Snow-covered Ice Research Articles

Ocean heat flux under Antarctic sea ice in the Bellingshausen and Amundsen Seas: two case studies

AbstractWe examine the role of ocean heat flux (OHF) in Antarctic sea-ice growth and melt using data from autonomous ice mass-balance buoys deployed on pack ice in the Bellingshausen Sea and on fast ice in the Amundsen Sea during the spring/summer (October-December 2007) and summer/ autumn (February-March 2009) transitions, respectively. OHFs are derived using two methods that examine changes in (1) sub-ice ocean water properties (OHF1) and (2) ice thickness (OHF2), the latter only applying to thick snow-covered ice (i.e. a near-zero temperature gradient near the ice bottom). Good agreement is found between the time-averaged estimates of OHF1 and OHF2. Average OHF measured was 8 ± 2 W m-2 under the pack ice and 17 ± 2 W m-2 under the landfast ice. Some short-term OHF values (OHF1) in both seas exceeded 55 W m-2. The spring OHF variations in the Bellingshausen Sea were periodic and controlled by semi-diurnal ice velocity fluctuations. Larger temperature fluctuations in the summer Amundsen Sea, originating from incursions of warm deep water masses, contributed to the OHF being twice as high as in the Bellingshausen Sea and also accounted for the irregular OHF variability there.

Separating snow, clean and debris covered ice in the Upper Indus Basin, Hindukush-Karakoram-Himalayas, using Landsat images between 1998 and 2002

Summary The Hindukush Karakoram Himalayan mountains contain some of the largest glaciers of the world, and supply melt water from perennial snow and glaciers to the Upper Indus Basin (UIB) upstream of Tarbela dam, which constitutes greater than 80% of the annual flows, and caters to the needs of millions of people in the Indus Basin. It is therefore important to study the response of perennial snow and glaciers in the UIB under changing climatic conditions, using improved hydrological modeling, glacier mass balance, and observations of glacier responses. However, the available glacier inventories and datasets only provide total perennial-snow and glacier cover areas, despite the fact that snow, clean ice and debris covered ice have different melt rates and densities. This distinction is vital for improved hydrological modeling and mass balance studies. This study, therefore, presents a separated perennial snow and glacier inventory (perennial snow-cover on steep slopes, perennial snow-covered ice, clean and debris covered ice) based on a semi-automated method that combines Landsat images and surface slope information in a supervised maximum likelihood classification to map distinct glacier zones, followed by manual post processing. The accuracy of the presented inventory falls well within the accuracy limits of available snow and glacier inventory products. For the entire UIB, estimates of perennial and/or seasonal snow on steep slopes, snow-covered ice, clean and debris covered ice zones are 7238 ± 724, 5226 ± 522, 4695 ± 469 and 2126 ± 212 km2 respectively. Thus total snow and glacier cover is 19,285 ± 1928 km2, out of which 12,075 ± 1207 km2 is glacier cover (excluding steep slope snow-cover). Equilibrium Line Altitude (ELA) estimates based on the Snow Line Elevation (SLE) in various watersheds range between 4800 and 5500 m, while the Accumulation Area Ratio (AAR) ranges between 7% and 80%. 0 °C isotherms during peak ablation months (July and August) range between ∼ 5500 and 6200 m in various watersheds. These outputs can be used as input to hydrological models, to estimate spatially-variable degree day factors for hydrological modeling, to separate glacier and snow-melt contributions in river flows, and to study glacier mass balance, and glacier responses to changing climate.

Vertical distribution and diel vertical migration of krill beneath snow-covered ice and in ice-free waters

A bottom mounted upward looking Simrad EK60 120-kHz echo sounder was used to study scattering layers (SLs) and individuals of the krill Meganyctiphanes norvegica. The mooring was situated at 150-m depth in the Oslofjord, connected with an onshore cable for power and transmission of digitized data. Records spanned 5 months from late autumn to spring. A current meter and CTD was associated with the acoustic mooring and a shore-based webcam monitored ice conditions in the fjord. The continuous measurements were supplemented with intermittent krill sampling campaigns and their physical and biological environment. The krill carried out diel vertical migration (DVM) throughout the winter, regardless of the distribution of potential prey. The fjord froze over in mid-winter and the daytime distribution of a mid-water SL of krill immediately became shallower associated with snow fall after freezing, likely related to reduction of light intensities. Still, a fraction of the population always descended all the way to the bottom, so that the krill population by day seemed to inhabit waters with light levels spanning up to six orders of magnitude. Deep-living krill ascended in synchrony with the rest of the population in the afternoon, but individuals consistently reappeared in near-bottom waters already <1 h after the ascent. Thereafter, the krill appeared to undertake asynchronous migrations, with some krill always being present in near-bottom waters even though the entire population appeared to undertake DVM.

Temperature fluctuations underneath the ice in Diamond Lake, Hennepin County, Minnesota

[1] Diamond Lake in Minnesota is covered every winter with ice and snow providing a modified thermal insulation between water and air. Autonomous temperature sensors, data loggers, were placed in this lake so that hourly measurements could be obtained from the snow-covered ice and water. The sensors that became frozen measured damped and delayed thermal response from the air-temperature fluctuation. Those sensors that were deeper within the snow-covered ice measured continuous, almost constant, temperature values near freezing. Several of them were within the liquid water and responded with a fluctuation of 24 h periods of amplitudes up to 0.2°C. Our analysis of the vertical temperature profiles suggested that the source of periodic water heating comes from the lake bottom. Because of the absence of daily temperature variations of the snow-covered ice, the influence of the air-temperature fluctuation can be ruled out. We attribute the heating process to the periodic inflow of groundwater to the lake and the cooling to the heat diffusion to the overlying ice cover. The periodic groundwater inflow is interpreted due to solid Earth tides, which cause periodic fluctuations of the groundwater pressure head.

Declining summer snowfall in the Arctic: causes, impacts and feedbacks

Recent changes in the Arctic hydrological cycle are explored using in situ observations and an improved atmospheric reanalysis data set, ERA-Interim. We document a pronounced decline in summer snowfall over the Arctic Ocean and Canadian Archipelago. The snowfall decline is diagnosed as being almost entirely caused by changes in precipitation form (snow turning to rain) with very little influence of decreases in total precipitation. The proportion of precipitation falling as snow has decreased as a result of lower-atmospheric warming. Statistically, over 99% of the summer snowfall decline is linked to Arctic warming over the past two decades. Based on the reanalysis snowfall data over the ice-covered Arctic Ocean, we derive an estimate for the amount of snow-covered ice. It is estimated that the area of snow-covered ice, and the proportion of sea ice covered by snow, have decreased significantly. We perform a series of sensitivity experiments in which inter-annual changes in snow-covered ice are either unaccounted for, or are parameterized. In the parameterized case, the loss of snow-on-ice results in a substantial decrease in the surface albedo over the Arctic Ocean, that is of comparable magnitude to the decrease in albedo due to the decline in sea ice cover. Accordingly, the solar input to the Arctic Ocean is increased, causing additional surface ice melt. We conclude that the decline in summer snowfall has likely contributed to the thinning of sea ice over recent decades. The results presented provide support for the existence of a positive feedback in association with warming-induced reductions in summer snowfall.

Formation of circular rings on the snow-covered ice field of Lake Baikal

Satellite images taken from the ice surface of Lake Baikal show dark rings 7–8 km in diameter. Physically, this phenomenon can be explained by the emission of warm natural gas from the sedimentary thickness on the Lake Baikal bed. When the natural gas ascends toward the surface, it cools down but has time to heat ambient cold water. This gives rise to toroidal convection around the site of natural gas emission in the water column. Convection carries the warmed water to the surface (to the lower surface of ice) clear of the natural gas column. The heat reaches the upper surface of ice by means of heat conduction, where snow starts intensely melting. As a result, a thaw hole in the form of a ring arises on the snow-covered ice.

Surface Emissivity of the Arctic Sea Ice at AMSR-E Frequencies

Surface emissivity is an essential quantity to retrieve surface and atmospheric parameters from satellite measurements. The surface emissivity of the Arctic sea ice is calculated using Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) radiance. The method accounts for the variation of the penetration depth in the snow-covered ice with frequency, air temperature, and sea-ice temperature. The variation of emissivity for different frequencies at different seasons is noticed, together with their correlations.

A Comparison of Airborne Microwave Brightness Temperatures and Snowpack Properties Across the Boreal Forests of Finland and Western Canada

The seasonal snowpack across the boreal forest is an important national resource in both Canada and Finland, contributing freshwater for agriculture, human consumption, and hydropower generation. In both countries, satellite passive microwave data are utilized to provide operational information on snow depth and snow water equivalent (SWE) throughout the snow cover season. Airborne passive microwave surveys conducted independently across Finland and western Canada during March and April 2005 and March 2006 provided the opportunity to assess the level of similarity in snowpack physical properties and brightness temperature response to snowpack qualities using two independent data sets. The primary objectives of these campaigns were to determine the influence of small-scale heterogeneity on satellite data, using relatively high resolution airborne measurements, and to assess the Helsinki University of Technology (HUT) snow emission model capability of predicting emitted brightness temperatures under varying snowpack and landscape conditions. Comparisons of brightness temperature emissions over different land cover types showed a clear distinction of wetlands and snow-covered ice from forested and open areas. This is reflected also as a strong relationship between 6.9-GHz measurements and fractional lake cover in both Canada and Finland, with relationships at 18 and 37 GHz being less consistent between data sets. Comparisons of experimental data versus HUT snow emission model predictions showed relatively good agreement between the simulations and airborne data, specifically for the Finnish data set.

Light limitation increases the edibility of Asterionella formosa Hass. for Daphnia during periods of ice cover

Morphological variations of Asterionella formosa were studied both in field samples from Bautzen Reservoir, Germany, and in culture experiments. It was observed that this diatom exhibited considerable variation in the number of cells per colony, ranging from unicells to colonies with more than 16 cells. The winter period of two consecutive years which differed with respect to ice- and snow cover were compared (1995: no ice cover; 1996: an ice cover lasting 4 months). A. formosa was obviously inedible for Daphnia in winter 1995 whereas in the same period in 1996 this species represented a main food source for Daphnia galeata, as was demonstrated by microscopic observation of the gut content of D. galeata during periods of Asterionella blooms. From feeding experiments with 14C-labelled A. formosa of different colony sizes and from microscopic observations of Daphnia feeding in a suspension of Asterionella colonies, I confirmed that only Asterionella colonies with up to 7 cells were effectively ingested by D. galeata. Above this threshold, the ingestion efficiency decreased to less than 30%. Steady-state populations of A. formosa in culture experiments showed a marked dependence on the number of cells per colony on light intensities. The mean colony size was usually less than 5 when light was limited (fell below a threshold of 20 μE m −2 s −1), and greater than 8 when light intensities exceeded 110 μE m −2 s −1. In Bautzen Reservoir, low light penetration owing to snow-covered ice in winter 1996 resulted, similar to culture experiments, in Asterionella colonies with 4 or less than 4 cells. Contrary to 1996, non-limited light penetration corresponded to 8-celled colonies in winter 1995. Light limitation during periods of ice cover should therefore be a strong environmental predictor of the colony size of A. formosa and, consequently, of the ingestion efficiency of a Daphnia population, thereby strongly modifying trophic interactions in pelagic food webs.

Reply to comment by E. T. DeWeaver et al. on “On the reliability of simulated Arctic sea ice in global climate models”

Reply to comment by E. T. DeWeaver et al. on “On the reliability of simulated Arctic sea ice in global climate models”

Are dust storm activities in North China related to Arctic ice–snow cover?

The generation and development of dust storms are controlled by land surface conditions and atmospheric circulations. The latter, in turn, is influenced by the global ice–snow cover. In this study, we examine the relationship between the characteristics of dust storm activities in north China and the changes of global climate patterns. In particular, we are interested in whether Arctic ice–snow cover is related to the dust storm frequencies and intensities in north China. Our analysis, based on the monthly data for the period from 1954 to 1994, shows that this is indeed the case. This result suggests that the Arctic ice–snow cover can be used for the long-term prediction of dust storm activities in north China, and dust storm activities also serve as an indicator of global climate change.

Surface Albedo of the Antarctic Sea Ice Zone

AbstractIn three ship-based field experiments, spectral albedos were measured at ultraviolet, visible, and near-infrared wavelengths for open water, grease ice, nilas, young “grey” ice, young grey-white ice, and first-year ice, both with and without snow cover. From the spectral measurements, broadband albedos are computed for clear and cloudy sky, for the total solar spectrum as well as for visible and near-infrared bands used in climate models, and for Advanced Very High Resolution Radiometer (AVHRR) solar channels. The all-wave albedos vary from 0.07 for open water to 0.87 for thick snow-covered ice under cloud. The frequency distribution of ice types and snow coverage in all seasons is available from the project on Antarctic Sea Ice Processes and Climate (ASPeCt). The ASPeCt dataset contains routine hourly visual observations of sea ice from research and supply ships of several nations using a standard protocol. Ten thousand of these observations, separated by a minimum of 6 nautical miles along voyage tracks, are used together with the measured albedos for each ice type to assign an albedo to each visual observation, resulting in “ice-only” albedos as a function of latitude for each of five longitudinal sectors around Antarctica, for each of the four seasons. These ice albedos are combined with 13 yr of ice concentration estimates from satellite passive microwave measurements to obtain the geographical and seasonal variation of average surface albedo. Most of the Antarctic sea ice is snow covered, even in summer, so the main determinant of area-averaged albedo is the fraction of open water within the pack.

The Return of the Butterflies

IT WAS a bitter cold morning, and it was early -- ungodly early for a night person like me. I clutched an insulated coffee cup in one hand and tugged a wheeled cart over snow-covered ice with the other. The cart contained the day's necessities -- my son's 1974 Star Wars lunch box packed with fruit and egg salad, a selection of children's books, a box of interesting keys I had collected over the last 10 years, a 1920s-era typewriter, and bags of toilet-paper rolls, meat trays, buttons, old jewelry, and other precious things. This morning was just one in a string of remarkably cold mornings I'd experienced since moving to Montana. On other such mornings, I would pull my hat lower to shield my face, utter a four-letter word or two, and ask myself, What were you thinking? It was a fair question. After all, I had traded the mild winters of Appalachian Georgia for almost- Canada, Montana. There was a reason I had made that decision, but sometimes I would forget what it was. However, on that February day, I did not curse the cold or question my judgment. I was excited, smiling, joyful, running on adrenaline, and eager to be on my way. I pushed a Dylan CD into the player, pulled on the four-wheel drive, and backed my Jeep out of the driveway. As I drove the 30 miles south to the reservation, I sipped my coffee and sang along with Dylan -- loudly and badly. As I sang, I noticed a flutter in my stomach. Butterflies, I said through a smile. I love butterflies, always have. And on that day, the flutter reminded me how nervous I was to meet the fifth-graders I would teach and learn from through the end of May. I had come to Montana to work in a teacher education program. The experience had proved less than rewarding. However, taking that job had allowed me to discover the Rocky Boy Reservation. Volunteering at Rocky Boy Elementary School had become the high point of my week and had reawakened my desire to work with young children. Still, only days earlier, I had thought that classroom teaching was forever behind me -- along with all the lunch duty, lesson plans, inside recess, faculty meetings, and paperwork that go with it. But that was before the principal asked me to stop by her office, before she explained that a teaching position had unexpectedly opened, and before she offered that position to me. With some schedule wrangling at Rocky Boy and at the university, we developed a plan that would allow me to meet my responsibilities to both student groups. I knew it would be difficult to balance two full- time teaching jobs, but I was convinced I could do it. And I wanted to do it more than I had wanted to do anything in a long time. It has been a terrific two months. My fifth-graders are in their glory, making monster goo, exploring magnets and electricity, studying tribal government, identifying and writing biographies of the family members they most honor, and building a model of the reservation. For the first time, I get to integrate technology across the curriculum. My kids have become fanatic shutterbugs. And my preservice teachers have had the benefit of authentic connections between our classroom learning and life in an elementary school. Still, the task has been neither easy nor simple. Nothing about teaching is ever easy or simple. It can't be. That's what I love about teaching -- the complexity, the lack of clarity, the never-ending need to find new answers to old questions, the constant intellectual challenge. The complexity and continuously growing need to know more and do better makes every day exciting, new, and different. And the ongoing search for deeper and broader understandings provides years of exciting, challenging, and, yes, exasperating days. How could anyone not love that? While my experiences at Rocky Boy are exciting, they are also humbling. Each day I learn more about how little I know and understand about Chippewa-Cree culture and history. …

Turbulent surface fluxes and air–ice coupling in the Baltic Air–Sea–Ice Study (BASIS)

AbstractTurbulent surface fluxes were studied using observations taken over sea ice in the Baltic Sea in March 1998. The fluxes of momentum and sensible heat were measured by a sonic anemometer and compared with fluxes derived from wind velocity and air-temperature profiles. The neutral 10 m drag coefficient showed no apparent dependence on wind speed (in the range 2–20 m s–1), resulting in a mean value of 1.0 × 10–3 for smooth snow-covered ice and 1.5 × 10−3 for deformed ice. The overall mean value was 1.28 × 10–3. The roughness length for temperature revealed a greater apparent dependence on wind speed and was slightly larger than the aerodynamic roughness for low wind speeds, and vice versa for moderate and high winds. We give an empirical expression that predicts how the scalar roughness depends on the aerodynamic roughness (drag coefficient) and wind speed. Agreement of the gradient-method results with the eddy-flux results supports the validity of the Monin-Obukhov similarity theory. Fluxes modelled by a coupled air-ice-sea model compared well with the eddy-flux and gradient methods. Surface temperature estimates by the three methods also agreed well. Tests and sensitivity analysis emphasize the need for especially accurate sensor calibration and strict information about the sensor heights for the gradient method.

Lake Baikal ice: analysis of AVHRR imagery and simulation of under-ice phytoplankton bloom

Generation and sample applications of an integrated set of multi-spectral remotely sensed products for investigations of Lake Baikal's ice cover variability are presented. Different ice-snow cover classes and unfrozen water distributions are estimated from calibrated and navigated Advanced Very High Resolution Radiometer (AVHRR) 1.1-km imagery of Lake Baikal for January 1994 through May 1998. The calculated downward irradiance field in the photosynthetic available radiance band has served as input for a bio-optical model of phytoplankton dynamics. It is shown that the relationship between the production of main taxonomic groups of Baikal's phytoplankton is highly sensitive to the variability of ice conditions.

Airborne line scanner measurements for ERS-1 SAR interpretation of sea ice

A new method is presented for interpretation of Synthetic Aperture Radar (SAR) images recorded with the first European Remote Sensing Satellite (ERS-1) with respect to classification of sea ice. Conventional interpretation of spaceborne radar images is often based on subjective classification of radar signatures. Themost promising approach is a region-based segmentation with subsequent interpretation of the segments. The definition of regions with common properties enables a characterisation by texture parameters besides backscatter coefficients. The major drawback of this method is the subjective selection and characterisation of the training segments on which the classification is based. To avoid this subjective influence, an attempt is made of an independent classification by the use of two airborne line scanner systems, one for the visible and the other for the infrared spectral range. The systems were installed on research aircraft (aeroplane and helicopter) during an experiment covering the marginal ice zone north of Spitsbergen in late winter 1993 and in the North East Water Polynya in summer 1993. Several underflights of ERS-1 were carried out during the SAR mode. Typical areal coverage of the line scanner images during a flight is 1.5% of a SAR scene. The line scanner images are classified using a two-dimensional feature space. By this procedure various ice types are identified. After matching the locations of the line scanner and the segmented SAR images, it is then possible to derive the characteristics of different ice types with respect to radar signatures. Backscatter coefficient and texture parameters are used for the discrimination of ice types. Texture parameters used are moments of the grey-level distribution and values of the co-occurrence matrices. The results of this work show, that the common method of a subjective characterisation of training regions runs into difficulties. SAR signatures are essentially dependent on the conditions during ice development. Regions with different ice types can have the same SAR signatures and different SAR signatures may be found for the same ice type. With the presented method it is possible to achieve classification accuracies up to 78% with a discrimination of young ice, first-year ice and old ice during winter situations. In summer, it is difficult to discriminate wind exposed water and sea ice. In this case, the classification of SAR images is derived exclusively by means of texture parameters since the backscatter coefficient is of little use. With the discrimination of water, snow-covered ice, and brash ice an accuracy of 73% is achieved under summer conditions.

Field observations of the electromagnetic properties of first-year sea ice

An interdisciplinary field experiment was conducted during April and May of 1994 at Point Barrow, AK, to investigate the relationship between the electromagnetic and physical-biological properties of first-year sea ice. Electromagnetic signatures of bare and snow-covered first-year ice were measured over a broad spectral range, including ultraviolet through near-infrared albedo, microwave emissivity, and radar backscatter. Observations indicated that the scattering of visible light varied significantly with depth in response to changes in the size and orientation of the ice crystals and in the number of brine and air inclusions. The scattering of visible light was greatest in the surface layer where there were numerous inclusions, and crystals tended to be small and randomly oriented. Changes in albedo over small horizontal distances were found to be related to surface layer conditions, including the number of air bubbles and particulate levels. Even for bare ice, transmittances were small with peaks in the blue-green. Scattering exceeds absorption throughout the snow and ice except in the skeletal layer colonized by bottom ice algae. Passive microwave emissivities showed a substantial difference between snow-covered and snow-free sites due to the effects of impedance matching at longer frequencies and volume scattering at higher frequencies produced by the snow, Spatial variability in the emissivity was quite small except at 90 GHz, where the emissivity was most sensitive to the amount of depth hoar. Radar backscatter coefficients were 5-6 dB larger for oblique viewing angles over snow-covered ice.

The influence of cloud cover on the radiation budget, physical properties, and microwave scattering coefficient (σ°) of first-year and multiyear sea ice

Over sea ice, the shift from predominantly clear conditions in winter to persistent stratus cloud cover in late spring and early summer coincides with a dramatic increase in the net radiation balance at the sea ice surface. Transformation of the boundary layer climate and the geophysical properties of the snow covered sea ice result from this cloud-induced rise in surface energy balance. In this paper, in situ data from the Seasonal Sea Ice Monitoring the Modeling Site (SIMMS'93) experiment are used to examine the extent to which changes in surface radiation, sea ice physical and electrical properties, and microwave scattering are a function of clear versus cloudy conditions over first-year and multiyear sea ice types. The authors use the surface observations to drive a simple forward scattering model used to diagnose the potential mechanisms responsible for the observed changes in microwave scattering by the Earth Resources Satellite-1 (ERS-1). Their results indicate that under cloudy conditions the surface temperature increases because of the surplus in the longwave net radiative energy. This causes an increase in the surface temperature and formation of a temperature wave down through the snow volume into the ice surface. This increases the dielectric constant of the snow basal layer and ice surface over first-year sea ice because of the thin snow cover (relative to the thicker multiyear ice snow cover) and because of the temperature effect on brine volume. The observed increase in scattering is limited to very smooth first-year sea ice types. Models used to diagnose the principal scattering mechanisms suggest that the cloud cover effects the scattering either by creating a dielectrically rough basal layer in the snow volume near the ice surface or by increasing the scattering contribution from snow grains within the basal layer volume. Under either scenario the increase in scattering is small (/spl sim/5 dB) and is only detectable if the target presents a scattering magnitude less than about -20 dB.

Classification of Baltic Sea ice types by airborne multifrequency microwave radiometer

An airborne multifrequency radiometer (24, 34, 48, and 94 GHz, vertical polarization) was used to investigate the behavior of the brightness temperature of different sea ice types in the Gulf of Bothnia (Baltic Sea). The measurements and the main results of the analysis are presented. The measurements were made in dry and wet conditions (air temperature above and below 0/spl deg/C). The angle of incidence was 45/spl deg/ in all measurements. The following topics are evaluated: a) frequency dependency of the brightness temperature of different ice types, b) the capability of the multifrequency radiometer to classify ice types for winter navigation purposes, and c) the optimum measurement frequencies for mapping sea ice. The weather conditions had a significant impact on the radiometric signatures of some ice types (snow-covered compact pack ice and frost-covered new ice); the impact was the highest at 94 GHz. In all cases the overall classification accuracy was around 90% (the kappa coefficient was from 0.86 to 0.96) when the optimum channel combination (24/34 GHz and 94 GHz) was used.

Nutrient and persistent pollutant deposition on the Bothnian Bay ice and snow fields

A study of atmospheric deposited nutrients and some persistent pollutants has been carried out on the ice and snow fields of the subarctic Bothnian Bay, the northernmost basin of the Baltic Sea. Total amounts of 600, 500 and 400 tons NO3-N, NH4-N and Norg-N, respectively are deposited in the snow while the corresponding amounts for Ptot-P is 40 tons. The corresponding amount for PCB and lindane are 1.0 and 0.2 kg, respectively. The measurements were carried out on the snow-covered ice four to six weeks old. A part of the deposited snow has been incorporated -into the snow-ice and an attempt to estimate its mean thickness and its amount of nutrients has been made. The total amounts now reach 1700, 1300 and 1100 tons of NO3-N and NH4-N and Norg-N, respectively in the snow and ice together. The results obtained support the use of land-based stations in estimates of seasonal atmospheric nutrient deposition to the Bothnian Bay. The observed concentrations of chloroorganic compounds correspond to those land-based observations reported from the same latitude in the northern hemisphere and reported in literature.