Polar Research (E-Journal)
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Feeding habits of harp and hooded seals in drift ice waters along the east coast of Greenland in summer and winter
No full textResults of analyses of stomach and intestinal contents from hooded (Cystophora cristata) and harp (Phoca groenlandica) seals captured in the pack ice belt of the Greenland Sea in summer (July-August) in 2000 and winter (February-March) in 2001 revealed that the diet of both species were comprised of relatively few prey taxa. Pelagic amphipods of the genus Parathemisto, the squid Gonatus fabricii, polar cod (Boreogadus saida) and capelin (Mallotus villosus) constituted 63-99% of the observed diet biomass in both seal species, irrespective of sampling period, but their relative contribution to the diet varied both with species and sampling period/area. For hooded seals, G. fabricii and capelin were the dominant food items in winter 2001, but the summer 2000 diet comprised a mixture of this squid and polar cod. Parathemisto was most important for the harp seals during summer 2000; in winter 2001 the contribution from krill and capelin were comparable to that of Parathemisto. Multivariate analyses revealed differences in the intestinal contents of hooded and harp seals in areas where the two species’ occurrence spatially overlapped. Different foraging depths of the two species may have contributed to the observed differences in diets
Walrus (Odobenus rosmarus) predation on adult thick-billed murres (Uria lomvia) at Coats Island, Nunavut, Canada
No full textAlthough the diet of walrus (Odobenus rosmarus) is considered varied, records of walrus consuming marine birds are rare in the published literature. In 2001 and 2002 we observed walrus foraging on adult thick-billed murres (Uria lomvia) at Coats Island in Nunavut, Canada. Approximately 46% of the attacks on murres were successful, and as many as 67 murres may have been killed in one day in August 2002. All soft parts of the murres were sucked out, with carcasses of only bones, feathers and skin left floating on the water. The extent to which predation on seabirds by walrus occurs across the eastern Arctic is unknown, but it could represent an important source of mortality for murres at some breeding colonies
Regional and annual variability in common eider nesting ecology in Labrador
No full textNesting densities are often used to estimate breeding population size and with other measures of reproductive performance can be useful indicators of population status. These aspects of breeding biology often show considerable spatial and temporal variation. Between 2000 and 2003, we surveyed nesting common eiders (Somateria mollissima) on 172 islands in three archipelagos (Nain, Hopedale, Rigolet) on the Labrador coast. Rigolet was the largest archipelago (2834 km2) followed by Nain then Hopedale, and island density varied inversely with archipelago size. Overall means were: nest density 52.0 ± 141.9 (SD) nests/ha; nest initiation 12 June ± 12 days; clutch size 3.7 ± 1.2 eggs/nest; egg volume 98.8 ± 10.4 cm3; and clutch volume 392.3 ± 135.0 cm3. Rigolet had the highest average egg volumes and nest densities, the highest single island nest density of 1053 nests/ha, and the earliest average nest initiation date. We found significant differences in nest densities among archipelagos and across years; significant archipelago and year interactions were detected for nest initiation date and clutch size. Significant differences were found among individual islands for all response variables except egg volume. For egg volume, within-archipelago island differences were not significant, but between-archipelago differences were significant. Thus egg volume may be a useful diagnostic to identify population affiliation
Glaciers in Svalbard: mass balance, runoff and freshwater flux
No full textGain or loss of the freshwater stored in Svalbard glaciers has both global implications for sea level and, on a more local scale, impacts upon the hydrology of rivers and the freshwater flux to fjords. This paper gives an overview of the potential runoff from the Svalbard glaciers. The freshwater flux from basins of different scales is quantified. In small basins (A < 10 km2), the extra runoff due to the negative mass balance of the glaciers is related to the proportion of glacier cover and can at present yield more than 20% higher runoff than if the glaciers were in equilibrium with the present climate. This does not apply generally to the ice masses of Svalbard, which are mostly much closer to being in balance. The total surface runoff from Svalbard glaciers due to melting of snow and ice is roughly 25 ± 5 km3 a?1, which corresponds to a specific runoff of 680 ± 140 mm a?1, only slightly more than the annual snow accumulation. Calving of icebergs from Svalbard glaciers currently contributes significantly to the freshwater flux and is estimated to be 4 ± 1 km3 a?1 or about 110 mm a?1
Variability and climate sensitivity of fast ice extent in the north-eastern Kara Sea
No full textThis work investigates the temporal and spatial variation of shore-fast ice extent in the north-eastern part of the Kara Sea during 1953–1990 and its sensitivity to interannual variability of the regional climate. The area of fast ice in spring months shows a bimodal distribution. This indicates the existence of two different regimes of fast ice formation driven by the system of prevailing winds. The westward wind transport during the cold season gives larger fast ice extent while the eastward wind transport suppresses the expansion of fast ice. There is a significant correlation (ca. –0.55) between the average winter temperature and the area of fast ice. Linear trends for time records of shore-fast ice area in spring show a decrease during 1953–1990. This decrease is most pronounced in April: the mean fast ice area in April is 12 % lower in 1988–1990 compared to 1953–55. A comparison of fast ice regimes for two particular years— 1979 and 1985—revealed a significant influence of cyclone activity on fast ice development over the course of the cold season. It is shown that partial break-ups of fast ice in spring 1985 are associated with the passage of cyclones across the area of fast ice
A hindcast simulation of Arctic and Antarctic sea ice variability, 1955-2001
No full textA hindcast simulation of the Arctic and Antarctic sea ice variability during 1955–2001 has been performed with a global, coarse resolution ice–ocean model driven by the National Centers for Environmental Prediction / National Center for Atmospheric Research reanalysis daily surface air temperatures and winds. Both the mean state and variability of the ice packs over the satellite observing period are reasonably well reproduced by the model. Over the 47-year period, the simulated ice area (defined as the total ice-covered oceanic area) in each hemisphere experiences large decadal variability together with a decreasing trend of ~1 % per decade. In the Southern Hemisphere, this trend is mostly caused by an abrupt retreat of the ice cover during the second half of the 1970s and the beginning of the 1980s. The modelled ice volume also exhibits pronounced decadal variability, especially in the Northern Hemisphere. Besides these fluctuations, we detected a downward trend in Arctic ice volume of 1.8 % per decade and an upward trend in Antarctic ice volume of 1.5 % per decade. However, caution must be exercised when interpreting these trends because of the shortness of the simulation and the strong decadal variations. Furthermore, sensitivity experiments have revealed that the trend in Antarctic ice volume is model-dependent
Erosion and sediment transport in High Arctic rivers, Svalbard
No full textThis paper discusses sediment yield, sediment delivery and processes of erosion in rivers subject to High Arctic conditions in Svalbard. Long-term measurements reveal large variations between rivers and from year to year in each individual river. In the unglacierized catchment of Londonelva, annual sediment transport varied between 28 and 93 t/yr, with a mean sediment yield of 82.5 t/km2/yr. In the glacier-fed rivers Bayelva and Endalselva, the suspended sediment transport varied in the range of 5126 t/yr to 22797 t/yr during a 12-year period. A mean of 11 104 t/yr gave rise to a mean sediment yield of 359 t/km2/yr for the whole Bayelva catchment area. The sediment yield of the glacier and the moraine area was estimated at 586 t/km2/yr. A conceptual model used to interpret the long- and short-term patterns of sediment concentration in the meltwater from the glacier and erosion of the neoglacial moraines is proposed. Evidence is found that a proportion of the sediments are delivered by a network of englacial and subglacial channels that exist even in cold ice. Regression analyses of water discharge versus suspended sediment concentration gave significant correlations found to be associated with the stability of ice tunnels in cold ice. Large floods have been found to flush the waterways and exhaust the sediment sources. A long-term change in the exponent of regression lines is attributed to changes in sediment availability caused by flushing and expansion of tunnels and waterways by large floods and a subsequent slow deformation of them caused by the ice overburden and the glacier movement. A comparison of sediment yields from a number of polythermal and temperate glaciers in various areas showed large differences that were attributed primarily to bedrock susceptibility to erosion and, secondarily, to glaciological parameters
The drainage pattern of Hansbreen and Werenskioldbreen, two polythermal glaciers in Svalbard
No full textTo improve our understanding of Svalbard-type polythermal glacier drainage, hydraulic geometry models of the subglacial hydrology of two contrasting glaciers in Svalbard have been constructed. The models are tested against a uniquely long and rich set of field observations spanning 45 years. Digital elevation models (DEMs) were constructed from bedrock data measured with ground penetrating radar and surface data of two medium-sized polythermal glaciers, Hansbreen and Werenskioldbreen, in south-west Spitsbergen. Hansbreen has a low angle bed with over-deepenings and a calving front, while Werenskioldbreen has steeper bed and terminates on land. Together they are representative of many Svalbard glaciers. The DEMs were used to derive maps of hydraulic potential and subglacial drainage networks. Validation of the models was done using field observations including location mapping and speleological exploration of active moulins, positions of main river outflows, dyetracing and water chemistry studies, and observations of water pressure inside moulins. Results suggest that the water pressure is generally close to ice overburden pressure but varies greatly depending on local conditions such as bed location, the thickness of cold ice layer, the thickness of the glacier and seasonal changes in meltwater input
Glacier extent in a Novaya Zemlya fjord during the “Little Ice Age” inferred from glaciomarine sediment records
No full textGlacier activity at Russkaya Gavan', north-west Novaya Zemlya (Arctic Russia), is reconstructed by particle size analysis of three fjord sediment cores in combination with 14C and 210Pb dating. Down-core logging of particle size variation reveals at least two intervals with sediment coarsening during the past eight centuries. By comparing them with reconstructions of summer temperature and atmospheric circulation, these intervals are interpreted to represent two cycles of glacier advance and retreat sometime during ca. AD 1400–1700 and AD 1700–present. Sediment accumulation thus appears to be sensitive to century-scale fluctuations of the Barents Sea climate. The identification of two glacier cycles in the glaciomarine record from Russkaya Gavan’ demonstrates that during the “Little Ice Age” major glacier fluctuations on Novaya Zemlya occurred in broad synchrony with those in other areas around the Barents Sea
Improving sea ice type discrimination by the simultaneous use of SSM/I and scatterometer data
No full textThe multi-year sea ice (MY) concentration as determined with the NASA Team algorithm (NTA) shows an increase during winter. This unrealistic feature can be reduced using combined active and passive remote sensing data, leading to a more realistic estimation of MY area. Our joint analysis of SSM/I, QuikSCATterometer (QSCAT) and meteorological data reveals events (i.e. intervals in space and time) where increased surface roughness and volume scattering, after a melt–refreezing episode, alters the passive microwave signature of the undisturbed sea ice surface. In these events, the calculation of MY and FY areas employing the NTA leads to false estimations of their amounts. It is shown that when such events occur, QSCAT backscatter values increase by more than 3 dB. This backscatter variation can be easily detected and the FY and MY area determination of the NTA can be corrected accordingly within defined event–regions. Using this method, called Simultaneous NTA, we found that in May 2000 12 % of the area detected by the NTA as MY has to be corrected to FY. As a consequence, a detailed reanalysis of the 20-year passive microwave data set is suggested to more precisely compute the MY area