Fast Ice Edge Research Articles

Spatial and Temporal Distribution of Vocalising Maile Bearded Seals - Implications for Male Mating Strategies

The bearded seal, Erignathus barbatus , is an ice breeding phocid that mates in the water. The most detailed studies of male behaviour among aquatic-mating phocids have concentrated primarily on temperate breeding harbour seals, Phoca vitulina , where females are dependent on stable substrates, rock or sand, for parturition. In contrast, female bearded seals give birth on ice floes or the edge of fast ice, a highly unstable substrate. In this study, spatial and temporal patterns of male bearded seal vocalisations were studied in Kongsfjorden, Svalbard from April 1999 to the end of May 2000. Males vocalised during a discrete 90-day period from early April to mid July, no calls were heard at any other time of the year during this study. Vocalisations increased in duration towards the middle of the mating season in late May, although no change was seen in inter vocal intervals of individuals. The frequency of occurrence of vocalisations varied significantly with the diel cycle. Vocalisations increased in number from 16:00 hrs onward into the 'night', peaking around 04:00 hrs. This peak coincides with the period when most females are in the water. Female bearded seals were found throughout Kongsfjorden. Their distribution at any particular point in time depends on the availability of suitable haul-out sites ( i.e. ice conditions), which are highly variable over time spans as short as a few hours. Males vocalised in higher densities around the fjord entrances and may use these 'geographical bottlenecks' to intercept passing females. We suggest that male distribution may reflect the unpredictable nature of female distribution. Aquatic mating phocids appear to exhibit variations in reproductive strategies, including spatial arrangements of displaying males, which reflect the varying constraints imposed on female movement patterns by their local habitats and ecological requirements.

Observed and modelled sea-ice drift response to wind forcing in the northern Baltic Sea

The wind dependence of sea-ice motion was studied on the basis of ice velocity and windobservations, and weather model output. The study area was a transition zone between openwater and the ice-covered ocean in the northern Baltic Sea. In the centre of the basin the seaicemotion was highly wind-dependent and the linear relationship between the wind and thedrift velocities explained 80% of the drift’s variance. On the contrary, the wind-drift dependencewas low near the coast. The wind-drift coherence was significant over a broader frequencyrange in the central part of the basin than for the coastal drift. The ice motion was simulatedby a numerical model forced with five types of wind stress and with two types of current data, and the outcome was compared with the observed buoy drift. The wind and the wind-inducedsurface current were the main factors driving the ice in the basin’s centre, while internal icestresses were of importance in the shear zone near the fast ice edge. The best wind forcing wasachieved by applying a method dependent on atmospheric stability and ice conditions. Theaverage air–ice drag coefficient was 1.4×10-3 with the standard deviation of 0.2×10-3. Theimprovement brought about by using an accurate wind stress was comparable with thatachieved by raising the model grid resolution from 18 km to 5 km.

The Laptev Sea flaw polynya, Russian Arctic: effects on the mesoscale hydrography

AbstractA detailed analysis of hydrographic data from a period of 20 years (1980−99) has shown that the persistent presence of a flaw polynya influences mesoscale hydrography of the Laptev Sea, Russian Arctic. Based on these data, the interannual variability of surface water salinity within the polynya has been estimated. As the salinity increase in the surface water layer is mainly caused by the formation of new ice within the polynya, the average ice-production rate of the polynya was calculated. The results indicate an ice production of 3−4 m per season. A further aim of this study was to calculate the probability that the convective mixing in the polynya penetrates to the sea-floor. It is demonstrated that the probability is maximal in the flaw-polynya area, but does not exceed 20% in the eastern and 70% in the western part of the polynya as a result of strong vertical density stratification from river runoff, especially in the eastern Laptev Sea. Additional studies of water circulation in the marginal zone of the flaw polynya were carried out during field observations in April-May 1999. On the basis of conductivity-temperature-depth and current measurements we deduce that high current velocities (62 cm s-1) recorded in surface waters near the fast-ice edge are caused by a convectively driven circulation system under the polynya. Our measurements indicate that these high-velocity currents are part of a cellular circulation, which results from the rejection of brine during intensive ice formation in the polynya. The observed azimuthal alignment of the crystalline structure of sea ice is also, most probably, the consequence of this quasi-stationary cellular circulation.

Simulation of pancake-ice dynamics in a wave field

AbstractFrom many field observations, it has become well known that pancake ice is ubiquitous in a wave-dominated sea. These strikingly uniform circular floes are consistently found in the Antarctic seas during the ice-formation season. Their presence has also been reported in the Bering Sea, the Greenland Sea and in polynyas and leads within pack ice. In one estimate made by P. Wadhams (personal communication, 1991) the areal coverage of pancake ice in the Southern Ocean marginal ice zone is around 6 × 106 km2. Pancake ice forms through a combination of thermodynamic growth and mechanical thickening, caused by rafting of floes that is driven by wave motion This complex growth process is much faster than pure thermodynamic growth and hence may be the main factor responsible for ice-edge advance in marginal ice zones. In this paper we simulate wave/ice-floe dynamics by combining a new three-dimensional discrete element model with wave hydrodynamics. In one set of simulations we calculate ice-drift speed as a function of wave amplitude and ice collisional dynamics. In a second set of simulations we place a non-reflecting vertical barrier meant to simulate the fast-ice edge. The simulation results show the rate of increase of the ice impact force on the barrier, and the accompanying thickening of the rafted region in front of the barrier, as a function of wave amplitude. Results from this study will help quantify the formation process for pancake-ice covers in a wave field.

Current variability under landfast sea ice in Lützow‐Holm Bay, Antarctica

Current measurements were made under landfast sea ice in Lützow‐Holm Bay, Antarctica, in 1991. In spite of no direct wind forcing and negligible thermohaline forcing, currents with a magnitude of 0.1–0.3 m s−1 were observed. It is suggested that current variability strongly depends on the extent of the landfast ice on the eastward continental shelf. Before the fast ice edge extends to the shelf break the current at Ongul Strait, located near the continental coast, is highly coherent with the wind with a time lag of 1–1.5 days and somewhat coherent with the adjusted sea level with no time lag at periods of 6–8 days. After the fast ice edge is stably located along the shelf break the current is not at all coherent with the wind or sea level. We infer that the variability at periods of 6–8 days is mainly due to the first‐mode shelf wave excited by the wind stress over the eastward continental shelf. The direction of the prevailing current at Ongul Strait changed drastically from southward (the same direction of the wind) to northward in May, although the prevailing wind direction did not change. This change in timing coincides with the rapid development period of the fast ice extent.

The coastal edge of the Northeast Water polynya in spring 1993

Multidisciplinary, marine ecological observations were conducted at the shallow water edge of the Northeast Water in June, 1993. Although variable in size and shape, a small polynya was constantly present at Eskimonaes, at the fast-ice edge of Ingolfsfjord. A shallow stratified layer developed at the water sufface at negative water and air temperatures—an effect of sea ice melting in cold water early in the season. Nutrients were recorded in considerable quantities, although by mid July NO3 had become depleted. The chlorophyll and phytoplankton maxima at 8–12 m depth had peak values of 2 mg chl a m−3, typical for Arctic algal blooms. The phytoplankton included over 90 species and was dominated by the Fragillariopsis group. Zooplankton was poor in biomass and density, but over 23 taxa were found, with the copepods Oithona similis and Pseudocalanus acuspes being numerically dominant. Sedimentation was approximately 0.2 g dry weight m−2 d−1 and suspended matter concentrations ranged from 4 to 19 mg l−1. The benthos was represented by hard bottom forms only, with a surprisingly dense cover of macrophytes. Juvenile sea urchins (Strongylocentrotus droebachiensis), brittle stars (Ophiocten sericeum) and amphipods were dominant. Higher trophic levels were represented by benthic feeders, such as eiders and walruses. The area observed was more similar to high Arctic fjord ecosystems than to the offshore central Northeast Water polynya.

Predation of Adélie penguins (Pygoscelis adeliae) by leopard seals (Hydrurga leptonyx) in Prydz Bay, Antarctica

The behaviour of leopard seals, Hydrurga leptonyx, feeding on Adélie penguins, Pygoscelis adeliae, was investigated between November 1993 and January 1994 in Prydz Bay, Antarctica. The seals were distributed along the fast-ice edge in locations where departing penguins congregated. Five different hunting techniques were observed, four of which were used through most of the summer. Individual leopard seals favoured specific hunting techniques. Hitherto, penguin hunting was believed to be carried out primarily by a few male seals; in this study, however, the predation observed involved many different individuals of both sexes. It is estimated that six leopard seals feeding in this area over a period of 120 days would consume 2.7% of the adult penguin population.

Reflection and transmission characteristics at the edge of shore fast sea ice

The reflection and transmission of ocean waves at a sea ice boundary is reconsidered. The sea ice is modelled as a continuous, thin elastic plate of uniform thickness, floating on water of arbitrary constant depth. Unlike earlier solutions, matching of potentials between the free surface domain and the ice‐covered domain is done at all depths; previous solutions were incompletely matched, as the potentials in each domain were deficient. In the present solution a number of the infinity of evanescent modes, which were hitherto ignored, are included in the solution and allow matching to be carried out by minimization of an integrated error term from surface to seafloor. Reflection and transmission are found to be markedly influenced by the inclusion of these modes, suggesting that conclusions based on the incomplete potentials may be substantially in error.

Breakup of Antarctic fast ice

The fast ice cover in McMurdo Sound, Antarctica, is subjected to numerous mechanical processes which are capable of inducing breakup. Thermal decay plays only a minor role in the destruction of the ice cover, making this region ideal for studying mechanical breakup processes without the complications caused by melting and internal deterioration. A previously developed thermodynamic ice-growth model is used to predict temporal changes in the physical properties of the ice sheet relevant to breakup, allowing the susceptibility of the ice to different destructive processes to be assessed on a seasonal basis. The analyses indicate that during most of the year wind-induced tensile failure is the only likely mode of fracture, while during the short summer period ocean swell incident on the fast ice edge becomes dominant. The importance of the pack ice cover in the Ross Sea in controlling breakup by attenuating potentially destructive ocean swell is clearly shown, and is in agreement with previous qualitative studies of fast ice breakup.

Food of the emperor penguin Aptenodytes forsteri on the Antarctic fast ice edge in late winter and early spring

The food of emperor penguins Aptenodytes forsteri at the edge of the sea ice off the Vestfold Hills was studied by faecal analysis. Fish, crustacean, cephalopod and gastropod remains were found in 151 droppings collected between August and October 1984. The main fish identified from otoliths was Pleurogramma antarcticum with an average standard length of 129.5 mm. Amphipods increased in frequency from August to October with gammarids predominating.

Ice Conditions of an Arctic Polynya: North Water in Winter

AbstractThe surface condition of the North Water was investigated during two winters (i.e. the three polynyas: Smith Sound polynya, Lady Ann Strait polynya, and Barrow Strait polynya). Since no detailed information was available on ice conditions and the extent of open water during winter, radiometric temperature measurements of the sea surface had to be taken along a flight line of 2650 km from an altitude of 300 m. From November to March 1978-79 and 1980-81, 14 remote-sensing flights were carried out. On the basis of the radiometric measurements, the following ice types were identified: ice-free, dark nilas, light nilas, grey ice, grey-white ice, and white ice. A comparison between the thermal and the visual ice classification (the latter being based on grey tones of the aerial images) showed a deviation of 3%. The analysis showed that in November, December, and January more than 50% of the Smith Sound polynya was covered by young ice, nilas, and ice-free, whereas in February and March white ice was dominant. Moreover, it was found that the two polynyas in Smith Sound and Lady Ann Strait were much smaller than previously believed. In Barrow Strait, a semi-permanent polynya was observed in the winter of 1980-81. The occurrence of polynyas in Barrow Strait seems to be connected with the location of the fast-ice edge. On the basis of the calculated ice-type distribution and heat-flux rates for different ice types, an energy loss of 178 W m-2 was found on the surface of the Smith Sound polynya due to open water and thin ice for the winter months November to March. Compared with other ice-covered sea surfaces in the Arctic, the heat release by the sea-water in the Smith Sound polynya is about 100 W m-2 larger.

Ice Conditions of an Arctic Polynya: North Water in Winter

AbstractThe surface condition of the North Water was investigated during two winters (i.e. the three polynyas: Smith Sound polynya, Lady Ann Strait polynya, and Barrow Strait polynya). Since no detailed information was available on ice conditions and the extent of open water during winter, radiometric temperature measurements of the sea surface had to be taken along a flight line of 2650 km from an altitude of 300 m. From November to March 1978-79 and 1980-81, 14 remote-sensing flights were carried out. On the basis of the radiometric measurements, the following ice types were identified: ice-free, dark nilas, light nilas, grey ice, grey-white ice, and white ice. A comparison between the thermal and the visual ice classification (the latter being based on grey tones of the aerial images) showed a deviation of 3%. The analysis showed that in November, December, and January more than 50% of the Smith Sound polynya was covered by young ice, nilas, and ice-free, whereas in February and March white ice was dominant. Moreover, it was found that the two polynyas in Smith Sound and Lady Ann Strait were much smaller than previously believed. In Barrow Strait, a semi-permanent polynya was observed in the winter of 1980-81. The occurrence of polynyas in Barrow Strait seems to be connected with the location of the fast-ice edge. On the basis of the calculated ice-type distribution and heat-flux rates for different ice types, an energy loss of 178 W m-2was found on the surface of the Smith Sound polynya due to open water and thin ice for the winter months November to March. Compared with other ice-covered sea surfaces in the Arctic, the heat release by the sea-water in the Smith Sound polynya is about 100 W m-2larger.