M. Årthun, T. Eldevik, L. H. Smedsrud, Ø. Skagseth, and R. B. Ingvaldsen.
Quantifying the Influence of Atlantic Heat on Barents Sea Ice Variability and Retreat
Journal of Climate, Volume 25, pages 4736-4743, doi:10.1175/JCLI-D-11-00466.1, 2012
T. Hattermann, O. A. Nøst, J. M. Lilly, and L. H. Smedsrud
Two years of oceanic observations below the Fimbul Ice Shelf, Antarctica
Geophys. Res. Lett., Volume. 39, L12605, doi:10.1029/2012GL051012, 2012. Copyright AGU. Further reproduction or electronic distribution is not permitted.
Lars H. Smedsrud
Causes of deep-water variations: Reply to comment by E. Fahrbach, M. Hoppema, G. Rohardt, M. Schroder and A Wisotzki
Deep Sea Research Part I (2006) Volume 53, March, Issue 3, 578-580. doi: 10.1016/j.dsr.2005.12.010, Copyright Elsevier. Further reproduction or electronic distribution is not permitted.
H. Smedsrud and Adrian Jenkins
Frazil Ice Formation in an Ice Shelf Water Plume
Journal of Geophysical Research - Oceans (2004) Volume 109, Number C3, C03025, 10.1029/2003JC001851, Copyright AGU. Further reproduction or electronic distribution is not permitted.
We present a model for the growth of frazil ice crystals and their accumulation as marine ice at the base of Antarctic ice shelves. The model describes the flow of buoyant water upwards along the ice shelf base, and includes the differential growth of a range of crystal sizes. Frazil ice formation starts when the rising plume becomes supercooled. Initially the majority of crystals have a radius of ~0.3 mm, and concentrations are below 0.1 g/l. Depending on the ice shelf slope, which controls the plume speed, frazil crystals increase in size and number. Typically crystals up to 0.8 mm in radius are kept in suspension, and concentrations reach a maximum of 0.4 g/l. The frazil ice in suspension decreases the plume density and so increases the plume speed. Larger crystals precipitate upwards onto the ice shelf base first, with smaller crystals following as the plume slows down. In this way marine ice is formed at rates of up to 4 m/year in some places, consistent with areas of observed basal accumulation on Filchner-Ronne Ice Shelf. The plume continues below the ice shelf as long as it is buoyant. If the plume reaches the ice front, its rapid rise produces high supercooling and the ice crystals attain a radius of several mm before reaching the surface. Similar ice crystals have been trawled at depth north of Antarctic ice shelves, but otherwise no observations exist to verify these first predictions of ice crystal sizes and volumes.
Lars H. Smedsrud
Formation of turbid ice during autumn freeze up in the Kara Sea
Polar Research (2003) Volume 22, Number 2, 267 - 286.
A 1-D (vertical) model is used to estimate the mass of ice rafted sediment in turbid sea ice on the shallow Kara Sea shelf during autumn freeze up. Sediment is entrained into the ice through aggregation with frazil ice crystals that are diffused downwards by wind-generated turbulence. Data from local meteorological stations are discussed and used to force the model, while water stratification and sediment concentrations from the area are used to initiate the model. Model results indicate a 0.2 m thick layer of slush ice created during 48 h with a mean wind of 6 m/s and an air temperature of -10°C. This ice contains ~ 20 mg/l of sediment, or in total ~ 2 % of the annual sediment discharge by nearby rivers. In shallow areas (< 20 m depth) the process is very effective with winds of ~12 m/s, and the process can incorporate many years of sediment discharge. In the deeper areas (> 20 m depth) the strong salinity stratification implies that winds above 18 m/s are needed for the process to be effective. For the rest of the winter months the same process may lead to additional sediment incorporated in a coastal polynya, but the freeze up alone has the capacity to incorporate the total summer discharge of sediment into the surface ice. Calculated sediment concentrations in the surface ice cover are in the range 3 mg/l - 19 g/l, in good agreement with available field data.
L. H. Smedsrud, T. M. Saloranta, P. M. Haugan, and T. Kangas
Sea ice formation on a very cold surface
Geophysical Research Letters (2003) Volume 30 , Number 6, 1284, doi:10.1029/2002GL016786, Copyright AGU. Further reproduction or electronic distribution is not permitted.
In this study laboratory experiments of sea ice formed on a vertical surface with initial temperature of -30 to -50°C are presented. The ice formation is rapid, and in 300 s >5 mm of sea ice is formed. Ice formation cooled and salinified the water, and induced a vertical down wards flow of ~5 mm/s with a boundary layer about 5 mm thick. This ice has a structure with columnar crystals that have small circular cross sections (0.2-1.0 mm) and sea ice salinities are between 24 and 32. A simple model approach indicate that the thermal conductivity of such ice is lower than for other types of sea ice.
Lars H. Smedsrud
A model for entrainment of sediment into sea ice by aggregation between frazil ice crystals and sediment grains
Journal of Glaciology (2002), Volume 48, Number 160, 51-61.
A vertical numerical model that simulates tank experiments of sediment entrainment into sea ice has been developed. Physical processes considered were: turbulent vertical diffusion of heat, salt, sediment, frazil ice and their aggregates; differential growth of frazil ice crystals; secondary nucleation of crystals; and aggregation between sediment and ice. The model approximated the real size distribution of frazil ice and sediment using 5 classes of each. Frazil crystals (25 mikro m to 1.5 cm) were modeled as disks with a constant thickness of 1/30 their diameter. Each class had a constant rise velocity based on the density of ice and drag forces. Sediment grains (1- 600 mikro m) were modeled as constant density spheres, with corresponding sinking velocities. The vertical diffusion was set constant for experiments based on calculated turbulent rms velocities and dissipation rates from current data. The balance between the rise/sinking velocities and the constant vertical diffusion is an important feature in the model. The efficiency of the modeled entrainmentprocess was estimated through ß, an aggregation factor . Values for ß are in the range < 0.0003, 0.1 >, but average values are often close to 0.01. Entrainment increases with increasing sediment concentration and turbulence of the water, and heat flux to the air.
Lars H. Smedsrud
Frazil ice entrainment of sediment: large-tank laboratory experiments
Journal of Glaciology (2001) Volume 47, Number 158, 461 - 471.
Laboratory experiments that simulate natural ice formation processes and sediment entrainment in shallow water are presented. A 10 - 30 cm/s current was forced with impellers in a 20 m long and 1 m deep indoor tank. Turbulence in the flow maintained a suspension of sediments at concentrations of 10 - 20 mg/l at a depth of 0.5 m. Low air temperatures (-15°C) and 5 m/s winds resulted in total upward heat fluxes in the range 140 - 260 W/m². The cooling produced frazil ice crystals up to 2 cm in diameter with concentrations up to 4.5 g/l at 0.5 m depth. Considerable temporal variability with time scales of less than 1 minute was documented. A close to constant portion of the smaller frazil crystals remained in suspension. After some hours the larger crystals, which made up the majority of the ice volume, accumulated as slush at the surface. Current measurements were used to calculate the turbulent dissipation rate, and estimates of vertical diffusion were derived. After 5 - 8 hours sediment concentrations in the surface slush were normally close to those of the water. After 24 hours, however, concentrations in the slush were 2-4 times higher. Data indicate that sediment entrainment depends on high heat fluxes and correspondingly high frazil ice production rates, as well as sufficiently strong turbulence. Waves do not seem to increase sediment entrainment significantly.
Lars H. Smedsrud
Incorporation of sediments into sea ice in coastal polynyas in the Kara sea
Report (2000) Norwegian Polar Institute, April 10.
Estimates for the mass of ice rafted sediments in coastal polynyas in the Kara Sea are given by use of a vertical numerical model. The incorporation of sediment take place as frazil ice crystals form and aggregate with sediments in suspension. Three different cases are considered: i) The autumn freeze up where there is no sea ice initially, ii) A mean monthly coastal polynya based on monthly SSMI derived ice drift, and iii) A case study in January - March 1994 with 3 day means of ice drift from SAR images. The model is forced by observed air temperature and wind speed from nearby meteorological stations. Results indicate that the process is capable incorporating about 10 % of the annual sediment discharge during an average winter, and that episodes with values substantially higher may take place. Several years of sediment discharge may be incorporated during an autumn freeze under high winds, and a mean monthly mass of ice rafted sediments may be incorporated during 3 days given a high northwards speed of the ice cover.
Lars H. Smedsrud
Frazil ice formation and incorporation of sediments into sea ice in the Kara Sea
Dr. Scient. Thesis (2000) Geophysical Institute.
Frazil ice formation in turbulent salt water is investigated through laboratory experiments and numerical modeling. Increasing frazil ice volumes and change in the size distribution are observed. Frazil ice aggregate with sediments in suspension, and form a surface ice cover. The efficiency of the process is estimated empirically and results are applied to field data from the Kara Sea continental shelf by use of the developed model. Field samples of sediment laden sea ice from the Kara Sea are presented and compared to the estimates. A substantial mass of sediments may be incorporated by the aggregation process given high levels of turbulence, i.e. strong wind under natural conditions.
Lars H. Smedsrud
Estimating aggregation between suspended sediments and frazil ice
Geophysical Research Letters (1998) Volume 25, Number 20, 3875 -3878. Copyright AGU. Further reproduction or electronic distribution is not permitted.
This paper aims to describe the scavenging process, one of the main processes for incorporating sediments (particles) into sea ice. An experiment with suspended sediment and frazil ice in a homogeneous turbulent flow is presented. At the end sediment where incorporated into the surface grease ice. The ice production was constant, and calculated from the salinity measurements, while the turbulent dissipation rate was calculated from high resolution current measurements. A model for aggregation between suspended sediment and frazil is also presented and used to simulate the experiment. The modeled aggregation process depends primarily on concentrations, on the turbulence levels, and on the (constant) radii of the sediments and ice. Efficiency of the aggregation process is estimated from the model and experimental results, and the "aggregation" factor is found to be ~ 0.025. This is consistent with theoretical estimates, qualitative observations from laboratory experiments, and field data. Sensitivity analyses suggest that the results do not depend greatly on uncertainty of model parameters.