Late Quaternary deglaciation and climate history of the Larsemann Hills (East Antarctica)

The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice‐covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedimentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene climate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold conditions are inferred from high lake‐water salinities, and low water levels and an extended duration of nearshore sea‐ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stratified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea‐ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea‐ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice‐core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long‐term climate change on the terrestrial environment. Copyright © 2004 John Wiley & Sons, Ltd.     

Abrupt climate warming in East Antarctica during the early Holocene

We report a centennial-scale warming event between 8600 and 8400 cal BP from Amery Oasis, East Antarctica, that is documented by the geochemical record in a lacustrine sediment sequence. The organic carbon content, the C/S ratio, and the sedimentation rate in this core have distinctly elevated values around 8500 y ago reflecting relatively warm and ice-free conditions that led to well-ventilated conditions in the lake and considerable sedimentation of both autochthonous and allochthonous organic matter on the lake bottom. This abrupt warming event occurred concurrently with reported warm climatic conditions in the Southern Ocean while the climate in central East Antarctic remained cold. The comparison of the spatial and temporal variability of warm climatic periods documented in various terrestrial, marine, and glacial archives from East Antarctica elucidates the uniqueness of the centennial-scale warming event in the Amery Oasis. We also discuss a possible correlation of the Amery warming event with the abrupt climatic deterioration around 8200 cal BP on the Northern Hemisphere.     

关于矿床学创新问题的探讨

2003年1月4日至2月15日期间,在5种不同情况下对南极海冰进行了调查研究。包括:(1)基于走航观测的威德尔海至普利茨湾之间海冰分布研究;(2)基于航空拍摄的普利茨湾海冰分布研究;(3)纳拉海峡固定冰和上浮雪厚度钻孔测量以及冰心钻取;(4)中山站附近融化冰的分布研究以及(5)中山站附近海冰早期冻结过程观测研究。结果表明,威德尔海至普利茨湾之间走航观测得到的海冰全部密集度为14.4%,大部分冰(99.7%~99.8%)属于一年冰,观测到冰的厚度在15~150 cm。沿观测航线上海冰最大密集度(80%)出现在威德尔海,从59°56 S到69°22 S以及从040°41 W到076°23 E的区域分布着广阔的水域。这一结果验证了Silvia的海冰漂移理论。普利茨湾沿岸海冰受制于沿岸地形、拉斯曼丘陵以及搁浅冰山的影响,其密集度呈现较大的空间变化。钻孔测量显示,纳拉海峡固定冰平均厚度为169.5 cm。风吹雪的重分布以及日照强度差异是导致纳拉海峡固定冰厚度差异的主要因素。观测表明,中山站附近海冰早期冻结遵循Lange的海冰早期冻结过程“饼状循环”最初的两个阶段。     

2003年南极威德尔海至普里兹湾之间海冰分布研究

Ship-based sea ice observation data (concentrations,ice thickness,topography and overlying snow cover) were collected from Middle Weddell Sea to Prydz Bay,Antarctic during the period of 4 to 17 Jan 2003.Antarctic ice chart of first week of Jan 2003 was derived from National Ice Center (NIC).The compared analysis of sea ice concentrations and thickness distributions were conducted though in situ data and NIC chart.Results from sea ice concentration-analysis indicated the presence of large-scale open water between 2000 and 4100 km along transit route resulted from sea ice drifting.We describe the existence of mostly smooth first-year sea ice in study region ranged between 30 and 120 era.We also display the derived overlying snow coverage.Our results reveal the strong correspondence between ship-based observations and remotely sensed ice charts whatever in ice concentrations and ice thickness distributions.     

浙江北湖桥岩芯记录的早-中全新世环境演变

通过对浙江余杭北湖桥钻孔(简称BHQ孔)沉积物中总有机碳(TOC)和碳同位素(δ13C_org)的分析,结合碳氮比(C/N)、粒度参数、年代和孢粉资料,探讨了研究区域早中全新世期间气候演变规律。结果表明,BHQ孔所在区域早中全新世期间,环境变化可以划分为3段:①11.4~8.7 ka B.P.,δ13C_org在-27.24‰~-23.4‰范围内波动升高,TOC含量(0.19%~0.69%)呈显著增加趋势,指示气候由冷干逐渐转向温湿。②8.7~8.0 ka B.P.,TOC含量偏低,δ13C_org(-24.91‰~-22.93‰)较为偏正,指示气候呈冷干-温湿-温干。③8.0~4.2 ka B.P.,TOC含量(0.18%~2.18%)和δ13C_org(-26.33‰~-19.09‰)变化频繁且幅度较大,但整体上TOC含量偏高,δ13C_org偏负,指示该段时期内气候总体呈暖湿特征,且存在不同尺度的冷暖波动。其中在8.0~5.7 ka B.P.期间,TOC含量(0.43%~2.18%)明显偏高,δ13C_org(-25.79‰~-23.15‰)明显偏负,指示气候温暖湿润,对应于区域全新世大暖期;此外本段时期内还记录到5.5 ka B.P.和4.2 ka B.P.两次冷事件。由此表明湖沼相沉积物TOC及δ13C_org可以记录降水量和温度的变化状况,能有效指示古气候的变化规律,同时研究结果初步揭示了浙北地区早中全新世期间气候演变特点。     

Timing of the progress granite,Larsemann hills: Additional evidence for early Palaeozoic orogenesis within the east Antarctic Shield and implications for Gondwana assembly

The Progress Granite is one of numerous S‐type granitoid plutons exposed in the Larsemann Hills region, southwest Prydz Bay, east Antarctica. The granite was emplaced into a migmatitised pelitic to felsic paragneiss sequence during a regional high‐grade transpressional event (D₂) that pre‐dates high‐grade extension (D₃). SHRIMP (II) U‐Pb dating for two occurrences of the Progress Granite from D₂ and D₃ structural domains gives ²⁰⁶Pb/²³⁸U ages of 516.2 ± 6.8 Ma and 514.3 ± 6.7 Ma, respectively. These ages are interpreted as crystallisation ages for the Progress Granite and confirm Early Palaeozoic orogenesis in the Larsemann Hills region. This orogen appears to have evolved during continental convergence and is probably responsible for widespread radiogenic isotopic resetting and the near‐complete exhumation of the adjacent northern Prince Charles Mountains which evolved during a ca 1000 Ma event. The identification of a major Early Palaeozoic orogen in Prydz Bay allows tentative correlation of other domains of Early Palaeozoic tectonism both within the east Antarctic Shield and other, once contiguous, Gondwana fragments and illustrates the potential complexity inherent within intercratonic mobile belts. One such possibility, tentatively offered here, suggests a continuous belt of Early Palaeozoic tectonism from Prydz Bay eastward to the West Denman Glacier region and into the Leeuwin complex of Western Australia.     

Shift in detrital sedimentation in the eastern Bay of Bengal during the late Quaternary

Down-core variations of granulometric, geochemical and mineral magnetism of a 70-cm long sediment core retrieved from the eastern Bay of Bengal abyssal region were studied to understand sedimentation pattern and sediment provenance during the last ～12 kyr BP. Based on down-core physical and elemental variations, three units were identified: unit 3 (70–43 cm) is a ～30 cm thick clayey silt organic carbon-rich (0.5–0.92%) turbidite probably delivered by the Brahmaputra River during the late Quaternary period. Units 2 (43–24 cm) and 1 (24–0 cm) represent enhanced and reduced supply of coarse-grained detrital sediments from the Ganges River during early and late Holocene period, respectively. Increased terrigenous supply dilutes calcium carbonate (CaCO₃) and biogenic elements (P, Ba and Cu) in units 3 and 2. On the contrary, a reduction in detrital input enhances CaCO₃ and biogenic elements in unit 1. Lithogenic elements (Ti, Al, K and Rb) and shale-normalized REE patterns in all three units suggest terrigenous source. The shift in provenance from the Brahmaputra to the Ganges derived sediments is evident by a sharp increase in sediment grain size, increased concentration and grain size assemblages of magnetic minerals, lithogenic elements concentration and La_n/Yb_n ratio. This study highlights terrigenous dilution on biogenic sedimentation in the eastern Bay of Bengal sediments.     

南极普里兹湾海域的近现代沉积速率

沉积速率主要受上层海洋生物生产的影响,而在湾口浅滩区沉积速率则主要受底栖生物的影响。此外,水流、水体稳定度、冰封期长短和海底地形等条件也对沉积速率产生一定的利用中国第21次南极科学考察获得的普里兹湾海域的沉积物样品,运用沉积地层同位素210Pb测年技术,探讨了该海域沉积物的近现代沉积速率及其影响因素。研究结果表明,南极普里兹湾海域的近现代沉积速率变化范围在0.47～1.88 mm/a之间,平均值为1.06 mm/a,高于南极罗斯海而低于威德尔海,总体上与南、北极多个海区的沉积速率相当。在湾内和冰架边缘区影响,沉积速率的分布是多种因素共同控制的结果。在生物量较高、水体条件较为稳定的湾内中心区域,沉积速率较高,而冰架边缘区的沉积速率则较低     

The structure and origin of Prydz Bay and MacRobertson Shelf, East Antarctica

A marine geophysical survey in early 1982, conducted by the Australian Bureau of Mineral Resources, indicated that much of Prydz Bay is underlain by a sedimentary basin. Severe seismic multiples preclude an accurate estimate of total sediment thickness, but interpretation of the seismic and magnetic data suggest that it is probably at least 5 km. The trends of the southeast basin margin and of mild faulting and folding in the southwest indicate an overall NNE trend, roughly orthogonal to the continental margin.In the south of Prydz Bay, two series of seismic sequences are evident, separated by a mildly erosional unconformity. The lower series ranges from poorly- to well-stratified, has minor folding and faulting, and probably derives from continental and perhaps shallow marine pre-breakup sediments. The upper series is generally well-stratified, and prograded near the shelf edge; it probably represents shallow marine post-breakup sediments. The seabed is distinctly unconformable with the underlying sediments, implying both that much of the upper series sediments and some of the lower series sediments have been bulldozed off by advances of the Amery Ice Shelf, and that present sedimentation rates are very low. Possible thin moraines or tillites in the northeast part of the Prydz Bay are also attributed to these glacial advances.The continental slope and rise sedimentary section ranges from at least 3 km thick off Prydz Bay, to thin off the MacRobertson Shelf to the west, reflecting the more prolific sediment source in Prydz Bay. The deep water section includes several seismic sequences, the most distinctive being interpreted as sheet volcanics and turbidite fans. The deepest visible unconformity is locally strongly faulted and may separate the pre-breakup and post-breakup sediments.Indo-Antarctic breakup has been tentatively dated as Early Neocomian (130 Ma) and the E-W orientation of the resultant Antarctic coast invites interpretation of the Lambert Glacier-Prydz Bay structure as a possible failed rift arm of a triple junction. Direct information on the age and nature of the sediments under Prydz Bay is lacking, but Permian continental sediments cropping out at Beaver Lake, to the south, may correspond to the lower pre-breakup series. This interpretation gains some support from analogies with fault-bounded intracratonic basins in India which contain Permian to Triassic continental strata and which may have been juxtaposed prior to breakup. The upper series probably consists of Upper Cretaceous and Cainozoic sands and shales, with moraines or tillites at the top of the section.     

Holocene climate variability from lake sediment core in Larsemann Hills,Antarctica

A sediment core (L2) from Larsemann Hills, Antarctica was analyzed for Biogenic Silica (BSi), Sand (%) and Total Organic Carbon (TOC). The 78 cm core length represents the time span of ∼8.3 cal ka BP. The values of BSi from the core show prominent high productivity from ∼8.3 to ∼6 cal ka BP in comparison to less productivity in mid-late Holocene (∼6 cal ka BP to recent). Moreover, high sand (%) infers the glacio-fluvial deposition from ∼8.3 to ∼5 cal ka BP TOC shows little variation through out the core, except in the upper ∼10 cm (∼4 cal ka BP) part wherein it is comparatively high. The increased TOC in the upper part of the core possibly indicates presence of algal mat due to exposure of the lake to the ice free (glacier free) conditions.     

Preliminary magnetic susceptibility characteristics of the Bharati promontory (Grovness Peninsula), Larsemann Hills,Prydz Bay region,East Antarctica

The coastal tract of the Prydz Bay region in the East Antarctica exposes Archean to Late Proterozoic magmatic and medium- to high grade (amphibolite — granulite facies) metamorphic rocks. The para- and ortho gneisses from the Bharati promontory (Grovness Peninsula) forming a part of the Larsemann Hills in the southern segment of Prydz Bay were investigated for magnetic characterization. In this small peninsula the upper amphibolite facies gneisses occur as NE-trending bands. The para-gneisses show a range of mineral assemblages (± cordierite ± sillimanite ±garnet) while ortho-gneiss mineralogy includes quartz, feldspar, biotite, garnet. All the lithological units in Bharati promontory contain ubiquitous magnetite, however, with wide variation in the volume proportions. This has resulted in a wide range in magnetic susceptibility (10^?4 to 10^?2 SI). Magnetic foliations show a correspondence with the general trend of lithounits (050° NE) and define a resulting geometry of mainly D₁ and D₂ foliations. The magnetic lineations show a preferred orientation with moderate easterly plunge (mean vector 093/36). The findings have implications for the magnetic field survey because such fabrics would impart a strong horizontal component of induced magnetization.     

Lithological and biochemical properties in sediments of Lama Lake as indicators for the late Pleistocene and Holocene ecosystem development of the southern Taymyr Peninsula, Central Siberia

In order to evaluate the sensitivity of aquatic and terrestrial ecosystems to climatic changes, lithological (sediment structure and color, grain size, physical properties) and biochemical (TOC, TOC/TN, δ¹³C of TOC and carbonates) investigations were carried out on an 11.12 m-long sediment core from Lama Lake (Central Siberia, Putorana Plateau). According to the pollen data, the sequence represents the termination of the Pleistocene, and the entire Holocene. It is composed of highly terrigenous and stratified clays and silts. Sediment structure, grain-size distribution, carbonate contents and physical properties of the sediment indicate that glaciers were present in the catchment area of Lama Lake during the period Oldest Dryas to AllerØd. For the same time period, δ¹³C values of TOC give indications of a perennial ice cover. Since the AllerØd, organic matter accumulation has increased, caused by an increasing input of land vegetation and aquatic primary production as revealed by relations TOC contents, TOC/TN ratios and δ¹³C values of TOC. During the Holocene climatic optimum, in late Preboreal and Boreal times, biogenic primary production in Lama Lake reached its maximum and the vegetation in the catchment area changed from grassy tundra to a dense forest. From the Atlantic period to the present, small variations in δ¹³C values of TOC and TOC contents are probably related to the location of Lama Lake on the border between grass and wooded steppe, leading to responses of environmental conditions to even small changes in climate.     

洱海沉积物粒度记录与气候干湿变迁

通过对洱海现代沉积物的精细采样,将放射性核素精确计年与沉积物粒度研究相结合,重建了600多年来洱海区域气候的干湿变迁,为恢复百年尺度的气候干湿变化提供了一条新途径。研究结果表明,15世纪是洱海地区最为湿润的一个世纪;洱海区域存在100a、200a两种时间尺度的气候干湿准周期波动;自19世纪末以来洱海区域气候整体上向干旱化方向发展,目前正处于干旱期末期,预计气候将由干旱转向湿润。     

苏北潮滩湿地不同生态带碳、氮、磷分布特征*

通过对比苏北潮滩湿地不同生态带的表层以及柱状沉积物中总有机碳、总氮、总磷和有机磷含量,并结合不同植被不同植株部位中碳、氮、磷的含量变化,分析了潮滩沉积物中碳、氮、磷的垂向和水平分布特征与规律,探讨了不同生态带以及潮滩植被对碳、氮、磷等生源要素的富集作用。对比分析结果表明:苏北潮滩湿地各生态带对不同的测量指标有着不同的富集作用,互花米草滩的总有机碳、总氮和有机磷含量要远大于其他几个生态带,光滩沉积物中总磷的含量最高; 粒度效应是控制互花米草前缘地带以及互花米草滩沉积物中有机碳和氮分布的一个重要因素,盐蒿和芦苇滩中有机碳和氮的分布更多的是受粒度之外的其他因素影响; 不同生态带表层沉积物中的C/N比值分布,大致可反映其有机物来源的差异,而不同生态带中柱状沉积物中的C/N比值相对接近,很难根据C/N比值大小来对不同生态带中的有机物来源进行判断,这可能是埋藏在柱状沉积物中的有机物更多的受到了早期成岩作用造成的。植被对潮滩湿地中碳、氮、磷的分布有着重要影响,3种物质在互花米草、盐蒿和芦苇中的含量差别不是很大,因此潮滩植被对沉积物中上述3种物质的贡献差别主要是由不同植被的生物量和其所处环境的沉积动力差异造成的。     

东南极普里兹湾陆隆区脊状沉积体的结构和形成过程

东南极普里兹湾陆隆区发育数个近垂直陆缘的脊状沉积体,这些沉积体记录了区域冰川活动和底流变化的历史。本文主要利用多道地震资料和水深资料对这些脊状沉积体的平面展布、走向上的结构差异进行了研究,在此基础上讨论了不同脊状沉积体的形成过程。结果表明研究区内脊状沉积体有两种不同结构类型:西部Wild峡谷两侧不对称发育的浊流堤岸沉积形成两个平行峡谷的脊状沉积体;东部数个脊状沉积体的形成与其下长期存在的浊流活动引起的穿时沉积间断面有关。不同峡谷的浊流活动起始时代不一,西部的Wild峡谷起始时代和陆隆区冰海沉积起始时代(P1)一致;东部Wilkins峡谷以及Murray峡谷从后期的P3(约26.1 Ma)开始,代表普里兹湾地区的一次冰川极盛事件。研究区所有峡谷及其浊流活动均随时间向海扩展,造成相应的脊状沉积体向海扩展。在脊状沉积体外缘区域,浊流输送而来的细粒沉积物在向西的底流作用下形成大型深海沉积物波。     

洱海沉积物粒度记录与气候干湿变迁

通过对洱海现代沉积物的精细采样,将放射性核素精确计年与沉积物粒度研究相结合,重建了 6 0 0多年来洱海区域气候的干湿变迁,为恢复百年尺度的气候干湿变化提供了一条新途径。研究结果表明,15世纪是洱海地区最为湿润的一个世纪;洱海区域存在 10 0a、2 0 0a两种时间尺度的气候干湿准周期波动;自 19世纪末以来洱海区域气候整体上向干旱化方向发展,目前正处于干旱期末期,预计气候将由干旱转向湿润。     

Holocene Climate Variability in Antarctica Based on 11 Ice-Core Isotopic Records

A comparison is made of the Holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east Antarctica (Vostok, Dome B, Plateau Remote, Komsomolskaia, Dome C, Taylor Dome, Dominion Range, D47, KM105, and Law Dome) and west Antarctica (Byrd), with temporal resolution from 20 to 50 yr. The long-term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations. All the records confirm the widespread Antarctic early Holocene optimum between 11,500 and 9000 yr; in the Ross Sea sector, a secondary optimum is identified between 7000 and 5000 yr, whereas all eastern Antarctic sites show a late optimum between 6000 and 3000 yr. Superimposed on the long time trend, all the records exhibit 9 aperiodic millennial-scale oscillations. Climatic optima show a reduced pacing between warm events (typically 800 yr), whereas cooler periods are associated with less-frequent warm events (pacing >1200 yr).     

青藏高原纳木错湖近150年来气候变化的湖泊沉积记录

高海拔地区的纳木错湖是研究过去气候环境变化的理想场所。本文结合附近气象站点实测数据与纳木错浅湖芯的研究结果,筛选出适用的气候环境代用指标,并对当地过去近150年来的气候变化记录进行重建。其结果显示,19世纪50年代至20世纪,以偏暖湿为主;20世纪初至20世纪50年代,该阶段气候总体上呈现出冷干特点,并从20世纪20年代左右逐渐向暖湿气候过渡;20世纪中叶至2005年,这期间气候有一定波动,但整体上以气温上升为主要趋势,在降水略减的情况下湖泊并未出现萎缩,表明气温升高可能导致冰川消融加快从而对入湖径流有一定补给作用。     

青藏高原西南部塔若错湖泊沉积物记录的近300年来气候环境变化

以青藏高原西南部塔若错的34cm浅湖芯为研究对象,对其沉积物样品进行总有机碳、无机碳、总氮、微量元素、正构烷烃含量及碳氮比等多项指标的分析测定。采用过剩210Pb和137Cs计年法对该湖芯进行了定年和沉积速率研究,获得了近300年的连续湖泊沉积环境序列。在明确了各指标气候环境指示意义的前提下,综合对比分析湖芯中各项气候环境指标,并结合定年结果重建了塔若错湖区近300年来的气候环境变化。结果表明：塔若错湖区气候环境变化可分为3个明显阶段：早期为1705～1778年,该地区气候环境温暖湿润,湖区植被广泛发育;中期为1778～1860年,湖区处于小冰期末次阶段,气候环境寒冷而湿润,植被发育受阻;后期为1860年至今,为小冰期结束后偏暖干化时期。其中,后期又可分为3个亚阶段：1860～1924年,湖区气候环境稍暖且干旱,植被稍有发育;1924～1969年,湖区气候环境呈现偏冷干特点,植被发育暂缓;1969年至今,湖区气候回暖,环境干旱化有所缓解,植被开始逐渐发育。在气候冷暖变化上,该湖芯记录与古里雅冰芯记录和青海湖湖泊沉积记录都有较好的可对比性,只是在起讫年代上存在一些差异。     

New insights in the evolution of Antarctic glaciation from depth conversion of well-log calibrated seismic section of Prydz Bay

The understanding of the evolution of the Antarctic Ice Sheet is crucial for the comprehension of the history of past global climate. The debate regarding the age of the transition to modern “dry- and cold-based” ice sheet after the Neogene polythermal conditions has taken place over more than 20 years. An evident change in the geometry of the depositional systems of the Prydz Bay continental margin demarked the initiation of the Prydz Channel Fan and has been inferred to correspond to this transition. The improvement in the age placement of this change contributes to unravel the last stages of the Antarctic glacial history. We predicted the spatial distribution of P-wave velocity data along both dip- and strike-oriented seismic profiles that intersect 3 Ocean Drilling Program (ODP) sites on the Prydz Bay continental shelf. We used this information to assist the correlation of the existing litho- and bio-stratigraphic information among the drilling sites and to produce an accurate geometric reconstruction of the Neogene shelf units through depth-migration of the seismic data. The revised stratigraphy that we obtained suggests an early late to late early Pliocene age for the seismic reflector at the base of the Prydz Channel Fan. This age, younger than previously proposed, is consistent with the age inferred for similar geometric changes identified in different Antarctic margins.