sympagic environment. We interpret them as biomarkers that indicate the existence of sympago–benthic coupling processes between the ice and the underlying waters and the seafloor. The population structure and the proportion of infested specimens are equal for the amphipods sampled from both the sympagic and the pelagic/benthic environment, indicating the existence of exchange (coupling) processes between the two habitats. Considering the annual ice cycle, local ice drift patterns, and the shallow water depth in the sampling area, we hypothesize that ice amphipods spend ice-free periods near the seafloor where they may serve as basibionts for protozoans and eventually re-colonize the ice with the onset of ice formation. Our observations strongly emphasize that shallow coastal areas serve as both retention (rather than sink) areas for ice fauna during ice-free periods, and as stepping-stones for re-colonizing the ice when the ice is formed in winter.

Mixed layer evolution in the Sea of Okhotsk observed with profiling floats and its relation to sea ice formation

The time evolution of the ocean mixed layer in the seasonal sea ice zone of the Okhotsk Sea has been observed with profiling floats. The heat storage rate in the mixed layer estimated from the float data well coincides with the surface heat flux. Mixed layer deepening and the onset of ice formation can be well reproduced by a bulk mixed layer model, suggesting that onset of ice formation can be predicted by local atmospheric conditions. This explains the remarkably high correlation of the onset day of sea ice formation with the surface heat loss in the preceding fall. The anomalously large heat loss in the fall of 2000 led to the anomalously early ice formation. Strong stratification due to the Amur River fresh water flux is indispensable for ice formation through suppression of deep convection.

Heat transfer at the subcooled‐scraped surface with/without phase change

AbstractContinuous heat extraction is important for the process of freeze concentration of aqueous solutions, in which water is removed as solid ice. Three typical unsteady heat transportation patterns were distinguished at the subcooled surface of a scraped‐surface heat exchanger (SSHE) in this study. They were found in different stages of freeze concentration. Experimental measurement of the heat‐transfer coefficient in an SSHE showed that the overall heat‐transfer coefficient of stage III, which was characterized by ice formation on the cooler surface, was about 1.5 times higher than stage I, where no ice formed. Although the ice layer (also known as ice fouling) on a heat exchanger surface may be considered disadvantageous for heat transfer, the initial ice formation actually “boosted up” the heat transportation in an SSHE. The mechanism analysis and mathematical modeling of this phenomenon, however, have not been found in the literature. A mathematical model is developed and a unified expression of the heat‐transfer coefficient in an SSHE with/without phase change is presented. The model predicts a step increase of heat transfer occurs at the onset of ice formation and the maximum heat‐transfer coefficient exists in a narrow range right after reaching the freezing point. These are consistent with the experimental results of this study.

Supercooling Capacity Increases from Sea Level to Tree Line in the Hawaiian Tree Species Metrosideros polymorpha.

Population-specific differences in the freezing resistance of Metrosideros polymorpha leaves were studied along an elevational gradient from sea level to tree line (located at ca. 2500 m above sea level) on the east flank of the Mauna Loa volcano in Hawaii. In addition, we also studied 8-yr-old saplings grown in a common garden from seeds collected from the same field populations. Leaves of low-elevation field plants exhibited damage at -2 degrees C, before the onset of ice formation, which occurred at -5.7 degrees C. Leaves of high-elevation plants exhibited damage at ca. -8.5 degrees C, concurrent with ice formation in the leaf tissue, which is typical of plants that avoid freezing in their natural environment by supercooling. Nuclear magnetic resonance studies revealed that water molecules of both extra- and intracellular leaf water fractions from high-elevation plants had restricted mobility, which is consistent with their low water content and their high levels of osmotically active solutes. Decreased mobility of water molecules may delay ice nucleation and/or ice growth and may therefore enhance the ability of plant tissues to supercool. Leaf traits that correlated with specific differences in supercooling capacity were in part genetically determined and in part environmentally induced. Evidence indicated that lower apoplastic water content and smaller intercellular spaces were associated with the larger supercooling capacity of the plant's foliage at tree line. The irreversible tissue-damage temperature decreased by ca. 7 degrees C from sea level to tree line in leaves of field populations. However, this decrease appears to be only large enough to allow M. polymorpha trees to avoid leaf tissue damage from freezing up to a level of ca. 2500 m elevation, which is also the current tree line location on the east flank of Mauna Loa. The limited freezing resistance of M. polymorpha leaves may be partially responsible for the occurrence of tree line at a relatively low elevation in Hawaii compared with continental tree lines, which can be up to 1500 m higher. If the elevation of tree line is influenced by the inability of M. polymorpha leaves to supercool to lower subzero temperatures, then it will be the first example that freezing damage resulting from limited supercooling capacity can be a factor in tree line formation.

Experimental results of the time to the onset of ice formation at metal surface and a correlation based on a sub-layer reactor model

Experimental results of the time to the onset of ice formation at metal surface and a correlation based on a sub-layer reactor model

The effects of cooling, freezing, and thawing on cardiac and skeletal muscle of the turtle, Chrysemys picta

1. 1. Seven adult painted turtles, after freeze anesthesia and pithing, were subjected to a prolonged cooling and freezing, followed by thawing and rewarming to room temperature. A 6 cm in diameter hole in the plastron allowed recording of ventricular temperature and tension plus the EKG. Stimulating electrodes and a thermocouple inserted a hind leg were used to monitor the responsiveness of the leg musculature. 2. 2. This preparation allowed simultaneous recording of ventricular contraction and EKG in relation to heart temperature and of leg muscle contraction relative to leg temperature. In spite of added insulation, the legs cooled and froze quicker and also thawed faster than did the body cavities. 3. 3. Both muscle tension and contraction time were strongly temperature dependent during cooling. Although the leg muscles continued to function for several minutes after the onset of ice formation, they ceased to respond at an average exotherm temperature of −0.6°C. Recovery of responsiveness, noted in five of the seven turtles, was slow and only first noted at temperatures ranging from 1.9 to 17.4°C. 4. 4. Cardiac tension and contraction times were likewise temperature dependent, and the contractions continued for several minutes after the onset of ice formation, eventually ceasing at an average exotherm temperature of −0.62°C. Some of the turtles showed a dramatic (i.e. ten-fold) slowing of the heart during the exotherm. Recovery of heart beat during the thaw was rapid and occurred at an average temperature of −0.4°C. The tensions during warming were higher than the corresponding tensions during cooling, perhaps due to a partial desiccation of the ventricle. 5. 5. The EKG was the most persistent of the responses monitored, and, in at least four turtles, continued well past the point of cessation of cardiac contractility. The explanation for this uncoupling of electrical and mechanical activity remains uncertain.

Environment and aquatic vegetation of a riverside lagoon in Northern Sweden

The environmental conditions and aquatic vegetation of a riverside lagoon (backwater, Sw. “ava”) in northern Sweden were studied during a 3-year period (1975–1977). Conditions were compared with those in the main river. During spring and summer, the lagoon is joined to the river by a back-eddy, up a channel. During the autumn and winter period, when the river flow is reduced and the water level sinks, the channel dries up and the lagoon becomes an isolated water-body. The coincidence of the time of lowest water level in the lagoon with the onset of ice formation in the autumn leads to freezing of the bottom sediments over wide areas, which induces rapid vegetational changes. The zonation of the littoral and sublittoral vegetation does not solely depend on hydrological factors; bottom freezing and tjaele formation (Sw. “tjäle”; frozen subsoil) are also important. The aquatic vegetation has been affected by human influences, such as timber floating and seine fishing. The aquatic vegetation in the lagoon is more species-rich than that in the main river, including, for instance, Stratiotes aloides L. This difference is due to the lentic, instead of lotic conditions and to the richer substrate in the lagoon. Four ecological groups of aquatic macrophytes were distinguished, one of which is entirely dependent on the environmental conditions prevailing in the lagoon.