the proximity of the Antarctic Peninsula, the South ShetlandIslands and the South Orkney Islands, allowing a much moregradual transition from the deep pack-ice to the open ocean bound-ary.

We wish to thank Brett Castillo, Robert Swayzer, PrestonSullivan, Peter Amati, and John Cavanaugh for recording hourlyice observations. Thanks are also extended to Herb Baker formaking and mounting the ice calibration stick over the side of theship, and to the captain and crew of the Nathaniel B. Palmer fortheir support. Thanks to everybody's cooperation, the mostcomplete set of ice observations were taken. This work wassupported by National Science Foundation grant DPP 90-24809.

References

Ackley, S. F., V. Lytle, B. Elder, and D. Bell. 1992. Sea-ice investigationson Ice Station Weddell #1: I. Ice Dynamics. Antarctic Journal of the U. S.,this issue.

Ackley, S. F. and V. I. Lytle. 1992. Sea-ice investigations on Ice StationWeddell #1: II. Ice thermodynamics. Antarctic Journal of the U.S., thisissue.

Ackley, S. F., A. J. Cow, V. I. Lytle, M. N. Darling, and N. E. Yankielun.1992. Sea-ice investigations on Nathaniel B. Palmer: Cruise 92-2.Antarctic Journal of the U.S., this issue.

Ackley, S. F., S. J . Smith, and D. B. Clarke. 1982. Observations of packice properties in the Weddell Sea. Antarctic Journal of the U.S., 17(5):104-106.

Allison, I. 1989. The East Antarctic Sea Ice Zone: Ice characteristics anddrift. GeoJournal, 18, 103-115.

Snow properties and surface-elevation profiles in thewestern Weddell Sea,

(Nathaniel B. Palmer 92-2)

V. I. LYTLE AND S. F. ACKLEY

Dartmouth College and USA CRRELHanover, New Hampshire 03755

During the Weddell Sea Cruise of the Nathaniel B. Palmer inMay and June 1992, we occupied 15 ice stations, the location ofwhich are shown in Ackley and Gow et al. 1992. At most of thesestations ice cores were collected, surface snow and ice elevationlines were measured, and snow characterization was performed.The core collection and initial results are described in Gow et al.1992; here we describe the snow pit measurements and thesurface elevation surveys. These data will be used to estimate theheat flux to the atmosphere and salt flux to the ocean on the bas-is of snow and ice properties, and also provide surface propertiesto help in the interpretation of microwave satellite remote-sens-ng data.

Thermodynamic ice-growth rate is determined by the heat.lux from the ocean to the atmosphere, which is in turn regulatedy the thickness and properties of the ice and snow cover. Thenow cover can provide an insulating layer, significantly reduc-g the heat flux and slowing down the ice-growth rate. Particu-

larly in the Weddell Sea it has been found, however, that theeight of the snow often depresses the ice surface below sea level

Ackley et al. 1990; Lytle et al. 1990; Lange etal. 1990), resulting inan influx of sea water above the ice surface. As the sea waterinfiltrates the snow pack, a slush layer is created at the snow/ice

terface. As this layer refreezes it will add to the ice thickness asell as acting as a vapor and heat source to modify the snow

cover. Significant algal growth can also occur in this layer(Sullivan et al. 1992). With the influx of this sea water, the ice

becomes isothermal, and continued ice formation occurs abovethe surface of the ice as this slush layer freezes, rather than at thebottom of the ice sheet. This ice formation process will result ina more rapid heat transfer rate to the atmosphere and possibly adifferent salt flux to the ocean than would the growth of congelat-ion ice formed by continued ice growth at the bottom of the icesheet.

This slush layer has been found repeatedly in the Weddell Seaice cover (Ackley and Lytle 1992; Ackley et al. 1990) and thesubsequent refreezing of this slush has been estimated to affect asmuch as 50 percent or more of the total ice area in the westernWeddell Sea. During this cruise, temperature, density, and grainsize measurements were taken in the snow pack to estimate theheat flux through the ice and overlying snow. In addition,elevation measurements were collected to estimate the amount ofice which was above or depressed below sea level and snow andice properties were collected to estimate the amount of ice whichhad been formed due to the refreezing of this slush layer. Thesemeasurements in conjunction with the ice core program in thesame area (Gow et al. 1992), will be used to describe whether thisprocess of the freezing of the slush had also occurred earlier, andto estimate the cumulative associated heat and salt flux.

Two snow pits were dug and analyzed at each station, onenear where the cores were extracted and a second where the radardata were collected (Yankielun and Ackley 1992). Figure 1 is anexample of the data collected from a snow pit on site number 5.Note the large grain sizes near the base of the snow pit, indicatingthat a significant amount of metamorphism has occurred. This ismost likely being influenced by the infiltration of brine, as sup-ported by the salinity (5 ppt) in the bottom layer of the snow.Additional snow pits were analyzed at four of the stations, wherethere were significant variations in snow or ice thickness acrossthe floe. Snow temperatures, densities, dielectric properties,grain sizes, and salinities were measured as a function of depth inthe snow pack. In addition, snow and ice samples were collectedfor stable isotope analysis which will help estimate the relativeamount of snow which had been incorporated in the sea ice.Snow depths for the pits varied from 10 centimeters to 85 centime-ters, with snow salinities varying from 0 ppt up to as much as 63ppt. We found significant variability in the pits both betweensites and at the same sites. The presence of layers in the snow

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Figure 1. Snow pit profile from site number 5. The snow grain size,density, and temperature for each layer are indicated.

Snow Surface

Figure 2. Example of surface profile data. Ice and snow surfaceelevations were measured every 0.5 meters over a 100-meter line.

resulted in order of magnitude variations in snow grain size(<0.25 to 5 millimeters), with many of the deeper pits containinglayers of well-developed depth hoar. Densities varied from 0.20to 0.60 grams per cubic centimeter. These snow data will also beused to help interpret the radar backscatter data which werecollected at each station (Yankielun and Ackley 1992).

In general, two 100-meter surface elevation lines at eachstation were measured. They were positioned at right angles toeach other and measurements of the snow thickness, and theice and snow elevations above sea level were collected at 0.5-meter spacing. In addition, when time allowed, ice thicknessholes were drilled and measured along these same lines at about10-meter spacing. A total of 22 surface elevation lines weremeasured. An example profile line is shown in figure 2. Thesemeasurements, which were taken during the austral winter, didnot in general show the significant below-sea-level portions thatwere seen both on the Ice Station during this year's austral fall(Ackley and Lytle 1992) or in data taken in austral spring (Lytleet al. 1990). We will be examining isotope and structural evi-dence to see if this is a result of freezeback of flooded snow as was observed on the Ice Station profile lines. Based on the ice andsnow elevations above freeboard, isostasy calculations will alsobe used to estimate an average ice thickness for the floe.

The momentum flux from the air to the ice and ocean can behighly dependent on the surface roughness (Andreas et al. 1984Andreas et al. 1992). The surface profiles described above willalso be used to calculate surface roughness spectra and theassociated momentum transfer to the ice due to wind.

We thank Naomi Darling, Brett Castillo, Peter Amati, JohnCavanaugh, and John Evans for their assistance in collecting theprofile measurements. This work was supported by NationalScience Foundation grant DPP 90-24809.

References

Ackley, S. F., M. A. Lange, and P. Wadhams. 1990. Snow cover effects onantarctic sea ice thickness. In S. F. Ackley and W. F. Weeks (Eds.), See,Ice Properties and Processes. CRREL Monograph 90-1.

Ackley, S. F. and V. I. Lytle. 1992. Sea-ice investigations on Ice Station Wed-dell #1:11. Ice thermodynamics. Antarctic Journal of the U.S., this issue.

Ackley, S. F., A. J.Gow, V. Lytle, M. N. Darling, and N. E. Yankielun. 1992.Sea-ice investigations on Nathaniel B. Palmer: Cruise 92-2. AntarcticJournal of the U.S., this issue.

Andreas, E. L, K. J . Claffey, A. P. Makshtas, and B. V. Ivanov. 1992.Atmospheric sciences on Ice Station Weddell. Antarctic Journal of theU.S., this issue.

Andreas, E. L, W. B. Tucker III, and S. F. Ackley. 1984. Atmospheriboundary layer modification, drag coefficient and surface heat flux irthe antarctic marginal ice zone. Journal of Geophysical Research, 89(C1 1)649-61.

Cow, A. J., V.1. Lytle, D. Bell, and S. F. Ackley. 1992. Ice-core studies in thwestern Weddell Sea (NBP92-2). Antarctic Journal of the U.S., this issue

Lange, M. A., P. Schlosser, S. F. Ackley, P. Wadhams, and C. S. Dieckmann. 1990.18' concentrations in sea ice of the Weddell Sea, AntarcticaJournal of Glaciology, 36:315-323.

Lytle, V. I., K. C. Jezek, S. Gogineni, R. K. Moore, and S. F. Ackley. 1990Radar backscatter measurements during the winter Weddell Gyrstudy. Antarctic Journal of the U.S., 25(5):123-125.

Sullivan, C. W., C. H. Fritsen, and C. W. Mordy. 1992. Microbial production in antarctic pack ice: Time-series studies at the U.S-Russian driftinice station. Antarctic Journal of the U.S., this issue.

Yankielun, N. E. and S. F. Ackley. 1992. Millimeter-wave radar backscattemeasurements over Weddell Sea pack-ice (NBP 92-2). Antarctic Journal of the U.S., this issue.

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