A hindcast simulation of Arctic and Antarctic sea ice variability, 1955–2001

A 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 Ø1% 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.     

Russian iceberg observations in the Barents Sea, 1933– 1990

Seasonal variations of iceberg distribution in the Barents Sea have been studied on the basis of Russian observations for the period 1933-1990. The maximum southern distribution is observed in January and the minimum in September and October. A significant correlation coefficient of 0.5 is calculated for the relationship between the latitude of the southern ice cover expansion and the corresponding expansion of iceberg distribution. There is a general temporal trend of increased southern locations of iceberg observations during the period considered. Some analyses of iceberg dimensions in the western part of the Barents Sea are based on observations obtained in 1988–1990 under the Ice Data Acquisition Programme (IDAP) and under the Soviet-Norwegian Occanographic Programme (SNOP).     

Trends and variability of sea ice in Baffin Bay and Davis Strait, 1953–2001

The extent and duration of sea ice in Baffin Bay and Davis Strait has a major impact on the timing and strength of the marine production along West Greenland. The advance and retreat of the sea ice follows a predictable pattern, with maximum extent typically in March. We examine the area of sea ice in March in three overlapping study regions centred on Disko Bay on the west coast of Greenland. Sea ice concentration estimates derived from satellite passive microwave data are available for the years 1979-2001. We extend the record back in time by digitizing ice charts from the Danish Meteorological Institute, 1953-1981. There is reasonable agreement between the chart data and the satellite data during the three years of overlap: 1979-1981. We find a significant increasing trend in sea ice for the 49-year period (1953-2001) for the study regions that extend into Davis Strait and Baffin Bay. The cyclical nature of the wintertime ice area is also evident, with a period of about 8 to 9 years. Correlation of the winter sea ice concentration with the winter North Atlantic Oscillation (NAO) index shows moderately high values in Baffin Bay. The correlation of ice concentration with the previous winter's NAO is high in Davis Strait and suggests that next winter's ice conditions can be predicted to some extent by this winter's NAO index.     

1979—2015 年罗斯海海冰运动速度变化

基于美国冰雪数据中心的月平均海冰运动和海冰密集度数据, 建立了1979—2015 年罗斯海海冰运动 速度时间变化序列, 揭示了海冰运动速度的年际和季节变化特征, 探讨了海冰运动速度和海冰范围之间可 能存在的联系, 最后对影响海冰运动速度变化的因素进行了分析。结果表明, 1979—2015 年罗斯海海冰运动 速度总体呈现加快趋势, 海冰运动速度增加趋势最快的季节为秋季, 其次是冬季、春季和夏季。冬季海冰平 均运动速度最大, 依次是秋季、春季和夏季。海冰运动速度与海冰范围在37 年间均呈现上升趋势, 海冰范 围变化滞后海冰运动速度1—2 个月, 两者呈显著正相关关系, 海冰运动速度的增加导致罗斯海海冰范围不 断扩张, 进而影响南极整体海冰分布。罗斯海海冰运动速度与风速之间存在显著正相关关系, 风场是影响海 冰运动速度的一个直接因素。除此之外, 海冰运动还受到包括气压场、洋流场以及海洋阻力系数等的影响。     

罗斯海和普里兹湾海域海冰范围变化对比分析

海冰范围的变化对气候变化、生态系统以及人类活动都会产生重大的影响,近年来极地海冰范围的变化受到广泛关注。对南极罗斯海与普里兹湾海域海冰范围进行时间序列分析,研究发现海冰范围季节性变化在罗斯海与普里兹湾海域差异较大,罗斯海地区表现出"快速缩小、迅速扩大"的特性,普里兹湾海域表现出"快速缩小、缓慢扩大"的特性。两地区的海冰范围在年际变化上都表现出扩大的趋势,2003—2014年罗斯海地区海冰变化趋势为(1.39±1.12)×104km2·a~(-1),普里兹湾海域海冰变化趋势为(0.61±0.26)×104km2·a~(-1)。罗斯海地区夏季的年际变化为减少趋势。     

Ice draft and current measurements from the north-western Barents Sea, 1993–96

From 1993 to 1996, three oceanographic moorings were deployed in the north-western Barents Sea, each with a current meter and an upward-looking sonar for measuring ice drafts. These yielded three years of currents and two years of ice draft measurements. An interannual variability of almost I m was measured in the average ice draft. Causes for this variability are explored, particularly its possible connection to changes in atmospheric circulation patterns. We found that the flow of Northern Barents Atlantic-derived Water and the transport of ice from the Central Arctic into the Barents Sea appears to be controlled by winds between Nordaustlandet and Franz Josef Land, which in turn may be influenced by larger-scale variations such as the Arctic Oscillation/North Atlantic Oscillation.     

High resolution simulations of Arctic sea ice, 1979–1993

To evaluate improvements in modelling Arctic sea ice, we compare results from two regional models at 1/12° horizontal resolution. The first is a coupled ice-ocean model of the Arctic Ocean, consisting of an ocean model (adapted from the Parallel Ocean Program, Los Alamos National Laboratory [LANL]) and the "old" sea ice model. The second model uses the same grid but consists of an improved "new" sea ice model (LANL/CICE) with a simple ocean mixed layer. Both models are forced with European Centre for Medium-range Weather Forecasts reanalysis data for 1979–1993. A comparison of the two sea ice models focuses on the winter of 1987 to emphasize the internal ice stress and to minimize biases towards a particular Arctic climate regime. The "new" sea ice model gives improved ice deformation and drift fields. These improvements are associated at least in part with the multi-category representation of the ice thickness distribution and more realistic parameterization of the ice strength. Long, narrow features in ice divergence and shear fields resemble those observed in SAR imagery, except that their average width is overestimated, possibly due to insufficient horizontal resolution. We also compare the mean sea ice drift and its decadal variability in two "old" sea ice models at different horizontal resolutions: 18-km and 9-km. We find no significant change in ice drift between the two models, except in areas of significant ice-ocean interactions due to more realistic ocean currents and water mass properties in the 9-km model.     

Nitrogen uptake rates in phytoplankton and ice algae in the Barents Sea

Uptake rates of NH₄⁺, NO₃⁻ and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a ¹⁵N-technique. NO₃⁻ was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in situ NO₃⁻ uptake rate in the ice algal communities was light-limited The in situ NO₃⁻ and NH₄⁻ uptake rates in the subsurface chlorophyll maximum were at times light-limited. It is hypothesised that NH₄⁺ may accumulate in low light in the bottom of the euphotic zone and inhibit the in situ NO₃⁻ uptake rate.     

The Barents Sea ice sheet - a sedimentological discussion

Sediment sampling and shallow seismic profiling in the western and northern Barents Sea show that the bedrock in regions with less than 300 m water depth is unconformably overlain by only a thin veneer (<10 m) of sediments. Bedrock exposures are probably common in these areas. The sediments consist of a Holocene top unit, 0.1–1.5 m in thickness, grading into Late Weichselian glaciomarine sediments. Based on average sedimentation rates (¹⁴C-dating) of the Holocene sediments, the transition between the two units is estimated to 10,000–12,000 B.P. The glaciomarine sediments are commonly 1–3 m in thickness and underlain by stiff pebbly mud, interpreted as till and/or glaciomarine sediments overrun by a glacier. In regions where the water depth is over 300 m the sediment thickness increases, exceeding 500 m near the shelf edge at the mouth of Bjørnøyrenna. In Bjømøyrenna itself the uppermost 15–20 m seem to consist of soft glaciomarine sediments underlain by a well-defined reflector, probably the surface of the stiff pebbly mud. Local sediment accumulations in the form of moraine ridges and extensive glaciomarine deposits (20–60m in thickness) are found at 250–300m water depth, mainly in association with submarine valleys. Topographic highs, probably moraine ridges, are also present at the shelf edge. Based on the submarine morphology and sediment distribution, an ice sheet is believed to have extended to the shelf edge at least once during the Pleistocene. Spitsbergenbanken and the northern Barents Sea have also probably been covered by an ice sheet in the Late Weichselian. Lack of suitable organic material in the glacigenic deposits has prevented precise dating. Based on the regional geology of eastern Svalbard, a correlation of this younger stage with the Late Weichselian is indicated.     

Sea ice algae in the White and Barents seas: composition and origin

To examine algae populations, three expeditions (in March 2001, April 2002 and February 2003) were conducted in the Guba Chupa (Chupa Estuary; north-western White Sea), and one cruise was carried out in the open part of the White Sea in April 2003 and in the northern part of the Barents Sea in July 2001. Sea ice algae and phytoplankton composition and abundance and the content of sediment traps under the land-fast ice in the White Sea and annual and multi-year pack ice in the Barents Sea were investigated. The community in land-fast sea ice was dominated by pennate diatoms and its composition was more closely related to that of the underlying sediments than was the community of the pack ice, which was dominated by flagellates, dinoflagellates and centric diatoms. Algae were far more abundant in land-fast ice: motile benthic and ice-benthic species found favourable conditions in the ice. The pack ice community was more closely related to that of the surrounding water. It originated from plankton incorporation during sea ice formation and during seawater flood events. An additional source for ice colonization may be multi-year ice. Algae may be released from the ice during brine drainage or sea ice melting. Many sea ice algae developed spores before the ice melt. These algae were observed in the above-bottom sediment traps all year around. Three possible fates of ice algae can be distinguished: 1) suspension in the water column, 2) sinking to the bottom and 3) ingestion by herbivores in the ice, at the ice-water interface or in the water column.     

Summer sea ice characteristics of the Chukchi Sea

During August 1999, we investigated sea ice characteristics; its distribution, surface feature, thickness, ice floe movement, and the temperature field around inter-borders of air/ice/seawater in the Chukchi Sea. Thirteen ice cores were drilled at 11 floe stations in the area of 72°24′ 77°18′N, 153°34′ 163°28′W and the ice core structure was observed. From field observation, three melting processes of ice were observed; surface layer melting, surface and bottom layers melting, and all of ice melting. The observation of temperature fields around sea ice floes showed that the bottom melting under the ice floes were important process. As ice floes and open water areas were alternately distributed in summer Arctic Ocean; the water under ice was colder than the open water by 0.4 2.8℃. The sun radiation heated seawater in open sea areas so that the warmer water went to the bottom when the ice floes move to those areas. This causes ice melting to start at the bottom of the ice floes. This process can balance effectively the temperature fluctuating in the sea in summer. From the crystalline structure of sea ice observed from the cores, it was concluded that the ice was composed of ice crystals and brine-ice films. During the sea ice melting, the brine-ice films between ice crystals melted firstly; then the ice crystals were encircled by brine films; the sea ice became the mixture of ice and liquid brine. At the end of melting, the ice crystals would be separated each other, the bond between ice crystals weakens and this leads to the collapse of the ice sheet.     

Shoreline trajectories on a glacially influenced stable margin – insight from the Barents Sea Shelf, NW Russia

This study describes shoreline migration paths for late Quaternary sediments on the inner Barents Sea shelf between Kola and the Pechora Sea. The depositional geometries provide an example of stratigraphical architecture in a glacially influenced basin prone to isostatic movements as well as rapid and high-amplitude changes in eustatic sea level. The depositional geometries reflect asymmetrical relative sea level changes characterised by marine inundation upon deglaciation and prolonged forced regressions. Thus, all deposition occurs during the falling stage and lowstand systems tracts. The transgressive and highstand systems tracts are lacking and the maximum landward position of the shoreline is coinciding with the basal surface of forced regression. Shoreline migration is dominated by downward and seaward trajectories, but aggradation occurs on the falling limb of the relative sea level curve due to superimposed eustatic cycles of lower hierarchical order. Fluvial aggradation behind the shoreline takes place during the lowstand systems tract, but is also linked to high sediment supply and may also respond to superimposed lower order sea level fluctuations. Lateral variations in isostatic load due to asynchronous ice advances lead to regional variations in shoreline trajectories. Significant differences in sea level history exist across former ice margins leading to time-transgressive and laterally discontinuous stratigraphical surfaces. Sequence boundaries are not only diachronous along the depositional profile, but also laterally, and basal surfaces of forced regression are strongly diachronous across former ice margins. Absolute age control allows for estimates of the time differences along significant stratigraphical surfaces.     

Hydrography in the north–western Barents Sea, July–August 1996

CTD profiles from the north–western Barents August 1996, have been analysed and characteristics of have been compared with former analyses and investigations The barotropic and baroclinic modes of the Rossby radius of deformation have been estimated in order to give an estimate in order to give an estimate of the spatial scale of variations. The first baroclinic mode of the Rossby radius of deformation is estimated to be around 3 km. Cold halocline water (CHW) is found in the southern part of the investigation area, supporting a hypothesis that the production of CHW is located in the area around Storbanken, and not closer to the shelf break further north. Another hypothesis is proposed: tidal induced horizontal circulation and vertical currents may explain a northward transport of warmer water across sills and banks in the north–western Barents Sea.     

Variability and climate sensitivity of fast ice extent in the north-eastern Kara Sea

This 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.     

Simulation of currents, ice melting, and vertical mixing in the Barents Sea using a 3-D baroclinic model

A baroclinic. 3-D model is described. It is adapted to the Barents Sea and includes thermodynamics and atmospheric input. The freezing and melting of ice is allowed for in the model. The main task of the study is to look at the development of the ice cover, the vertical mixing, and the vertical and horizontal density gradients.
Despite simple approximations in the air temperature input, realistic ice-cover is produced in the model area during simulation of a "freezing period" (winter). This intermediate result is briefly discussed and also forms the start of a "melting period" simulation (spring/summer). Atmospheric input data (wind, air pressure, and heat flux) from the spring and summer 1983 is used, and details about vertical mixing, temperature, and salinity are discussed. The simulation results demonstrate the temporal variation of the thermocline depth, the variation of the ice cover, and the horizontal changes of density. The conclusion is that despite often simplified input, the model seems to produce a physical picture characteristic of the Barents Sea.     

Decadal decrease of Antarctic sea ice extent inferred from whaling records revisited on the basis of historical and modern sea ice records

In previous work, whaling catch positions were used as a proxy record for the position of the Antarctic sea ice edge and mean sea ice extent greater than the present one spanning 2.8° latitude was postulated to have occurred in the pre-1950s period, compared to extents observed since 1973 from microwave satellite imagery. The previous conclusion of an extended northern latitude for ice extent in the earlier epoch applied only to the January (mid-summer) period. For this summer period, however, there are also possible differences between ship and satellite-derived measurements. Our work showed a consistent summer offset (November-December), with the ship-observed ice edge 1 - 1.5° north of the satellite-derived ice edge. We further reexamine the use of whale catch as an ice edge proxy where agreement was claimed between the satellite ice edge (1973-1987) and the ship whale catch positions. This examination shows that, while there may be a linear correlation between ice edge position and whale catch data, the slope of the line deviates from unity and the ice edge is also further north in the whale catch data than in the satellite data for most latitudes. We compare the historical (direct) record and modern satellite maps of ice edge position accounting for these differences in ship and satellite observations. This comparison shows that only regional perturbations took place earlier, without significant deviations in the mean ice extents, from the pre-1950s to the post-1970s. This conclusion contradicts that previously stated from the analysis of whale catch data that indicated Antarctic sea ice extent changes were circumpolar rather than regional in nature between the two periods.     

Phototrophic and heterotrophic nano- and microorganisms of sea ice and sub-ice water in Guba Chupa (Chupa Inlet), White Sea, in April 2002

Autotrophic and heterotrophic flagellates, microalgae and ciliates sampled at four stations in the White Sea in April 2002 were studied using epifluorescence microscopy. The concentrations of phototrophic 1.5 μm algae in the middle and lower part of the ice core were very high: up to 6.1 ± 10⁸ cells I⁻¹ and 194 μg C I⁻¹. Heterotrophic algae made up the largest proportion of the nanoplankton (2-20 μm) and microplankton (20-200 μm) at depths 10-25 m below the ice. The proportion of ciliates ranged from about 0.01% to 18% at different stations and depths. Most of the ciliate biomass in the ice was made up of typical littoral zone species, whereas the water under the ice was dominated by phototrophic Myrionecta rubra . Ice algae, mainly flagellates in the upper ice layer and diatoms in the bottom ice layer, supported the proliferation of heterotrophs, algae and ciliates in early spring. Small heterotrophs and diatoms from the ice may provide food for early growth and development of pelagic copepods. Mass development of the ice algae in early spring appears typical for the seasonal ice of the White Sea. Ice algae differ in species composition from the spring pelagic community and develop independently in time and space from the spring phytoplankton bloom.     

The distribution and diel movements of Brünnich's Guillemot Uria lomvia in ice covered waters in the Barents Sea, February/March 1987

The distribution of Brünnich's Guillemot in ice covered waters and near the marginal ice zone in the southern part of the Barents Sea was mapped from ship and helicopter in February/March 1987. High densities of Brünnich's Guillemot (up to 1,300 ind./km²) were found in ice leads. The density of birds was especially high over shallow banks where the sea depth was 40-80 m.
A diel movement was also recorded. In the evening the birds left the leads and flew south. Next morning they returned to feed in the open leads. How far they migrated is uncertain, but possibly they flew down to the open sea or to leads close to the marginal ice zone. The migration may have been a means of avoiding to become trapped if leads closed after dark.     

Vertical material flux under seasonal sea ice in the Okhotsk Sea north of Hokkaido, Japan

Downward material fluxes under seasonal sea ice were measured using a time-series sediment trap installed at an offshore site in the Okhotsk Sea north of Hokkaido, Japan, from 13 January to 23 March 2005. The maximum fluxes of lithogenic material (753 mg m⁻² day⁻¹) and organic matter (mainly detritus; 333 mg m⁻² day⁻¹) were recorded during the period in which sea ice drifted ashore and increased in extent, from 13 January to 9 February. Organic matter as fecal pellets (81–93 mg m⁻² day⁻¹) and opal as biosilica (51–67 mg m⁻² day⁻¹), representing diatom fluxes, were abundant in sediment trap samples obtained during the period of full sea ice coverage from 10 February to 9 March. Microscopic observations revealed that fecal pellets were largely diatom frustules, suggesting that zooplankton actively grazed on ice algae during the period of full sea ice coverage. During the period of retreating sea ice, from 10 to 23 March, the phytoplankton flux showed a rapid increase (from 9.5 to 22.5 × 10⁶ cells m⁻² day⁻¹), reflecting their release into the water column as the sea ice melted. Our results demonstrate that the quantity and quality of sinking biogenic and lithogenic materials vary with the seasonal extent of sea ice in mid-winter.