Lars H. Smedsrud and Ragnheid Skogseth
Field measurements of Arctic grease ice properties and processes
Cold Regions Science and Technology (2006), Volume 44, Issue 3, April, 171-183,  doi:10.1016/j.coldregions.2005.11.002. Copyright Elsevier. Further reproduction or electronic distribution is not permitted.

In situ measurements of grease ice from fjords on Svalbard reveal new basic properties of the surface ice cover. New ice formation often takes place as growing frazil crystals in a surface layer of grease ice. A method for sampling grease ice is described. The grease ice layer is found to be as thick as 70 cm in places, but many of the measurements are around 10 cm. Salinity of the bulk grease ice is around 25 psu, while the drained grease has salinity around 20 psu. Ice concentration is calculated based on the measured salinity and is around 25% for the grease, and above 60% for the new solid ice. Atmospheric and oceanographic forcing, as well as hydrography of the polynya in Storfjorden on Svalbard, are also presented. Salt release from the growing grease ice clearly influences local hydrography, and local tidal currents, as strong as 53 cm/s, keep the polynya open during calm wind conditions. This indicates the strong links between the grease ice layer and the boundary layers above and below. Existing parameterizations for grease ice thickness in relation to wind speed are discussed and found to be inadequate. We suggest that tidally driven turbulence and the effect of snow drift is significant to include in future theoretical descriptions of grease ice processes.
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Lars H. Smedsrud, Adrian Jenkins, David M. Holland and Ole A. Nøst
Modeling ocean processes below Fimbulisen, Antarctica
Journal of Geophysical Research (2006) Volume 111, C01007, doi:10.1029/2005JC002915. Copyright AGU. Further reproduction or electronic distribution is not permitted.

Model simulations of circulation and melting beneath Fimbulisen, Antarctica, obtained using an isopycnic coordinate ocean model, are presented. Model results compare well with available observations of currents and hydrography in the open ocean, to the north of Fimbulisen and suggest that Warm Deep Water exists above the level of a sub ice shelf bedrock sill - the principal pathway for warm waters to enter the sub ice shelf cavity. The model shows a southward inflow of Warm Deep Water over this sill and into the cavity, producing a mean cavity temperature of -1.0 C. This leads to high levels of basal melting (>10 m/a) at the grounding line of Jutulstraumen, and an average melting over the ice shelf base close to 1.9 m/a. The southward inflow is a compensating flow caused by the northward outflow of fresh, cold water produced by the basal melting. Results on inflow and melting are difficult to validate as no in situ measurements yet exist in the cavity. If such high melt rates are realistic, the mass balance of Fimbulisen must be significantly negative and the ice shelves along Queen Maud Land must contribute about 4.4 mSv of melt water to the Weddell Sea, about 15% of the total Antarctic meltwater input to the Southern Ocean.
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Lars H. Smedsrud , W. Paul Budgell, Alastair D. Jenkins , and Bjørn Ådlandsvik
Fine scale sea ice modelling of the Storfjorden polynya
Accepted for publication in Annals of Glaciology (2006)

A polynya appears regularly in Storfjorden on the east side of the Svalbard archipelago. It is mainly forced by offshore winds and contributes around 10% of the brine water produced on Arctic shelves. We apply a regional ocean model (ROMS), including a sea ice model, on a fine grid (2~km) that allows us to reproduce some key processes of the polynya opening and closing events during January-April 2000. The polynya remains open as long as the offshore winds exist, and reaches a width along the direction of the wind of 10-20 km. We suggest using a mean sea ice thickness of less than 0.3 m as the polynya criterion, as our computations show no sharp changes in the horizontal gradients in sea ice concentration and thickness. Results show a general freezeup during December and January, with a mean polynya area within the fjord of 33 by 50 km. Some model results including sea ice cover and drift speed can be partially validated using satellite imagery, but in general are there no measurements available at this scale.
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Lars H. Smedsrud
Warming of the deep water in the Weddell Sea along the Greenwich meridian: 1977 - 2001
Deep Sea Research Part I (2005)  Volume 52, February, Issue 2, 241 - 258. Copyright Elsevier. Further reproduction or electronic distribution is not permitted.

The Weddell Deep Water (WDW) has warmed substantially along the Greenwich meridian after the Weddell Polynya of the 1970's. Areas affected by the polynya received ~14 GJ/m² more heat in 2001 than in 1977. This warming would require a flux of ~ 390 W/m² if it were to take place over a year. Large variations in heat content of the WDW is found between the Antarctic coast and Maud Rise (64°S). The small variation found north of Maud Rise is in opposite phase to that to the south, and the warming was  close to monotonic south of 68°S. The mean warming of WDW along the section is ~0.032°C per decade, comparable to the warming of the Antarctic Circumpolar Current. The mean warming compares with a surface heat flux of 4 W/m² over the 25 year period, an order of magnitude higher than the warming of the global ocean. As variation in mean salinity of the WDW follows the warming/cooling events, variation in inflow probably explains a cooling event between 1984 and 1989, and a warming event between 1989 and 1992.  Cooling during the late 1990's is probably related to re-appearance of a polynya like feature in some winter months as an area of 100 km in diameter close to Maud Rise with 10-20 % lower sea ice concentrations than the surrounding ocean.
E. Fahrbach, M. Hoppema, G. Rohardt, M. Schröder and A. Wisotzki
Causes of deep-water variation: Comment on the paper by L.H. Smedsrud “Warming of the deep water in the Weddell Sea along the Greenwich meridian: 1977–2001”
Deep Sea Research Part I (2006) Volume 53, March, Issue 3, 574-577. doi: 10.1016/j.dsr.2005.12.003, Copyright Elsevier. 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.
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Ragnheid Skogseth and Lars H. Smedsrud
Report from ProClim field survey in the Storfjorden polynya and on fast ice in Storfjorden April 16 to 24 2004
Geophysical Institute, University of Bergen, Report No.3- 2005. ISBN 82-8116-005-5

During April 2004 a field survey was conducted along the northern edge of the polynya in Storfjorden. In periods with persistent and strong easterly winds, the polynya length (east-west) reached a size of 20-30 km, and the polynya width (north-south) was from the northern fast ice border to the southern tip of Edgeøya. The subsequent refreezing was followed along the northern edge of the polynya, measuring new ice formation and water properties. The water column was close to the freezing point with salinity around 34.6. Newly formed slush and niilas gathered along the edge. Tidal currents reached 50 cm/s in Freemansundet, and were observed
to be strong enough to open up a small polynya in a period with calm wind and little pack ice. Data collected include air temperature, humidity and wind, CTD profiles, ocean currents, as well as sea ice and slush thickness and salinity. To our knowledge, this is the first in-situ data set from a refreezing Arctic polynya, and will serve as good validation for ongoing regional numerical modelling. Sea ice properties will be valuable for ground-truth validation of remote sensing of sea ice growth.

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Lars 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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.