极地研究

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The ⁴⁰Ar-³⁹Ar ages of hornblendes in Grt-Pl-bearing amphibolite from the Larsemann Hils, East Antarctica and their geological implication

Tong Laixi, Liu Xiaohan, Zhang Liansheng, Chen Haihong, Chen Fukun, Wang Yanbin, Ren Liudong

1998, 9 (2-English): 79-91.

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In this paper we reported the ⁴⁰Ar-³⁹Ar dating results of hornblendes in Grt-P1-bearing amphibolite from the Larsemann Hills, East Antarctica. Their apparent ages respectively are 1586 Ma, 1011-1080 Ma, 761 Ma, 529-582 Ma. Their plateau ages of 1036 Ma and 554 Ma as well as an Ar-Ar isochron age of 1010 Ma have also been obtained respectively. These isotopic dating results for the first time by the Ar-Ar method for hornblendes completely record almost all the structural metamorphic thermal events that this region experienced, and provide an answer to the controversial question on the structural metamorphic thermal events of this region in recent several years, namely, which one is more important, the late Proterozoic 1000 Ma event (Grenvillian) or the early Palaeozoic 500 Ma event ( Pan African), as well as whether the former exists or not. The ⁴⁰Ar-³⁹Ar dating results of hornblendes show that the Larsemann Hills experienced a complicated poly metamorphic evolutionary history, and their protoliths were probably formed in early to mid Proterozoic. The late Proterozoic 1000 Ma event (Grenvillian) has been confirmed to be a predominant tectonothermal event whilst the early Palaeozoic 500 Ma event (Pan-African) has been confirmed just to be the last strong tectonothermal event in this region.

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Carbon cycle in the Arctic terrestrial ecosystems in relation to the global warming

Fang Jingyun, Fei Songlin

1998, 9 (2-English): 92-100.

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The relationship between the global warming and carbon cycle in the Arctic terrestrial ecosystem was discussed based on a literature survey. As a result, atmospheric carbon dioxide (CO₂) and methane (CH₄) concentrations increased markedly during the past few centuries. The increase in concentration of these greenhouse gases was coupled with the global warming. Summer temperature in the Arctic regions showed a rapid rising. The Arctic soil is a huge organic carbon pool, with a mean estimate of 355×10⁹ tC, being 23.7%-32.3% of global soil carbon pool. At present the Arctic terretrial ecosystem is functioning as a sink of atmospheric CO₂. The rising global temperature resulting from an increase in atmospheric CO₂ would influence markedly the Arctic soil carbon and CO₂ source/sink relation of the Arctic ecosystems.

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Analysis of sedimentary environment of core AB-67 at Barrow

Wang Guo, Zhang Qingsong, Li Yuanfang

1998, 9 (2-English): 101-108.

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A total of 48 samples from the core AB-67 at Barrow are analyzed for 25 grain size items and 44 geochemical items. Q-mode factor analysis applied to these data yielded 4 factors. Mapping of there factor showed their close affinity to sedimentary environment; these core sedimentary rate, precipitation, sea level change, annual temperature. Paleoenvironmentary transfer functions were defined to estimate mean annual temperature and annual precipitation from corelationship between 5 samples at core-top and observation record from Barrow Meteorology Observatory. Sedimentary rate was determinated from dating by ²¹⁰Pb and several environment events, and sea level from changes of sedimentary phase. The reconstructed temperature and precipitation curves show that Barrow climate is colder and drier in the 16th and the 17th century, temperature rose up and precipitation fluctuated sharply in the 18th and the 19th century, these two changes are greater in the 20th century. The reconstructed temperature curves agree with the variation of assemblages of micropaleontology.

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Characteristics of ion concentrations in snowpits in Longyearbyen, Svalbard, Arctic

Kang Shichang, Qin Dahe, Ren Jiawen, Yngvar Gjessing

1998, 9 (2-English): 109-117.

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Snowpits samples were collected from three glaciers in the Longyearbyen region, Svalbard during March to May, 1996. Among major chemical species (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, NO₃^- and SO₄^2-), Cl^- and Na⁺, which come mainly from sea salt aerosol, are the dominant soluble impurities in snowpits. In dirty layers of snowpits (representing autumn), the crustal cation Ca²⁺ has the highest concentration among all species. Thus, snowpits have been dated by high values of Ca²⁺ concentrations and less negative δ¹⁸O, which represent autumn and summer layers respectively. Seasonal variations in concentrations of sea salt ions ( Na⁺, Mg²⁺ and Cl^-), SO₄^2- and NO₃^- have been identified. Results indicate that concentrations of these ions show high value in spring and summer. The spring maximum value likely results from long range transport of marine aerosol from north Atlantic storms( Na⁺, Mg²⁺ and Cl^-) and mid latitude anthropogenic pollution (SO₄^2- and NO₃^-). In summer, high concentrations of the sea salt species are attributed to local marine aerosol. The summer SO₄^2- maximum likely reflects a combination of local marine aerosol, high scavenging ratios, and oxidation of marine biogenic emissions. In comparison, NO₃^- maximum may reflect lightening in the atmosphere and high scavenging ratios. In general, the major ion concentrations in snowpits in Svalbard is high in comparison with those found in snowpits from other remote regions, such as Greenland, Antarctic and Qinghai Tibetan Plateau, especially for sea salt species.

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The extraction of elevation information of ice-sheet surface on south area of the Larsemann Hills in East Antarctica

Sun Jiabing, Liu Jilin, Liu Liangming, Sun Zhaohui

1998, 9 (2-English): 118-124.

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Based on the setting up of the function relation between the radiant brightness of ice surface and the elevation control point in Antarctica, the experiments for the extraction of elevation information by using thermal infrared image of Landsat TM band 6, and the ice-surface topographical maps in area nearby Larsemann Hills have been performed.

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Late Palaeogene palynoflora from Point Hennequin of the Admiralty Bay, King George Island, Antarctica with reference to its stratigraphical significance

Duan Weiwu, Cao Liu

1998, 9 (2-English): 125-132.

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The present paper is to discuss the geological age and sedimentary environment based mainly on the characteristics of the palynological assemblage in the intercalated tuffaceous sand mudstones of the Upper Point Hennequin Group in the Admirelty Bay, King George Island, Antarctica. More than 40 species, mainly the Late Paleogene plant community in Gondwana and belonging to Weddellian biogeographic Province, were encountered within the volcano sedimentary rocks of the Upper Point Hennequin Group. The index member is the genus Nothofagidites. The occurrence of N. cf. saraensis and N. cf. flemingii and the absence of Proteacidites spp. indicates that the sporopollen bearing rocks is of Oligocene age, which were deposited in a limnetic zone near medium lower mountains environment with warm and humid climate.

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Ecology features of coastal saline lakes related to environmental evolution in the area of Antarctic continental ice edge

Wang Zipan, Patrick Deprez

1998, 9 (2-English): 133-140.

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An investigation has been made on the ecology of some saline lakes in the Vestfold Hills (60°38′S, 78°06′E), East Antarctica. The results indicate that changes of natural environment and physico chemical factors, as well as the variation and evolution of biological species do occur in some lakes. This can be attributed to seasonal and local climate changes and geographic differences in this regions. These findings are believed to be indicative to the effects from the processes of globle climate change, ice sheet retreat, and isostatic uplift, are presently occuring, and a study of the chemistry and biology of these Antarctic lakes may be a significant means of monitoring effects of global climate change in the Antarctic.

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The depletion of nutrients and the estimation of the new production in the ice-edge of the Prydz Bay, Antarctica

Chen Zhiqiang, Wang Yuheng, Liu Jidi

1998, 9 (2-English): 141-148.

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The distributions and changes of nutrients in the Prydz Bay were investigated during CHINARE-6 (the 6th Chinese National Antarctic Research Expedition) and CHINARE-9, and the new productions were estimated by using mass balance method. The results showed that in CHINARE 6, the depletion of NO₃-N, PO₄-P, SiO₃-Si were 1064.8, 69.2, 2196.9 mmol/m² ,respectively, the uptake ratios of N and Si to P were 15.3, 31.7, respectively, and new production was 992.4 mgC/(m²·d); in CHINARE-9, the depletion of NO₃-N, PO₄-P were 551.9 , 41.2 mmol/m² , respectively, the uptake ratio of N to P was 13.4,and the new production was 390.1 mgC/(m²·d) , indicating significant annual and/or seasonal variation. New productions were both greater than the primary production determined by ¹⁴C-trace method, demonstrating there existed rather higher new production in the Prydz Bay in austral summer. The uptake ratio of nutrients in the Prydz Bay, however, is different from the previous values obtained from the open sea, showing the regional difference of uptake and regeneration of nutrients in the Southern Ocean. Finally the annual change of new production and the characteristics of phytoplankton production were discussed.

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Impact of the formation and ablation of Antarctic ice sheet on the global geoid and sea level

Zhang Chijun, Lu Yang

1998, 9 (2-English): 149-153.

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It is convenient to investigate the gravimetry using a harmonic spheric function for the description of the distribution and thickness of the Antarctic ice sheet. The gravitational theory and the Stokes' harmonic spheric function formula were used to determine the impact of the Antarctic ice cap on the global geoid. The Antarctic ice cap is formed from the condensation of seawater vapour whose mass is equal to a layer of seawater 59 m thick of covering the earth's surface, i.e. 2.7×10¹⁹ kg. This will cause the global averaged geoid to decrease for around 23 m. The authors' computations show that the Antractic ice cap has a great impact on the global geoid, which increases (+) in some regions, but decreases (-) in other reigions. The geoid is +115 m, -37 m and +8 m at the South Pole, the 25°S parallel and the North Pole, respectively. If the Antarctic ice cap melts completely, on the rigid Earth's surface the seawater and geoid will return to its original position (and height) due to the balancing force of the fluid. Since the crust is almost in a state of isostasy, assuming that the crust is an elastic solid and the mantle is an incompressible fluid, the load of seawater will deflect the crust and drive the mantle material to flow. The material above the isostatic surface compensates mutually. If the densities of the mantle and seawater are 3270 kg/m³ and 1030 kg/m³, respectively, then the variation in the elevation of the continent is only 2.8 m with respect to the sea level after the Antarctic ice cap melts; it is not larger than that estimated by some people.It is worth noting that the above results were derived from an ideal Earth model. In the real Earth, the mantle and crust are visco elastic.

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Three species of bryophytes from the Fildes Peninsula of Antarctica under the observation of SEM

Liu Jiaxi, Li Xuedong, Chen Fudong

1998, 9 (2-English): 154-156.

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This article is to describe the characteristics of morphological structure of sporogona of three bryophytes observed under the SEM from the Fildes Peninsula, Antarctica, which has riched research information of bryophyte study of the area.

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