The variation features of the Antarctic sea ice (Ⅱ)

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南极海冰和陆架冰的变化特征

利用美国冰中心和雪冰中心提供的海冰资料和我国南极考察现场的海冰观测资料,对南极海冰的长期变化进行了研究.研究表明20世纪70年代后期是多冰期;80年代是少冰期;90年代南极海冰属于上升趋势,后期偏多,区域性变化差别大,东南极海冰偏多,西南极海冰即南极半岛两侧尤其是威德尔海区和别林斯高晋海的冰明显偏少.东南极和西南极海冰的变化趋势总是反相的.90年代后期普里兹湾的海冰明显偏多,南极大陆陆架冰外缘线总体没有明显的收缩,有崩解也有再生的自然变化现象.西南极威德尔海的龙尼冰架和罗斯海冰架东部崩解和收缩趋势明显,东南极的冰架也有崩解和收缩,但没有西南极明显.陆架冰崩解向海洋输送的冰山对全球海平面升高有一定的影响.目前南极冰盖断裂崩解形成的冰山,向海洋输入的水量可使全球海平面上升约14mm.南极海冰没有随着全球气候温暖化而明显减少,而是按照东南极和西南极反相的变化规律进行周期性的变化、调整和制约.     

The production of biogenic silica in the Weddell and Scotia Seas

During the EPOS leg 2 cruise (European Polarstern Study, November 1988–January 1989), the production rate of biogenic silica in the euphotic zone was measured by the ³⁰Si method at stations in the Scotia and Weddell Seas.The highest integrated production rates were observed in the Scotia Sea (range: 11.2–20.6 mmol Si m⁻² day⁻¹), the marginal ice zone of the Weddell Sea exhibiting somewhat lower values (range: 6.0–20.0 mmol Si m⁻²day⁻¹).Our results demonstrate that as far as biogenic silica production is concerned the marginal ice zone of the Weddell Sea is considerably less productive than that of the Ross Sea. Our results also indicate that the water of the Antarctic Circumpolar Current (ACC) could be more productive in late spring and early summer than at the beginning of spring. Possible reasons for the differences among the three subsystems (Ross Sea, Weddell Sea and ACC) are discussed.     

Sea ice characteristics between the middle Weddell Sea and the Prydz Bay, Antarctica during the austral summer of 2003

The antarctic sea ice was investigated upon five occasions between January 4 and February 15, 2003. The investigations included: (1) estimation of sea ice distribution by ship-based observations between the middle Weddell Sea and the Prydz Bay; (2) estimation of sea ice distribution by aerial photography in the Prydz Bay; (3) direct measurements of fast ice thickness and snow cover, as well as ice core sampling in Nella Fjord; (4) estimation of melting sea ice distribution near the Zhongshan Station; and (5) observation of sea ice early freeze near the Zhongshan Station. On average, sea ice covered 14.4% of the study area. The highest sea ice concentration (80%) was observed in the Weddell Sea. First-year ice was dominant (99.7%-99.8%). Sea ice distributions in the Prydz Bay were more variable due to complex inshore topography, proximity of the Larsemann Hills, and/or grounded icebergs. The average thickness of landfast ice in NeUa Fjord was 169.5 cm. Wind-blown snow redistribution plays an important role in affecting the ice thickness in Nella Fjord. Preliminary freezing of sea ice near the Zhongshan Station follows the first two phases of the pancake cycle.     

A Scenario of the Late-Pleistocene-Holocene Changes in the Distributional Range of Antarctic Krill (Euphausia superba)

Abstract. Oceanographic evidence along with the data on Euphausia superba distribution indicate that the reproductive range of this species is related to the southernmost core of the Antarctic Circumpolar Current (ACC), the Weddell Gyre, the Ross Gyre, and the systems of mesoscale eddies in the Bellingshausen Sea, in the Prydz Bay area. and the D'Urville Sea. During the Last Glaciation Maximum, at ca. 18 ka BP, both the Weddell and the Ross Gyres as well as near-coastal circulations probably lost their importance in the maintenance of Antarctic krill populations due to cooling of the water column and development of multi-year sea ice. Within the ACC at that time, some smaller-scale circulations related to islands and seamounts could have played a major role in controlling krill distribution. If, nevertheless. refugia for self-maintained krill populations remained in the near-coastal zone, particularly in the eastern Indian sector, geographical isolation might have caused divergence between the two species of the gregarine Cephaloidophora commonly infesting krill at present.     

The seasonal growth of ice in the Antarctic

Composite pictures of the areal extent of Antarctic sea ice derived from satellite photographs, show that the growth and the rate of growth of the pack ice compare favorably to the values previously estimated on other bases. Anomalous growth patterns are found in the Weddell Sea. Possible causes of this anomaly include surface and subsurface advection of ice crystals. The rate of retrogradation of the pack ice is found to exceed the rate of progradation.     

Distribution and Adaptations of Sea Ice Inhabiting Harpacticoida (Crustacea, Copepoda) of the Weddell Sea (Antarctica)

Abstract. Seven harpacticoid species were found to be associated with sea ice collected during 5 Antarctic cruises of the RV Polarstern. Their distribution within the fast ice and pack ice zones of the Weddell Sea is presented. Whereas some individuals probably become entrapped into the ice only accidentally, at least 4 species arc genuinely sympagic. These have evolved remarkable adaptations, as evidenced by field and laboratory studies of Dresclieriella glacialis , which is by far the most abundant. Such adaptations include: the ability to penetrate deep into ice; a comparatively high salinity tolerance allowing it to endure large salinity fluctuations associated with ice crystal formation and melting; good swimming ability, necessary both for horizontal dispersal and for a planktonic intermezzo after annual melting of the sea ice. D. glacialis is the first polar non-vertebrate mctazoan to be cultivated through its entire life cycle. Its life history suggests an r-stratcgy; this would be the first indication of such a trait in the polar environment. A new species of Drescheriella , on the other hand, exhibits resting stages (C IV-V) known to date only for Calanoidu but not reported for Harpacticoida.     

The ecology and biogeography of tintinnid ciliates in the Atlantic sector of the Southern Ocean

Qualitative and quantitative analyses of the tintinnids retrieved in surface and vertical (down to 1150 m ) samples in the Scotia, Weddell, Bransfield and Bellingshausen areas allow us to define three distinct zones: (A) the Scotia Sea, Bransfield Strait and oceanic waters of the northern-central Weddell Sea, dominated by Codonelopsis gaussi and Cymatocylis affinis/conmllaria; (B) shelf and mostly ice-covered areas of the southernmost Weddell Sea and the Bellingshausen Sea, characterized by Laackmanniella prolongata and Cymatocylis drygalskii; (C) Bransfield-Weddell waters around the tip of the Antarctic Peninsula, where Codonellopsis balechi accounts for 80% of the tintinnids. These areas have (often significantly) different ice regimes, water-column depths, surface salinities, bulk planktonic settling volumes and microplanktonic concentrations. On the other hand, the composition of tintinnid assemblages is very similar on both sides of the Antarctic Peninsula. Causal interpretations for these heterogeneous distribution patterns and probable specific adaptations to the dissimilar environmental settings involved are analyzed.     

南极海冰快速下降历史事件的时空特征分析

卫星记录以来,南极海冰范围发生5次快速下降事件,研究这5次事件的时空特征,对进一步认识海冰快速下降事件的物理机制具有重要意义。基于海冰范围和海冰密集度的卫星数据,从时间和空间两个维度总结5次南极海冰快速下降事件的特征,再结合大气和海洋各项环境因素的再分析数据,探讨海冰快速下降的影响因素及其驱动过程。结果显示:南极海冰快速下降的空间分布存在季节性差异, 2021年8～12月以及2016年8～12月的春季南极海冰快速下降由别林斯高晋海、威德尔海、印度洋和西太平洋区域的海冰减少所主导; 2010年12月至2011年4月以及1985年12月至1986年4月的夏季南极海冰快速下降由威德尔海、罗斯海沿岸和西太平洋区域的海冰减少所主导;2008年4～8月的冬季南极海冰快速下降则由别林斯高晋海和西太平洋的部分区域的海冰减少所主导。探究影响海冰的环境因素发现,海表面温度和海表面净热通量对海冰减少的热力效应影响具有区域性差异。此外,南极海冰快速下降受阿蒙森低压的影响,相应的海表面风异常既通过经向热输运的热力效应导致海冰减少,也通过风的动力效应驱动海冰漂移使得海冰密集度降低。     

Recognition of contour-current influence in mixed contourite-turbidite sequences of the western Weddell Sea,Antarctica

Sedimentary processes and structures across the continental rise in the western Weddell Sea have been investigated using sediment acoustic and multichannel seismic data, integrated with multibeam depth sounding and core investigations. The results show that a network of channels with associated along-channel ridges covers the upper continental slope. The seismic profiles reveal that the channels initially developed as erosive turbidite channels with associated levees on their northern side due to Coriolis force. Later they were partly or fully infilled, probably as a result of decreasing turbidite activity. Now the larger ones exist as erosive turbidite channels of reduced size, whereas the smaller ones are non-erosive channels, their shape being maintained by contour current activity. Drift bodies only developed where slumps caused a distinctive break in slope inclination on the upper continental rise, which served to initiate the growth of a drift body fed by contour currents or by the combined action of turbidites and contourites. The history of sedimentation can be reconstructed tentatively by correlation of seismo-stratigraphic units with the stages of evolution of the drifts on the western side of the Antarctic Peninsula. Three stages can be distinguished in the western Weddell Sea after a pre-drift stage, which is delimited by an erosional unconformity at the top: (1) a growth stage, dominated by turbidites, with occasional occurrence of slumps during its initial phase; (2) during a maintenance stage turbiditiy-current intensity (and presumably sedimentation rate also) decreased, probably as a result of the ice masses retreating from the shelf edge, and sedimentation became increasingly dominated by contour current activity; and (3) a phase of sheeted-sequence formation. A southward decrease in sediment thickness shows that the Larsen Ice Shelf plays an important role in sediment delivery to the western Weddell Sea. This study shows that the western Weddell Sea has some characteristics in common with the southern as well as the northwestern Weddell Sea: contour currents off the Larsen Ice Shelf have been present for a long time, probably since the late Miocene, but during times of high sediment input from the shelves as a result of advancing ice masses a channel-levee system developed and dominated over the contour-current transport of sediment. At times of relatively low sediment input the contour-current transport dominated, leading to the formation of drift deposits on the upper continental rise. Seaward of areas without shelf ice masses the continental rise mainly shows a rough topography with small channels and underdeveloped levees. The results demonstrate that sediment supply is an important, maybe the controlling factor of drift development on the Antarctic continental rise.     

The distribution of tritium and CFCs in the Weddell Sea during the mid-1980s

Transient tracer data (tritium, CFC11 and CFC12) from the southern, central and northwestern Weddell Sea collected during Polarstern cruises ANT III-3, ANT V-2/3/4 and during Andenes cruise NARE 85 are presented and discussed in the context of hydrographic observations. A kinematic, time-dependent, multi-box model is used to estimate mean residence times and formation rates of several water masses observed in the Weddell Sea.Ice Shelf Water is marked by higher tritium and lower CFC concentrations compared to surface waters. The tracer signature of Ice Shelf Water can only be explained by assuming that its source water mass, Western Shelf Water, has characteristics different from those of surface waters. Using the transient nature of tritium and the CFCs, the mean residence time of Western Shelf Water on the shelf is estimated to be approximately 5 years. Ice Shelf Water is renewed on a time scale of about 14 years from Western Shelf Water by interaction of this water mass with glacial ice underneath the Filchner-Ronne Ice shelf. The Ice Shelf Water signature can be traced across the sill of the Filchner Depression and down the continental slope of the southern Weddell Sea. On the continental slope, new Weddell Sea Bottom Water is formed by entrainment of Weddell Deep Water and Weddell Sea Deep Water into the Ice Shelf Water plume. In the northwestern Weddell Sea, new Weddell Sea Bottom Water is observed in two narrow, deep boundary currents flowing along the base of the continental slope. Classically defined Weddell Sea Bottom Water (θ ≤ −0.7°C) and Weddell Sea Deep Water (−0.7°C ≤ θ ≤ 0°C) are ventilated from the deeper of these boundary currents by lateral spreading and mixing. Model-based estimates yield a total formation rate of 3.5Sv for new Weddell Sea Bottom Water (θ = −1.0°C) and a formation rate of at least 11Sv for Antarctic Bottom Water (θ = −0.5°C).     

An estimate of water mass transformation in the southern Weddell Sea

Bottom water formation changes the characteristics of water masses entering the southern part of the Weddell Sea through atmosphere-ice-ocean interaction in which both sea and shelf ice play an important role. Modified water, in particular Weddell Sea Bottom Water, recirculates in the west. By comparing the in- and outflowing water masses we have estimated transformation rates on the basis of a data set obtained during the Winter Weddell Gyre Study from September to October 1989. This consisted of a salinity-temperature-depth (CTD) section carried out by R/V “Polarstern” from the northern tip of the Antarctic Peninsula to Kapp Norvegia and data from three current meter moorings maintained from 1989 to 1990 in the eastern boundary current off Kapp Norvegia. Because of the lack of sufficient direct current measurements in the interior and the western boundary current, it was necessary to derive mass transports on the basis of available data combined with physical and geometrical arguments. At the mooring site barotropic currents were measured. They were extrapolated to the interior under the assumption that wind-driven, baroclinic and barotropic current fields are of similar shape. The location of the gyre centre was determined from drifting buoy tracks and geopoten-tial anomaly. A linear current profile from the eastern boundary current to the centre of the gyre was assumed, and the western outflow was determined according to mass conservation. Different assumptions on the transition from the boundary current to the interior and the location of the centre result in a wide range of transports with most likely values between 20 and 56 Sv. The total mass transport was split into individual water masses. Differences between inflow and outflow result in a transformation rate of 3–4 Sv from Winter and Warm Deep Water to Antarctic and Weddell Sea Bottom Water. The net heat and salt transport across the transect implies heat fluxes from the ocean to the atmosphere of 3–10 W m⁻² and ice formation rates of 0.2–0.35 m year⁻¹.     

利用探地雷达(GPR)观测加拿大北极群岛和陆架区海冰厚度空间分布特征

Ground Penetrating Radar(GPR) measurements of sea ice thickness including undeformed ice and ridged ice were carried out in the central north Canadian Archipelago in spring 2010. Results have shown a significant spatial heterogeneity of sea ice thickness across the shelf. The undeformed multi-year fast ice of(2.05±0.09) m thick was investigated southern inshore zone of Borden island located at middle of the observational section,which was the observed maximum thickness in the field work. The less thick sea ice was sampled across a flaw lead with the thicknesses of(1.05±0.11) m for the pack ice and(1.24±0.13) m for the fast ice. At the northernmost spot of the section, the undeformed multi-year pack ice was(1.54±0.22) m thick with a ridged ice of 2.5 to 3 m,comparing to the multi-year fast ice with the thickness of(1.67±0.16) m at the southernmost station in the Prince Gustaf Adolf Sea.     

南极大陆边缘研究进展

本文综合国外有关资料,介绍了70年代以来南极大陆边缘地球物理调查、尤其是多道反射地震调查,深海钻探,地震地层研究,以及面积大、赋有油气远景的两个海区——威德尔海和罗斯海研究的进展情况。     

Seismic stratigraphy of the Adare Trough area, Antarctica

The Adare Trough, located 100 km NE of Cape Adare, Antarctica, is the extinct third arm of a Tertiary spreading ridge that separated East from West Antarctica. We use seismic reflection data, tied to DSDP Site 274, to link our seismic stratigraphic interpretation to changes in ocean-bottom currents, Ross Sea ice cover, and regional tectonics through time. Two extended unconformities are observed in the seismic profiles. We suggest that the earliest hiatus (early Oligocene to Mid-Miocene) is related to low sediment supply from the adjacent Ross Shelf, comprised of small, isolated basins. The later hiatus (mid-Miocene to late Miocene) is likely caused by strong bottom currents sourced from the open-marine Ross Sea due to increased Antarctic glaciation induced by mid-Miocene cooling (from Mi-3). Further global cooling during the Pliocene, causing changes in global ocean circulation patterns, correlates with Adare Basin sediments and indicate the continuing but weakened influence of bottom currents. The contourite/turbidite pattern present in the Adare Trough seismic data is consistent with the 3-phase contourite growth system proposed for the Weddell Sea and Antarctic Peninsula. Multibeam bathymetry and seismic reflection profiles show ubiquitous volcanic cones and intrusions throughout the Adare Basin that we interpret to have formed from the Oligocene to the present. Seismic reflection profiles reveal trans-tensional/strike-slip faults that indicate oblique extension dominated Adare Trough tectonics at 32–15 Ma. Observed volcanism patterns and anomalously shallow basement depth in the Adare Trough area are most likely caused by mantle upwelling, an explanation supported by mantle density reconstructions, which show anomalously hot mantle beneath the Adare Trough area forming in the Late Tertiary.     

Improved Seismic Stratigraphy of the Mesozoic Weddell Sea

We present a compilation of more than 45,000 km of multichannel seismic data acquired in the last three decades in the Weddell Sea. In accordance with recent tectonic models and available drillhole information, a consistent stratigraphic model for depositional units W1–W5 is set up. In conjunction with existing aeromagnetic data, a chronostratigraphic timetable is compiled and units W1.5, W2 and W3 are tentatively dated to have ages of between 136 Ma and 114 Ma. The age of W3 is not well constrained, but might be younger than 114 Ma. The data indicate that the thickest sediments are present in the western and southern Weddell Sea. These areas formed the earliest basins in the Weddell Sea and so the distribution of Mesozoic sediments is in accordance with the tectonic development of the ocean basin. In terms of Cenozoic glacial sediments, the largest depocenters are situated in front of the Filchner–Ronne Shelf, i.e. at the Crary Fan, with a thickness of up to 3 km.     

南极威德尔海区域海冰异常对初夏东亚大气环流和天气影响的数值研究

利用经过改变用于长期数值预报的CCM1(R15L7)模式以1975年1月16日00Z模式适应场为初始场积分5个月,研究南极威德尔海附近(60°W～30°E)海冰的面积异常对东亚初夏环流转换季节的影响.发现当南极海冰偏多时,在亚洲北部冷空气活动在初夏仍然很多,势力还很强,东亚南北两支急流分支仍很明显,各种环流特征更偏向于冬季型,不利于东亚初夏的环流季节转换.海冰异常偏少时则相反,亚洲北部的冷空气活动明显减弱,南方暖气流势力明显加强北移,东亚的两支急流也趋于合并北抬,环流形势更接近于夏季型,海冰的减少促进了东亚初夏的环流季节转换过程.     

DISTRIBUTION, ECOLOGY AND RESOURCE CONSERVATION OF THE SPOTTED SEAL IN THE HUANGHAI AND BOHAI SEAS

The Phoca largha is found in the coastal waters of China from the Huanghai Sea and Bohai Sea to the northern part of East China Sea. Its breeding ground is situated in ice packs in the Liaodong Gulf., from about 40°10′ to 40°45′ N, from 121 °15′ to 122°E. At the breeding season, male and female seals in pairs form many family groups. The pup is born with white lanugo fur on ice packs in Liaodong Gulf during a period from January to the middle of February, and usually carried by its mother on her back to run away. However, from February to March, it could be caught around some islands in Bohai Strait. In recent years, these species resources have been reduced rapidly. It must be strengthened to protect the seals from extinction.     

On the future navigability of Arctic sea routes: High-resolution projections of the Arctic Ocean and sea ice

The rapid Arctic summer sea ice reduction in the last decade has lead to debates in the maritime industries on the possibility of an increase in cargo transportation in the region. Average sailing times on the North Sea Route along the Siberian Coast have fallen from 20 days in the 1990s to 11 days in 2012–2013, attributed to easing sea ice conditions along the Siberian coast. However, the economic risk of exploiting the Arctic shipping routes is substantial. Here a detailed high-resolution projection of ocean and sea ice to the end of the 21st century forced with the RCP8.5 IPCC emission scenario is used to examine navigability of the Arctic sea routes. In summer, opening of large areas of the Arctic Ocean previously covered by pack ice to the wind and surface waves leads to Arctic pack ice cover evolving into the Marginal Ice Zone. The emerging state of the Arctic Ocean features more fragmented thinner sea ice, stronger winds, ocean currents and waves. By the mid 21st century, summer season sailing times along the route via the North Pole are estimated to be 13–17 days, which could make this route as fast as the North Sea Route.     

Trace metal concentrations in the Ross Sea and their relationship with nutrients and phytoplankton growth

Dissolved and particulate trace metal concentrations (dissolved Fe, Zn, Cd, Co, Cu and Ni; particulate Fe, Mn and Al) were measured along two transects in the Ross Sea during austral summer of 1990. Total Fe concentrations in southern Ross Sea and inshore waters were elevated >3.5 times that of northern waters. Dissolved Zn, Cd and Co concentrations were lower by factors of 4.5, 3.5 and 1.6 in southern surface waters relative to northern waters. Dissolved Cu and Ni concentrations were similar in both areas. Elevated Fe concentrations coincided with areas of increased productivity, phytoplankton biomass and nutrient drawdown, indicating that Fe is an important factor controlling the location of phytoplankton blooms in the Ross Sea. Particulate concentrations of Fe, Mn and Al indicate two possible sources of iron to the Ross Sea, resuspension of continental shelf sediments and iron incorporated in annual sea ice and released with meltwaters.